Journal of Applied Botany and Food Quality 89, 98 - 104 (2016), DOI:10.5073/JABFQ.2016.089.012 1 ICAR − Directorate of Groundnut Research, Junagadh, Gujarat, India 2 ICAR − Directorate of Medicinal and Aromatic Plants Research, Boriavi, Anand Gujarat, India Water deficit stress affects photosynthesis and the sugar profile in source and sink tissues of groundnut (Arachis hypogaea L.) and impacts kernel quality K. Chakraborty1, M.K. Mahatma1*, L.K. Thawait1, S.K. Bishi1, K.A. Kalariya1, 2, A.L. Singh1 (Received August 14, 2015) * Corresponding author Summary Water deficit stress conditions disturb photosynthetic activity of plants and thereby affect further growth and the mobilization of as- similates towards sink tissues. The influence of mid-season drought on sugar metabolism in both source and sink tissues and its sus- tained effect on kernel quality across three different habit groups of groundnut was investigated. The experiment was conducted in Kharif 2012 and water deficit stress was created by withholding irrigation for 40 days between 30 -70 days after sowing under rain- out shelter to simulate mid-season drought condition. Imposition of water deficit stress reduced net photosynthesis rate, which significantly altered the sugar profiles in leaf. The content of glucose, fructose and sucrose decreased in the leaf tissue, whereas the content of sugar alcohol (inositol and mannitol) and trehalose increased. The sugar profile of the sink tissue (kernel) was also altered under stress but changes were slightly different. The sugar alcohol and oligosaccharides (RFOs) showed significant increase, but the level of mono- and di-saccharides did not show significant change. The results suggested different drought tolerance strategies in source and sink tissues. The kernel quality was also affected under stress with lower oil and higher protein content. The content of oleic acid was reduced, while linoleic acid increased resulting in a decrease of the O/L ratio and oil stability. Alteration of quality traits was least in Spanish genotypes, suggesting a relatively better tolerance of this group for water deficit stress. Introduction Groundnut is an important oil seed legume grown worldwide most- ly in arid and semi arid region. Over 60 % of global groundnut production is crushed for extraction of oil for edible and industrial uses, while 40 % is consumed in food uses and as seed for sowing the next season crop (BIRTHAL et al., 2010). For the food industries, nutritional composition (oil, protein, fatty acid, amino acids and sugars) of groundnut is equally important with physical and sensory characteristics. The groundnut, mostly grown as rainfed in the arid and semi-arid regions is highly vulnerable to drought stresses of varying duration and intensity due to uncertain rainfall pattern (SINGH et al., 2013). Depending on the time of occurrence, drought has been characterized as early season, mid-season, and end-of-the-season drought. Mid- and end-of-the-season droughts are critical as they affect the pod yield and quality (JANILA et al., 2013). Water deficit stress during pod-development phase is detrimental to several physiological and biochemical processes (NAUTIYAL et al., 1991).Water stress conditions disturb photosynthetic activity of plants and thereby affects further vegetative growth and the mobilization of assimilates towards storage or sink tissues. Sugars in plants, derived from photosynthesis, act as substrates for energy metabolism and the biosynthesis of complex carbohydrates, providing sink tissues with the necessary resources for growth and development. Responses to a specific stress can vary with the genotype, but some general reactions occur in all. Under sugar depleted condition, substantial physiological and bio- chemical changes occur to sustain respiration and other metabolic processes (JOURNET et al., 1986) Sucrose and glucose either act as the substrates for cellular respiration or as the osmolytes to maintain cellular osmotic potential (GUPTA et al., 2005). Sugars have also been shown to directly protect membranes and proteins in vitro, possibly by replacing water molecules and altering physical properties through the formation of hydrogen bonds (CROWE et al., 1992). The production and partitioning of metabolically important non-structural carbohydrates (starch and sugar alcohols) have been reported to accumulate during drought (KELLER and LUDLOW, 1993). A linear polyhydric alcohol, mannitol, has been reported to increase in response to salt stress mostly due to the osmotic factor of salt stress than its ionic toxicity (PHARR et al., 1995). Expression of the mtlD gene for the biosynthesis of mannitol improved tolerance to water stress in transgenic groundnut plants (BHAUSO et al., 2014). Another important sugar alcohol which has diverse role in plant biology is myo-inositol, a six carbon cyclohexane hexitol. Myo-inositol is not only required in plant growth and development, but also required as a precursor and substrate for many crucial metabolites in plants such as phytate, phosphatidylinositol, galactinol, raffinose-family oligosaccharides (RFOs), ascorbate, indole acetic acid conjugate, ononitol, and pinitol. These inositol derivatives were shown to be implicated in various physiological and signal processes including plant stress adaptation (LOEWUS and MURTHY, 2000; DONAHUE et al., 2010). Although, there are a few reports on the effect of drought stress on yield and kernel quality of groundnut (DWIVEDI et al., 1996; CHAKRABORTY et al., 2013), yet adequate information on its impact on sugar profiles of the source and sink tissues and kernel quality is not available. Thus, present investigation was conducted to study the impact of mid-season drought on the sugar profile in source and sink tissues and also consequent effect on kernel quality traits. Materials and methods Plant material and growing condition An experiment was conducted in Kharif 2012 (June-October) using 12 popular groundnut cultivars, four each from three different habit groups (Spanish bunch type (SB): AK 159, DRG 1, JL 286, TPG 41; Virginia bunch (VB) type: GG 20, HNG 10, ICGS 76, Kadiri 3; Virginia runner (VR) type: GG 11, GG 16, CSMG 84-1, Somnath) at the research farm of the Directorate of Groundnut Research, Junagadh, Gujarat, India. The cultivars were raised in both open field (rain-fed with protective irrigation, unstressed) and rain-out shelter (ROS; imposed water deficit stress). The water deficit stress was imposed by withholding the irrigation after 30 days after sowing (DAS) and continued up to 70 DAS in the ROS. Samples were collected from third upper leaf in triplicate from 70 days old plants. The crop was harvested at full maturity and after curing, the kernel Water deficit stress alters sugar profile in groundnut 99 samples were collected from both control and water deficit stressed plots for analysis of quality attributes. The weather condition during the study period was presented in Tab. 1. Due to imposition of water deficit stress by withholding irrigation for 40 days from 30-70 DAS, soil moisture content was reduced from 18.5 % to 10.9 % at 0-15 cm soil depth and 19.1 % to 12.3 % at 15-30 cm soil depth compared to irrigated control plot where optimum moisture level (18.5-19.1 %) was maintained throughout the crop growth period (Fig. 1). These values correspond to the threshold value below which groundnut productivity is se- verely affected. All the cultivars studied started experiencing water deficit conditions at about 45 DAS, some cultivars (DRG 1, Kadiri 3, Somnath) started a few days before. Measurement of net photosynthesis rate (PN) Net photosynthesis rate (PN) was measured using a portable photo- synthesis system (Model LI-6400, LI-COR, USA) between 09:30- 11:30 h local time. Temperature was set at ambient with a stable Tleaf reading. Photosynthetically active radiation (PAR) was set at 1,650 μmol(photon) m-2 s-1 inside the cuvette, and CO2 was supplied artificially to keep the concentration stable at 400 μmol m-2 s-1 inside the chamber (SINGH et al., 2014). Oil and protein content Oil and protein content of groundnut meal were determined by standard methods i.e. Soxhlet and Kjeldahl method, respectively. Fatty acid analysis The fatty acids methyl esters (FAME) of groundnut oil were prepared and analyzed by gas chromatography. In a 10 ml screw cap test tube, 200 μl oil was mixed with 3 ml hexane and kept for 1 h at room temperature with intermittent mixing using vortex. After that 3 ml of freshly prepared Sodium methoxide (80 mg NaOH in 100 ml methanol) was added and incubated at room temperature for 30 min. Then 3 ml of 0.8 % aqueous sodium chloride was mixed with gentle shaking. Solution was allowed to settle for 5 min and the upper layer of hexane containing the methyl-esters were transferred in screw capped glass vial containing 100 mg anhydrous sodium sulphate (MISRA and MATHUR, 1998). The FAME (10 μl) of groundnut oil were analysed by Gas Chromatograph (Netel India Ltd., Model MICHRO 9100), using 15 % DEGS packed column. The oven temperature during analysis kept at 190 °C, injector temperature at 240 °C and FID detector temperature at 260 °C. Carrier gas (nitrogen) flow rate was maintained at 30 ml min-1 and fuel gas (hydrogen) flow at 30 ml min-1. Extraction of sugars, free amino acids and total phenolics The 500 mg of defatted flour was homogenized with 10 ml of 80 % ethanol in glass vial and kept in boiling water bath for 10 min. After that, samples were centrifuged at 5000 rpm for 10 min. Extraction was repeated three times with 10 ml of 80 % ethanol and supernatants were pooled into 100 ml volumetric flasks and referred as ethanol extract hereafter. Estimation of free amino acids and total phenolics The total free amino acids and total phenolics from ethanol extract were determined by using ninhydrin and Folin-Ciocalteu reagents respectively, as described in our earlier reports (BISHI et al., 2015). Briefly, for total free amino acid estimation, 0.4 ml of ethanol extract was taken in test tube. A 5 ml of ninhydrin reagent (5:12:2; 1 % ninhydrin in 0.5 M citrate buffer pH5.5: Glycerol: 0.5 M Citrate buffer pH 5.5) was added and mixed thoroughly. The tubes were then placed in a boiling water bath for 12 min and brought to room temperature under running water. The absorbance of the colour was read at 570 nm. The standard curve was prepared by using glycine in the range of 0-80 μg. For total phenols, one ml of ethanol extract was transferred to a test tube and evaporated till dryness. The residue was dissolved in 1.0 ml water and 0.5 ml of Folin-ciocalteu reagent (1 N), was added to each test tube, mixed, and allowed to stand for 3 min. Subsequently, 2 ml of 20 % Na2CO3 was added, mixed thoroughly and then placed in a boiling water bath for one min. After that test tubes were cooled in ice water and the colour was read at 650 nm. Catechol in the range of 0-25 μg was used as the standard. Tab. 1: Monthly mean weather data during crop growth period (Kharif 2012). Figures in parenthesis under the field rainfall represent total number of rainy days during that month. Month Temperature (oC) Relative humidity (%) Evaporation (mm) Rainfall (mm) Max Min Mean Max Min Mean June 36.5 27.0 31.7 79 50 64 234.0 84.2 (3) July 33.7 26.2 30.0 86 64 75 139.5 67.6 (6) August 32.0 25.0 28.5 91 69 80 105.4 79.5 (7) September 32.0 24.5 28.2 89 67 78 102.0 193.7 (10) October 37.0 21.5 29.2 66 30 48 186.0 0.0 (0) Total 766.9 425.0 (26) Fig. 1: Changes in soil moisture content (w/w) at different soil depth due to imposition of water deficit stress 100 K. Chakraborty, M.K. Mahatma, L.K. Thawait, S.K. Bishi, K.A. Kalariya, A.L. Singh Sugar profiles by ion chromatography Sugars extracted in ethanol were separated by ion chromatograhy as reported in our earlier paper (BISHI et al., 2013). Glucose, fructose, myo-inositol, lactose, sucrose, raffinose, stachyose, and verbascose were used as standards. Lactose was used as internal standard du- ring the analysis. The concentrations of various components in the standard mixture were adjusted to such levels that a distinct peak for each was obtained in the chromatogram. Ethanol extracts were membrane-filtered and an aliquot of 25 μl of samples was injected in the ion chromatograph (ICS 3000 Dionex, USA) equipped with amino trap column, CarboPac PA10 guard column followed by CarboPac PA10 analytical column. Sugars were eluted from column in 150 mM NaOH with a flow rate of 1 ml min-1. Data integration was attained by using Chromeleon software supplied with the equipment. Statistical analysis All the data recorded were the mean values of at least three independent assays with three replications each. The data was subjected to analysis of variance appropriate to the experimental design. Differences at LSDP=0.05 were considered statistically significant. Results Effect of water deficit stress on photosynthesis Water deficit stress significantly reduced the rate of photosynthesis in all the genotypes; however there were enough variations observed in the genotypes of different habit group (Fig. 2). In terms of per- centage change in net photosynthetic rate Virginia genotypes showed greater reduction compared to Spanish type. At individual genotype level, HNG 10 showed highest reduction (32.7 %) in photosynthesis rate followed by Somnath (29.7 %) and Kadiri 3 (28.1 %). This result suggested, for photosynthetic parameters relatively greater susceptibility of Virginia type peanut cultivars to water deficit stress than Spanish type. Changes in the sugars profile in the leaf tissue Imposition of water deficit stress altered the sugar profile in leaf tissues as a result of changes in the net photosynthesis as well as partitioning of the net photosynthate for production of carbohydrates (Tab. 2). Content of both inositol and mannitol increased in the leaf tissue under water deficit stress in all the genotypes across different habit groups. On an average the inositol content almost doubled in Spanish group, whereas the increase in Virginia group was about 50 %. Among the genotypes JL 286 and TPG 41 showed highest increase (148 and 125 %, respectively) in inositol content under stress compared to the control plants. Similarly, accumulation of mannitol in the leaf tissue also showed the increasing trend under stress. The increase was highest in SB habit group (86 %), followed by VR (46 %) and VB (33 %) group. Among the genotypes, again JL 286 showed highest increase in mannitol accumulation and it increased to 521 ppm under stress from the control value of 245 ppm, whereas genotype ICGS 76 showed least increase (10 %). Tab. 2: Sugar profiles (ppm) of groundnut leaves during water deficit stress Habit Cultivar Inositol Mannitol Trehalose Glucose Fructose Sucrose Group Control Stress Control Stress Control Stress Control Stress Control Stress Control Stress AK 159 7119 7774 206 435 254 443 19613 13719 14416 10106 19926 8110 Spanish DRG 1 5065 10167 259 357 219 304 12103 6214 10248 4602 11914 3779 Bunch JL 286 4915 12209 245 521 150 643 10732 8386 9296 6143 16699 5931 TPG 41 5022 11315 211 390 180 569 19593 11105 16662 8406 20607 13498 GG 20 5492 10970 273 347 260 192 14418 11777 9446 8987 21165 9445 Viginia HNG 10 7629 9694 169 293 ND ND 14198 7853 10574 5746 21284 11203 Bunch ICGS 76 6035 9707 281 307 440 402 13406 9070 11657 7249 22417 15442 Kadiri 3 7724 11869 280 340 13 ND 13453 9536 10264 7087 20339 13406 CSMG 84-1 5169 5884 307 372 369 203 9748 7411 7056 5767 12558 7586 Virginia GG 11 7078 7961 251 393 ND ND 13689 7049 10265 5839 22593 11293 Runner GG 16 6687 8478 316 469 243 154 10885 10694 8196 8072 18435 2263 Somnath 5507 10296 191 304 119 250 13273 11490 9582 9090 17438 13692 LSD Variety (V) 71.3 14.2 14.4 118.4 130.1 222.9 (P=0.05) Treatment (T) 299.8 NS 27.3 450.5 282.5 78.4 V × T 100.9 20.1 20.4 167.4 184.1 315.3 ND: not detected, NS: means non-significant Fig. 2: Changes in net photosynthesis rate (PN) in groundnut leaves under water deficit stress Water deficit stress alters sugar profile in groundnut 101 On the other hand, the content of different mono- and disaccharide were reduced with imposition of stress, except trehalose (Tab. 2). Under stress, trehalose content in the leaf showed significant increase mostly in SB genotypes; however for Virginia genotypes it remained either unchanged or even reduced in some cases, except Somnath which showed almost 67 % increase. Among the genotypes JL 286 and TPG 41 showed highest increase up to 643 and 569 ppm from a control value of 150 and 180 ppm, respectively. The content of other free sugar viz. glucose, fructose and sucrose reduced in all the genotypes under stress and the highest reduction was observed in SB genotypes (36, 42 and 57 % reduction, respectively for glucose, fructose and sucrose), followed by VB and VR group. Changes in the sugars profile in the kernel Like that of leaf sugar alcohols level, similar increasing trend was also observed in kernel under stress (Tab. 3). The level of inositol was more than doubled in the kernel of Spanish genotypes under stress, whereas the increase was less than half for Virginia genotypes. Among the genotypes JL 286 and TPG 41 showed highest increase (150 and 115 % respectively), under stress quite similar to that of leaf tissue. Mannitol content in the kernel also increased significantly under stress and among different habit groups SB showed highest increase, followed by VR and VB group. The genotype JL 286 again showed highest increase mannitol content (144 %), while least increase was observed for HNG 10 (14 %). Trehalose content in the kernel was increased under stress only in SB group, but it was significantly reduced in both VB and VR group (Tab. 3). Highest increase in trehalose content was observed in JL 286 (103 %), followed by TPG 41 (69 %), while the genotype CSMG 84-1 showed highest reduction (69 %). The glucose content in the kernel was increased under stress in almost all the genotypes except GG 11 and GG 16 (Tab. 3). More than 75 % increase in kernel glucose content was observed in TPG 41 and Somnath under stress, while in some of the genotypes like Kadiri 3 and CSMG 84-1, the increase was as low as 20 %. Unlike that of leaf, the sucrose content in the kernel increased under stress in most of the genotypes except AK 159 and JL 286 (Tab. 3). Highest increase in kernel sucrose content was observed in Somnath, followed by GG 11, where it was increased up to 47.6 and 65.3 mg g-1 seed weight under stress from the control value of 27.9 and 47.1mg g-1 seed weight, respectively. Total raffinose family oligosaccharides (RFOs) content (raffinose and stachyose) was also increased in the kernel under stress (Tab. 3). On an average the SB group showed 39 % increase in RFOs content under stress, whereas, it was 31 and 16 % for VR and VB group respectively. Among the genotypes TPG 41 showed highest increase (84 %) in RFOs content under stress, followed by JL 286 (47 %), while the genotypes ICGS 76 and CSMG 84-1 showed least change in RFOs content when the stress was imposed. Changes in kernel quality parameters Imposition of water deficit stress significantly reduced the oil yield and altered different kernel quality parameters in all the genotypes (Tab. 4). Among different habit groups, SB showed least loss in oil content, where highest oil loss was observed in VR group. Among the genotypes JL 286 showed the least reduction (1.8 %) in oil con- tent whereas Somnath showed the highest reduction (13.1 %). Unlike oil the total protein content increased under stress, the genotype CSMG 84-1 showed highest increase (23.4 %), followed by JL 286 (22.7 %). The free amino acid content was also increased under stress and the highest increase was observed in CSMG 84-1, where increased up to 4.30 mg g-1 seed weight from a control value of 2.23. This increase in free amino acid content might possibly be due to increase in kernel protein content as well as stress induced breakdown of it. The total phenol content showed a mixed response under stress. Although the varietal differences were significant, but no significant treatment effect was observed in the present study. Changes in oil quality parameters Imposition of water deficit stress altered the relative content of oleic and linoleic acid in the groundnut kernel, ultimately altering the O/L ratio and the keeping quality of the oil (Fig. 3). Oleic acid content Tab. 3: Sugar profiles (ppm) of groundnut kernels during water deficit stress Habit Cultivar Inositol Mannitol Trehalose Glucose Sucrose RFOs Group Control Stress Control Stress Control Stress Control Stress Control Stress Control Stress AK 159 464 826 207 387 601 894 86 124 26768 22061 1614 1855 Spanish DRG 1 517 910 290 575 311 489 ND 120 22626 30043 1273 1403 Bunch JL 286 320 807 300 731 751 1524 69 99 40704 34354 1867 2749 TPG 41 512 1094 577 1026 74 124 170 299 31925 40505 1440 2650 GG 20 368 698 368 424 292 110 ND 71 36569 50318 3341 4088 Viginia HNG 10 700 840 553 635 50 64 83 140 53065 73576 4111 5155 Bunch ICGS 76 694 911 505 703 211 103 ND 172 54806 57069 3667 3668 Kadiri 3 670 892 611 930 57 67 158 191 45567 63218 4178 4810 CSMG 84-1 996 1429 473 835 579 178 104 126 47063 65350 3777 3540 Virginia GG 11 545 739 760 995 449 254 99 ND 35931 50344 2643 3863 Runner GG 16 1093 1246 459 601 234 198 111 ND 51852 63565 2253 3200 Somnath 347 579 660 936 313 127 78 139 27888 47652 2251 3167 LSD Variety (V) 31.6 39.6 52.3 5.1 198.1 67.7 (P=0.05) Treatment (T) 33.7 10.6 NS NS 548.4 105.1 V × T 44.7 55.9 74.1 7.1 280.1 95.8 ND: not detected, NS: means non-significant 102 K. Chakraborty, M.K. Mahatma, L.K. Thawait, S.K. Bishi, K.A. Kalariya, A.L. Singh significantly reduced in all the cultivars under water deficit stress (Fig. 3A) however, highest reduction observed in Virginia genotypes than that of Spanish ones. The genotype Kadiri 3 showed the high- est reduction (12.9 %) in oleic acid content under stress, followed by HNG 10 (11.3 %). Linoleic acid content showed the opposite trend and was found to be increased under stress (Fig. 3B). The increase was highest in HNG 10 (31.4 %), followed by Kadiri 3 (28.2 %), whereas AK 159 showed least change (4.5 %) under stress. With the decrease in oleic acid content and concomitant rise in linoleic acid fraction resulted in an obvious decrease in O/L ratio in the groundnut kernels in all the genotypes in the present study (Fig. 3C). The genotypes HNG 10 and Kadiri 3 showed highest reduction in O/L ratio, which was 32.4 and 32.0 %, respectively under water deficit stress. Discussion In the present study imposition of prolonged water deficit stress led to significant alternation of physiological and metabolic activities in both source (leaf) and sink (kernel) tissue in groundnut, however the impact varies across different habit groups. Although groundnut is a moderately drought tolerant crop, the imposition of drought stress especially during mid or late season of crop growth significantly reduces various metabolic activities of the crop mainly due to lack of adequate water supply to the active tissue and eventual closure of stomata (DEVI et al., 2009). KALARIYA et al. (2013) also reported a 11-30 % reduction in net photosynthesis in groundnut during water deficit stress. Limitation of photosynthetic activity under severe wa-ter deficit stress was also attributed to rapid degradation of thylakoid membranes in groundnut apart from stomatal constraint (LAURIANO et al., 2000). A decreased rate of photosynthesis in water deficit stress affects carbon delivery from source to sink tissue and its subsequent metabolism. The photosynthetic rate of leaves decreases as relative water content and water potential decreases. A reduction of the net photosynthetic rate in moisture stressed plants mainly happens through stomatal closure as a mechanism to reduce total transpiration (SINGH, 2004; ROSAS-ANDERSON et al., 2014). As a result of reduced photosynthetic activities under water de- Tab. 4: Effect of water deficit stress on oil, protein, free amino acids and total phenol content of groundnut kernels Habit Group Cultivar Oil (%) Protein (%) Free amino acids (mg-1 g) Total Phenol (mg-1 g) Control Stress Control Stress Control Stress Control Stress AK 159 54.50 53.30 20.60 21.75 2.09 1.82 4.96 4.44 DRG 1 53.10 51.90 23.50 26.05 2.55 2.85 4.55 4.95 JL 286 48.05 47.20 30.40 32.90 2.38 2.63 4.21 4.27 TPG 41 49.75 46.40 24.25 29.75 2.90 2.73 5.25 5.05 GG 20 52.15 48.00 25.70 30.20 2.95 3.80 4.87 5.90 HNG 10 45.85 43.75 33.75 35.25 2.95 4.28 5.41 5.13 ICGS 76 48.75 46.95 30.60 32.60 3.02 3.89 5.53 7.05 Kadiri 3 46.05 43.90 33.05 35.80 3.39 5.04 7.04 6.84 CSMG 84-1 48.80 45.15 27.50 33.95 2.23 4.30 4.07 5.83 GG 11 51.65 45.55 26.55 31.70 2.83 3.85 5.15 5.82 GG 16 46.30 45.25 32.90 34.50 4.13 5.63 5.22 6.52 Somnath 53.20 46.25 23.15 32.65 2.41 3.69 4.77 5.00 Variety (V) 0.81 1.05 0.13 0.27 LSD (P=0.05) Treatment (T) 1.98 0.74 0.64 NS V × T 1.16 1.48 0.19 NS NS: means non-significant (a) (b) (c) Fig. 3: Changes in Oleic (a), Linoleic (b) acid content and O/L ratio (c) in groundnut cultivars under water deficit stress Spanish Bunch Viginia Bunch Virginia Runner Water deficit stress alters sugar profile in groundnut 103 ficit stress, significant alteration in the sugar profile was observed in different groups of groundnut cultivars. Due to lower supply of net assimilate, the carbon partitioning in the leaf tissue changed sig- nificantly. The content of readily available carbohydrates (glucose, sucrose and fructose) dropped, whereas carbohydrates necessary for stress tolerance (inositol, mannitol and trehalose) increased upon imposition of stress. Similar increase in the levels of sugar alcohol, particularly the pinitol, and decrease in the levels of sucrose was observed by Keller and LUDLOW (1993) in the leaves of pigeon pea after imposition of drought stress. MORSY et al., (2007) reported higher accumulation of osmo-protectants like trehalose, inositol and mannitol in the more salt and water-deficit tolerant rice genotype, which suggested role of these organic solutes in osmo-tolerance mechanism in plants. Mannitol, an important photoassimilate which participates in a wide range of physiological processes including car- bon storage and translocation, regulation of the pool of the cellular reductant in plants (STOOP and MOOIBROEK, 1998), scavenging of hydroxyl radicals and serving as an osmotically active compatible solute (POPP and SMIRNOFF, 1995). In the presents study, increase in the content of inositol, mannitol and trehalose occurs at the expense of simpler carbohydrates such as glucose, fructose and sucrose con- tent in the leaves of stressed plants. Like the sugar alcohols, trehalose is also proposed as an osmopro- tectant during periods of drought or water-deficit stresses (PENNA, 2003). This sugar possesses the unique capacity for reversible water absorption, and appears to be superior to other sugars in protecting biological molecules from desiccation-induced damage (RONTEIN et al., 2002). Adverse conditions such as heat, chilling or water stress correlate with the accumulation of high concentrations of trehalose in yeast (GODDJIN and VAN DUN, 1999) and highly desiccation- tolerant resurrection plants (ITURRIAGA et al., 2000). Differential responses of cultivars from different habit groups to water deficit stress implied their variable ability to tolerate stress. In the present study, Spanish group of cultivars showed highest induction in accu- mulation of organic solute in response to external water deficit con- dition suggesting their superior ability to tolerate drought stress than Virginia group of cultivars. Reduction of sucrose content in the leaf tissue during stress condition may contribute to either higher trans- port towards kernels or its rapid conversion to more complex sugars for better osmo-protection. Thus results from the present study sug- gest decrease of hexoses under stress condition is likely to be utilized in the biosynthesis of higher sucrose content in the sink tissues. In general, sucrose levels of stressed ovaries are higher or at least simi- lar to those of non-stressed ovaries as reported in maize (SCHUSSLER and WESTGATE, 1995; ZINSELMEIER et al., 1995). Although the sugar profile of the kernel (sink tissue) changed sig- nificantly like that of leaf (source tissue), the pattern of change was found somewhat different in the present study. Similar to the changes in leaf tissue, the content of sugar alcohols increased along with in- crease in stress induced oligosaccharide (Raffinose and Stachyose) content, but the level of monosaccharide and disaccharides did not show significant alteration in the kernel tissue. Inositol and its de- rivatives are implicated in stress tolerance through various ways such as protecting cellular structures from reactive oxygen species, controlling turgor pressure or by acting as stress signaling molecules (LOEWUS and MURTHY, 2000). As non-reducing carbohydrates, RFOs are good storage compounds, being able to accumulate in large quantities without affecting primary metabolic processes. Few previous studies reported that desiccation tolerance is strongly cor- related with accumulation of RFOs, primarily raffinose, stachyose, and verbascose in the seeds (HORBOWICZ and OBENDORF, 1994; LIN and HUANG, 1994). Water deficit stress has dual impact on the end product synthesis in groundnut kernels. Being primarily an oilseed crop, water deficit stress significantly reduced oil yield and thus altered kernel compo- sition. The lack of adequate C-supply from the source tissue (both due to reduced photosynthesis and conversion of assimilate for biosynthesis of organic osmo-protectants) resulted in reduction in kernel oil content, but a relative increase in protein content in the present study. Similarly, CONKERTON et al. (1989) also reported that mid-season drought reduced total oil content in groundnut. Oil has negative correlation with protein content thus decrease in oil con- tent may eventually results in increased protein content. However, we do differ from some of the previous reports that total oil and total protein were not significantly affected by mid-season drought (DWIVEDI et al., 1996). Under drought stress, due to shortening of pod development and seed filling period alteration of oil/protein ratio in legume seeds were reported, which was mainly because of the fact that during seed filling accumulation of carbohydrate and protein were much faster than that of oil (DORNBOS and MCDONALD, 1986; KAMBIRANDA et al., 2011). HASHIM et al. (1993) also observed comparatively higher percentage of linoleic acid (18:2) and lower percentage of oleic acid (18:1) in the groundnut kernels when it was grown under water deficit condition. Our results also suggest that there is a shift of oleic to linoleic acid under water deficit stress resulting in reduced O/L ratio and oil stability. In conclusion, mid-season water deficit stress in groundnut sig- nificantly affects the carbohydrate composition and source and sink sugar profiles. The increase in relative proportions of stress induced complex sugars (myo-inositol and mannitol) in the leaf tissue show- ing the adaptive response to osmo-tolerance. On the contrary, re- duction in simple sugars under stress in the leaf with subsequent translocation to sink tissue suggests a drought escape mechanism in groundnut. Oleic acid content, a measure of oil stability and qua- lity, was also decreased due to water deficit condition. The quality traits were comparatively less affected in Spanish genotypes than in Virginia genotypes due to water deficit stress; hence the Spanish cul- tivars would be a better choice for the farmers in rain-fed groundnut growing areas. Acknowledgement Authors are thankful to the Director, ICAR-Directorate of Groundnut Research, Junagadh, India for providing necessary facilities. 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