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 VOLUME Vol.05 Issue05 2025 

PAGE NO. 1-5 

 
 
 
 
 

Enhancing Urea Metabolism and Stress Tolerance in 

Tomato Through Foliar Nickel Application 
 

Simon Johnson 

Department of Plant Sciences, University of California, Davis, USA 

 

Rio Martinez 

Department of Horticultural Science, University of Madrid, Spain 

 

Received: 03 March 2025; Accepted: 02 April 2025; Published: 01 May 2025 

 

Abstract: Nickel (Ni) is recognized as an essential micronutrient pivotal for urea metabolism and stress mitigation 
in plants. This study synthesizes research findings to examine the role of foliar Ni application in improving urea 
conversion efficiency and enhancing abiotic stress resilience in tomato (Solanum lycopersicum). Highlighting 
biochemical, physiological, and agronomic perspectives, the article elaborates how Ni influences urease 
activation, antioxidant defense systems, and stress alleviation mechanisms. Results from previous studies 
demonstrate the critical contribution of Ni in managing nutrient assimilation, fruit quality, and disease resistance, 
suggesting a promising agricultural strategy to ensure tomato productivity under environmental challenges.   

 

Keywords: Nickel (Ni) nutrition, urease activity, urea metabolism, tomato (Solanum lycopersicum), abiotic stress 
tolerance, nitrogen use efficiency (NUE), foliar fertilization, antioxidant defense, blossom-end rot, climate change 
resilience. 

 

Introduction: Tomato (Solanum lycopersicum), a 
globally significant horticultural crop, is highly 
susceptible to abiotic stresses, including salinity, 
drought, and nutrient imbalance [11, 19, 28, 31]. 
Climate change further exacerbates these stress 
conditions, necessitating innovative agronomic 
strategies to sustain tomato yield and quality [12, 44]. 

Nickel (Ni) has been increasingly acknowledged as a 
crucial micronutrient essential for the functioning of 
urease, the enzyme responsible for hydrolyzing urea 
into usable nitrogen forms for plant metabolism [6, 24, 
32]. Urea-based fertilization, although widely adopted 
for its high nitrogen content, can suffer from inefficient 
conversion without sufficient Ni availability, leading to 
reduced nitrogen-use efficiency and environmental 
nitrogen losses [1, 35, 46]. 

Several studies emphasize that foliar Ni application not 
only enhances urease activity but also bolsters 
antioxidant mechanisms, thus providing dual benefits 
of improved nutrient utilization and abiotic stress 
mitigation [2, 14, 23]. In tomatoes, Ni has also been 
linked to improved calcium accumulation, reduced 

blossom-end rot incidence, and overall enhancement 
of fruit development [20, 21, 22]. 

Given these multifaceted roles, the present review 
systematically explores the impacts of foliar Ni 
application on urea conversion and stress mitigation in 
tomatoes, drawing upon findings across agronomy, 
plant physiology, and molecular biology domains. 

Tomato (Solanum lycopersicum) is one of the most 
widely cultivated and economically significant crops 
globally, providing essential nutrients and vitamins to 
millions of people. However, its growth and 
productivity are often constrained by various 
environmental factors, including abiotic stresses such 
as drought, high temperature, and soil nutrient 
imbalances. Among these, nitrogen (N) is a critical 
macronutrient that influences tomato growth, 
development, and fruit yield. Urea, a widely used 
nitrogen fertilizer, plays a pivotal role in meeting the 
nitrogen demands of crops. However, the efficiency of 
urea utilization in plants can be suboptimal, often 
leading to nitrogen losses in the environment through 
processes such as volatilization and leaching. This 

 



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inefficiency not only compromises crop yield but also 
exacerbates environmental pollution, making nitrogen 
management a crucial aspect of sustainable 
agriculture. 

Recent studies have explored the potential of 
micronutrients in improving nitrogen metabolism in 
plants, particularly in enhancing the efficiency of urea 
conversion. Among these micronutrients, nickel (Ni) 
has gained significant attention due to its essential role 
in various plant physiological processes, including 
nitrogen metabolism. Nickel is a co-factor for the 
enzyme urease, which catalyzes the hydrolysis of urea 
into ammonia and carbon dioxide. Adequate nickel 
availability is crucial for optimal urease activity, which 
in turn enhances nitrogen use efficiency (NUE) and 
minimizes nitrogen losses in the soil. Despite its 
importance, nickel deficiency is often overlooked in 
agricultural practices, especially in regions with low 
nickel content in the soil. 

The application of nickel as a foliar fertilizer has 
emerged as a promising strategy for mitigating nickel 
deficiency in plants and improving urea conversion 
efficiency. Foliar application allows for the direct 
absorption of nickel by the leaves, ensuring a more 
rapid response compared to soil application. Studies 
have shown that foliar nickel application can enhance 
urease activity, promote better nitrogen assimilation, 
and improve overall plant growth and productivity. 
Furthermore, nickel’s role in plant stress tolerance has 
also been well-documented. It has been found to boost 
antioxidant defense systems and reduce the negative 
impacts of various abiotic stresses, including oxidative 
stress induced by drought and salinity. 

Tomato plants, in particular, exhibit increased 
susceptibility to various forms of abiotic stress, 
including drought, salinity, and nutrient deficiencies. 
These stresses often lead to reduced yield, poor fruit 
quality, and increased susceptibility to diseases such as 
blossom-end rot. Nickel, through its involvement in 
antioxidant metabolism and stress signaling pathways, 
has shown potential in mitigating these stresses, 
thereby improving plant resilience. Moreover, the 
interplay between nickel and calcium in tomatoes has 
been an area of particular interest. Blossom-end rot, a 
common disorder in tomatoes, has been associated 
with calcium deficiency, but recent studies suggest that 
nickel can help reduce its incidence, even under 
conditions of calcium deficiency. 

The importance of optimizing nutrient management 
strategies, particularly for micronutrients like nickel, is 
becoming increasingly evident in the face of climate 
change and its associated impacts on crop production. 
As global temperatures rise and water availability 

becomes more uncertain, the ability to enhance crop 
resilience and nutrient efficiency through 
micronutrient supplementation could be a critical tool 
for ensuring food security. Therefore, understanding 
the role of foliar nickel application in improving urea 
conversion, mitigating abiotic stress, and enhancing 
overall tomato productivity is of paramount 
importance for sustainable agricultural practices in the 
coming decades. 

This review aims to explore the role of foliar nickel 
application in tomato cultivation, focusing on its effects 
on urea conversion, nitrogen metabolism, and abiotic 
stress mitigation. By synthesizing current research 
findings, this article provides a comprehensive 
overview of the physiological mechanisms underlying 
nickel's action in plants and its potential as a tool for 
enhancing tomato growth under challenging 
environmental conditions. 

METHODS 

Literature Search Strategy 

A comprehensive literature search was conducted in 
scientific databases including Web of Science, Scopus, 
and Google Scholar, targeting peer-reviewed articles 
published between 1987 and 2024. Keywords such as 
"nickel nutrition," "urea hydrolysis," "abiotic stress in 
tomato," "urease activity," and "foliar micronutrient 
application" were utilized. 

Selection Criteria 

Studies selected for inclusion specifically addressed: 

• Effects of Ni supplementation (particularly via 
foliar application) on tomatoes or related crops. 

• Observations related to urea metabolism, 
antioxidant enzyme activity, and stress resistance. 

• Experimental designs including field trials, 
greenhouse experiments, and hydroponic systems. 

Data Extraction 

Key findings, methods, and conclusions were 
systematically extracted and cross-referenced. 
Attention was given to studies linking biochemical, 
physiological, and agronomic outcomes with Ni 
applications. 

RESULTS 

1. Importance of Nickel in Plant Urea Metabolism 

Nickel is a cofactor for urease, which catalyzes the 
hydrolysis of urea into ammonium ions, critical for 
nitrogen assimilation in plants [6, 36, 32]. Deficiency in 
Ni can lead to urea accumulation, resulting in cellular 
toxicity and impaired growth [6, 38]. 

Tan et al. (2000) demonstrated that tomatoes supplied 
with urea as the sole nitrogen source showed 



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significantly improved growth when supplemented 
with Ni, underlining the element's necessity for 
effective nitrogen utilization [45]. Similarly, Myrach et 
al. (2017) reported that the urease activation complex 

depends on Ni delivery via accessory proteins [36]. 

 

2. Foliar Application: A Targeted Approach 

Foliar application of Ni offers a precise method to 
correct micronutrient deficiencies and enhance 
physiological processes without relying solely on soil 
nutrient availability [16, 42]. Studies on soybeans 
(Barcelos et al., 2018) and barley (Kumar et al., 2018) 
have shown that foliar Ni treatments significantly 
increased urease activity and improved overall nutrient 
status [2, 25]. 

Macedo et al. (2022) found that foliar Ni application in 
tomatoes boosted calcium accumulation in fruits, 
helping mitigate blossom-end rot, a major quality issue 
[21]. 

3. Role of Nickel in Abiotic Stress Mitigation 

Abiotic stresses such as drought, salinity, and heat 
disrupt plant metabolism, primarily by inducing 
oxidative stress [11, 13, 15]. Ni plays a vital role in 
activating antioxidant enzymes, thus reducing oxidative 
damage under stress conditions [14, 18]. 

Garai et al. (2020) highlighted the role of glyoxalase 
systems in stress recovery, where Ni-dependent 
enzymes help detoxify harmful metabolites [13]. 
Nickel-mediated enhancement of the antioxidant 
defense system has also been linked to improved 
tolerance to salt and drought stresses in tomato plants 
[19, 28, 29]. 

4. Influence on Fruit Development and Quality 

Nickel application has profound effects on fruit 
development processes. Macedo et al. (2021) reported 
that Ni supplementation altered calcium distribution 
patterns in tomato fruits, promoting uniform ripening 

and better structural integrity [22]. Moreover, proper 
Ni nutrition reduces the incidence of physiological 
disorders like blossom-end rot by enhancing calcium 
and nitrogen metabolism [20, 21, 50]. 

According to Sovarel et al. (2016), foliar fertilizers 
containing micronutrients, including Ni, significantly 
improved tomato yield and fruit quality traits such as 
sugar content, firmness, and color [43]. 

DISCUSSION 

Synergistic Role of Nickel in Nutrient Assimilation and 
Stress Response 

Nickel enhances nitrogen-use efficiency not only by 
activating urease but also by facilitating a broader 
range of physiological responses vital under stress 
conditions [24, 32, 36]. The antioxidant properties 
conferred by Ni supplementation help protect plant 
cells against ROS accumulation, a common 
consequence of abiotic stresses [14, 18, 29]. 

The strong interplay between urease activation, 
antioxidant defense, and calcium metabolism 
underscores the multi-dimensional benefits of foliar Ni 
applications. 

Practical Implications for Tomato Cultivation 

Applying Ni through foliar sprays can be a practical 
intervention for improving urea-based fertilization 
strategies, particularly under stress-prone 
environments [42, 43, 49]. Given the projected increase 
in climate-related stress events [12, 44, 47], foliar Ni 
supplementation could serve as an essential 
component of resilient tomato production systems. 

Moreover, managing soil and tissue Ni levels could 



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prevent hidden deficiencies, a concept increasingly 
emphasized in recent soil fertility studies [46]. 

Future Research Directions 

Further investigations are warranted to: 

• Optimize foliar Ni dosage and application 
timing specific to tomato growth stages. 

• Explore molecular mechanisms underpinning 
Ni-regulated gene expression during stress responses 
[31, 41]. 

• Assess long-term environmental impacts of 
increased Ni usage in agricultural systems. 

CONCLUSION 

Foliar application of nickel emerges as a promising 
strategy to enhance urea conversion, optimize nitrogen 
metabolism, and strengthen abiotic stress resilience in 
tomato cultivation. By simultaneously improving 
nutrient efficiency and physiological robustness, Ni 
supplementation aligns with sustainable agricultural 
goals aimed at ensuring crop productivity amidst 
climatic and environmental challenges. 

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