Quiñones M A, Lu Z, Zeiger E
Department of Biology, University of California, Los Angeles, CA 90024, USA.
Proc Natl Acad Sci U S A. 1996 Mar 5;93(5):2224-8. doi: 10.1073/pnas.93.5.2224.
Fluorescence spectroscopy was used to characterize blue light responses from chloroplasts of adaxial guard cells from Pima cotton (Gossypium barbadense) and coleoptile tips from corn (Zea mays). The chloroplast response to blue light was quantified by measurements of the blue light-induced enhancement of a red light-stimulated quenching of chlorophyll a fluorescence. In adaxial (upper) guard cells, low fluence rates of blue light applied under saturating fluence rates of red light enhanced the red light-stimulated fluorescence quenching by up to 50%. In contrast, added blue light did not alter the red light-stimulated quenching from abaxial (lower) guard cells. This response pattern paralleled the blue light sensitivity of stomatal opening in the two leaf surfaces. An action spectrum for the blue light-induced enhancement of the red light-stimulated quenching showed a major peak at 450 nm and two minor peaks at 420 and 470 nm. This spectrum matched closely an action spectrum for blue light-stimulated stomatal opening. Coleoptile chloroplasts also showed an enhancement by blue light of red light-stimulated quenching. The action spectrum of this response, showing a major peak at 450 nm, a minor peak at 470 nm, and a shoulder at 430 nm, closely matched an action spectrum for blue light-stimulated coleoptile phototropism. Both action spectra match the absorption spectrum of zeaxanthin, a chloroplastic carotenoid recently implicated in blue light photoreception of both guard cells and coleoptiles. The remarkable similarity between the action spectra for the blue light responses of guard cells and coleoptile chloroplasts and the spectra for blue light-stimulated stomatal opening and phototropism, coupled to the recently reported evidence on a role of zeaxanthin in blue light photoreception, indicates that the guard cell and coleoptile chloroplasts specialize in sensory transduction.
荧光光谱法被用于表征皮马棉（陆地棉）近轴保卫细胞叶绿体和玉米胚芽鞘尖端对蓝光的响应。通过测量蓝光诱导的叶绿素a荧光的红光刺激猝灭增强来量化叶绿体对蓝光的响应。在近轴（上部）保卫细胞中，在饱和红光通量率下施加低通量率的蓝光可使红光刺激的荧光猝灭增强高达50%。相比之下，添加蓝光不会改变远轴（下部）保卫细胞的红光刺激猝灭。这种响应模式与两个叶片表面气孔开放的蓝光敏感性平行。蓝光诱导的红光刺激猝灭增强的作用光谱在450nm处有一个主峰，在420和470nm处有两个次峰。该光谱与蓝光刺激气孔开放的作用光谱紧密匹配。玉米胚芽鞘叶绿体也显示出蓝光对红光刺激猝灭的增强作用。这种响应的作用光谱在450nm处有一个主峰，在470nm处有一个次峰，在430nm处有一个肩峰，与蓝光刺激胚芽鞘向光性的作用光谱紧密匹配。这两种作用光谱都与玉米黄质的吸收光谱相匹配，玉米黄质是一种叶绿体类胡萝卜素，最近被认为与保卫细胞和胚芽鞘的蓝光光感受有关。保卫细胞和胚芽鞘叶绿体蓝光响应的作用光谱与蓝光刺激气孔开放和向光性的光谱之间的显著相似性，再加上最近报道的关于玉米黄质在蓝光光感受中作用的证据，表明保卫细胞和胚芽鞘叶绿体专门用于感觉转导。
