Primary metabolites and organic acid metabolism in apple (Malus sylvestris) fruit callus culture

In-vitro culture cells were obtained from seven different varieties of Indian apples (Malus sylvestris L). The cultivar Golden Delicious showed the highest yield of callus tissue followed by Maharaji and American Epirouge. Cultured apple cells exhibited some deviation from the apple fruit in primary metabolism as well as primary metabolite profiles. In callus cultures, the pool size of free amino acids and organic acids increased considerably while the free sugar pool decreased drastically compared with apple fiuit. There was higher incorporation of ¹⁴C acetate, ¹⁴C citrate, ¹⁴C malate and ¹⁴C succinate into the CO₂, lipid, protein, carbohydrate and amino acid fractions and lower incorporation into the free sugar fraction in cultured cells compared with the explant. The incorporation of ¹⁴CO₂ showed a similar trend. Qualitatively, there was some similarity between the callus and explant in free amino acid and sugar profiles and dissimilarity in organic acids. Compounds such as citrate, succinate and fumarate and also some amino acids (methionine, arginine, leucine and proline) were present at higher concentration in callus cultures whereas they were almost absent in the original tissue. There were also differences in the carbohydrate and protein profiles of explant ana callus as judged by their sugar and amino acid make-up respectively.