Changes in appearance, volume and activity during the early stages of disintegration in isolated chloroplasts

Successive stages in the disintegration of tobacco chloroplasts isolated in sucrose phosphate buffer were followed in a series of scanning and sectioning electron micrographs. Changes of particle size and rates of the photochemical reduction of 2,6-dichlorophenol-indophenol (DPIP) were measured simultaneously. An orderly correlation exists between the stepwise degradation of structure, volume and metabolism. Volume changes of purely osmotic origin influence the Hill reaction. At some intermediate point structural alterations begin to interfere with the proper utilization of absorbed light energy. A temporary difference of efficiency suddenly appears for DPIP reduction going on in blue and red saturating illumination. It disappears again some time later when a still lower level of reaction rates has been reached. This event depends solely on the osmotic strength of the suspension medium and can be temporarily reversed by increasing the solute concentration of the latter.