title: Nitrate enhancement of CAM activity in two Kalanchoë species is associated with increased vacuolar proton transport capacity.
abstract: Among species that perform CAM photosynthesis, members of the genus Kalanchoë have been studied frequently to investigate the effect of environmental factors on the magnitude of CAM activity. In particular, different nitrogen sources have been shown to influence the rate of nocturnal CO2fixation and organic-acid accumulation in several species of Kalanchoë. However, there has been little investigation of the interrelationship between nitrogen source (nitrate versus ammonium), concentration and the activity of the vacuolar proton pumps responsible for driving nocturnal organic-acid accumulation in these species. In the present study with Kalanchoë laxiflora and Kalanchoë delagoensis cultivated on different nitrogen sources, both species were found to show highest total nocturnal organic-acid accumulation and highest rates of ATP- and PPi-dependent vacuolar proton transport on 2.5 mM nitrate, whereas plants cultivated on 5.0 mM ammonium showed the lowest values. In both species malate was the principal organic-acid accumulated during the night, but the second-most accumulated organic-acid was fumarate for K. laxiflora and citrate for K. delagoensis. Higher ATP- and PPi-dependent vacuolar proton transport rates and greater nocturnal acid accumulation were observed in K. delagoensis compared with K. laxiflora. These results show that the effect of nitrogen source on CAM activity in Kalanchoë species is reflected in corresponding differences in activity of the tonoplast proton pumps responsible for driving sequestration of these acids in the vacuole of CAM-performing cells.
authors.affiliation: Department of Botany, Institute of Biosciences, University of São Paulo, São Paulo, 05508-090, Brazil.
authors.forename: Paula Natália
authors.identifier: http://orcid.org/0000-0001-9416-5997
authors.initials: PN
authors.lastname: Pereira
authors.affiliation: Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK.
authors.forename: James Andrew Charles
authors.initials: JAC
authors.lastname: Smith
authors.affiliation: Department of Botany, Institute of Biosciences, University of São Paulo, São Paulo, 05508-090, Brazil.
authors.forename: Helenice
authors.initials: H
authors.lastname: Mercier
mesh_terms: D017136:Ion Transport; D031962:Kalanchoe / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis; D010940:Plant Proteins / Q000378:metabolism; D017494:Proton Pumps / Q000378:metabolism*; D011522:Protons; D014617:Vacuoles / Q000378:metabolism
chemical_list: D009566:Nitrates; D010940:Plant Proteins; D017494:Proton Pumps; D011522:Protons; D009584:Nitrogen