Abstract
Cold stress is one of the most limiting factors for plant growth and development. Cold stress adversely affects plant physiology, molecular and biochemical processes by determining oxidative stress, poor nutrient and water uptake, disorganization of cellular membranes and reduced photosynthetic efficiency. Therefore, to recover impaired plant functions under cold stress, the application of bio-stimulants can be considered a suitable approach. Melatonin (MT) is a critical bio-stimulant that has often shown to enhance plant performance under cold stress. Melatonin application improved plant growth and tolerance to cold stress by maintaining membrane integrity, plant water content, stomatal opening, photosynthetic efficiency, nutrient and water uptake, redox homeostasis, accumulation of osmolytes, hormones and secondary metabolites, and the scavenging of reactive oxygen species (ROS) through improved antioxidant activities and increase in expression of stress-responsive genes. Thus, it is essential to understand the mechanisms of MT induced cold tolerance and identify the diverse research gaps necessitating to be addressed in future research programs. This review discusses MT involvement in the control of various physiological and molecular responses for inducing cold tolerance. We also shed light on engineering MT biosynthesis for improving the cold tolerance in plants. Moreover, we highlighted areas where future research is needed to make MT a vital antioxidant conferring cold tolerance to plants.
Highlights
Cold stress is a severe abiotic stress that significantly limits crop growth and productivity, in temperate areas (Aazami et al, 2021; Feng et al, 2021)
The exogenous MT application improved the synthesis of photosynthetic pigments and maintains membrane stability, plant water status, increasing the nutrient and water uptake, which improved plant growth under cold stress
The genes manipulation associated with enhanced MT biosynthesis appreciably improved the cold tolerance in plants by favoring the antioxidant activities, photosynthetic performance and accumulation of different osmolytes
Summary
Cold stress is a severe abiotic stress that significantly limits crop growth and productivity, in temperate areas (Aazami et al, 2021; Feng et al, 2021). Cold stress induces the formation of crystal which reduces membrane integrity, causes electrolyte leakage and lipid saturation, reduces root growth which in turn decreases the water and nutrient uptake. MT supplementation maintains higher Fv/Fm and plant water relationships, while it reduces MDA and H2O2 by improving antioxidant activities (Table 2: ascorbate peroxidase: APX, CAT, POD, and SOD), enhancing plants tolerance to cold stress (Li et al, 2018a). MT supplementation was shown to markedly reduce MDA accumulation and ROS deleterious impact on cellular membranes of rice seedlings, which in turn resulted in appreciably improved plant growth under cold stress (Han et al, 2017). Chilling stress reduced the seedling growth, biomass production, RWC, and increased the MDA contents membrane permeability, proline accumulation, and APX, CAT, POD, and SOD activities. Cold stress reduced the leaf moisture contents, RWC, dry matter contents, photosynthetic, and transpiration rates of wheat crop
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