title: Leaf anatomical traits which accommodate the facultative engagement of crassulacean acid metabolism in tropical trees of the genus Clusia.
abstract: Succulence and leaf thickness are important anatomical traits in CAM plants, resulting from the presence of large vacuoles to store organic acids accumulated overnight. A higher degree of succulence can result in a reduction in intercellular air space which constrains internal conductance to CO2. Thus, succulence presents a trade-off between the optimal anatomy for CAM and the internal structure ideal for direct C3 photosynthesis. This study examined how plasticity for the reversible engagement of CAM in the genus Clusia could be accommodated by leaf anatomical traits that could facilitate high nocturnal PEPC activity without compromising the direct day-time uptake of CO2 via Rubisco. Nine species of Clusia ranging from constitutive C3 through C3/CAM intermediates to constitutive CAM were compared in terms of leaf gas exchange, succulence, specific leaf area, and a range of leaf anatomical traits (% intercellular air space (IAS), length of mesophyll surface exposed to IAS per unit area, cell size, stomatal density/size). Relative abundances of PEPC and Rubisco proteins in different leaf tissues of a C3 and a CAM-performing species of Clusia were determined using immunogold labelling. The results indicate that the relatively well-aerated spongy mesophyll of Clusia helps to optimize direct C3-mediated CO2 fixation, whilst enlarged palisade cells accommodate the potential for C4 carboxylation and nocturnal storage of organic acids. The findings provide insight on the optimal leaf anatomy that could accommodate the bioengineering of inducible CAM into C3 crops as a means of improving water use efficiency without incurring detrimental consequences for direct C3-mediated photosynthesis.
authors: School of Biology, Newcastle University, Newcastle upon Tyne NE17RU, UK.
authors: V Andrea
authors: VA
authors: Barrera Zambrano
authors: School of Biological Sciences, University of Essex, Colchester CO4 3SQ, UK.
authors: Tracy
authors: T
authors: Lawson
authors: CEBAS-CSIC Campus Universitario de Espinardo, Department of Abiotic Stress and Plant Pathology, 30100 Murcia, Spain.
authors: Enrique
authors: E
authors: Olmos
authors: CEBAS-CSIC Campus Universitario de Espinardo, Department of Abiotic Stress and Plant Pathology, 30100 Murcia, Spain.
authors: Nieves
authors: N
authors: Fernández-García
authors: School of Biology, Newcastle University, Newcastle upon Tyne NE17RU, UK Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6407, USA Anne.Borland@ncl.ac.uk.
authors: Anne M
authors: AM
authors: Borland
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D031251:Clusia / Q000033:anatomy & histology* / Q000502:physiology; D008027:Light; D058503:Mesophyll Cells; D010641:Phenotype; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism; D054046:Plant Stomata / Q000033:anatomy & histology / Q000502:physiology; D018526:Plant Transpiration; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D014197:Trees; D014867:Water / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D014867:Water; D002245:Carbon Dioxide; D010730:Phosphoenolpyruvate Carboxylase; D012273:Ribulose-Bisphosphate Carboxylase
keywords: CAM; Clusia; PEPC; leaf anatomy; photosynthesis; stomata.