Lateral root development in a woody plant,Quercus suberL. (cork oak)

Abstract

The distribution and the ontogenesis of lateral roots have been investigated in the Mediterranean woody species Quercus suber L. (cork oak). Lateral roots arose in protoxylem-based ranks and a tendency to clumping was observed. Three stages are distinguished in lateral root primordium development. Lateral root primordia are derived mainly from pericycle cells. The endodermis contributed to the initial lateral root development, forming an endodermal cover that sloughs off with lateral root emergence. The unemerged lateral roots show an incipient layered root meristem; this meristem can be classified as a closed type meristem. Primary vascular connection takes place with the xylem strand opposite the lateral root primordium and the two adjacent phloem strands. Primary vascular connector elements are derived from pericyclic derivative cells. Vascular parenchyma cells contribute mainly in the development of the cambium and the subsequent secondary xylem and phloem connector elements. The secondary vascular elements of the lateral root and parent root differentiate in continuity. Vascular connection is discussed in relation to the root vascular plexus described in monocotyledonous and in some herbaceous dicotyledonous plants. An endodermis with suberized lamellae is continuous between the lateral and parent root in emerged lateral roots.Key words: lateral root, development pattern, apical lateral root meristem, root vascular connection, Quercus suber L.