Heavy metal (HM) stress is threatening agricultural crops, ecological systems, and human health worldwide. HM toxicity adversely affects plant growth, physiological processes, and crop productivity by disturbing cellular ionic balance, metabolic balance, cell membrane integrity, and protein and enzyme activities. Plants under HM stress intrinsically develop mechanisms to counter the adversities of HM but not prevent them. However, the exogenous application of abscisic acid (ABA) is a strategy for boosting the tolerance capacity of plants against HM toxicity by improving osmolyte accumulation and antioxidant machinery. ABA is an essential plant growth regulator that modulates various plant growth and metabolic processes, including seed development and germination, vegetative growth, stomatal regulation, flowering, and leaf senescence under diverse environmental conditions. This review summarizes ABA biosynthesis, signaling, transport, and catabolism in plant tissues and the adverse effects of HM stress on crop plants. Moreover, we describe the role of ABA in mitigating HM stress and elucidating the interplay of ABA with other plant growth regulators.

Plant growth regulators (PGRs) are naturally occurring signaling molecules that modulate numerous phenological traits and physicochemical features of plants throughout their life cycles. Exogenous supplementation of PGRs is an effective strategy for improving the productivity of important agricultural crops. This research was planned to evaluate the effects of six PGRs, namely indole-3-acetic acid (IAA), 24-epibrassinolide (EBL), gibberellic acid (GA₃), putrescine (put), salicylic acid (SA) and triacontanol (Tria), on morphology, photosynthesis, nutrient acquisition, and the yield and quality characteristics of three mustard cultivars, i.e., Chutki, Nath Sona, and Rohini. Two foliar sprays each of water, IAA (10⁻⁶ M), EBL (10⁻⁶ M), GA₃ (10⁻⁵ M), put (10⁻³ M), 10⁻⁵ M SA, and Tria (10⁻⁶ M) were applied to plants at fifty and seventy days after sowing (DAS). The crops’ phenological, physicochemical and microscopic parameters were evaluated at ninety DAS, and yield characteristics were evaluated at harvest (120 DAS). The observations of this study indicated that foliar feeding with PGRs increased all studied parameters, relative to water-spray treatment. The Nath Sona cultivar displayed a stronger response than Rohini and Chutki. Among the leaf-applied PGRs, 24-EBL, followed by IAA and GA₃, proved the most effective and improved all the studied parameters. Moreover, the exogenous application of PGRs, especially EBL, significantly enhanced stomatal dimensions and root cell longevity. Treatment with EBL enhanced plant dry weight by 34.7, 35.4, and 37.6%, the net photosynthetic rate by 65.3, 64.7, and 60.2%, seed yield per plant by 67.1, 65.2, and 67.3%, and oil yield per plant by 42.6, 48.2, and 41.1%, in the Chutki, Nath Sona, and Rohini cultivars, respectively, relative to the water-spray treatment. It may be concluded that of the tested PGRs, 24-EBL proved most effective at enhancing the morphological, physicochemical, and yield features of the mustard cultivars.

Background: Due to increasing domestic and industrial demand, edible oil production is not keeping up with demand. To fill this gap, the productivity of oilseeds can be increased by applying adequate nutrients, particularly sulphur (S), at the crucial growth stage. Purpose: The present study aims to explore the best concentration of S for its foliar application on various cultivars of mustard. Methods: A factorial randomized pot experiment was conducted to investigate the role of leaf-applied S on growth, physiobiochemistry, yield and quality traits of three cultivars of Brassica juncea L. (mustard). Five levels of S viz. 0 (water), 15, 30, 45 and 60 ppm S constituted one variant, and the three cultivars (Chutki, Nath Sona and Rohini) were the other variants. The various levels of S were sprayed at 50 and 70 days after sowing (DAS). The growth and physio-biochemical characteristics were studied at 90 DAS, and yield and quality attributes at 120 DAS (harvest). Results: The data indicated that increasing S levels up to 45 ppm S improved all parameters of mustard and thereafter (at the level above 45 ppm S) decreased. Cultivar Nath Sona, followed by Rohini and Chutki, performed best. Among the foliar spray treatment of different levels of S, the application of 45 ppm S increased plant dry weight by 40.21, 35.65 and 30.96%, photosynthetic rate by 28.27, 27.44 and 36.29%, pods of a plant by 15.23, 12.12 and 10.80%, seed yield of a plant by 7.54, 3.89 and 4.91%, oil content by 48.70, 46.31 and 43.15% and oil yield of a plant by 24.56, 23.93 and 22.35% in cultivar Nath Sona, Rohini and Chutki, respectively, compared with their respective water-treated plants. Moreover, the oil was examined by GC-MS technique for its various components. The analysis revealed that there were 36 compounds in the oil of the non-treated plants and 44 compounds in the oil of plants treated with 45 ppm S. The extra compounds resulted from the application of 45 ppm S. Conclusion: It may be concluded that two sprays of 45 ppm S proved effective in improving the growth, physio-biochemical characteristics, yield and quality of cultivars of mustard, particularly Nath Sona.