Unravelling the effect of sucrose and cold pretreatment on cryopreservation of potato through sugar analysis and proteomics.

Apical shoot tips were dissected from donor plants (cultured in several conditions) and cryopreserved using the droplet-vitrification technique. The effect of two preculture treatments (sucrose pretreatment medium or cold-culturing during two weeks) on donor plants of four potato species (Solanum commersonii, S. juzepcukii, S. ajanhuiri, and Solanum tuberosum) was studied. Post-cryopreservation meristem growth and plant recovery were influenced by the treatments, but the effect on the regeneration was strongly genotype-dependent. The highest post-rewarming plant recovery percentage was obtained using meristems dissected from donor plants of S. commersonii cultured on sucrose pretreatment medium or cold-cultured. Both preculture conditions also enhanced plant recovery in S. juzepcukii compared to control cultures. Cold preculture, however, proved to be undesirable for S. tuberosum whereas sucrose pretreatment had a positive impact on the plant regeneration of this species. The determination of changes in the concentration of soluble sugars revealed sugar accumulation, especially of sucrose and the raffinose family of oligosaccharides (RFOs), which can be linked to tolerance towards the cryopreservation. Additionally, a study of the proteome of the donor plantlets after the pretreatments by 2D-fluorescence difference gel electrophoresis (DIGE) was carried out to identify differentially abundant proteins. Carbon metabolism-related proteins, together with stress-response and oxidative-homeostasis related proteins were the main class of proteins that changed in abundance after the pretreatments. Our results suggest that oxidative homeostasis-related proteins and sugars may be associated with the improved tolerance to cryopreservation and the ability to cold acclimate by S. commersonii in contrast to the other genotypes. The increased accumulation of sucrose and RFOs play a fundamental role in the response to stress in potato and may help to acquire tolerance to cryopreservation.