细胞分裂素在植物抗逆和延衰中的作用

本文综述了细胞分裂素类物质的种类、分布和在植物抗水分胁迫、低温冷害、病虫害等方面的作用以及在延缓果实、叶片、切花等衰老中的效果,讨论了其生理机制、细胞分裂素与其它植物激素的相互关系,并提出了有关细胞分裂素类物质作用机理中值得深入研究的若干问题,如嘌呤型与苯基脲型细胞分裂素的作用特点,细胞分裂素与生长素、脱落酸的协调作用和拮抗作用细胞分裂素的从头合成途径和tＲＮＡ途径等。     

细胞分裂素类物质在植物组织培养中的作用机制

论述了细胞分裂素类物质及新近正被广泛应用的具有细胞分裂素活性的苯基脲衍生物在植物组织培养过程中的作用及其机理。     

果树叶片外渗液中扩散型玉米素的测定

细胞分裂素是广泛存在于植物体内,与植物生长发育过程密切相关的一大类植物激素。自发现以来,人们对它的生物合成、代谢、生理功能及作用机制等方面做了大量研究,目前已深入到利用分子生物学手段探讨其对基因表达过程的调控等方面[5]。在研究细胞分裂素对植物体中不同生理生化过程的调节与控制时,往往需要测定植物体中细胞分裂素的含量。测定的细胞分裂素包括可扩散型、可提取型和束缚型3种。有人[2,6]利用豌豆茎尖及苹果中心果收集可扩散型IAA;在光周期诱导白芥成花生理研究中,Lejeune等[7]利用离体茎尖收集可扩散型细胞分裂素。…     

对紫云英根瘤菌突变株的生长情况及产生细胞分裂素能力的考察

紫云英根瘤菌突变株96号,只有增强了原来培养基的缓冲能力并增加了氮源后,才能使其正常生长。96号突变株产生细胞分裂素的能力随着生长过程的不同而异。它产生细胞分裂素的最大量在菌体生长的稳定初期,为15.01μg/L,比出发菌株的2.18 μg/L提高了近7倍。经修改后的根瘤菌常规培养基能用于该菌株的发酵培养,并能正常产生细胞分裂素类物质。在培养液中加入腺嘌呤对菌体合成细胞分裂素类物质有强烈的诱导效应。     

棉花子房中存在细胞分裂素的专一结合蛋白

棉花子房细胞提取物1000r/min沉淀组分(P_1)和10 000r/min沉淀组分(P_(10))均能与6-BA专一结合,但不能与ABA专一结合。非标记的激动素、玉米素和6-BA等细胞分裂素类物质均可将与P_1结合的[~3H]6-BA取代下来,其它激素IAA和ABA、细胞分裂素的结构类似物cAMP和腺嘌呤均无取代作用。胰蛋白酶处理可明显降低P_1和6-BA的专一结合,说明在棉花子房中存在细胞分裂素的专一结合蛋白。二硫苏糖醇(DTT)、半胱氨酸和还原型谷胱甘肽强烈抑制P_1的专一结合,提示某种可还原基团,很可能是二硫键,定位于结合蛋白,且与其结合活性有关。在子房细胞里存在能钝化细胞分裂素结合蛋白活性的物质,其钝化能力是热不稳定的。     

细胞分裂素: 代谢、信号转导、交叉反应与农艺性状改良

在高等植物中, 细胞分裂素通过对细胞分裂与分化的调节而广泛参与了对植物生长发育的调控。在过去的10余年, 利用模式植物拟南芥的研究, 在阐明细胞分裂素的代谢、转运与信号转导等方面取得了重要的进展。同时, 关于细胞分裂素与其它信号途径之间存在的广泛交叉反应也受到了人们的注意。根据我们现有的知识, 细胞分裂素信号转导是通过磷酸基团在一个双元组分系统之间的系列传递而完成的, 该过程被称之为“磷酸接力传递”(phosphorelay)。细胞分裂素与其它信号途径的互作可能也主要是通过双元组分系统链接的。双元组分系统中目前已知的主要信号元件不仅表现出功能冗余性, 同时在调控特定的植物生长发育过程时也具有特异性。本文在对细胞分裂素的代谢与转运过程简要评述的基础上,对其信号转导以及与其它信号途径间交叉反应的研究进展进行重点讨论, 并展望细胞分裂素研究对重要农业性状改良的意义。     

细胞分裂素:代谢、信号转导、交叉反应与农艺性状改良

在高等植物中,细胞分裂素通过对细胞分裂与分化的调节而广泛参与了对植物生长发育的调控。在过去的10余年,利用模式植物拟南芥的研究,在阐明细胞分裂素的代谢、转运与信号转导等方面取得了重要的进展。同时,关于细胞分裂素与其它信号途径之间存在的广泛交叉反应也受到了人们的注意。根据我们现有的知识,细胞分裂素信号转导是通过磷酸基团在一个双元组分系统之间的系列传递而完成的,该过程被称之为“磷酸接力传递”（phosphorelay）。细胞分裂素与其它信号途径的互作可能也主要是通过双元组分系统链接的。双元组分系统中目前已知的主要信号元件不仅表现出功能冗余性,同时在调控特定的植物生长发育过程时也具有特异性。本文在对细胞分裂素的代谢与转运过程简要评述的基础上,对其信号转导以及与其它信号途径间交叉反应的研究进展进行重点讨论,并展望细胞分裂素研究对重要农业性状改良的意义。     

细胞分裂素合成基因ipt研究进展(综述)

异戊烯基转移酶是细胞分裂素生物合成第一步的催化酶,也是限速酶。其编码基因ipt已被克隆,运用生物信息学方法,在拟南芥中鉴定出与微生物同源的编码异戊烯基转移酶的基因家族,推测这些基因可能存在特殊时空表达来调控细胞分裂素的合成途径。本文着重介绍ipt在细胞分裂素合成中的作用和研究进展。     

细胞分裂素信号转导分子机制

细胞分裂素受体家族与细菌二元组分系统的感受器组氨酸激酶具有同源性,证实下游事件与传统的磷酸转运作用具有相似性.借助于AHP蛋白的瞬间转运作用,细胞分裂素信号通过定位在细胞膜的类组氨酸激酶受体传到细胞核内,AHP蛋白使B型ARR活化,随后B型ARR激活A型ARR或其它靶基因的转录,逐步形成从质膜接受部位到激活核内基因表达的细胞分裂素信号转导模式.     

用气-液相色谱仪测定细胞分裂素

我们实验室曾用生物鉴定法和高效液相色谱测定细胞分裂素类物质。前者不能辨出细胞分裂素的各成分,测得的只是总活性。后者虽能快速测定细胞分裂素的各成分,但对样品的纯化程度要求较高,都有一定局限性;气相色谱仪则对样品纯化程度要求相对较低,并能准确、快速地测定细胞分裂     

Exogenous zeatin accumulation in wheat-root cells and its role in regulation of cytokinin transport

It was shown that the cytokinin content in the xylem sap of a wheat plant treated with exogenous zeatin was about ten times lower than in the nutrient solution in 24 h. Cytokinins were accumulated in roots rather shoots of treated plants. These data demonstrate the existence of a barrier in the cytokinin pathway from the nutrient solution to plant shoots. The deposition of lignin and suberin in stele detected with Sudan @III is enlarged with an increase in the distance from the tip of the root. The augmented content of suberin and lignin coincided with reduced cytokinin immunolabeling in root cells revealed by monoclonal antibodies to cytokinin and secondary gold-labeled antibodies. The accumulation of exogenous cytokinin in root stele cells shows that Casparian bands are not the only barrier on the cytokinin pathway to plant shoots. Intensive cytokinin immunolabeling in parenchyma cells surrounding stele vessels indicates the accumulation of cytokinin by these cells and suggests that there are mechanisms that limit the hormone loading in xylem vessels during transport to the shoot. The role of cytokinin transporters in this process is discussed.     

The discovery of cytokinin receptors and biosynthesis of cytokinins: A true story

The year 2001 saw an amazing progress in cytokinin studies. Ten years ago, cytokinin receptor genes and genes encoding cytokinin biosynthetic enzymes together with the corresponding proteins were identified in plants. These studies elucidated the molecular mechanism of cytokinin effects on the expression of cytokinin responsive genes and ultimately established the endogenous synthesis of cytokinins in plant cells, justifying their membership among plant hormones. The paper describes in short the edifying and sometimes paradoxical story of these fundamental and captivating discoveries.     

Exogenous zeatin accumulation in wheat root cells shows its role in regulation of cytokinin transport

Here we have shown that 24 hours after addition of zeatin to the nutrient solution the cytokinin content in xylem sap of wheat plants appears to be about 10 times lower that in the nutrient solution. Cytokinins accumulated mostly in roots and not in shoots of treated plants. These data demonstrate the existence of some barrier on cytokinin pathway from the nutrient solution to the plant shoot. With the help of Sudan III an increase in lignin and suberin deposition in the endodermis could be detected, being stronger with the increase in the distance from the root tip. The increase in deposition of suberin and lignin coincided with the decrease in cytokinin immunolabeling in root cells revealed with the help of monoclonal cytokinin antibodies and the second gold-labelled antibodies. Simultaneously exogenous cytokinins accumulated in root stele cells showing that the Casparian band was not only barrier on cytokinin pathway to plant shoot. It is concluded that high cytokinin immunolabe ling in the stele parenchyma cells around the stele vessels demonstrated accumulation of cytokinins by these cells, which could be important in regulation of cytokinin loading to the xylem vessels during there transport to the shoot. The role of cytokinin transporters is discussed.     

Phenotypically normal transgenic T-cyt tobacco plants as a model for the investigation of plant gene expression in response to phytohormonal stress

The tumour-inducing T-DNA gene 4 (T-cyt gene) of the nopaline Ti plasmid pTiC58 was cloned and introduced into tobacco cells by leaf disc transformation using Agrobacterium plasmid vectors. Tobacco shoots exposed to elevated cytokinin levels were unable to develop roots and lacked apical dominance. Using exogenously applied phytohormone manipulations we were able to regenerate morphologically normal transgenic tobacco plants which differed in endogenous cytokinin levels from normal untransformed plants. Although T-cyt gene mRNA levels, as revealed by dot-blot hybridization data, in these rooting plants were only about half those in primary transformed shoots the total amount of cytokinins was much lower than in crown gall tissue or cytokinin-type transformed shoots as reported by others. Nevertheless the cytokinin content in T-cyt plants was about 3 times greater than in control tobacco plants.Elevated cytokinin levels have been shown to change the expression of several plant genes, including some nuclear genes encoding chloroplast proteins. Our results show that the mRNA levels of chloroplast rbcL gene increase in cytokinin-type transgenic tobacco plants as compared with untransformed plants. Data obtained suggest that T-cyt transgenic plants are a good model for studying plant gene activity in different parts of the plant under endogenous cytokinin stress.     

Degradation of cytokinins by cytokinin oxidases in plants

The degradation metabolism of cytokinins is an important process that controls the levels of cytokinin active forms and their distribution in plant tissues. It appears to be due, in large part, to the activity of a specific enzyme, cytokinin oxidase. This review attempts to collate the limited information available about this enzyme and introduce new facts, obtained in our laboratory, concerning the mechanism of degradation of cytokinins bearing unsaturated isoprene side chains. However, complete clarification of the effects of cytokinin oxidase on cytokinin regulation and its molecular and biochemical properties will be dependent upon the purification of the protein with cytokinin oxidase activity to homogeneity and progress in the development of requisite molecular probes.     

Genes involved in cytokinin signal transduction

Although cytokinin plays a central role in plant development, our knowledge about the signal transduction pathway initiated by this plant hormone is fragmentary. By randomly introducing enhancer elements into theArabidopsis genome throughAgrobacterium-mediated transformation, 5 cytokinin independent mutant calli (cki1-1, −2, −3, −4 andcki2) were obtained. These mutants exhibit typical cytokinin responses, including rapid proliferation, chloroplast differentiation, shoot induction and inhibition of root formation, in the absence of cytokinin. TheCKl1 gene encodes a product similar to the sensor histidine kinases of two-component systems, and its overexpression in plants induces typical cytokinin responses (Kakimoto 1996). Here I report that overexpression of this gene did not alter the auxin reqirement ofArabidopsis. Another mutant,many shoots, which was also identified on the same screening, produced many adventitious shoots on cotyledons, petioles and true leaves. The extended abstract of a paper presented at the 13th International Symposium in Conjugation with Award of the International Prize for Biology “Frontier of Plant Biology”     

Cytokinins: Biosynthesis metabolism and perception

Summary Cytokinins are essential hormones for plant growth and development. They are also of vital importance for in vitro manipulations of plant cells and tissues. The biological activities and chemistry of cytokinins are well defined but very little is known about their mode of action and it is only recently that cytokinin genes have been identified in plants. This review summarizes the current status of knowledge on cytokinin biosynthesis, metabolism and signal transduction, with an emphasis on genes encoding metabolic enzymes and putative receptors, and genes rapidly induced by cytokinins.     

Design and synthesis of photolabile caged cytokinin

Cytokinins are phytohormones that regulate diverse developmental processes throughout the life of a plant. trans-Zeatin, kinetin, benzyladenine and dihydrozeatin are adenine-type cytokinins that are perceived by the AHK cytokinin receptors. Endogenous cytokinin levels are critical for regulating plant development. To manipulate intracellular cytokinin levels, caged cytokinins were designed on the basis of the crystal structure of the AHK4 cytokinin receptor. The caged cytokinin was photolyzed to release the cytokinin molecule inside the cells and induce cytokinin-responsive gene expression. The uncaging of intracellular caged cytokinins demonstrated that cytokinin-induced root growth inhibition can be manipulated with photo-irradiation. This caged cytokinin system could be a powerful tool for cytokinin biology.