Cosgrove D J
Department of Biology, Pennsylvania State University, University Park 16802, USA.
Photochem Photobiol. 1985;42(6):745-51. doi: 10.1111/j.1751-1097.1985.tb01642.x.
These experiments tested the hypothesis that phototropic bending arises when a light gradient across the stem differentially inhibits cell elongation because of direct inhibition of cell elongation by light (the Blaauw hypothesis). Continuous irradiation of dark-grown cucumber seedlings (Cucumis sativus L.) with unilateral blue light inhibited hypocotyl elongation within 30 s, but did not induce phototropic curvature until 4.5 h after the start of irradiation. Marking experiments showed that curvature began simultaneously at the top and bottom of the growing region. In situ measurements of the light gradient across the stem with a glass fiber optic indicated that a 5- to 6-fold difference in fluence rate was established on the two sides of the stem. The light gradient established at the start of irradiation was the same as that after 6 h of irradiation. Changes in gravitropic responsiveness during this period were also ruled out. Calculations show that the light gradient should have caused curvature which would be detectable within 30 to 60 min and which would extrapolate to the start of irradiation--if the Blaauw hypothesis were correct. The long lag for phototropism in this case indicates that rapid inhibition of cell elongation by blue light does not cause the asymmetrical growth of phototropism. Rather, phototropism is superimposed upon this separate light growth response.
当茎上的光梯度因光对细胞伸长的直接抑制而差异抑制细胞伸长时，向光弯曲就会出现（布劳假说）。用单侧蓝光持续照射黑暗中生长的黄瓜幼苗（黄瓜），在30秒内就抑制了下胚轴伸长，但直到照射开始4.5小时后才诱导出向光弯曲。标记实验表明，弯曲在生长区域的顶部和底部同时开始。用玻璃纤维光学器件对茎上的光梯度进行原位测量表明，茎两侧的光通量率建立了5至6倍的差异。照射开始时建立的光梯度与照射6小时后的光梯度相同。在此期间重力反应性的变化也被排除。计算表明，如果布劳假说正确，光梯度应该会导致在30至60分钟内可检测到的弯曲，并且可以外推到照射开始时。在这种情况下，向光性的长时间延迟表明蓝光对细胞伸长的快速抑制不会导致向光性的不对称生长。相反，向光性叠加在这种独立的光生长反应之上。
