Light-Induced Chloroplast [alpha]-Amylase in Pearl Millet (Pennisetum americanum)

In pearl millet (Pennisetum americanum) seedlings light induces the appearance of a leaf alpha]-amylase isozyme. The leaf alpha]-amylase isozyme was present in enriched amounts in isolated chloroplast but it could not be detected in isolated etioplasts. The chloroplast alpha]-amylase was present in both mesophyll and bundle-sheath chloroplasts. Preliminary characterization indicated that molecular properties of chloroplast alpha]-amylase were like those of a typical alpha]-amylase. The plastidic alpha]-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 alpha]-amylase activity after sodium dodecyl sulfate-polyacrylamide 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 alpha]-amylase. In vivo 35S]methionine labeling of bundle-sheath strands isolated from light-grown leaves followed by immunoprecipitation revealed that bundlesheath strands synthesized plastidic alpha]-amylase de novo.