ANS-deficient Arabidopsis is sensitive to high light due to impaired anthocyanin photoprotection.

Light attenuation and antioxidation are the main mechanisms of photoprotection by anthocyanin under high light (HL) stress. Anthocyanin synthase (ANS) is the key enzyme in the downstream portion of anthocyanin synthetic pathways. To explore the role of ANS in photoprotection by anthocyanin under HL stress, homozygous ANS -deficient Arabidopsis mutants were screened from SALK_073183 and SALK_028793. Here, we obtained two deficient mutants, ans - 1 and ans - 2 , which had ANS gene expression levels equal to 5.9 and 32.9% of that of Col respectively. By analysing their physiological and biochemical responses to HL stress, we found that there were positive correlations among ANS expression level, anthocyanin content and resistance to HL. The line with the lowest ANS expression level, ans - 1 , was also the most sensitive to HL, showing the lowest anthocyanin content, chlorophyll content, F _v/ F _m ratio, and Rubisco content and the highest O₂^•− accumulation and membrane leakage rate, although it also had the highest antioxidant capacity. Experimental evidence suggests that ANS mainly regulated the light-attenuating function of anthocyanin in photoprotection under HL. Blocking excess light is an important function of anthocyanin that protects plants from HL stress, and a high antioxidant capacity cannot compensate for the absence of the light-shielding function of anthocyanin. Upon high light stress, light-shielding and antioxidation are the main mechanisms of photoprotection by anthocyanin, the final key enzyme in whose synthetic pathways is anthocyanin synthase (ANS). This investigation tackled the role of ANS in photoprotection: ANS mainly regulates the light-shielding of anthocyanin in photoprotection. Additionally, we found that light-shielding is the important function in photoprotection of anthocyanins, and high antioxidant capacity cannot compensate for the absence of the light-shielding. [ABSTRACT FROM AUTHOR]