| Abstract: | Abstract Fixation of carbon dioxide by galls of CUSCUTA AUSTRALIS. — The mechanism of the carbon dioxide fixation by Cuscuta is a controversial biochemical topic. Light induced reactions are involved in MacLeod's opinion while others as Ciferri and Poma believe that mainly a dark-fixation occurs. In this study use is made of the galls, caused by the insect Smicronyx on Cuscuta australis, that appear more green coloured than the normal tissues. Equal weights of excised galls were kept both in light and in darkness in contact with C14O2for different incubation times, and the magnitude of the fixation was compared under these two conditions by measuring radioactivity of both soluble and acid hydrolysed fractions. After short exposures to the tracer the fixation in light greatly exceeds that in dark (25–19/1) while with more prolonged exposures the ratio sharply decreases (to about 5/1): these figures can be interpreted with the assumption that a strong light-induced fixation superimposes itself to a low but definite dark-fixation activity. The ratio does not change if radioactivity is measured in the hydrolysed fractions. These results are of course referred to as being largerly preliminar and requiring further and more extensive studies. |
