Department of Biological Sciences, Graduate School of Science, Osaka Prefecture University, Gakuen-cho 1-2, Minami-ku, Sakai, Osaka 599-8570, Japan.
J Plant Physiol. 2013 Jan 1;170(1):18-24. doi: 10.1016/j.jplph.2012.08.008. Epub 2012 Aug 31.
In studies on the mechanism of cell separation during abscission, little attention has been paid to the apoplastic environment. We found that the apoplastic pH surrounding abscission zone cells in detached roots of the water fern Azolla plays a major role in cell separation. Abscission zone cells of detached Azolla roots were separated rapidly in a buffer at neutral pH and slowly in a buffer at pH below 4.0. However, cell separation rarely occurred at pH 5.0-5.5. Light and electron microscopy revealed that cell separation was caused by a degradation of the middle lamella between abscission zone cells at both pH values, neutral and below 4.0. Low temperature and papain treatment inhibited cell separation. Enzyme(s) in the cell wall of the abscission zone cells might be involved in the degradation of the pectin of the middle lamella and the resultant, pH-dependent cell separation. By contrast, in Phaseolus leaf petioles, unlike Azolla roots, cell separation was slow and increased only at acidic pH. The rapid cell separation, as observed in Azolla roots at neutral pH, did not occur. Indirect immunofluorescence microscopy, using anti-pectin monoclonal antibodies, revealed that the cell wall pectins of the abscission zone cells of Azolla roots and Phaseolus leaf petioles looked similar and changed similarly during cell separation. Thus, the pH-related differences in cell separation mechanisms of Azolla and Phaseolus might not be due to differences in cell wall pectin, but to differences in cell wall-located enzymatic activities responsible for the degradation of pectic substances. A possible enzyme system is discussed.
在研究细胞分离的机制过程中，脱落过程中的胞外环境并没有引起人们太多的关注。我们发现，在水蕨（Azolla）离断根的脱落区域细胞的胞外环境中，pH 值起着重要的作用。离断水蕨根的脱落区域细胞在中性 pH 值的缓冲液中迅速分离，在 pH 值低于 4.0 的缓冲液中缓慢分离。然而，在 pH 值 5.0-5.5 时，细胞分离很少发生。光镜和电镜观察揭示，在中性和 pH 值低于 4.0 的条件下，细胞分离都是由脱落区域细胞之间的中层的降解引起的。低温和木瓜蛋白酶处理抑制了细胞分离。脱落区域细胞细胞壁中的酶可能参与了中层果胶的降解，从而导致了依赖 pH 值的细胞分离。相比之下，在菜豆叶片叶柄中，与水蕨根不同，细胞分离缓慢，仅在酸性 pH 值时增加。在中性 pH 值下观察到的水蕨根中快速的细胞分离并没有发生。用抗果胶单克隆抗体进行的间接免疫荧光显微镜观察表明，水蕨根和菜豆叶片叶柄的脱落区域细胞细胞壁中的果胶看起来相似，并且在细胞分离过程中变化方式相似。因此，水蕨和菜豆的细胞分离机制中与 pH 值相关的差异可能不是由于细胞壁果胶的差异，而是由于负责果胶物质降解的细胞壁定位酶活性的差异。讨论了一种可能的酶系统。
