Effect of Salt Stress on Nutritional Value of Vegetables

Vegetables serve as a source of pharmacologically active molecules. However, due to increased environmental stresses the concentration of bioactive compounds and the valuable constituents of vegetables are getting deteriorated day by day. Salt stress is one of the major environmental stresses affecting the plants nutritional value. Salt stress influences the plant growth by inducing adverse effects on different physiological and biochemical processes and thus leads to nutrient disorder. Therefore, there is a need to develop some tools/techniques which would be helpful for the farmers whose soil or irrigation water are saline as well as those people who frequently consume vegetables for nutritional purposes. Effect of Salt Stress on Nutritional Value of Vegetables Sheo Mohan Prasad1*, Parul Parihar1 and Vijay Pratap Singh2* 1Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad-211002, Uttar Pradesh, India 2Govt. Ramanuj Pratap Singhdev Post Graduate College, Baikunthpur, Korea-497335, Chhattisgarh, India *Corresponding author: Vijay Pratap Singh, Govt. Ramanuj Pratap Singhdev Post Graduate College, Baikunthpur, Korea-497335, Chhattisgarh, India E-mail: vijaypratap.au@gmail.com Sheo Mohan Prasad, Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad-211002, Uttar Pradesh, India, E-mail: profsmprasad@gmail.com Received March 28, 2014; Accepted March 29, 2014; Published Aprile 7, 2014 Citation: Prasad SM, Parihar P, Singh VP (2014) Effect of Salt Stress on Nutritional Value of Vegetables. Biochem Pharmacol 3: e160. doi:10.4172/21670501.1000e160 Copyright: © 2014 Prasad SM, et al. This is an open-access article 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.


Introduction
Vegetables are the immense source of pharmacologically active molecules which have been used for treatment of diseases without any adverse effect and therefore constitute a major portion of human diet. They contain nutritional values like micronutrients, macronutrients, antioxidants, vitamins etc. However, the increased environmental stresses have strong influence on the concentration of bioactive compounds and the valuable constituents of vegetables are getting deteriorated day by day. Salt stress is one of the major environmental stresses affecting the plants nutritional value. The adverse effect of excess minerals on plant is called salt stress and it is a huge problem negatively affecting physiological and metabolic processes in plant life, ultimately diminishing growth and yield. This editorial shed light on adverse impact of salt stress on nutritional value of vegetables

Effect of Salt Stress on Nutritional Value of Vegetables
Salt taken up by the plants influence the plant growth by inducing adverse effects on different physiological and biochemical processes, including turgor, photosynthesis and enzymatic activities and all these processes are regulated by the nutrients in plants. Due to salt uptake there is reduced uptake of the nutrients that leads to nutrient disorder. Nutrient imbalance results from the effect of salinity on nutrient availability, competitive uptake, transport or partitioning within the plant or may be caused by physiological inactivation of a given nutrient resulting in an increase in the plant's internal requirement for that essential element [1]. For example, salinity reduces phosphate uptake and accumulation in crops grown in soils primarily by reducing phosphate availability. Salinity dominated by Na + salts not only reduces Ca² + availability but also reduces its transport and mobility to growing regions of the plant, affecting the quality of both vegetative and reproductive organs. These disorders are aggravated in the environment with high transpirational demands. Salinity directly affects nutrient uptake such as Na + reducing K + uptake or by Clreducing NO₃uptake. The occurrence of these disorders ultimately affects crop yield and quality. Nitrogen (N), in one form or another, accounts for about 80% of the total mineral nutrients absorbed by plants [2]. Moreover, inadequate nitrogen is often acts as a growthlimiting nutritional stress in field soils. N uptake, translocation, and assimilation as well as nitrogen natural isotopic signature appear to be especially sensitive to salinity [3].
Potassium being the most prominent inorganic plant solute makes a major contribution to the low osmotic potential in the stele of the roots that is a prerequisite for turgor-pressure-driven solute transport in the xylem and the water balance of plants [2]. But under saline condition i.e. high level of external Na + not only interferes with K + acquisition by the roots, but also may disrupt the integrity of root membranes and alters their selectivity. Calcium plays an essential role in processes that preserve the structural and functional integrity of plant membranes, stabilise cell wall structures, regulate ion transport and selectivity, and control ion-exchange behaviour as well as cell wall enzyme activities [4]. As the salt concentration in the root zone increases, plant requirement for Ca² + also increases. At the same time, the uptake of Ca² + from the substrate may be depressed because of ion interactions, precipitation, and increases in ionic strength. These factors reduce the activity of Ca² + in solution thereby decreasing Ca² + availability to the plant which leads to calcium disorders in plants.
Magnesium being an important component of chlorophyll is adversely affected by increased salinity. Calcium is strongly competitive with Mg² + and the binding sites on the root plasma membrane appear to have less affinity for the highly hydrated Mg² + than for Ca² + [2]. Thus, high concentrations of substrate Ca² + often result in increased leaf-Ca along with a marked reduction in leaf-Mg and this might lead to reduced photosynthetic activity of plants.
The availability of most micronutrients depends on the pH of the soil solution as well as the nature of binding sites on organic and inorganic particle surfaces. In saline soil, the solubility of micronutrients (e.g. Cu, Fe, Mn, Mo and Zn) is particularly low, and plants grown in these soils often experience deficiencies in these elements [5], but not in all cases. Differences can be attributed to plant type, plant tissue, salinity level and composition, micronutrient concentration, growing

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conditions and the duration of study. Consequently, the relationship between salinity and trace element nutrition is complex and salinity may increase, decrease, or have no effect on the micronutrient concentration in plant shoots.
Salinity not only influences the nutrients of vegetable crops but also degrades the antioxidant property. Bano et al. [6] have found a significant salt-induced suppression in plant growth, total phenolics, total soluble proteins, and activities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD). On the other hand, they observed a considerable increase in leaf turgor potential, Na + and Clcontents, proline, glycinebetaine (GB), ascorbic acid (AsA), and H₂O₂ contents in the leaf or root tissues of carrot plants under similar condition. These results suggest that the nutritional value in terms of antioxidants declines under salt stress.

Conclusion
Vegetables are essentially required to safeguard health particularly by precluding diseases as they are good source of vitamins, mineral nutrients and antioxidants but the increased salinity problem possesses threat to the nutritional values of the vegetables. Therefore, there is a need to develop some tools/techniques which would be helpful for the farmers whose soil or irrigation water are saline as well as those people who frequently consume vegetables for nutritional purposes. Developing such techniques would also curtail the crop losses due to salinity problem which is a major area of concern these days.