On the Relevance and Control of Leaf Angle

Plants can have constitutive leaf angles that are fixed and do not vary much among different growth environments. Several species, however, have the ability to actively adjust their leaf angles. Active leaf repositioning can be functional in avoiding detrimental environmental conditions, such as avoidance of heat stress and complete submergence, or can be, for example, utilized to maximize carbon gain by positioning the leaves relative to the incoming radiation. In recent years, major advances have been made in the understanding of the molecular mechanisms, and the underlying hormonal regulation of a particular type of leaf movement: hyponastic growth. This differential petiole growth-driven upward leaf movement is now relatively well understood in model systems such as Rumex palustris and Arabidopsis thaliana. In the first part of this review we will discuss the functional consequences of leaf orientation for plant performance. Next, we will consider hyponastic growth and describe how exploitation of natural (genetic) variation can be instrumental in studying the relevance and control of leaf positioning.