Exogenous Melatonin Modulates the Physiological and Biochemical Mechanisms of Drought Tolerance in Tartary Buckwheat (Fagopyrum tataricum (L.) Gaertn)

Abstract

Tartary buckwheat is one of the nutritious minor cereals and is grown in high-cold mountainous areas of arid and semi-arid zones where drought is a common phenomenon, potentially reducing the growth and yield. Melatonin, which is an amphiphilic low molecular weight compound, has been proven to exert significant effects in plants, under abiotic stresses, but its role in the Tartary buckwheat under drought stress remains unexplored. We evaluated the influence of melatonin supplementation on plant morphology and different physiological activities, to enhance tolerance to posed drought stress by scavenging reactive oxygen species (ROS) and alleviating lipid peroxidation. Drought stress decreased the plant growth and biomass production compared to the control. Drought also decreased Chl a, b, and the Fv/Fm ratio by 54%, 70%, and 8%, respectively, which was associated with the disorganized stomatal properties. Under drought stress, H2O2, O2•−, and malondialdehyde (MDA) contents increased by 2.30, 2.43, and 2.22-folds, respectively, which caused oxidative stress. In contrast, proline and soluble sugar content were increased by 84% and 39%, respectively. However, exogenous melatonin (100 µM) could improve plant growth by preventing ROS-induced oxidative damage by increasing photosynthesis, enzymatic antioxidants (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase), secondary metabolites like phenylalanine ammonialyase, phenolics, and flavonoids, total antioxidant scavenging (free radical DPPH scavenging), and maintaining relative water content and osmoregulation substances under water stress. Therefore, our study suggested that exogenous melatonin could accelerate drought resistance by enhancing photosynthesis and antioxidant defense in Tartary buckwheat plants.

Melatonin alleviates drought impact on growth and essential oil yield of lemon verbena by enhancing antioxidant responses, mineral balance, and abscisic acid content

“…Our data also showed that 200 μM melatonin was more effective compared to 100 μM melatonin in stimulating the activities of SOD, CAT and APX, and in diminishing the levels of H 2 O 2 and MDA in the leaves of lemon verbena plants upon increasing drought intensity from mild to severe (Figure3A-E). In accordance with our findings,Ahmad et al (2019) andHossain et al (2020) reported that melatonin acted as a crucial bioregulator enhancing the antioxidant system of F. tataricum and Zea mays plants to promote drought tolerance.We further explored the medicinal values of lemon verbena leaves by estimating the contents of TPC and several phenolic acids like ChA, CA, and ChgA, following the application of melatonin to drought-exposed plants (Figure4A-D). Results revealed that drought exposure reduced the levels of TPC, ChA, CA, and ChgA in a dose-dependent manner, indicating that drought negatively impacted the biosynthesis of these secondary metabolites, as previously observed in the leaves of Echinacea purpurea and Vitis vinifera under severe water-shortage conditions…”

“…Plant height, leaf number and shoot DW were determined according to the methods of Hosseini et al (2018). The relative water content (RWC) of the leaves was determined based on the method of Weatherley (1950).…”

Mechanistic insights on melatonin‐mediated drought stress mitigation in plants

“…Recently, several reports showed that melatonin treatment has enhanced the enzymatic antioxidants CAT, APX, MDHAR, and DHAR activities in maize (Alharby & Fahad, 2020); CAT, POD, SOD, and APX activities in buckwheat (Hossain et al, 2020); GT, CAT, POD, SOD, and GR activities in Salvia sp. (Bidabadi et al, 2020); indole acetic acid and phenolic contents; TSS, CAT, POD, and SOD activities in flax plants ; proline content and antioxidant CAT, POD, SOD, and GR activities in rapeseed (Khan et al, 2020); root catalase activity in rapeseed (Dai et al, 2020); and acid and alkaline invertase activities in anthers of cotton (Hu et al, 2020).…”

Melatonin-Induced Water Stress Tolerance in Plants: Recent Advances

“…It promotes the physiological aspects, including the antioxidant system [ 27 , 59 ], to alleviate the oxidative damage, leading to less accumulation of reactive oxygen and nitrogen species (ROS and RNS) [ 25 , 52 ], less electrolyte leakage [ 41 ], lower lipid peroxidation (malondialdehyde reduction) [ 27 , 65 ], lower relative conductivity [ 57 ], the easing of toxic substances content [ 60 ], cellular redox disruption limitation [ 52 ], better nitro-oxidative homeostasis [ 52 ], and enhanced ascorbate (AsA)–glutathione(GSH) cycle capacity (higher GSH and AsA contents) [ 54 ]. Such beneficial effects are carried out by regulating enzymatic activity involving peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD), as well as nonenzymatic antioxidants and osmoprotectants (proline and others) [ 37 , 44 , 64 ], and also secondary metabolites such as flavonoids, phenolics, and phenylalanine ammonialyase [ 48 ]. Simultaneously, melatonin improves the plant photosystem, as indicated by higher chlorophyll content [ 58 ], greater photosynthetic rates [ 43 ], and higher transpiration rates [ 31 ].…”