Photosynthesis and starch metabolism of chloroplasts during prolonged illumination

The starch metabolism of the chloroplasts in the leaves of Stellaria media was studied by means of electron microscopy. During the night the starch grains diminished in size but did not disappear entirely. In the light they grew due to photosynthesis. After prolonged illumination of the plant the grains almost filled up the chloroplasts. However, after an illumination of 26-27 hr a sudded disintegration took place. This was apparently caused by the increased activity of β-amylase observed in an earlier investigation to occur at this time in the chloroplasts. After the disintegration the starch grains of the chloroplasts showed irregular changes.The rate of photosynthesis and respiration was measured by an infra-red gas analyser. During prolonged illumination Stellaria media showed a rather intensive and constant rate of assimilation. The role of starch disintegration and β-amylase synthesis in making possible this constant assimilation has been discussed.