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Botany & plant ecology.

Article Excerpt
Keynote Address: The Rare Flora of Michigan; Status and Research Needs for Conservation. Michael Penskar, Senior Conservation Scientist-Lead Botanist, Michigan Natural Features Inventory.

The Integrin-binding Peptide, RGD, Causes Cell Death in Suspension Culture Cells of Daucus carota. Emily Williams, Tristan Kemps ton, Robert Bradley, Mark Staves, and Sheila Blackman, Grand Valley State University, Biology Department

The aim of our work is to understand the processes controlling plant cell development, particularly the involvement of cues from neighboring cells. We have previously shown that an integrin inhibiting peptide (arginine-glycine-aspartic acid -abbreviated RGD) specifically disrupts somatic embryogenesis in carrot (Daucus carota). Integrin is a plasma membrane-spanning protein that links the extracellular matrix on the outside of the cell to the cytoskeleton inside the cell in animals. Here, we show that, regardless of the stage of embryo development at which RGD is applied, cellular disorganization, growth arrest, and cell death ensues within 24 h. The peptide also has toxic effects when applied to non-differentiating suspension culture cells. The emergence of this effect of RGD is accompanied by the peptide's uptake by the cells. In contrast to the rapid and dramatic toxic effects on whole carrot cells, we found that RGD was not toxic to plant cells from which the cell wall had been removed (protoplasts). We conclude that RGD may be promoting cell death via a signal passed through the cell wall, and arc investigating whether the effect of RGD is mediated through programmed-cell-death.

Interaction between Light and Gravity Signals in Single Plant Cells. Mark P. Staves, Grand Valley State University, Biology Department

The "shoots" of Chara corallina are composed of large internodal cells alternating with smaller, node-forming cells. We find that these shoots are both negatively gravitropic as well as positively phototropic. Differential growth in response to both gravity and light typically takes place in the two most apical internodal cells, however the plants can be manipulated so that all curvature takes place in a single cell. Experimental plants were allowed to develop to a stage where they had one or two visible internodal cells. In the absence of light, internodal cells are negatively gravitropic. If gravistimulated (horizontal) internodal cells are illuminated with white light from above, gravity and light act together and more rapid curvature ensues. If however, gravistimulated internodal cells arc illuminated from below, gravity and light act antagonistically and light can overcome the gravity signal. We find that gravistimulated cells illuminated from below will bend up (i.e. negatively gravitropic and negatively phototropic) at light intensities below ca. 1 ([micro]mol m-2 s-1, whereas they curve downward (positively gravitropic and positively phototropic) at higher light intensities. Chara thus provides a system in which a single, statolith-free cell responds to both light and gravity and in which the interactions of the light- and gravity-induced signal transduction pathways can be investigated.

Assessment of Phytoplankton Populations and Associated Toxins in West Michigan Lakes. Janel Hagar and Richard R. Rediske, Annis Water Resources Institute, Grand Valley State University

The increasing prevalence of algal blooms in freshwater arising from cultural euttophication and the. action of non-indigenous species is creating issues related to the use of water for drinking and recreational purposes. Cyanobacteria are well known for their ability to produce potent...

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