Quantitative changes in calmodulin and NAD kinase during early cell development in the root apex of Pisum sativum L

Calmodulin and NAD kinase were extracted from serial developmental sections of the pea root apex. Highly purified samples of calmodulin were assayed by NAD-kinase activation, and whole-cell extracts were examined by two-dimensional polyacrylamide gel electrophoresis. Calmodulin was found to vary 17-fold in concentration over the apical 2 mm, being high in the region of the root cap and meristem, falling rapidly at the base of the meristem during early stages of rapid cell elongation. The rate of decline was different between stele and cortex. Except for a minor increase in concentration 2.5-5 mm from the apex, which coincides with the region of localised meristematic activity during initiation of lateral root primordia, the concentration of calmodulin remained at the lower level throughout the more basal sections of the apical 10 mm. In-vitro NAD-kinase activity was found to increase 17-fold per cell over the apical 30 mm, almost entirely as the result of an increase in calmodulin-dependent activity. Quantitative estimates of both calmodulin and NAD kinase were found to be highly dependent on extraction procedures.