Comparison of Three Photochemical Activities of Chloroplasts.

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Abstract
The ability of sugar beet chloroplasts to catalyze 3 photochemical reactions following various treatments has been investigated. The 3 photochemical reactions followed are: (1) the Hill reaction with 2,6-dichlorophenol-indophenol as electron acceptor; (2) the photoreduction of indigo carmine in the presence of ascorbic acid and 2,6-dichlorophenolindophenol; and (3) the photochemical oxidation of ascorbic acid in the presence of O2 and 2,6-dichlorophenolindophenol. It was found that the Hill reaction was inhibited preferentially by either incubation of chloroplasts at a pH of 8.5 or by heating the chloroplasts in 51[degree] C for 10 minutes. Sonic oscillation for 10 minutes, and incubation in ion low water preferentially inhibited the photoreduction of indigo carmine: Also, addition of sodium azide or incubation at pH 5.5 produced a preferential inhibition of indigo carmine photoreduction. Addition of Zn ion caused preferential inhibition of ascorbic acid photooxidation. Extraction of chloroplasts with digitonin resulted in almost complete loss of activity for the Hill reaction and for indigo carmine photoreduction, yet stimulated ascorbic acid by more than 6-fold, when compared on a chlorophyll basis. Of the 3 photochemical reactions studied, the photooxidation of ascorbic acid is least sensitive to various treatments, and appears to be the most primitive reaction. The different behavior of the chloroplasts for the Hill reaction and indigo carmine photoreduction following the various treatments, indicates that these 2 photoreactions differ in terms of the chloroplast components necessary for the reactions.