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首页> 外文期刊>Protoplasma: An International Journal of Cell Biology >Characterization of natural leaf senescence in tobacco (Nicotiana tabacum) plants grown in vitro
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Characterization of natural leaf senescence in tobacco (Nicotiana tabacum) plants grown in vitro

机译：体外生长的烟草（Nicotiana tabacum）植物中天然叶片衰老的表征

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Leaf senescence is a highly regulated final phase of leaf development preceding massive cell death. It results in the coordinated degradation of macromolecules and the subsequent nutrient relocation to other plant parts. Very little is still known about early stages of leaf senescence during normal leaf ontogeny that is not triggered by stress factors. This paper comprises an integrated study of natural leaf senescence in tobacco plants grown in vitro, using molecular, structural, and physiological information. We determined the time sequence of ultrastructural changes in mesophyll cells during leaf senescence, showing that the degradation of chloroplast ultrastructure fully correlated with changes in chlorophyll content. The earliest degenerative changes in chloroplast ultrastructure coinciding with early chromatin condensation were observed already in mature green leaves. A continuum of degradative changes in chloroplast ultrastructure, chromatin condensation and aggregation, along with progressive decrease in cytoplasm organization and electron density were observed in the course of mesophyll cells ageing. Although the total amounts of endogenous cytokinins gradually increased during leaf ontogenesis, the proportion of bioactive cytokinin forms, as well as their phosphate precursors, in total cytokinin content rapidly declined with ageing. Endogenous indole-3-acetic acid (IAA) levels were strongly reduced in senescent leaves, and a decreasing tendency was also observed for abscisic acid (ABA) levels. Senescence-associated tobacco cysteine proteases (CP, E.C. 3.4.22) CP1 and CP23 genes were induced in the initial phase of senescence. Genes encoding glutamate dehydrogenase (GDH, E.C. 1.4.1.2) and one isoform of cytosolic glutamine synthetase (GS1, E.C. 6.3.1.2) were induced in the late stage of senescence, while chloroplastic GS (GS2) gene showed a continuous decrease with leaf ageing.
机译：在大量细胞死亡之前，叶片衰老是叶片发育的高度调控的最终阶段。它导致大分子的协同降解以及随后的养分迁移到其他植物部位。关于正常叶片发育过程中不受压力因素触发的叶片衰老的早期阶段，人们还知之甚少。本文利用分子，结构和生理学信息，对体外生长的烟草植物的天然叶片衰老进行了综合研究。我们确定了叶衰老过程中叶肉细胞超微结构变化的时间序列，表明叶绿体超微结构的降解与叶绿素含量的变化完全相关。在成熟的绿叶中已经观察到叶绿体超微结构的最早的退化变化与早期的染色质凝结相吻合。在叶肉细胞衰老过程中，观察到叶绿体超微结构，染色质凝集和聚集的降解性连续变化，以及细胞质组织和电子密度的逐渐降低。尽管内源性细胞分裂素的总量在叶片发育过程中逐渐增加，但是随着年龄的增长，生物活性细胞分裂素形式及其磷酸盐前体的比例在总细胞分裂素含量中迅速下降。衰老叶片中内源吲哚-3-乙酸（IAA）的含量大大降低，而脱落酸（ABA）的含量也有下降的趋势。衰老相关的烟草半胱氨酸蛋白酶（CP，E.C. 3.4.22）在衰老的初期诱导了CP1和CP23基因。衰老后期诱导了编码谷氨酸脱氢酶（GDH，EC 1.4.1.2）和一种胞质谷氨酰胺合成酶（GS1，EC 6.3.1.2）同工型的基因，而叶绿体GS（GS2）基因随着叶片衰老而持续下降。

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