How Dynamic Changes in Leaf Anatomy affect Photosynthesis

Plant leaves are intricate organs that show a wide range of variation in form and structure. It has long been recognized that their anatomy is tightly linked to biological function. The most characteristic functions of plant leaves are related to the capture of light and carbon dioxide (CO2) for use in photosynthesis. Photosynthesis is the basis of the world`s food web, and understanding how this process responds to changes in the environment, in particular to a limited water availability, is of great social and economic interest. Much of the recent research has focused on how leaf photosynthesis in response to the environment is determined by biochemical processes. The role of anatomy has proven difficult to describe quantitatively and has often been ignored. Interestingly, recent developments suggest that the leaf anatomy cannot be assumed to be static, but changes rapidly and reversibly in response to a water deficit. Fortunately, this dynamic nature of anatomy provides an unique opportunity to examine the effect of the leaf internal structure on photosynthesis. To this end, leaves of drought- tolerant and sensitive poplar cultivars will be exposed to a water deficit and changes in anatomy, leaf water status and photosynthesis will be closely monitored. In contrast to most earlier work, advanced new microscopy techniques will be employed to analyze the anatomy in three dimensions down to the subcellular level. This will allow for characterization of the leaf anatomy to an unprecedented level of detail. In addition, the resulting three-dimensional representation of the leaf structure makes it possible to describe photosynthesis and the diffusion of CO2 through the leaf using a mechanistic model of the biophysical processes involved. The proposed experiments will clarify what kind of short-term changes in anatomy are induced by changes in the leaf water status and how such changes correlate with differences in photosynthesis. In combination with a mechanistic model of the photosynthetic process, this will allow for the identification and quantification of key anatomical traits that limit photosynthesis under a water deficit. Such traits may find use in future breeding programs for drought-tolerant plants.