Impact of Mammalian Two-Pore Channel Inhibitors on Long-Distance Electrical Signals in the Characean Macroalga Nitellopsis obtusa and the Early Terrestrial Liverwort Marchantia polymorpha

Inhibitors of human two-pore channels (TPC1 and TPC2), i.e., verapamil, tetrandrine, and NED-19, are promising medicines used in treatment of serious diseases. In the present study, the impact of these substances on action potentials (APs) and vacuolar channel activity was examined in the aquatic characean algae Nitellopsis obtusa and in the terrestrial liverwort Marchantia polymorpha. In both plant species, verapamil (20–300 µM) caused reduction of AP amplitudes, indicating impaired Ca2+ transport. In N. obtusa, it depolarized the AP excitation threshold and resting potential and prolonged AP duration. In isolated vacuoles of M. polymorpha, verapamil caused a reduction of the open probability of slow vacuolar SV/TPC channels but had almost no effect on K+ channels in the tonoplast of N. obtusa. In both species, tetrandrine (20–100 µM) evoked a pleiotropic effect: reduction of resting potential and AP amplitudes and prolongation of AP repolarization phases, especially in M. polymorpha, but it did not alter vacuolar SV/TPC activity. NED-19 (75 µM) caused both specific and unspecific effects on N. obtusa APs. In M. polymorpha, NED-19 increased the duration of repolarization. However, no inhibition of SV/TPC channels was observed in Marchantia vacuoles, but an increase in open probability and channel flickering. The results indicate an effect on Ca2+ -permeable channels governing plant excitation.

The herbaceous lacustrine macrophytes of Indiana, United States of America

We provide the first checklist of the obligate aquatic macrophytes of Indiana, including the geographical distribution and frequency of occurrence of each taxon. The checklist is composed of 216 taxa distributed among 85 genera within 43 families. Families exhibiting the greatest richness of taxa are the Potamogetonaceae and Cyperaceae. Approximately 50 % of these taxa are widespread, whereas only 3.7 % are restricted to either the northern or southern regions of the state. An identification code is provided for each taxon and coefficients of conservatism (C values) are given for 189 native taxa, including 18 species of characean algae. C values assigned to native taxa range from 0-10, with a median value of 6. The C values of aquatic macrophytes presented here bear greater similarity to those proposed by Rothrock (2004) for the State of Indiana than to those established by Swink and Wilhelm (1994) for the Chicago region.

A furtive stare at an intra-cellular flow

Rarely do intra-cellular flows amount to much: cells are small, and so are their Reynolds numbers. The extraordinarily large cells of the Characean algae provide a fascinating counter-example, as their geometry precludes the standard methods of distributing food and waste. van de Meent et al. (J. Fluid Mech., 2010, this issue, vol. 642, pp. 5–14) present nuclear magnetic resonance (NMR) velocimetry measurements of the fluid flow within individual living cells, which agree quantitatively with their fluid mechanical model and confirm a long-standing hypothesis. In addition to biomimetic parallels with microfluidic labs on chips, this work showcases NMR velocimetry as an under-appreciated but immensely powerful technique. The non-invasive tracer-free high-resolution flow measurements it enables – even in opaque and heterogeneous fluids – should find wide application.

Sensitivity of freshwater macrophytes to UV radiation: relationship to depth zonation in an oligotrophic New Zealand lake

The ultraviolet radiation (UVR) responses of photosynthesis by two freshwater vascular plants, Potamogeton cheesemanii and Isoetes alpinus, and the characean algae Chara fibrosa and C. corallina in Lake Coleridge, New Zealand, were investigated. Experiments comprised 4–5 h of exposure to different UV wavelengths followed by 17 h of recovery in low light. Photosynthetic competence was assessed by pulse-amplitude-modulated fluorometry. The four species showed different sensitivities to UVR, which were consistent with their upper depth limits. The shallowest-growing species, P. cheesemanii, was uninhibited by UVR, whereas after 5 h of exposure to UVR, inhibition of 15%, 38% and 48% was measured for I. alpinus, C. fibrosaand C. corallinacollected from 4 m, 6.2 m and 16.5 m, respectively. Not all plants recovered fully from UVR inhibition. Plants from upper and lower depths of their growth range did not generally differ in inhibition sustained or ability to recover photosynthesis. The species with greatest tolerance of UVR also contained the highest concentrations of UVR-absorbing pigments. Freshwater macrophytes have differing abilities to tolerate UVR exposure through repair and/or protection strategies and these may be related to their vertical zonation.