Summary• Organelles of ectomycorrhizal fungi are known to respond to changes in the extracellular environment. The response of vacuoles, mitochondria and microtubules to short-term nickel (Ni 2+ ) exposure were investigated in hyphal tip cells of a Paxillus involutus from a heavy metal-rich soil.• Vacuoles, mitochondria and microtubules were labelled with Oregon Green ® 488 carboxylic acid diacetate, 3,3 ′ -dihexyloxacarbocyanine iodide (DiOC 6 (3)) and anti-α -tubulin antibodies, respectively; hyphae were treated with NiSO 4 in the range of 0-1 mmol l − 1 and examined microscopically.• Untreated hyphal tip cells contained tubular vacuole and mitochondrial networks. Ni 2+ caused loss of organelle tubularity and severe microtubule disruption that were exposure-time and concentration dependent. Fine tubular vacuoles thickened and eventually became spherical in some hyphae, tubular mitochondria fragmented and microtubules shortened and aggregated into patches in most hyphae. Tubular vacuoles reformed on NiSO 4 removal and tubular mitochondria in the presence of NiSO 4 suggesting cellular detoxification.• These results demonstrate that Ni 2+ induces changes in organelle and microtubule morphology. Recovery of tubular organelles to pretreatment morphology after Ni 2+ exposure suggests cellular detoxification of the metal ion.
Organelles are known to respond to challenges caused by many stress factors. The morphology of the microtubular cytoskeleton and mitochondria during mutual interaction in coculture of Laccaria laccata with Trichoderma harzianum and T. virens were examined. Hyphae from the interaction region were sampled between 4 and 12 days of growth. Microtubules were labelled with a specific antibody and mitochondria with 3,3'-dihexyloxacarbocyanine iodide, and the organelles were examined microscopically. The morphology of microtubules and mitochondria were similar in all three fungi. Microtubules were arranged in long arrays parallel to the hyphal axis and mitochondria formed an interconnected network. In hyphae growing within the interaction zone, microtubules became wavy and eventually fragmented or depolymerised, and mitochondria also became fragmented. The effects were time-dependent. In general, the organelles of all three fungi were affected during the interaction, but L. laccata was affected the least and to the same extent by each of the saprotrophic fungi. The saprotrophic fungi were affected by L. laccata to a similar extent at 4 and 8 days of interaction. Our results suggest that the studied fungi antagonistically affect each other at the cellular level, although the mechanisms involved remain to be elucidated.
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