Abstract:

Photosynthetic C₄-microcycle and its function in different genotype rices were explored comparatively using PEPC transgenic rice and homozygous wild genotype (WT) rice (Oryza sativa L. subsp. japonica Kitaake) as experimental material. In untransformed WT, there existed an intact C₄ photosynthetic enzyme system detected by the activities of enzymes of photosynthetic C₄ pathway, i.e. phosphoenolpyruvate carboxylase (PEPC), NADP⁺-malic enzyme (NADP⁺-ME), NADP⁺-malate dehydrogenase (NADP⁺-MDH), pyruvate orthophosphate dikinase (PPDK), and indicating that there is a primitive photosynthetic C₄-pathway with increased photosynthetic rate in leaf discs or chloroplasts fed with exogenous oxaloacetate (OAA) or malate (MA). Furthermore, photosynthetic C₄ microcycle was promoted in a great range in transgenic rice introduced a maize specific PEPC gene. Enhancement of photosynthetic C₄-microcycle further played some role in raising the net photosynthetic rates (Pn) and debasing the ratio of Pr/Pn by comparing the CO₂ gas exchange rates in different genotype rices, WT rice and PEPC transgenic rice. Analyzing the chlorophyll a fluorescence characteristics showed that increase of photosynthetic C₄-microcycle companied with the raising PSⅡmaximum photochemical efficiency (Fv/Fm) and photochemical quenching (qP), and the lowering of non-photochemical quenching (qN). These results will provide scientific evidence for genetic breeding to improve photosynthetic efficiency in crops by gene engineering.

Key words: transgenic rice, C4-bicarboxylate, chlorophyll a fluorescence, phosphoenolpyruvate car boxylase (PEPC), photosynthetic C4-microcycle