Department of Physiology-Anatomy, University of California, Berkeley, California 94720.
J Cell Biol. 1970 Nov 1;47(2):332-51. doi: 10.1083/jcb.47.2.332.
Light changes the structure of chloroplasts. This effect was investigated by high resolution electron microscopy, photometric methods, and chemical modification. (a) A reversible contraction of chloroplast membrane occurs upon illumination, dark titration with H(+), or increasing osmolarity. These gross structural changes arise from a flattening of the thylakoids, with a corresponding decrease in the spacing between membranes. Microdensitometry showed that illumination or dark addition of H(+) resulted in a 13-23% decrease in membrane thickness. Osmotically contracted chloroplasts do not show this effect. (b) Rapid glutaraldehyde fixation during actual experiments revealed that transmission changes are closely correlated with the spacing changes and therefore reflect an osmotic mechanism, whereas the light scattering changes have kinetics most similar to changes in membrane thickness or conformation. (c) Kinetic analysis of light scattering and transmission changes with the changes in fluorescence of anilinonaphthalene sulfonic acid bound to membranes revealed that fluorescence preceded light scattering or transmission changes. (d) It is concluded that the temporal sequence of events following illumination probably are protonation, changes in the environment within the membrane, change in membrane thickness, change in internal osmolarity accompanying ion movements with consequent collapse and flattening of thylakoid, change in the gross morphology of the inner chloroplast membrane system, and change in the gross morphology of whole chloroplasts.
光改变叶绿体的结构。这种效应通过高分辨率电子显微镜、光度法和化学修饰来研究。（a）在光照、用 H(+)暗滴定或渗透压增加时，叶绿体膜会发生可逆收缩。这些宏观结构变化是由于类囊体扁平化，膜间距相应减小。显微光度计显示，光照或暗加 H(+)导致膜厚度减少 13-23%。渗透压收缩的叶绿体没有这种效应。（b）在实际实验中快速戊二醛固定时发现，透射变化与间距变化密切相关，因此反映了一种渗透机制，而光散射变化的动力学最类似于膜厚度或构象的变化。（c）用结合在膜上的对氨基萘磺酸的荧光变化与光散射和透射变化的动力学分析表明，荧光先于光散射或透射变化。（d）可以得出结论，光照后事件的时间顺序可能是质子化、膜内环境的变化、膜厚度的变化、离子运动伴随的内部渗透压的变化，导致类囊体的坍塌和平坦化、内叶绿体膜系统的宏观形态的变化和整个叶绿体的宏观形态的变化。
