| Abstract
| - Recently, transgenic potato plants were created showing underexpression of the 20R isoform of the14-3-3 protein. The transgenic plants grown in tissue culture showed a significant increase in nitratereductase activity and a decrease in nitrate level. The transgenic line with the lowest 14-3-3 quantitywas field-trialed (1997−2000) and analyzed. The reduction in the 14-3-3 protein level consistentlyresulted in a starch content increase and in an increase in the ratio of soluble sugars to starch in thetubers, although the latter was only barely visible. The determination of amino acid composition inthe tubers showed a significant increase in methionine, proline, and arginine content and a slight butconsistent increase in hydrophobic amino acid and lysine content in the cells of the transgenic potatoplants. We also observed an increase in the crude protein content, from 19 to 22.1% of the controlvalue in consecutive years. It is proposed that all of these changes might have resulted from thedownregulation of nitrate reductase and sucrose phosphate synthase activities by 14-3-3, althoughother potential mechanisms cannot be excluded (e.g., an increase in enzyme protein level). 14-3-3-repressed transgenic plants showed a significant increase in calcium content in their tubers. It isthus proposed that a function of the isolated 14-3-3 isoform is in the control of amino acid synthesisand calcium metabolism. However, the mechanism of this control is as yet unknown. Keywords: 14-3-3 protein; transgenic plant; amino acids; minerals; Solanum tuberosum
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