CYANOGENESIS INHIBITS ACTIVE PATHOGEN DEFENSE IN PLANTS - INHIBITION BY GASEOUS HCN OF PHOTOSYNTHETIC CO2 FIXATION AND RESPIRATION IN INTACT LEAVES

The action of cyanide, a compound liberated from injured or infected c yanogenic planes, on plane respiration and photosynthesis of intact ti ssues has been studied. A method for quantified application of HCN to plant tissue is presented. HCN diffuses rapidly through the leaf blade s and it inhibits photosynthetic CO2 fixation (PCF) and respiration in intact cells. Inhibition of PCF consists of (1) a reversible acute in hibition and (2) an irreversible, destructive photoinhibition of the p hotosynthetic dark reaction with subsequent photooxidation of the phot osynthetic apparatus. As long as free HCN is present in leaf tissue, t he PCF is blocked. It is suggested that this block in carbon flow is t he main reason for the impairment of active, synthesis-dependent defen ce reactions.