(100-54) Exogenous riboflavin (vitamin B2) application enhances salinity tolerance through the activation of its biosynthesis in rice seedlings under salinity stress
Student Hiroshima University Higashihiroshima, Hiroshima, Japan
Body of Abstract: Salinity stress triggers reactive oxygen species (ROS) accumulation and leads to plant growth impairment. Riboflavin (RIB), vitamin B2, is synthesized by plants, fungi, and microorganisms, being a precursor of coenzymes flavin adenine dinucleotide and flavin mononucleotide that are important for metabolisms. This study aimed to elucidate the mechanistic basis of the RIB-mediated alleviation of salinity stress in rice. The results exhibited that higher biomass accumulation and lower accumulations of malondialdehyde and hydrogen peroxide were observed in RIB-pretreated seedlings under salinity stress. In vitro assays showed that hydrogen peroxide was scavenged as the RIB concentration rose, implying that RIB may function in ROS detoxification as a non-enzymatic antioxidant. RIB-pretreated seedlings accumulated Na+ in roots instead of leaf blades as the contribution of OsHKT2;1, OsNHX1, and OsHKT1;4 in the roots and leaf sheaths, respectively. Importantly, LCMS/MS analysis revealed that RIB concentration was increased and up-regulation of the genes for the key RIB biosynthesis (OsRIBA1, OsGCHI, OsLS, OsRS) was observed in the roots of RIB-pretreated seedlings. Taken together, these results elucidated that RIB pretreatment ameliorates salinity stress in rice through the improvement of (1) oxidative stress tolerance as increased RIB concentration may function as a non-enzymatic antioxidant and (2) ionic stress tolerance as RIB pretreatment limits Na+ accumulation in leaf blades and maintain favorable Na+/K+ balance.