Investigations into the biochemical mechanisms responsible for the initiation of the plant defense response and biotin-mediated delivery of macromolecules into plant cells

Mark Alan Horn, Purdue University

Abstract

One of the most important interactions in plant biochemistry is the interaction between the plant and its environment. Unlike animals, plants cannot move away from harmful environments or toward more ideal environments. This lack of mobility requires that plants have both highly effective self-defense mechanisms and very efficient nutrient gathering processes. In this study we have investigated the plant cell's ability to detect very low levels of molecules derived from its cell wall and how the presence of these molecules can trigger the plant defense response. We determined that the plant detects these molecules via the saturable binding of these molecules to plasma membrane receptors. We found that the presumed signal transduction system activated by this binding does not involve intracellular pH changes. In addition, we discovered that after the plant detects the presence of these molecules and begins its defense response, it removes these highly potent biomolecules from the extracellular matrix via receptor-mediated endocytosis. In a second study, we found that the soybean cell's natural biotin transport pathway could be exploited to deliver large numbers of intact, native proteins to the cytoplasm of the soybean cell. In addition, we determined that the biotin-labeled protein bound to a limited number of sites on the soybean cell and that this binding was biotin-mediated. This delivery to the cytoplasm is temperature-sensitive and vesicle-mediated. The maximum size limit of molecules that could be efficiently delivered via this process was $\sim$70,000 daltons. This size limit arose from the cell wall pore size and not from an inherit limitation of the process. Unfortunately, several different modifications of the extracellular matrix did not result in an increase of the upper size limit of the molecules internalized via this process.

Degree

Ph.D.

Advisors

Low, Purdue University.

Subject Area

Biochemistry|Botany

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