The present study assessed the effect of abscisic acid (ABA; 25 µM) and/or nitrogen (N; 10 mM) in minimization of salinity (NaCl; 100mM)-impact on growth, photosynthetic efficiency, Rubisco activity, nitrogen and sulfur assimilation, oxidative stress (H2O2), lipid peroxidation measured as thiobarbituric acid reactive substances, (TBARS), osmolyte (Proline) content, and the activity of antioxidant enzymes (superoxide dismutase, SOD glutathione reductase, GR; ascorbate peroxidase, APX) in cultivar RH0-749 of Brassica juncea L. NaCl stress caused significant elevations in H2O2 and TBARS, and differentially modulated proline content, the activity of antioxidant enzymes, and impaired growth and photosynthetic functions. Exogenously applied 25 µM ABA negatively affected plant growth and photosynthesis in B. juncea without NaCl. In contrast, exogenously applied 25 µM ABA and 10 mM N, alone or in combination minimized oxidative stress, and maintained a fine-tuning between proline content and the activity of antioxidant enzymes, and thereby improved plant growth and photosynthetic functions in NaCl exposed B. juncea.

Photosynthesis is a pivotal process that determines the synthesis of carbohydrates required for sustaining growth under normal or stress situation. Stress exposure reduces the photosynthetic potential owing to the excess synthesis of reactive oxygen species that disturb the proper functioning of photosynthetic apparatus. This decreased photosynthesis is associated with disturbances in carbohydrate metabolism resulting in reduced growth under stress. We evaluated the importance of melatonin in reducing heat stress-induced severity in wheat plants (Triticum aestivum L.). The plants were subjected to 25 ˚C (optimum temperature) or 40 ˚C (heat stress) for 15 days at 6 hours time duration and then developed the plants for 30 days. Heat stress led to oxidative stress with increased production of TBARS and H2O2 content and reduced accrual of total soluble sugars, starch and carbohydrate metabolism enzymes which are reflected in reduced photosynthesis. Application of melatonin not only reduced oxidative stress through lowering TBARS and H2O2 content, through augmenting the activity of antioxidative enzymes but also increased the photosynthesis in plant and carbohydrate metabolism that is needed to provide energy and carbon skeleton to the developing plant under stress. However, the increase in these parameters with melatonin was mediated via hydrogen sulfide (H2S), as the inhibition of H2S by hypotaurine (HT; H2S inhibitor) reversed the ameliorative effect of melatonin. This suggests a crosstalk of melatonin and H2S in protecting heat stress-induced photosynthetic inhibition via regulation of carbohydrate metabolism.

In the present study, the potential of ethylene as ethephon (an ethylene source) was investigated individually or with a combination of the split dosage of nitrogen (N) and sulfur (S) soil treatments for the removal of damaging effects of salt stress (100 mM NaCl) in mustard (Brassica juncea L.). Plants were grown with 50 mg N plus 50 mg S kg−1 soil at sowing time and an equivalent dosage at 20 days after sowing ([N50 + S50]0d + [N50 + S50]20d). Ethephon at 200 μL L‒1 was applied to combined split dosage of N and S with or without NaCl. Plants subjected to NaCl showed a deceased in growth and photosynthetic characteristics as well as N and S assimilation, though, proline metabolism and antioxidants increased. The application of ethephon to plants grown with split N and S dosages significantly enhanced the photosynthetic efficiency by increasing the assimilation of N and S, improving the content of proline and induction of the antioxidant system with or without NaCl. The regulation of ethylene and/or split form N and S application may be the potential tools for overcoming salt stress effects in this species and in related Brassicaceae.

The effect of four soil-applied sulfur [S; 100 mg S kg-1 soil (100S) and 200 mg S kg-1 soil (200S)] in different sources (elemental S, ammonium sulfate, gypsum or magnesium sulfate) in protecting mustard (Brassica juncea L. Czern & Coss.) from cadmium effects was studied. Based on the observed reduction in growth and photosynthesis in plants subjected to 100 and 200 mg Cd kg-1 soil, B. juncea cv. Giriraj was selected as the most Cd-tolerant among five cultivars (namely, Giriraj, RH-0749, Pusa Agrani, RH-406, and Pusa Tarak). Sulfur applied to soil mitigated the negative impact of Cd on sulfur assimilation, cell viability and photosynthetic functions, with a lower lipid peroxidation, electrolyte leakage, and contents of reactive oxygen species (ROS: hydrogen peroxide, H2O2, and superoxide anion, O2•−). Generally, added S caused a higher activity of antioxidant enzymes (ascorbate peroxidase, catalase and superoxide dismutase), and contents of ascorbate (AsA) and reduced glutathione (GSH), and increases in the activities of their regenerating enzymes (dehydroascorbate reductase and GSH reductase), as well as rises in S assimilation, biosynthesis of non-protein thiols (NPTs) and phytochelatins (PCs). Compared to the other S-sources tested, elemental S more prominently protected B. juncea cv. Giriraj against Cd-impacts by minimizing Cd-accumulation and its root-to-shoot translocation; decreasing cellular ROS and membrane damage, and improving Cd-chelation (NPTs and PCs), so strengthening the defense machinery against Cd. The results suggest the use of elemental S for favoring the growth and development of cultivated plants also in Cd-contaminated agricultural soils.