Nucleotide metabolism in common bean pods during seed filling phase reveals the essential role of seed coats

Abstract

Common bean is a legume with high demand for human consumption and with high protein content on its seeds. The seed filling stage is a crucial step to obtain high-quality seeds with a good level of nutrients. For this, it is necessary for a correct communication between the different seed compartments. Nucleotides are essential components with nitrogen and phosphorous on its molecules, and its metabolism in seed development has not been studied in detail. In this manuscript, we have studied nucleotide metabolism in common bean pods during seed filling stage at pod valves, seed coats, and embryos. Nuclease and ribonuclease activities were assayed as nucleotide-generating enzymes, and nucleotidase, nucleosidase, and allantoinase as nucleotide-degrading activities. Nuclease was predominant in seed coats whereas ribonuclease was equally determined in seed coats and valves, although with differences in the three ribonucleases determined (16, 17, and 19 kDa). Nucleotidase and nucleosidase activities were detected in the three pods parts, and differently to nucleic degrading activities with significant activity in embryos. The relative expression of gene families coding for all these activities (S1 nuclease, S-like T2 ribonuclease, nucleotidase, nucleosidase and allantoinase) in the three pods parts was also studied. We have found the highest level of expression for some members of each family in seed coats. The allantoinase data suggest that nucleotide might be fully degraded in valves and seed coats but not in embryos. Overall, the data presented allow to conclude that there is an intense nucleotide metabolism in fruits during the seed filling stage with an especial involvement of seed coats in the process.