Gibberellin-mediated changes in carbohydrate metabolism during flower stalk elongation in tulips

We investigated the effects of a gibberellin synthesis inhibitor (ancymidol) and gibberellin (GA(4+7)) on carbohydrate metabolism and elongation in internodes of the tulip (Tulipa gesneriana L.) flower stalk during greenhouse growth. During the initial stages of flower stalk growth, the lowermost internode was mainly responsible for total flower stalk length, whereas the uppermost internode mostly contributed to total length during later stages. High concentrations of hexose sugar (mainly glucose) and increased activity of acid invertase were observed when internodes were rapidly elongating. Inhibition of gibberellin biosynthesis with ancymidol reduced the elongation rate of internodes, and inhibited the hexose sugar accumulation and acid invertase activity. Application of GA(4+7) to ancymidol-treated plants reversed these effects. The degree of response to ancymidol and GA(4+7) was, however, different in different internodes such that the lowermost internode was most responsive and the uppermost internode was least responsive. The results indicate that de novo biosynthesis of gibberellins is a requirement for expression of high acid invertase activity during the rapid elongation phase in tulip internodes which enables cleavage of imported sucrose to hexoses that can be readily utilized in elongating cells.