Ultrastructure of cells in an initiating lateral root primordium of Raphanus sativus

Lateral root primordia in Raphanus sativus had developed 10 hours after main root decapitation. The primordia consisted of three cell layers — basal layer continuous with the pericycle. The primordia were initiated by activated groups of pericycle cells. Inactive pericycle cells with a thin layer of parietal cytoplasme large central vacuole and well developed leucoplasts with starch grains were trans-formed into meristematic cells. During transformation the amount of cytoplasm and number of cytoplasmic organelles greatly increased, the central vacuole disappeared, and an ER system continuous in many places with the nuclear envelope evolved. The lamellar structure of plastids underwent almost complete reduction; the dictyosomes became active. The newly formed meristem differed apparently from the apical root meristem only in the lack or scarcity of lipid bodies and starch.