Elucidating role of melatonin foliar spray in ameliorating adverse effects of drought stress on growth and physio-biochemical attributes of Brassica rapa plants

Abstract

Melatonin is tryptophan derivative, a multipurpose phytochemical that ameliorate adversity of abiotic stress on plants. However, melatonin (Mel) role in ameliorating stress in growth cycles of various plant species needs investigation. In this study, diverse concentrations of Mel (100 µM, 150 µM, and 200 µM) were applied to determine which one could effectively reduce the harmful effect of water stress on turnip (Brassica rapa) plants. B. rapa leaves and roots exhibited lower growth and increased Na+ uptake (18%, 17%) due to drought stress. However, foliar-applied Mel significantly enhanced the growth characteristics, photosynthetic pigments and total phenolics in B. rapa plants under drought stress conditions. Mel foliar supplementation to B. rapa plants increased K+ and Zn+ uptake in the leaves and roots. Mel induced growth of B. rapa plants, especially under conditions of water deficiency was found to be related with higher levels of photosynthetic pigments, total soluble sugars, total soluble proteins and total free amino acids. Therefore, it is hypothesized that exogenous Mel treatment might be useful in enhancing plants' ability to survive under water stressed conditions.