Ascorbic acid sinthesys and accumulation in tomato callus culture

Ascorbic acid (AsA) is essential for the animal and human cell protection against oxidative stresses, which are associated with many human diseases. Due to its significant consumption at worldwide level, there is an increasing interest for breeding tomato for fruit quality through classical breading and gene transferring techniques. Despite this, very little is known about AsA genetic regulation in tomato. In order to develop an alternative method to identify changes in the AsA expression we previously obtained callus from petiole and fruit of Solanum lycopersicum cv. M82 and S. pennellii introgression lines (IL7-3 and IL12-4). Callus tissue, compared with the whole plant, offers the possibility to avoid effects due to the physiological status of the plant that can often masks single gene activity. After 60 days of in vitro culture, when no increase of callus growth on petiole explants was observed, AsA accumulation was found to be lower than the differentiated tissues in all assayed genotypes. A number of transcripts involved in fruit AsA regulation was selected from a microarray experiment and assayed in calli through qPCR. In calli, a decrease of expression of genes involved in the cell wall metabolism was observed in both ILs than the relative differentiated tissues. In calli from fruit, despite the increased AsA level, a decrease of gene expression was observed. Compared to M82, an increase of polygacturonase, glycosyl hydrolase and beta-glucuronidase expression was evidenced in petioles of ILs. Further functional characterization of candidate genes will elucidate genetic mechanisms controlling AsA accumulation in tomato.