Influence of Light and Darkness upon Carbon Dioxide Fixation.

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Abstract
A study of the light and dark fixation of CO2 as it may be related to photoperiodism was carried out using two short-day species (Biloxi soybean and cocklebur) and one long-day species (Wintex barley). Plants in precisely controlled states of photoperiodic induction were exposed to atmospheres containing C14O2, and after fixation had occurred the leaves were killed and extracted in ethanol and the soluble materials into which the carbon had entered were identified by paper chromatography and autoradiography. The following conclusions were drawn the light period has an influence on dark fixation of CO2. The longer the interval after light cessation, the slower the dark fixation by cocklebur leaves. The dark period influences photosynthetic fixation of CO2. The longer the preceding dark period, the lower the photosynthetic rate regardless of the photoperiodic requirement of the species. In addition, light fixation products were found to be rapidly changed in the dark. In particular, there was a rapid depletion of sugars, and usually a rise in organic and amino acids in the course of the night. A very rapid depletion of radioactivity in alanine was found. It is concluded that there are compounded interactions between the light and the dark periods in photoperiodism, and that these interactions are reflected in altered patterns of CO2 fixation both in light and in darkness.