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ISHS Acta Horticulturae 908: I International Symposium on Cryopreservation in Horticultural Species

THERMAL ANALYSES BY DIFFERENTIAL SCANNING CALORIMETRY FOR CRYOPRESERVATION OF POTATO SHOOT TIPS

Authors:   A. Kaczmarczyk, C. Zanke, A. Senula, M. Grübe, E.R.J. Keller
Keywords:   DMSO droplet method, S. tuberosum 'Désirée', S. demissum, crystallization, glass transition
DOI:   10.17660/ActaHortic.2011.908.2
Abstract:
Differential scanning calorimetry (DSC) belongs to thermal analysis methods that can be used for measurement and determination of glass transition phases and crystallization in tissues used for cryopreservation. The aim of this study was to analyze the physical state of water in potato shoot tips during cooling and rewarming applying the DMSO droplet method. Results should give insight into the function of the method. Thermal characterization was done with freshly isolated and cryoprotected shoot tips as well as for the applied solutions. Two accessions were compared. These were the frost-resistant, wild potato Solanum demissum and the frost-sensitive, cultivated potato S. tuberosum ‘Désirée’. Influence of cooling rate on thermal characteristics of free water was compared for slowly (10°C/min) and ultra-rapid (ca. 12.000°C/min) directly in liquid nitrogen quenched samples. Results showed glass transitions for the 10% DMSO solution and cryoprotected samples of S. tuberosum ‘Désirée’. In contrast, S. demissum did not show glass transition. Freshly isolated and cryoprotected shoot tips as well as the cryoprotectant solution proper showed melting of ice during rewarming. Of the three investigated materials, the amount of freezable water was the smallest in the cryoprotected samples. It can be concluded that DMSO lowers the freezing point and the amount of freezable water in the tissue. The comparison of cooling rates in S. tuberosum ‘Désirée’ showed two glass transition phases during rewarming of the samples cooled directly in liquid nitrogen in comparison to one transition in samples cooled within the DSC device. Therefore, it can be concluded that the DMSO droplet method is based on ultra-rapid cooling with partial ice formation in the tissue.

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