Format: ORAL

Thibaud F.E. Messerschmid1, Jurriaan M. de Vos2, Jessica A. Berasategui3, Susanne E. Hamburger4, Sophie C. Simon4, Glsem Kara4, Siwi A.W. Astuti3 Gudrun Kadereit1,3

1 Botanischer Garten München-Nymphenburg, München, Germany 2 Universität Basel, Basel, Switzerland 3 Ludwig-Maximilans-Universität München, München, Germany 4 Johannes Gutenberg-Universität Mainz, Mainz, Germany

CAM photosynthesis involves the nocturnal assimilation and storage of carbon in the form of malic acid in the vacuole. It is mostly but not exclusively associated with succulence which may optimize the vacuolar storage capacity of malic acid. Plants that express CAM rely on diurnal closure of stomata while internal CO2concentrations are high, limiting transpiration to its cuticular rather than stomatal component during parts of the day. Cuticular transpiration barrier properties may thereby represent an understudied trait related to CAM. To investigate the interrelation and evolution of cuticular transpiration barrier properties, succulence and CAM expression, we set up a climate chamber experiment sampling most species ofAeoniumandAichryson(Crassulaceae), the iconic houseleeks that largely diversified on the Canary Islands. Under varied treatments of heat and drought, over-night acidification of leaves was quantified as a means to study CAM expression patterns. Transpiration barrier properties of the cuticle as well as the degree of succulence were quantified through leaf drying curves and measurement of minimum conductance (gmin). Our results reveal a negative correlation of CAM activity andgminsuch that species with strong or constitutive CAM were more likely to have an efficient cuticular transpiration barrier. However, leaf succulence was not correlated with CAM activity which is in contrast to the remarkable role of succulence in the function of CAM photosynthesis. In conclusion, we present first evidence for the need of reduced cuticular transpiration in CAM plants which is to be expected under selection for high water-use efficiency.