The extent of starch degradation in the light in pea leaves

When 16-d-old plants of Pisum sativum, grown in a 12-h photoperiod, were transferred to continuous illumination, the starch content of the leaves rose steadily for 20 h but then declined appreciably. Plants of the same age, grown in an 18-h photoperiod, were, after 9 h light, exposed to (14)CO2 in the light for 15 min, and then transferred to (12)CO2 in the light or dark for up to 4.25 h. In (12)CO2 in the dark there was a marked decline in the amount and labelling of starch in the leaves. In the light in (12)CO2 the amount of starch in the leaves increased steadily but no change in its radioactivity could be detected. Thus, although pea leaves can degrade starch in the light, extensive degradation does not necessarily accompany starch synthesis.