The effect of genetic transformations for pest resistance on foliar solanidine-based glycoalkaloids of potato (Solanum tuberosum)

Foliage of potato cv. Desiree was harvested from glasshouse-cultivated plants of five experimental transgenic lines expressing three different insecticidal proteins (snowdrop lectin, Galanthus nivalis agglutinin (GNA); jackbean lectin, Concanavalin A (Con A), cowpea trypsin inhibitor; (CpTi)), tissue-cultured control plants and standard control (non-tissue cultured) plants. The foliage was subdivided into stems, upper, middle and lower leaves and analysed separately by HPLC for the solanidine-based glycoalkaloids alpha-solanine and alpha-chaconine. The results demonstrate that one or more stages in the plant transformation process (i.e. insecticidal- and marker-gene insertions, gene expression and tissue culture) resulted in a lower level of leaf glycoalkaloids than that found in either the tissue-cultured controls or standard controls, based on the selected potato lines transformed for insecticidal protein expression. However, the distribution of glycoalkaloids throughout the plant foliage was unaffected by genetic transformation and tissue culture, with the highest glycoalkaloid levels being observed in the top third of the plant. The importance of investigating unexpected effects of genetic engineering on plant secondary metabolism is discussed from an ecological viewpoint.