Ultrastructural changes of vacuolar organelle with the expression of vacuolar processing enzyme in Arabidopsis

拟南芥有三种类型的液泡处理酶同系物：αVPE、βVPE和γVPE。利用pVPE：：GUS转化拟南芥植株的GUS组织化学染色检测这些VPE基因的时空表达。αVpe启动子和γVpe启动子控制根和叶的表达。相反，pβvpe：：GUS基因在花粉粒中表达较强。在本研究中，我们阐明了pVPE-gus基因表达后的液泡细胞器的超微结构变化。用冷冻/冷冻置换电子显微镜观察其超微结构。在未表达pβVpe：：GUS基因的未成熟花粉粒中，液泡的形态与营养细胞中的液泡相似。在生殖细胞形成之前，细胞质中出现了一个大液泡。高尔基体不活跃地产生分泌小泡，即使在细胞壁形成期间也是如此。在开花前的成熟花粉粒中，表达了pβvpe：：GUS基因的花粉中，营养液泡消失，出现了被RER包围的储藏液泡、大量囊泡和脂滴。含有βVPE的贮藏液泡中的物质可用于花粉萌发和花粉管的早期伸长。在盛开的花的花粉中，出现了溶解的液泡。对这种液泡转化与液泡功能的关系进行了讨论。

Arabidopsis has three types of vacuolar processing enzyme homologues ; αVPE, βVPE, and γVPE. The temporal and spatial expression of these VPE genes were detected with GUS histochemical staining of pVPE::gus transformed Arabidopsis plants. The αVPE and γVPE promoters directed the expression in root and leaves. On the contrary, pβVPE::gus gene was strongly expressed in pollen grains. In this investigation, we have clarified the ultrastructural changes of the vacuolar organelle with the pVPE-gus gene-expression. The ultrastructure was examined with cryo-freezing/freezesubstitution electron microscopy. In immature pollen grain, in which pβVPE::gus gene had not been expressed, vacuoles kept similar appearance as those in vegetative cells. A large vacuole was occurred in the cytoplasm just before generative cell formation. Golgi bodies did not actively produce secretory vesicles, even during cell wall formation. In mature pollen grains of the flowers just before bloom, in which pβVPE::gus gene was expressed, the vegetative vacuoles had disappeared and storage vacuoles, many vesicles, and lipid droplets surrounded by rER appeared. The materials in the storage vacuoles with βVPE would be used for pollen germination and early pollen tube elongation. In the pollen of blooming flowers, lytic vacuoles appeared. This vacuole-transformation was discussed in relation to the vacuole functions.