The major photoprotective role of anthocyanins in leaves ofArabidopsis thalianaunder long-term high light treatment: antioxidant or light attenuator?

Anthocyanins are water-soluble pigments in plants known for their photoprotective role against photoinhibitory and photooxidative damage under high light (HL). However, it remains unclear whether light-shielding or antioxidant activity plays a major role in the photoprotection exerted by anthocyanins under HL stress. To shed light on this question, we analyzed the physiological and biochemical responses to HL of threeArabidopsis thalianalines (Col,chi,ans) with different light absorption and antioxidant characteristics. Under HL,anshad the highest antioxidant capacity, followed byCol, and finallychi;Colhad the strongest light attenuation capacity, followed bychi, and finallyans. The lineanshad weaker physiological activity of chloroplasts and more severe oxidative damage thanchiafter HL treatment.Colwith highest photoprotection of light absorption capacity had highest resistance to HL among the three lines. The lineanswith high antioxidant capacity could not compensate for its disadvantages in HL caused by the absence of the light-shielding function of anthocyanins. In addition, the expression level of theAnthocyanin Synthase(ANS) gene was most upregulated after HL treatment, suggesting that the conversion of colorless into colored anthocyanin precursors was necessary under HL. The contribution of anthocyanins to flavonoids, phenols, and antioxidant capacity increased in the late period of HL, suggesting that plants prefer to synthesize red anthocyanins (a group of colored antioxidants) over other colorless antioxidants to cope with HL. These experimental observations indicate that the light attenuation role of anthocyanins is more important than their antioxidant role in photoprotection.