Ultrastructural and Photometric Evidence for Light-Induced Changes in Chloroplast Structure in vivo

Abstract

Photometric evidence for a reversible, red-light induced transmission decrease in excised leaf tissue or the thalli of certain marine algae was obtained under conditions corresponding to the occurrence of a light-induced shrinkage of chloroplasts within the cells. Evidence supporting this conclusion is: the kinetics of the nonspecific transmission changes are similar to those observed in chloroplasts in vitro; the magnitude of the response is larger than could be accounted for by any known pigment which absorbs at 546 m [mu]; the light-induced transmission changes are optimal at pH 5.5 to 6.5 in the presence of electron flow cofactors and weak acid anions, conditions which are optimal for light-induced chloroplast shrinkage in isolated chloroplasts and; examination of chloroplast ultrastructure in dark incubated and illuminated chloroplasts reveals a flattening of the chloroplast structure and shrinkage.