Glanz-Idan Noga, Lach Michael, Tarkowski Petr, Vrobel Ondřej, Wolf Shmuel
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Center of the Region Haná for Biotechnological and Agricultural Research, Czech Advanced Technology and Research Institute, Palacký University, Olomouc, Czechia.
Front Plant Sci. 2022 Jul 6;13:922106. doi: 10.3389/fpls.2022.922106. eCollection 2022.
Cytokinins (CKs) regulate numerous plant developmental processes, including photosynthesis and leaf senescence. Isopentenyltransferase (IPT) is a rate-limiting enzyme in the CK-biosynthesis pathway. We overexpressed ipt under tissue-specific promoters to study the long-range effect of CK on the functioning of tomato source leaves. Photosynthetic activity over time provided the measure for leaf aging. Significantly delayed leaf senescence was observed in plants expressing ipt under a root-specific promoter, but not in those expressing the gene under a source leaf-specific promoter. The root-derived influence on leaf aging was further confirmed by grafting experiments. CK concentration in source leaves of both transgenic lines increased significantly, with different proportions of its various derivatives. On the other hand, root CK concentration was only slightly elevated. Nevertheless, the significant change in the proportion of CK derivatives in the root indicated that CK biosynthesis and metabolism were altered. Partial leaf defoliation upregulates photosynthetic rate in the remaining leaf; however, overexpression of ipt in either tissues eliminated this response. Interestingly, stem girdling also eliminated the photosynthetic response. Taken together, our findings suggest that leaf senescence is regulated by a CK-mediated root-shoot communication network. We propose that CK-mediated signal is translocated to the leaf via the xylem where it alters CK biosynthesis, resulting in delayed senescence.
细胞分裂素（CKs）调控众多植物发育过程，包括光合作用和叶片衰老。异戊烯基转移酶（IPT）是CK生物合成途径中的限速酶。我们在组织特异性启动子下过表达ipt，以研究CK对番茄源叶功能的远距离影响。光合活性随时间的变化为叶片衰老提供了衡量指标。在根特异性启动子下表达ipt的植株中观察到叶片衰老显著延迟，但在源叶特异性启动子下表达该基因的植株中未观察到这种现象。嫁接实验进一步证实了根对叶片衰老的影响。两个转基因系的源叶中CK浓度均显著增加，其各种衍生物的比例不同。另一方面，根中CK浓度仅略有升高。然而，根中CK衍生物比例的显著变化表明CK的生物合成和代谢发生了改变。部分叶片去叶处理可上调剩余叶片的光合速率；然而，在任何一个组织中过表达ipt都消除了这种反应。有趣的是，茎环割也消除了光合反应。综上所述，我们的研究结果表明叶片衰老受CK介导的根-梢通讯网络调控。我们提出CK介导的信号通过木质部转运到叶片，在那里它改变CK生物合成，从而导致衰老延迟。
