小麦颖果腹部维管束韧皮部细胞的超微结构与功能分析

Ultrastructure and Its Function of Phloem Cell in Abdominal Vascular Bundle of Wheat Caryopsis

利用透射电镜技术 ,对小麦颖果发育过程中韧皮部细胞的超微结构进行了观察和分析。结果表明 ,在颖果发育的早期和中期 ,韧皮薄壁细胞与伴胞、中间细胞间 ,以及韧皮薄壁细胞之间都有丰富的胞间连丝。筛分子 (SE)与伴胞(CC)间、SE CC复合物之间、筛分子与韧皮薄壁细胞间缺少胞间连丝。但SE和CC与中间细胞间、以及中间细胞相互之间均有丰富的胞间连丝。筛分子内有较丰富的线粒体、P 型质体 ,有些筛分子有珠光壁。伴胞有稠密的胞质和核质 ,电子染色深。中间细胞也有稠密的胞质 ,且沿胞壁分布。中间细胞与周围细胞间有胞间连丝 ,并且中间细胞间有分枝状胞间连丝通道 ,说明中间细胞是一种适应于共质体运输的特化伴胞。在颖果发育后期 ,筛分子内含物消失 ,线粒体数量减少。伴胞和韧皮薄壁细胞电子染色变浅 ,但中间细胞内仍有丰富的线粒体 ,且形成类似筛分子的结构 ,可能在颖果灌浆后期起重要作用。根据韧皮部细胞的超微结构特点和胞间连丝的分布 ,对光合同化物在颖果韧皮部的卸载和运转途径进行了分析。

The ultrastructure of phloem cell in developing wheat( Triticum aestivum L )caryopsis was investigated and analyzed by transmission electron microscopy during the entire developmental process of the fruit. The results showed that, during the early and middle developmental stages of caryopsis, numerous plasmodesmata were found between phloem parenchyma cells and companion cells (CCs), between intermediary cells, and between phloem parenchyma cells. There was short of plasmodesma between SE and CC, between SE/CC complexes and between SEs and phloem parenchyma cells; but there were numerous plasmodesmata between SEs and intermediary cells, between CCs and intermediary cells. The SEs were rich in mitochondria, P type plastids, and some SEs had nacreous wall. CCs contained electron-dense protoplasm and nucleus. Intermediary cells also contained electron-dense protoplasm distribution along intermediary cell wall. Numerous plasmodesmata were found between intermediary cells and surrounding cells, and there were some furcated plasmodesmata channels between two intermediary cells, indicating that intermediary cells might act as some special companion cells that suited to symplastic transport. During the later developmental stage of caryopsis, the substance in SEs disappeared and the number of mitochondria decreased. The CCs and phloem parenchyma cells contained electron-light protoplasm, but intermediary cells still contained numerous mitochondria to form a similar structure to SE, suggesting that intermediary cell had an important function during later filling stage. The photoassimilate unloading and transport path in phloem was analyzed according to the ultrastructure of phloem cells and the distribution of plasmodesmata.