小麦原胚基端组织的结构变化与营养物质的摄取

THE STRUCTURAL CHANGES OF THE BASAL REGION OF WHEAT PROEMBRYO IN RELATION TO NURTURE ABSORPTION

小麦(Triticum aestivum)原胚发育过程中基端一侧边缘持续地出现少数细胞呈现衰退与结构解体的现象。电镜观察揭示,解体原生质与外围胚乳解体产物相混和;相邻的原胚存活细胞通过界面壁上存留的胞间连丝或开放孔道与外围介质间建立起直接的沟通,从而各种物质可通经类似“外连丝”的共质体通道或质膜上的内吞过程进入原胚内部。外围原生质解体产物中大分子物质因之而掺入,如解体核物质、线粒体、胞质颗粒等的迁移以及富含丝状物囊泡的内吞等,是原胚获得营养的一种重要方式。同时,原胚内部密集分布的胞间连丝中有一部分转变为开放态,大分子结构物经此而穿越,有利于加速细胞内含物在原胚内部的再分配。原胚基端经历的这种结构变动,可以认为是与摄取营养相适应的一种特定的分化,因之而加强了物质的内外交流,显然有效地保证了原胚细胞增殖、生长、分化时的营养需求。

There are some cellular fail and degeneration in the parietal area of the basal region of developing wheat proembryo.Electron microscopic studies reveal that the envelopment of peri- pheral wall to the proembryo is partly ruptured in this area and the disassembled protoplasm of the degenerated cells mixes with the disintegrated constituents of adjacent endosperm cells. Hence,in the limited area a direct communication between the inner surviving proembryo cells and the surrounding medium is established.A irumber of ectodesma-like plasmodesmata and open channels appear at the boundary wall,various nutrients may enter the proembryo via symplastic pathway or by endocytosis.The surrounding macromolecules(disassembled nuclei, mitochondria,cytoplasmic granules and vesicles packed with fibrils)appear to traverse across the wall continually,and it seems that this is an important mode of nurture translocation. Also,within the proembryo some of the densely distributed plasmodesmata undergo modifica- tion and become fully opened for macromolecules traversing,which is in favor of re-distribu- tion of cell contents amongst proembryo cells. Presumably,the structural changes occurred in the basal region is a special kind of dif- ferentiation which results in function of this local area as apparatus of nurture absorption. Evidently,it would enhance the incorporation of external materials into the proembryo,and then the normal proliferation,development and differentiation of proembryo cells would be ensured.