Electrorotational spectra of protoplasts generated from the giant marine alga Valonia utricularis

Protoplasts of Valonia utricularis is lacking the large central vacuole can be generated by cutting multi-nucleated, giant ''mother'' cells into small pieces after short exposure to air. When the protoplasmic content was squeezed out into sea water, irregularly shaped, green coloured aggregates were formed which changed into spherical protoplasts (radius of 20-60 mu m) after about 2 h. In these protoplasts the dense internal material (consisting mainly of organelles) was separated from the plasmalemma by a thin transparent layer containing a large number of small lipid vesicles. Cell wall regeneration occurred rapidly after protoplast formation. A central vacuole developed after about 10 h. The regenerated cells continued to grow and were viable for several months. Electrorotation studies on 2-3 h old protoplasts at pH 7 in low- and fairly high-conductivity solutions showed one or two anti-field rotation peaks (depending on medium conductivity) between 10 kHz to 1 MHz as well as one co-field rotation peak between 10 MHz to 100 MHz. The rotation spec tra could not be fitted on the basis of the single- (or multi-) shell model (i.e., by modelling the cells as a homogeneous sphere surrounded by one or more layers). However, fairly good agreement between the experimental data and theory could be obtained by assuming that the rotational behaviour of the protoplasts depends not only on passive electrical properties of the plasmalemma but is influenced by ''mobile charges'' of carrier transport systems and/or the dielectric behaviour of the aggregated chloroplasts and vesicles.