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Melatonin is a pleiotropic signaling molecule that reduces the adverse effects of abiotic stresses, and enhances the growth and physiological function of many plant species. Several recent studies have demonstrated the pivotal role of melatonin in plant functions, specifically its regulation of crop growth and yield. However, a comprehensive understanding of melatonin, which regulates crop growth and yield under abiotic stress conditions, is not yet available. This review focuses on the progress of research on the biosynthesis, distribution, and metabolism of melatonin, and its multiple complex functions in plants and its role in the mechanisms of metabolism regulation in plants grown under abiotic stresses. In this review, we focused on the pivotal role of melatonin in the enhancement of plant growth and regulation of crop yield, and elucidated its interactions with nitric oxide (NO) and auxin (IAA, indole-3-acetic acid) when plants are grown under various abiotic stresses. The present review revealed that the endogenousapplication of melatonin to plants, and its interactions with NO and IAA, enhanced plant growth and yield under various abiotic stresses. The interaction of melatonin with NO regulated plant morphophysiological and biochemical activities, mediated by the G protein-coupled receptor and synthesis genes. The interaction of melatonin with IAA enhanced plant growth and physiological function by increasing the levels of IAA, synthesis, and polar transport. Our aim was to provide a comprehensive review of the performance of melatonin under various abiotic stresses, and, therefore, further explicate the mechanisms that plant hormones use to regulate plant growth and yield under abiotic stresses.

Plant density is one of the most important factors influencing the physiological, morphological characteristics, and yield of sesame. Sesame is an important oilseed and cash crop production in Sudan. The effects of different rows spacing on the growth attributes, yield and yield compound on three sesame seeds varieties were investigated at rainfall conditions in semi-arid regions. Two field experiments were conducted in 2014-2015 and 2015-2016. Three varieties were planted at four rows spacing [5(control), 10, 20 and 30cm]. The experiment was laid out in RCBD in split plots with three replications. There were significant differences between row spacing, varieties and interaction between row spacing and varieties for all parameters except the 1000 seeds weight. Moreover, Abo Nama has recorded the highest plants, number of branches and number of capsules per plant, while the abo Radom recorded the highest number of seeds per capsule and seed yield, and abo sofa had the highest weight of 1000 seeds. Planted varieties at the 5 cm between rows can increase the seed yield (210.18 kg/h). The interaction between Abo Radom and control recorded the high seed yield by 265.30 kg per h-1. This study suggests that the appropriate rows spacing can actively increase the yield of the sesame plant.

Castor bean (Ricinus communis L.) as a bioenergy crop, received more and more attention in recent years. However, the yield of castor bean seeds is affected by adverse environmental conditions. The objective of this study was to assess the effects of exogenous application of Paclobutrazol (PBZ) on castor bean growth, yield and physiology as well as on its response to environmental stress during grain filling. In the present field study, three PBZ concentrations [0 g•ha-1 (control), 75 g•ha-1 and 150 g•ha-1] were applied twice, once at grain filling of main panicle and once at grain filling of branched panicle. The growth and physiological responses of castor bean were measured four times throughout flowering and seed formation stages [1-early initiation stage of main inflorescence (E), 2- anthesis of main inflorescence (A), 3-maturity of main panicle (M) and 4-maturity of branched panicle (B)]. Plant growth was not affected by the application of PBZ, but leaves remained later on the plant when 75 g•ha-1 of PBZ was applied. With the application of PBZ, the concentration of starch was higher in panicles than in leaves and stems. Also, PBZ application increased the number of seeds per plant without affecting seed size and weight. These results suggest that exogenous application of PBZ can enhance sink strength of panicles and improve seed yield and that application of PBZ at flower initiation can alter photosynthetic partitioning in favor to seed production. On the other hand, PBZ had no effect on antioxidant enzyme activity in the seeds in response to stress.