Comparative anatomy of pod dehiscence of legumes1

Pod dehiscence in legumes is an important process for the release of mature seeds to the environment. An anatomical study of pod development and dehiscence was undertaken with four groups of legumes from commercial sources. Immature, mature, and nearly dehiscent tissue samples were processed from Glycine max, Lupinis sp., Phaseolus vulgaris, and Pisum sativum. All four legume groups had an epidermis, bundle cap cells, and mesocarp cells in their sutures. Soybean pods had a dehiscent zone of fragile cells that the other three legume groups did not have in their dehiscent areas. The dorsal suture of soybean was very fortified with extensive bundle cap cells and lignified epidermal cells. Ventral suture apices of lupines had collapsed cells at a depression on the surface near a small group of bundle cap cells. Unlike the other species, pea samples had only one row of bundle cap cells with a large number of vascular bundles beneath. Immature samples of bean pods had no bundle cap cells. Carpel tissues varied among the four groups of legumes. Lupine and peas had a thickened endocarp early in development that was maintained throughout development while soybean and beans pods only developed a thickened endocarp layer later in development. Most carpel cells had thin cell walls and the majority of these cells collapsed prior to dehiscence. The death of thin-walled carpel cells and the loss of moisture from carpels may have a major role in dehiscence. Overall, carpels of the four groups of legumes had a variety of anatomical characteristics throughout maturity.