Using Exogenous Melatonin, Glutathione, Proline, and Glycine Betaine Treatments to Combat Abiotic Stresses in Crops

Abstract

Abiotic stresses, such as drought, salinity, heat, cold, and heavy metals, are associated with global climate change and hamper plant growth and development, affecting crop yields and quality. However, the negative effects of abiotic stresses can be mitigated through exogenous treatments using small biomolecules. For example, the foliar application of melatonin provides the following: it protects the photosynthetic apparatus; it increases the antioxidant defenses, osmoprotectant, and soluble sugar levels; it prevents tissue damage and reduces electrolyte leakage; it improves reactive oxygen species (ROS) scavenging; and it increases biomass, maintains the redox and ion homeostasis, and improves gaseous exchange. Glutathione spray upregulates the glyoxalase system, reduces methylglyoxal (MG) toxicity and oxidative stress, decreases hydrogen peroxide and malondialdehyde accumulation, improves the defense mechanisms, tissue repairs, and nitrogen fixation, and upregulates the phytochelatins. The exogenous application of proline enhances growth and other physiological characteristics, upregulates osmoprotection, protects the integrity of the plasma lemma, reduces lipid peroxidation, increases photosynthetic pigments, phenolic acids, flavonoids, and amino acids, and enhances stress tolerance, carbon fixation, and leaf nitrogen content. The foliar application of glycine betaine improves growth, upregulates osmoprotection and osmoregulation, increases relative water content, net photosynthetic rate, and catalase activity, decreases photorespiration, ion leakage, and lipid peroxidation, protects the oxygen-evolving complex, and prevents chlorosis. Chemical priming has various important advantages over transgenic technology as it is typically more affordable for farmers and safe for plants, people, and animals, while being considered environmentally acceptable. Chemical priming helps to improve the quality and quantity of the yield. This review summarizes and discusses how exogenous melatonin, glutathione, proline, and glycine betaine can help crops combat abiotic stresses.

Non-Protein Thiol Compounds and Antioxidant Responses Involved in Bryophyte Heavy-Metal Tolerance

“…Glutathione exists either in a reduced form (i.e., GSH) with a free thiol group or in an oxidized form (i.e., GSSG) with a disulphide bond linking two glutathione molecules [ 105 , 109 ]. GSH plays an important role in the regulation of developmental processes such as cell division [ 110 , 111 ], flowering [ 110 , 112 ], and in protecting plants against abiotic stresses such as nutritional starvation, heavy metal exposure, drought, salinity, heat, cold, and certain exogenous and endogenous organic-chemical agents [ 16 , 110 , 113 , 114 ]. GSH is also a major transport and storage form of reduced sulphur in plants [ 16 ].…”

Integrated Physiological and Transcriptomic Analyses Revealed Improved Cold Tolerance in Cucumber (Cucumis sativus L.) by Exogenous Chitosan Oligosaccharide

“…This study systematically analyzed the important role of exogenous GB, CTS, and COS in cold tolerance in cucumber for the first time. As an important osmoprotectant and antioxidant, GB improves plant resistance to abiotic stresses [ 42 ]. It has long been reported that exogenous GB can increase chilling- and freeze-tolerance in plants [ 43 , 44 , 45 , 46 ].…”

Carbon dots enhanced cold tolerance of lettuce (Lactuca sativa L.): scavenging reactive oxygen species, modulating hormones and up-regulating gene expression

“…Studies have shown that proline can regulate intracellular osmotic pressure under stress conditions and protect protein molecules. 55 Moreover, compared with CK, the Na + content of lettuce was significantly decreased, and the K + content was significantly increased after foliar spraying of CDs (Fig. S10a and b †), indicating that CDs could maintain osmotic pressure balance and reduce damage caused by dehydration of cells due to cold stress.…”