Ultrastructures of phloem and its surrounding parenchyma cells in the developing Zizyphus jujuba Mill.cv Dongzao fruit

The ultrastructures of phloem and its surrounding parenchyma cells in jujube(Zizyphus jujuba Mill.cv Dongzao) fruit were systematically investigated using transmission electron microscopy during the whole developmental process of fruit.The results showed that only a few plasmodesmata(PD) existed between the SE/ CC complex and its surrounding phloem parenchyma cells at the early and late stage of jujube fruit development,while the number of PD increased at the middle stage,suggesting a possible shift of the phloem unloading pathway of photoassimilates in the developmental jujube fruit.The companion cells contained plenty of organelles such as mitochondria,endoplasmic reticulum,and golgi apparatus.Plenty of vesicles were found between SE/CC complex and its surrounding phloem parenchyma cells at the early stage.There were also abundant organelle in phloem parenchyma cells including mitochondria,endoplasmic reticulum,golgi apparatus,and vesicles which began to dissolve at the late stage,suggesting that metabolism and transport capacity changed in phloem parenchyma cells with the fruit development.