| Medicago truncatula is a model species for legume studies. Despite the great advances in the study of M. truncatula and development of a vast array of genetic tools and genomic resources, there is a lack of knowledge regarding the nutrient movement and accumulation in its pods and seeds. This study used a combination of the microscopic analysis, histochemical localization and the fluorescent tracers to identify the cellular course and location of nutrient movement. Temporal histochemical localization revealed that the longer duration of the accumulation of protein bodies and lipid droplets combined with the high hexoses concentration in seed apoplasm might be responsible for high protein content of M. truncatula seeds. Histochemical analysis also revealed that the pod wall cells undergo most changes in their cell wall composition during progression of development. Since lignin was not detected as a secondary cell wall component in the cells other than xylem fibers, absence of lignin from sclerenchyma could be considered a species specific phenomenon. The fluorescent probe 5-(6)-6-carboxyfluorscein diacetate (CFDA) outlined that the phloem unloading and post-phloem pathway is symplastic in M. truncatula seed coat. The use of Sulphorhodamine G (SRG) and Calcofluor White (CFW) revealed absence of apoplastic barrier and that cotyledon epidermal layer have active proton pumps. Thus, suggesting that cotyledon epidermal cells are the key site for the symplastic uptake and subsequent movement of nutrients into the storage parenchyma cells along with passive diffusion. The results of this study would supplement the ongoing research to enhance the nutritional quality and yield of legumes. |
