Essential protein required during embryogenesis (PubMed:15266054). Catalyzes the reversible epimerization of D-ribulose 5-phosphate to D-xylulose 5-phosphate (By similarity). Essential for the early steps of nematode feeding sites (NFS, multinucleated root cells) formation induced by the root-knot nematodes Heterodera schachtii, Meloidogyne incognita, M.javanica and M.hapla (PubMed:9843485). D-ribulose 5-phosphate = D-xylulose 5-phosphate Binds 1 divalent metal cation per subunit. Active with Co(2+), Fe(2+), Mn(2+) and Zn(2+). Carbohydrate biosynthesis; Calvin cycle. Homooctamer. Present in roots, seeds and flowers (PubMed:9843485). Accumulates in nematode feeding sites (NFS) (PubMed:9843485). During root development, expressed in the meristems, in part of the elongation zone, in which cells divide and expand, and initiation sites of lateral roots (PubMed:9843485). In mature embryos from dry seeds, observed in the zone corresponding to the root apical meristem and in cotyledons (PubMed:9843485). Induced by both root-knot and cyst nematodes when nematode feeding sites (NFS, giant cells) are developped and form galls. Defective embryo arrested at cotyledon stage (PubMed:15266054). Reduced germination capacity, leading to the development of some dwarf seedlings unable to grow on soil (PubMed:9843485). Reduced sensitivity to nematodes associated with reduced number of cysts and limited number of galls upon infection with Meloidogyne incognita and Heterodera schachtii (PubMed:9843485). Belongs to the ribulose-phosphate 3-epimerase family.