Induction of poplar leaf nitrate reductase: a test of extrachloroplastic control of isoprene emission rate.
Induction of poplar leaf nitrate reductase: a test of extrachloroplastic control of isoprene emission rate.
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DOI：
10.1055/s-2003-44722
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发表时间：
2004
期刊：
影响因子：
3.9
通讯作者：
T. Rosenstiel;Allison L. Ebbets;W. C. Khatri;Ray Fall;Ray Fall;R. K. Monson;R. K. Monson
中科院分区：
文献类型：
--
作者：
T. Rosenstiel;Allison L. Ebbets;W. C. Khatri;Ray Fall;Ray Fall;R. K. Monson;R. K. Monson
最近的几项研究表明，异戊二烯排放速率的控制部分是由叶绿体外的磷酸烯醇丙酮酸供应。为了验证这一假设，我们改变PEP供应的差异诱导的胞质硝酸还原酶（NR）和PEP羧化酶（PEPC）在植物生长的美洲黑杨NO3-或NH 4+作为唯一的氮源。生长与8 mM NH 4+产生了高的叶片氮浓度，与8 mM NO 3-相比，以及轻微升高的光合作用速率和显着增强的异戊二烯排放率和二甲基烯丙基二磷酸（DMAPP，异戊二烯生物合成的前体），叶绿素（a+B）和类胡萝卜素的含量。生长与8 mM NO3-导致两个叶异戊二烯排放速率和DMAPP平行减少。当植物生长与4 mM的氮，NH 4+或NO3-的生长的差异效应没有观察到。减少DMAPP可用性的影响是特定的异戊二烯排放量，并没有传播到更高的类异戊二烯，氮含量和叶叶绿素（a+B）或总类胡萝卜素之间的相关性不受氮源。生化分析表明，显着较高水平的NR和PEPC活性在叶片中的8毫米NO3-生长的植物，与他们的基本作用，硝酸盐同化。两者合计，这些结果支持的假设，叶面同化NO3-减少异戊二烯排放率竞争的碳骨架（介导的PEPC）内的细胞质和可能的还原剂内的叶绿体。PEP的胞质竞争是叶绿体DMAPP供应的主要调节器，我们提出了一个新的“安全阀”假说来解释为什么植物排放异戊二烯。
Several recent studies have suggested that control of isoprene emission rate is in part exerted by supply of extrachloroplastic phosphoenolpyruvate to the chloroplast. To test this hypothesis, we altered PEP supply by differential induction of cytosolic nitrate reductase (NR) and PEP carboxylase (PEPC) in plants of Populus deltoides grown with NO3- or NH4+ as the sole nitrogen source. Growth with 8 mM NH4+ produced a high leaf nitrogen concentration, compared with 8 mM NO3-, as well as slightly elevated rates of photosynthesis and significantly enhanced rates of isoprene emission and content of dimethylallyl diphosphate (DMAPP, a precursor to isoprene biosynthesis), chlorophyll (a+b) and carotenoids. Growth with 8 mM NO3- resulted in parallel reductions in both leaf isoprene emission rate and DMAPP. The differential effects of growth with NH4+ or NO3- were not observed when plants were grown with 4 mM nitrogen. The effects of reduced DMAPP availability were specific to isoprene emission and were not propagated to higher isoprenoids, as the correlations between nitrogen content and either leaf chlorophyll (a+b) or total carotenoids were unaffected by nitrogen source. Biochemical analysis revealed significantly higher levels of NR and PEPC activity in leaves of 8 mM NO3- -grown plants, consistent with their fundamental roles in nitrate assimilation. Taken together, these results support the hypothesis that foliar assimilation of NO3- reduces isoprene emission rate by competing for carbon skeletons (mediated by PEPC) within the cytosol and possibly reductant within the chloroplast. Cytosolic competition for PEP is a major regulator of chloroplast DMAPP supply, and we offer a new "safety valve" hypothesis to explain why plants emit isoprene.