Plasmalemma invaginations, contraction and locomotion in normal and caffeine-treated protoplasmic drops of Physarum.

The de novo formation of plasmalemma invaginations and vacuoles of light microscopic dimension in protoplasmic drops at different age-stages was studied quantitatively by applying morphometric methods and marker techniques. The study includes: i) the normal morphogenetic development to a drop age of 1 hour, ii) the influence of caffeine treatment, and iii) the effects of removal of this drug. In untreated drops, formation of invaginations and vacuoles is accomplished within 10 to 15 min. By application of 5 mM caffeine, the formation of plasmalemma invaginations is inhibited for 20 to 30 min. The onset of oscillating contraction activity is delayed, but not hindered by the drug. Drug removal 20 min after drop generation leads to an immediate initiation of plasmalemma infolding. Although caffeine does not hinder initiation of normal contraction activity, the locomotory ability of the drop is blocked if the drug is not removed from the drop and the substrate. Thus, caffeine uncouples motive force generation from locomotion in all plasmodial stages of Physarum. The cellular sites of drug action are discussed.