Role of Melatonin in mitigating salt stress in maize (Zea mays L.)

Abstract

Soil salinity is a major yield reducing factor that limits plant growth in their natural habitat. It is an ever increasing problem in arid to semi arid regions that represent 40 % of total earth land. To meet the increasing global demand of food and to meet nutritional requirement of rapidly growing population, there is a need to develop salt tolerant genotypes that are able to grow and produce maximum yield on saline soils. Melatonin (N-acetyl-5methoxytryptamine) is a crucial biological hormone whose antioxidant capacity fortifies a number of plant species against salt stress. To investigate the effects of salt stress on maize hybrids growth, physiological, ionic and biochemical attributes and possible acclimation of maize hybrids against deleterious effects of salinity, two solution culture, one pot study and one field experiment were conducted. Initially 10 maize hybrids were screened in solution culture against four salinity levels (control, 40 mM L-1, 80 mM L-1 and 120 mM L-1). On the basis of biomass accumulation, water relations and K+/Na+ ratio, maize hybrid 2225 and 1574 emerged as salt tolerant while maize hybrid 8441 and 8711 as salt sensitive. Subsequently, physiology and biochemistry of maize hybrids of both categories were evaluated in another solution culture experiment with interactive salinity and melatonin levels and two maize hybrids 2225 (salt tolerant) and 8711 (salt sensitive) were further evaluated in soil culture (pot study) and in saline field with two melatonin levels 0.5 µM L-1 and 1 µM L-1. Salt stress significantly reduced plant dry matter accumulation, relative water contents (RWC), membrane stability index (MSI), chlorophyll contents, plant nutrition and photosynthetic parameters along with inferior antioxidant enzymes activities. Melatonin application significantly alleviates the detrimental effects of salinity by regulating plant physiology, improving plant morphology, civilizing photosynthetic activity and activities of antioxidant enzymes. Maize hybrid 2225 conspicuously responds to melatonin application and exhibits improved growth under low and elevated salt stress. Our results suggested that melatonin induced salt tolerance in maize hybrids. Furthermore salt tolerant maize hybrids can serve as a potential source to get sustainable production from salt affected lands however, there is still much that need to be elucidated in future.