Poster: Intracellular Signaling

Abs # 821: Analysis of the gene regulation system involved in cytosolic ascorbate peroxidase response under the high light stress

Presenter:	Yabuta, Yukinori , gs900201@nara.kindai.ac.jp
Authors	Yabuta, Yukinori  (A)   Maruta, Takanori  (B)   Mieda, Takahiro  (A)   Yoshimura, Kazuya  (B)   Ishikawa, Takahiro  (C)   Shigeoka, Shigeru  (A) (B)
Affiliations:	(A): Advanced Life Science, Graduate School, Kinki University (B): Department of Food and Nutrition, Faculty of Agriculture, Kinki University (C): Faculty of Life and Environmental Science, Simane University

Here we studied the signal transduction system associated with the induction of cytosolic ascorbate peroxidase (cAPX) in spinach and tobacco leaves. When the detached spinach leaves were treated with 3-aminotriazole or methyl viologen, the steady-state transcript level of cytosolic APX (cAPX) and the cellular H₂O₂ level increased. The treatment of detached leaves with H₂O₂ also increased the transcript level of cAPX. The treatment of DCMU inhibited the induction of cAPX expression under high light intensity. In contrast, the treatment with DBMIB increased the transcript level of cAPX under low light intensity. These results suggest the possibility that cAPX is regulated by the redox status of photosynthetic electron transport or the cellular H₂O₂ level. Next, to examine whether the H₂O₂ level or the redox changes in the electron transport of chloroplasts mediates the induction of cAPX expression under high light intensity, we used transgenic tobacco plants expressing the E. coli catalase (T43-1) and thylakoid-membrane bound APX (TpTAP-12) in chloroplasts (Yabuta et al., Plant J. 32, 915-925, 2002). No significant difference in the transcript level of cAPX was detected among the wild-type, T43-1, and TpTAP-12 under low or high light intensity. The q_P values of these plants decreased under high light intensity after 1 h exposure. In wild-type plants, the H₂O₂ level slightly increased under high light conditions, while those in T43-1 and TpTAP-12 plants did not. These results suggest that the induction of cAPX expression under high light intensity is mediated by the redox changes in the electron transport of chloroplasts at the early stage.