Expression of sugars biosynthesis-related genes during fruit ripening in normal and salt-exposed fig plants.

Fig (Ficus carica L.) is a moderately important fruit crop in the world. The fig fruit is commonly consumed in its fresh form, which contains high nutritional values that are important for human health. In view of the world market and of the recent discoveries of its healthy characteristics, studies on the fig fruit and its conservation in the post-harvest are intensifying. The taste of fruit, in general, is largely influenced by the concentration of soluble sugars and organic acids. In this study it was intended to investigate changes of the expression of different genes involved in the metabolism of sugars during the fruit ripening of the cv. Dottato, by qRTPCR. In particular, the main genes involved in the conversion of sucrose and sorbitol into fructose and glucose and different sugar transporters were analysed: sucrose synthase, invertase, sorbitol dehydrogenase and D-sorbitol 6-phosphate dehydrogenase NADP + -dependent and sucrose, sorbitol, mannitol and hexose transporters-encoding genes. Our experiments showed the induction of genes involved in sucrose and sorbitol conversion into fructose and glucose during the fruit maturation process. Actually, the analysis of the concentration of sugars in ripening fruits, showed a higher concentration of fructose and glucose compared to sucrose, with no significant differences between fructose and glucose concentrations. Other genes showed different expression profiles. In the second part of this work we studied the same genes involved in sugars metabolism in mature fruits of plants cultivated under salinity stress, i.e. plants of Ficus carica L. cv Dottato exposed to 100 mM sodium chloride for 48 days. The analysis showed an enhanced expression level of the metabolism for sorbitol and sucrose in glucose, UDP-glucose and fructose. Since fig is apparently suitable for cultivation in saline soils, our data suggest that such culture conditions might even increase the nutritional value of fig fruits.