植物微管骨架参与下胚轴伸长调节机制研究进展

微管作为细胞骨架的重要成员, 在植物生长发育过程中起重要作用。下胚轴作为研究细胞伸长的模式系统之一, 其伸长受到多种信号的调节。该文综述了微管骨架在响应环境和生长发育信号调节下胚轴伸长过程中的作用及机制, 旨在帮助读者深入理解微管骨架响应上游信号在植物下胚轴伸长中的作用机理。     

拟南芥下胚轴伸长与向光性的分子调控机理

下胚轴快速伸长和向光性是高等植物进行固着生活的重要适应性机制,是子叶钻出土层进行光形态发生和光合作用的必要前提。拟南芥下胚轴因其简单的生理形态结构和特异的生理功能而成为剖析植物细胞伸长和向性生长的理想模式系统。本文主要介绍光和植物激素调控拟南芥下胚轴伸长和向光性弯曲的生理基础、遗传学功能及其分子调控机理的最新进展。     

LaHY5基因对独行菜下胚轴低温伸长的影响

独行菜种子下胚轴伸长存在低温停滞现象,是研究温度对植物下胚轴伸长影响的良好材料。为了揭示下胚轴伸长相关转录因子HY5在独行菜下胚轴低温伸长中的作用,该研究从独行菜种子转录组中获得LaHY5序列,并进行了克隆、序列分析,通过实时定量PCR技术研究了该基因表达与低温诱导及萌发阶段的关系,并通过转化拟南芥分析该基因表达对下胚轴低温伸长的影响。结果表明:(1)LaHY5基因的cDNA序列包含447 bp的完整阅读框序列,其编码产物为富含丝氨酸的149个氨基酸组成的肽链,包含典型的BRLZ结构域,相对分子质量为16.830 kD,分子式为C_(692)H_(1156)N_(228)O_(246)S_7,理论等电点为8.73,与十字花科植物同源序列高度一致。(2)LaHY5基因在独行菜萌发过程中的种子或幼苗中受低温诱导快速上调表达。(3)转LaHY5基因拟南芥种子在常温或低温条件下,下胚轴伸长均比野生型植株快。研究表明,LaHY5转录因子在种子低温萌发及幼苗耐受低温胁迫中起重要作用,但LaHY5基因并不是造成独行菜下胚轴伸长低温停滞的限制性因素。     

红光和Ca~(2 )对与绿豆下胚轴伸长有关的细胞壁酶的影响

作为去黄化过程中的一个反应——植物茎伸长受光抑制的现象,已有不少研究。人们发现,胚轴长度受光的调节,对红光尤其敏感（lion1982）。红光抑制绿豆下胚轴切段伸长（王小菩和潘瑞炽1990）,却促进绿豆下胚轴原生质体膨大,钙在此过程中起第二信使的作用（龙程等1994a,b）,但红光促进原生质体膨大却抑制切段伸长的机理尚不清楚。我们认为问题的症结可能在细胞壁,因为植物细胞的生长（伸长和扩大）在很大程度上取决于细胞壁的松弛和伸展。植物细胞只有当细胞壁酶作用于细胞壁使之松弛时,才能在膨压的作用下吸水长大（Taiz1984）。因…     

种子萌发出苗过程中胚轴的伸长和胚根的发展

在讲种子的萌发时,对胚各部分的发展变化,曾听到过如下的解释:胚轴发育成植物的主茎,胚根发展成植物的根系.这样说是否确切呢?下面谈谈与此有关的问题. 一株植物的主茎是否完全由胚轴发育而成的问题,了解了胚轴伸长的情况,就很容易得到答案.大家知道,双子叶植物种子胚中的胚轴以子叶为界可区分为两部分:子叶以下与胚根连接的部分叫下胚轴,从子叶着生位置以上至第一真叶着生处之间的部分叫上胚轴.单子叶植物常见的禾本科种子胚的胚轴则可区分为下胚轴(子叶即盾状体着生处以下与胚根连接的部分)、中胚轴(盾状体着生处以上至胚芽鞘着     

胚轴—有胚植物的一种特殊结构

在研究有胚植物营养体时,人们常注重根、茎和叶三类器官,而较少注意胚轴。实际上,胚轴不仅在胚、幼苗和成株中均有独特作用,而且在其生长习性和结构上也较特殊。在胚中,圆轴状的胚轴连接着胚根、胚芽、子叶和禾本科植物的胚芽鞘,并因此而可以分为上胚轴（子叶节或胚芽鞘节至胚芽的一段）,下胚轴（子叶节或禾本科的盾片节至胚根的一段）和中胚轴（禾本科植物盾片节至胚芽鞘节的一段）。在绝大多数植物的成株中,主茎的第一个节间是由上胚轴发育形成的,极少数植物甚至终生以胚轴为其主体。如世界著名的奇异植物百岁兰,除下胚轴伸长将…     

拟南芥QUA1基因在光信号途径中的表达与功能分析

光信号在植物生长发育过程中具有非常重要的作用。不同的光信号通过调节植物下游基因的表达,进而影响细胞分化、结构和功能的改变,以及组织和器官的形成,参与植物光形态建成。QUA1 (QUASIMODO1)是拟南芥糖基转移酶家族中的一个成员,参与植物细胞壁中果胶的合成。本文以拟南芥qua1-1/cry1以及qua1-1/phyB双突变体为材料,对QUA1基因在光信号途径中的功能进行了分析。结果显示,qua1-1突变体在暗、蓝光、红光以及远红外光培养条件下下胚轴的伸长均受到抑制,QUA1基因的表达同样受到光信号的调节,而且突变体中多种光信号调节基因的表达也受到了影响。通过对qua1-1突变体下胚轴的观察发现,突变体下胚轴表皮细胞长度明显变短。与cry1以及phyB突变体相比,qua1-1/cry1和qua1-1/phyB双突变体下胚轴长度明显变短,而且双突变体中光信号调节基因的表达也有明显变化,表明QUA1可能参与了CRY1以及PHYB介导的蓝光及红光信号传导。以上结果表明QUA1影响了下胚轴细胞的伸长以及光信号调节基因的表达,并参与调控多种光信号传导途径。     

IAA和Ca^2＋对绿豆下胚轴切段伸长的影响及其相互关系

0.01 mmol/L IAA可以明显促进绿豆下胚轴切段的伸长,≤0.1 mmol/L CaCl_2也可促进其伸长,但当浓度为0.5 mmol/L时则有抑制作用。低浓度CaCl_2尚能加强IAA对绿豆下胚轴切段伸长的促进作用。Ca~(2+)专一性螯合剂EGTA、Ca~(2+)竞争性抑制剂LaCl_3及CaM拮抗剂CPZ均能抑制IAA促进绿豆下胚轴切段伸长的作用。增加培养介质中CaCl_2浓度可以逆转LaCl_3的抑制效应。     

UVB诱导的绿豆下胚轴原生质体收缩效应

ＵＶ－Ｂ处理外起绿豆幼苗下胚轴原生质体的收缩;绿豆幼苗的下胚轴的伸长亦受ＵＶ－Ｂ处理的显著抑制。统计分析证实两者呈显著正相关（ｒ＾２＝０．８０６６）。这一结果表明,ＵＶ－Ｂ对绿豆下胚轴生长的抑制作用与不胚轴细胞伸长受到抑制相关。     

镉(Cd)与UV-B复合胁迫影响大豆胚轴生长的生理调节机制研究

通过研究大豆胚轴生长及内源吲哚乙酸(IAA)、赤霉素(GAs)、过氧化物酶(POD)和吲哚乙酸氧化酶(IAA oxidase)活性变化对Cd、UV-B辐射和Cd UV-B(复合胁迫)的响应。分析了激素水平、酶活性变化以及胚轴生长变化特性。结果表明,UV—B辐射引起大豆上胚轴伸长减小;但Cd对上胚轴伸长无明显影响;Cd UV—B使上胚轴长度比UV—B作用时明显增加。UVB辐射显著降低了胚轴IAA含量;而GAs含量却显著升高;Cd胁迫下IAA和GAs变化并不明显;但Cd UV—B使IAA含量显著升高,而对GAs无明显影响。UVB辐射使IAA氧化酶和POD活性显著增强,而Cd对这两种酶活性影响并不明显;但Cd UV—B复合胁迫下胚轴的IAA水平较高。尽管UVB辐射引起胚轴中GAs含量显著增加,但研究结果显示IAA含量变化是胁迫下引起胚轴生长改变的更直接原因。研究还表明Cd UV—B时,大大削弱了UV—B辐射下IAA氧化酶活性增强,加之Cd对POD活性的抑制,导致复合胁迫下胚轴的IAA水平较高。证明复合胁迫可以改变单一胁迫下植物激素的调控机制。     

ZEITLUPE positively regulates hypocotyl elongation at warm temperature under light in Arabidopsis thaliana

Hypocotyl cell elongation has been studied as a model to understand how cellular expansion contributes to plant organ growth. Hypocotyl elongation is affected by multiple environmental factors, including light quantity and light quality. Red light inhibits hypocotyl growth via the phytochrome signaling pathways. Proteins of the FLAVIN-BINDING KELCH REPEAT F-BOX 1 / LOV KELCH PROTEIN 2 / ZEITLUPE family are positive regulators of hypocotyl elongation under red light in Arabidopsis. These proteins were suggested to reduce phytochrome-mediated inhibition of hypocotyl elongation. Here, we show that ZEITLUPE also functions as a positive regulator in warmth-induced hypocotyl elongation under light in Arabidopsis.     

MDP25, a novel calcium regulatory protein, mediates hypocotyl cell elongation by destabilizing cortical microtubules in Arabidopsis

The regulation of hypocotyl elongation is important for plant growth. Microtubules play a crucial role during hypocotyl cell elongation. However, the molecular mechanism underlying this process is not well understood. In this study, we describe a novel Arabidopsis thaliana microtubule-destabilizing protein 25 (MDP25) as a negative regulator of hypocotyl cell elongation. We found that MDP25 directly bound to and destabilized microtubules to enhance microtubule depolymerization in vitro. The seedlings of mdp25 mutant Arabidopsis lines had longer etiolated hypocotyls. In addition, MDP25 overexpression resulted in significant overall shortening of hypocotyl cells, which exhibited destabilized cortical microtubules and abnormal cortical microtubule orientation, suggesting that MDP25 plays a crucial role in the negative regulation of hypocotyl cell elongation. Although MDP25 localized to the plasma membrane under normal conditions, increased calcium levels in cells caused MDP25 to partially dissociate from the plasma membrane and move into the cytosol. Cellular MDP25 bound to and destabilized cortical microtubules, resulting in their reorientation, and subsequently inhibited hypocotyl cell elongation. Our results suggest that MDP25 exerts its function on cortical microtubules by responding to cytoplasmic calcium levels to mediate hypocotyl cell elongation.     

Growth and stomata development of Arabidopsis hypocotyls are controlled by gibberellins and modulated by ethylene and auxins

The plant hormones gibberellin (GA), ethylene and auxin can promote hypocotyl elongation of Arabidopsis seedlings grown in the light on a low nutrient medium (LNM). In this study, we used hypocotyl elongation as a system to investigate interactions between GA and ethylene or auxin and analysed their influence on the development of stomata in the hypocotyl. When applied together, GA and ethylene or auxin exerted a synergistic effect on hypocotyl elongation. Stimulated cell elongation is the main cause of hypocotyl elongation. Furthermore, hypocotyls treated with GA plus either ethylene or auxin show an increased endoreduplication. In addition, a small but significant increase in cell number was observed in the cortical cell files of hypocotyls treated with ethylene and GA together. However, studies with transgenic seedlings expressing CycB1::uidA genes revealed that cell division in the hypocotyl occurs only in the epidermis and mainly to form stomata, a process strictly regulated by hormones. Stomata formation in the hypocotyl is induced by the treatment with either GA or ethylene. The effect of GA could be strongly enhanced by the simultaneous addition of ethylene or auxin to the growth medium. Gibberellin is the main signal inducing stomata formation in the hypocotyl. In addition, this signal regulates hypocotyl elongation and is modulated by ethylene and auxin. The implication of these three hormones in relation to cell division and stomata formation is discussed.     

Two dominant photomorphogenic mutations of Arabidopsis thaliana identified as suppressor mutations of hy2

By screening suppressor mutants of the hy2 mutation of Arabidopsis thaliana , two dominant photomorphogenic mutants, shy1-1D and shy2-1D , for two genetic loci designated as SHY1 and SHY2 ( s uppressor of hy 2 mutation) have been isolated. Both of these non-allelic, extragenic suppressor mutations of hy2 are located on chromosome 1 of the Arabidopsis genome. Both mutations suppress the elongated hypocotyl phenotype of hy2 by light-independent inhibition of hypocotyl growth as well as by increasing the effectiveness of light inhibition of hypocotyl elongation. The shy1-1D mutation is partially photomorphogenic in darkness with apical hook opening and reduced hypocotyl elongation. The shy2-1D mutant displays highly photomorphogenic characteristics in darkness such as true leaf development, cotyledon expansion, and extremely reduced hypocotyl growth. In regard to hypocotyl elongation, however, the shy2-1D mutation is still light sensitive. Examination of red/far-red light responses shows that the shy1-1D mutation suppresses the hypocotyl elongation of the hy2 mutation effectively in red light but not effectively in far-red light. The shy2-1D suppresses hypocotyl elongation of the hy2 mutation effectively in both red and far-red light. Both mutations can also suppress the early-flowering phenotype of hy2 and have a distinct pleiotropic effect on leaf development such as upward leaf rolling. The data obtained suggest that SHY1 and SHY2 represent a novel class of components involved in the photomorphogenic pathways of Arabidopsis . This is the first report on the identification of dominant mutations in the light signal transduction pathway of plants.     

Gene expression profile of zeitlupe/lov kelch protein1 T-DNA insertion mutants in Arabidopsis thaliana: Downregulation of auxin-inducible genes in hypocotyls

Elongation of hypocotyl cells has been studied as a model for elucidating the contribution of cellular expansion to plant organ growth. ZEITLUPE (ZTL) or LOV KELCH PROTEIN1 (LKP1) is a positive regulator of warmth-induced hypocotyl elongation under white light in Arabidopsis, although the molecular mechanisms by which it promotes hypocotyl cell elongation remain unknown. Microarray analysis showed that 134 genes were upregulated and 204 genes including 15 auxin-inducible genes were downregulated in the seedlings of 2 ztl T-DNA insertion mutants grown under warm conditions with continuous white light. Application of a polar auxin transport inhibitor, an auxin antagonist or an auxin biosynthesis inhibitor inhibited hypocotyl elongation of control seedlings to the level observed with the ztl mutant. Our data suggest the involvement of auxin and auxin-inducible genes in ZTL-mediated hypocotyl elongation.     

The Effects of Cytokinin and Light on Hypocotyl Elongation in Arabidopsis Seedlings Are Independent and Additive

Cytokinin has been reported to mimic some of the effects of light on de-etiolation responses in dark-grown Arabidopsis seedlings. The interaction between cytokinin and light was examined by analyzing cytokinin dose and light fluence effects on hypocotyl elongation in wild-type and mutant Arabidopsis seedlings with defects in light or hormone responses. It was found that (a) cytokinin and light-response systems have independent and additive effects on the inhibition of hypocotyl elongation and (b) either cytokinin or light can saturate the morphogenic responses. As a consequence, cytokinin has no effect on hypocotyl elongation under normal growth conditions because light levels saturate the hypocotyl inhibition response. To determine whether a functional light-response pathway is required for cytokinin responses, light-insensitive long hypocotyl (hy) mutants were tested for cytokinin responses. The hy mutants (hy1 to hy6) had normal cytokinin responses, except phyB-1 (hy3-1), in which hypocotyl elongation was insensitive to cytokinin. Cytokinin insensitivity in phyB-1 was attributed to an indirect effect of the mutation on cytokinin responses. The effects of cytokinin on the inhibition of hypocotyl elongation are largely mediated by ethylene, and blocking the ethylene-response pathway through the action of a cytokinin-resistant, ethylene-insensitive mutant (ckr1/ein2) had no effect on the light inhibition of hypocotyl elongation. These results do not support the idea that cytokinin mediates the action of light on hypocotyl elongation.     

Evolution and distribution of growth in etiolated hypocotyls ofLupinus albus

The variations in length and fresh and dry mass of etiolated hypocotyls of lupin during the growth have been studied. The growth exhibited by the different zones delimited along the hypocotyl was dependent on the localization of the zone as well as on the age of seedlings, but in both cases the pattern of growth was similar. During the period of growth studied (seedlings 7 to 21 d old), the growth of hypocotyl was basically due to cell elongation, since the relative elongation of cells was positively correlated with the relative elongation of the hypocotyl.     

Gibberellins control Arabidopsis hypocotyl growth via regulation of cellular elongation

The gibberellins (GAs) are endogenous regulators of plant growth. Experiments are described here that test the hypothesis that GA regulates hypocotyl growth by altering the extent of hypocotyl cell elongation. These experiments use GA-deficient and altered GA-response mutants of Arabidopsis thaliana (L.) Heyhn. It is shown that GA regulates elongation, in both light- and dark-grown hypocotyls, by influencing the rate and final extent of cellular elongation. However, light- and dark-grown hypocotyls exhibit markedly different GA dose-response relationships. The length of dark-grown hypocotyls is relatively unaffected by exogenous GA, whilst light-grown hypocotyl length is significantly increased by exogenous GA. Further analysis suggests that GA control of hypocotyl length is close to saturation in dark-grown hypocotyls, but not in light grown hypocotyls. The results show that a large range of possible hypocotyl lengths is achieved via dose-dependent GA-regulated alterations in the degree of elongation of individual hypocotyl cells.Key words: Arabidopsis, cell elongation, gibberellin (GA), GA mutants, hypocotyl.      

Cell Elongation and Microtubule Behavior in the Arabidopsis Hypocotyl: Responses to Ethylene and Auxin

During elongation of the Arabidopsis hypocotyl, each cell reacts to light and hormones in a time- and position-dependent manner. Growth in darkness results in the maximal length a wild-type cell can reach. Elongation starts at the base and proceeds in the acropetal direction. Cells in the upper half of the hypocotyl can become the longest of the whole organ. Light strongly inhibits cell elongation all along the hypocotyl, but proportionally more in the upper half. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is known to stimulate hypocotyl elongation in the light. Here we show that this stimulation only occurs in cells of the apical half of the hypocotyl. Moreover, ACC application can partially overcome light inhibition, whereas indole-3-acetic acid (IAA) cannot. On low-nutrient medium (LNM) in the light, elongation is severely reduced as compared to growth on rich medium, and both ACC and IAA can stimulate elongation to the levels reached on a nutrient-rich medium. Furthermore, microtubule orientation was studied in vivo. During elongation in darkness, transverse and longitudinal patterns are clearly related with rates of elongation. In other conditions, except for the association of longitudinally orientated microtubules with growth arrest, microtubule orientation is merely an indicator of developmental age, not of elongation activity. A hypothesis on the relation between microtubules and elongation rate is discussed.     

PHYSIOLOGICAL RESPONSES OF LIGHT-GROWN CUCUMBER HYPOCOTYLS TO HELMINTHOSPOROL AND ITS DERIVATIVES

Helminthosporol, helminthosporic acid and dihydrohelminthosporicacid stimulated hypocotyl elongation of light-grown cucumberseedlings. The relative activities of the three compounds werein the order H₂-H-acid> H-acid> H-ol. The higher the dosage,the longer the promotion of the hypocotyl elongation lasted.The response of the hypocotyl to H-acid depended on the presenceof cotyledons. As the amount of the cotyledon attached to thehypocotyl was reduced, the response decreased. When IAA-oxidase was estimated as IAA metabolized per dry weightof the hypocotyl, there was an inverse relationship betweenIAAoxidase activity and H-ol-induced elongation of the hypocotyl.However, there was no difference between control and H-ol treatedmaterials when IAA metabolized per plant was compared. It isunlikely that the mechanism of H-ol action is closely relatedto IAA-oxidase activity of the plant. (Received April 5, 1967; )