Bio-molecular markers for traceability of organic vs. conventional potato tubers: a preliminary investigation

Organic products are steadily gaining importance in the global market scenario. However, most of the comparative analyses regarding organic vs. conventional products have focused on the detection of chemicals or dealt with traditional nutritional parameters rather than approaching the issue of possible physiological differences. These differences would be valuable resources to be exploited both as markers for traceability and diversification/qualification of the products. Here we report a pilot experiment regarding comparative analysis of protein patterns in potato, cv. 'Vivaldi', grown in the field according to conventional vs. organic regimes. SDS-PAGE followed by MALDI-TOF of tuber extracts loaded on equal FW basis was used to quickly analyse, quantify and identify proteins. At least two proteins, i.e. patatin and granule-bound starch-synthase I (GBSSI), were induced in organic tubers. Patatin is known to bear a sugar-responsive element in its promoter region. GBSSI induction was accompanied by an overall stimulation of starch synthesis machinery, as tuber starch content was higher in organic tubers, whereas no significant changes were observed in other starch parameters (e.g. amylose/amylopectin ratio). As it is known, one of the most reproducible parameters that differentiates the organic vs. conventional regimes is lower N bio-availability in organic fertilisation procedures (as also indicated by higher NO3 levels routinely detected in conventional produce). Thus, our preliminary findings would be consistent with preferential C fixation and partitioning in organic tubers towards N-poor compounds as carbohydrates. The opposite would happen in conventional tubers since high N would divert assimilated carbon to other sinks (e.g. production of C-skeletons for N assimilation).