Identification of a GLDH-overexpressing Arabidopsis mutant and its responses to high-light stress

Ascorbic acid (AsA) is an important antioxidant protecting plant against environmental stresses. L-galactono-1,4-lactone dehydrogenase (GLDH) is a key enzyme in AsA synthesis pathway. To investigate the roles of AsA in mitigating high light (HL) damage, Arabidopsis GLDH mutants SALK_060087 and SALK_008236 with altered GLDH-expression were screened for homozygotes. No homozygotes were identified from SALK_060087, but most individuals of the SALK_008236 line (GLDH-236OE) were GLDH-overexpressing homozygous mutants accumulating more AsA than wild type (WT). An investigation of the physiological responses to HL demonstrated that the chlorophyll fluorescence parameters were significantly higher in GLDH-236OE than that in WT after 14-d HL. The degradation of photosynthetic pigment in WT was more severe than that in GLDH-236OE. GLDH-236OE accumulated more AsA, anthocyanins, flavonoids, and phenolics, while WT accumulated more reactive oxygen species (ROS) during HL. Our results suggest that GLDH-236OE have lesser sensitivity and higher tolerance to HL due to a higher capacity to eliminate ROS, absorb extra light, and dissipate thermal energy.