Reactions of photosystems I and II in spinach chloroplast fragments treated with ethylene glycol

Abstract

Photochemical reactions of chloroplast fragments isolated from spinach leaves were measured in the presence of ethylene glycol or were measured after washing with an ethylene glycol-containing medium. 2,6-Dichlorophenolindophenol (DPIP) photoreduction, oxygen evolution and oxygen uptake (a photosystem I reaction) were investigated in ethylene glycol-treated chloroplast fragments. By washing with ethylene glycol, oxygen evolution was strongly inhibited, but oxygen uptake was not much affected by ethylene glycol washing. Chloroplast fragments in 50% ethylene glycol maintained a high rate of DPIP photoreduction (85% of the control activity in an ethylene glycol-less medium). In 67% ethylene glycol, DPIP photoreduction mediated by photosystem II was eliminated and only a small rapid reduction mediated by photosystem I was observed. Chloroplast fragments inhibited by ethylene glycol photoreduced DPIP in the presence of p-aminophenol added as an artificial electron donor to photosystem II. The restored activity of DPIP photoreduction was inhibited by 3-(3′,4′- dichlorophenyl)-1,1 -dimethylurea.