The role of the cytoskeleton in regulation of the division plane, mitosis and morphogenesis will be investigated in stomatogenesis in the fern ally, Selaginella. This simple system takes advantage of two of the most dramatic examples of precisely defined morphogenetic pathways known in plants: stomatogenesis and monoplastidic cell division. In stomatogenesis, the guard mother cell differentiates from epidermal initials to depart on a pathway leading to formation of a pair of specialized guard cells. In monoplastidic division, nuclear and plastid division are intimately coordinated by precise morphogenetic plastid migrations and by organization of the spindle at the plastids. The overall objective of this research is to use the determinated pathway of stomatogenesis and the phenomenon of morphogenetic plastid migration to answer questions of fundamental importance in plant morphogenesis. Morphogenetic plastid migration provides an accurate marker of changes in polarity during the cell cycle. This migration will be compared with the better known circadian and photostimulated chloroplast migration in Selaginella. Movement of chloroplasts has been well studied and provides one of the better understood examples of actin driven motility in plants. Proposed studies include live observations and direct and indirect localization of f-actin and microtubules using light (video enhanced differential interference contrast, fluorescence, confocal laser scanning) and transmission electron microscopy. Drugs will be used to perturb cytoskeletal proteins to determine function in control of division plane, organelle migration, and division, and in cell shaping and wall deposition that leads to the distinctive form of mature guard cells. Such studies will increase our understanding of the phenomenon of plastid polarity in monoplastidic cell division, and will contribute to the general knowledge of the role of the cytoskeleton in patterned development in a multicellular plant tissue.
