Polyploidy, the multiplication of all the chromosomes of an organism, and therefore all the genes, occurs in many plant groups. Moreover, plant species often contain substantial polyploid variation, so that neighboring individuals may have widely different numbers of chromosomes. The function of this variation (polymorphism) is unclear. Using an innovative application of biotechnology, flow cytometry, this research tests one of the major explanations of polyploid polymorphism: that multiple polyploids adapt plant populations to variation in physical and biological stress. Focusing on the dominant and economically important prairie grass, big bluestem (Andropogon gerardii), two crucial experiments manipulate the physical (water availability) and biological (grazing) stresses on plants of two ploidy levels in the well-defined environments of common garden and greenhouse. Complementing the controlled experimental results, a well-designed investigation surveys the distribution of the different polyploid levels in native grasslands along an east-west transect. Thus, experimental response to important naturally occurring stresses will be related to new information on how native populations vary in chromosome number. This project takes advantage of recent improvements in biotechnology to address questions in population biology that have previously been technically difficult. In relating polyploid polymorphism to environmental stress, this study provides theoretical and practical insights. It contributes to understanding the adaptations of native plants that allow them to prosper in harsh, unpredictable environments, and provides knowledge of plant responses to stress that facilitate management of forage and crop plants and can be incorporated into improved plant breeding programs.
