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Carbon isotope discrimination and the integration of carbon assimilation pathways in terrestrial CAM plants
Author(s) -
GRIFFITHS H.
Publication year - 1992
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/j.1365-3040.1992.tb01655.x
Subject(s) - crassulacean acid metabolism , carboxylation , isotopes of carbon , assimilation (phonology) , photosynthesis , biology , carbon cycle , phosphoenolpyruvate carboxylase , chemistry , ecology , ecosystem , botany , total organic carbon , biochemistry , linguistics , philosophy , catalysis
Measurement of carbon isotope discrimination (Δ) of organic plant material integrates the combination of C 4 and C 3 carboxylation processes during the phases of CAM through dark and light periods. These processes are tempered by environmental conditions which regulate CAM activity at the molecular, biochemical and ecological level. The factors contributing to short‐term changes in Δ are discussed in terms of the day‐night changes in metabolite pools and integration via on‐line, instantaneous discrimination techniques. Thus, the isotope signature of newly fixed carbon in malic acid reflects the balance between diffusion and carboxylation limitation together with direct and indirect effects of respiratory metabolism. Leakage of CO 2 during decarboxylation leads to greater discrimination being expressed than is predicted from existing models. Over the timescales of seasonal growth and productivity, most constitutive CAM and C 3 ‐CAM intermediate plants show little variation in Δ (2–4‰). The changes induced by developmental and environmental signals and genetic regulation of CAM are compared for stem and leaf succulents. The role of CAM as a potentially highly productive photosynthetic pathway is contrasted with the induction of CAM as a maintenance mechanism in response to environmental stresses. Analyses of Δ have already contributed much to our understanding of the distribution and regulation of CAM, and in turn can also be used to analyse phylogenetic relationships and the origins of CAM as determined from palaoecological evidence.