Heavy metal toxicity is one of the most devastating abiotic stresses. Heavy metals cause serious damage to plant growth and productivity, which is a major problem for sustainable agriculture. It adversely affects plant molecular physiology and biochemistry by generating osmotic stress, ionic imbalance, oxidative stress, membrane disorganization, cellular toxicity, and metabolic homeostasis. To improve and stimulate plant tolerance to heavy metal stress, the application of biostimulants can be an effective approach without threatening the ecosystem. Melatonin (N-acetyl-5-methoxytryptamine), a biostimulator, plant growth regulator, and antioxidant, promotes plant tolerance to heavy metal stress by improving redox and nutrient homeostasis, osmotic balance, and primary and secondary metabolism. It is important to perceive the complete and detailed regulatory mechanisms of exogenous and endogenous melatonin-mediated heavy metal-toxicity mitigation in plants to identify potential research gaps that should be addressed in the future. This review provides a novel insight to understand the multifunctional role of melatonin in reducing heavy metal stress and the underlying molecular mechanisms.

Maize (Zea mays L.) is one of the most important cereal crops cultivated around the world. Waterlogging stress is a major production constraint of maize production in rain-fed agricultural systems. The main objective of this experiment was to investigate the effect of continuous waterlogging on morphological and biochemical traits of maize genotypes at the vegetative stage. Ten maize genotypes were treated under no waterlogging (control) and continuous waterlogging of five centimeters depth for 10 days. The treatments were applied to the plants at their 45 days of age. Visual leaf injury scores from Leaf 4 (youngest leaf is the reference point) to Leaf 7 separated tolerant and susceptible genotypes. Waterlogging stress significantly reduced the total number of live leaves and chlorophyll content in leaf tissues in susceptible genotypes. The anatomical study revealed that tolerant maize genotypes produce a large number of aerenchyma cells under waterlogging stress compared to susceptible genotypes. The enzymatic activities of ascorbate peroxidase (APX) and peroxidase (POD) exhibited a greater increase in tolerant genotypes than susceptible genotypes whereas the contents of reactive oxygen species (H2O2) greatly increased in susceptible genotypes than tolerant genotypes under waterlogging stress compared to control. Principal component 2 (PC2) indicated that increasing plant height in the genotypes BHM-14, BHM-13 and BHM-9 was associated with waterlogging tolerance. The findings of this experiment will add value to maize breeding to screen out maize genotypes for waterlogging stress tolerance.

The E2F family gene is one of the most important G ₁ –S checkpoint regulatory transcription factors to monitor and regulate the accurate DNA replication and progression of the cell cycle in eukaryotes. Expression of this gene in multiple environmental factors has been reported in diversified plant species. However, characterization and investigation of the putative influential role of this family gene in Brassica species were not reported. In addition to expression profiling and mRNA target analysis, we have comprehensively identified and characterized 14 Br E2F/DP transcription factors from the data in available databases of Brassica rapa and compared them with five other species. Six pairs of segmentally duplicated BrE2F/DP paralogous genes were identified in this study, with Ka/Ks values of < 1.0. The findings indicated their evolution through segmental duplication across the chromosome after the Brassica splits from Arabidopsis and functional similarities with Brassica oleracea proteins. Most of the stress‐responsive microRNA (miRNA) targeted BrE2F/DP5 , BrE2F/DP12 , BrE2F/DP1, and BrE2F/DP8. Cis‐element composition and diversified functional expressions indicated their involvement in biological pathways for adaptation under multiple stress resistances, including cell cycle progression during growth and development. The findings provided comprehensive information on the multifunctional roles of the E2F/DP family in Brassica spp., importantly, biotic and abiotic stress resistance.