Studies On The Germination Characteristics Of Populus Euphratica Seed And The Reasons For Rapid Decline Of Seed Viability

Populus euphratic, distributed along the sides of inland rivers, is the only species that can form the forest community in the Northwestern desert regions of China. The desert ecosystems faded the dangers of degrading or even collapsing due to the irrational water utilization by human being. It was an urgent demand to protect Populus euphratica population from endangering. In the thesis, studies on germination characteristics and the reasons of seed viability decline of Populus euphratica seed were presented, and these data would provide theoretical evidence for artificial forestation.1. Light microscopy and scanning electron microscopy and transmission electron microscopy were used to observe morphological structures of Populus euphratica seed. Result Showed: a mature seed included seed coat, cotyledon and embryo. The structure of seed coat was consisted of singal or multi-layers of parenchyma cells. The cell walls had obviously intercellular connection and the inside cell walls was evidently thickened. The mature Populus euphratica seed was composed of two pieces of cotyledons which joined with the hypocotyle. The cotyledon was composed of vascular bundle tissue and parenchyma cells which were approximate circular and lots of cell population. The epidermal cells of cotyledon arranged compactly and regularly, and transverse section cells were almost quadrate, the inclusion of them was enriched and stained deeply. In submicroscopic structure of mature non-germinated seed, the cell inclusion was mainly contained protein bodies and lipid bodies. The protein bodies, composed of crystalloid and protein stroma, were surrounded by many lipid bodies which were filled up with the whole cell. Exception of above two types of bodies, other organelles were almost not observed in the seed cells.2. Populus euphratica Oliv. seeds with pappus were beneficial to prolong its viability under room temperature condition. Germination percentage of pappus seeds did not decreased obviously after 20 d storage. The activities of peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) were increased during the early days of storage, then decreased. Slightly different with dehydrogenase, its activity increased first followed by decreasing, then with another slightly increasing. Acid phosphoesterase activity would decrease with seed germination percentage decreasing. Polyphenol oxidase activity remained stable in earlier stage, and rose obviously in middle stage, and decline rapidly in later period. After 40 days, germination percentage of the seeds with pappus still remained 23.3% under room temperature condition.3. Populus euphratica seeds with different germination rate were employed as experimental materials. The study of continuous zymogram change of esterase isozyme, peroxidase isozyme and superoxide isozyme were investigated before and after germination. The results indicated: (1) With the imbibition seed, esterase isozyme was expressed and with the highest activity in seeds with middle germination rate; peroxidase isozyme didn't express; superoxide isozyme did expressed, but not in seeds with high germination rate. (2) With dry seed, esterase isozyme did not express; while peroxidase isozyme and superoxide isozyme expressed, the highest activity of peroxidase isozyme displayed in seeds with middle germination rate.