title: Water-use efficiency and nitrogen-use efficiency of C(3) -C(4) intermediate species of Flaveria Juss. (Asteraceae).
abstract: Plants using the C(4) pathway of carbon metabolism are marked by greater photosynthetic water and nitrogen-use efficiencies (PWUE and PNUE, respectively) than C(3) species, but it is unclear to what extent this is the case in C(3) -C(4) intermediate species. In this study, we examined the PWUE and PNUE of 14 species of Flaveria Juss. (Asteraceae), including two C(3) , three C(4) and nine C(3) -C(4) species, the latter containing a gradient of C(4) -cycle activities (as determined by initial fixation of (14) C into C-4 acids). We found that PWUE, PNUE, leaf ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) content and intercellular CO(2) concentration in air (C(i) ) do not change gradually with C(4) -cycle activity. These traits were not significantly different between C(3) species and C(3) -C(4) species with less than 50% C(4) -cycle activity. C(4) -like intermediates with greater than 65% C(4) -cycle activity were not significantly different from plants with fully expressed C(4) photosynthesis. These results indicate that a gradual increase in C(4) -cycle activity has not resulted in a gradual change in PWUE, PNUE, intercellular CO(2) concentration and leaf Rubisco content towards C(4) levels in the intermediate species. Rather, these traits arose in a stepwise manner during the evolutionary transition to the C(4) -like intermediates, which are contained in two different clades within Flaveria.
authors.affiliation: Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Vogan
authors.forename: Rowan F
authors.initials: RF
authors.lastname: Sage
mesh_terms: D005075:Biological Evolution; D001692:Biological Transport; D002245:Carbon Dioxide / Q000378:metabolism; D037142:Flaveria / Q000201:enzymology / Q000378:metabolism*; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D010802:Phylogeny; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D018526:Plant Transpiration; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen