Photosynthesis by Isolated Chloroplasts IX. Photosynthetic Phosphorylation and CO2 Assimilation in Different Species

Abstract

Until recently the only experimentally documented photochemical activity of isolated chloroplasts was the Hill reaction. In the last 5 years, work with isolated spinach chloroplasts has demonstrated their capacity for carrying out 3 new basic reactions: non-cyclic photophosphorylation (Equation 1), cyclic photophosphorylation (Equation 2) and CO2 assimilation to the level of carbohydrates (Equation 3). CO2 assimilation in Reaction 3 is driven by the "assimi-latory power", i.e. reduced triphosphopyridine nucleotide (TPNH2) formed by Reaction 1 and by adenosine triphosphate (ATP) formed by Reactions 1 and 2.[image].In a non-physiological variant of Reaction 1, TPN is replaceable by ferricyanide (Equation 4):.[image].The authors consider the Hill reaction to be a fragment of Reaction 4 in which electron transport (measured here by ferricyanide reduction) is uncoupled from a normally concurrent phosphorylation. Because of the importance of Reactions 1, 2, 3 and 4 to the understanding of the mechanism of photosynthesis these have been investigated and found to be present in chloroplasts isolated from 4 species other than spinach: sugar beet, sunflower, pokeweed, and Tetragonia expansa.