棉花地上部反馈调节叶片早衰的细胞分裂素和脱落酸机制研究

Premature senescence has become one of the major constraints to cotton production in China. We have found that cotton shoot plays a major role in mediating senescence induced by potassium deficiency via influencing cytokinins (CKs) and abscisic acid (ABA) levels in xylem sap and leaves. In this project, we will continue to select cotton cv. CCRI41 and SCRC22, two contrasting cultivars in sensitivity to premature senescence, to perform diverse grafting, such as one scion/one rootstock, two scions/one rootstock, one scion/two rootstocks, inter-stock and top grafting, so that the action site of feedback signal(s) from shoots to regulate xylem CKs and ABA could be precisely identified. Then, we will observe whether the anatomy of vascular band around the site of feedback regulation could influence the levels of xylem CKs and ABA. Most importantly, we will unveil how CKs and ABA in xylem sap and leaves change in terms of biosynthesis, metabolism, and both short- and long-distance transport under the action of feedback signal(s), by measuring endogenous CKs and ABA and their metabolites, tracing isotope labeled CKs and ABA, and cloning genes associated with biosynthesis, metabolism and transport of CKs and ABA as well as their expression and immunohistochemical localization. The disclosure of mechanism of phytohormone involvement in feedback regulation of cotton leaf senescence will lead to a better understanding of communication between shoot and root, and is beneficial for the development of approaches to managing premature senescence of some cotton cultivars.

针对棉花生产中的早衰问题，根据已确定的棉花地上部反馈调节叶片早衰现象（缺钾诱导），继续选用抗早衰程度不同的中棉所41和鲁棉研22，首先开展单接穗单砧木、双接穗单砧木、单接穗双砧木、中间砧木和高位嫁接等多种嫁接研究，以明确地上部反馈调节木质部细胞分裂素（CKs）和脱落酸（ABA）的作用位点；其次探明反馈调节位点及其附近的维管系统结构是否影响木质部CKs和ABA的水平；最后通过内源CKs和ABA及其代谢物的测定、同位素标记CKs和ABA的示踪、与CKs和ABA合成、代谢及运输有关基因的克隆、表达、组织定位等，揭示木质部和叶片中的CKs、ABA在反馈信号的作用下如何发生合成、代谢、短距离运输和长距离运输的变化，以实现对衰老的反馈调节。阐明棉花早衰的植物激素反馈调节机制，不仅可以加深对植物根冠通讯多样性和复杂性的了解，而且对制定有效措施防止一些棉花品种发生早衰有指导作用。

易衰老棉花品种中棉所41（41）与不易衰老品种鲁棉研22（22）的I型（单接穗单砧木，嫁接位点为下胚轴）、Y型（双接穗单砧木，嫁接位点为下胚轴）和砧木高位Y型嫁接（接穗下胚轴嫁接于砧木主茎第2-3节间）试验表明，地上部可能通过反馈调节下胚轴的活性细胞分裂素（ZR+Z，iPA+iP）和游离脱落酸（ABA）的合成、代谢和横向转运能力（而不是根系的合成和输出量及下胚轴木质部管状分子的运输能力）对叶片衰老起主要决定作用。中间砧木嫁接（一个品种自下胚轴处切断，将另一个品种1.5 cm长的下胚轴嫁接到其间）的结果表明，中间砧木木质部的ZR+Z和ABA流量具有自治性，与砧木和接穗的流量差异显著，提示中间砧木部分ZR+Z和ABA的合成、代谢及转运比较活跃。I型嫁接砧木不影响接穗下胚轴的ZR+Z流量，但显著影响接穗的14C-ZR（自根系引入）放射性强度；Y型嫁接无论砧木为何品种22接穗下胚轴木质部的ZR+Z流量显著高于41接穗，但2个接穗的14C-ZR放射性强度无显著差异。此外，Y型嫁接22接穗下胚轴韧皮部（实际为韧皮部+皮层+表皮）的CK合成限速酶基因GhIPT表达量显著高于41接穗，与CK运输相关的2个基因GhPUP和GhENT在22接穗韧皮部和木质部（实际为木质部+髓部）的表达量也显著高于接穗41。14C-ZR示踪和基因表达量试验分别为接穗下胚轴参与对该部位木质部ZR+Z流量的调节提供了间接证据和直接证据。