Exogenous melatonin improves the salt tolerance of cotton by removing active oxygen and protecting photosynthetic organs

Abstract

Background As damage to the ecological environment continues to increase amid unreasonable amounts of irrigation, soil salinization has become a major challenge to agricultural development. Melatonin (MT) is a pleiotropic signal molecule and indole hormone, which alleviates the damage of abiotic stress to plants. MT has been confirmed to eliminate reactive oxygen species (ROS) by improving the antioxidant system and reducing oxidative damage under adversity. However, the mechanism by which exogenous MT mediates salt tolerance by regulating the photosynthetic capacity and ion balance of cotton seedlings still remains unknown. In this study, the regulatory effects of MT on the photosynthetic system, osmotic modulators, chloroplast, and anatomical structure of cotton seedlings were determined under 0–500 μM MT treatments with salt stress induced by treatment with 150 mM NaCl. Results Salt stress reduces the chlorophyll content, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, transpiration rate, PSII photochemical efficiency, PSII actual photochemical quantum yield, the apparent electron transfer efficiency, stomata opening, and biomass. In addition, it increases non-photochemical quenching. All of these responses were effectively alleviated by exogenous treatment with MT. Exogenous MT reduces oxidative damage and lipid peroxidation by reducing salt-induced ROS and protects the plasma membrane from oxidative toxicity. MT also reduces the osmotic pressure by reducing the salt-induced accumulation of Na+ and increasing the contents of K+ and proline. Exogenous MT can facilitate stomatal opening and protect the integrity of cotton chloroplast grana lamella structure and mitochondria under salt stress, protect the photosynthetic system of plants, and improve their biomass. An anatomical analysis of leaves and stems showed that MT can improve xylem and phloem and other properties and aides in the transportation of water, inorganic salts, and organic substances. Therefore, the application of MT attenuates salt-induced stress damage to plants. Treatment with exogenous MT positively increased the salt tolerance of cotton seedlings by improving their photosynthetic capacity, stomatal characteristics, ion balance, osmotic substance biosynthetic pathways, and chloroplast and anatomical structures (xylem vessels and phloem vessels). Conclusions Our study attributes help to protect the structural stability of photosynthetic organs and increase the amount of material accumulation, thereby reducing salt-induced secondary stress. The mechanisms of MT-induced plant tolerance to salt stress provide a theoretical basis for the use of MT to alleviate salt stress caused by unreasonable irrigation, fertilization, and climate change.

Exogenous Melatonin Promotes the Salt Tolerance by Removing Active Oxygen and Maintaining Ion Balance in Wheat (Triticum aestivum L.)

“…Exogenous MT partially mitigated the salt stress-induced inhibition of whole-plant growth by reducing the accumulation of H 2 O 2 in wheat leaf and increasing endogenous MT content and polyamine contents (Ke et al, 2018). Rice and cotton plants pretreated with MT also reduced H 2 O 2 contents in leaf and roots, which accumulate high H 2 O 2 concentration induced by salt stress Jiang et al, 2021). In our research, the changing rule of H 2 O 2 content in root was also decreased with salt and MT treatments compared with NaCl alone treatment.…”

“…The possible reason was that roots receive stress signals to turn on the defense system including recognizing and appointing exogenous MT as a stress regulator in a short time; for leaf, there was delayed effects for that MT has been reported as a potent long-distance signal to translocate stress message from roots to leaf (Li H. et al, 2017). Whether seeds of rice and wheat were pretreated with MT for 3-7 days, or the cotton seedling was treated with foliar spray MT every 24 h for 12 days, plants have been finished antistress training Ke et al, 2018;Jiang et al, 2021). Besides playing a vital signaling role during stress responses, H 2 O 2 was induced by respiratory burst oxidase homologs (RBOH) to convert eventually into other ROS (OH) by the Fenton reaction and Haber-Weiss reaction (Liu et al, 2020;Michard and Simon, 2020).…”

“…Different concentrations of MT may have differential effects in mediating abiotic stress defense. MT at 200 µmol L −1 can effectively inhibit ROS production, improve the biomass and chlorophyll content, and regulate the photosynthetic characteristics of cotton seedlings under salt stress (Jiang et al, 2021). MT at 300 µmol L −1 alleviates the negative effect of water stress on wheat germination and promotes morphological development including radicle length, radicle number, and plumule length of germinated seeds (Li et al, 2020).…”

Overexpression of GhABF3 increases cotton(Gossypium hirsutum L.) tolerance to salt and drought

“…Plants absorb water and nutrients mainly through their roots, so strong root system can provide more water and nutrients to plants [40]. Salting is toxic to plants and inhibits plant growth, including reducing photosynthetic rate; and inhibiting root and stem elongation [41]. Exorbitant soil salt content also leads to osmotic stress, making plant roots absorbing water difficult [42,43].…”

The Caucasian Clover Gene TaMYC2 Responds to Abiotic Stress and Improves Tolerance by Increasing the Activity of Antioxidant Enzymes

“…This change trend was more consistent with the change trend of SOD and POD activity in plants under cold stress [ 45 ]. SOD, POD, and CAT are important antioxidant enzymes in plants that are involved in resistance to adversity and remove active oxygen [ 46 , 47 ]. Therefore, TaMYC2 may participate in the regulation of plant protection-related mechanisms, promote the production of plant protection-related enzymes, and enhance the ability of plants to resist low temperature stress.…”