Effect of Glycine Betaine on some Morphological Traits, Osmolyte Accumulations and Antioxidant System of Sports Grass under Salt Stress

IntroductionGrasses are narrow-leaved plants that are used as cover plants in landscape. These plants are one of the basic and necessary components of the green cover of most gardens, parks and as the background color of landscape. In Iran, due to the high costs of planting and management of grass, high water requirements, climatic incompatibility and damage to water and soil salinity, it is recommended to remove from the green space in some cities, especially in areas with low water and water and soil saline. If it is possible to benefit from the role and influence of these plants by observing the technical points and choosing the best species for each area. Salinity stress is the second limiting factor for the growth of plants in the world after drought, which affects the efficiency and performance of plants. Increase in salinity causes a decrease in the water potential in the soil. In this condition, the plant spends most of its energy to maintain the water potential, cell mass, and water absorption to have minimal growth. The aim of this research is the effect of external application of glycine betaine on the accumulation of osmolality compounds and the antioxidant system of sports grass under salt stress. Materials and Methods This research was carried out in 2022 in pots in the research greenhouse of Ilam University as a factorial  based on a completely random design with three replications. Experimental treatments included three salinity levels with sodium chloride salt (without salinity, 50 and 100 mM sodium chloride) and three levels of glycine betaine foliar spraying (0, 5 and 10 mM). Glycine betaine application was performed after mowing twice with a distance of 48h from each other, and then salinity with sodium chloride salts was applied. 4 weeks after application of salinity stress, some morphological and biochemical characteristics of plants were  measured. The results were analysed using SAS software (v.9.2), and Tukey's test was used to compare the means at the 5% probability level. Results and DiscussionThe results showed that salinity stress decreased all the study morphological, physiological and biochemical parameters including plant height, shoot fresh and dry weight, number of tiller, leaf area, chlorophyll content, protein and total antioxidant capacity in the studied plants. It also increased peroxidase enzyme, H2O2 and proline in plants, but glycine betaine application significantly improved the morpho-physiological characteristics of plants compared to the control under salt stress conditions. Thus, the highest height, shoot fresh and dry weight, leaf area, number of tiller, chlorophyll content, and protein and antioxidant capacity were observed in plants sprayed with glycine betaine. Also, the highest content of glycine betaine and activity of catalase and peroxidase enzymes and the lowest content of glycine betaine and H2O2 were observed in in plants sprayed with glycine betaine and 10 mM glycine betaine was more effective than 5 mM. The occurrence of salinity in plants disrupts the absorption of ions and causes the reduction of nutrients and increases sodium ions. One of the effects of salinity in plants is the reduction of photosynthetic activity, which results in the reduction of chlorophyll, carbon dioxide absorption, photosynthetic capacity, plant height, shoot fresh and dry weight, number of tiller and leaf area. One of the most strategies to deal with stress is accumulation of osmolyte and increasing the antioxidant activity, which makes plants resistant to environmental stresses. Salinity, through the toxic effect of Na+ and Cl- ions, affects the growth and performance of the plant by reducing the soil water potential, disrupting water absorption and imbalance of nutrients in the plant. The results obtained from comparing the average results of glycine betaine show that glycine betaine increased plant height, shoot fresh and dry weight, number of tiller, leaf area, chlorophyll content, total protein and antioxidant capacity, but on the other hand, it increased proline and H2O2 decreased, which is due to the accumulation of glycine betaine as a protector in plants under salt stress conditions. In stress conditions, glycine betaine can protect photosynthetic activities including photosynthetic enzymes, proteins and lipids in thylakoid membranes in the combination of photosystem II, and also the task of protecting cell membranes against osmotic stresses in the plant. ConclusionThe results obtained from this research showed that salinity stress reduced all the morphological, physiological and biochemical characteristics in the sport grass plants, but glycine betaine application played a positive role in reducing salinity damage and maintaining plant quality. Glycine betaine is known as one of the effective molecules in stress signaling, so it can protect the plant cells against stress by reducing the destruction of the membrane and by increasing the salt tolerance mechanisms. Also, glycine betaine 10 mM is introduced as the best treatment to reduce salinity damage in sport grass during present study.