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Transgenic potato tubers accumulate high levels of 1‐kestose and nystose: functional identification of a sucrose sucrose 1‐fructosyltransferase of artichoke ( Cynara scolymus ) blossom discs
Author(s) -
Hellwege Elke M.,
Gritscher Dominique,
Willmitzer Lothar,
Heyer Arnd G.
Publication year - 1997
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1997.12051057.x
Subject(s) - sucrose , biology , sugar , botany , jerusalem artichoke , chemistry , food science
Summary By screening a cDNA library of artichoke ( Cynara scolymus ) blosssom discs for fructosyltransferases, we isolated a clone designated Cy21 . The deduced amino acid sequence shows homology to acid β‐fructosyl hydrolases and to the sucrose‐fructan 6‐fructosyltransferase (6‐SFT) of barley. Transiently expressed in Nicotiana tabacum protoplasts, the Cy21 gene‐product synthesized 1‐kestose, indicating that Cy21 codes for a sucrose sucrose 1‐fructosyltransferase (1‐SST). The enzyme worked at physiologically relevant sucrose concentrations (25 mM sucrose). In the protoplast system, 1‐kestose seemed to be the only fructan product of the 1‐SST. The enzyme activity was not affected by pyridoxal‐HCl, an inhibitor of both the β‐fructosyl hydrolase and the fructosyltransferase activity of invertases. The fructosyltransferase activity of the Cy21 gene‐product, however, could be inhibited by Zn 2+ , Ag + and Cu 2+ ions. In artichoke plants the Cy21 transcript was highly abundant in primary roots and blossom discs. Transgenic potato tubers expressing Cy21 contain high levels of 1‐kestose along with nystose and traces of fructosyl‐nystose, supporting the conclusion that the Cy21 clone encodes a sucrose sucrose 1‐fructosyltransferase.