Propagation Of Dendrobium Protocorm Like Body And Its Dissication Tolerance Induced By ABA

In this thesis,tissue culture of Dendrobium nobile L .and Dendrobium candidum Wall, ex Lindl. as well as the desiccation tolerance of protocorm like body(PLB) of D. candidum induced by ABA and its mechanism were studied.The results are as follows: 1.TISSUE CULTURE OF D. NOBILE L. AND D.CANDIDUM Wall.ex Lindl.We have got germ-free seedlings of D. candidum at MS medium without any phytohormone by mature seed. It was better for PLB induction on medium of 1/2MS with TDZ and NAA, 6-BA would result in differentiation at the same time. The repropagation rate was almost the same while PLB was transfered to 1/2MS + 0.1mg/L NAA + 3%sucrose and 1/2MS + 3%sucrose.But the PLB on medium without NAA showed worse in quality.The best result was obtained while young stems were used as explant . Although it was easy to induce the growth of axillary buds, the small quantity might restrict in practice use. There were many disadvantages when old stems were used as explant, because of the difficulty in sterilizing and to inducing the growth of axillary buds. But the quantity advantage was showed up by pretreatment and improved sterilizing method. The growth rate of Axillary buds was rose while a medium choised from a cross test, contained 0.1mg/L NAA and 1mg/L 6-BA, was used.2.STUDIES OF DESICCATION TOLERANCE OF D. CANDIDUM PLB INDUCED BY ABA AND ITS MECHANISMDesiccation tolerance of D candidum PLB was induced by ABA preculture at a concentration below 50μmol/L. The best result was obtained while ABA concentration is 5μmol/L and the duration of preculture was 24h. PLB viability rate was 10 times higher than the control after 2h desiccation.Detection results of cytoplasmic osmoticums showed that ABA preculture could not induce the accumulation of sucrose and proline etc. But the content ofpolysaccharide rose conspicuously. So we think that the accumulation of polysaccharide may play an important role in desiccation tolerance induced by ABA preculture.Starch grain degradation were obtained in microstructure research during ABA preculture . It may relate to the accumulation of substances which take role in desiccation tolerance. As detection results of cytoplasmic osmoticums showed that only polysaccharide was accumulated. It suggested that the accumulation of polysaccharide may take role in desiccation tolerance induced by ABA.The mitochondrion, chloroplast and vacuolus membrane of ABA precultured PLB kept a better status than control after desiccation. Although slight plasmolysis was occurred, they have almost no changes in shape after ABA preculture. The cellstructure retained better after desiccation but plasmolysis became more seriously. In spite of the plasmolysis was not obtained in control PLB, plasma membrane was seriously destructed after desiccation. This results showed that the plasmolysis during ABA preculture may be related to the desiccation tolerance induced by ABA.116 differential cDNA fragments were choiced from DD gels. After examining by Northern blot of some differential fragments, 3 cDNA fragments were proved to be positive. One of which was inhibited by ABA, another was promoted and the third was induced by ABA preculture.Homologous analysis showed that none of this three cDNA fragment hashomologous gene. So it is difficult for us to suggestion its possible function. As it may relate to desiccation tolerance induced by ABA , further studies would give us more result significance.