Alleviation of Drought Stress Inhibition on Photosynthesis by Overexpression of PEPC in Rice

Introducing enzymes involved in photosynthesis of C4 plants into rice (Oryza sativa L.) is supposed to enhance the photosynthesis and crop productivity. However, only a few researches showed that the photosynthesis and crop productivity have been improved by introducing phosphoenolpyruvate carboxylase (PEPC) gene into rice. In the present study, the photosynthetic rates (Pn) in 42 rice lines overexpressing PEPC gene were investigated. The average Pn value of transgenic lines was almost the same as that of the wild type (control) in paddy field, but was much higher than that of the control in upland field. Only a few transgenic lines showed higher Pn in paddy field and most of them showed higher Pn in upland field. Similar results were found in the water controlled experiment. Two transgenic lines with different relative activities of PEPC (10 and 25 folds) were selected to study their photosynthesis under different water potentials (0, −20, and −40 kPa). In both lines, the Pn values were similar to that in the wild type under normal condition (0 kPa) and higher under drought conditions (−20 kPa and −40 kPa). In both experiments, the transgenic lines had higher Pn under drought conditions, with a slower decreasing rate than the wild type. Therefore, the present results suggested that the overexpressed PEPC could not improve the photosynthetic rate of transgenic rice plants. But the photosynthetic rate of transgenic rices declined slowly under drought condition. It is supposed that PEPC might be involved in drought resistance to decrease the inhibition of drought stress on photosynthesis in rice.

摘 要为了明确磷酸烯醇式丙酮酸羧化酶(PEPC)过量表达能否提高水稻的光合速率, 测定了42个表达不同PEPC水平的转玉米PEPC基因水稻株系及对照(受体亲本中花8号)开花期和灌浆期的光合速率。结果表明, 在水田条件下, 转基因株系光合速率与未转基因对照相比没有明显差异; 而在旱地条件下, 转基因水稻的光合速率显著高于对照(27%和24%)。随机选取2个PEPC相对活性分别为10倍和25倍的转基因株系进行网室精确控水盆栽实验得到相似的结果。说明单纯导入PEPC并不能提高水稻的光合速率, 而干旱胁迫下转基因水稻的光合优势可能是由于PEPC参与水稻的抗旱反应而减轻了干旱胁迫对光合作用的抑制作用。