Studies On Sugar Unloading And Transport Mechanism In Ziziphus Jujuba Mill Cv.Lingwuchangzao Fruit

Ziziphus jujube Mill cv.lingwuchangzao fruit was sweet and refreshing and rich in multiple minerals and vitamins, was an excellent variety of Nningxia fresh jujube with local characteristics. Yield and quality of jujube fruit largely depend on kinds and amount of sugar accumulation in fruit, but the ways of phloem unloading also influence the accumlulation of fruit sugar. In this study, we selected Ziziphus jujube Mill cv.lingwuchangzao fruit as test materials, applied plant anatomy, phytochemistry and plant physiology and so on, used paraffin section techniques, ultramicrotomy, chromatography and other means. The ultrastucture of phloem and its surrounding parenchyma cells, the distribution and changes of ATPase subcellular in different developmental stages of Ziziphus jujube Mill cv.lingwuchangzao fruit was respectively observed and analysed. Physiological mechanisms after the phloem sugar transport and the ability of the sugar transmembrane transport were studied and the cytology ways of vascular bundle phloem and its surrounding parenchyma cells unloading were explored. The results showed that:1. The Ziziphus jujube Mill cv.lingwuchangzao fruit consisted of exocarp, mesocarp and endocarp and it was a drupe. The vascular bundles were mainly distributed in mesocarp and the number of vascular bundles in the same field of vision gradually decreased with fruit maturation and volume growth. The ultrastructural structures of Ziziphus jujube Mill cv.lingwuchangzao fruit was researched and the results showed that the unloading of photoassimilates from sieve tube element was symplast pathway in the first rapid growth Rl and adopted apoplastic pathway after unloading into vacuole storage and utilization.In the S2 period, the unloading transportant of photoassimilates took the symplast and apoplastic concomitant pathway. Transportation of photoassimilates from sieve tube element to storage parenchyma cells was apoplastic pathway based in the R2 period of fruit development.2. Fruit wafers were treated by PCMBS (carrier inhibitor) and EB, DNP, NO3- (ATPase inhibitors), and the results found that the transportation of Ziziphus jujube Mill cv.lingwuchangzao fruit sugar after unloading was an active transport that required carrier coupled with ATPase in slow growth period S1, the first rapid growth period R1, the second rapid growth period R2 and slow growth period S3. Transportation of fruit sugar existed simultaneously active and passive transport in slow growth period S2. These indicated that the photoassimilates unloading pathway in phloem existed differences in different developmental stages of fruit.3. Maturity period fruit mainly accumulated sucrose and the ratio of reducing sugar and sucrose was 1.2:1. The research of plasma membrane, V-ATPase and V-PPase activities in different developmental stages of fruit indicated that the change of p-ATPase activity was low-high-low-high-low trend. And the P-ATPase provided a driving force for sugars across the plasma membrane transport by using energy of ATP produced. The variation trend of tonoplast H+-ATPase activity was similar to tonoplast H+-PPase activity during fruit development. Tonoplast H+-PPase activity was higher throughout than tonoplast H+-ATPase activity except the second rapid growth period R2. And the tonoplast H+ gradient that was generated by these enzymes provided a motive power for sugar transportation in tonoplast.4. The distribution of phloem ATPase in different developmental stages of fruit display:In the first rapid growth R1 of fruit, ATPase reaction was mainly distributed in plasma membrane, vesicle membrane and nuclear membrane of various cells. In slow growth period S2, ATPase reaction was concentrated in where vesicular transported activily of phloem parenchyma cells and plasma membrane and plasmodesmata of pulp plasmodesmata cells. ATPase activity was higher in plasma membrane, tonoplast, vesicle membrane, cytoderm and intercellular space in the second rapid growth R2 of fruit. They both provided energy supply for apoplastic pathway of after the phloem sugar transport.In summary, the unloading and transportant of Ziziphus jujube Mill cv.lingwuchangzao fruit sugar were distinct in different developmental stages of fruit. Photoassimilates took symplast pathway from sieve tube element unloading in the first rapid growth R1 and adopted apoplastic pathway after unloading into vacuole storage and utilization. In the slower growth period S2, the unloading and transportation of photoassimilates took the symplast and apoplastic concomitant pathway. The discharge and after the phloem sugar transport of the photoassimilates all adopted mainly apoplastic pathway in the second rapid growth period R2. In other words, the photosynthetic products unloaded through the molecular sieve by symplastic-symplastic and apoplastic coexistence-apoplastic pathway; then turned apoplastic-symplasic and apoplastic-apoplatic pathway into the vacuole for storage and use.