Alterations of Antioxidative Enzymes and Total Phenolics of Grain Sorghum Seedling Tissues Under Salt Stress

Sorghum (Sorghum spp) is one of the world's significant warm-climate cereals, used both as animal feed and human food. It demonstrates better adaptation to saline soils and diverse climatic conditions compared to other cereals. Salt stress significantly limits plant growth, development, yield, and quality. This study aimed to investigate the changes in antioxidant defense enzymes and total phenolic compounds in sorghum under salt stress. Different salinity levels (0, 50, 100, 150, and 200 mM NaCl) were applied to the Acme Brom Corn sorghum variety grown in Hoagland nutrient medium. The experiments were conducted under controlled conditions in a climate chamber for 10 days, both under salt stress and non-stress conditions, with three replicates. At the end of the experiments, the roots and leaves of the plants were harvested separately, homogenized, and placed in aluminium foil in portions of 0.5 g and 0.25 g, shock-frozen in liquid nitrogen, and stored at -20 °C. Antioxidant enzymes induced by salt stress, as well as chlorophyll and carotenoids, were determined spectrophotometrically. Statistically significant correlations were found between root glutathione reductase (GR), proline, and ascorbate peroxidase (APX) activities, and between antiradical capacity, glutathione S-transferase (GST), MDA, total phenolics, catalase (CAT), and superoxide dismutase (SOD) activities. In leaves, significant correlations were observed between SOD, total phenolics, and GST, as well as between Chl a, CAT, antiradical capacity, APX, and carotenoids. Significant correlations were also identified between total chlorophyll and carotenoids, GR and Chl b, and MDA and proline. Although increased antioxidant enzyme activity and total phenolics support the salt stress resistance of sorghum plants, these mechanisms were insufficient at high salinity levels. Therefore, it was concluded that further studies are needed to better understand the relationships between salt stress and antioxidant enzyme activities at higher salt concentrations using the investigated sorghum variety. It should be noted that the findings should not be generalized, as the results depend on the experimental year, genotype, salt doses applied, enzyme activities investigated, and methods used.