Aerobic photobleaching capacity as related to electron microscopical data on particle size distribution of chloroplast fragments from Vischeria stellata and Spinacia oleracea

1. The chloroplast of Vischeria stellala shows the general features of algal chloroplasts. The thylakoids are arranged in bands containing three of them each. 2. A correlation between increase of both aerobic photobleaching rate and relative amount of particles with dimensions ranging from 16 to 49 nm is observed for Vischeria stellata chloroplast fragments upon interruption, either by storage or by centrifugation, of the preparative sonication procedure. 3. With spinach chloroplast fragments no such increase in both bleaching rate and relative amount of the mentioned particles is found. 4. The time course of aerobic photobleaching for Vischeria chloroplast fragments is the same after grinding and sonication. For spinach, however, sonication results in a time course pattern different from that of ground preparations. The pattern of sonicated preparations resembles that of Vischeria. 5. The data support a previous suggestion holding that structural effects are involved in determining the aerobic photobleaching capacity.