Mechanisms of action of Polymyxin B on Chlorella and Scenedesmus.

Neither the P32-phosphate nor the S35-sulfate were metabolized by intact seeds until after radicle protrusion (15 to 18 hours after beginning of imbibition). Punctured seeds, however, metabolized the radioactive phosphate or sulfate within 3 hours after the beginning of imbibition. We concluded that the coats surrounding the embryo are impermeable to phosphate and sulfate ions. Most of the organic P32 extracted, whether from punctured seeds before radicle protrusion or from unpunctured seeds after protrusion, was found in phosphorylcholine and phospholipids. S35 was detected in cysteine, methionine, and numerous unidentified compounds, both from punctured seeds before radicle protrusion and from unpunctured seeds after radicle protrusion. Thus within 3 hours after the beginning of imbibition, punctured seeds could esterify phosphate and reduce sulfate to the level of sulfhydryl.