Effect of leaf age on light and dark 14CO2 fixation in a CAM plant, Bryophyllum calycinum

Leaves of different ages from B. calycinum were exposed to 14CO2 in light during day and night. The labelling pattern on the chromatogram differed with leaf age. Young leaves had similar patterns to those of C3 plants during both day and night. Mature leaves showed high incorporation of 14C into C4 acids, especially at night. In contrast, no significant difference with leaf age was observed in the pattern of dark 14CO2 fixation products. Study of the enzyme activity and the content of titratable acid at each leaf age suggested that high incorporating of 14C in C4 acids during the night was due to the simultaneous absorption of CO2 by both enzymes RuDP carboxylase and PEP carboxylase. (author)