Influence of Lithium ions on conidiophore size in Neurospora crassa

Abstract

Lithium (Li) ions are known to affect Neurospora crassa’s growth speed and circadian clock period, while elevated temperatures abolish these influences. We wondered whether Li has also an effect on conidia size. We used cryo-SEM to investigate this question and report here the results of 1720 measurements showing that at 20°C the long and short conidial axes are significantly reduced at high Li concentrations (10-15 mM), while the ratio between the long and short axes remains approximately constant. An increased temperature (30°C) appears to abolish the Li effect on conidia size. Creative Commons License This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License. This regular paper is available in Fungal Genetics Reports: http://newprairiepress.org/fgr/vol53/iss1/10 34 Fungal Genetics Newsletter Influence of Lithium ions on conidiophore size in Neurospora crassa Bodil Aase, Ingunn W. Jolma and Peter Ruoff Department of Mathematics and Natural Science, University of Stavanger, N-4036 Stavanger, Norway corresponding author. email: peter.ruoff@uis.no. # Fungal Genetics Newsletter 53:34-36 Lithium (Li) ions are known to affect Neurospora crassa’s growth speed and circadian clock period, while elevated temperatures abolish these influences. We wondered whether Li has also an effect on conidia size. We used cryo-SEM to investigate this question and report here the results of 1720 measurements showing that at 20°C the long and short conidial axes are significantly reduced at high Li concentrations (10-15 mM), while the ratio between the long and short axes remains approximately constant. An increased temperature (30°C) appears to abolish the Li effect on conidia size. Lithium (Li) has a profound influence on Neurospora crassa’s growth rate and circadian period (Engelmann 1987; Davis 2000; Dunlap and Loros 2004). Typically, at extracellular concentrations of 10 mM LiCl, the growth rate is significantly reduced and the circadian clock begins to get disrupted (Engelmann 1987; Lakin-Thomas 1993; Jolma et al. 2006). Interestingly, increased temperature can abolish the Li effect, possibly by an increased dissociation between Li and its assumed targets (Jolma et al. 2006). Because of the macroscopically distinct differences in conidiation when Neurospora is grown in the presence or absence of Li, we wondered whether there might be also a difference in microscopic conidiation, for example conidia size. In order to answer this question, we performed a study using a Zeiss Supra VP35 scanning electron microscope (SEM) with a Polaron cryo stage. The bd a strain (FGSC #1859) was grown on Petri dishes in LD (12h:12h) at 20°C or 30°C using Vogel’s medium as previously described (Jolma et al. 2006). Li was added to the medium as LiCl. Samples were taken from Petri dishes that showed approximately the same amount of total growth (=growth speed X growth time). Because of the dependence of the speed of this organism’s growth on temperature and LiCl concentrations (Jolma et al. 2006) the growth time prior sampling varied as shown in Table 1. Table 1: Growth times prior analysis T, °C LiCl, mM GT, days 20 0 3 20 5 3 20 10 10 20 15 10 30 10 1 T: temperature; LiCl: concentration of LiCl; GT: growing time Figure 1. Measurement of conidia size as long and short axis, l and s, respectively. The picture shows conidia grown at 20°C with 15 mM Li. Samples were cut out using a cork-borer covering the growth zone and approximately 5 mm behind the growth zone. The cut-out samples were put on a Al-stub that had glue with colloidal graphite on its surface. The glued sample was rapidly frozen in nitrogen slush and then transferred to the pre-cooled SEM stage. Samples were then coated with a gold-palladium alloy for 80 seconds. In the SEM analysis the ‘In-Lens’ detector of the microscope was used. Conidia have an ellipsoidal-like shape and the long and short axes l and s (Fig. 1), which could be determined directly on the sample, were used as an approximate measure for conidia size. Published by New Prairie Press, 2017