In vitro phosphorylation of proteins in IAA-treated mesocotyls in Zea mays

Abstract

Five-mm sections of elongation zones of Zea mesocotyls were incubated for designated periods with various concentrations of IAA. In vitro protein phosphorylation in the soluble fraction (85,000 x g supernatant) prepared from the sections was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The phosphorylation of proteins in the soluble fraction that had been prepared from sections incubated for 20 min in the presence of 10-5M IAA was greater than that in the sections incubated for 20 min without IAA. The amount of phosphorylation of proteins per protein became higher when higher concentrations increased (106-8~10-5 M). The growth of sections incubated in the presence of 10-8 M IAA or higher concentrations was greater than that of sections incubated in the absence of IAA. The promotion of growth by IAA was greater at higher concentrations of IAA. Proteins in the soluble fraction, prepared from sections incubated for 20 min in the presence of 10-5 M IAA, were phosphorylated in the presence of either 10/μM cAMP, 10/μM cGMP, 100 μM W-7, 100 μM W-5, 20 μM H-7 or 20/μM HA1004. The calmodulin antagonist, W-7, and the inhibitor of protein kinase C, H-7, inhibited the phosphorylation of proteins stimulated by incubation with IAA. These results suggest that IAA promotes cell elongation via protein phosphorylation that depends on calmodulin-dependent protein kinase and protein kinase C.