Light-induced chloroplast α-amylase in pearl millet (Pennisetum americanum)

Abstract

In pearl millet (Pennisetum americanum) seedlings light induces the appearance of a leaf α-amylase isozyme. The leaf α-amylase isozyme was present in enriched amounts in isolated chloroplasts but it could not be detected in isolated etioplasts. The chloroplast α-amylase was present in both mesophyll and bundle-sheath chloroplasts. Preliminary characterization indicated that molecular properties of chloroplast α-amylase were like those of a typical α-amylase. The plastidic α-amylase had a molecular mass of 46 kD, pH optimum of 6.2, required Ca2+ for activity and thermostability, but lost activity in the presence of ethylenediaminetetracetate. Plastidic α-amylase activity after sodium dodecyl sulfate-polyacryl-amide gel electrophoresis could be renatured in situ by Triton X-100. Western blot analysis demonstrated that this protein was antigenically similar to a maize seed α-amylase. In vivo [35S]methionine labeling of bundle-sheath strands isolated from light-grown leaves followed by immunoprecipitation revealed that bundle-sheath strands synthesized plastidic α-amylase de novo.