不同型式氮源對水稻懸浮細胞中蔗糖轉運蛋白家族基因表現之調控

碳水化合物的累積及運輸效能為決定作物產量的重要因素，部分研究指出低氮素或缺氮逆境會促進碳水化合物於作物各器官間重新分配。蔗糖為植物體中醣類運輸的主要形式，而蔗糖轉運蛋白（sucrose transporter, SUT）則為調控蔗糖進出韌皮部的主要蛋白質。本研究利用水稻（Oryza sativa）懸浮細胞系統探討培養液中銨態氮及硝酸態氮含量改變對水稻蔗糖轉運蛋白家族基因（OsSUTs）表現之影響。研究結果顯示OsSUT2、4及5基因表現會受氮供應源濃度所調控，而OsSUT1基因表現於缺氮培養的細胞中並無明顯變化。OsSUT2及4基因表現會受缺氮誘導，而此誘導現象於恢復供氮六小時後即消失，且銨態氮（NH_4^+-N）之效應較硝酸態氮（NO_3^--N）顯著。另一方面，OsSUT5之基因表現則受缺氮刺激所抑制，但於細胞重新培養於含氮源之培養基兩天後可使OsSUT5基因表現回復，且此回復反應僅於NO_3^--N處理下呈現，NH_4^+-N則不具調控效應。分析帶有OsSUT4基因啟動子不同長度片段接合GUS報導基因（POsSUT4::GUS）之轉殖水稻懸浮細胞，發現OsSUT4基因啟動子上受缺氮調控之cis - acting elements位置應位於OsSUT4基因轉譯起始點至上游434 bp間。

Carbohydrate accumulation and transport are important factors to determine crop yields. Several studies indicated that low nitrogen supplying or nitrogen deficiency promotes reallocation of carbohydrates in various organs of plants. Sucrose is the major sugar that is transported in phloem. Sucrose transporters (SUTs) play an important role in the loading of sucrose into phloem. In this study, effects of different types of nitrogen nutrients such as ammonium and nitrate on OsSUT family gene expressions in rice (Oryza sativa ) suspension cells were investigated. The results showed nitrogen starvation modified OsSUT2, 4 and 5 expressions, but there was no significant change presented in OsSUT1 expressions. Nitrogen starvation induced OsSUT2 and 4 gene expressions, and the effect was suppressed after 6 hrs of nitrogen re-supplying treatment. The effects of nitrogen replenishment treatment with ammonium (NH_4^+-N) on OsSUT2 and 4 gene expressions were more significant than that treated with nitrate (NO_3^--N). On the other hand, OsSUT5 gene expression was inhibited under nitrogen starvation, while OsSUT5 gene expression was increased to a level equivalent to control after nitrogen re-supplying for 2 days. Moreover, the nitrogen recovery effect on OsSUT5 expression was presented in NO_3^--N treatment conditions but not under NH_4^+-N culture conditions. Based on OsSUT4 promoter activity analysis in transgenic rice suspension cells, it was suggested that the cis -acting elements related to nitrogen regulations were located at the region within 434-bp upstream from the translation start codon.