摘要
Electron microscopic observations revealed that the tissues of poplar ( Populus deltoides Bartr. ex Marsh) apical bud cells, which were fixed by a modified procedure of potassium permanganate fixative, showed a distinct endomembrane organization, in particular, the structural associations of the endoplasmic reticulum (ER) with other membrane systems. The striking findings are that some ER elements were in connection with the nuclear envelopes of two adjacent cells through plasmodesmata, and many ER elements were also associated with mitochondria, plastids, Golgi bodies or the plasma membrane (PM), forming a bridge_like continuum among various endomembrane systems or between nucleus to nucleus. A great number of plasmodesmata existed between cells, indicating a perfectly integrated symplasmic structure in poplar apical bud meristem grown in a long day environment. During the short day_induced dormancy, ER contracted, leading to its disassociation between nuclei, and between the nucleus and organelles/plasmalemma in many cells. After dormancy broke and shoots growth resumed, contracted ER was no longer observed in the apical bud cells. The ER associations with other endomembrane systems and the intercellular communication channels were re_established similar to that of plants before dormancy induction. These observations suggest that ER may play an important role in linking_up between the nucleus and organelles, and between the nucleus and the nucleus (or cell_to_cell), and seemingly coordinating various physiological processes by the bridging_like associations. And the contraction of ER under short_day may result in the growth cessation and the development of dormancy in poplar.
杨树 (PopulusdeltoidesBartr.exMarsh)顶芽分生组织细胞经一种改良的高锰酸钾固定法固定后 ,显示出一种十分清晰的内膜结构 ,尤其展现了内质网与其他膜系统存在一种结构上的密切联系。一些与核膜相连接的内质网伸展到细胞质中与线粒体、质体及高尔基体发生联系 ,或延伸到质膜。还有些内质网的一端与一个细胞的核膜相连结 ,其另一端穿过胞间连丝与邻近的另一个细胞的核膜相连结 ,在两个相邻的细胞核之间形成一种结构上的“内质网桥”。这种“内质网桥”结构的揭示 ,进一步完善了共质体的概念。在植物细胞间 ,不仅通过胞间连丝造成细胞质的沟通 ;而且通过“内质网桥”形成核与核之间的联络。在短日照诱导的休眠过程中 ,内质网出现收缩现象 ,导致内质网与其他膜系统联系的中断 ,胞间连丝的中断 ,以及核与核之间“桥通道”的中断。在芽休眠被打破和复苏生长后 ,内质网的收缩现象消失 ,内质网与其他膜系统间联系 ,以及相邻细胞核之间重建“内质网桥”。这些结果揭示 ,内质网在沟通细胞核与各细胞器 ,以及核与核之间生命活动的关系上可能起着重要的作用。
