PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Salt-induced response in ascorbate peroxidase and catalase in rice ( Oryza sativa ). Jeung-suk Koo^*,1, Byoung Yong Moon², Chin Bum Lee¹, ¹ Biology Department, Busan, Korea² Biology Department, Kimhae, Kyoungsangnamdo, Korea

ABSTRACT- We studied how the relationship between salinity and oxidative stress influenced the growth, photosynthetic efficiency, and activity and expression of antioxidant enzymes in roots and leaves of rice (Oryza sativa L. Dongjin). Seedlings of rice (15days) were exposed to NaCl for 24h. Dark-adapted leaves showed a decrease in Fv/Fm (an indicator of photochemical efficiency of PS II) in comparison with control. In the leaves of the rice, salt stress preferentially enhanced the contents of hydrogen peroxide and the activity of superoxide dismutase (SOD). On the other hand, both catalase (CAT) and ascorbate peroxidase (APX) activities increased in treatments with up to 100 mM NaCl, then decreased at higher concentrations. In order to analyze the change of antioxidant enzyme isoforms against salt stress, plant extracts were subjected to native PAGE. Leaves of the rice plant had three isoforms of catalase. The intensities of CAT-2 and -3 were enhanced to salt stress. The transcript levels of Cat by RT-PCR were differently changed. In higher salinity, Cat A and B were increased but Cat C was decreased. Seven APX isoforms were presented in the leaves of the rice plants. Especially APX-1 to -3 isoforms were decreased by salt stress. Interestingly, APX-1 isoform was not changed by drought and chilling stress. On the other hand, the levels of activity for most antioxidant enzymes changed little in the roots of stressed plants compared to the control plants. These results collectively suggest that SOD leads to the overproduction of hydrogen peroxide in the leaves of rice plants subjected to salt stress. The overproduction of hydrogen peroxide functions the signal of salt stress, which affects the expression of specific APX isoforms such as APX-1 under catalase deactivation.

KEY WORDS: salt stress, antioxidant enzyme, ascorbate peroxidase, catalase