Tokyo University of Agriculture and Technology, Fuchu-Tokyo, Japan.
Ann Bot. 2012 Sep;110(4):887-95. doi: 10.1093/aob/mcs148. Epub 2012 Jul 26.
Angiosperm trees generally form tension wood on the upper sides of leaning stems. The formation of tension wood is an important response to gravitational stimulus. Gibberellin appears to be involved in the differentiation of secondary xylem, but it remains unclear whether gibberellin plays a key role in the formation of tension wood and plant gravitropism. Therefore, a study was designed to investigate the effects of gibberellin and of inhibitors of the synthesis of gibberellin, namely paclobutrazole and uniconazole-P, on the formation of tension wood and negative stem gravitropism in Acacia mangium seedlings.
Gibberellic acid (GA(3)), paclobutrazole and uniconazole-P were applied to seedlings via the soil in which they were growing. Distilled water was applied similarly as a control. Three days after such treatment, seedlings were tilted at an angle of 45° from the vertical, and samples of stems were collected for analysis 2 weeks, 2 months and 6 months after tilting. The effects of treatments on the stem recovery degree (Rº) were analysed as an index of the negative gravitropism of seedlings, together the width of the region of tension wood in the upper part of inclined stems.
It was found that GA(3) stimulated the negative gravitropism of tilted seedling stems of A. mangium, while paclobutrazole and uniconazole-P inhibited recovery to vertical growth. Moreover, GA(3) stimulated the formation of tension wood in tilted A. mangium seedlings, while paclobutrazole and uniconazole-P strongly suppressed the formation of tension wood, as assessed 2 weeks after tilting.
The results suggest that gibberellin plays an important role at the initial stages of formation of tension wood and in stem gravitropism in A. mangium seedlings in response to a gravitational stimulus.
被子植物的树木通常在上部形成张力木材倾斜的茎。张力木材的形成是对重力刺激的重要反应。赤霉素似乎参与了次生木质部的分化，但尚不清楚赤霉素在张力木材的形成和植物向重力性中是否起关键作用。因此，设计了一项研究，以调查赤霉素及其合成抑制剂，即多效唑和烯效唑-P，对印楝幼苗张力木材形成和负向茎向重力性的影响。
通过幼苗生长的土壤向幼苗施加赤霉素（GA（3））、多效唑和烯效唑-P。类似地，用蒸馏水作为对照进行处理。处理后 3 天，将幼苗倾斜 45°从垂直方向，在倾斜后 2 周、2 个月和 6 个月收集茎样进行分析。将处理对茎恢复度（Rº）的影响作为幼苗负向向重力性的指标进行分析，同时分析倾斜茎上部张力木材区域的宽度。
结果发现，GA（3）刺激了 A. mangium 倾斜幼苗茎的负向向重力性，而多效唑和烯效唑-P抑制了向垂直生长的恢复。此外，GA（3）刺激了倾斜的 A. mangium 幼苗中张力木材的形成，而多效唑和烯效唑-P强烈抑制了张力木材的形成，在倾斜后 2 周进行评估。
研究结果表明，赤霉素在 A. mangium 幼苗对重力刺激形成张力木材和茎向重力性的初始阶段发挥重要作用。
