Changes in the pattern of organization of microtubules during microspore formation in rice (Oryza sativa L.)

Abstract

Changes in the pattern of organization of microtubules in the developing microspore of rice ( Oryza sativa L. ) have been followed using immunofluorescence confocal microscopy. At the microsporocyte stage of development the cell possessed a network of highly branched and thickened microtubule bundles. In the central cytoplasm numerous bundles mn circumferentially around the nucleus. From the circumferentially distributed microtubule bundle network some microtubule bundles radiated towards the conical region of the cell. The microsporocyte after Meiosis Ⅰ became a dyad. In the dyad cell microtubule bundles emanated radially from the nucleus. In the cortex of the dyad cell some of the microtubule bundles became randomly oriented. The dyad then underwent Meiosis Ⅱ to become tetrad. Microtubule bundles in the tetrad cell radiated from the nucleus. No randomly oriented microtubule bundles were present in the cortical region of the tetrad cell. Mter- wards the four cells that made up the tetrad dissociated from each other and each became a microspore. At the early stage of the microspore development most of the microtubule bundles were randomly distributed. Later, some of the microtubules converged towards a bud-like cytoplasmic protrusion. This bud-like protrusion later developed into a germ pore (or pollen pore). At the late stage of microspore formation, microtubule bundles became thinner and reticulately oriented to form a tightly knitted network.

對水稻(Oryza saiva L.)小孢子發育過程中微管變化的研究表明，微管在小孢子不同發育階段呈 現多樣性。在花粉母細胞內，微管形成許多粗束和分支，圍繞著核分佈形成一個網絡。花粉母細胞經第一次減數分裂形成二分體。在每一個二分體細胞內，有許多微管束，從核週輻射至細胞質各部位;在細胞質存在一個疏鬆的微管束網絡。二分體經第二次減數分裂形成四分體，在每一個四分體細胞內，微管束呈輻射狀，從核膜輻射入細胞質內。四分體形成後不久，四分體的四個細胞便分開，每一個細胞變成一個獨立的小孢子。在早期的小孢子細胞內，微管束呈疏鬆網狀分佈。其中有些微管束朝向胞質一個小突起聚集。當小子包子進入中期發育階段，在胞質的小突起部位微管束密度增大。小突起最終形成為萌發孔。當小孢子發育至成熟期，細胞內的微管束變得纖細，而網絡則變得緊密。之後的發育階段(即花粉發育不同階段)因熒光標記難以進入細胞，元法獲得清晰的圖像。