Endoplasmic veins from plasmodia of Physarum polycephalum: a new strand model defined age, structure, and behavior.

Pure endoplasm from plasmodia of Physarum polycephalum taken up into glass pipettes and subsequently extruded into water forms a long protoplasmic cylinder uniform in diameter, which is designated as an "endoplasmic vein". This new experimentally obtained model has proven advantageous for tensiometric investigation of contraction activity. During the process of aging, this model undergoes processes of 1. actin transformations, 2. cytoplasmic actomyosin fibrillogenesis and 3. development of a new plasmalemma invagination system. Within approximately 20 min the newly formed plasmalemma invaginations delimit an endoplasmic channel and shuttle streaming along the longitudinal axis appears in the artificially generated protoplasmic strands. The geometrical shape of this strand model permits unidirectional tensiometric measurements of contractile and mechanical properties of the endoplasm during the early stages of its transformation to an ectoplasmic tube. Tensiometric and morphologic observations reveal that the process of actomyosin fibrillogenesis in the early stage of development of endoplasmic veins is temporally correlated with an increase in the force output under isometric conditions of tensiometric measurement. Young's modulus, which represents mechanical properties of the model (0.8-1.4 X 10(5) dyne/cm2), is in the range of values observed in normal isolated protoplasmic strands. The advantages of the new model for the investigation of cyclic contraction behaviour are discussed.