Gibberellin-regulated expression of neutral and vacuolar invertase genes in petioles of sugar beet plants

A full-length cDNA clone (BVInv-N) encoding a polypeptide with high similarity to neutral invertases was isolated from sugar beet (Beta vulgaris) plants. The analysis of the expression pattern of the BVInv-N gene revealed a predominant expression in petioles of juvenile plants and mature tap roots. The decrease in neutral invertase expression in petioles of mature plants correlated with a decrease in the corresponding activity, suggesting a growth related function for neutral invertase in sugar beet plants. Treatment of plants with the gibberellin biosynthesis inhibitor, paclobutrazol, decreased the amount of BVInv-N and vacuolar invertase (BVInv-V3) transcripts in petioles, whereas the expression of cell wall invertases (BVInv-CW1 and BVInv-CW2) was not significantly affected in any of these organs. Gibberellic acid treatment reverted the effect of paclobutrazol on soluble invertase expression; however, gibberellic acid alone had no effect on the expression of these genes in the petioles probably due to saturated expression by internal GAs, as suggested by the high transcript levels of GA 20-oxidase (BVGA20ox), a gene involved in gibberellic acid biosynthesis. The coordinated developmental and gibberellin-regulated expression in petioles of juvenile sugar beet plants supports a role of neutral and vacuolar invertases in the active growth of this tissue.