Gibberellin mediates tension wood formation
Angiosperm trees generally form tension wood, a special type of secondary xylem, in response to a gravitational stimulus. Nugroho et al. find that pre-treatment with paclobutrazole and uniconazole-P, inhibitors of the synthesis of gibberellin, to inclined Acacia mangium seedlings inhibits negative gravitropism of the stems. The inhibitors suppress increases in the thickness of gelatinous layers and the elongation of gelatinous fibres in the tension wood. In contrast, pre-treatment with gibberellin stimulates the elongation of these fibres. The results suggest that gibberellin is important for the development of gelatinous fibres, and therefore in gravitropism.