Effect of malonate on respiration and photosynthesis of coffee leaves, 1: Lack of aerobic fermentation induced by the inhibitor

The application of malonate on coffee leaves strongly inhibited apparent photosynthesis (ca. 50 per cent of oxygen evolution per dry matter unit and 90 per cent of CO2 uptake per leaf area unit) and dark respiration (30 per cent of oxygen uptake per dry matter unit of leaf discs). Since the application of malonate did not promote aerobic alcoholic fermentation, it could not have been the cause of the comparatively higher respiratory quotients (RQ) recorded in the treated tissue. For the same reason the inhibition of photosynthesis cannot be imputed to an increased accumulation of alcohol. Malonate also reduced the rate of photorespiration (CO2 production in CO2 free air in the light). Contrary to its effect on oxygen uptake (per dry matter unit; measured manometrically), malonate enhanced the production of CO2 in the dark (per leaf area unit; measured by infra-red gas analysis), sometimes by as much as 40 per cent. Only a small fraction of this increase in CO2 emission in treated leaves in the dark seems to be due to metabolization of malonate