PARENT SESSION
Posters P6C Photosynthesis, respiration and alternative electron sinks. Abstracts (660-680)

An NADPH dehydrogenase in panicle chloroplasts of Oryza sativa. Hualing Mi^*,1, Ji Yu Ye¹, ¹ National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai, China

ABSTRACT- Since chloroplast ndh genes with high homologous to those encoding subunits of mitochondrial NADH ubiquinone reductase were found in chloroplasts (Ohyama et al, 1986, Shinozaki et al., 1986), research on the entity (NDH) has been aroused attention. An NADH-specific dehydrogenase bound to thylakoid membranes has been identified, partially characterized in barley (Cuello et al. 1995), pea (Sazanov et al. 1998). However, NADPH specific NDH in chloroplasts remains to be elucidated. In this work, an NADPH specific NDH was identified in chloroplasts from panicle of Oryza sativa. Compared with flag leaves, chloroplasts from panicle of Oryza sativa showed a higher activity of NADPH-NBT oxidoreductase. Western blot analysis indicated that the NADPH-NBT oxidoreductase contained subunits of NDH, NDH-K and NDH-H. Oxidation of NADPH but not NADH driven by photosystem I (PSI) in panicle chloroplasts was much faster and was inhibited by rotenone, a specific inhibitor of mitochondrial NDH. These suggest that higher activity of NADPH-specific NDH exists in panicle chloroplasts. Transient increase in chlorophyll fluorescence after turning of off actinic light and initial rate of P700 re-reduction was evident faster, indicating cyclic electron flow around PSI is highly active in panicle. 9AA-fluorescence quenching in the presence of DCMU was obvious in panicle chloroplasts, implying proton gradient across thylakoid membranes through cyclic electron flow is significant in panicle. The physiological significant and the possible mechanism is discussed. References: Ohyama K, Fukuzawa H, Kohchi T, et al. Nature, 1986, 322: 572-574. Shinozaki K, Ohme M, Tanaka M, et al. EMBO J, 1986, 5: 2043-2049. Cuello J, Quiles MJ, Albacete ME, et al. Plant cell physiol, 1995, 36: 265-271. Sazanov LA, Burrow PA, Nixon PJ. Proc Natl Acad Sci USA, 1998a, 95, 1319-1324.

KEY WORDS: panicle, Cyclic electron flow around PS I, Oryza sativa, NADPH dehydrogenase