| Summary: | 碩士 === 國立中興大學 === 植物學系 === 89 === 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.
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