Changes In Microtubule Orientation Research Articles

“CLASPing” tungsten's effects on microtubules with “PINs”

Tungsten, supplied as sodium tungstate, inhibits root elongation in Arabidopsis thaliana, which has been attributed to a diminishing of PIN2 and PIN3 auxin efflux carriers. In this work, we sought to analyze the effect of tungsten on cortical microtubules and CLASP (Cytoplasmic Linker Associated Protein), which are also involved in the anisotropic cell expansion of root cells. Seedlings grown in a tungsten-free substrate for 4 d and then transplanted into a tungsten-containing substrate exhibited randomly oriented microtubules in a time-dependent manner. While tungsten had no effect on roots treated for 3 h, microtubule alignment was obviously affected in the transition and elongation zones after a 6, 12, 24, 48 h tungsten treatment, at prolonged tungsten administrations and in seedlings grown directly in the presence of tungsten. This change in microtubule orientation may be associated with the reduction of CLASP protein expression induced by tungsten, as evidenced in experiments with plants expressing the CLASP-GFP protein. A possible mechanism, by which the coordinated functions of CLASP, PIN2 and microtubules are affected, as revealed by inhibited root growth, is discussed.

Microtubule dynamics is required for root elongation growth under osmotic stress in Arabidopsis

Osmotic stress caused by drought and soil salinity is one of the factors that affect plant root system growth and development. Previous studies have shown that microtubule plays a critical role in plant roots response to osmotic stress, however, the underlying mechanism remains unclear. In the present study, the microtubule orientations in Arabidopsis roots growing under osmotic stress were determined using confocal fluorescence microscopy. The results showed that osmotic stress could significantly inhibit primary root elongation in Arabidopsis, and pharmacological tests confirmed that microtubules were involved in Arabidopsis roots response to osmotic stress. In vivo visualization of microtubule structures with the microtubule-binding domain–green fluorescent protein (GFP) reporter revealed altered microtubule orientation in rhizodermal cells under osmotic stress. These results above indicated that osmotic stress could inhibit the elongation growth of Arabidopsis primary root, and the inhibition effects might result from the changes in microtubule orientation.

RETRACTED:ArabidopsisAUGMIN Subunit8 Is a Microtubule Plus-End Binding Protein That Promotes Microtubule Reorientation in Hypocotyls

In plant cells, cortical microtubules provide tracks for cellulose-synthesizing enzymes and regulate cell division, growth, and morphogenesis. The role of microtubules in these essential cellular processes depends on the spatial arrangement of the microtubules. Cortical microtubules are reoriented in response to changes in cell growth status and cell shape. Therefore, an understanding of the mechanism that underlies the change in microtubule orientation will provide insight into plant cell growth and morphogenesis. This study demonstrated that AUGMIN subunit8 (AUG8) in Arabidopsis thaliana is a novel microtubule plus-end binding protein that participates in the reorientation of microtubules in hypocotyls when cell elongation slows down. AUG8 bound to the plus ends of microtubules and promoted tubulin polymerization in vitro. In vivo, AUG8 was recruited to the microtubule branch site immediately before nascent microtubules branched out. It specifically associated with the plus ends of growing cortical microtubules and regulated microtubule dynamics, which facilitated microtubule reorientation when microtubules changed their growth trajectory or encountered obstacle microtubules during microtubule reorientation. This study thus reveals a novel mechanism underlying microtubule reorientation that is critical for modulating cell elongation in Arabidopsis.

Microtubule reorientation in shoots precedes bending during the gravitropic response of cut snapdragon spikes

The microtubule reorientation during the gravitropic bending of cut snapdragon (Antirrhinum majus L.) spikes was investigated. Using indirect immunofluorescence methods, we examined changes in microtubule orientation in the cortex, endodermis and pith tissues of the shoot bending zone, in response to gravistimulation. Our results show that dense microtubule arrays were visible throughout the cortical, endodermal and pith shoot tissues, and that the transverse orientation of the microtubules (perpendicular to the growth axis) was specifically associated with the shoot growing bending zone. Microtubules showed gravity-induced kinetics of changes in their orientation, which occurred only in the upper stem flank and preceded shoot bending. While this observation, that the gravity-induced microtubule orientation precedes bending, was previously reported only in special above-ground organs such as coleoptiles and hypocotyls, our present study is the first to show that such patterns of change occur in mature flowering shoots. These changes were exhibited first in the upper flank of the cortex and then in the upper flank of the endodermis. No changes in microtubule orientation were observed in the cortex or endodermis tissues of the lower flanks or in the pith, suggesting that these tissues continue to grow during shoot gravistimulation. Our results imply that microtubules may be involved in growth cessation of the upper shoot flank occurring during the gravitropic bending of snapdragon cut spikes.

Glyphosate-induced anther indehiscence in cotton is partially temperature dependent and involves cytoskeleton and secondary wall modifications and auxin accumulation.

Yield reduction caused by late application of glyphosate to glyphosate-resistant cotton (Gossypium hirsutum; GRC) expressing CP4 5-enol-pyruvylshikmate-3-P synthase under the cauliflower mosaic virus-35S promoter has been attributed to male sterility. This study was aimed to elucidate the factors and mechanisms involved in this phenomenon. Western and tissue-print blots demonstrated a reduced expression of the transgene in anthers of GRC compared to ovules of the same plants. Glyphosate application to GRC grown at a high temperature regime after the initiation of flower buds caused a complete loss of pollen viability and inhibition of anther dehiscence, while at a moderate temperature regime only 50% of the pollen grains were disrupted and anther dehiscence was normal. Glyphosate-damaged anthers exhibited a change in the deposition of the secondary cell wall thickenings (SWT) in the endothecium cells, from the normal longitudinal orientation to a transverse orientation, and hindered septum disintegration. These changes occurred only at the high temperature regime. The reorientation of SWT in GRC was accompanied by a similar change in microtubule orientation. A similar reorientation of microtubules was also observed in Arabidopsis (Arabidopsis thaliana) seedlings expressing green fluorescent protein tubulin (tubulin alpha 6) following glyphosate treatment. Glyphosate treatment induced the accumulation of high levels of indole-3-acetic acid in GRC anthers. Cotton plants treated with 2,4-dichlorophenoxyacetic acid had male sterile flowers, with SWT abnormalities in the endothecium layer similar to those observed in glyphosate-treated plants. Our data demonstrate that glyphosate inhibits anther dehiscence by inducing changes in the microtubule and cell wall organization in the endothecium cells, which are mediated by auxin.

Microtubule dynamics in compatible and incompatible interactions of soybean hypocotyl cells with Phytophthora sojae

The arrangement of microtubules in soybean (Glycine max) cells was examined during compatible and incompatible interactions of hypocotyls of soybean cv. Harosoy (susceptible) and cv. Haro 1272 (resistant) with race 1 of the soybean‐specific pathogen Phytophthora sojae. Both reaction types were similar during the first 3 h after zoospore inoculation in terms of the number of cells penetrated, and depth penetrated into the cortex. By 3 h postinoculation, clear differences had developed between the two interaction types: incompatible interactions were characterized by a hypersensitive response that was confined to single penetrated cells; while compatibly responding cells appeared unchanged. Both types of response were characterized by autofluorescence of cell walls or cytoplasm and, at 6 h after inoculation, complete disorganization of cell cytoplasm. Reorientation and loss of microtubules was seen in the early stages of the incompatible interaction in association with cellular hypersensitivity, but not in compatible responses. In cells adjacent to those that reacted hypersensitively, there was little evidence of change in microtubule orientation. Treatment of hypocotyls with the microtubule depolymerizer oryzalin prior to inoculation did not alter the compatible response, but led to breakdown of the incompatible response. Changes in microtubule orientation and state are thus among the first structural changes that are visible within cells during incompatibility in this system.

The Hormonal Regulation of Cell Elongation Through Changes in Microtubule Orientation

Previous articleNext article No AccessThe Hormonal Regulation of Cell Elongation Through Changes in Microtubule OrientationRobert W. SeagullRobert W. Seagull Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by International Journal of Plant Sciences Volume 153, Number 2Jun., 1992 Article DOIhttps://doi.org/10.1086/ijps.153.2.2995636 Views: 4Total views on this site Citations: 4Citations are reported from Crossref Copyright 1992 The University of ChicagoPDF download Crossref reports the following articles citing this article: Robert W. Seagull Cytoskeletal Stability Affects Cotton Fiber Initiation, International Journal of Plant Sciences 159, no.44 (Oct 2015): 590–598.https://doi.org/10.1086/297577Cheryl A. Telmer, W. Newcomb, Daina H. Simmonds Cellular changes during heat shock induction and embryo development of cultured microspores ofBrassica napus cv. Topas, Protoplasma 185, no.1-21-2 (Mar 1995): 106–112.https://doi.org/10.1007/BF01272758K. Zandomeni, P. Schopfer Reorientation of microtubules at the outer epidermal wall of maize coleoptiles by phytochrome, blue-light photoreceptor, and auxin, Protoplasma 173, no.3-43-4 (Sep 1993): 103–112.https://doi.org/10.1007/BF01378999Robert W. Seagull Cytoskeletal involvement in cotton fiber growth and development, Micron 24, no.66 (Jan 1993): 643–660.https://doi.org/10.1016/0968-4328(93)90042-Y

The effects of microtubule and microfilament disrupting agents on cytoskeletal arrays and wall deposition in developing cotton fibers

The effects of various cytoskeletal disrupting agents (cholchicine, oryzalin, trifluralin, taxol, cytochalasins B and D) on microtubules, microfilaments and wall microfibril deposition were monitored in developing cotton fibers, using immunocytochemical and fluorescence techniques. Treatment with 10−4 M colchicine, 10−6 M trifluralin or 10−6 M oryzalin resulted in a reduction in the number of microtubules, however, the “drug-stable” microtubules still appear to influence wall deposition. Treatment with 10−5 M taxol increased the numbers of microtubules present within 15 minutes of application. New microtubules were aligned parallel to the existing ones, however, some evidence of random arrays was observed. Microtubules stabilized with taxol appeared to function in wall organization but do not undergo normal re-orientations during development. Microtubule disrupting agent had no detectable affect on the microfilament population. Exposure to either 4×10−5 M cytochalasin B or 2×10−6M cytochalasin D resulted in a disruption of microfilaments and a re-organization of microtubule arrays. Treatment with either cytochalasin caused a premature shift in the orientation of microtubules in young fibers, whereas in older fibers the microtubule arrays became randomly organized. These observations indicate that microtubule populations during interphase are heterogeneous, differing at least in their susceptibility to disruption by depolymerizing agents. Changes in microtubule orientation (induced by cytochalasin) indicate that microfilaments may be involved in regulating microtubule orientation during development.

Regions of Cell Wall Expansion in the Protonema of a Fern

Protonemata of Onoclea sensibilis were grown for 7 days in darkness and were then transferred into light on new media, either liquid or agar-solidified, which contained 0.15% colchicine. The growth of individual plants was observed on solid media in microchambers. Unequivocal evidence was obtained that cell wall expansion and an increase in cell diameter occurred in regions well behind the apex of the protonema. This finding is related to an hypothesis which proposes light-induced changes in microtubule orientation and cell wall structure as an explanation for certain changes in cell form in fern gametophytes.

REGIONS OF CELL WALL EXPANSION IN THE PROTONEMA OF A FERN

Protonemata of Onoclea sensibilis were grown for 7 days in darkness and were then transferred into light on new media, either liquid or agar‐solidified, which contained 0.15% colchicine. The growth of individual plants was observed on solid media in microchambers. Unequivocal evidence was obtained that cell wall expansion and an increase in cell diameter occurred in regions well behind the apex of the protonema. This finding is related to an hypothesis which proposes light‐induced changes in microtubule orientation and cell wall structure as an explanation for certain changes in cell form in fern gametophytes.