ACCUMULATION PATTERN OF IGG ANTIBODIES AND F-AB FRAGMENTS IN TRANSGENIC ARABIDOPSIS-THALIANA PLANTS

For the further optimization of antibody expression in plants, it is e ssential to determine the final accumulation sites of plant-made antib odies. Previously, we have shown that, upon secretion, IgG antibodies and F-ab fragments can be detected in the intercellular spaces of leaf mesophyll cells of transgenic Arabidopsis thaliana plants. However, i mmunofluorescence microscopy showed that this is probably not their fi nal accumulation site. In leaves, IgG and F-ab fragments accumulate al so at the interior side of the epidermal cell layers and in xylem vess els. These accumulation sites correspond with the leaf regions where w ater of the transpiration stream is entering a space impermeable to th e proteins or where water is evaporating. In roots, plant-made F-ab fr agments accumulate in intercellular spaces of cortex cells, in the cyt oplasm of pericycle and, to a lesser extent, endodermis cells, and in cells of the vascular cylinder. In other words, antibody accumulation occurs at the sites where mater passes on its radial pathway towards a nd within the vascular bundle, Taken together, our results suggest tha t, upon secretion of plant-made antibodies or F-ab fragments, a large proportion of these proteins are transported in the apoplast of A. tha liana, possibly by the water flow in the transpiration stream.