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Effects of sucrose pretreatment and cold acclimation on the tolerance to vitrification solution (PVS2) and the changes of physiological properties of cassava
|摘要:||本試驗以樹薯(Cassava; Manihot esculenta Crantz)組織培養苗為材料，主要目的在研究最適合樹薯莖頂之冷凍保存冷馴化處理時間。測定冷馴化處理下之各項生理變化及其意義，證明0.3 M蔗糖配合15C冷馴化一~二週，可提高樹薯莖頂對超低溫冷凍保存流程中玻璃化溶液(PVS2)的忍受能力。
樹薯莖頂經冷馴化處理而累積滲透溶質，降低滲透潛勢。累積的溶質包括sucrose、proline及soluble protein。由sucrose及proline在低溫處理下累積的time course圖型，間接推測冷馴化最佳處理時間為15C冷馴化一~二週，與膜系顯現出對低溫適應性的時期吻合。Sucrose及proline可能具有維持低溫下膜系及蛋白質穩定的功能。此外，soluble protein含量因冷馴化處理而增加，但趨勢並不穩定。
This study investigates the suitable period of cold acclimation for cryopreservation of cassava (Manihot esculenta Crantz). Measurement of several physiological parameters showed that cassava shoot tips treated with 0.3M sucrose in accompanied with cold acclimation at 15℃ for one to two weeks enhanced the tolerance to vitrification solution (PVS2) used for cryopreservation. Ion leakage and MDA production of cassava shoot tips decreased during one to two weeks acclimation period. The results suggested that lipid peroxidation declined and the structure of membrane acclimated to low temperature. As the time of cold treatment persisted, ion leakage and MDA production rose gradually suggesting the damage of membrane system by prolonged low temperature treatments. System of cellular antioxidation cannot be activated by cold acclimation successfully. With the exception of the activity of SOD increasing continuously, the activities of APX, MDHAR, DHAR and GR did not increase along with the extending period of cold acclimation. As the results from the activities of antioxidative enzymes, antioxidant system of cassava shoot tips did not effectively scavenge the reactive oxygen radicals generated by low temperature treatment including the ability of scavenging H2O2 and generation of ascorbate. This may be one of the reasons that leaded to the decreased tolerance to PVS2 after cold acclimation for more than two weeks. The accumulation of osmoregulatory solutes leaded to the decrease of osmotic potential. The solutes accumulated include sucrose, proline and soluble protein. The time course of sucrose and proline accumulation under low temperature suggested that the most suitable period of cold acclimation treatment is at one to two weeks at 15℃, that match the period of the membrane to adapt low temperature. Sucrose and proline may have the ability to stabilized the structure of proteins and membrane under low temperature but the trends of increase was not steady. Based on the results shown above, treatment of 0.3 M sucrose and cold acclimation one to two weeks at 15℃ can enhance the tolerance to vitrification solution (PVS2) of cryopreservation. The results presented here can be used as a model for pretreatment of cassava cryopreservation.
|Appears in Collections:||生命科學系所|
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