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。     

隐花素在生长素调控拟南芥下胚轴伸长中的作用分析

以拟南芥野生型(Col-4)和隐花素双突变体cry1cry2为材料,研究不同光照条件下不同浓度吲哚乙酸(IAA)和IAA极性运输抑制剂氨基酞氨酸(NPA)对幼苗下胚轴伸长的影响。结果显示,低浓度IAA(10-7mol/L)可促进连续白光和红光下cry1cry2幼苗下胚轴伸长,而连续蓝光下cry1cry2下胚轴的伸长则受到抑制。蓝光下相同浓度的NPA对cry1cry2幼苗下胚轴伸长的抑制程度比野生型要小。RT-PCR分析结果显示,瞬时蓝光处理时IAA合成关键酶基因IGPS以及生长素应答基因IAA1和IAA5在cry1cry2突变体中的转录水平比野生型中要高。这表明隐花素可能部分通过调节IAA合成和/或IAA极性运输,介导蓝光调控拟南芥下胚轴的伸长。     

高等植物下胚轴伸长的调控机制

自然条件下,植物种子在地下萌发后需要穿透土层,才能吸收阳光开始光合作用并逐步进入自养阶段。双子叶植物种子萌发后主要借助下胚轴伸长来实现出苗,单子叶植物则依靠胚芽鞘的生长来破土。下胚轴的伸长速度及长度关系到植物能否破土出苗以及苗势,因此,下胚轴的伸长生长是植物生长发育的第一个关键阶段。本文综述了高等植物下胚轴的伸长过程、伸长的细胞学机制以及植物激素、环境信号和营养代谢状况调控下胚轴伸长的分子机制及其最新研究进展。     

拟南芥复制因子C亚基1在胚胎发生中起重要作用

复制因子C包含1个大亚基和4个小亚基,在DNA复制、损伤修复和细胞增殖中起重要作用,拟南芥复制因子C亚基1(AtRFC1)是人类复制因子C大亚基p140的同源蛋白。在对3个复制因子C亚基1的T-DNA插入突变株系rfc1-1、rfc1-2和rfc1-3的检验中,证实插入位点分别位于第16、19号外显子和启动子区域。T-DNA在外显子中的插入突变引起胚胎发育异常并导致胚胎和种子败育。将野生型拟南芥复制因子C亚基1基因转化到突变株系rfc1-1和rfc1-2后恢复了突变株的野生型表型,证明胚胎发生异常表型是由拟南芥复制因子C亚基1基因突变所引起的,AtRFC1在拟南芥胚胎发生中起重要作用。     

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ABI5基因对BR胁迫响应及其对下胚轴生长的调节作用

植物脱落酸不敏感蛋白5(abscisic acid-insensitive 5,ABI5)是种子中大量表达的碱性亮氨酸拉链类型(basic leucine zipper,bZIP)转录因子,在调节种子萌发和幼苗早期生长的脱落酸(abscisic acid,ABA)信号中起着核心作用.油菜素内酯(brassinoster...     

赤霉素和脱落酸对黑稻黄化幼苗中胚轴伸长生长的作用研究

研究了不同浓度的GA和ABA对三种黑稻黄化幼苗中胚轴伸长生长的影响。结果表明 :1.2 5 μmol/L的GA和ABA对三种黑稻黄化幼苗中胚轴的伸长生长有显著的促进作用 ,GA效应高于ABA ;三个供试稻种中 ,黑帅对GA和ABA的反应最为显著 ,且GA和ABA对其有叠加效应     

拟南芥下胚轴原生质体的膜片钳全细胞记录（简报）

建立了拟南芥下胚轴原生质体的膜片钳全细胞记录方法,观测到的全细胞电流主要是外向K＋电流,其对胞外K＋浓度具有一定的依赖性,并为K＋通道阻断剂Ba2 显著抑制,外源ATP和Ca2 分别对拟南芥下胚轴原生质体的全细胞外向K 电流有显著影响,表明拟南芥下胚轴细胞质膜外向K＋通道,可能通过蛋白磷酸化或Ca2 信使调控的机制,参与细胞信号转导。     

胞壁钙在红光抑制绿豆下胚轴伸长中的作用

研究了胞壁钙在红光抑制黄化绿豆（ＰｈａｓｅｏｌｕｓｒａｄｉａｔｕｓＬ．）下胚轴切段伸长生长中的作用。培养在有Ｃａ２＋介质中的切段胞壁钙含量比无Ｃａ２＋介质中的高３倍多,但不论介质中有无外源Ｃａ２＋,红光对下胚轴伸长的抑制程度都为２０％～２５％。乙醇双乙胺醚Ｎ,Ｎ,Ｎ′,Ｎ′四乙酸（ＥＧＴＡ）减少胞壁钙含量,相应地抵消红光对伸长的抑制;ｖｅｒａｐａｍｉｌ、Ｌａ３＋处理的切段胞壁钙含量与黑暗对照接近,但削弱红光的抑制作用;Ａ２３１８７减少胞壁钙,相应地抵消红光作用,甚至促进伸长生长。此外,氯丙嗪不影响胞壁钙含量,却阻止红光抑制伸长。表明红光无需外源Ｃａ２＋也能抑制切段伸长生长,但并非完全不需要Ｃａ２＋,可能胞壁自身的Ｃａ２＋基本能满足伸长生长所需。胞壁Ｃａ２＋的作用很复杂,它既可作为钙库起内流Ｃａ２＋信号的作用,也可在壁区起生长调节作用。     

蔗糖诱导拟南芥幼苗胚轴维管束细胞数量增多

为揭示蔗糖能否引起植物胚轴维管束细胞数量增多,将拟南芥播种于添加88mmol·L-1蔗糖和不添加糖的MS培养基上,对生长在不同培养基上的幼苗胚轴横切,显微镜下统计切片上维管束细胞数量。结果显示,与不加糖相比,加糖条件下萌发4d后幼苗维管束细胞总数增加约70％,维管薄壁细胞和导管分子都增加100％以上,筛管分子增加约90％,中柱鞘细胞数量不变。显然,蔗糖不仅使维管束薄壁细胞数量增多,也使筛管分子和导管分子数量增多。因此认为,添加蔗糖对拟南芥幼苗胚轴维管束具有双重效应,既引起维管薄壁细胞增殖,又促进维管薄壁细胞分化,从而使导管分子和筛管分子数量增多。     

Strigolactone-Regulated Hypocotyl Elongation Is Dependent on Cryptochrome and Phytochrome Signaling Pathways in Arabidopsis

Seedling development including hypocotyl elongation is a critical phase in the plant life cycle. Light regula- tion of hypocotyl elongation is primarily mediated through the blue light photoreceptor cryptochrome and red/far-red light photoreceptor phytochrome signaling pathways, comprising regulators including COP1, HY5, and phytochrome- interacting factors （PIFs）. The novel phytohormones, strigolactones, also participate in regulating hypocotyl growth. However, how strigolactone coordinates with light and photoreceptors in the regulation of hypocotyl elongation is largely unclear. Here, we demonstrate that strigolactone inhibition of hypocotyl elongation is dependent on cryp- tochrome and phytochrome signaling pathways. The photoreceptor mutants cry1 cry2, phyA, and phyB are hyposensi- tive to strigolactone analog GR24 under the respective monochromatic light conditions, while cop1 and pifl pif3 pif4 pif5 （pifq） quadruple mutants are hypersensitive to GR24 in darkness. Genetic studies indicate that the enhanced respon- siveness of cop1 to GR24 is dependent on HY5 and MAX2, while that of pifq is independent of HY5. Further studies demonstrate that GR24 constitutively up-regulates HY5 expression in the dark and light, whereas GR24-promoted HY5 protein accumulation is light- and cryptochrome and phytochrome photoreceptor-dependent. These results suggest that the light dependency of strigolactone regulation of hypocotyl elongation is likely mediated through MAX2-dependent promotion of HY5 expression, light-dependent accumulation of HY5, and PIF-regulated components.     

Distinct modes of adventitious rooting in Arabidopsis thaliana

The literature describes different rooting protocols for Arabidopsis thaliana as models to study adventitious rooting, and results are generally perceived as comparable. However, there is a lack of investigations focusing on the distinct features, advantages and limitations of each method in the study of adventitious rooting with both wild-type (WT) ecotypes and their respective mutants. This investigation was undertaken to evaluate the adventitious rooting process in three different experimental systems, all using A. thaliana, analysing the same rooting parameters after transient exposure to auxin (indole-3-acetic acid) and control conditions: excised leaves, de-rooted plants and etiolated seedlings. The founding tissues and sites of origin of roots differed depending on the system used, whereas all rooting patterns were of the direct type (i.e., without callus formation). None of the systems had an absolute requirement for exogenous auxin, although rooting was enhanced by this phytohormone, with the exception of de-rooted plants, which had adventitious rooting strongly inhibited by exogenous auxin. Root elongation was much favoured in isolated leaves. Auxin-overproducing mutants could not be used in the detached leaf system due to precocious senescence; in the de-rooted plant system, these mutants had a WT-like rooting response, whereas the expression of the 'rooty' phenotype was only evident in the etiolated seedling system. Adventitious rooting of etiolated WT seedlings in the presence of exogenous auxin was inhibited by exogenous flavonoids, which act as auxin transport inhibitors; surprisingly, the flavonoid-deficient mutant chs had a lower rooting response compared to WT. Although Arabidopsis is an excellent model system to study adventitious rooting, physiological and developmental responses differed significantly, underlining the importance of avoiding data generalisation on rooting responses derived from different experimental systems with this species.