Light-Induced Chloroplast Shrinkage in vivo Detectable After Rapid Isolation of Chloroplasts From Pisum sativum.

A light-induced shrinkage of chloroplasts in vivo could be detected with chloroplasts isolated within 2 minutes of harvesting pea plants. As determined both by packed volume and Coulter counter, the mean volume of chloroplasts from plants in the dark was 39 mu(3), whereas it was 31 mu(3) for chloroplasts from plants in the light. Upon illumination of the plants, the half-time for the chloroplast shrinkage in vivo was about 3 minutes, and the half-time for the reversal in the dark was about 5 minutes. A plant growth temperature of 20 degrees was optimal for the volume change. The chloroplast shrinkage was half-maximal for a light intensity of 400 lux incident on the plants and was light-saturated near 2000 lux. The light-absorbing pigment responsible for the volume change was chlorophyll. This light-induced shrinkage resulted in a flattening and slight indenting of the chloroplasts. This chloroplast flattening upon illumination of the plants may accompany an increase in the photosynthetic efficiency of chloroplasts.