Growth bioregulation of heat stressed maize by exogenous application of thiourea

Abstract

Heat stress is a main growth reducing factor for most crop plants. It is a serious risk for crop production around the world due to high ambient temperature. High temperature stress reduces yield of maize by negatively affecting the stomatal conductance, net photosynthetic rate, chlorophyll content and metabolites biosynthesis. Tolerance to heat stress can be increased by using different growth regulators. Thiourea has since long been known for its stress tolerance. The experiments were performed to determine physiological role of medium-supplemented thiourea (0.25 mM) in improving heat stress tolerance in maize using five hybrids (30Y87, DK6789, 30R50, 31R88 and 32B33) in autumn and spring seasons of the years 2014 and 2015. Data were recorded for growth, photosynthetic pigments, gas exchange, oxidative stress and antioxidants, osmoprotectant and mineral elements. The result revealed that autumn conditions were more toxic as compared to spring. Data on interactive studies of heat stress and thiourea showed that medium supplemented thiourea ameliorated the adverse effect of heat stress and improved proliferation of roots. Thiourea applied to heat stressed plants enhanced chlorophyll a and chlorophyll b, while its influence was more prominent on the sensitive (32B33) than tolerant (30Y87) maize hybrids. Thiourea application enhanced the net assimilation rate (A) and stomatal conductance (gs) and reduced sub-stomatal CO2 concentration (Ci). Moreover, thiourea application was effective in improving the contents of soluble phenolics, anthocyanins, ascorbic acid, niacin and riboflavin, which proved of great advantage to scavenge hydrogen peroxide and reduced malondialdehyde synthesis. Medium supplementation of thiourea enhanced the tissue contents of mineral nutrients such as N, P, K+, S, Ca2+ and Mg2+ in the shoot and root of maize meagerly under control and excessively under heat stress, which appeared to improve the root area and its function. In short, these studies described some specific properties of thiourea in enhancing growth of plant under heat stress which makes thiourea as an important bioregulator for root proliferation under control and stressful conditions.