Melatonin regulates the functional components of photosynthesis, antioxidant system, gene expression, and metabolic pathways to induce drought resistance in grafted Carya cathayensis plants

Melatonin-induced Water Stress Tolerance in Plants: Recent Advances

“…(ii) By increasing drought severity, melatonin, which is biosynthesized in mitochondria and chloroplasts [76,77], exhibits more defence strategies. It promotes the physiological aspects including antioxidant system [28,59] to alleviate the oxidative damage, leading to less accumulation of H2O2, O −2 and NO [26,53], less electrolyte leakage [42], lower lipid peroxidation (MDA reduction) [28,65], lower relative conductivity [57], toxic substances content easing [60] cellular redox disruption limitation [53], better nitro-oxidative homeostasis [53], and enhanced ascorbate (AsA)-glutathione(GSH) cycle capacity (higher GSH and AsA contents) [55]. Such beneficial effects are carried out by regulating the enzymatic activities such as ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), as well as non-enzymatic antioxidants and osmoprotectants (proline and others) [45,64], and also secondary metabolites such as flavonoids, phenolics and phenylalanine ammonialyase [49].…”

“…In this respect, melatonin enhances plant resistance via higher stomatal conductance [43], higher cell turgor and water holding capacity [65], and stomatal opening regulation [78]. Consequently, the whole plant status is enhanced including seed germination efficiency [48], root generation vitality and strengthen [61], growth and flowering [37,51], visual quality [65], seed yield [39], leaf senescence alleviation [55] and quickly recovering after rehydration [59].…”

“…Melatonin regulates ROS/RNS levels and antioxidants-related genes including SOD, POD, CAT, APX, glutathione S-transferase (GSTP), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) [28,31,33,38,44,46,53,59,79,80], as well as osmoprotective elements via regulation of proline biosynthesis genes [53]. Melatonin is not only alleviating oxidative damage, but also regulating plant build-in-associated genes, including carbohydrate/fatty and amino acids metabolism [27,37,38], carbon metabolic pathway [67], nitrogen metabolism and transport [38,55], plant secondary metabolism [59] energy production [38,80], carotenoids metabolism and photosynthesis [28,37,38,59] and cuticle wax biosynthesis [75]. In this regard, the metabolism of carbohydrate/fatty acids is reported to be up-regulated via seed-coating of soybean with melatonin solution as a means to improve its tolerance to drought stress [37].…”

“…The key physiological aspects that are much regulated by phytohormones in response to drought stress include antioxidants metabolism, carbohydrate production (carbon metabolism), stomatal movement, and leaf senescence [84]. Drought stress up-regulates ABA, BRs, and JA [59,84] and down-regulates CKs and GAs [52,59], while melatonin enhances the levels of BRs, GAs, JA and CKs [59] and decreases ABA level [59] (Figure 2).…”

“…Water scarcity stimulates ABA biosynthesis [14,85], which in turn down-regulates the main metabolic pathways [59], induces stomatal closure [84] and contributes to leaf senescence [84]. Moreover, the over-accumulation of ABA up-regulates the ROS generation pathways and causes oxidative damage [14].…”