Does pre-culture in sugar-rich media affect carbohydrate content and post-thawing recovery rate of cryopreserved potato (Solanum phureja) shoot tips?

Abstract

Shoot tips of Potato (Solanum phureja) were cryopreserved with the encapsulation-dehydration method, including: coating of shoot tips in calcium alginate beads, pre-culture in a solution containing 0.75 M of sugar (0.1 M of sucrose +0.65 M of another cryoprotectant sugar), and dehydration (for 4.5 h) on silica gel to reduce water content to 21–27%. Regrowth of shoot tips was assessed after freezing in liquid nitrogen. After cryopreservation, coated shoot tips were cultivated on a medium enriched with growth substances to measure concentrations of soluble carbohydrates. Maltose and trehalose ensured a better cryopreservation (88% and 91% of regrowth, respectively). Regrowth rates of potato shoot tips in the presence of polyols were very low and no recovery was obtained after freezing of shoot tips that were pre-cultivated in monosaccharides. Concentration of soluble carbohydrates increased in shoot tips pre-cultivated in sucrose, trehalose or glucose, especially when sucrose was applied as the cryoprotectant. The application of sucrose helped potato shoot-tips to acquire a certain tolerance to dehydration and cryofreezing. The analysis of soluble carbohydrates in potato shoot tips confirmed the accumulation of sugars during the pre-culture process, principally in the form of sucrose. The statistical analysis showed that soluble carbohydrate contents in shoot tips increased when total carbohydrates increased in the cultivation medium. The modelling approach indicated that the contents of soluble carbohydrates increased when pre-cultivation of potato shoot-tips was conducted in sucrose media compared to the control and other sugars. Keywords: Cryopreservation, Pre-culture, Soluble carbohydrates, Liquid nitrogen, Coated shoot tips, Encapsulation-dehydration, Potato