拟南芥根原生韧皮部筛管分子的超微结构

运用高压冷冻替代方法固定处理材料，在透射电镜下观察了拟南芥（Arabidopsis thaliana L.)根原生韧皮部筛管分子在发育过程中的超微结构变化。结果表明：在筛管分子发育过程中，细胞核具有细胞程序死亡的典型特征，出现核膜内陷、核质聚集并边缘化，核膜破毁以及最后核消失，核膜在破毁前一直呈饱满状态，未出现核膜皱缩，核裂瓣和核周腔明显膨大等现象。在成熟筛管分子的细胞质内，具单层膜的淀粉状颗粒，这些淀粉状态颗粒常与线粒体在一起，可能为线粒体的产能活动提供基质，小液泡发生于内质网，未见大液泡的形成。

Ultrastructural Studies on the Sieve Elements in Root Protophleom of Arabidopsis thaliana

The ultrastructures of the root protophleom sieve element at different developmental stages of Arabidopsis thaliana L. were investigated using the technique of high pressure freezing and freeze substitution fixing specimen. The results show that in the development of the sieve elements, the nuclei undergo typical characteristics of the programmed cell death (PCD): the nuclear envelopes form emboli, the chromatin condenses and aggregates towards the nuclear envelope, which degrades and fully disappears later. Before the nucleus degradation, neither the nuclear envelope undulation, nucleus lobe nor marked dilation (or bleb) of perinuclear space could be observed. In the cytoplasm of the mature sieve element, there are starch_like granules separately sheathed with a layer of membrane and usually with mitochondria around. These granules seem to provide substrates to mitochondria in their function. Small vacuoles originate from endoplasmic reticulum (ER), and no bigger vacuole was found.