Specialized anatomical and biochemical features mark the presence of a previously uncharacterized cell layer in the pod wall of soybean (Glycine max L.). The cells of this layer, termed the mid-pericarp layer (MPL), are larger than other cells of the mesocarp and are highly branched. The entire MPL appears to form an elaborate interdigitated network running in a single plane parallel with the pod surface just outside vascular bundles between the dorsal and ventral sutures. A striking feature of the cell walls between individual MPL cells are regions of abrupt cell wall thinning, ~30 nm. These thin cell walls are occasionally found disrupted. Following mechanical wounding of the pod wall 40 kD F-dextran moves extensively into the MPL. In addition, cutting through the pod wall causes exudate flow from the MPL. Isoforms of lipoxygenase constitutes over 38% of the total soluble protein in this exudate and these extracts contain active lipxoygenases as assayed by O2 consumption using linolenic and linoleic acids as substrates. The exudate is relatively high in the vegetative lipoxygenase isoforms, VLXA, -B and -C which specifically co-localize to the cytoplasm in cells of the MPL. The MPL may function during mechanical wounding by generating lipoxygenase-derived compounds as a general defense mechanism found in leguminous plants.

Key words: Glycine max,lipoyxgenase,mesocarp,pod,soybean,wounding