Studies on the formation of the crown root primordia of rice plant - Position and number of crown root primordia in the elongated part of the stem

Light microscope observations were conducted to clarify the position and number of crown root primordia formed along the elongated portion of the stem in rice. The results were as follows. 1) Each node of elongated stem, except the neck node of the panicle, could be divided into three parts based on the formation of the peripheral cylinder of the longitudinal vascular bundle (PV);that is, Divided Portion I (PV was divided at only one or two sites at midrib, DP I),DP II (PV was divided into many parts by large and/or small vascular bundles coming from the leaf sheath), and non-DP along the stem. 2) Crown root primordia were formed only at the DP II of nodes along the elongated stem, except the neck node of the panicle. The diameters of the crown root primordia were small due to the size of the divided PV where crown root primordia were formed. 3) There was no tendency in the number of crown root primordia along the elongated stem, and the number of crown root primordia had no relation to the number of large and/or small vascular bundles coming from the leaf sheath. From these results and our previous reports, the former theory put forwarded by others, in which crown root primordia were said to be formed in both upper and lower portions of the node, is not applicable to the rice plant.