Studies On Biological Mechanism Of Desiccation Sensitivity Of Seed In Ginkgo(Ginkgo Biloba L.)

Recalcitrant Ginkgo seeds had the characters of desiccation sensitivity.Two represent species were selected to study the changes of seed vigor,activity of Reactive-oxygen-scavenging Enzymes, content of hormone,specific protein and content of inclusion in desiccation. Upon them severaltypical period of desiccation were chose to research the physiologicalmechanism by microstructure and ultrastructure observation. The main resultswere as follows:1.The changes of vigor in Ginkgo seeds with desiccationWith the lost of water, the germination percentage, vigor index,germination energy, germination index decreased rapidly. The germinationpercentage of LongYan and MeiHe respectively got to 85.1% and 90.5% whenthe moisture content was in 50%. The germination percentage of LongYan andMeiHe decrease under 10% when the moisture content below 30%. Thechange tendency of vigor of big-scale seed of LongYan and small-scale seedof MeiHe was in a same.Desiccation over freeze-dry-machine fast while desiccation over CaO wasslow in the two styles of desiccation. It was just needed seven days to makethe moisture content below to7% with cold-dry-machine ,while is was needed55 days to make the moisture content below to the same level with CaO. Nomatter what styles of desiccation, the vigor guideline was decreased all thetime, but the decrease tendency of desiccation over freeze-dry-machine wascomparatively smoothly.2.The changes of activity of Reactive-Oxygen-Scavenging Enzymes in Ginkgoseeds with desiccation.In the desiccation of Ginkgo seeds, the tendency of the activity of peroxidase (POD) was increased and then decreased. activity of POD get to the peak when the moisture content decreased to 30%. The activity of POD decreased rapidly when the moisture content below 30%. The activity of POD in embryo is higher than in endosperm. No matter in embryo or in endosperm, the change tendency of superoxide dismutase (SOD) and catalase (CAT) was decreased-increasde-decreased. The change tendency in the activity of CAT and SOD in big-scale seed of LongYan and small-scale seed of MeiHe was in a same. With the lost of water, the content of malonaldehyde (MDA) in embryoand endosperm increased. The rate of electrolyte leakage increased and seedvigor decreasd rapidly. Furthermore, the content of MDA in embryo is higherthan in endosperm. The change tendency in the content of MDA in big-scaleseed of LongYan and small-scale seed of MeiHe was in a same. The change tendency of the activity of POD, CAT and SOD overfreeze-dry-machine was comparatively smoothly. The activities of POD, CATand SOD of Ginkgo seeds over CaO were higher than over freeze-dry-machineat earth desiccation stage; the activities of POD, CAT and SOD of Ginkgoseeds over freeze-dry-machine were higher than over CaO when moisturecontent below 30%. 5. The changes of ABA content with desiccation ABA had the ability of promoting seeds development, preventing seeds premature and germinate, inducing desiccation tolerance of seeds. With the lost of water, the endogenous ABA content of Ginkgo seeds decreased all the time. The cause of desiccation sensitivity of Ginkgo seeds might be the high moisture contend and low ABA content. 6.The changes of inclusion content with desiccation The content of soluble sugar in endosperm decreased, while the contentof soluble sugar in embryo increased slightly. At earth desiccation stage. thecontent of soluble sugar in endosperm increased, while the content of soluble...