Actin filaments are involved in cellular graviperception of the basidiomycete Flammulina velutipes.

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Inhibitor studies demonstrate a major role of the actin cytoskeleton in cellular graviperception of the basidiomycete Flammulina velutipes. Treatment of explanted fruiting body stipes with 10(-4) M of the actin filament-disrupting agent cytochalasin D causes specific suppression of gravitropic curvature to 21% of the control value. Elongation growth is depressed to 48%. In contrast, curvature and elongation remain almost unaffected by 10(-4) M of the microtubule inhibitor oryzalin. Immunohistochemical labeling of actin filaments in stipe hyphae of Flammulina reveals a close colocalization with the nuclei. The label pattern is destroyed upon 10(-4) M cytochalasin treatment. The role of the actin cytoskeleton in graviperception in Flammulina parallels aspects of gravisensing in Chara rhizoids and thus points at basic similarities between fungal and plant mechanisms of cellular gravity perception.