Differences in sucrose-to-starch metabolism of Solanum tuberosum and Solanum brevidens

Sucrose-to-starch metabolism of the tuberising species Solanum tuberosum and that of the non-tuberising Solanum brevidens was studied using in vitro stem cuttings cultured under tuber inducing conditions. The shoots growing from axillary buds of S. brevidens and the in vitro induced stolons and tubers of S. tuberosum were characterised with respect to their carbohydrate composition by measuring the glucose, fructose, sucrose and starch contents. Expression of the genes encoding vacuolar- and cell-wall-bound invertases, vascular- and tuber-specific sucrose synthases was studied by Northern blot hybridisation. Enzyme activity patterns of alkaline and acid invertases, sucrose synthase, hexokinase and ADP-glucose pyrophosphorylase were determined in both species. Major differences between S. brevidens and S. tuberosum were detected in the starch content, in the expression of cell-wall-bound invertase (cwInv), tuber-specific sucrose synthase (SusyI) and in the activities of sucrose synthase and ADP-glucose pyrophosphorylase that were low in S. brevidens. Genes homologous to the cwInv and SusyI were detected in S, brevidens, however; expression of the SusyI, unlike in S, tuberosum, was not sucrose-inducible in the non-tuberising species. These data together with previous findings (Z. Banfalvi, A. Molnar, G. Molnar, L. Lakatos, L. Szabo, FEES Lett. 383 (1996) 159-164) further support the idea that cell-wall-bound invertase, tuber-specific sucrose synthase and ADP-glucose pyrophosphorylase are important elements of regulatory and biosynthetic pathways resulting in storage starch synthesis and in the expression of tuber storage protein genes. The cwInv mRNA could be detected only in developing stolons and, thus, it can be a good molecular marker of stolen growth. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.