Stress Proteins and Isozymology of Acid Phosphatase, Esterase, and Peroxidase in Phaseolus vulgaris Following Peanut Mottle Virus Infection

The present work was undertaken to study soluble protein changes and enzyme alterations in Topcrop bean ( Phaseolus vulgaris L.) primary leaves following inoculation with peanut mottle virus (PMV) in an attempt to elucidate the biochemical basis of the hypersensitive reaction in this host virus combination. Using the discontinuous polyacrylamide gel electrophoresis (disc-PAGE) technique, at least four apparently novel protein bands at Rf values of 0.80, 0.77, 0.74 and 0.68 were observed in infected tissue. The band at Rf 0.76 seems to be injury related and is shown here to be an isozyme of acid phosphatase. It is believed that these proteins are neither the cause nor the product of necrosis and may thus play a role in the active defense mechanism of the plant. In this virus host combination it was found that heating soluble protein fractions at 55 °C for 10 min before electrophoresis dramatically reduced the background and improved resolution on gels. While the biological function(s) of these proteins needs further investigations it is almost certain that none of them is an isozyme of alkaline phosphatase, acid phosphatase, esterase, or peroxidase. Zymogram analysis has additionally revealed the absence of alkaline phosphatase activity in untreated, abraded and PMV-infected primary leaves and no qualitative or quantitative changes in esterase isozymes have been observed in primary leaf tissues following abrasion or PMV–infection. By contrast, qualitative alterations in acid phosphatase after PMV-infection and both qualitative and quantitative changes in peroxidase after mechanical abrasion and PMV-infection have also been demonstrated.