Experimental Studies on Lateral Root Formation in Radish Seedling Roots. I. General Methods, Developmental Stages, and Spontaneous Formation of Laterals

Abstract

Three-day-old radish (Raphanus sativus) seedling roots were used in these studies, either as part of intact seedlings or as cultured excised segments. Observations and measurements were made on the growth and development of seedling roots. Anatomical studies were performed on seedling roots and on developing lateral root primordia (LRP). In longitudinal sections, oblique cross wall formation in the pericycle was observed, as was the subsequent formation of cuneiform cells during the very early ontogeny of LRP. Procedures are described for the quantitative assessment of the effects of experimental treatments on (1) LRP initiation in terms of the number of LRP that form per centimeter of seedling root, and (2) LRP development utilizing six numbered developmental stages. Five to six LRP formed spontaneously per centimeter of seedling root in the absence of treatment designed to influence LRP initiation. We speculated, based on our observations, that a spontaneously forming LRP could develop from a small population of pericycle cells that do not stop cycling after emerging from the apical meristem region.