The Mid-Pericarp Cell Layer in Soybean Pod Walls Is a Multicellular Compartment Enriched in Specific Lipoxygenase Isoforms

Specific lipoxygenase isoforms immunolocalize to the cytosol of a single cell layer in the soybean (Glycine max L.) pod wall. The cells of this layer, termed the mid-pericarp layer (MPL), are larger than adjacent cells and are highly branched. The entire MPL appears to form an elaborate interdigitated network within the pod wall. A particularly striking feature of the MPL is the presence of extensive regions of very thin, approximately 30 nm, cell wall, which connect the cells of the MPL. It was demonstrated that after mechanical wounding of the pod wall, 40-kD fluorescein-dextran was able to move throughout the MPL. In addition, when pod walls are cut, an exudate flows from the MPL that is highly enriched in lipoxygenase isoforms (approximately 40% of the total protein). The MPL of soybean pod walls may represent a novel multicellular compartment involved in defense of leguminous plants.