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

拟南芥有三种类型的空泡加工酶同源物；αVPE, βVPE, γVPE。利用GUS组织化学染色检测这些VPE基因在拟南芥植株中的时空表达。αVPE和γVPE启动子在根和叶中表达。相反，pβVPE::gus基因在花粉粒中强烈表达。本研究阐明了pVPE-gus基因表达对液泡细胞器超微结构的影响。用冷冻/冷冻取代电镜观察超微结构。在未表达pβVPE::gus基因的未成熟花粉粒中，液泡保持了与营养细胞相似的外观。在生殖细胞形成前，细胞质中出现一个大液泡。即使在细胞壁形成过程中，高尔基体也不积极产生分泌囊泡。在pβVPE::gus基因表达的开花前成熟花粉粒中，营养液泡消失，出现了被rER包围的储存液泡、许多囊泡和脂滴。含有β - vpe的贮藏液泡内的物质可用于花粉萌发和早期花粉管伸长。在开花的花粉中，出现了裂解液泡。从液泡函数的角度讨论了这种液泡转换。

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.