Phloem Unloading And Sugar Accumulation In Chinese Jujube Fruit

Phloem unloading is believed to play a key role in the partitioning of photoassimilates.Sugar varieties and content have important influence on fruit quality and taste. Jujube(Ziziphus jujuba Mill.) belonging to the genus of Ziziphus in Rhamnaceae is one of the most important economic tree species in china.To understand the anatomic and sugar accumulation in jujube fruit, dry jujuba cultivar Ziziphus jujuba Mill. cv Muzao and dual-purpose cultivar Goutouzao fruit were used for study. The anatomic of vascular bundles were studied by dying method and paraffin section technology. The pathway of phloem unloading was studied in developing jujube fruit by electron microcopy. Using the high performance liquid chromatography detected fructose,glucose, sucrose contents in fruit development.The main results were as follows:(1) The dying imaging showed that jujube fruit vascular bundles had three distribution types : bundle in kernel, endocarp bundle and mesocarp bundle. All these bundles were developed from the 12 bundles in pedicel, 2 of them developed into bundle in kernel, the others 10 developed into another two types of vascular bundles. The phloem of jujube fruit vascular bundles developed well. Paraffin section showed that jujube vascular bundles belonged to collateral and open vascular bundle genre.(2) Structural investigations showed that plasmodesmata existed between sieve elements and companion cells, sieve element-companion cell complex and surrounding parenchyma cells, parenchyma cells themselves, fruit cells themselves. Plasmodesmata density between sieve element-companion cell complex and surrounding parenchyma cells varied obviously in different develop stages, having more plasmodesmata and higher plasmodesata density in middle stage than early and stage in both cultivars.(3) The sugar detection showed that fructose, glucose and total sugar content in development of Goutouzao and Muzao, as 0~60 days after bloom changed slightly, 60 days later accumulated quickly until fruit matured. Sucrose content showed a different change in both jujube cultivars. In the ripen stage, sugar content in Goutouzao were sucrose>fructose>glucose, Muzao were sucrose>glucose>fructose; all the sugar content inMuzao were higher than Goutouzao but sucrose content. Fruit mainly accumulated fructose and glucose in the early and middle stage while accumulated sucrose at late stage.In conclusion: jujube fruit followed a aplplasmic — symplasmic — aplplasmic phloem unloading pathway with no difference between different jujube cultivars. Sugar contents changing may have effect on phloem unloading pathway, aplplasmic phloem unloading pathway maybe a good choice for the fruit to accumulate high levels of sugar in the late stage.