Melatonin Pretreatment Alleviated Inhibitory Effects of Drought Stress by Enhancing Anti-Oxidant Activities and Accumulation of Higher Proline and Plant Pigments and Improving Maize Productivity

Abstract

Drought stress has been shown to have harmful effects on crop productivity worldwide, including in Pakistan, due to rapid climate change scenarios. Extensive work has been reported on the influential role of melatonin (MEL) in either foliar or seed-primed applications; however, its role in root application is seldom reported. We investigated plant biochemical responses, including anti-oxidants, plant pigments, leaf water characteristics, and maize crop production, with MEL treatment under mild and severe drought stress. Maize Cvar. Jalal was subjected to drought stress (60% and 80% of full irrigation) at the four-leaf stage, and MEL was applied as pretreatment with irrigation water at different doses (0, 100, and 200µM). The findings of the study revealed that the Chl a, b, and a + b contents and the carotenoid content significantly increased with MEL application during severe and mild drought stress. After applying 200 µM MEL, leaf water attributes, comprising relative water content (RWC), leaf water content (LWC), and relative saturation deficit (RSD), increased by 1.9%, 100%, and 71.2%, respectively, during mild drought and 17%, 133%, and 32% under severe drought. The anti-oxidant activities of POD, CAT, and APX were remarkably enhanced with MEL during drought stress. Our results showed that root application of 200 µM melatonin boosted seed yield and water productivity by 31% and 38%, and plant biomass increased by 32% and 29% under mild and severe drought stressors compared to plants with no MEL, leading to increased drought tolerance.