The uhrastructure and intercellular connection of the sugar unloading zone (i. e. the phloem in the dorsal vascular bundle and the phloem-surrounding the assimilate sink-cells) of grape ( Vitis vinifera x V. labrusca cv. Jingchao) berry was observed via transmission electron microscopy. The results showed that during the early developmental stages of grape berry, numerous plasmodesmata were found in the phloem between sieve element (SE) and companion cell (CC), between SE/CC complexes, between SE/CC complex and phloem parenchyma cell and in between phloem parenchyma cells, which made the phloem a symplastic integration, facilitating sugar unloading from sieve elements into both companion cells and phloem parenchyma cells via a symplastic pathway. On the contrary, there was almost no plasmodesma between phloem and its surrounding flesh photoassimilate sink-cells, neither in between the flesh photoassimilate sink-cells giving rise to a symplastic isolation both between phloem and its surrounding flesh photoassimilate sink-cells, as well as among the flesh photoassimilate sink-cells. This indicated that both the sugar unloading from phloem and pestphloem transport of sugars should be mainly via an apoplastic pathway. Dining the ripening stage, most of the plasmodesmata between SE/CC complex and the surrounding phloem parenchyma cells were shown to be blocked by the electron-opaque globules, and a phenomenon of plasmolysis was found in a number of companion cells, indicating a symplastic isolation between SE/CC complex and its surrounding parenchynm cells during this phase. The symplastic isolation between the whole phloem and its surrounding photoassimilate sink-cells during the early developmental stages shifted to a symplastic isolation within the phloem during the ripening phase, and thus the symplastic pathway of sugar unloading from SE/CC complex during the early development stages should be replaced by a dominant apoplastic unloading pathway from SE/CC complex in concordance.
葡萄果肉同化物卸载区细胞间的共质体联系与隔离
夏国海1 张大鹏1,2*
（1.中国农业大学果树分子发育生物学实验室，北京100094；2. 中国农业大学农业部植物生理生化重点开放实验室，北京100094）
摘要：应用透射电镜技术对葡萄果肉同化物卸载区细胞 (周缘维管束韧皮部及其周围同化物库细胞 )的超微结构及胞间联系进行了系统观察。结果表明 :在葡萄果实发育前期 ,韧皮部筛分子 (SE)与伴胞 (CC)之间、SE/CC复合体之间、SE/CC复合体与韧皮薄壁细胞之间、以及韧皮薄壁细胞相互之间都有十分丰富的胞间连丝 ,因此 ,韧皮部内细胞之间形成了一个共质体紧密联系的整体。但是 ,韧皮部细胞与相邻的果肉库细胞之间、以及果肉库细胞相互之间几乎不存在胞间连丝 ,说明韧皮部与周围果肉库细胞之间、以及果肉库细胞相互之间形成了共质体隔离。在果实成熟期 ,筛管与伴胞和周围韧皮薄壁细胞间的胞间连丝都被深色颗粒状物质堵塞 ,许多伴胞也发生质壁分离 ,这些特征标志着SE/CC复合体与周围薄壁细胞间的共质体联系被阻断 ,果实发育前期的整个韧皮部与周围同化物库细胞之间的共质体隔离 ,演变为韧皮部内部SE/CC复合体与周围细胞之间的共质体隔离。根据果实周缘维管束韧皮部细胞与周围细胞的超微结构变化和胞间联系特点 ,对葡萄果实同化物卸载的细胞学路径进行了讨论。
关键词： 韧皮部；胞间连丝；同化物卸载；葡萄果肉
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