Mitigation of salinity stress by exogenous application of cytokinin in faba bean (Vicia faba L.)

Soil salinity limits agricultural land use and crop productivity, thereby a major threat to global food safety. Plants treated with several phytohormones including cytokinins were recently proved as a powerful tool to enhance plant’s adaptation against various abiotic stresses. The current study was designed to investigate the potential role of 6-benzyladenine (BA) to improve broad bean (Vicia faba L.) salinity tolerance. The salt-stressed broad bean plantlets were classified into two groups, one of which was sprayed with water and another was sprayed with 200 ppm of BA. Foliar applications of BA to salt-exposed plants promoted the growth performance which was evidenced by enhanced root-shoot fresh and dry biomass. Reduced proline was strongly connected to the enhanced soluble proteins and free amino acids contents, protecting plant osmotic potential following BA treatment in salt-stressed broad bean. BA balanced entire mineral homeostasis and improved mineral absorption and translocation from roots to shoots, shoots to seeds and roots to seeds in salt-stressed plants. Excessive salt accumulation increased malondialdehyde level in leaves creating oxidative stress and disrupting cell membrane whereas BA supplementation reduced lipid peroxidation and improved oxidative defence. BA spray to salinity-stressed plants also compensated oxidative damage by boosting antioxidants defence mechanisms, as increased the enzymatic activity of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase. Moreover, clustering heatmap and principal component analysis revealed that mineral imbalances, osmotic impairments and increased oxidative damage were the major contributors to salts toxicity, on the contrary, BA-augmented mineral homeostasis and higher antioxidant capacity were the reliable markers for creating salinity stress tolerance in broad bean. In conclusion, the exogenous application of BA alleviated the antagonistic effect of salinity and possessed broad bean to positively regulate the osmoprotectants, ion homeostasis, antioxidant activity and finally plant growth and yield, perhaps suggesting these easily-accessible and eco-friendly organic compounds could be powerful tools for the management of broad bean growth as well as the development of plant resiliency in saline prone soils

Zinc limitation and toxicity in crops and effects of Silicon in ameliorating stress response.

Agriculture is the primary food source for human sustainability. The improvement of food provision through agriculture represents a major topic for plant biology. In addition to drought, salinity and starvation, the remediation from soil contaminations by metalloids and heavy metals is important to guarantee food safety. Metalloids are beneficial and necessary elements for higher plants at low concentrations, but high levels of these result severely toxic both for plants and humans. Soil contamination induced by an excess of some metalloids is a widespread problem over the world, causing economic disease and health threatens by human consumption. In addition to metalloids, heavy metal pollution is rapidly increasing and present many environmental problems. Among heavy metals, some metals such as cadmium (Cd), lead (Pb) and chromium (Cr) have no known biological role while others such as copper (Cu), manganese (Mn) and zinc (Zn) are required in small amount for normal plant growth and developments but are extremely toxic to plants and animals slightly larger than the required concentrations. While some metalloids and heavy metals effects are largely identified, a number of potential ameliorative effects of silicon (Si) are actually discussed. In fact, the silicon utilization as fertilizer is a recent suggestion to guarantee a compatible and sustainable agriculture inducing plant growth and to improve biotic and abiotic stress tolerance, such as metalloids deficiency or toxicity. In the present doctoral thesis, we analyzed three horticultural plants of great agronomic importance, exhibiting different tolerance to Zn, Lactuca sativa cv. Phillipus, Brassica oleracea cv. Bronco, and barley (Hordeum vulgare). These species were exposed to Zn toxicity and deficiency in order to evaluate the contribution of compatible osmolytes, in the mechanism(s) of tolerance to Zn stress. As further control, the effects of a heavy metal such as cadmium were tested on barley plants in order to discriminate and confront the damages induced by polluting metals with those caused by limitation or excess of a nutritional microelement as zinc. Furthermore, we studied the possible beneficial effect of Si on ameliorating plant stress conditions in Hordeum vulgare. In conclusion, this project suggests that metals excess and/or deficiency induces in crops substantially similar responses depending on their capability to manage the stress induced by pollutants. Furthermore, stress symptoms induced by metals are clearly mitigated by Si supply, thus improving plant tolerance mechanisms such as photosynthesis and photorespiratory systems

Citric Acid-Mediated Abiotic Stress Tolerance in Plants

Several recent studies have shown that citric acid/citrate (CA) can confer abiotic stress tolerance to plants. Exogenous CA application leads to improved growth and yield in crop plants under various abiotic stress conditions. Improved physiological outcomes are associated with higher photosynthetic rates, reduced reactive oxygen species, and better osmoregulation. Application of CA also induces antioxidant defense systems, promotes increased chlorophyll content, and affects secondary metabolism to limit plant growth restrictions under stress. In particular, CA has a major impact on relieving heavy metal stress by promoting precipitation, chelation, and sequestration of metal ions. This review summarizes the mechanisms that mediate CA-regulated changes in plants, primarily CA's involvement in the control of physiological and molecular processes in plants under abiotic stress conditions. We also review genetic engineering strategies for CA-mediated abiotic stress tolerance. Finally, we propose a model to explain how CA's position in complex metabolic networks involving the biosynthesis of phytohormones, amino acids, signaling molecules, and other secondary metabolites could explain some of its abiotic stress-ameliorating properties. This review summarizes our current understanding of CA-mediated abiotic stress tolerance and highlights areas where additional research is needed

Sodium selenate treatment using a combination of seed priming and foliar spray alleviates salinity stress in rice

Soil salinity is one of the important abiotic stress factors that affect rice productivity and quality. Research with several dicotyledonous plants indicated that the detrimental effects associated with salinity stress can (partly) be overcome by the external application of antioxidative substances. For instance, sodium selenate (Na2SeO4) significantly improved the growth and productivity of several crops under various abiotic stress conditions. At present there is no report describing the impact of Na2SeO4 on salinity stressed cereals such as rice. Rice cultivation is threatened by increasing salinity stress, and in future this problem will further be aggravated by global warming and sea level rise, impacting coastal areas. The current study reports on the effect of Na2SeO4 in alleviating salinity stress in rice plants. The optimal concentration of Na2SeO4 and the most efficient mode of selenium application were investigated. Selenium, sodium, and potassium contents in leaves were determined. Antioxidant enzyme activities as well as proline, hydrogen peroxide (H2O2), and malondialdehyde (MDA) concentrations were analyzed. In addition, the transcript levels for OsNHX1, an important Na+/H+ antiporter, were quantified. Treatment of 2-week-old rice plants under 150 mM NaCl stress with 6 mg l(-1) Na2SeO4 improved the total biomass. A significantly higher biomass was observed for the plants that received Na2SeO4 by a combination of seed priming and foliar spray compared to the individual treatments. The Na2SeO4 application enhanced the activity of antioxidant enzymes (SOD, APX, CAT, and GSH-Px), increased the proline content, and reduced H2O2 and MDA concentrations in plants under NaCl stress. These biochemical changes were accompanied by increased transcript levels for OsNHX1 resulting in a higher K+/Na+ ratio in the rice plants under NaCl stress. The results suggest that Na2SeO4 treatment alleviates the adverse effect of salinity on rice plant growth through enhancing the antioxidant defense system and increase of OsNHX1 transcript levels

Plant Oxidative Stress: Biology, Physiology and Mitigation

This Special Issue, “Plant Oxidative Stress: Biology, Physiology, and Mitigation”, published 11 original research works and 1 review article that discussed the various aspects of ROS Biology, metabolism, and the physiological mechanisms and approaches to mitigating oxidative stress. These types of research studies show further directions for the development of crop plants that are tolerant to abiotic stress in the era of climate change

Salicylic Acid: An All-Rounder in Regulating Abiotic Stress Responses in Plants

Salicylic acid (SA) is an endogenous growth regulator of phenolic nature and also a signaling molecule, which participates in the regulation of physiological processes in plants such as growth, photosynthesis, and other metabolic processes. Several studies support a major role of SA in modulating the plant response to various abiotic stresses. It is a well-founded fact that SA potentially generates a wide array of metabolic responses in plants and also affects plant-water relations. This molecule also found to be very active in mitigating oxidative stress under adverse environmental conditions. Since abiotic stress remained the greatest constraints for crop production worldwide, finding effective approaches is an important task for plant biologists. Hence, understanding the physiological role of SA would help in developing abiotic stress tolerance in plants. In this chapter, we will shed light on the recent progress on the regulatory role of SA in mitigating abiotic stress

Salicylic acid and thiourea ameliorate the negative impact of salt stress in wheat (Triticum aestivum L.) seedlings by up-regulating photosynthetic pigments, leaf water status, and antioxidant defense system

Salinity is one of the most important abiotic stress inhibiting wheat (Triticum aestivum L.) growth and development. Therefore, finding efficient strategies to prevent salt-induced growth retardation and yield loss is critical for modern agriculture to sustain production. The role of exogenous salicylic acid (SA) and thiourea (TU) in regulating salt tolerance was investigated by evaluating morpho-physiological characteristics and antioxidant response in two wheat genotypes at the seedling stage. In both wheat genotypes, salt stress reduced growth characteristics and leaf water status, photosynthetic pigments, while simultaneously increasing the Na+/K+ ratio, hydrogen peroxide (H2O2), and malondialdehyde (MDA). In contrast, exogenous application of SA and/or TU alone in the salt-stressed plants significantly reduced the negative effects of salt stress and improved the growth performance by up-regulating photosynthetic pigments, leaf water status, and proline content in both genotypes. Besides, when compared to seedlings treated only with salt stress, SA and TU played an important role in maintaining lower Na+/K+ levels and reducing oxidative stress by lowering MDA and H2O2 levels in salt-stressed plants through boosting the activities of antioxidant enzymes such as catalase, ascorbate peroxidase, and peroxidase. In addition, hierarchical clustering and principal component analysis revealed a significant interaction among growth characteristics, chlorophyll content, carotenoid content and antioxidant activity with the salt, SA, and/or TU treatments. The findings suggested that exogenous application of SA or TU could be a useful technique for reducing the negative effects of salinity on wheat growth and development

Approaches in Enhancing Antioxidant Defense in Plants

This Special Issue, “Approaches in Enhancing Antioxidant Defense in Plants” published 13 original research works and a couple of review articles that discuss the various aspects of plant oxidative stress biology and ROS metabolism, as well as the physiological mechanisms and approaches to enhancing antioxidant defense and mitigating oxidative stress. These papers will serve as a foundation for plant oxidative stress tolerance and, in the long term, provide further research directions in the development of crop plants’ tolerance to abiotic stress in the era of climate change

Physiological Role of Ascobin on Quality and Productivity of Sunflower Plants Irrigated with Sodium Chloride Solution

Ascobin had a promotion effect on growth and active constituents’ compounds of various plants under normal and stressed conditions. The physiological response of sunflower plant to foliar application of ascobin treatments (200,400,600 ppm) was investigated either under normal or salinity stressed conditions (5000 ppm NaCl solution) in pot experiments at the wire-house of the National Research Centre, Dokki, Cairo, Egypt. Data revealed that salinity stress caused significant decreases in shoot height, leaf area chlrorophyll b, carotenoids, total photosynthetic pigments, seed yield, yield components, oil and protein content of the yielded seeds relative to control. The decrease in oil percentage was more obvious by salinity than protein percentage. Since salinity caused decreases in oil % by10.42% and decreases in protein % by 3.44% relative to control. Meanwhile, salinity stress caused significant increases in H2O2, MDA and activity of antioxidant enzymes (CAT, SOD, APX and GR) as well as total soluble carbohydrate, phenolic content, proline, free amino acids. Salinity stress caused significant increases in sum of stearic acid and palmitic acid accompanied by significant decreases in sum of oleic and linoleic acids as well as ratio of oleic/linoleic and total unsaturated fatty acids/total saturated fatty acids. On the other hand, ascobin treatments caused significant increases in most of growth parameters and activity of all antioxidant enzymes under investigation accompanied by significant decreases in H2O2 and MDA under normal and stressed conditions relative to corresponding controls. Ascobin treatment at 400 ppm showed significant increases in all components of photosynthetic pigments under normal condition relative to control. Meanwhile ascobin treatments significantly decreased total soluble carbohydrate, phenolic content and increased proline and free amino acids. It was noted that all treatments alleviate the harmful effect of salinity stress on sunflower yield and yield components. Since all treatments caused significant increases in yield and yield components as well as oil and protein percentages. Ascobin treatment at 400 ppm was the most optimum treatments in increasing seed yield/plant by 44.78% under normal condition and by 45.43% under stressed conditions relative to corresponding controls. Oleic acid and linoleic acid significantly increased by ascobin treatment at 400 ppm leading to non-significant decrease in total saturated fatty acid and significant increase in total unsaturated fatty acids