Leaf Structural Properties that Influence Photosynthesis: Interactions Between Gradients of Light and Photosynthetic Capacity

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9409139 Vogelmann Functional significance has not been ascribed to many leaf structural features such as palisade and spongy mesophyll. These tissues presumably optimize photosynthesis, possibly by maximizing overlap between internal concentrations of light and carbon dioxide. The proposed research will examine the relationship between leaf anatomy, internal gradients of light, carbon dioxide and the distribution of photosynthetic activity within the leaf. In most leaves, light enters from the top whereas carbon dioxide enters primarily from the bottom where the majority of the stomata occur. This may create two opposing internal gradients, either one of which may limit photosynthesis of the individual cell layers. In turn, such internal limitations could influence photosynthetic performance at the level of the whole-leaf. Leaf anatomy (sun vs. shade leaves) and the placement of variable numbers of stomates on the lower and upper leaf surfaces (hypo- vs. amphistomy) could influence internal limitations to light and carbon dioxide, and affect whole-leaf photosynthetic performance. By using radiolabeling and microautoradiography, it is proposed to examine more directly the interactions between light and gradients of photosynthetic performance within the leaf. These experiments will comprise a first step towards understanding the importance of leaf structure to photosynthetic performance in both agricultural and native species. ***