The sensory system of the sporangiophores of Phycomyces blakesleeanus has been of interest for many years. The sporangiophores are large single cells that detect and respond to several different environmental stimuli with either a symmetric or an asymmetric change in elongational growth rate. Thus, fundamental to a detailed understanding of the sensory system is an in-depth quantitative understanding of the regulation of the sporangiophore's growth rate. The long-term objective of the proposed research is to establish quantitative relationships (Growth Equations) for sporangiophore growth rate and water transport rate, for all stages of sporangiophore development. Previously, it was demonstrated that the sporangiophore may transpire up to 85% of its water uptake, thus transpiration is an important process which must be included in the quantitative relationships. The immediate objective of this project is to extend the Growth Equations to include transpiration, and to study the transpiration process as a function of development and environmental conditions. The results obtained may provide new insight into the transpiration process, water transport, plant cell growth and growth regulation, plant cell development, and sensory transduction. %%% Dr. Ortega proposes to experimentally determine the magnitude of, and changes in, biophysical and biochemical properties of the giant single cells of the fungus Phycomyces in order to establish a quantitative mathematical model for the growth rate and behavior of these cells. These large cells detect and respond to several different environmental stimuli such as light, with either a symmetric or asymmetric change in elongational growth rate and have thus been used as a model system for elucidating the sensory transduction process. He here will determine the effects of transpiration (water retention or loss) on growth rates and incorporate this information into his mathematical models. The results will have a wider significance in understanding the mechanics of cell wall growth and water transport in other fungi and also in green plants.
