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Diurnal changes in the regulatory properties of PEP‐carboxylase in Crassulacean Acid Metabolism (CAM)
Author(s) -
KLUGE M.,
BRULFERT J.,
QUEIROZ O.
Publication year - 1981
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11611032
Subject(s) - crassulacean acid metabolism , phosphoenolpyruvate carboxylase , phos , diurnal temperature variation , kalanchoe , pyruvate carboxylase , chemistry , crassulaceae , enzyme assay , botany , biology , enzyme , biochemistry , photosynthesis , atmospheric sciences , geology
. The CAM plants Kalanchoe tubiflora and K. blossfeldiana were grown under photoperiodically controlled conditions (short days). In these plants, phos‐phoenolpyruvate carboxylase capacity and the sensitivity of the enzyme to the effectors L‐malate (inhibitor) and glucose‐6‐phosphate (activator) were measured throughout the diurnal CAM cycle. In K. tubiflora , enzyme capacity was higher if measured at pH 7.0 than at pH 8.0 and displayed a rhythmical behavior with highest values at the end of the light period. As reported earlier, in K. blossfeldiana PEP‐C capacity was higher during the night. It was more pronounced when plants were kept in CO 2 ‐free air during the dark period. In both plants, the sensitivity of the enzyme to the effectors showed very clear diurnal changes: inhibition by malate and activation by glucose‐6‐phosphate were strikingly higher during the day than during the night; the effect depended on PEP concentration. The changing activation of the enzyme by glucose‐6‐phos‐phate reflects diurnal changes of the Km for PEP which was found to be higher during the day than during the night. Manipulations of malate accumulation by nocturnal application of CO 2 ‐free air did not influence these effects. The results are discussed in context with the metabolic control of CAM.