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Abstract : Cyclic nucleotide-gated channels have been proposed to mediate the electrical response to light in the ventral photoreceptor cells of the horseshoe crab, Limulus polyphemus . However, a cyclic nucleotide-gated channel has not been identified from Limulus . We have cloned a putative full-length cyclic nucleotide-gated channel cDNA by screening cDNA libraries constructed from Limulus brain using a probe developed from Limulus ventral eye nerves. The putative full-length cDNA was derived from two overlapping partial cDNA clones. The open reading frame encodes 905 amino acids ; the sequence shows 44% identity to that of the α subunit of the bovine rod cyclic GMP-gated channel over the region containing the transmembrane domains and the cyclic nucleotide binding domain. This Limulus channel has a novel C-terminal region of ~200 amino acids, containing three putative Src homology domain 3 binding motifs and a putative coiled-coil domain. The possibility that this cloned channel is the same as that detected previously in excised patches from the photoreceptive membrane of Limulus ventral photoreceptors is discussed in terms of its sequence and its expression in the ventral eye nerves.  相似文献   

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Calcium Channel Activity during Pollen Tube Growth and Reorientation   总被引:18,自引:4,他引:18       下载免费PDF全文
We have shown previously that the inhibition of pollen tube growth and its subsequent reorientation in Agapanthus umbellatus are preceded by an increase in cytosolic free calcium ([Ca2+]c), suggesting a role for Ca2+ in signaling these processes. In this study, a novel procedure was used to measure Ca2+ channel activity in living pollen tubes subjected to various growth reorienting treatments (electrical fields and ionophoretic microinjection). The method involves adding extracellular Mn2+ to quench the fluorescence of intracellular Indo-1 at its ca2+-insensitive wavelength (isosbestic point). The spatial and temporal kinetics of Ca2+ channel activity correlated well with measurements of [Ca2+]c dynamics obtained by fluorescence ratio imaging of Indo-1. Tip-focused gradients in Ca2+ channel activity and [Ca2+]c were observed and quantified in growing pollen tubes and in swollen pollen tubes before reoriented growth. In nongrowing pollen tubes, Ca2+ channel activity was very low and [Ca2+]c gradients were absent. Measurements of membrane potential indicated that the growth reorienting treatments induced a depolarization of the plasma membrane, suggesting that voltage-gated Ca2+ channels might be activated.  相似文献   

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Cyclic nucleotide-gated (CNG) ion channels are nonselective cation channels, essential for visual and olfactory sensory transduction. Although the channels include voltage-sensor domains (VSDs), their conductance is thought to be independent of the membrane potential, and their gating regulated by cytosolic cyclic nucleotide–binding domains. Mutations in these channels result in severe, degenerative retinal diseases, which remain untreatable. The lack of structural information on CNG channels has prevented mechanistic understanding of disease-causing mutations, precluded structure-based drug design, and hampered in silico investigation of the gating mechanism. To address this, we built a 3D model of the cone tetrameric CNG channel, based on homology to two distinct templates with known structures: the transmembrane (TM) domain of a bacterial channel, and the cyclic nucleotide-binding domain of the mouse HCN2 channel. Since the TM-domain template had low sequence-similarity to the TM domains of the CNG channels, and to reconcile conflicts between the two templates, we developed a novel, hybrid approach, combining homology modeling with evolutionary coupling constraints. Next, we used elastic network analysis of the model structure to investigate global motions of the channel and to elucidate its gating mechanism. We found the following: (i) In the main mode of motion, the TM and cytosolic domains counter-rotated around the membrane normal. We related this motion to gating, a proposition that is supported by previous experimental data, and by comparison to the known gating mechanism of the bacterial KirBac channel. (ii) The VSDs could facilitate gating (supplementing the pore gate), explaining their presence in such ‘voltage-insensitive’ channels. (iii) Our elastic network model analysis of the CNGA3 channel supports a modular model of allosteric gating, according to which protein domains are quasi-independent: they can move independently, but are coupled to each other allosterically.  相似文献   

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ABSTRACT Calcium, as a ubiquitous second messenger, plays essential roles in tip-growing cells, such as animal neu-rons, plant pollen tubes, and root hairs. However, little is known concerning the regulatory mechanisms that code anddecode Ca2+ signals in plants. The evidence presented here indicates that a calcium-dependent protein kinase, CPK32,controls polar growth of pollen tubes. Overexpression of CPK32 disrupted the polar growth along with excessive Ca2+accumulation in the tip. A search of downstream effector molecules for CPK32 led to identification of a cyclic nucleotide-gated channel, CNGC18, as an interacting partner for CPK32. Co-expression of CPK32 and CNGC18 resulted in activationof CNGC18 in Xenopus oocytes where expression of CNGC18 alone did not exhibit significant calcium channel activity.Overexpression of CNGC18 produced a growth arrest phenotype coupled with accumulation of calcium in the tip, simi-lar to that induced by CPK32 overexpression. Co-expression of CPK32 and CNGC18 had a synergistic effect leading tomore severe depolarization of pollen tube growth. These results provide a potential feed-forward mechanism in whichcalcium-activated CPK32 activates CNGC18, further promoting calcium entry during the elevation phase of Ca2+ oscilla-tions in the polar growth of pollen tubes.  相似文献   

7.
The effects of nitric oxide (NO) and other cysteine modifying agents were examined on cyclic nucleotide-gated (CNG) cation channels from rat olfactory receptor neurons. The NO compounds, S-nitroso-cysteine (SNC) and 3-morpholino-sydnonomine (SIN-1), did not activate the channels when applied for up to 10 min. The cysteine alkylating agent, N-ethylmaleimide (NEM), and the oxidising agent, dithionitrobensoate (DTNB), were also without agonist efficacy. Neither SNC nor DTNB altered the cAMP sensitivity of the channels. However, 2-min applications of SIN-1, SNC and DTNB inhibited the cAMP-gated current to approximately 50% of the control current level. This inhibition showed no spontaneous reversal for 5 min but was completely reversed by a 2-min exposure to DTT. The presence of cAMP protected the channels against NO-induced inhibition. These results indicate that inhibition is caused by S-nitrosylation of neighboring sulfhydryl groups leading to sulfhydryl bond formation. This reaction is favored in the closed channel state. Since recombinantly expressed rat olfactory α and β CNG channel homomers and α/β heteromers are activated and not inhibited by cysteine modification, the results of this study imply the existence of a novel subunit or tightly bound factor which dominates the effect of cysteine modification in the native channels. As CNG channels provide a pathway for calcum influx, the results may also have important implications for the physiological role of NO in mammalian olfactory receptor neurons. Received: 30 March 1998/Revised: 17 June 1998  相似文献   

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钙调素对花粉萌发和花粉管生长的效应   总被引:1,自引:0,他引:1  
牛脑和玉米胚CaM能显著促进花粉萌发和花粉管生长(图1),而CaM抑制剂TFP、CPZ及另外两个专一性更强的抑制剂Compound48/80和W7均严重抑制甚至阻止花粉的萌发(图2,3)。用对CaM亲和性较低的W7同系物W5,在与W7同样浓度下,对花粉萌发和花粉管生长无明显影响。此外,W7对花粉萌发和花粉管生长的抑制效应可被外源CaM所消除(图4)。在花粉萌发过程中,其内源CaM含量显著上升,在花粉萌发率接近最大值时,花粉CaM含量达最高水平(图5)。上述结果表明CaM对花粉萌发和花粉管生长的调控起重要作用。  相似文献   

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In lily (Lilium formosanum) pollen tubes, pectin, a major component of the cell wall, is delivered through regulated exocytosis. The targeted transport and secretion of the pectin-containing vesicles may be controlled by the cortical actin fringe at the pollen tube apex. Here, we address the role of the actin fringe using three different inhibitors of growth: brefeldin A, latrunculin B, and potassium cyanide. Brefeldin A blocks membrane trafficking and inhibits exocytosis in pollen tubes; it also leads to the degradation of the actin fringe and the formation of an aggregate of filamentous actin at the base of the clear zone. Latrunculin B, which depolymerizes filamentous actin, markedly slows growth but allows focused pectin deposition to continue. Of note, the locus of deposition shifts frequently and correlates with changes in the direction of growth. Finally, potassium cyanide, an electron transport chain inhibitor, briefly stops growth while causing the actin fringe to completely disappear. Pectin deposition continues but lacks focus, instead being delivered in a wide arc across the pollen tube tip. These data support a model in which the actin fringe contributes to the focused secretion of pectin to the apical cell wall and, thus, to the polarized growth of the pollen tube.Pollen tubes provide an excellent model for studying the molecular and physiological processes that lead to polarized cell growth. Because all plant cell growth results from the regulated yielding of the cell wall in response to uniform turgor pressure (Winship et al., 2010; Rojas et al., 2011), the cell wall of the pollen tube must yield only at a particular spot: the cell apex, or tip. To accomplish the extraordinary growth rates seen in many species, and to balance the thinning of the apical wall due to rapid expansion, the pollen tube delivers prodigious amounts of wall material, largely methoxylated pectins, to the tip in a coordinated manner. Recent studies suggest that the targeted exocytosis increases the extensibility of the cell wall matrix at the tip, which then yields to the existing turgor pressure, permitting the tip to extend or grow (McKenna et al., 2009; Hepler et al., 2013). There are many factors that influence exocytosis in growing pollen tubes; in this study, we investigate the role of the apical actin fringe.For many years, it has been known that an actin structure exists near the pollen tube tip, yet its exact form has been a matter of some contention (Kost et al., 1998; Lovy-Wheeler et al., 2005; Wilsen et al., 2006; Cheung et al., 2008; Vidali et al., 2009; Qu et al., 2013). The apical actin structure has been variously described as a fringe, a basket, a collar, or a mesh. Using rapid freeze fixation of lily (Lilium formosanum) pollen tubes followed by staining with anti-actin antibodies, the structure appears as a dense fringe of longitudinally oriented microfilaments, beginning 1 to 5 µm behind the apex and extending 5 to 10 µm basally. The actin filaments are positioned in the cortical cytoplasm close to the plasma membrane (Lovy-Wheeler et al., 2005). More recently, we used Lifeact-mEGFP, a probe that consistently labels this palisade of longitudinally oriented microfilaments in living cells (Vidali et al., 2009; Fig. 1A, left column). For the purposes of this study, we will refer to this apical organization of actin as a fringe.Open in a separate windowFigure 1.The actin fringe and the thickened pollen tube tip wall are stable, although dynamic, structures during pollen tube growth. A, The left column shows a pollen tube transformed with Lifeact-mEGFP imaged with a spinning-disc confocal microscope. Maximal projections from every 15 s are shown. The right column shows epifluorescence images of a pollen tube stained with PI. Again, images captured every 15 s are shown. Bars = 10 μm. B, The data from the pollen tube in A expressing Lifeact-mEGFP were subjected to kymograph analysis using an 11-pixel strip along the image’s midline. C, The first three frames from the pollen tube in A and B were assigned the colors red, blue, and green, respectively, and then overlaid. Areas with white show the overlap of all three. The fringe is stable, but most of its constituent actin is not shared between frames.Many lines of evidence demonstrate that actin is required for pollen tube growth. Latrunculin B (LatB), which blocks actin polymerization, inhibits pollen tube growth and disrupts the cortical fringe at concentrations as low as 2 nm. Higher concentrations are needed to block pollen grain germination and cytoplasmic streaming (Gibbon et al., 1999; Vidali et al., 2001). Actin-binding proteins, including actin depolymerizing factor-cofilin, formin, profilin, and villin, and signaling proteins, such as Rho-of-Plants (ROP) GTPases and their effectors (ROP interacting crib-containing proteins [RICs]), also have been shown to play critical roles in growth and actin dynamics (Fu et al., 2001; Vidali et al., 2001; Allwood et al., 2002; Chen et al., 2002; Cheung and Wu, 2004; McKenna et al., 2004; Gu et al., 2005; Ye et al., 2009; Cheung et al., 2010; Staiger et al., 2010; Zhang et al., 2010a; Qu et al., 2013; van Gisbergen and Bezanilla, 2013).Our understanding of the process of exocytosis and pollen tube elongation has been influenced by ultrastructural images of pollen tube tips, which reveal an apical zone dense with vesicles (Cresti et al., 1987; Heslop-Harrison, 1987; Lancelle et al., 1987; Steer and Steer, 1989; Lancelle and Hepler, 1992; Derksen et al., 1995). It has long been assumed that these represent exocytotic vesicles destined to deliver new cell wall material. This model of polarized secretion has been challenged in recent years in studies using FM dyes. Two groups have suggested that exocytosis occurs in a circumpolar annular zone (Bove et al., 2008; Zonia and Munnik, 2008). However, other studies, using fluorescent beads attached to the cell surface, indicate that the maximal rate of expansion, and of necessity the greatest deposition of cell wall material, occurs at the apex along the polar axis of the tube (Dumais et al., 2006; Rojas et al., 2011). Similarly, our experiments with propidium iodide (PI; McKenna et al., 2009; Rounds et al., 2011a) and pectin methyl esterase fused to GFP (McKenna et al., 2009) show that the wall is thickest at the very tip and suggest that wall materials are deposited at the polar axis, consistent with the initial model of exocytosis (Lancelle and Hepler, 1992). Experiments using tobacco (Nicotiana tabacum) pollen and a receptor-like kinase fused to GFP also indicate that exocytosis occurs largely at the apical polar axis (Lee et al., 2008).Many researchers argue that apical actin is critical for exocytosis (Lee et al., 2008; Cheung et al., 2010; Qin and Yang, 2011; Yan and Yang, 2012). More specifically, recent work suggests that the fringe participates in targeting vesicles and thereby contributes to changes in growth direction (Kroeger et al., 2009; Bou Daher and Geitmann, 2011; Dong et al., 2012). In this article, using three different inhibitors, namely brefeldin A (BFA), LatB, and potassium cyanide (KCN), we test the hypothesis that polarized pectin deposition in pollen tubes requires the actin fringe. Our data show that during normal growth, pectin deposition is focused to the apex along the polar axis of the tube. However, when growth is modulated, different end points arise, depending on the inhibitor. With BFA, exocytosis stops completely, and the fringe disappears, with the appearance of an actin aggregate at the base of the clear zone. LatB, as shown previously (Vidali et al., 2009), incompletely degrades the actin fringe and leaves a rim of F-actin around the apical dome. Here, we show that, in the presence of LatB, pectin deposition continues, with the focus of this activity shifting in position frequently as the slowly elongating pollen tube changes direction. With KCN, the actin fringe degrades completely, but exocytosis continues and becomes depolarized, with pectin deposits now occurring across a wide arc of the apical dome. This dome often swells as deposition continues, only stopping once normal growth resumes. Taken together, these results support a role for the actin fringe in controlling the polarity of growth in the lily pollen tube.  相似文献   

12.
Actin filaments are often arranged into higher-order structures, such as the longitudinal actin cables that generate the reverse fountain cytoplasmic streaming pattern present in pollen tubes. While several actin binding proteins have been implicated in the generation of these cables, the mechanisms that regulate their dynamic turnover remain largely unknown. Here, we show that Arabidopsis thaliana ACTIN-DEPOLYMERIZING FACTOR7 (ADF7) is required for turnover of longitudinal actin cables. In vitro biochemical analyses revealed that ADF7 is a typical ADF that prefers ADP-G-actin over ATP-G-actin. ADF7 inhibits nucleotide exchange on actin and severs filaments, but its filament severing and depolymerizing activities are less potent than those of the vegetative ADF1. ADF7 primarily decorates longitudinal actin cables in the shanks of pollen tubes. Consistent with this localization pattern, the severing frequency and depolymerization rate of filaments significantly decreased, while their maximum lifetime significantly increased, in adf7 pollen tube shanks. Furthermore, an ADF7–enhanced green fluorescent protein fusion with defective severing activity but normal G-actin binding activity could not complement adf7, providing compelling evidence that the severing activity of ADF7 is vital for its in vivo functions. These observations suggest that ADF7 evolved to promote turnover of longitudinal actin cables by severing actin filaments in pollen tubes.  相似文献   

13.
花柱和花粉胞外钙调素对花粉萌发和花粉管伸长的影响   总被引:6,自引:0,他引:6  
以烟草为材料,通过半体内实验,就花柱和花粉胞外钙调素对花粉萌发和花粉管伸长的影响进行了观察。发现用EGTA及钙调素抗血清处理柱头或花粉均可抑制花粉在柱头上的萌发;向花柱引导组织中显微注射纯化钙调素可促进花粉管束伸长,而注射钙调素抗血清可抑制花粉管束伸长;同时证实玉米花柱和花粉细胞壁中均存在钙调素及钙调素结合蛋白,而且花粉和花柱细胞壁中钙调素结合蛋白的种类有差异。结果表明存在于花粉和花柱细胞外的钙调素对花粉萌发和花粉管伸长均有促进作用。  相似文献   

14.
Various oligosaccharides were studied with regard to their effecton the in vitro growth of Camellia japonica pollen tube. Sucrose,raffinose, melezitose, cellobiose, turanose and isomaltose,especially the first four, promoted pollen tube growth, whilemaltotriose, trehalose, gentiobiose, palatinose, melibiose,lactose and lactulose had little effect. Maltose strongly inhibitednot only the tube growth on sugar-free medium but also sugar-stimulatedgrowth, except in the case of sucrose stimulation. Glycosidaseactivities toward the growth-stimulating oligosaccharides weredetected in the extract of sucrose-grown pollen, but the activitiesof -glucosidase and -galactosidase were much lower than thoseof ß-fructosidase and ß-glucosidase. Maltosesuppressed the increase in UDP-glucose level of the glucose-grownpollen but not that of the sucrose-grown one. These resultssuggest that maltose acts, directly or indirectly, somewherein the pathway from glucose to UDP-glucose via glucose-1-phosphate,but does not interfere with the direct conversion of sucroseto UDP-glucose. (Received December 1, 1984; Accepted May 24, 1985)  相似文献   

15.
Phosphorus (P) enters roots as inorganic phosphate (Pi) derived from organic and inorganic P compounds in the soil. Nucleic acids can support plant growth as the sole source of P in axenic culture but are thought to be converted into Pi by plant-derived nucleases and phosphatases prior to uptake. Here, we show that a nuclease-resistant analog of DNA is taken up by plant cells. Fluorescently labeled S-DNA of 25 bp, which is protected against enzymatic breakdown by its phosphorothioate backbone, was taken up and detected in root cells including root hairs and pollen tubes. These results indicate that current views of plant P acquisition may have to be revised to include uptake of DNA into cells. We further show that addition of DNA to Pi-containing growth medium enhanced the growth of lateral roots and root hairs even though plants were P replete and had similar biomass as plants supplied with Pi only. Exogenously supplied DNA increased length growth of pollen tubes, which were studied because they have similar elongated and polarized growth as root hairs. Our results indicate that DNA is not only taken up and used as a P source by plants, but ironically and independent of Pi supply, DNA also induces morphological changes in roots similar to those observed with P limitation. This study provides, to our knowledge, first evidence that exogenous DNA could act nonspecifically as signaling molecules for root development.Phosphorus (P) is an essential macronutrient that limits plant growth in many situations due to a low availability in soils (for review, see Schachtman et al., 1998; Raghothama, 1999; Vance et al., 2003; Lambers et al., 2008). P enters plant roots as orthophosphates (Pi) via active transport across the plasma membrane (Smith et al., 2003; Park et al., 2007; Xu et al., 2007). Concentrations of Pi in soil solution are generally very low (<10 μm; Bieleski, 1973) and plants have evolved root specializations to access P from inorganic and organic sources (Raghothama, 1999; Hinsinger, 2001; López-Bucio et al., 2003; Vance et al., 2003; Lambers et al., 2008). Roots exude enzymes and chemicals to mobilize P directly from soil compounds or indirectly via enhanced activity of soil microbes, and form symbioses with P-mobilizing mycorrhizal fungi (Schachtman et al., 1998; Raghothama, 1999; Bucher, 2007).However, similar to other nutrients, notably nitrogen, research on P nutrition of plants has focused on inorganic sources although organic P (Porg) in soil can account for 40% to 80% of the total P pool of mineral and organic soils, respectively (Bower, 1945; Raghothama, 1999; Vance et al., 2003). Porg compounds in soils are derived from plant residues, soil biota, and from synthesis by soil microbes (Jencks et al., 1964). Soil Porg is composed primarily of phospholipids, nucleic acids, and phytin (Dyer and Wrenshall, 1941). Phytic acid (inositol hexaphosphate) and its salts phytate, account for a large proportion of the Porg pool of soils (Anderson, 1980). Nucleic acids (RNA, DNA) represent approximately 1% to 2% of the soil Porg pool (Dalal, 1977). It can be released from prokaryotic and eukaryotic cells after death and protected against nuclease degradation by its adsorption on soil colloids and sand particles (Pietramellara et al., 2009).Although Porg can be a substantial constituent of the soil P pool, its contribution to the P nutrition of plants is poorly understood. Porg can be converted to Pi via root-exuded enzymes (Tarafdar and Claassen, 1988; Marschner, 1995; Vance et al., 2003). Secretion of nucleolytic enzymes and breakdown of nucleic acid were considered the reason for the observed growth of axenic Arabidopsis (Arabidopsis thaliana) and wheat (Triticum aestivum) on nucleic acid substrates as the sole P source (Chen et al., 2000; Richardson et al., 2000).Whether plants take up intact DNA has not been reported. We recently showed that roots take up protein, possibly via endocytosis (Paungfoo-Lonhienne et al., 2008). We hypothesized that roots may take up DNA by a similar process and grew Arabidopsis in the presence of phosphorothioate oligonucleotides (S-DNA) labeled with Cy3-fluorescent dye. S-DNA has a sulfur backbone and cannot be digested by plant nucleases, allowing tracking DNA of known size into cells (Spitzer and Eckstein, 1988). We examined if S-DNA of 25 nucleotides in length enters root hairs and pollen tubes as both types of cells are strongly elongated and have similar polarized growth (Schiefelbein et al., 1993; Hepler et al., 2001). We also assessed if addition of DNA to the growth medium affects the morphology of roots and pollen tubes. Here, we present evidence that plants take up DNA and demonstrate that the presence of DNA in the growth medium enhances lateral branching of roots, and the length of root hairs and pollen tubes, irrespective of Pi supply.  相似文献   

16.
高亢  杜娟  侯名语  赵婧  潘延云 《植物学报》2013,48(2):210-218
肌醇磷脂信号系统以肌醇磷脂代谢循环为基础, 由多种磷酸磷脂酰肌醇分子和多磷酸肌醇分子及催化代谢的磷脂酶、激酶组成。该信号系统参与调节动、植物细胞生长发育及应答环境刺激等多种生理过程。花粉发育和花粉管的生长是植物有性生殖的基础, 肌醇磷脂信号系统中多种组分参与其生理过程的调节。该文综述了植物肌醇磷脂信号系统中各组分的相互关系, 以及相关组分调节花粉发育和花粉管生长生理过程的研究进展。  相似文献   

17.
The deals with the effects of nifedipine (Nif), a Ca2+ channel blocker of rather high specificity, on pollen germination, pollen tube growth and division of generative nucleus (GN) in experimentlly germinated pollen tubes of Nicotiana tabacurn L. Pollen germination was inhibited by the addition of 10-4 mol/L Nif whereas no significant inhibition by 10-7~10-5 mol/L Nif was observed. The effects of Nif on pollen tube growth were related to its concentration and duration of treatment. At the earlier stage, tube growth was promoted at the lower concentrations (10-7~10-5 mol/L), but was significantly inhibited at a concentration of 10 4 mol/L Nif. With increasing time of culture, even the lower concentrations also became harmful; the stronger the concentration, the earlier the transition from promotion to inhibition. Generally, inhibition of tube growth occurred within 24 hours of culture with different extent in various concentrations. Moreover, higher concentrations also tended to disturb tube morphology and cytoplasmic streaming. Nif was observed to perturb GN division at various concentrations, either blocked it completely at 10-4 mol/L, or only delayed it at 10-7~10-5 mol/L. The dynamics of membrane-associated calcium in pollen tubes was tested with chlorotetracycline (CTC). With increasing time of culture and escalating Nif concentration, CTC fluorescence weakened gradually, indicating that the physiological effects of Nif is mediated by its in hibition on Ca2+ channel activities.  相似文献   

18.
钙和硼对蓝猪耳花粉萌发及花粉管生长的影响   总被引:31,自引:1,他引:31  
研究了钙(Ca^2 )和硼(H3BO3)对蓝猪耳花粉萌发和花粉管生长的影响。结果表明:(1)在一定范围内Ca^2 几乎不影响花粉萌发频率,而主要影响花粉萌发速度和花粉管生长速度;低Ca^2 不利于花粉管生长,而高Ca^2 抑制花粉萌发速度和花粉管生长;在稍高于最适Ca^2 浓度的条件下,花粉管生长早期呈现波浪形。(2)硼明显影响花粉萌发频率及花粉管形态;花粉管生长必需硼,但不同浓度的硼对花粉管生长速度影响不明显;在高浓度硼条件下,较长时间内花粉管均呈现出波浪形。(3)Cooled-CCD动态跟踪观察进一步证实Ca^2 影响花粉管生长速度,而硼则不明显。  相似文献   

19.
With radical global climate change and global warming, high temperature stress has become one of major factors exerting a major influence on crop production. In the cotton (Gossypium hirsutum L.)-growing areas of China, especially in the Yangtze River valley, unexpected periodic episodes of extreme heat stress usually occur in July and August, the peak time of cotton flowering and boll loading, resulting in lower boll set and lint yield. Breeding programs for screening high temperature-tolerant cotton germplasm and cultivars are urgent in order to stabilize yield in the current and future warmer weather conditions. In the present study, 14 cotton cultivars were quantified for in vitro pollen germination and pollen tube growth in response to temperatures ranging from 10 to 50 ℃ at 5 ℃ intervals. Different cotton genotypes varied in their in vitro pollen germination and pollen tube length responses to the different temperatures. Maximum pollen germination and pollen tube length ranged from 25.2% to 56.2% and from 414 to 682 μm, respectively.The average cardinal temperatures (Tmin, Topt, and Tmax) also varied among the 14 cultivars and were 11.8,27.3, and 42.7 ℃ for pollen germination and 11.8, 27.8, and 44.1 ℃ for maximum pollen tube length. Variations in boll retention and boll numbers per plant in field experiments were found for the 14 cotton cultivars and the boll retention and boll retained per plant on 20 August varied considerably in different years according to weather conditions. Boll retention on 20 August was highly correlated with maximum pollen germination (R2=0.84) and pollen tube length (R2=0.64). A screening method based on principle component analysis of the combination of pollen characteristics in an in vitro experiment and boll retention testing in the field environment was used in the present study and, as a result, the 14 cotton cultivars could be classified as tolerant, moderately tolerant, moderately susceptible and susceptible to high temperature.  相似文献   

20.
花粉管的极性顶端生长是一个复杂的动力学过程, 在高等植物有性生殖过程中起着重要的作用。花粉管的生长过程包括许多方面, 其中最为重要的是花粉管细胞骨架动态和胞质运动。本文较全面地综述了花粉管的结构、细胞骨架、胞质运动、囊泡转运及循环、线粒体运动以及内质网和高尔基体之间囊泡运动等。  相似文献   

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