During phototropic curvature, indolyl-3-acetic acid (IAA) remains evenly distributed in the hypocotyl of sunflower (Helianthus annuus L.) and in the oat (Avena sativa L.) coleoptile. At the irradiated side, growth inhibiting substances accumulate. In sunflower, basipetal movement of a growth factor is not involved, since the top of the seedling can be covered or removed without affecting the photo-tropic response; this response, moreover, is independent of the rate of elongation growth. The chemical nature of the growth-inhibiting substances is only partly known. In the hypocotyl they occur in the neutral fraction: in sunflower cis-xanthoxin is one of them, in radish (Raphanus sativus L.) cis- and trans-raphanusanins, and possibly raphanusamide, are involved. The inhibitor(s) in the oat coleoptile are acidic. During curvature, their amount remains rather constant but the distribution changes with an accumulation at the irradiated side. It is concluded that phototropic curvature is brought about by an accumulation, at the irradiated side, of growth-inhibiting substances that unilaterally reduce cell elongation even though the IAA distribution is uniform.

中文翻译：

---

向光性涉及生长抑制剂的横向梯度，而不是生长素的横向梯度。回顾

在向光性弯曲期间，吲哚基-3-乙酸 (IAA) 保持均匀分布在向日葵 (Helianthus annuus L.) 的下胚轴和燕麦 (Avena sativa L.) 的胚轴中。在照射侧，生长抑制物质积聚。在向日葵中，不涉及生长因子的基叶运动，因为可以覆盖或移除幼苗的顶部而不影响向光性响应；此外，这种反应与伸长率的增长速度无关。生长抑制物质的化学性质仅是部分已知的。在下胚轴中，它们出现在中性部分：在向日葵中，顺式黄嘌呤是其中之一，在萝卜 (Raphanus sativus L.) 中，顺式和反式萝卜硫素以及可能的萝卜酰胺都参与其中。燕麦胚芽鞘中的抑制剂是酸性的。在弯曲过程中，它们的数量保持相当稳定，但分布随着辐照侧的积累而变化。得出的结论是，向光性弯曲是由在照射侧积累的生长抑制物质引起的，即使 IAA 分布是均匀的，这些物质也会单方面降低细胞伸长率。