外源C_4二羧酸对转玉米PEPC基因水稻C_4光合途径的促进作用

Promotive Effect of Exogenous C_4-Bicarboxylate on Photosynthetic C_4 Pathway in Transgenic Rice Plant Expressing Maize Specific PEPC Gene

以转PEPC基因水稻和野生型水稻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) ,说明野生型水稻叶片中具有完整的C4 光合酶体系 ;用外源草酰乙酸 (OAA)或苹果酸 (MA)饲喂叶切片或叶绿体后明显增加光合速率 ,证明野生型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)

Photosynthetic C 4 microcycle and its function in different genotype rices were explored comparatively using PEPC transgenic rice (PC) and homozygous wild genotype rice (WT) Kitaake as experimental materials. In WT rice, there existed an intact C 4 photosynthetic enzyme system which were verified through detecting photosynthetic C 4 pathway related key enzymes, i.e. phosphoenol pyruvate carboxylase (PEPC), NADP malic enzyme (NADP ME), NADP malate dehydrogenase (NADP MDH) and pyruvate, orthophosphate dikinase (PPDK), and a primitively limited photosynthetic C 4 microcycle pathway through assaying increased photosynthetic rate in leaf discs or chloroplasts fed with exogenous oxaloacetate (OAA) or malate (MA). Furthermore, photosynthetic C 4 microcycle was promoted in a great range in PC rice. Enhancement of photosynthetic C 4 microcycle further played some role in raising the net photosynthetic rates (P n) and debasing the ratio of photorespiratory rate and net photosynthetic rate( P r/P n ), which were comfirmed through determining the CO 2 gas exchange rate in different genotype rices, WT or PC. Analyzing the chlorophyll fluorescence characteristics showed that enhancement of photosynthetic C 4 microcycle companied with the raising PSⅡelectron transport efficiency (F v /F m ) and photochemical quenching (q p ), and the lowering of non photochemical quenching (q N ). These results will provide scientific evidence for genetic breeding to improve photosynthetic efficiency in crops by gene engineering.