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.
低温逆境中不同抗寒性植物细胞内Ca2+ 稳定平衡的区别
简令成1 孙龙华1 李积宏2 王红1 孙德兰1 Paul H LI 2
（1. 中国科学院植物研究所，北京100093；2. Laboratory of Plant Hardiness, Department of Horticultural Science and Plant Biological Sciences Program, Universoty of Minnesota,St. Paul,MN 55108,USA)
摘要：电镜细胞化学观察揭示 ,不抗寒的玉米 (Zeamays L .cv.BlackMexicanSweet)和抗寒的小偃麦 (Triticum sect.Trititrigia mackey)细胞在 2 6℃悬浮培养时 ,标志Ca2 + 定位的锑酸钙沉淀物主要分布在液泡内 ,细胞质和细胞核中很少见到Ca2 + 沉淀 ;标志Ca2 + _ATPase活性反应的磷酸铈沉淀物丰富地分布在质膜上 ,显示这两种植物质膜Ca2 + _ATPase在 2 6℃培养中有着较高的活性。当这二者的细胞在 4℃低温培养 1h和 3h后 ,二者细胞质和细胞核中的Ca2 + 浓度都明显地增加 ,但质膜Ca2 + _ATPase活性没有明显改变。在继续延长低温培养后 ,二者之间的Ca2 +水平和Ca2 + _ATPase活性发生明显的区别 :在不抗寒的玉米细胞中 ,质膜Ca2 + _ATPase活性显著降低 ,甚至完全失活 ,细胞内增加的Ca2 + 水平不降低 ,不能恢复Ca2 + 的稳定平衡 ,细胞的精细结构受破坏 ;抗寒的小偃麦细胞则相反 ,在 3h以后的低温培养过程中 (至 3d) ,质膜Ca2 + _ATPase仍然保持高活性 ,细胞内增加的Ca2 + 浓度迅速降低 ,恢复Ca2 + 的稳定平衡 ,并提高抗寒力。这些结果表明 ,植物在低温条件下 ,质膜Ca2 +-ATPase活性的维持亦即细胞内Ca2 + 稳定平衡的恢复与其抗寒性有着密切的关系 ,对于它们在逆境中生存起着重要作用。
关键词： Ca2+ ；质膜Ca2+-ATPase；Ca2+ 的稳定平衡；植物抗寒性；玉米；小偃麦
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