Summary
The cortical cytoplasm of the young guard cells ofAdiantum capillus veneris is locally differentiated. At an early post-telophase stage, numerous microtubules diverge from the cytoplasm occupying the junctions of the midregion of the ventral wall with the periclinal ones, towards the periclinal and ventral wall faces as well as towards the inner cytoplasm. Microtubule-vesicle complexes (MVCs) are detected in these regions. Their appearance is accompanied by the initiation of local wall thickenings in the same areas.
Afterwards, more distinct MVCs anchored to the plasmalemma were seen in the cortical cytoplasm of the periclinal walls, close to the growing thickenings, usually at a distance up to 3μm from them. Sometimes, they seemed to contain an electron dense substance in which the microtubules were embedded. Cortical microtubules converging from more than one direction terminate at the MVCs. Besides, the microtubule population lining the periclinal walls radiate from the regions where the above cytoplasmic formations are localized. The overlying cellulose microfibrils exhibit the same orientation. The vesicles localized at the MVCs appear to be of dictyosomal origin, very electron dense and react positively to periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) test. Another population of microtubules fan out from the MVCs, entering deeper into the cytoplasm. They become associated with the nucleus and mitochondria, and traverse the peridictyosomal cytoplasm. In some instances the nucleus formed a protrusion towards an MVC and appeared associated with it via microtubules which radiate from the MVC and flank the nuclear envelope.
The observations favour the hypothesis that prominent microtubule organizing centres (MTOCs) function in the cortical cytoplasm of the midregion of the periclinal walls surrounding the ventral one for a relatively long time. The MVCs and/or their adjacent plasmalemma sites may represent MTOCs or at least they specify the cortical cytoplasmic sites where microtubules are nucleated.
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Galatis, B., Apostolakos, P. & Katsaros, C. Microtubules and their organizing centres in differentiating guard cells ofAdiantum capillus veneris . Protoplasma 115, 176–192 (1983). https://doi.org/10.1007/BF01279808
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DOI: https://doi.org/10.1007/BF01279808