Trees (2004) 18: 553–558 DOI 10.1007/s00468-004-0347-6 ORIGINAL ARTICLE Annika Berg . Birgit Orthen . Eduardo Arcoverde de Mattos . Heitor Monteiro Duarte . Ulrich Lüttge Expression of crassulacean acid metabolism in Clusia hilariana Schlechtendal in different stages of development in the field Received: 10 June 2003 / Accepted: 10 May 2004 / Published online: 9 June 2004 # Springer-Verlag 2004 Abstract Expression of crassulacean acid metabolism (CAM) in the obligate CAM-tree Clusia hilariana SCHLTDL. was studied in the restinga of Jurubatiba National Park, on the Atlantic coast of Rio de Janeiro state, Brazil, comparing plants at different developmental stages. Between young and mature plants there were trends of differences in six parameters, which are all related to CAM expression. From young to mature plants there were tendencies for a decrease of (1) the degree of succulence, (2) the degree of day/night changes of malic acid levels, (3) titratable acidity with nocturnal acid accumulation, (4) the degree of day/night changes of free hexoses with nocturnal break down, (5) effective quantum use efficiency of photosystem II at high photosynthetic photon flux density, and (6) protection from photoinhibi- tion. These tendencies form a clear pattern which suggests that CAM was somewhat more pronounced in leaves of young plants than in leaves of mature plants. A develop- mental regulation may be involved. However, the observations are probably best explained by stress, since in the dry soils of the restinga young plants have no access to the ground water table while adult trees develop extensive root systems. Keywords Clusia . Crassulacean acid metabolism (CAM) . Development . Photoinhibition . Restinga Introduction Crassulacean acid metabolism (CAM) is a photosynthetic adaptation for CO 2 -acquisition under stress, which is mediated by nocturnal dark-fixation of CO 2 via phospho- enolpyruvate carboxylase (PEPC) (Phase I of CAM sensu Osmond 1978). The malic acid produced via PEPC and stored in the vacuole overnight is remobilized during the subsequent day, decarboxylated and the recovered CO 2 assimilated via ribulose-bis-phosphate carboxylase/oxyge- nase (RuBISCO) and the Calvin cycle in the light behind closed stomata (Phase III of CAM). In some CAM species, especially in Clusia, diurnal oscillations of malate are accompanied by day/night changes of citrate levels (Lüttge 1988). The expression of CAM is often age dependent. Even in obligate CAM species of the genus Kalanchoë CAM increases with leaf age and is only fully expressed in mature leaves (Kluge and Ting 1978). All CAM plants possess flexibility because during transition phases, i.e. Phase II in the morning and Phase IV in the afternoon, direct fixation of atmospheric CO 2 via RuBISCO is also possible, of which CAM plants can make use to smaller or larger extent, depending on environmental conditions. However, there are also many true C 3 -photosynthesis/ CAM intermediate species. In the annual Aizoaceae Mesembryanthemum crystallinum it is a developmental programme which drives a switch from C 3 -photosynthesis to CAM as plants age, and this is strongly enhanced by the environmental stress of drought and salinity (Cushman and Bohnert 2002). In the genus Clusia, comprising perennial neotropical shrubs and trees, there are also very many C 3 /CAM intermediate species. A developmental programme driving a C 3 /CAM switch in one direction has not been considered appropriate for the leaves of these plants which are used for several seasons and need to adapt repeatedly to varying environmental conditions. A. Berg . H. M. Duarte . U. Lüttge (*) Institut für Botanik, Technische Universität Darmstadt, Schnittspahnstrasse 3-5, 64287 Darmstadt, Germany e-mail: luettge@bio.tu-darmstadt.de Tel.: +49-6151-163700 Fax: +49-6151-164630 B. Orthen Departamento de Botânica, Universidade de Brasília, Caixa Postal 04457, Brasília, 70919-970, Brazil E. A. de Mattos Departamento de Ecologia, Universidade Federal do Rio de Janeiro, Caixa Postal 68020, Cep 21941-590 Rio de Janeiro, Brazil