Integrin-like proteins ape localized to plasma membrane fractions, not plastids, in Arabidopsis

Integrins are a large family of integral membrane proteins that function in signal transduction in animal systems. These proteins are conserved in ver tebrates, invertebrates, and fungi. Evidence from previous research suggest s that integrin-like proteins may be present in plants as well, and that th ese proteins may function in signal transduction during gravitropism. In pa st studies, researchers have used monoclonal and polyclonal antibodies to l ocalize beta(1) integrin-like proteins in plants. However, there is a dispa rity between data collected from these studies, especially since molecular weights obtained from these investigations range from 55-120 kDa for integr in-like proteins. To date, a complete investigation which employs all three basic immunolabeling procedures, immunoblotting, immunofluorescence micros copy, and immunogold labeling, in addition to extensive fractionation and e xhaustive controls, has been lacking. In this paper, we demonstrate that us e of a polyclonal antibody against the cytoplasmic domain of avian beta(1)- integrin can produce potential artifacts in immunolocalization studies. How ever, these problems can be eliminated through use of starchless mutants or proper specimen preparation prior to electrophoresis. We also show that th is antibody, when applied within the described parameters and with careful controls, identifies a large (100 kDa) integrin-like protein that is locali zed to plasma membrane fractions in Arabidopsis.