Sugiharto B, Sugiyama T
Department of Agricultural Chemistry, School of Agriculture, Nagoya University, Nagoya 464-01, Japan.
Plant Physiol. 1992 Apr;98(4):1403-8. doi: 10.1104/pp.98.4.1403.
We previously showed that the selective accumulation of phosphoenolpyruvate carboxylase (PEPC) in photosynthetically maturing maize (Zea mays L.) leaf cells induced by nitrate supply to nitrogen-starved plants was primarily a consequence of the level of its mRNA (B Sugiharto, K Miyata, H Nakamoto, H Sasakawa, T Sugiyama [1990] Plant Physiol 92: 963-969). To determine the specificity of inorganic nitrogen sources for the regulation of PEPC gene expression, nitrate (16 millimolar) or ammonium (6 millimolar) was supplied to plants grown previously in low nitrate (0.8 millimolar), and changes in the level of PEPC and its mRNA were measured in the basal region of the youngest, fully developed leaves of plants during recovery from nitrogen stress. The exogenous supply of nitrogen selectively increased the levels of protein and mRNA for PEPC. This increase was more pronounced in plants supplemented with ammonium than with nitrate. The accumulation of PEPC during nitrogen recovery increased in parallel with the increase in the activity of glutamine synthetase and/or ferredoxin-dependent glutamate synthase. Among the major amino acids, glutamine was the most influenced during recovery, and its level increased in parallel with the steady-state level of PEPC mRNA for 7 hours after nitrogen supply. The administration of glutamine (12 millimolar) to nitrogen-starved plants increased the steady-state level of PEPC mRNA 7 hours after administration, whereas 12 millimolar glutamate decreased the level of PEPC mRNA. The results indicate that glutamine and/or its metabolite(s) can be a positive control on the nitrogen-dependent regulation of PEPC gene expression in maize leaf cells.
我们之前的研究表明，向缺氮植物供应硝酸盐可诱导光合成熟的玉米（Zea mays L.）叶细胞中磷酸烯醇式丙酮酸羧化酶（PEPC）的选择性积累，这主要是其mRNA水平所致（B Sugiharto、K Miyata、H Nakamoto、H Sasakawa、T Sugiyama [1990] Plant Physiol 92: 963 - 969）。为了确定无机氮源对PEPC基因表达调控的特异性，将硝酸盐（16毫摩尔）或铵（6毫摩尔）供应给先前在低硝酸盐（0.8毫摩尔）条件下生长的植物，并在植物从氮胁迫恢复过程中，测定最幼嫩、完全展开叶片基部区域PEPC及其mRNA水平的变化。外源供应氮选择性地增加了PEPC的蛋白质和mRNA水平。这种增加在补充铵的植物中比补充硝酸盐的植物中更明显。氮恢复过程中PEPC的积累与谷氨酰胺合成酶和/或铁氧还蛋白依赖性谷氨酸合成酶活性的增加平行。在主要氨基酸中，谷氨酰胺在恢复过程中受影响最大，其水平在供氮后7小时内与PEPC mRNA的稳态水平平行增加。向缺氮植物施用谷氨酰胺（12毫摩尔）后7小时，PEPC mRNA的稳态水平增加，而12毫摩尔谷氨酸则降低了PEPC mRNA的水平。结果表明，谷氨酰胺和/或其代谢产物可能是玉米叶细胞中PEPC基因表达氮依赖性调控的正调控因子。
