转玉米PEPC基因水稻中有限的C4光合微循环及其生理作用

用转PEPC基因水稻(Oryza sativa L. subsp.japonica Kitaake)和原种水稻Kitaake为材料,研究了不同基因型水稻叶片中的C4光合微循环及其功能.通过测定与光合C4途径有关的关键酶,如磷酸烯醇式丙酮酸羧化酶(PEPC)、NADP -苹果酸酶(NADP -ME)、NADP -苹果酸脱氢酶(NADP -MDH)和丙酮酸磷酸双激酶(PPDK),说明原种水稻叶片中具有完整的C4光合酶体系;用外源OAA或MA饲喂叶切片或叶绿体后明显增加光合速率,证明原种水稻中具有一个有限的光合C4微循环.将玉米的PEPC基因导入原种水稻后,可大幅度提高光合C4微循环的速率.测定不同基因型的CO2交换速率,看出水稻中C4光合微循环的增强有提高净光合速率(Pn)和降低光呼吸速率/净光合速率(Pr/Pn)比值的作用.叶绿素荧光特性分析表明,C4光合微循环的增强伴随着PSⅡ电子传递效率(Fv/Fm)和光化学猝灭(qP)的增加以及非光化学猝灭(qN)的降低;这些结果为通过基因工程手段提高作物光合效率的遗传育种提供了科学根据.

A Limited Photosynthetic C4-Microcycle and Its Physiological Function in Transgenic Rice Plant Expressing the Maize PEPC Gene

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.