Melatonin Enhances the Photosynthesis and Antioxidant Enzyme Activities of Mung Bean under Drought and High-Temperature Stress Conditions

Abstract

Mung bean, a legume, is sensitive to abiotic stresses at different growth stages, and its yield potential is affected by drought and high-temperature stress at the sensitive stage. Melatonin is a multifunctional hormone that plays a vital role in plant stress defense mechanisms. This study aimed to evaluate the efficiency of melatonin under individual and combined drought and high-temperature stress in mung bean. An experiment was laid out with five treatments, including an exogenous application of 100 µM melatonin as a seed treatment, foliar spray, and a combination of both seed treatment and foliar spray, as well as absolute control (ambient condition) and control (stress without melatonin treatment). Stresses were imposed during the mung bean’s reproductive stage (31–40 DAS) for ten days. Results revealed that drought and high-temperature stress significantly decreased chlorophyll index, Fv/Fm ratio, photosynthetic rate, stomatal conductance, and transpiration rate through increased reactive oxygen species (ROS) production. Foliar application of melatonin at 100 µM concentration enhanced the activity of antioxidant enzymes such as superoxide dismutase, catalase, and ascorbate peroxidase and the concentration of metabolites involved in osmoregulation and ion homeostasis; thereby, it improves physiological and yield-related traits in mung bean under individual and combined stress at the reproductive stage.

“Salicylic acid enhances thermotolerance and antioxidant defense in Trigonella foenum graecum L. under heat stress”

“…Heat stress induced a notable increase in enzymatic activities compared to the control temperature, indicating that plants undergo oxidative stress under such challenging conditions. These findings parallel the earlier findings in different crops such as B. oleracea [ 77 ], Tomato [ 78 ], cucumber [ 79 ], Capsicum frutescens [ 80 ] and Mung bean [ 81 ]. Among all other enzymes, SOD plays the most crucial role in protecting cellular membrane integrity by efficiently scavenging reactive oxygen species (ROS).…”

Role of Melatonin in Directing Plant Physiology

“…In addition, MT-treated seedlings showed increased expression of anti-stress responsive genes like TaMYB80, TaWRKY26, and TaWRKY39 as well as ROS-related genes TaCAT, TaPOD, and TaSOD [90]. MT treatment increases the root length; leaf area; plant height; fresh and dry root weight; shoot weight; CAT, SOD, POD, and APX activities; soluble sugar content; and protein content of maize [120] and mung bean [73] (Figure 4) under stressful conditions.…”

“…MT regulates the opening of stomata through upregulation of the ABA catabolism process and simultaneously downregulates ABA anabolism that results in reduced accumulation of the endogenous ABA level. The decreased ABA level by MT reduces the production of H 2 O 2 in guard cells of stomata that makes the stomata remain open and maintains the water status of the plant [73]. Leaf water status and leaf temperature are positively regulated by transpiration rate.…”

Drought Tolerance of Legumes: Physiology and the Role of the Microbiome

“…The role of melatonin in drought-resistant crops is poorly understood, but a number of studies show that the exogenous treatment of several legumes promotes drought resistance through inhibiting membrane injury [ 15 , 16 ]. The physiological and molecular activity of melatonin in plants shows that it is an important substance to stimulate Fabaceae plants, especially under the action of abiotic stress [ 17 ].…”