Transformations of labeled formic acid, formaldehyde, methanol, & CO2 absorbed by bean & barley leaves from air

Abstract

A comparative study was carried out on the uptake from the atmosphere of highly diluted C14-labelled monocarbon compounds having a different degree of reduction. The aliquots of fresh bean and barley leaves were introduced into a transparent chamber floated over mercury and filled with air and dilute vapor of 1 of the C14-labelled compounds: formic acid (FAC), formaldehyde (FAL), methanol (MeOH) or CO2. The main experiments were carried out under illumination of 2,000 lux, and in the dark, in an atmosphere free from CO2 and in the presence of 5% CO2, at 25-26[degree]C. After exposure the leaves were killed by boiling in a 0.5% water solution of FAC. The soluble material was fractionated and analyzed by radioautography. It was calculated that leaves are capable of rather rapid absorption of monocarbon compounds from the atmosphere. CO2 having the highest rate is first followed by FAC, FAL, and MeOH. The greatest inhibiting effect of CO2 is shown by the assimilation of FAC followed by that of FAL. Dark assimilation is shown to be several times smaller than that in light. Investigation of the dynamics of formation of the labelled products and identification of many of them show in light the early appearance of radioactive phosphoric esters. When exposures were prolonged, radioactivity was found also in several other substances (sugars, amino acids and organic acids). These data show that FAC, FAL and MeOH are oxidized at first to CO2 and then assimilated by means of the usual reductive photosynthetic pathway. Apart from the main oxidative path of conversion of FAC, FAL, and MeOH certain other transformations take place leading to the formation of serine as well as of certain other substances.