The Regulation of Photosynthesis and Nitrogen Assimilation Genes by Nitrogen in C4 Plants

(1)在玉米叶肉细胞中，硝酸还原酶(NR)、可塑性谷氨酰胺合成酶(GS2)和铁氧还蛋白-谷氨酸合成酶(FD-GOGAT)基因的转录是短暂的，并且先于磷酸烯醇式丙酮酸羧化酶(C4-PEPC)的基因转录。(2)氮诱导的PEPC和碳酸酐酶(CA)基因的积累需要细胞分裂素和谷氨酰胺作为阳性信号；细胞分裂素上调它们的转录，谷氨酰胺上调它们的mRNAs的积累。(3)C4-PEPC依赖细胞分裂素的转录需要蛋白质的合成(S)，C4-PEPC的mRNAs的积累似乎是由蛋白激酶和蛋白磷酸酶活性介导的，而NR和GS2的mRNAs的积累不需要蛋白质的合成。(4)氮诱导的NR、GS2、而FD-GOGAT不需要细胞分裂素，而谷氨酰胺则是NRmRNAs积累的负信号。这表明蛋白磷酸酶活性参与了硝酸盐依赖的NRNAs的积累。(5)克隆了NAD-ME型C4植物--谷氨酸氨基转移酶基因。定位于叶肉细胞的同工酶基因表达受氮素供应的选择性调节。

(1)The nitrate-inducible transcription of genes for nitrate reductase (NR), plastidic glutamine synthetase (GS2), and ferredoxin-glutamate synthase (Fd-GOGAT) is transient and precedes the gene transcription for phosphoenolpyruvate carboxylase (C4-PEPC) in maize mesophyll cells.(2)The nitrogen-inducible accumulation of mRNAs for PEPC and carbonic anhydrase (CA) requires cytokinin and glutamine as positive signals ; cytokinin up-regulates their transcription and glutamine up-regulates the accumulation of their mRNAs.(3)The cytokinin-dependent transcription of C4-PEPC requires the synthesis of protein(s) and the accumulation of C4-PEPC mRNA appears to be mediated by protein kinase and protein phosphatase activities, whereas the accumulation of mRNAs for NR and GS2 does not require the synthesis of protein.(4)The nitrogen-inducible accumulation of mRNAs for NR, GS2, and Fd-GOGAT does not requite cytokinin and glutamine acts as a negative signal for the accumulation of NR mRNA.It was suggested that protein phosphatase activity involves in the nitrate-dependent accumulation of mRNAs for NR and GS2.(5)Aspartate aminotransferase genes in Panicun miliaceum, an NAD-ME type of C4-plant, were cloned and sequenced. The gene expression of the isozyme which is located in the mesophyll cells was found to be selectively regulatee by nitrogen-availability.