Gibberellins (GAs) are growth-promoting hormones that regulate organ growth, mainly via cell elongation. Contradicting reports leave an open question of whether GA is as important for root elongation as it is for stem elongation. Here we have addressed this question focusing on tomato (Solanum lycopersicum) primary-root elongation. We used a combination of physiological, molecular and genetic approaches to tackle this question. Tomato has three GA receptors; GID1a, GID1b1 and GID1b2. The loss of all three receptors, strongly suppressed stem elongation and leaf expansion, but had a relatively minor effect on primary root elongation. The effect of GA on cell elongation and gene-expression was much weaker in roots, than in shoots, reaching saturation at lower hormone concentrations. Our results imply that this differential response to GA in shoots and roots is caused by the lower expression of the dominant GA receptor GID1a in roots. We show that the differential activity of GA between shoots and roots affects root-to-shoot ratio, and speculate that this evolved as an adaptive mechanism to changing environments.

中文翻译：

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地下赤霉素活性：番茄嫩芽和根中赤霉素反应不同

赤霉素（GAs）是主要通过细胞延长来调节器官生长的促生长激素。矛盾的报告留下了一个未解决的问题，即GA对于根伸长是否与茎伸长一样重要。在这里，我们已针对番茄（Solanum lycopersicum）初生根延长问题进行了讨论。我们结合了生理学，分子学和遗传学方法来解决这个问题。番茄具有三种GA受体；GID1a，GID1b1和GID1b2。所有三种受体的丧失，强烈抑制茎伸长和叶片膨胀，但对初生根伸长的影响相对较小。与根部相比，GA对根部细胞伸长和基因表达的影响要弱得多，在较低的激素浓度下达到饱和。我们的结果暗示，这种对芽和根中GA的差异反应是由根中显性GA受体GID1a的较低表达引起的。我们表明，芽与根之间GA的差异活性会影响根与芽的比率，并推测这已演变为对不断变化的环境的适应性机制。