Changes in cell wall polysaccharides and cell wall degrading enzymes during ripening of Fragaria chiloensis and Fragaria cananassa fruits

摘要

Chilean strawberry (Fragaria chiloensis) is arising as a new fruit crop that can diversify the world supply of berries. Fruit softening is thought to be linked to an extensive modification of pectin and hemicellulosic cell wall fractions which in turn is determined to a great extent by the action of some cell wall-modifying enzymes. The objective of this work was to compare cell wall changes and the enzyme activities of pectin methylesterase (PME), polygalacturonase (PG), endoglucanase (EGase), l-arabinofuranosidase (AFase), o-galactosidase (oGal), and o-xylosidase (oXyl) between F. chiloensis and Fragaria cananassa (cv. Chandler) at three fruit developmental stages: large green (LG), turning (T) and ripe (R). A rapid decrease in fruit firmness between LG and T stages was observed in both species; nevertheless firmness reduction in F. chiloensis was steeper than in F. cananassa. This could be related to a faster loss of HCl-soluble polymers (HSP fraction) presented in F. chiloensis fruit. However, commercial F. cananassa showed a greater depolymerization of HSP polymers than F. chiloensis. With the exception of PME, the activity of all assayed enzymes was higher in F. chiloensis than in F. cananassa fruits. The role of PG and EGase seems to be central in both species: these enzymes are correlated to the decrease in the content of HSP and NaOH-soluble polymers (NSP fraction), respectively. In addition, activity levels of oGal and oXyl were significantly correlated with fruit firmness reduction in F. chiloensis and F. cananassa, respectively.