Growth of tobacco in short-day conditions leads to high starch, low sugars, altered diurnal changes in the Nia transcript and low nitrate reductase activity, and inhibition of amino acid synthesis
Growth of tobacco in short-day conditions leads to high starch, low sugars, altered diurnal changes in the Nia transcript and low nitrate reductase activity, and inhibition of amino acid synthesis
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DOI：
10.1007/s004250050452
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发表时间：
1998-12-01
期刊：
影响因子：
4.3
通讯作者：
Stitt, M
中科院分区：
文献类型：
--
作者：
Matt, P;Schurr, U;Stitt, M
比较了烟叶碳水化合物和硝酸还原酶（NR）活性的日变化。L.cv。长（18小时光照/6小时黑暗）和短（6小时光照/18小时黑暗）生长的植物，或光照条件短期变化后的植物。在长时间生长的植物中，源叶在光照和黑暗时期都含有高水平的糖。在短日照生长的植物中，蔗糖和还原糖的含量在夜晚结束时非常低，尽管它们在光照期间有所上升，但仍然比长日照时期低得多，并在午夜时分再次下降到非常低的水平。短日照植物的淀粉积累速度比长日照植物快。淀粉在短白天的夜间被完全重新动员起来，但在长白天则不然。一个短暂的白天/漫长的夜晚周期足以刺激淀粉在接下来的光照期积累。在长时间生长的植物中，Nia转录物浓度在夜间高，白天低，夜间逐渐恢复。在短日照植株中，Nia转录本水平在夜晚结束时相对较低，在光照期结束时下降到极低水平，在午夜达到显著的最大值，在黑暗期的最后5 h下降。长日生长植物源叶片NR活性在光照前期上升2 ~ 3倍，在光照后期下降。在短日照植物中，NR活性在夜间较低，光照后仅略有增加。源叶NR暗失活在长日照植物中部分逆转，而在短日照植物中则没有。在两种生长条件下，与野生型植物相比，具有一个而不是四个Nia基因功能拷贝的突变体在源叶片中最大NR活性降低了60%。在较长白天，突变体NR活性的日变化几乎完全被抑制，而在较短的白天，突变体的日变化与野生型相似或略大。短日照植物转长日照3 d后，NR活性和日变化与长日照植物相似。短日生植物源叶韧皮部输出在一个光暗循环的冷带处理下受到一定程度的抑制。在暗期结束时，叶片糖含量的增加伴随着Nia转录物水平的显著增加和NR活性的2倍增加。当野生型植物遭受单一的昼短夜长周期时，当内源糖含量低于约3 μ mol己糖（g FW）时，源叶片中NR活性下降（-1）。在短日照条件下，与同一植物源叶片相比，库叶片的糖含量更高，光诱导的NR活性上升幅度也要大得多。与长时间生长的植物相比，短日照条件下野生型植物的源叶中硝酸盐含量很高，谷氨酰胺含量很低，总氨基酸含量很低，蛋白质和叶绿素含量也较低。在短时间内生长的植物，谷氨酸和天冬氨酸的含量相对较高，而在夜晚结束时，其来源叶片中大多数次要氨基酸的含量极低。光照导致谷氨酸的减少和次要氨基酸的增加。单一的短昼长夜循环导致谷氨酸增加，在黑暗期结束时次要氨基酸大量减少，重新照明导致谷氨酸减少和次要氨基酸增加。研究人员提出，当糖供应不足时，糖介导的Nia表达和NR活性的控制超过了氮化合物的调节，导致硝酸盐同化受到严重抑制。糖对氮代谢的调节的重要性通过烟草在短日照条件下生长时碳和氮受到限制的发现得到了显著的说明。
Diurnal changes in carbohydrates and nitrate reductase (NR) activity were compared in tobacco (Nicotiana tabacum. L.cv. Gatersleben) plants growing in a long (18 h light/6 h dark) and a short (6 h light/18 h dark) day growth regime, or after short-term changes in the light regime. In long-day-grown plants, source leaves contained high levels of sugars throughout the light and dark periods. In short-day-grown plants, levels of sucrose and reducing sugars were very low at the end of the night and, although they rose during the light period, remained much lower than in long days and declined to very low levels again by the middle of the night. Starch accumulated more rapidly in short-day-than long-day-grown plants. Starch was completely re mobilised during the night in short days, but not in long days. A single short day/long night cycle sufficed to stimulate starch accumulation during the following light period. In long-day-grown plants, the Nia transcript revel was high at the end of the night, decreased during the day, and recovered gradually during the night. In short-day-grown plants, the Nia transcript level was relatively low at the end of the night, decreased to very low levels at the end of the light period, increased to a marked maximum in the middle of the night, and decreased during the last 5 h of the dark period. In long-day-grown plants, NR activity in source leaves rose by 2- to 3-fold in the first part of the light period and decreased in the second part of the light period. In short-day-grown plants, NR activity was low at the end of the night, and only increased slightly after illumination. Dark inactivation of source-leaf NR was partially reversed in long-day-grown plants, but not in short day-grown plants. In both growth regimes, mutants with one instead of four functional copies of the Nia gene had a 60% reduction in maximum NR activity in the source leaves, compared to wild-type plants. The diurnal changes in NR activity were almost completely suppressed in the mutants in long days, whereas the mutants showed similar or slightly larger diurnal changes than wild-type plants in short days. When short-day-grown plants were transferred to long-day conditions for 3 d, NR activity and the diurnal changes in NR activity resembled those in long-day-grown plants. Phloem export from source leaves of short-day-grown plants was partially inhibited by applying a cold-girdle for one light and dark cycle. The resulting increase in leaf sugar was accompanied by an marked increase in the Nia transcript level and a 2-fold increase in NR activity at the end of the dark period. When wild-type plants were subjected to a single short day/long night cycle of increasing severity, NR activity in source leaves at the end of the night decreased when the endogenous sugars declined below about 3 mu mol hexose (g FW)(-1). In sink leaves in short-day conditions, sugars were higher and the light-induced rise in NR activity was much larger than in source leaves on the same plants. The source leaves of wild-type plants in short-day conditions contained very high levels of nitrate, very low levels of glutamine, low levels of total amino acids, and lower protein and chlorophyll, compared to long-day-grown plants. Plants grown in short days had relatively high levels of glutamate and aspartate, and extremely low levels of most of the minor amino acids in their source leaves at the end of the night. Illumination led to a decrease in glutamate and an increase in the minor amino acids.A single short day/long night cycle led to an increase in glutamate, and a large decrease in the minor acids at the end of the dark period, and reillumination led to a decrease in glutamate and an increase in the minor amino acids. It is proposed that sugar-mediated control of Nia expression and NR activity overrides regulation by nitrogenous compounds when sugars are in short supply, resulting in a severe inhibition of nitrate assimilation. It is also proposed that sugars exert a global control on amino acid metabolism The importance of sugars for the regulation of nitrogen metabolism is strikingly illustrated by the finding that tobacco is carbon and nitrogen limited when it is grown in short-day conditions.