Crassulacean acid metabolism in sedum dasyphyllum L

Crassulacean Acid Metabolism (CAM) in Sedum dasyphyllum L. (Crassulaceae) was analysed by studying four ecotypes collected in sites at different altitudes in the Campania region (Italy), ana grown in well-watered conditions at the Botanical Garden of Naples. During the growth season, from winter to late spring, the overall malate content at dusk and at dawn declined strongly, thus snowing a negative correlation with photoperiod. Overnight malate accumulation occurred even in plants kept in well-watered conditions, but its extent varied with time and among the ecotypes. It was not related to photoperiod but to the daily temperature excursion which, when below a certain value, could prevent CAM activity. The specific activity of the enzymes involved in CAM also showed a seasonal pattern with a significant increase for phosphoenolpyruvate carboxylase, but a decrease for NAD- dependent malate dehydrogenase and NADP-dependent malic enzyme, at least in two.ecotypes. Because phosphoenolpyruvate carboxykinase activity was not detected, S. dasyphyllum could be placed in the group of malic enzyme CAM species. None of the activities were correlated to overnight malate accumulation, but, like overall malate content, to photoperiod, at least in two ecotypes. No statistically significant changes in the day/night activities of phosphoenolpyruvate carboxylase and NADP-dependent malic enzyme were detected. Overnight malate accumulation ana phosphoenolpyruvate carboxylase activity were higher in leaves from flowering stems than in those from vegetative ones, suggesting that CAM activity can also contribute to the reproductive success of the species in its habitat, where water can be limited when flowering and seed ripening occur. © 1999 Taylor & Francis Group, LLC.