Vierstra R D, Poff K L
MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824.
Plant Physiol. 1981 Oct;68(4):798-801. doi: 10.1104/pp.68.4.798.
The herbicide, 4 chloro-5-(methylamino)-2-(alpha,alpha,alpha,-trifluoro-m-tolyl)-3 (2H)-pyridazinone (SAN 9789), which blocks the synthesis in higher plants of colored carotenoids but not of flavins, was used to examine the involvement of carotenoids in corn seedling phototropism. It was concluded that "bulk" carotenoids are not the photoreceptor pigment based on the results that increasing concentrations of SAN 9789 (up to 100 micromolar) did not alter the phototropic sensitivity to 380 nanometers light (using geotropism as a control) and did not increase the threshold intensities of fluence response curves for both 380 and 450 nanometers light even though carotenoid content was reduced to 1 to 2% of normal. SAN 9789 treatment, however, did reduce seedling sensitivity toward 450 nanometers light indicating that carotenoids are involved in phototropism. Carotenoids, which are located mainly in the primary leaves, may act in phototropism as an internal screen, enhancing the light intensity gradient across the seedling and thus contributing to the ability of the seedling to perceive light direction. These results indicate that the action spectra for phototropic responses can be significantly affected by the absorbance of screening pigments in vivo thus altering its shape from the in vitro absorption spectrum of the photoreceptor pigment.
除草剂4-氯-5-（甲氨基）-2-（α，α，α-三氟间甲苯基）-3（2H）哒嗪酮（SAN 9789）可阻断高等植物中有色类胡萝卜素的合成，但不影响黄素的合成，该除草剂被用于研究类胡萝卜素在玉米幼苗向光性中的作用。基于以下结果得出结论：“大量”类胡萝卜素不是光受体色素，即即便类胡萝卜素含量降至正常水平的1%至2%，增加SAN 9789的浓度（高达100微摩尔）也不会改变对380纳米光的向光敏感性（以向地性作为对照），并且不会提高380和450纳米光的光通量响应曲线的阈值强度。然而，SAN 9789处理确实降低了幼苗对450纳米光的敏感性，表明类胡萝卜素参与向光性。主要位于初生叶中的类胡萝卜素，可能在向光性中作为内部屏障起作用，增强幼苗上的光强梯度，从而有助于幼苗感知光的方向。这些结果表明，向光性反应的作用光谱会受到体内筛选色素吸收的显著影响，从而使其形状与光受体色素的体外吸收光谱不同。
