Nováková Marie, Motyka Václav, Dobrev Petre I, Malbeck Jirí, Gaudinová Alena, Vanková Radomíra
Institute of Experimental Botany AS CR, Rozvojova 135, 165 02 Prague 6, Czech Republic.
J Exp Bot. 2005 Nov;56(421):2877-83. doi: 10.1093/jxb/eri282. Epub 2005 Sep 12.
As many processes are regulated by both light and plant hormones, evaluation of diurnal variations of their levels may contribute to the elucidation of the complex network of light and hormone signal transduction pathways. Diurnal variation of cytokinin, auxin, and abscisic acid levels was tested in tobacco leaves (Nicotiana tabacum L. cv. Wisconsin 38) grown under a 16/8 h photoperiod. The main peak of physiologically active cytokinins (cytokinin bases and ribosides) was found after 9 h of light, i.e. 1 h after the middle of the light period. This peak coincided with the major auxin peak and was closely followed by a minor peak of abscisic acid. Free abscisic acid started to increase at the light/dark transition and reached its maximum 3 h after dark initiation. The content of total cytokinins (mainly N-glucosides, followed by cis-zeatin derivatives and nucleotides) exhibited the main peak after 9 h of light and the minor peak after the transition to darkness. The main, midday peak of active cytokinins was preceded by a period of minimal metabolic conversion of tritiated trans-zeatin (less than 30%). The major cytokinin-degrading enzyme, cytokinin oxidase/dehydrogenase (EC 1.5.99.12), exhibited maximal activity after the dark/light transition and during the diminishing of the midday cytokinin peak. The former peak might be connected with the elimination of the long-distance cytokinin signal. These cytokinin oxidase/dehydrogenase peaks were accompanied by increased activity of beta-glucosidase (EC 3.2.1.21), which might be involved in the hydrolysis of cytokinin O-glucosides and/or in fine-tuning of active cytokinin levels at their midday peak. The achieved data indicate that cytokinin metabolism is tightly regulated by the circadian clock.
由于许多生理过程受光照和植物激素共同调控，评估它们水平的昼夜变化可能有助于阐明光照和激素信号转导途径的复杂网络。在16/8小时光周期下生长的烟草叶片（Nicotiana tabacum L. cv. Wisconsin 38）中检测了细胞分裂素、生长素和脱落酸水平的昼夜变化。生理活性细胞分裂素（细胞分裂素碱基和核苷）的主要峰值出现在光照9小时后，即光照期中间过后1小时。该峰值与主要生长素峰值重合，随后紧接着是一个较小的脱落酸峰值。游离脱落酸在光/暗转换时开始增加，并在黑暗开始后3小时达到最大值。总细胞分裂素（主要是N-葡萄糖苷，其次是顺式玉米素衍生物和核苷酸）的含量在光照9小时后出现主要峰值，在转换到黑暗后出现较小峰值。活性细胞分裂素的主要午间峰值之前是一段氚标记反式玉米素代谢转化率最低的时期（低于30%）。主要的细胞分裂素降解酶，细胞分裂素氧化酶/脱氢酶（EC 1.5.99.12），在暗/光转换后以及午间细胞分裂素峰值下降期间表现出最大活性。前一个峰值可能与长距离细胞分裂素信号的消除有关。这些细胞分裂素氧化酶/脱氢酶峰值伴随着β-葡萄糖苷酶（EC 3.2.1.21）活性的增加，β-葡萄糖苷酶可能参与细胞分裂素O-葡萄糖苷的水解和/或在午间峰值时对活性细胞分裂素水平的微调。所获得的数据表明，细胞分裂素代谢受生物钟严格调控。
