单侧光与植物向光性的关系

着重讨论了生长素促进植物茎生长与单侧光照的关系,从单侧光与生长素的合成的关系,单侧光对胚芽鞘尖端的影响,以及单侧光对生长素由胚芽鞘尖端向下运输的影响等3个方面进行了分析,旨在剖析生长素促进植物茎向光生长的基本原理。     

生长素结合蛋白研究进展

生长素(auxin)是植物体内普遍存在的一类植物激素,它对植物的生长发育起着多方面的调节作用,如促进细胞伸长,诱导细胞分化,促进生根和单性果实(parthenocarpic fruit)的发育等,同时生长素还抑制芽的发生及果实的衰老。生长素作用机理的研究表明,生长素可以诱导一些特殊基因的快速表达,促进RNA和蛋白质的合成。因此,生长素可能是通过调节基因的表达来发挥作用。“酸生长理论”(acid growth theory)则认为,在细胞膜上存在着生长素的受体,生长素与之结合后激活了细胞质膜上的质子泵,破除了细胞壁纤维结构间的交织点,细胞壁的可塑性增加,从而使细胞伸长。尽管对“酸生长理论”一直存在争议,但植物体内存在生长素受体的证据在不断积累。70年代末,关于生长素受体的研究工作虽已全     

问：为什么高浓度的生长素会抑制植物的生长？

问：为什么高浓度的生长素会抑制植物的生长？答：生长素的主要作用是促进植物细胞纵向伸长生长。生长素对植物生长的促进作用与其浓度大小有一定的关系,在一般情况下,只有在较低浓度范围内’。能促进生长,如果浓度过高,则会起抑制生长的作用。这是因为生长素可以．促...     

对燕麦胚芽鞘"向光性"解释的一点看法

中学课本中 ,通过燕麦胚芽鞘的向光性实验说明 :“胚芽鞘的尖端能产生生长素 ,并从尖端运输到下部 ,能促使下部生长”。而对生长素为什么能使植物显示出向光性是这样解释的 :“这与单侧光引起的生长素分布不均匀有关。光线能改变生长素的分布 :向光的一侧生长素分布得少 ,背光的一侧生长素分布得多。因此 ,向光的一侧 ,细胞生长得慢 ,背光的一侧 ,细胞生长得快。结果 ,茎朝向生长慢的一侧弯曲 ,也就是朝向光源的一侧弯曲 ,使植物的茎表现出向光性。”受单侧光的照射发生生长素分布不均的部位究竟是胚芽鞘尖端、胚芽鞘下部、还是整个部分 ,在…     

关于生长素“促进”和“抑制”细胞生长的误区

生长素生理作用的两重性一直是一个非常重要的考点,在近几年的高考题中多次出现,多以胚芽鞘或茎段的弯曲为背景。生长素生理作用的两重性指:一般情况下,生长素在浓度较低时促进生长;在浓度过高时则会抑制生长,甚至杀死植物。到底生长素抑制生长指的是什么?是不长,还是越来越短?许多老师和学生对这一点的认识都存在疑惑,我觉得促进和抑制生长都是相对而言的,是和正常生长情况相比。     

每期5题

一、非选择题1.有一实验现象:将生理状况相同的胚芽鞘分成甲、乙两组,甲组给单侧光照,乙组不给光照。同样培养一段时间后,甲组向光弯曲生长,乙则直立向上生长。请简答下列问题:　　(1)本实验结果能证明胚芽鞘具有的生理特性。(2)实验中胚芽鞘的生长方式与植物生长素的调节作用有关。甲组受到单侧光照后,胚芽鞘上部生长素分布的特点是,由于生长素的生理作用而使其向光弯曲生长;此时乙组未受到光照,生长素在胚芽鞘中可能分布,因而导致其直立向上生长。(3)作为对照,若要使乙组同时也受到光照,你会如何设计乙组实验装置?请将你的设计图示于下,并…     

棉纤维细胞伸长生长与过氧化物酶和IAA氧化酶的关系

棉纤维细胞于开花当天从棉胚珠表皮上发生,随即开始伸长生长,星S型生长曲线。棉纤维细胞的可溶性蛋白、过氧化物酶活性和IAA氧化酶活性同伸长生长的关系不大;而离子型结合的细胞壁蛋白质含量、过氧化物酶活性和IAA氧化酶活性同棉纤维细胞的伸长生长关系较大,表现在棉纤维细胞快速伸长期活性较低,而在伸长生长停止时出现活性高峰,同棉纤维细胞的伸长生长有负相关现象。     

问题解答

问:在中学《植物学》课本中提到“茎背光的一面得到的生长素较多,因而这一面的细胞伸长得快”;在讲到顶芽和侧芽的关系时又提到“顶芽产生的生长素向下运输,使侧芽含生长素较多,因而就抑制了侧芽的生长”,这两段话应该怎样理解?答:这是因为:不同浓度的生长素(IAA)可使不同的器官有不同的反应。研究指出:10~(-10) M 生长素促进根的生长,对芽和茎的伸长仅有很少的反应;10~(-8) M 时抑制根的生长,却     

吲哚乙酸对向日葵下胚轴生长区单向K~+(~(86)Rb~+)通量的影响

植物生长素在刺激某些植物组织生长的同时促进K~+吸收和H~+分泌(Hager等1971,Cleland1975,赖寿鹏和倪晋山1983),可能是由于生长素刺激位于植物细胞质膜上的H~+泵ATP酶(Scherer 1984,赖寿鹏和倪晋山1985)。但以往的文献中只测定了生长素促进的植物组织对K~+的净吸收速率,即组织中K~+的累积速率或吸收溶液中K~+的减少速率。自从MacRobbie和Dainty(1958)首先运用放射性     

油菜素内酯（BR）促进植物生长机理研究进展

介绍了油菜素内酯促进植物生长、提高作物产量的作用,并简述了促进生长的生理代谢基础。通过比较油菜素内酯与生长素、赤霉素促进生长作用方式的异同,提出油菜素内酯促进生长的信号传导路径不同于其它植物激素。另外从细胞的形态发生、细胞壁扩展的机制和细胞骨架在细胞伸长中的作用等几个方面对油菜素内酯促进植物生长的细胞及分子生物学机制进行了详尽的论述。     

Action of Inhibitors of RNA and Protein Synthesis on Cell Enlargement

Further studies with inhibitors of protein synthesis are presented to support the conclusion, drawn from work with chloramphenicol, that protein synthesis is a critical limiting factor in auxin-induced cell expansion. The indoleacetic acid-induced elongation of oat coleoptile sections was strongly inhibited by dl-p-fluorophenylalanine, and the inhibition is antagonized by phenylalanine. Puromycin at 10(-4)m very strongly inhibited the indoleacetic acid-induced growth of oat coleoptile and artichoke tuber sections and exerted a less powerful effect on pea stem sections. As found earlier with chloramphenicol, concentrations of puromycin effective in inhibiting the growth of coleoptile sections had quantitatively similar effects on protein synthesis, as measured by the incorporation of C(14)-leucine into protein of the coleoptile tissue. Several analogues of RNA bases were also tested, but while 8-azaguanine very strongly inhibited growth of artichoke tuber disks, 6-azauracil was the only one of this group clearly inhibitory to growth in coleoptile or pea stem sections. Actinomycin D actively inhibited both elongation and the incorporation of C(14)-leucine into protein in oat coleoptile sections. Inhibition of the 2 processes went closely parallel. Actinomycin D also powerfully inhibited growth of artichoke tuber disks. All the compounds effective in inhibiting growth generally inhibited the uptake of leucine as well.The possibility that auxin causes cell enlargement in plants by inducing the synthesis of a messenger RNA and of one or more new but unstable enzymes, is discussed. Possible but less favored alternative explanations are: A) that auxin induces synthesis of a wall protein, or B) that the continued synthesis of some other unstable protein (by a process independent of auxin) may be a prerequisite for cell enlargement.     

Timing of the Auxin Response in Coleoptiles and Its Implications Regarding Auxin Action

The timing of the auxin response was followed in oat and corn coleoptile tissue by a sensitive optical method in which the elongation of about a dozen coleoptile segments was recorded automatically. The response possesses a latent period of about 10 min at 23°C, which is extended by low concentrations of KCN or by reducing the temperature, but is not extended by pretreatments with actinomycin D, puromycin, or cycloheximide at concentrations that partially inhibit the elongation response. Analysis of the data indicates that auxin probably does not act on the elongation of these tissues by promoting the synthesis of informational RNA or of enzymatic protein. Not excluded is the possibility that auxin acts at the translational level to induce synthesis of a structural protein, such as cell wall protein or membrane protein. While the data do not provide direct support for this hypothesis, the speed with which cycloheximide inhibits elongation suggests that continual protein synthesis may be important in the mechanism of cell wall expansion.     

Changes in the Activities and Polypeptide Levels of Exo- and Endoglucanases in Cell Walls during Developmental Growth of Zea mays Coleoptiles

Exo- and endoglucanases present in cereal coleoptile cell wallsare capable of mediating hydrolysis of non-cellulosic rß-(l,3)(l,4)-glucanin situ. To assess the relationship with cell elongation, glucanaseactivities and the respective polypeptide abundance were determinedas a function of Zea mays coleoptile development. Both exo-and endoglucanase activities were quite low initially, but increasedto achieve maximum levels by days 5 or 6. Western blots revealedthat the density of the protein bands increased with coleoptiledevelopment generally in correspondence to activity levels.However, in bioassays with 3 d old coleoptile segments we foundthat auxin stimulation of glucanase activities did not resultfrom increased glucanase polypeptide levels. Hence, there wasno evidence for de novo protein synthesis in excised coleoptilesin response to added auxin. While glucanase antibodies stronglyinhibited IAA-induced elongation of coleoptile segments on days2–4, these same antibodies had little effect on day 1.We conclude that glucanases contribute to auxin mediated coleoptilegrowth only during a limited developmental interval. We proposethat when elongation is dominate, the physical properties ofthe cell wall adjust in response to metabolism of cell wallrß-(l,3)(l,4)-glucans but the enhancement of suchactivity is governed by factors other than glucanase proteinlevels. (Received December 24, 1997; Accepted April 30, 1998)     

Rapid-growth responses of corn root segments: Effect of auxin on elongation

The effect of indole-3-acetic acid (IAA) on the elongation rates of 2 mm corn (Zea mays L.) root segments induced by citrate-phosphate buffer (or unbuffered) solutions of pH 4.0 and 7.0 was studied. At pH 7.0, auxin initially reduced the elongation rate in both buffered and unbuffered solutions. Only in buffer at pH 7.0 was auxin at a concentration of 0.1 M found to promote the elongation rate though briefly. THis promoted rate represented only ca. 20% of the rate achieved with only buffer at pH 4.0. Auxin in pH 4.0 buffered and unbuffered solutions only served to reduce the elongation rates of root segments. Some comparative experiments were done using 2 mm corn coleoptile segments. Auxin (pH 6.8) promoted the elongation rate of coleoptile segments to a level equal or greater than the maximal H ion-induced rate. The two responses of root segments to auxin are compared to auxin action in coleoptile growth.     

Inside or outside? Localization of the receptor relevant to auxin-induced growth

The localization of the auxin receptor relevant to the control of elongation growth is still a matter of controversy. Auxin-induced elongation of maize coleoptile segments was measured by means of a high resolution auxanometer. When indole-3-acetic acid (IAA) was removed from the bathing solution, a rapid cessation of auxin-induced elongation was detected. This decline was delayed when the auxin efflux carrier was blocked by the phytotropins naphthylphthalamic acid (NPA) and pyrenoylbenzoic acid (PBA) or by triiodobenzoic acid (TIBA). The IAA concentration in NPA-pretreated segments was 2–3 times higher than in NPA-free controls 35 min after the removal of IAA in the bathing medium.
A similar rapid drop of growth after removal of auxin was observed for the rapidly-transported synthetic auxin, naphthaleneacetic acid (NAA). When the auxin efflux was blocked, growth induced by NAA was sustained much longer than IAA-stimulated elongation.
In comparison with NAA, the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) is known to be excreted very slowly by the efflux carrier. 2,4-D-induced growth remained at a stimulated level when the auxin was washed off, even in the absence of any auxin efflux inhibitor. We conclude from these results that the presence of intracellular auxin is a necessary and sufficient condition for sustained auxin-induced elongation growth, at least for the phases during the 2 h after its application. Consequently, we postulate the existence of an intracellular auxin receptor relevant to the control of growth.     

Conversion of isatin to isatate as related to growth promotion in Avena coleoptile and pisum stem sections

Isatin, (indole 2,3-dione), which promotes elongation of Pisum stem sections at concentrations exceeding 0.1 mm, promotes elongation of Avena coleoptile sections only at higher concentrations, exceeding 1 mm. Aged isatin solutions are more active than fresh solutions, due to the slow, spontaneous conversion to isatate (o-aminophenylglyoxylate). A concentration of 0.1 mm aged isatin is as active in Avena coleoptile sections as in peas. Isatate has been independently synthesized and its auxin activity in both Avena coleoptile and Pisum stem sections confirmed. The synthetic isatate is more effective than isatin in both systems. This suggests that the auxin activity of isatin is due to its conversion to isatate.     

Polar auxin transport and auxin-induced elongation in the absence of cytoplasmic streaming

Summary When cytoplasmie streaming in oat and maize coleoptile cells is completely inhibited by cytochalasin B (CB), polar transport of auxin (indole-3-acetic acid) continues at a slightly reduced rate. Therefore, cytoplasmic streaming is not required for polar transport. Auxin induces elongation in CB-inhibited coleoptile and pea stem segments, but elongation rate is reduced about 40% by CB. Therefore, stimulation of cytoplasmic streaming cannot be the means by which auxin promotes cell elongation, but streaming may be beneficial to elongation growth although not essential to it. A more severe inhibition of elongation develops after several hours in CB. With coleoptiles this could be due to inhibition of sugar uptake; in pea tissue it may be due to permeability changes and cytoplasmic degeneration. CB does not disorganize or disorient microfilament bundles when it inhibits streaming in maize, but appears instead to cause hypercondensation of microfilament material.     

Effect of temperature on the dose–response curves for auxin-induced elongation growth in maize coleoptile segments

The dose–response curves for IAA-induced growth in maize coleoptile segments were studied as a function of time and temperature. In addition, the kinetics of growth rate responses at some auxin concentrations and temperatures was also compared. It was found that the dose–response curves for IAA-induced elongation growth were, independently of time and temperature, bell-shaped with an optimal concentration at 10⁻⁵ M IAA. The kinetics of IAA-induced growth rate responses depended on IAA concentration and temperature, and could be separated into two phases (biphasic reaction). The first phase (very rapid) was followed by a long lasting one (second phase), which began about 30 min after auxin addition. For coleoptile segments incubated at 30°C, the amplitudes of the first and second phase were significantly higher, when compared with 25°C, at all IAA concentrations studied. However, when coleoptile segments were incubated at 20°C, the elongation growth of coleoptile segments treated with suboptimal IAA concentrations was diminished, mainly as a result of both phases reduction. In conclusion, we propose that the shape of the dose–response curves for IAA-induced growth in maize coleoptile segments is connected with biphasic kinetic of growth rate response.     

Galactose inhibition of auxin-induced cell elongation in oat coleoptile segments

Auxin-induced cell elongation in oat coleoptile segments was inhibited by galactose; removal of galactose restored growth. Galactose did not appear to affect the following factors which modify cell elongation: auxin uptake, auxin metabolism, osmotic concentration of cell sap, uptake of tritium-labeled water, auxin-induced wall loosening as measured by a decrease in the minimum stress-relaxation time and auxininduced glucan degradation. Galactose markedly prevented incorporation of [¹⁴C]-glucose into cellulosic and non-cellulosic fractions of the cell wall. It was concluded that galactose inhibited auxin-induced long-term elongation of oat coleoptile segments by interfering with cell wall synthesis.     

CELL WALL SYNTHESIS AND CELL ELONGATION IN OAT COLEOPTILE TISSUE

Ray , Peter M. (U. Michigan, Ann Arbor.) Cell wall synthesis and cell elongation in oat coleoptile tissue. Amer. Jour. Bot. 49(9): 928–939. Illus. 1962.—Cell wall synthesis in oat coleoptile cylinders tends to run parallel with but not usually proportional to cell elongation both under promotion by auxin and sugar and under inhibition by supraoptimal auxin or sugar, or by a variety of other inhibitors. Inhibitors of elongation fall into 2 classes with respect to their effects on wall synthesis: (1) those which inhibit the 2 processes approximately equally (galactose, mannose, mannitol, azide, iodoacetate, dinitrophenol, low temperature, supraoptimal auxin) and (2) those which inhibit elongation percentagewise much more strongly than wall synthesis, so that as complete inhibition of elongation is approached, substantial wall synthesis continues (Ca^{+ +}, fluoride, arsenite, mercurials). When coleoptile cylinders elongate in the absence of sugar, the cell walls appear to become markedly thinner, and in some experiments negligible increase in total wall material apparently occurs. However, the amount of α-cellulose does rise. Increase in cell wall material occurs during elongation of cylinders at 2 C. The results are interpreted as indicating that during elongation the bulk of new cell wall material is added by apposition, but a certain proportion of the new material is probably introduced within the existing wall structure and induces its expansion.