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Crassulacean acid metabolism: a continuous or discrete trait?
Author(s) -
Winter Klaus,
Holtum Joseph A. M.,
Smith J. Andrew C.
Publication year - 2015
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.13446
Subject(s) - crassulacean acid metabolism , rubisco , carbon fixation , biology , photosynthesis , fixation (population genetics) , nocturnal , phosphoenolpyruvate carboxylase , isotopes of carbon , botany , evolutionary biology , ecology , gene , biochemistry , total organic carbon
Summary The key components of crassulacean acid metabolism ( CAM ) – nocturnal fixation of atmospheric CO 2 and its processing via Rubisco in the subsequent light period – are now reasonably well understood in terms of the biochemical reactions defining this water‐saving mode of carbon assimilation. Phenotypically, however, the degree to which plants engage in the CAM cycle relative to regular C 3 photosynthesis is highly variable. Depending upon species, ontogeny and environment, the contribution of nocturnal CO 2 fixation to 24‐h carbon gain can range continuously from close to 0% to 100%. Nevertheless, not all possible combinations of light and dark CO 2 fixation appear equally common. Large‐scale surveys of carbon‐isotope ratios typically show a strongly bimodal frequency distribution, with relatively few intermediate values. Recent research has revealed that many species capable of low‐level CAM activity are nested within the peak of C 3 ‐type isotope signatures. While questions remain concerning the adaptive significance of dark CO 2 fixation in such species, plants with low‐level CAM should prove valuable models for investigating the discrete changes in genetic architecture and gene expression that have enabled the evolutionary transition from C 3 to CAM .ContentsSummary 73 I. Introduction 73 II. Phenotypic diversity 74 III. Ecological context 74 IV. Structure–function context 75 V. Biochemical–genomics context 76 VI. Transitional states? 76 VII. Conclusions – what is a CAM plant? 77Acknowledgements 77References 77