Investigation into the Relationship between Spermidine Degradation and Phenolic Compounds Biosynthesis in Barley Seedlings under Ultraviolet B Stress.

Barley germination under ultraviolet B (UV-B) illumination stress induces effective accumulation of phenolic compounds in the barley. Spermidine can enhance the biosynthesis of phenolic compounds and alleviate the oxidative damage caused by UV-B. To better understand the function of spermidine, inhibitors of enzymes that are involved in the degradation of spermidine and the synthesis of gamma-aminobutyric acid (GABA), the product of spermidine degradation, were applied to barley germinated under UV-B treatment. The results showed a more severe oxidative damage, and a decrease in phenolic acid contents were observed when spermidine degradation was inhibited. However, GABA application did attenuate an increase in electrolyte permeability and MDA content caused by UV-B induced oxidative damage and improved the respiration rate. Meanwhile, GABA application can elevate the accumulation of phenolic compounds by ca. 20%, by elevating the activities of some key enzymes. Furthermore, the application of GABA, together with the inhibitor of spermidine degradation, can alleviate its suppression of the synthesis of phenolic acids, and resistance to UV-B stress. In conclusion, spermidine alleviated oxidative damage and enhanced the accumulation of phenolic compounds using its degradation product.

Spermidine alleviates oxidative damage and enhances phenolic compounds accumulation in barley seedlings under UV-B stress.

BACKGROUND: Ultraviolet B (UV-B) radiation can enhance the accumulation of phenolic compounds (PCs) in barley seedling, although this may result in severe oxidative damage. In the present study, the role of spermidine in alleviating oxidative damage and regulating synthesis of PCs in barley seedlings under UV-B stress was investigated. RESULTS: Exogenous spermidine increased the length and fresh weight as well as PCs contents of barley seedlings under UV-B stress. Application of dicyclohexylamine, an inhibitor of endogenous spermidine synthesis, significantly inhibited the growth and PC accumulation of barley seedlings under UV-B stress, although this inhibitory effect can be alleviated by exogenous spermidine. Exogenous spermidine increased the contents of vanillic acid, syringic acid, protocatechuic acid and p-coumaric acid in barley seedlings under UV-B stress by 20-200% through enhancing the activities of enzymes related to synthesis of these acids. In addition, exogenous spermidine enhanced activities and gene expression of antioxidant enzymes in barley seedlings under UV-B stress, including peroxidase, glutathione reductase and glutathione S-transferase. CONCLUSION: Spermidine can alleviate oxidative damage of barley seedlings under UV-B stress and enhance the accumulation of PCs. © 2022 Society of Chemical Industry.