Permeability of the Giant Axon of Dosidicus gigas to Calcium Ions

I t is a commonly accepted fact that calcium ions, apart from regulating the permeabil-ity oi cell membranes to various ionic species, determine the level of membrane lec-trical potential at which nerve fibers fire impulses. Since these properties ascribed to Ca ++ seem to be of great importance, a great deal could be gained by having detailed information regarding the permeability of nerve fibers to Ca ++, the physical state of intracellular calcium, or, in general, any chemical reaction in which nerve fiber con-stituents and calcium ions participate. The techniques of microinjection and internal perfusion used in this work have been shown previously to work successfully in the giant axon of Dosidicus (1-3). Only results obtained in nerve fibers whose electrical properties were undamaged through the whole experiment were considered. In the microinjection technique, action poten-tials were recorded only with external electrodes, whereas in the internally perfused fibers the additional control of internal recording was also effected. Stimulating elec-trodes were externally applied in both techniques. The details of the methods have been (4) and will be published elsewhere

Differentiation of haploid and diploid fertilities in Gracilaria chilensis affect ploidy ratio

Background Algal isomorphic biphasic life cycles alternate between free-living diploid (tetrasporophytes) and haploid (dioicious gametophytes) phases and the hypotheses explaining their maintenance are still debated. Classic models state that conditional differentiation between phases is required for the evolutionary stability of biphasic life cycles while other authors proposed that the uneven ploidy abundances observed in the field are explained by their cytological differences in spore production. Results We monitored the state and fate of individuals of the red seaweed Gracilaria chilensis periodically for 3 years in five intertidal pools from two sites with distinct conditions. We tested for differentiation in fecundity and spore survival among the gametophyte males and females (haploids) and the tetrasporophytes (diploids). We tested for the influence of fecundity and spore survival on the observed uneven ploidy abundances in recruits. The probability of a frond becoming fecund was size-dependent, highest for the haploid males and lowest for the haploid females, with the diploids displaying intermediate probabilities. Fecund diploids released more tetraspores than carpospores released by the haploid females. Spore survival depended on ploidy and on the local density of co-habiting adult fronds. An advantage of diploid over haploid germlings was observed at very low and very high adult fronds densities. Conclusions Neither spore production nor spore survival determined the highly variable ploidy ratio within G. chilensis recruits. This result invalidates the hypothesis of natural cytological differences in spore production as the only driver of uneven field ploidy abundances in this species. Diploid spores (carpospores) survived better than haploid spores (tetraspores), especially in locations and time periods that were associated with the occurrence of strong biotic and abiotic stressors. We hypothesise that carpospore survival is higher due to support by their haploid female progenitors passing-on nutrients and chemical compounds improving survival under stressful conditions.AHE was supported by fellowships SFRH/BPD/63703/2009, SFRH/BPD/ 107878/2015 and UID/Multi/04326/2016 of the National Science Foundation FCT of Portugal.info:eu-repo/semantics/publishedVersio