Aaron is a senior Biology major at Southwestern University.

RESEARCH PROJECT 

Drought and Salinity Responses In C₄ Grasses
Daniel Max Taub (Biology) and Emily Niemeyer (Chemistry)
Merck 2004 Scholar David Aaron Guel

The Panicoideae and Chloridoideae grass subfamilies together comprise the great majority of the grass flora of tropical and subtropical regions of the world.  These subfamilies differ in their distributions across natural precipitation and salinity gradients, with species of the Chloridoideae found in drier and more saline environments than those of the Panicoideae.  As little is known of physiological differences between the two subfamilies that might account for these distributional differences, we will therefore compare the physiology of a selected group of species from these subfamilies grown under several different conditions of imposed drought and soil salinity.  Plant tolerance of these factors will be assessed by examining several aspects of plant functioning known to be affected by drought and salinity stress, including biomass accumulation, membrane integrity, leaf chlorophyll content, stomatal conductance of water vapor, and rates of leaf photosynthesis and transpiration.

Detailed examination of leaf chemistry will allow us to examine a variety of specific mechanisms of drought and salinity tolerance in these plants. One mechanism that enables some species of plants to tolerate soil salinity is the secretion of excess Na⁺ and Cl^- from specialized salt glands onto leaf surfaces. We will compare secretion rates among species by washing leaf surfaces and analyzing the rinsate using potentiometry.  We will also assess the concentrations of several key ions (e.g., Na⁺, Cl^-, Ca⁺², and K⁺) within the leaf tissue using ion chromatography.  Species that are drought and salinity tolerant are often able to adjust the osmolarity of their cellular fluids by accumulating physiologically compatible solutes, such as proline and glycine betaine in grasses.  We will therefore measure the concentration of these solutes in expressed leaf tissue sap using high performance liquid chromatography.