Poster: Photosynthesis

Abs # 358: Regulatory phosphorylation of C4-form phosphoenolpyruvate carboxylase (PEPC) is affected not only by light but also by various nutritional and stress conditions.

Presenter:	Agetsuma, Masakazu , age@lif.kyoto-u.ac.jp
Authors	Agetsuma, Masakazu  (A)   Imanari, Eiji  (A)   Furumoto, Tsuyoshi  (A)   Izui, Katsura  (A)
Affiliations:	(A): Labolatory of Plant Physiology, Graduate School of Biosudies, Kyoto University

PEPC, one of the key enzymes of the C4 pathway, is regulated by reversible phosphorytlation at a conserved Ser near the N-terminus. The phosphorylation causes a decrease in sensitivity to a feedback inhibitor of L-malate. The preparation of antibodies which react only with the phosphorylated PEPC (Ueno et al. Plant J., 21, 17-26, 2000) made it easy to monitor the phosphorylation state (P-state). 1) Close examination of the changes of P-state in maize leaves during a whole day revealed a temporary up-regulation before dawn and before sunset, in addition to light-dependent changes, which suggests some additional unknown phosphorylation system. 2) When seedlings were grown under water-deficient or high CO₂ (700 ppm) conditions, the P-state was elevated or depressed, respectively. Furthermore, application of DCDP, a specific inhibitor of PEPC, to detached leaves elevated the P-state. Thus the demand of L-malate for C4-photosynthesis seems to be adjusted at this phosphorylation step. 3) When maize plants were subjected to oxidative stress conditions such as the transfer of seedlings from 25 to 6^oC under light and the application of diamide to detached leaves, decreases in the photosynthesis and the P-state was observed, though it remains to be clarified whether the decrease is due to the oxidative inactivation of PEPC kinase or not.