On the First Lateral Root Primordium Formation Closer to Crown Root Apex of Rice Plants

[摘要] In a crown root of rice plants (fig. 24), protophloem elements (PP) were the first of all vascular elements to show maturation usually at about 1 mm from the apex, and secondary wall layer starts covering protoxylem elements (PX) at a distance of 4-5 mm region from the apex. At about 7-8 mm from the apex, nuclei and cytoplasm in the protoxylem elements have degenerated and successively the secondary thickening ends. A first lateral primordium (I) of the crown root seems to originate in pericyclic cells between two protoxylems in which nuclei are degenerating and secondary thickening is going on. While covering by secondary wall in early metaxylem elements (MXI), anticlinal divisions of the first lateral root primordium (II) in the pericyclic cells begin to take place. Before and after periclinal division of the pericyclic cells of the first lateral root primordium, a certain grains (fig. 17 and 18, G) gather near the end wall as well as along protoplasmic membrane of metaphloem elements (fig. 24, MP) and a rounded shape of nucleolus in the metaphloem has changed to a chestnut-in-burs like shape (fig, 19) and the nucleolus is found near the sieve plate of the mature metaphloem as an extruded nucleolus. At a half-way penetration of the cortex (fig. 24, IV), secondary thickening of the early metaxylem completes and maturation of the metaphloem takes place. Before the first lateral root emerges on the surface of crown roots (V), late metaxylem elements (MXII) begin to be covered by secondary wall and all vascular elements except the late metaxylem have matured. A certain causal relation between the first lateral root primordium formation and the development of the vascular element, especially the protoxylem, may be estimated generally in any roots of rice plants.

[学科分类] 农业科学（综合）