Faiss M, Zalubìlová J, Strnad M, Schmülling T
Universität Tübingen, Lehrstuhl für Allgemeine Genetik, Germany.
Plant J. 1997 Aug;12(2):401-15. doi: 10.1046/j.1365-313x.1997.12020401.x.
This study investigated whether an increased production of the plant hormone cytokinin in roots, the main site of its synthesis and putative signaling organ, can influence developmental events, such as growth of axillary shoot meristems or leaf senescence, in the plant shoot. To this end, transgenic tobacco plants (Nicotiana tabacum L.) were generated that conditionally overproduce cytokinins. These plants harbour the ipt gene under the transcriptional control of a modified 35S promoter that is repressed in plants with high titers of tetracycline repressor protein. De-repression of transcription led to a rapid more than 50-fold increase of hormone concentration. The time course of changes in the steady-state levels of 16 different cytokinin metabolites, as a consequence of IPT enzyme activity, was monitored in different plant tissues. Zeatin riboside was the first and most dramatically increased product; zeatin, dihydrozeatin and glucosides accumulated later. The consequences of enhanced cytokinin synthesis remained mainly restricted to the site of hormone production. For example, de-repression of ipt gene transcription in lateral buds caused the growth of single buds only at the site of tetracycline application. In reciprocal grafts of transgenic plants with wild-type plants, no biological cytokinin effects, i.e. growth of lateral shoot meristems or sequential leaf senescence, were observed in the non-transgenic plant part. Also, the increase in steady-state levels of cytokinins remained restricted mainly to the transgenic part, despite a specific increase of the zeatin riboside concentration in the transpiration stream. These results question the role of cytokinins as a long-range root-to-shoot signal in correlative control of apical dominance and sequential leaf senescence of tobacco, and support the assumption that this hormone is relevant to paracrine signaling.
本研究调查了植物激素细胞分裂素在其主要合成部位及假定的信号传导器官——根中产量的增加，是否会影响植物地上部分的发育事件，如腋芽分生组织的生长或叶片衰老。为此，构建了条件性过量产生细胞分裂素的转基因烟草植株（烟草）。这些植株含有ipt基因，该基因受修饰的35S启动子转录控制，在四环素阻遏蛋白含量高的植株中该启动子被抑制。转录去抑制导致激素浓度迅速增加50倍以上。在不同植物组织中监测了16种不同细胞分裂素代谢物稳态水平因IPT酶活性而发生变化的时间进程。玉米素核苷是首个且增加最为显著的产物；玉米素、二氢玉米素和糖苷随后积累。细胞分裂素合成增强的后果主要局限于激素产生部位。例如，侧芽中ipt基因转录的去抑制仅导致四环素施用部位的单个芽生长。在转基因植株与野生型植株的相互嫁接中，在非转基因植株部分未观察到生物学上的细胞分裂素效应，即侧芽分生组织的生长或叶片顺序衰老。此外，尽管蒸腾流中玉米素核苷浓度有特定增加，但细胞分裂素稳态水平的增加仍主要局限于转基因部分。这些结果对细胞分裂素作为烟草顶端优势和叶片顺序衰老相关控制中从根到地上部分的长距离信号的作用提出了质疑，并支持了这种激素与旁分泌信号传导相关的假设。
