Physiological And Biochemical And Structure Characteristics Of Chrysanthemum Shoot Tips During Cryopreservation

Chrysanthemum is one of the most important global cut flower. Chrysanthemum originated from China and there are rich genetic resources in China. The traditional conservation methods are always costly and laborious. In this thesis, two chrysanthemum cultivars, 27-2 and 31-12,are tested to investigate dehydrogenase activity,histological and ultrastructural changes of shoot tips during cryopreservation, as well as to study physiological changes during preculturing of shoot tips.The results are as follows.1. Compared the effects of different sucrose concentration and preculture time,different sucrose concentration with manital or sorbitol,different DMSO medium on chrysanthemum shoot tips. The results showed that 0.7 mol·L^-1Suc and 10 days is suitable for chrysanthemum. MS+0.3 mol·L^-1Sucrose+0.2 mol·L^-1Sorbital was better than the others. DMSO was unsuitable for the shoot tips of chrysanthemum.2. Experiments were conducted about dehydration time with PVS2,thawing temperature and time,washing method,recovery medium. The suitable dehydration time for 27-2 was 60%PVS2 60min and PVS2 10min, 60%PVS2 10min and PVS2 60min for 31-12.Thawing in a water bath (25°C,2min) and washing with 1.2 mol·L^-1 sucrose MSliquid medium(twice,10min each) can promote survival rate. The suitable recovery medium was MS+0.1%AC.3. The water content,soluble sucrose content and four antioxidant enzyme activities in shoot tips of chrysanthemum were measured after preculturing on different sucrose concentration medium and for different time. The results showed that with increasing of sucrose concentration and preculture time, the water content decreased and the soluble content increased. Antioxidant enzyme activities increased after sucrose preculture. As such, sucrose preculture enhanced chilling resistance of shoot tips of chrysanthemum.4. The histological studies showed that PVS2 was harmful to the shoot tips of chrysanthemum, preculture can reduce the injury caused by PVS2.Cryopreservation by liquid nitrogen and thawing seriously hurt the shoot tips. Cells of parenchyma were broken after cryopreservation, some area even became empty.The cell of apical meristem were not broken after cryopreservation, it is suggested that the activityty dividing cells have the higher chilling resistance than the others.5. Ultrastructure of cells of chrysanthemum shoot tips was observed. Preculture enhanced chilling resistance of celts,with smaller vacuoles and denser cytoplasm. Encapsulation with Sodium-alginate acid reduced the injury caused. by PVS2 cryopreservation by liquid nitrogen and thawing,which reliefed the degradation of cell nucleus. Cells were still seriously damaged during the freezing and thawing process, which could not be repaired and accounted for the death of cells.The cell organelles were degradating step bu step during recovery culture.The pretreatment before cryopreservation protected the cell and kept the cell wall to be completed after cryopreservation.