Characeaen internodal cells have been used by leading scientists in search of the mechanism of plant action potentials (APs) since the early 20th century [1]. High amplitude (up to 150 mV) and long duration (tens of seconds) of characeaen APs make them suitable to be registered extracellularly [2] and intracellularly [3] and used in biophysical research. However, electrical signaling of Nitellopsis obtusa unicellular chloroplast-free rhizoids, which anchor the body of algae to the substrate, has not been described previously. Therefore, wider research and analysis of rhizoids' properties would contribute to the extensive application of Nitellopsis obtusa cells, since rhizoids and internodal cells are distinct - rhizoids do not need constant lighting nor chloroplasts to carry out their functions [4].
Since the parameters describing electrical signaling of internodal cells of Nitellopsis obtusa have been characterized in detail, we aimed to explore the same parameters in their rhizoids as well. Electrophysiological experiments were conducted using intracellular microelectrode and two pair current clamp method placing an oblong cylinder-shaped rhizoid of Nitellopsis obtusa along the chamber with electrically isolated compartments.
Results show that Nitellopsis obtusa rhizoids are, in fact, excitable and their APs are more rapid. In comparison to the APs of internodal cells, APs of rhizoids do not have the overshoot (peak is negative) and the excitation threshold is more hyperpolarized: the amplitude of action potentials of rhizoids varies around 100 ± 3 mV, threshold: -140 ± 2 mV and peek: -40 ± 2 mV (n=28).
Summarizing current clamp results we affirm that neither constant lighting nor chloroplasts are needed for rhizoids in order to generate action potentials which can contribute to the algae's physiology, for example, gravitational sensing. However, further analysis of rhizoids' electrical active and passive properties should be carried out in order to determine additional possible applications of Nitellopsis obtusa rhizoids along the internodal cells in biophysical research.