The proposed research involves studies on the development and structure of leaves of selected C3 and C4 plants, utilizing bright.field, phase and electron microscopy. The developmental and structural studies are complemented by experimental studies aimed at determining: 1) the pathways followed by photoassimilates in immature (sink) and mature (source) leaves; 2) the sites of phloem unloading in sink leaves and of phloem loading in source leaves; and 3) the pathways followed by water and solutes entering the leaf apoplast in the transpiration stream in leaves at different stages of development. The experimental studies include: plasmolytic studies aimed at determining the solute concentrations of various cells of the leaf; microautoradiographic studies aimed at determining pathways followed by .1.4C.sucrose and .1.4C.assimi lates in leaves; ATPase localization studies aimed at determining the sites of active phloem unloading or loading; free.space marker studies aimed at determining the pathways followed by water and solutes entering the leaf apoplast in the transpiration stream; and whole leaf autoradiographic studies aimed at following patterns of sink.to.source conversion and water movement in developing leaves. These studies will provide a greater understanding of the structural changes of leaf development related to sink.to.source transition in leaves, and of the way in which substances manufactured in the leaf are loaded into the food conducting cells of the leaf veins for export from the plant.
