Turnover of Shikimate Pathway Metabolites during Shoot Initiation in Tobacco Callus Cultures

The turnover of shikimate pathway intermediates and end products was examined in tobacco (Nicotiana tabacum L. Wisconsin 38) callus cultured under shoot-forming and non-shoot-forming conditions. In shoot-forming tissue there was a higher rate of net synthesis of quinic and shikimic acids than in proliferating callus. Post-incubation, there was a decrease in labeled quinate and an increase in shikimate. The changes in activity of quinate:NAD$ oxidoreductase were in agreement with the above. The aromatic amino acids, tyrosine, phenylalanine and tryptophan, showed little turnover in the proliferating tissues. On the other hand, higher rates of net synthesis and degradation, mainly of tyrosine, were observed in shoot-forming tissues. These findings are discussed in relation to the shoot-initiation process.