Genetic analysis of D-xylose metabolism by endophytic yeast strains of Rhodotorula graminis and Rhodotorula mucilaginosa

Two novel endophytic yeast strains, WP1 and PTD3, isolated from within the stems of poplar (Populus) trees, were genetically characterized with respect to their xylose metabolism genes. These two strains, belonging to the species Rhodotorula graminis and R. mucilaginosa, respectively, utilize both hexose and pentose sugars, including the common plant pentose sugar, D-xylose. The xylose reductase (XYL1) and xylitol dehydrogenase (XYL2) genes were cloned and characterized. The derived amino acid sequences of xylose reductase (XR) and xylose dehydrogenase (XDH) were 32%∼41% homologous to those of Pichia stipitis and Candida. spp., two species known to utilize xylose. The derived XR and XDH sequences of WP1 and PTD3 had higher homology (73% and 69% identity) with each other. WP1 and PTD3 were grown in single sugar and mixed sugar media to analyze the XYL1 and XYL2 gene regulation mechanisms. Our results revealed that for both strains, the gene expression is induced by D-xylose, and that in PTD3 the expression was not repressed by glucose in the presence of xylose

Effect of vacuum infused cryoprotectants on the freezing tolerance of strawberry tissues

Whole strawberries were vacuum infused with cryoprotectants to improve their freezing tolerance. The strawberries were infused with 12 g/100 g trehalose solution; 0.2 g/100 g cold-acclimated wheatgrass solution (AWWE) containing antifreeze protein (AFP) or combination of 12 g/100 g trehalose with 0.2 g/100 g AWWE under vacuum for 14 min. The fruits were frozen in liquid nitrogen and thawed at room temperature before being evaluated for cell viability, drip loss and preservation of texture. The results showed that the combined effects of both cryoprotectants significantly improved the freezing tolerance of the treated strawberries. The cryoprotection effect was influenced by the heterogeneity of the tissues in the fruits

Cryoprotective treatment of strawberries

Whole strawberries were impregnated using vacuum infusion with different cryoprotective solutions to improve their freezing tolerance. The cryoprotective solutions used were: 12% (w/w) trehalose solution; 0.2 % (w/w) cold acclimated wheatgrass solution (AWWE) containing antifreeze protein (AFP) and combination of 12% (w/w) trehalose with 0.2 % (w/w) AWWE. The strawberries (70±5 g) were immersed in the coresponding solution under vacuum for 14 min. After the infusion the fruits were removed from the solution, blotted, dipped in liquid nitrogen for 25 s to freeze and then thawed for 2 h at room temperature. The quality of the strawberries after one freezing/thawing cycle was evaluated trough determination of the cell viability, drip loss, colour loss and preservation of texture firmness. The cryoprotective effect of the solutions depended on the heterogeneity of the tissues in the fruit. The results proved that there was evident reduction in the drip loss of the strawberries by using the combined effects of both cryoprotectants. Furthermore this combination significantly improved the overall freezing tolerance of the treated fruits, by obtaining cell viability in most of the tissues; reducing the colour loss to non-significant level when compared to the fresh strawberries and preserving the flesh firmness