PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

The photosynthetic performances of chilling-resistant plants are supported by up-regulating the pool size of the xanthophyll cycle pigments during cold stress. Hyun-Ju Kim^*,1, In-Soon Kang¹, Chin Bum Lee², Choon-Hwan Lee³, Byoung Yong Moon¹, ¹ Departmnet of Biology, Gimhae, Korea² Department of Biology, Busan, Korea³ Department of Molecular Biology, Busan, Korea

ABSTRACT- Plants posess the ability to dissipate the excess light energy to protect their photosynthetic apparatuses from the photodamage. Heat dissipation is regulated by xanthophyll cycle in thylakoid membranes of chloroplasts. In the present study we explored the mechanistic basis of xanthophyll cycle-depenent photoprotection in plants having different sensitivity to chilling. Using chilling-resistant barley and chilling-sensitive rice plants, we analyzed chilling-induced chlorophyll fluorescence, xanthophyll cycle pigments and mRNA expression of the zeaxanthin epoxdidase which serves a role in the conversion of zeaxanthin to violaxanthin. The photosynthetic performances of barley plants were little affected by chilling. During chilling stress, little changes were observed in chlorophyll fluorescence quenching, either of photochemical and non-photochemical nature, and electron transport transport rate (ETR). Chilled barley plants up-regulated the pool size of the xanthophyll pigments with little alterations in the pigment composition of xanthophyll cycle. Contrastingly, the photosynthetic peformances of rice plants were greatly affected by chilling. They showed a decline in ETR as well as in 1-qP and NPQ during chilling stress. Although chilled rice plants depressed the size of the xanthophyll cycle pigments, they increased the formation of antheraxanthin plus zeaxanthin from violaxanthin. To understand the molecular basis of different regulation of the xanthopyll cycles between both types of plants, we carried out RT-PCR analysis of mRNA expression of zeaxanthin epoxidase. Chilled barley plants showed increased expression of the gene, in contrast to chilled rice plants that showed a depression in its expression. The results imply that barley plants, when exposed to cold stress, are able to mobilize xanthophyll pigments at a higher rate. Chilling-resistant plants, incluing barley, are likely to tolerate cold temperatures, during the daytime, by regulating the operation of xanthophyll cycle as well as by enhancing the pool size of the xanthophyll pigments. Therefore, we suggest that regulation in the pool size of the xanthophyll pigments and in the activity of xanthophyll cycle play a pivotal role in determining the sensitivity of plants to cold stress.

KEY WORDS: chilling sensitivity, chlorophyll fluorescence, xanthophyll cycle, zeaxanthin epoxidase