Abstract: | The nature and rate of degradation of carboxyl-14C-labelledindol-3y1-acetic acid (IAA-l-14C]) were studied in apple leaves.The labelled auxin was applied to the cut surface of the growingshoot after the apical part had been removed. The respiratoryCO2 absorbed by chromatographic paper as Na2CO3 then freed byphosphoric acid was quantitatively measured by an internal gascounter. It was found that the concentration of 14CO2 evolvedby leaves was 77 times higher in daylight than in darkness.The ratio of 14CO2/CO2 obtained from respiration from the uppersurface of leaf blades was two and seven times higher than thatfrom the lower surface after 15 and 30 h of daylight, respectively.No such differences were noticed in darkness. Similarly, thetotal radioactivity of leaf tissues tripled in daylight, presumablybecause of photosynthetic incorporation of radioactive CO2 evolvedduring decomposition of LAA. These facts demonstrate the photolyticcharacter of auxin decarboxylation in apple leaves. Prolongeddarkness seemed to provoke a large metabolite withdrawal fromleaves and, to some extent, to protect auxin against decarboxylation. |