Promotive Effect of Exogenous C4-Bicarboxylate on Photosynthetic C4 Pathway in Transgenic Rice Plant Expressing Maize Specific PEPC Gene
ZHU Su-qin 1; JI Ben-hua 1; 2; JIAO De-mao2
1Department of Life Sciences and Technology; Nantong Normal College; Nantong 226007; China; 2Institute of Agrobiological Genetics and Physiology; Jiangsu Academy of Agricultural Sciences; Nanjing 210014; China
Photosynthetic C4 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 C4 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 C4 microcycle further played some role in raising the net photosynthetic rates (Pn) and debasing the ratio of photorespiratory rate and net photosynthetic rate( Pr/Pn ), which were comfirmed through determining the CO2 gas exchange rate in different genotype rices, WT or PC. Analyzing the chlorophyll fluorescence characteristics showed that enhancement of photosynthetic C4 microcycle companied with the raising PSⅡelectron transport 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.