摘要
当大蒜的蒜瓣鞘由肥厚鳞片向坚韧薄片转变时,大多数的外表皮细胞的胞壁随次生沉积而加厚,但其中有像气孔那样分布方式的少数细胞的胞壁初期及中期却不加厚。不加厚细胞大致仍维持原来形状与原生质结构,而在加厚细胞中的胞核与细胞质结构却开始有些解除装配,从一个细胞到另一个细胞的'核穿壁'现象时常可见。在加厚与不加厚细胞中,用细胞化学方法检验几种酶活性,显示出两种细胞间有着显著的差异,不加厚细胞中ATP酶(以及细胞色素氧化酶,过氧化物酶)的活性很强,而加厚细胞却无表现;反之加厚细胞富有酸性磷酸酯酶(以及多酚氧化酶)活性,而不加厚细胞却十分微弱或无。结果显示,不加厚细胞具有较强的生活力,它们可能在细胞降解物的集结及向表皮下组织的转移中起着一定作用,并给予这种细胞'驿站细胞'的名称。这种细胞也逐步次生沉积而加厚,并最终撤空其内含物,胞腔成为较细狭的空腔。
During the transformation of the protective sheath of garlic from a fleshy scale into a tough skin, most cells of the outer epidermis undergo wall thickening by secondary deposition, yet among them, a few cell interspersed after the fashion of stomatal distribution, remain unthickened at the early stage of development (Plate Ⅰ, Fig. 1). While the unthiekened cell maintains its original shape and protoplasmic contents, the nucleus and cytoplasmic constituents in the thickening cell begin to disassemble themselves to some extent and "nuclear extrusion" from one cell into the other (Plate Ⅰ, Fig. 2) can fre quently be detected under microscope after the specimen is treated with a nuclear stain (Plate Ⅰ, Fig. 3). During middle stage of senescence cytochemical localization of several enzyme activities in the thickening and the unthiekened cells (Plate Ⅰ, Fig. 5- 8) have revealed striking contrast between the two kinds of cells: The unthiekened cell is rich in ATPase (as well as in cytochrome oxidase and peroxidase) activity; whereas the thickening cell fails to show any. Conversely, the thickening cell is full of APase (and in polyphenol oxidase) activity but the unthickened cell shows none or very weak. Nevertheless, the conspicuous differences of the two kinds of cells do not last long, the unthickened cell also transforms itself into the thickening one in succession at the late stage of senescence. Finally, the unthickened cell is composed of secondary deposition of wall materials and a narrow empty cell cavity (Plate Ⅰ, Pig. 4). Prominent differences in cellular structure and in enzymic activity at middle stage and their final transformation into the same rigid structure toward the end of senescence seem to indicate that the unthickened cell is reserved to collect a large part of the evacuating cellular contents from adjoining thickening cells and to transpose them to the tissue underneath epidermis, hence the name "post cell" is given.
