AB , Swarthmore College, Swarthmore, PA, Biology, Chemistry
M.S., University of Wisconsin, Madison, WI, Plant Physiology, Soils.
Ph.D., Duke University, Durham, NC, Plant Physiology, Biochemistry
My presence in our laboratory is full time only during the winter and thus my involvement with students is shared with other faculty. Our research investigates how water affects plants with specific emphasis on water deficits. Early efforts established thermodynamic principles of water potential as well as vapor pressure and pressure chamber methods of measuring it. With these tools, we were able to repeat experiments readily. We found that the activity of specific enzymes respond to water deficits when co-factors, substrates, or inducers of gene expression were altered in availability as water was lost from the cells. During this work, we discovered that growth itself caused a slightly lower water potential, that is, a growth-induced water potential. This allowed the growing cells to extract water from surrounding tissues to support the growth process. We also discovered that water deficits caused plant tissues to adjust osmotically in a way that helped maintain water uptake from the soil. These two discoveries pointed toward the need to investigate the fundamental nature of the growth process with the finding that pectin, a normal constituent of plant cell walls, underwent a specialized chemistry on its way to the wall. The chemistry controlled not only the growth rate of the cells but also the deposition of new wall, which is essential for maintaining wall integrity as the cell enlarges. The whole process was driven by the rate of release of pectin to the wall and the generation of enough turgor pressure above a threshold level. Consequently, a main objective of subsequent work will be to investigate how widely these growth principles apply, with emphasis on roots whose extension is critical as water shortages develop.
At the same time the growth experiments were done, measurements confirmed that water deficits were more inhibitory to photosynthesis than to respiration, that is, plants lose the ability to feed themselves while remaining alive. As a result, crops such as maize lose the ability to produce grain during drought. It occurred to us that feeding photosynthetic products to the plant might reverse this result and we developed a way to do that. Grain was produced during a drought where otherwise none would occur. While this “intravenous feeding” is not directly practical for agriculture, it allows the myriad effects of water deficits to be narrowed to just a few biochemical steps. These in turn allow us to determine the genes involved and how they respond to feeding. So far, it has been possible to prevent abortion of young embryos with this feeding technique. Therefore, another major goal of our work will be to pursue genetic means of preventing abortion to enhance grain production in agricultural practice.