【摘要】 利用透射电镜技术 ,对发育过程中的苹果 (MalusdomesticaBorkh)果实韧皮部及其周围薄壁细胞的超微结构进行了观察研究。结果表明 ,在主脉和细脉的筛分子 (SE)和伴胞 (CC)之间存在胞间连丝 ,胞间连丝在筛分子一侧是单通道 ,在伴胞一侧呈多分枝通道。在细脉中筛分子小 ,伴胞大 ,在主脉中则是筛分子大 ,伴胞小。伴胞内胞质和核质稠密 ,富含线粒体、内质网和高尔基体 ,液泡内往往呈现多膜包被的囊泡结构 ,有时还可以看到壁旁体。细脉中伴胞的内膜有轻微内陷。细脉和主脉的筛分子腔内均存在类似囊泡的结构和丝状不定形物。主脉中筛分子胞壁往往形成珠光壁 ,内含大量的淀粉型质体。筛分子和伴胞与周围薄壁细胞之间几乎不存在胞间连丝 ,形成了SE/CC复合体与周围薄壁细胞间的共质体隔离。在韧皮薄壁细胞之间存在大量的胞间连丝 ,在果肉普通薄壁细胞之间也存在着大量的胞间连丝 ,韧皮薄壁细胞与果肉普通薄壁细胞之间也有丰富的胞间连丝联系。综合观察结果认为 ,苹果果实中同化物的SE/CC复合体卸出 ,可能以质外体卸出为主 ;而同化物卸出后的运输积累过程则可能是共质体和质外体途径并存的过程。更多还原

【Abstract】 The ultrastructure of phloem and its surrounding parenchyma cells in the developing apple (Malus domestica Borkh) fruit was for the first time systematically investigated through transmission electron microscopy during the entire developmental process of the fruit. The results showed that plasmodesmata exist at the thickened part of the cell wall between the sieve elements (SEs) and companion cells (CCs) both in the minor and main veins, with the plasmodesmata being furcated at the CC side and keeping a single oriface at the SE side. In the minor veins the SEs are smaller than the CCs, while the reverse seen in the main veins. The CCs contain electron_dense protoplasm and nucleus, and are enriched with mitochondria, endoplasmic reticulum and Golgi apparatus or dictyosomes in their cytoplasm; and they also contain some paramural bodies at the cell wall adjacent to SE and numerous vesicles in their vacuoles. In the minor vein there is a slightly invagination of the plasmalemma of CC into the protoplasm. Many vesicles and microfibril_like structures exist in the SEs of both minor and main veins. In the main veins the cell wall of SEs often become thickened to create a nacreous wall, and a great deal of starch_typed plastids are present in the SEs. There is almost no plasmodesmata between the SE/CC complex and its surrouding phloem parenchyma cells, resulting in the symplastic isolation between them, which may be associated to apoplastic transportation. Plasmodesmata were found numerous both between phloem parenchyma cells and between flesh parenchyma cells (non_phloem parenchyma cells), as well as between phloem parenchyma cell and flesh parenchyma cell. The relationships between the ultrastructure of the fruit phloem and its surrounding parenchyma cells and the photoassimilate unloading pathway in the developing apple fruit are discussed. It is considered that the apoplastic unloading may be the main pathway of the photoassimilates unloaded from SE/CC complex, and that the apoplastic and symplastic pathways may coexist during postphloem transport of photoassimilates in the developing apple fruit.更多还原