Submitted to: Scanning Microscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/1998
Publication Date: N/A
Interpretive Summary: Higher protein content of soybean seeds would be desirable commercially but efforts to increase soybean seed protein content to 50% have resulted in an unacceptable decrease in seed oil content and yield. Understanding the nitrogen nutrition of the soybean plant is important for scientists to solve this problem. The soybean pod represents a model system to study nitrogen nutrition because pod tissues act as a buffer, i. e. they store protein when nitrogen is abundant and mobilize the stored nitrogen as needed by the plant. The anatomy of the soybean pod was examined by electron microscopy to determine the likely cell types that may actively participate in nitrogen metabolism. The parenchyma cells were judged to be the most likely to be involved in nitrogen metabolism because of their large vacuoles where nitrogen could be stored and the number of chloroplasts that they contain throughout seed development. Further studies will determine whether the nitrogen is stored in the form of protein in the parenchyma cells. These data will be used by scientists working on soybean nitrogen metabolism.
Technical Abstract: The pericarp (pod wall) of the carpel (pod) of soybean [Glycine max (L.) Merr.] was examined by conventional and low temperature scanning and transmission electron microscopy. The pericarp consists of an exocarp of a single layer of epidermal cells whose surface contains clavate and setaceous trichomes, a cuticle and elevated stomates, and a single layer of hypodermal cells that are fusiform in shape and have thick, sclerified walls. The mesocarp consists of 10 to 14 rows of parenchyma cells that are about twice as long as they are wide with an extensive vascular system embedded within it. The endocarp consists of two types of sclerenchyma cells, aerenchyma, and an endodermis of parenchyma cells. The two layers of sclerenchyma are thick walled with the upper layer hexagonal in cross section, shorter and more blunt. The lower sclerenchyma are longer, fusiform and spherical in shape. The aerenchyma cells are anastomosing, lobed, irregular, tubular cells. The endodermis of parenchyma cells appear to be homogeneous and isodiametric in size. The cells walls were the most conspicuous structures of the pericarp, and the vacuole was the most prominent organelle. Chloroplasts were found in all of the cell types during development. The different cell types in the carpel were differentiated early in development and further growth consisted of maturation of the cells.