Inhibition of deacidification (loss of titratable acidity by photosynthetic inhibitors in leaves of a cam plant

Abstract

The photosynthetic inhibitors DCMU and DL-glyceraldehyde were vaccum infiltrated into leaf segments of Kalanchoë pinnatum after acidification (measured as an increase in titratable acidity) in the dark; subsequent deacidification (measured as a decrease in titratable acidity) under illumination was observed in these leaves but deacidification was markedly inhibited by these compounds. The leaf segments infiltrated with 10 −5 M DCMU proceeded with deacidification to only about 13% of the initial acidity and the 14C-activity contained in [ 14C] malate which was produced during the dark period diminished only slightly. Hence, photosynthetic 14CO 2 fixation products due to 14CO 2 released by deacidification were hardly observed in DCMU-treated leaves. From these studies we propose that deacidification under illumination is closely related to photosynthetic CO 2 fixation within the leaf.