Mark Alan Horn

Receptor-Mediated Endocytosis in Plant Cells.

We have employed fluorescein and 125l-labeled elicitors of the defense response in soybeans to monitor the cellular distribution and movement of elicitors following their addition to a soybean cell suspension culture. Our results indicate that the macromolecular elicitors first bind to the cell surface and then internalize in a temperature- and energy-dependent endocytotic process. Within a few hours, virtually all of the elicitor is concentrated in the major vacuole or tonoplast of the cell. Nonspecific (control) proteins neither bound to the cell surface nor internalized in parallel assays.

Induction of Secondary Metabolite-Phytoalexin Formation in Plant Cell Suspension Cultures

Plants have the capability to synthesize a great variety of natural products. In general, compounds of interest have physiological and antimicrobial activity but were thought to be inert in the cells of origin and were therefore called secondary metabolites. More recently secondary natural products have been implicated in the defense response of plants against phytopathogens and were called phytoalexins. Besides having promise in the genetic development of disease resistant plant varieties, secondary products and their formation in plant cells suspension cultures has been of considerable interest. Plant cell suspension cultures which are high producers of the desired secondary metabolite would be an excellent model system to study biosynthetic and regulatory mechanisms. Although, growing plant cells in suspensions is not difficult, to stimulate these cells to produce the desired secondary metabolite in quantities sufficient for experimentation is considerably more difficult. Therefore, utilizing the stress or defense mechanism in plant cells could be beneficial in stimulation of plant cells to synthesize secondary natural products. We report here our efforts in elucidating the biochemical mechanism(s) of the induction of secondary metabolite formation.