Glyphosate-Induced Anther Indehiscence in Cotton Is Partially Temperature Dependent and Involves Cytoskeleton and Secondary Wall Modifications and Auxin Accumulation

Abstract

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 a 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 SWTabnormalities 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.

Auxin RegulatesArabidopsisAnther Dehiscence, Pollen Maturation, and Filament Elongation

“…This treatment induced the accumulation of high levels of indole-3-acetic acid, and flowers exhibited delayed anther dehiscence due to changes in cell wall lignification of endothecium cells (Yassuor et al, 2006). This study was designed to confirm and extend our previous suggestion that auxin plays a key role in regulating the late stages of stamen development (Cecchetti et al, 2004).…”

“…Additional indirect evidence comes from a study by Yassuor et al (2006) on cotton (Gossypium hirsutum) and Arabidopsis thaliana flowers treated with the herbicide glyphosate. This treatment induced the accumulation of high levels of indole-3-acetic acid, and flowers exhibited delayed anther dehiscence due to changes in cell wall lignification of endothecium cells (Yassuor et al, 2006).…”

Sub-lethal glyphosate exposure alters flowering phenology and causes transient male-sterility in Brassica spp

“…Studies in morning glory have revealed population variability in the survival of glyphosate application and surviving plants often have functionally female flowers due to abnormal stamens [29]. Similarly, studies in cotton have shown glyphosate-induced changes in microtubules in anthers, leading to poor dehiscence [30], possibly similar to the mechanism contributing to the reduction in anther dehiscence we observed. Glyphosate resistant corn and cotton varieties that have reduced transgene expression in male tissues also suffer from shortened anther filaments leading to reduced pollen transfer between anther and pistil [31] and reduced pollen viability [32].…”

The Arabidopsis ARCP Protein, CSI1, Which Is Required for Microtubule Stability, Is Necessary for Root and Anther Development

“…dehiscence program (Yasuor et al, 2006). Our observation reveals that microtubules in csi1 cells are depolymerized more rapidly under dehydration for 4 to 12 h (this time period is sufficient for anther dehydration, bud opening, and anthesis in wild-type anthers) (Smyth et al, 1990).…”