PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Vitamin C is important for acclimation to and growth in high light. Patricia Müller-Moule^*,1, Talila Golan², Krishna Niyogi², ¹ Institute for Developmental and Molecular Plant Biology, Düsseldorf, Germany² Department of Plant and Microbial Biology, Berkeley, CA, USA

ABSTRACT- To understand the importance of vitamin C and zeaxanthin as photoprotective mechanisms, several ascorbate-deficient Arabidopsis mutants were subjected to growth in high light (HL) or to a transfer from low light (LL) to HL. The vtc2 mutant has only 10 to 30% ascorbate compared to the wild type, while the vtc2npq1 mutant in addition lacks zeaxanthin, which is necessary for nonphotochemical quenching (NPQ), mechanisms that dissipate excess light energy harmlessly as heat. Lastly, the vtc2npq4 mutant is also impaired in nonphotochemical quenching, but has a normal xanthophyll content. All mutants were obviously impaired when grown in HL compared to the wild type. They had lower electron transport and oxygen evolution rates and lower quantum efficiency of PSII compared with the wild type, implying that they experienced chronic photo-oxidative stress. The mutants lacking NPQ in addition to ascorbate were only slightly more affected than vtc2. All three mutants had higher glutathione levels than the wild type in HL, suggesting a possible compensation for the lower ascorbate content. In addition, when transferring vtc2 and vtc2npq1 plants from LL to HL, the mature rosette leaves bleached partially or fully, respectively. The bleaching in vtc2npq1 and vtc2 was paralleled by an increase in lipid peroxidation and a drastic decrease in Fv/Fm, a fluorescence parameter used to estimate photoinhibition. These results demonstrate the importance of ascorbate for acclimation to HL and growth in HL. The more drastic phenotype of vtc2npq1 plants after transfer to HL also support the proposed role of zeaxanthin as an antioxidant.

KEY WORDS: zeaxanthin, ascorbate, photoprotection, antioxidants