Impaginato 419 Adv. Hort. Sci., 2020 34(4): 419­430 DOI: 10.13128/ahsc­8966 Growth and chlorophyll fluorescence characteristics of Sinningia speciosa under red, blue and white light­ emitting diodes and sunlight M. Moazzeni, S. Reezi (*), M. Ghasemi Ghehsareh Department of Horticulture Science, Agriculture Faculty of Shahrekord University, P.O. Box 8818634141 Shahrekord, Iran. Key words: Greenhouse, growth chamber, light­emitting diodes, light spectra, transplant production. Abstract: Determining the most reasonable LED spectral composition wave­ lengths on Sinningia speciosa transplants was the main focus of present experi­ ment. Seeds were sown in cell trays under chambers with distinct spectral com­ position including white+blue+red (WBR), blue+red (BR) and white+red (WR) LEDs with equal light quality proportions (70 mmol m­2s­1 photon flux density) and under sunlight (400 mmol m­2s­1 photon flux density) in constant conditions of 14h photoperiod, 70% relative humidity and day/night temperature of 23/18°C for 50 days. In this stage, LED treatments led to higher germination percentage and better results in biomass, canopy width, leaf width and leaf area as well as chlorophyll and carotenoids accumulation were obtained in comparison with sunlight. Extracted and technical parameters of chlorophyll fluorescence induction kinetics and maximum quantum efficiency of photosys­ tem II (Fv/Fm) were decreased by sunlight­grown seedlings. Fv/Fmwas induced by WBR and BR treatments, correlated with maximum yield of primary photo­ chemistry (jP0). Quantum efficiencies (jP0, jE0 and y0) and performance index of absorption energy flux (PIABS) were increased in BR­exposed transplants. In pot stage, LED­treated plants exhibited better results in morphological features with earlier marketable flowering stage especially under WBR, which can com­ pensate costs of production in marketing stage. 1. Introduction Sinningia speciosa (Lodd.) Hiern. is a perennial potted flowering plant commonly known as Gloxinia, which is a herbaceous tropical species native to Brazil and belongs to Gesneriaceae family (Larson, 1992). Proper seasonally light adjustments are critical for production of Gloxinia, hence various source of artificial light has been effectively applied including fluo­ rescent, high­pressure metal halide, high­pressure sodium with the opti­ mal intensity of 45 to 70 mmol m­2s­1 (Larson, 1992; Dole and Wilkins, 2005). Even though aforementioned sources induce an increase in daily (*) Corresponding author: sreezi57@yahoo.com Citation: MOAZZENI M., REEZI S., GHEHSAREH M.G., 2020 ­ Growth and chlorophyll fluorescence characteri‐ stics of Sinningia speciosa under red, blue and white light‐emitting diodes and sunlight. ­ Adv. Hort. Sci., 34(4): 419­430 Copyright: © 2020 Moazzeni M., Reezi S., Ghehsareh M.G. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 31 May 2020 Accepted for publication 26 October 2020 AHS Advances in Horticultural Science http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2020 34(4): 419­430 420 photosynthetic flux intensity, they are not energeti­ cally efficient as desired and there is no capability of spectral manipulation. Light­emitting diodes, includ­ ing diverse size, long lifetime, solid state construction (Heo et al., 2002; Kim et al., 2004), low thermal out­ put, specific wavelength, adjustable light quality and intensity (Okamoto et al., 1997) and high electrical efficiency (Bula et al., 1991), represent a promising technology for the greenhouse industry which has technical advantages over other artificial light sources (Mitchel et al., 2012). Capability of LED’s spectrum adjustment results in better responses of photoreceptors, influencing plant physiology and morphology and ultimately enhances production (Morrow, 2008). Horticultural crop seedlings are intensively influenced by light spectrum which affects their morphological properties (McNellis and Deng, 1995). Production of transplants under desirable light spectrum and suitable control of environmental con­ ditions can improve transplant quality compared to traditional greenhouse production conditions in which accordingly affects their growth and yield after transplantation (Oda, 2007). Producing a large num­ ber of seedlings in a small area justifies high electrici­ ty consumption that is economically advantageous. Developing various light spectral ratio recipes for dif­ ferent horticultural transplants based on their demand, would influence growth rate and improve quality (Hernández et al., 2016), as different wave­ bands were proved to have significant physiological effects on plants (Kim et al., 2004; Johkan et al., 2010) and can be assembled according to the light quality which plants need (Goins et al., 1997). Detecting specific optimal light spectrum prevents energy loss for physiologically none­useful wave­ lengths (Kim et al., 2004; Johkan et al., 2010) and it can regulate a variety of plant development path­ ways from germination to flowering induction (Jiao et al., 2007). Based on previous studies, it has been shown uti­ lizing red (600­700 nm) and blue (400­500 nm) LEDs have the greatest impact on plant growth (Yorio et al., 2001) since they mainly contain range of wavelengths essential for plants photosynthesis (Cosgrove, 1981; Kasajima et al., 2008). Although blue light is photo­ synthetically less efficient than red light (McCree, 1972; Dougher and Bubgee, 2001), it has considerable photomorphogenic effects on chlorophyll biosynthe­ sis, stomatal opening, enzyme synthesis, photosyn­ thetic capacity on chloroplast (Tibbits et al., 1983), fresh and dry matter accumulation, flowering (Withelam and Halliday, 2007; Johkan et al., 2010), stem elongation and leaf expansion (Hoenecke et al., 1992; Dougher and Bubgee, 2001). Researches have demonstrated that combination­ al light regimes may help to optimize growth (Brown et al., 1995). Various number of studies have sug­ gested that combination of red, blue and white LED lighting in different ratios is a favorable lighting con­ dition for plants in many aspects (Lin et al., 2013; Ouzounis et al., 2014). Combination of red­blue, red­ white, red­blue­white provides the highest photon efficiency as compared to monochromatic LED illumi­ nation (Lin et al., 2013; Nelson and Bubgee, 2014; Ouzounis et al., 2014; Nicole et al., 2016). Few stud­ ies on continuous­spectrum LED lamps fit to a theo­ retical model of the maximum photosynthetic response has been recorded since McCree’s (1972) experiments on cultivated plants. It has been shown that chlorophyll fluorescence data can help with analyzing energy flow and informa­ tion related to the structure and function of photo­ synthetic apparatus (Brestic and Zivcak, 2013). The non­destructive analysis of polyphasic fast chlorophyll transient by the so­called OJIP test was developed for quick evaluation of biophysical aspects of photosyn­ thesis (Strasser, 1995; Mathur et al., 2013). This test which is based on energy flow in thylakoid mem­ branes provides detailed information about the bio­ physics of the photosynthetic system through mea­ surement of fluorescence signals (Kalaji et al., 2017). The main objective of this study was to investigate different ratios of blue and white with the red spec­ tral composition (WR, BR, WBR) to determine the most effective combination of waveband in compari­ son with natural light condition. 2. Materials and Methods Plants material and lighting treatments This experiment was carried out in 2018­2019 in specialized chambers in Shahrekord University research greenhouses. Sinningia speciosa F1 (bro­ cade blue) pelleted seeds were sown into 288 cell trays filled with a peat moss with the pH of 5.5­6 and EC of 1 dS/m­1 (1:2 dilution). Cell trays were placed inside three chambers with LED Lighting treatments and one cell tray under 50% shaded sunlight in greenhouse, as control, using a completely random­ ized design. Day/night temperature (23/18°C), rela­ tive humidity (70%) and photoperiod (14­hour) were maintained constant in all (LED and sunlight) treat­ ments. Plants were grown under LED modules Moazzeni et al. ‐ Production of Sinningia speciosa transplants under different light spectra 421 (Shezhen Sunled Lighting Co., Ltd, CN Manufacturer, China) yielding approximately 70 mmol m­2s­1 mea­ sured and adjusted using PARmeter (Apogee Quantum meter, MQ500, USA). The peak emissions of blue (460 nm), red (620 nm) and white (in the range of 380­750 nm) were measured and recorded using spectrometer (BLACK­Comet CXR­SR­50, StellarNet, Inc., USA) with range of 300­800 nm (Table 1). During transplant production cell trays were exposed to 50% white + 50% red (WR), 50% blue + 50% red (BR) and 33.3% white + 33.3% blue + 33.3% red (WBR) LED and 50% shaded sunlight (SL) treatments (Table 1). The relative spectral distribu­ tion of light treatments are presented in figure 1. Cell trays were rotated frequently in order to ensure equal growth conditions. Subsurface irrigation was applied every 3 days and plants were irrigated as needed with a 500­1000 ppm water­soluble Radixol fertilizer (N:P:K + microelements; 15:17:15 + 0.12% Mg, 0.02% B, 0.0075% Cu, 0.04% Mn, 0.01% Mo, 0.012% Zn). Measurements were conducted in both transplant and flowering stages. Transplant stage measurements Germination and morphological characteristics. After 50 days under light treatments (10 days for ger­ mination + 40 days for growth till four fully expanded leaves observed), germination percentage was calcu­ lated. Plugs with four fully expanded true leaves, were then transplanted to 12 cm pots, in a complete­ ly randomized design with five replications (n=5). Morphological traits of five randomly selected plants from each replicate including shoot fresh and dry weight, root fresh and dry weight, leaf area, leaf width and canopy width was measured. Shoots and roots were dried in a drying oven at 72°C for 24 hours Table 1 ­ Light intensity, different light spectra and light quality were used for growing Sinningia speciosa transplants *: For comparing sunlight quality with LEDs, sunlight has purple/blue : green/yellow : orange/red (400­492 : 493­597 : 598­700 nm) with the relationship of 23 : 28 : 39 according to Aphalo et al. (2012). LED treatment Proportion (white: blue: red) Light intensity (mmol m­2.s­1) WBR 33.3% : 33.3% : 33.3% 70 ± 3.1 BR 0% : 50% : 50% 70 ± 1.0 WR 50% : 0% : 50% 70 ± 2.1 Control light treatment Average light intensity (mmol m‐2.s‐1) %50 Shaded sunlight (SL) 400 ± 50 Light quality Light spectrum (nm) White 380­750 Blue 460 Red 620 SL (control) 400­700* Fig. 1 ­ Relative distribution spectra of white+blue+red (WBR), blue+red (BR), white+red (WR) and sunlight (SL) treat­ ments. Wavelength peaks are indicated by values above each peak. Adv. Hort. Sci., 2020 34(4): 419­430 422 FluorPen FP 100 max, Photon System Instrument, PSI, Czech Republic) with the same method (20 min­ utes dark adaption) was used to measure OJIP­test whilethe last fully expanded intact leaf of randomly selected transplants was used to investigate biophys­ ical and phenomenological parameters of Photo System II status (Strasser, 1995). The transient fluo­ rescence measurement was induced by a saturating light of 3000 μmol m−2s−1. The OJIP transients were done according to the JIP test (Strasser et al., 2000). F0, Fi, Fj, Fm, Fv, Vj, Vi, Fm/F0, Fv/F0, Fv/Fm, jP0, jE0, jD0, ABS/RC, TR0/RC, DI0/RC, ET0/RC, PIABS and y0 were extracted using FluorPen software. More information on formulas are presented in Table 2. Table 2 ­ Summary of OJIP­test formula using data extracted from OJIP chlorophyll fluorescence transient. Formulas to determine dry weight. The leaf area of plants was measured by Digimizer V. 5.4.6 software. Biochemical measurements. Biochemical mea­ surements included chlorophyll a, chlorophyll b, total chlorophyll (a + b), carotenoid and total soluble sugar contents. Chlorophyll and carotenoid contents were extracted from 0.5 g fresh leaf tissue from five ran­ domly selected transplants (n=5) and the pigments were eluted with 10 ml of 80% acetone centrifuged at 4000 g for 10 min and the amount of chlorophyll was estimated spectrophotometrically (using PG instruments T80+) at 470, 646 and 663 nm by the method of Lichtenthaler and Welburn (1983). Total soluble sugars was quantified in 95% ethanol extracts of leaf tissue from five randomly selected transplants (n=5). A sample of 0.5 g of fresh­ ly harvested leaves was crushed in 5 ml of 95% (V/V) ethanol. The insoluble fraction of the extract was washed twice with 5 ml of 70% ethanol. All soluble fractions were centrifuged at 3500 g for 10 min. The supernatants were collected and stored at 4°C for TSS determination. TSS were analyzed by reacting 0.1 ml of the alcoholic extract with 3 ml freshly prepared anthrone reagent (150 mg anthrone + 100 ml 72% [W/W] H2SO4) and placed in a boiling water bath for 10 min. After cooling, the absorbance at 625 nm was determined (Irrigoyen et al., 1992) in a PG instru­ ments T80+ spectrophotometer and the data was pooled and extracted with standard curve (y = 0.002x ­ 0.009, R² = 0.992). Chlorophyll fluorescence and OJIP test parameters After 50 days of growth (at four true leaves stage), a portable PAR­FluorPen FP 100 max (Photon System Instrument, PSI, Czech Republic) was used to mea­ sure maximal quantum efficiency of Photo System II (Fv/Fm) photochemistry. The most recent fully expanded leaf attached to plants of five randomly selected transplants (n=5) in each treatment were used for this measurement. A custom­ made method (Genty et al. , 1989; Aliniaeifard et al. , 2014; Aliniaeifard and van Meeteren, 2014) was used for the calculation of Fv/Fm. After reaching steady state fluorescence, during short measuring flash in dark­ ness and during saturating light flash (by exposing to 3900mmol m­2s­1 saturating light pulse) F0 and Fm were digitized and averaged, respectively. These two images were applied to obtain maximal variable fluo­ rescence (Fv = Fm ­ F0). Fv/Fm was calculated using expression (Fm ­F0)/Fm. The average value and stan­ dard deviation of Fv/Fm per image were calculated by Fluor Cam V.7.0 software.The same device (PAR­ Formula abbreviation Formula explanation F0 F0= F50μs, fluorescence intensity at 50 μs Fj Fj= fluorescence intensity at J­step (at 2 ms) Fi Fi= fluorescence intensity at i­step (at 60 ms) Fm Fm= maximal fluorescence intensity Fv Fv= Fm­F0 (maximal variable fluorescence) Vj Vj= (Fj­F0)/(Fm­F0) Vi Vi= (Fi­F0)/(Fm­F0) Fm / F0 Fv / F0 Fv / Fm jP0 jjP0= 1­(F0/Fm)=Fv/Fm y0 y0= 1­Vj jE0 jE0= [1­(F0/Fm)] x y0 jD0 jD0= 1­jP0 ­ (F0 /Fm) PIABS PIABS= (RC/ABS)×[jP0/(1­jP0)]×[y0/(1­y0)] ABS / RC ABS/RC= M0×(1/Vj)×(1/jP0) TR0 / RC TR0/RC= M0× (1/Vj) ET0 / RC ET0/RC= M0× (1/VJ) × y0 DI0 / RC DI0/RC= (AB/RC)­(TR0/RC) M0 M0= (TR0/RC)­(ET0/RC)=4(F300­ F0)/(Fm­ F0) ABS= absorption energy flux; CS= excited energy cross­section of leaf sample; DI= dissipation energy flux at the level of the anten­ na chlorophyll; ET= flux of electron from QA ­ into the electron transport chain; jD0= quantum yield of dissipation; jE0= probabi­ lity that an absorbed photon will move an electron into electron transport further than QA ­; jP0= maximum quantum yield of pri­ mary photochemistry; PIABS= performance index; y0= efficiency by which a trapped exaction, having triggered the reduction of QA to QA ­, can move an electron further than QA ­ into the electron transport chain; RC= reaction center of PSII; RC/CS= fraction of active reaction centers per excited cross­section of leaf; TR, PSII; RC/CS= fraction of active reaction centers per excited cross­secti­ on of leaf; TR= excitation energy flux trapped by a RC and utilized for the reduction of QA to QA ­. Moazzeni et al. ‐ Production of Sinningia speciosa transplants under different light spectra 423 Pot stage (mature plants) measurements Time to flowering and morphological characteris‐ tics. During pot stage, morphological traits such as number of flowers, flower diameter, number of leaves and number of days to flowering were mea­ sured and recorded. Statistical analysis Analysis of variance (ANOVA) was performed using SPSS (SPSS 15.0, SPSS Inc.) software and the means were compared with Tukey’s test at p ≤ 0.05. 3. Results Transplant stage Germination. Seeds grown under all LED lighting treatments performed better germination rate com­ pared to SL. WBR, BR, WR and SL treatments had 96%, 94%, 96% and 87% germination, respectively (Table 3). Morphological characteristics. Forty­five days after sowing seeds when all transplant had four fully expanded leaves, growth parameters were measured and analyzed (presented in Table 3). Seedlings grown under WBR and WR LED light exhibited significantly higher shoot fresh weight compared with control. Furthermore, shoot dry weight of plants grown under WBR and SL treatment had the highest and lowest average values, respectively. Average root fresh and dry weight values were maximum in WBR, however in the absence of blue LED, root biomass in WR­ grown transplants was greatly reduced. All three LED lighting treatments had significantly greater canopy width than SL. Leaf area and leaf width of plants were significantly influenced by WBR light, though the SL treatment had the least average values. This prominence of WBR (with 33% blue LED ratio com­ pared to 0% and 50%) was visible on leaf features and canopy width (Table 3). Biochemical measurements Plants grown under sunlight had the lowest chlorophyll a content while WBR and WR lighting treatments resulted in the highest content of chloro­ phyll a. LED light composed of blue and red had most profound effect on chlorophyll b synthesis. Control treatment and WR LED treatment had the lowest amount of chlorophyll b content. Additionally, identi­ cal proportion of white, red and blue light (WBR) led to the highest total chlorophyll (chl a+b) content among all the other treatments whereas SL had the lowest values. Carotenoid content was highly affect­ ed by WBR and WR LED lighting treatments while SL­ treated plants showed the lowest carotenoid content (Table 3). Transplants grown under sunlight in green­ house condition (SL) exhibited higher total soluble sugar content in comparison with all LED treatments (Table 3). Chlorophyll fluorescence parameters Measurements of chlorophyll fluorescence para­ meters were used to study the photosystem II activi­ Table 3 ­ Influence of light quality of white+blue+red (WBR), blue+red (BR), white+red (WR) and sunlight (SL) on germination, morpho­ logical and physiological characteristics of Sinningia speciosa transplants represented by means values ± standard deviation (n=5) Values followed by the same letter within a row do not significantly differ (by the tukey’stest, p≤0.05). Parameters Light quality WBR BR WR SL (as control) Germination (%) 96 a 94 a 96 a 87 b Shoot fresh weight (g) 1.122 ± 0.08 a 0.862 ± 0.05 b 1.084 ± 0.14 a 0.608 ± 0.12 c Shoot dry weight (g) 0.065 ± 0.004 a 0.044 ± 0.003 bc 0.053 ± 0.01 ab 0.037 ± 0.012 c Root fresh weight (g) 0.148 ± 0.008 a 0.088 ± 0.008 bc 0.080 ± 0.01 c 0.098 ± 0.008 b Root dry weight (g) 0.0102 ± 0.0024 a 0.0084 ± 0.0011 ab 0.006 ± 0.0007 c 0.0078 ± 0.0013 bc Canopy width (cm) 7.6 ± 0.3 a 7.9 ± 0.3 a 7.7 ± 0.02 a 6.1 ± 0.4 b Leaf width (cm) 2.6 ± 0.1 a 2.4 ± 0.1 ab 2.5 ± 0.3 ab 2.2 ± 0.1 b Leaf area (cm2) 4.8 ± 0.3 a 3.6 ± 0.2 c 4.2 ± 0.5 b 3.2 ± 0.2 c Chlorophyll a (mg.g­1 FW) 0.122 ± 0.002 a 0.091 ± 0.026 ab 0.114 ± 0.031 a 0.077 ± 0.009 b Chlorophyll b (mg.g­1 FW) 0.089 ± 0.011 ab 0.099 ± 0.024 a 0.064 ± 0.022 b 0.064 ± 0.005 Chlorophyll a + b (mg.g­1 FW) 0.212 ± 0.013 a 0.194 ± 0.027 ab 0.1946 ± 0.057 ab 0.141 ± 0.008 b Carotenoid (mg.g­1 FW) 2.840 ± 0.23 a 2.038 ± 0.47 ab 2.470 ± 0.77 a 1.580 ± 0.18 b Total soluble sugar (mg.g­1 FW) 49.42 ± 2.05 c 61.81 ± 1.98 b 47.05 ± 1.65 c 94.80 ± 0.65 a 424 Adv. Hort. Sci., 2020 34(4): 419­430 ty (Table 4). Based on this result, the fluorescence signal intensity of transplants grown under WR LED light, increased from F0 to Fj and then to Fm, howev­ er, SL treatment showed the lowest values of extract and technical fluorescence parameters (F0, Fi, Fj, Fm, Fv, Vi, Fm/F0, Fv/F0) as well as Fv/Fm. Transplants grown under WR LED lighting and control condition (SL) showed the highest and lowest values as for F0, respectively. WBR and WR lighting treatments led to the significantly highest Fj value while it had the low­ est significant value in SL treatment. All LED treat­ ments (WBR, BR, WR) exhibited higher fluorescence yield at Fi, Fm, Fv compared to SL. The Highest Vj obtained in WBR and WR­grown plants and the low­ est values were detected in BR­grown seedlings. The highest Vi value was from plants grown under WR lighting; however, SL treatment had the lowest value among the treatments. Plants exposed to BR LED light resulted in higher Fm/F0value than other plants grown under different lighting conditions. Fv/F0 was also decreased for all except BR­grown plants. The Fv/Fm ratio was higher in plants exposed to BR and WBR LED lights compared to SL which had the great­ est decrease. Analyzed parameters for specific ener­ gy fluxes per reaction center (ABS/RC, TR0/RC and DI0/RC) increased in WR treated plants, in contrast BR light treatment had the greatest decrease among lighting treatments in DI0/RC ratio while SL treatment had the highest increase of the same ratio. Also, SL and WBR showed the highest and lowest values of ET0/RC, respectively. By analyzing the parameters that estimate quantum efficiencies or flux ratio (yields and efficiency of electron transport chain) the highest calculated values for jP0, jE0, PIABS and y0 were obtained under BR treatment. In addition, plants grown under BR and WBR treatments had sim­ ilarly the highest significant value in jP0. Plants of WBR and BR treatments had the lowest values in jD0 in compare with SL which had the highest values. Pot stage (mature plants) Morphological characteristics Based on the results, there was a significant effect of LED lighting treatments on flower quantity where­ Table 4 ­ Chlorophyll fluorescence of transplants grown under white+blue+red (WBR), blue+red (BR), white+red (WR) and sunlight rep­ resented by means values ± standard deviation (n=5) Values followed by the same letter within a row do not significantly differ (by the tukey’s test, p≤0.05). Parameters Light quality SL (as control) WBR BR WR F0 9802 ± 1083 ab 8794 ± 663.5 bc 10517 ± 649 a 8031 ± 750 c Fi 39013 ± 3447 a 36843 ± 2126 a 41150 ± 2688 a 29808 ± 3230 b Fj 27919 ± 3109 a 23611 ± 2439 b 28439 ± 1890 a 20392 ± 2299 b Fm 42752 ± 2254 a 39793 ± 2655 a 43443 ± 3162 a 32758 ± 3599 b Fv 32949 ± 1755 a 30999 ± 2222 a 32925 ± 2530 a 24798 ± 2661 b Vj 0.5508 ± 0.0628 a 0.4768 ± 0.0310 b 0.5448 ± 0.0236 a 0.4856 ± 0.018 ab Vi 0.913 ± 0.022 ab 0.905 ± 0.011 bc 0.931 ± 0.013 a 0.886 ± 0.006 c Fm/F0 4.228 ± 0.171 b 4.535 ± 0.242 a 4.128 ± 0.069 b 3.944 ± 0.169 b Fv/F0 3.230 ± 0.171 b 3.535 ± 0.242 a 3.128 ± 0.069 b 2.944 ± 0.169 b Fv/Fm 0.771 ± 0.021 a 0.778 ± 0.012 a 0.758 ± 0.004 ab 0.746 ± 0.011 b jP0 0.771 ± 0.021 a 0.778 ± 0.012 a 0.758 ± 0.004 ab 0.746 ± 0.011 b jE0 0.348 ± 0.059 b 0.408 ± 0.028 a 0.345 ± 0.019 b 0.387 ± 0.008 ab jD0 0.229 ± 0.021 b 0.221 ± 0.012 b 0.242 ± 0.004 ab 0.254 ± 0.011 a ABS/RC 3.449 ± 0.271 b 3.133 ± 0.170 c 3.771 ± 0.095 a 3.477 ± 0.038 b TR0/RC 2.654 ± 0.147 b 2.439 ± 0.128 c 2.857 ± 0.072 a 2.594 ± 0.01 bc ET0/RC 1.217 ± 0.070 b 1.273 ± 0.037 ab 1.301 ± 0.082 ab 1.337 ± 0.04 a DI0/RC 0.796 ± 0.127 ab 0.697 ± 0.060 b 0.914 ± 0.028 a 0.887 ± 0.048 a PIABS 0.700 ± 0.149 c 1.163 ± 0.161 a 0.696 ± 0.072 c 0.895 ± 0.001 b y0 0.449 ± 0.063 c 0.523 ± 0.031 a 0.455 ± 0.024 bc 0.515 ± 0.018 ab Moazzeni et al. ‐ Production of Sinningia speciosa transplants under different light spectra 425 as the SL treatment resulted in the lowest number of flowers (presented in figure 2A). Largest flowers, in terms of flower diameter was detected in plants grown under WBR treatment, however WR treat­ ment resulted in smallest dimeter of flowers (Fig. 2B). The results also indicated that treatments had significantly different number of days to flowering and plants grown under partial sunlight (SL) in green­ house had longer time to flowering in pot stage in comparison with WBR, BR and WR­treated plants (Fig. 2D). The transplants grown under LED treat­ ments had greatly higher number of leaves than SL at flowering stage (Fig. 2C). 4. Discussion and Conclusions In this experiment, significantly higher percentage of germination under LED light treatments, highlight­ ed the effect of light quality on germination rate. It is known that orange/red and blue regions of light spectrum are most effective in germination process (Tozzi et al., 2005). Germination rate was satisfactory in absence of both blue and white LED lighting in WR and BR treatments, respectively. Overall, germination rate was highly affected under LED treatments com­ pared to SL and it can be derived that presence of red light in all treatment resulted in a partially better germination in Sinningia speciosa. Using different light spectra for tomato seedlings revealed that exposing seedlings to monochromatic red light showed higher shoot dry weight than 80% RB but small proportion of blue (95% RB) contributes getting more shoot dry weight (Gόmez and Mitchell, 2015). Moreover, it was reported that lamps with substantial red but small blue waveband radiation energy, produced more weight yields in tomato com­ pared to high blue and less red biased lamps (Warrington and Mitchell, 1976). Furthermore, among sodium lamp (1:1 RB), 100% R, 50% RB, 70% RB, 90% RB and white LEDs lighting treatments 90% RB led to significantly higher dry matter content (Wojciechowska, 2015). In another study with RW, RB, RBW and FL (fluorescent lamp) lighting treat­ ments, WBR enhanced yield of lettuce plants includ­ ing shoot FW, shoot DW, root FW, root DW and Leaf area (Lin et al., 2013). Our Results on fresh and dry weight and leaf features (leaf area and leaf width) were consistent with quoted reports and it can be concluded that a small blue proportion in combina­ tion with red and white spectrum will result in a high­ er biomass. Blue light is considered to be a substan­ tial stimulator for leaf expansion which enhances leaf area and biomass production (Li et al., 2010; Cope ad Bugbee, 2013), on the other hand it has been proved that plant growth typically tends to decrease as the fraction of blue photons exceeds 5­10%, high levels of blue light in the spectrum results in inhibition of cell expansion, cell division, and leaf area expansion, Fig. 2 ­ Morphological characteristics and time to reach flower of transplants grown under white+blue+red (WBR), blue+red (BR), white+red (WR) and sunlight in pot stage. The mean of values ± Standard deviation (n=5) is displayed. Values with the same letter in column do not significantly differ (by the tukey’s test, p≤0.05). The explanations for the treatment abbreviations are provi­ ded in Table 1. tron transport chain and excess light dissipated as heat from the electron transport system (Aliniaeifard et al., 2018). The higher total soluble sugar content of plants grown under SL compared to other plants grown under artificial LED lights, suggesting that under high­ er light intensity elevated level of soluble sugar helps transplants to avoid excessive light intensity and unlike LED treatments, they had less utility for photo­ synthesis (Ciereszko et al. , 2001; Havaux and Kloppstech, 2001). In this study, WR treatment showed the highest rate of increase in minimal fluorescence intensity (F0) and this value decreased asproportion of blue light­ but the opposite trend was observed as white pro­ portion of light increased. This was also observed in Fi, Fj, Fm, Fv and Viparameters. The maximum efficien­ cy of photosystem II (Fv/Fm) increased in BR followed by WBR, however it was reduced in WR treatment (in the absence of blue LED). In an experiment using 32% BW and 40% BR lighting treatments on Phalaenopsis ‘purple star ’showed higher amount in Fv/Fm in com­ parison with 0% BR (Ouzounis et al., 2014) which necessitates certain amount of blue light for proper photosynthesis (Hogewoning et al., 2010). Fv/Fm value ranges between 0.72­0.84 in many plants (Maxwell and Johnson, 2000), although the Fv/Fm of SL­grown transplants was in this range but it showed the least efficiency among other treatments, which is not surprising as this value changes with environ­ mental conditions (Ouzounis et al., 2014). Further­ more, it was shown that existenceof UV and yellow light in sunlight reduce photosynthesis efficiency (Takashi et al., 2010). In addition, Sinningia speciosa has no optimum photosynthetic activity under sun­ light (Larson, 1992; Dole and Wilkins, 2005). Transplants under highest blue proportion (BR) had the highest value in PIABS and jE0 and the lowest value of DI0/RC. The WR exposed transplants (which had no high ratio of blue light but high red ratio) showed the lowest PIABS and jE0 and higher ABS/RC, TR0/RC and DI0/RC as the result. In an experiment investigating on photosynthetic and growth respons­ es of purple variety of basil under white, blue and red LED lamps results shown that red light had the high­ est increase in ABS/RC, TR0/RC and DI0/RC and this amount was decreased under blue light (Hosseini et al., 2019). Inactivation of reaction centers and a decrease in active QA reducing centers occur as ABS/RC increases (Strasser and Stirbet, 1998). WR and WBR­grown transplants (with higher white and Adv. Hort. Sci., 2020 34(4): 419­430 426 which ends up in less photon capture and diminished growth (Bugbee, 2016). Exposing to red light results in enhanced stem elongation (Hoenecke et al., 1992), also absorbing high ratio of red light by plant photore­ ceptors can lead to production of a plant hormone called metatopolin (Steele, 2004), which can stimulate cell division as well as leaf expansion. Addition of white LED light may further increase plant growth, as white light might penetrate deeper in to the canopy and enhance photosynthesis compared to combina­ tion of red and blue light. Perhaps the combination of white, blue and red light perform a balanced spectral environment by providing a favorable amount of white light to plants (Lin et al., 2013). White light is more capable of increasing chloro­ phyll than blue light, however some reports stated that blue light had significant effect on chlorophyll a synthesis (Wynne and Rhee, 1986; Rivkin, 1989; Aidar et al., 1994; Sanchez­Saavedra and Voltolina, 1994; Mercado et al., 2004; Hogewoning et al., 2010; Vadiveloo et al., 2015), also it was reported that red light plays an important role in chlorophyll content enhancement (Kubota et al., 1996). In addition, it has been reported combinational red light with blue and white light can increase carotenoid content accumu­ lation (Lefsrud et al., 2008; Kopsell et al., 2014; Chen et al., 2016; Kopsell et al., 2016), however Lin et al. (2013) reported versus result, claiming that WBR LED has no effect on carotenoid content compared to RB LED and FL light. It can be concluded that white, red and blue light conjointly can enhance chlorophyll and carotenoid content but plant exact response to light quality varies with species and cultivars. In present experiment, the maximum yield of pri­ mary photochemistry (jP0) was in correlation with maximum quantum efficiency of photosystem II (Fv/Fm) which confirmed the enhancement of chloro­ phyll concentration under WBR treatment. We would suggest that transplants under WBR light treatment contained more chloroplast which maximized light capture for photosynthesis. Based on our results, we would suggest that the lowest photosynthetic rate in plants grown under SL is the result of low means of chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content which was confirmed by the decline in Fv/Fm and jP0 and increase in jD0 and it can be concluded that increased jD0 in SL treated transplants explains that due to highest amount of quantum yield of energy dissipation (jD0), the major of natural light absorbed by the plant in high intensi­ ty was not used for the photochemical yield of elec­ Moazzeni et al. ‐ Production of Sinningia speciosa transplants under different light spectra 427 red ratios) represented lower ET0/RC which indicates that absorbed energy is briefly conveyed to the elec­ tron transport chain (Sarkar and Ray, 2016). This con­ firms that plants grown under BR light are more capable of transporting electrons from absorbed photons into electron transport chain and beyond QA ­1y0 which could efficiently regulate energy level in the center of R reaction (Strasser et al., 2004). SL­ grown transplants showed highest soluble sugar con­ tent; however they had the second increase in PIABS, it is possible that in case of an environmental stress­ such as high light intensity, in which excess energy beyond photosynthetic capacity is existing, led to production of ROS which results in oxidative damage to photosystem II (Pospíšil, 2016). In transplants grown under WBR and BR LED lighting, an increment in jP0 value was observed, while there was no increase of the same value in transplants grown under sunlight. The results for jP0 were in correla­ tion with Fv/Fm which impacted chlorophyll and leaf area as explained in aforementioned chlorophyll measurements. At flowering stage, transplants grown under LED lighting treatments resulted performed better orna­ mental criteria including number of flowers, flower diameter and number of leaves. Also it could be sug­ gest that, those plants grown under LED lighting treatments could reach flowering stage sooner which will result in higher profit especially in commercial scale. Totally, in this experiment, this scenario was the case for plants grown under WBR treatment. Application of LED light in greenhouse in combination of red, blue and white wavelengths with a high pho­ ton efficiency are suitable for the production of horti­ cultural plants (Kozai et al., 2015; Nicole et al., 2016). Our results are consistent with previous studies find­ ings which indicate thatlighting source composed of red, blue and white light spectrum enhance morpho­ logical development of seedlings compared to mono­ chromic light of each waveband (Brown et al., 1995; Gόmez and Mitchell, 2015; Hogewoning et al., 2010; Ouzounis et al., 2014). Desirable morphological and physiological charac­ teristics in Sinningia speciosa transplants achieved under LED lighting treatments with identical propor­ tion of white, blue and red led to enhanced morpho­ logical and physiological features at marketing stage including higher number of flowers, flower diameter, number of leaves as well as fewer days to flowering. Shorter time interval to flowering may help commer­ cial growers to save time and costs of production while enhancing Sinningia speciosaplants quality in comparison with sunlight­grown transplants in con­ ventional greenhouse condition. Moreover, it should be noted that using LEDs have higher expenses due to the cost of providing LEDs and growth chambers and also high consumption of electricity. Additional investigation is required to evaluate different ratios of spectral composition to optimize environmental condition for Gloxinia transplant production. References AIDAR E., GIANESELLA­GALVAO S.M.F., SIGAUD T.C.S., ASANO C.S., LIANG T.H., REZENDE K.R.V., OISHI M.K., ARANHA F.J., MILANI G.M., SANDES M.A.L., 1994 ­ Effects of light quality on growth, biochemical composi‐ tion and photosynthetic production in Cyclotella caspia Grunow and Tetraselmis gracilis (Kylin) Butcher. ­ J. Exp. Mar. Biol. Ecol., 180(2): 175­187. ALINIAEIFARD S., MALCOLM MATAMOROS P., VAN MEETEREN U., 2014 ­ Stomatal malfunctioning under low VPD conditions: induced by alterations in stomatal morphology and leaf anatomy or in the ABA signaling?. ­ Physiol. Plant., 152(4): 688­699. ALINIAEIFARD S., SEIF M., ARAB M., ZARE­MEHRJERDI M., LI T., LASTOCHKINA O., 2018 ­ Growth and photosyn‐ thetic performance of Calendula officinalis under mono‐ chromatic red light. ­ Int. J. Hort. Sci., Techn., 5(1): 123­ 132. ALINIAEIFARD S., VAN MEETEREN U., 2014 ­ Natural varia‐ tion in stomatal response to closing stimuli among Arabidopsis thaliana accessions after exposure to low VPD as a tool to recognize the mechanism of disturbed stomatal functioning. ­ J. Exp. Bot., 65(22): 6529­6542. APHALO P.J., ALBERT A., BJÖRN L.O., YLIANTTILA L., FIGUEROA F.L., HUOVINEN P., 2012 ­ Introduction, pp. 1­33. ­ In: APHALO P.J., A. ALBERT, L.O. BJÖRN, A. MCLEOD, T.M. ROBSON, and E. ROSENQVIST (eds.) Beyond the Invisible: a handbook of best practice in plant UV photobiology. Division of Plant Biology, Helsinki, Finland, pp. 206. BRESTIC M., ZIVCAK M., 2013 ­ PSII fluorescence tech‐ niques for measurement of drought and high tempera‐ ture stress signal in crop plants: protocols and applica‐ tions, pp. 87­131. ­ In: ROUT G.R., and A.B. DAS (eds.) Molecular stress physiology of plants. Springer, India, pp. 440. BROWN C.S., SCHUERGER A.C., SAGER J.C., 1995 ­ Growth and photomorphogenesis of pepper plants under red light‐emitting diodes with supplemental blue or far‐red lighting. ­ J. Am. Soc. Hortic. Sci., 120(5): 808­813. BUGBEE B., 2016 ­ Towards an optimal spectral quality for plant growth and development: the importance of radi‐ ation capture. ­ Acta Horticulturae, 1134(1): 1­12. grown under red light‐emitting diodes. ­ HortSci., 27(5): 427­430. HOGEWONING S.W., TROUWBORST G., MALJAARS H., POORTER H., VAN IEPEREN W., HARBINSON J., 2010 ­ Blue light dose‐responses of leaf photosynthesis, mor‐ phology, and chemical composition of Cucumis sativus grown under different combinations of red and blue light. ­ J. Expt. Bot., 61(11): 3107­3117. HOSSEINI A., ZARE MEHRJERDI M., ALINIAEIFARD S., SEIF M., 2019 ­ Photosynthetic and growth responses of green and purple basil plants under different spectral compositions. ­ Physiol. Mol. Biol. Plants, 25: 741­752. IRRIGOYEN J.H., EMERICH D.W., SANCHEZ DIAZ M., 1992 ­ Water stress induced changes in concentration of pro‐ line and total soluble sugars in nodulated alfalfa plant. ­ Physiol. Plant., 84: 55­66. JIAO Y., LAU O.S., DENG X.W., 2007 ­ Light‐regulated tran‐ scriptional networks in higher plants. ­ Nat. Rev. Genet., 8: 217­230. JOHKAN M., SHOJI K., GOTO F., HASHIDA S., YOSHIHARA T., 2010 ­ Blue light‐emitting diode light irradiation of seedlings improves seedling quality and growth after transplanting in red leaf lettuce. ­ HortSci., 45(12): 1809­1814. KALAJI M.H., GOLTSEV V.N., ZIVCAK M., BRESTIC M., 2017 ­ Chlorophyll fluorescence: understanding crop perfor‐ mance. Basics and applications. ‐ CRC Press Boca Raton, USA, pp. 236. KASAJIMA S., INOUE N., MAHMUD R., KATO M., 2008 ­ Developmental responses of wheat cv. Norin 61 to fluence rate of green light. ‐ Plant Product. Sci., 11: 76­ 81. KIM H.H., GOINS G.D., WHEELER R.M., SAGER J.C., 2004 ­ Stomatal conductance of lettuce grown under or expo‐ sured to different light qualities. ­ Ann. Bot., 94 (5): 691­697. KOPSELL DA., SAMS C.E., BARICKMAN T.C., MORROW R.C., 2014 ­ Sprouting broccoli accumulate higher concentra‐ tions of nutritionally important metabolites under nar‐ row‐band light‐emitting diode lighting. ­ J. Am. Soc. Hort. Sci., 139 (9): 469­477. KOPSELL D.A., SAMS C.E., MORROW R.C., 2016 ‐ Interaction of light quality and fertility on biomass, shoot pigmentation and xanthophyll cycle flux in Chinese kale. ­ J. Sci. Food Agric., 97(3): 911­917. KOZAI T., NIU G., TAKAGAKI M., 2015 ­ Plant factory, an indoor vertical farming system for efficient quality food production, first ed. ­ Academic Press, San Diego, USA, pp. 432. KUBOTA C., RAJAPAKSE N.C., YOUNG R.E., 1996 ­ Low‐tem‐ perature storage of micropropagated plantlets under selected light environments. ­ HortSci., 31 (3): 449­452. LARSON R.A., 1992 ­ Introduction to floriculture, Second edition. ­ Academic Press Inc, San Diego, USA, pp. 290. LEFSRUD M.G., KOPSELL D.A., SAMS C.E., 2008 ­Irradiance from distinct wavelength light‐emitting diodes affect Adv. Hort. Sci., 2020 34(4): 419­430 428 BULA R., MORROW R., TIBBITTS T., BARTA D., IGNATIUS R., MARTIN T., 1991 ­ Light‐emitting diodes as a radiation source for plants. ­ HortSci., 26(2): 203­205. CIERESZKO I., JOHANSSON H., KLECZKOWSKI L.A., 2001 ­ Sucrose and light regulation of a cold‐inducible UDP‐ glucose pyrophosphorylase gene via a hexokinase inde‐ pendent and abscisic acid‐insensitive pathway in Arabidopsis. ­ Biochem. J., 354(1): 67­72. CHEN X., XUE X., GUO W., WANG L., QIAO X., 2016 ­ Growth and nutritional properties of lettuce affected by mixed irradiation of white and supplemental light pro‐ vided by light‐emitting diode. ­ Sci. Hortic., 200: 111­ 118. COPE K.R., BUGBEE B., 2013 ­ Spectral effects of three types of white light‐emitting diodes on plant growth and development: absolute versus relative amounts of blue light. ­ HortSci., 48(4): 504­509. COSGROVE D.J., 1981 ­ Rapid suppression of growth by blue light occurrence, time course, and general charac‐ teristics. ­ Plant. Physiol., 67: 584­590. DOLE J.M., WILKINS H.F., 2005 ­ Floriculture: principles and species, second ed. ­ Pearson/Prentice Hall, New Jersey, USA, pp. 483. DOUGHER T.A.O., BUGBEE B., 2001 ­ Differences in the response of wheat, soybean and lettuce to reduced blue radiation. Photochem. ­ Photobiol., 73(2): 199­207. GÓMEZ C., MITCHELL C.A., 2015 ­ Growth responses of tomato seedlings to different spectra of supplemental lighting. ­ HortSci., 50: 112­118. GENTY B., BRIANTAIS J.M., BAKER N.R., 1989 ­ The relation‐ ship between the quantum yield of photosynthetic elec‐ tron transport and quenching of chlorophyll fluores‐ cence. ­ Biochim. Biophys. Acta (BBA)­General Subjects, 990: 87­92. GOINS G.D., YORIO N.C., SANWO M.M., BROWN C.S., 1997 ­ Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light‐emitting diodes (LEDs) with without supplemental blue lighting. ­ J. Exp. Bot., 48: 1407­1413. HERNÁNDEZ R., EGUCHI T., DEVECI M., KUBOTA C., 2016 ­ Tomato seedling physiological responses under differ‐ ent percentages of blue and red photon flux ratios using LEDs and cool white fluorescent lamps. ­ Sci. Hortic., 213: 270­280. HAVAUX M., KLOPPSTECH K., 2001 ­ The protective func‐ tions of carotenoid and flavonoid pigments against excess visible radiation at chilling temperature investi‐ gated in Arabidopsis npq and tt mutants. ­ Planta, 213: 953­966. HEO J., LEE C., CHAKRABARTY D., PAEK K., 2002 ­ Growth responses of marigold and salvia bedding plants as affected by monochromic or mixture radiation provided by a light‐emitting diode (LED). ­ Plant Growth Regul., 38: 225­230. HOENECKE M.E., BULA R.J., TIBBITTS T.W., 1992 ­ Importance of blue photon levels for lettuce seedlings Moazzeni et al. ‐ Production of Sinningia speciosa transplants under different light spectra 429 secondary metabolites in kale. ­ HortSci., 43 (7): 2243­ 2244. LI H., XU Z., TANG C., 2010 ­ Effect of light‐emitting diodes on growth and morphogenesis of upland cotton (Gossypium hirsutum L.) plantles in vitro. ­ J. Plant. Biotech., 103: 155­163. LICHTENTHALER H.K., WELBURN A.R., 1983 ­Determination of total carotenoids and chlorophylls a and b of leaf extracts in different solvents. ­ Biochem. Soc. Transac., 11(5): 591­592. LIN K.H., HUANG M.Y., HUANG W.D., HSU M.H., YANG Z.W., YANG C.M., 2013 ­ The effects of red, blue, and white light‐emitting diodes on the growth, develop‐ ment, and edible quality of hydroponically grown let‐ tuce (Lactuca sativa L. var. capitata). ­ Sci. Hortic., 150: 86­91. MAXWELL K., JOHNSON G.N., 2000 ­ Chlorophyll fluores­ cence a practical guide. ­ J. Exp. Bot., 51(345): 659­668. MCCREE K.J., 1972 ­The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. ­ Agric. Meteorol., 9: 191­216. MCNELLIS T.W., DENG X.W., 1995 ­ Light control of seedling morphogenetic pattern. ­ Plant Cell, 7(11): 1749­1761. MERCADO J.M., SANCHEZ­SAAVEDRA M.D., CORREA­REYES G., LUBIAN L., MONTERO O., FIGUEROA F.L., 2004 ­ Blue light effect on growth, light absorption character‐ istics and photosynthesis of five benthic diatom strains. ­ Aquat. Bot., 78(3): 265­277. MITCHELL C.A., BOTH A.J., BOURGET C.M., BURR J.F., KUB­ OTA C., LOPEZ R.G., MORROW R.C., RUNKLE E.S., 2012 ­ LEDs: the future of greenhouse lighting. ­ Chronica Hortic., 52: 6­10. MORROW R.C., 2008 ­ LED lighting in horticulture. ­ HortSci., 43 (7): 1947­1950. MATHUR S., MEHTA P, JAJOO A., 2013 ­ Effects of dual stress (high salt and high temperature) on the photo‐ chemical efficiency of wheat leaves (Triticum aestivum). ­ Physiol Mol. Biol. Plants, 19: 179­188. NELSON J.A., BUGBEE B., 2014 ­ Economic analysis of greenhouse lighting: light emitting diodes vs. high intensity discharge fixtures. ­ Plos One, 9(6): 1­10. NICOLE C.C.S., CHARALAMBOUS F., MARTINAKOS S., VAN DE VOORT S., LI Z., VERHOOG M., KRIJN M., 2016 ­ Lettuce growth and quality optimization in a plant fac‐ tory. ­ Acta Horticulturae, 1134: 231­238. ODA M., 2007 ­ Raising of vigorous and valuable seedlings. ­ Regul. Plant Grow. Develop., 42(2): 176­182 (in Japanese). OKAMOTO K., YANAGI T., KONDO S., 1997 ­ Growth and morphogenesis of lettuce seedlings raised under differ‐ ent combinations of red and blue light . ­ Acta Horticulturae, 435: 149­157. OUZOUNIS T., FRETTÉ X., OTTOSEN C.O., ROSENQVIST E., 2014 ­ Spectral effects of LEDs onchlorophyll fluores‐ cence and pigmentation in Phalaenopsis “Vivien” and “Purple Star”. ­ Physiol. Plant., 154(2): 314­327. POSPÍŠIL P., 2016 ­ Production of reactive oxygen species by photosystem II as a response to light and tempera‐ ture stress. ­ Front. Plant Sci., 7: 1­12. RIVKIN R.B., 1989 ­ Influence of irradiance and spectral quality on the carbon metabolism of phytoplankton. I. Photosynthesis, chemical composition and growth. ­ Mar. Ecol. Prog., 55(2/3): 291­304. SANCHEZ­SAAVEDRA M.P., VOLTOLINA D., 1994 ­ The chemical composition of Chaetoceros sp. (Bacillariophyceae) under different light conditions. ­ Comp. Biochem. Physiol. B: Comp. Biochem., 107: 39­ 44. SARKAR R., RAY A., 2016 ­ Submergence‐tolerant rice with‐ stands complete submergence even in saline water: probing through chlorophyll a fluorescence induction OJIP transients. ­ Photosynthetica, 54(2): 275­287. STEELE R., 2004 ­ Understanding and measuring the shelf‐ life of food. ­ Woodhead Publishing Limited and CRC Press, Cambridge, pp. 448. STRASSER B.J., 1995 ­ Measuring fast fluorescence tran‐ sients to address environmental questions: the JIP test, pp.977­980. ­ In: MATHIS P. (ed.) Photosynthesis: from light to biosphere. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp 125. STRASSER R.J., STIRBET A.D., 1998 ­ Heterogeneity of pho‐ tosystem II probed by the numerically simulated chloro‐ phyll a fluorescence rise (O‐J‐I‐P). ­ Math. Comput. Simul., 48: 3­9. STRASSER R.J., SRIVASTAVA A., TSIMILLI­MICHAEL M.G., 2000 ­ The fluorescence transient as a tool to charac‐ terize and screen photosynthetic samples,pp. 445­483. ­ In: YUNUS M., PATHRE U., MOHANTY P. (eds.) Probing photosynthesis: mechanisms, regulation and adapta‐ tion. CRC press, London and New York, pp. 214. STRASSER R.J., TSIMILLI­MICHAEL M., SRIVASTAVA A., 2004 ­ Analysis of the chlorophyll a fluorescence transient. pp. 321­362. ­ In: PAPAGEORGIOU G.C., GOVINDJEE (eds.)Chlorophyll a fluorescence. Springer, Dordrecht, pp. 174. TAKAHASHI S., MILWARD S.E., YAMORI W., EVANS J.R., HILLIER W., BADGER M.R., 2010 ­ The solar action spec‐ trum of photosystem II damage. ­ Plant physiol., 153(3): 988­993. TIBBITS T.W., MORGAN D.C., WARRINGTON T.J., 1983 ­ Growth of lettuce, spinach, mustard and wheat plants under four combinations of high‐pressure sodium, metal halide and tungsten halogen lamps at equal PPFD. ­ J. Am. Soc. Hortic. Sci., 108 (4): 622­630. TOZZI S., LERCARI B., ANGELINI L.G., 2005 ­ Light quality influences indigo precursors production and seed ger‐ mination in Isatis tinctoria L. and Isatis indigotica Fort. ­ Photochem. Photobiol., 81(4): 914­919. VADIVELOO A., MOHEIMANI N.R., COSGROVE J.J., BAHRI P.A., PARLEVLIET D., 2015 ­ Effect of different light spectra on the growth and productivity of acclimated Adv. Hort. Sci., 2020 34(4): 419­430 430 Nannochloropsis sp. (Eustigmato‐phyceae). ­ Algal Res., 8: 121­127. WARRINGTON I.J., MITCHELL K.J., 1976 ­ The influence of of blue‐ and red‐biased‐light spectra on the growth and development of plants. ­ Agric. Meteorol., 16: 247­262. WOJCIECHOWSKA R., DŁUGOSZ­GROCHOWSKA O., KOŁTON A., ŻUPNIK M., 2015 ­ Effects of LED supple‐ mental lighting on yield and some quality parameters of lamb’s lettuce grown in two winter cycles. ­ Sci. Hortic., 187: 80­86. WHITELAM G.C., HALLIDAY K.J., 2007 ­ Light and Plant Development. ­ Blackwell Publishing, Oxford. pp. 325. WYNNE D., RHEE G.Y., 1986 ­ Effects of light intensity and quality on the relative N and P requirement (the opti‐ mum N:P ratio) of marine planktonic algae. ­ J. Plankton Res., 8: 91­103. YORIO N.C., GOINS G.D., KAGIE H.R., WHEELER R.M., SAGER J.C., 2001 ­ Improving spinach, radish, and let‐ tuce grown under red light emitting diodes (LEDs) with blue light supplementation. ­ HortSci., 36: 380­383.