9320218 Evert The proposed research involves studies on the development and structure of the leaves of maize and barley, utilizing bright- field, transmission electron, epifluorescence, and confocal laser scanning microscopy. The developmental and structural studies will be complemented by experimental studies aimed at determining: 1) the pathways followed by photoassimilates in source and sink leaves; 2) the sites and mechanisms of phloem loading and unloading in source and sink leaves, respectively; 3) the structural modifications associated with the sink-to-source conversion; and 4) the pathways followed by water, which enters the leaf in the transpiration stream, to intermediate, small, and transverse veins at various levels of leaves undergoing sink-to-source conversion. Maize and barley, as other grass leaves, provide an excellent system for following a sequence of cellular and subcellular events precisely because polarized cell division at the base of the leaf results in an unmixed gradient of cell development. This same system should be ideal for determining the underlying mechanisms of the sink-to-source transition. The leaves of maize and barley differ in many details both structurally and developmentally. Parallel studies on the leaves of both of these economically important grasses will provide a more balanced picture of structure-function relations in grass leaves than would an investigation of only one of them. The results of these studies will have long-term practical importance in relation to crop productivity and will be of value to investigators interested in relations of viruses, insects, mycoplasmas, and other parasites to their hosts and in the movement of insecticides and growth regulating substances in cultivated plants. ***
