Physio biochemical and molecular insights into melatonin mediated drought tolerance in upland cotton Gossypium Hirsutum L

Abstract

Melatonin (N-acetyl-5-methoxytryptamine), an indolic compound was first discovered in bovine pineal gland and has diverse biological functions in animals that include regulating circadian rhythm, body temperature, appetite, mood, sexual behavior, etc. Since its discovery in plants in 1995, several studies have reported its multifaceted roles in plant growth and development including tolerance to biotic and abiotic stresses. This compound regulates redox homeostasis and thus provides the first line of defense during exposure of plants to adverse conditions. The level of reactive oxygen species (ROS) in drought-sensitive and drought-tolerant varieties varies so as the possibility of melatonin s mode of action under stress conditions. There have been no reports on how melatonin regulates drought tolerance in varieties differing in their tolerance levels. Moreover, the role of melatonin on drought stress tolerance is not yet investigated in cotton, an economically important fiber crop. Thus, the present study aimed to investigate the drought stress responses of drought-sensitive (var. L-799) and drought-tolerant (var. Suraj) varieties after melatonin priming with respect to physiological, biochemical, and molecular aspects to gain mechanistic insights into drought tolerance in upland cotton (Gossypium hirsutum L.). Melatonin priming enhanced the tolerance of L-799 variety to drought stress by improving the antioxidant system, photosynthetic activity, water-use efficiency, and nitrogen metabolism. Priming the seeds with melatonin led to an increase in endogenous melatonin content as well as enhanced the expression of candidate stress-responsive genes in stressed plants of L-799 suggesting the involvement of melatonin in drought tolerance. The upregulated expression of autophagosome marker [lipidated (ATG8-PE)] at both transcript and protein levels in melatonin-primed drought-stressed plants of L-799 suggests the role of autophagy in alleviating drought stress. Interestingly, melatonin-priming did not exhibit pronounce