CHANGES IN MOTILITY OF PYTHIUM-ZOOSPORES INDUCED BY CALCIUM AND CALCIUM-MODULATING DRUGS

Zoospores of Pythium aphanidermatum, P. catenulatum and P. dissotocum swam in an extended helix, with periodic abrupt changes of direction. Their locomotory attributes were not altered by isotopic backgrounds o f amino acids (7 mm), monovalent cations (Na+, K+, Li+) up to 1000 mum or Fe3+ or Cr3+ up to 250 mum (sub-toxic). However, zoospores of P. a phanidermatum could be maintained in five distinct swimming modes (nor mal, and four perturbed modes) by addition or chelation of divalent ca tions or treatment with Ca2+-modulating drugs. The divalent cations (C a2+, Ba2+, Mg2+, Mn2+, Sr2+; up to 500 mum) and Ca2+ channel-blockers (La3+, verapamil) caused perpetual circular swimming. EGTA (Ca2+ chela tor) caused perpetual straight swimming. A23187 (Ca2+ ionophore) and a miloride (membrane ion flux inhibitor) caused irregular, jerky swimmin g. Dibucaine and trifluoperazine (calmodulin antagonists) caused slow, spiral 'skidding'. Spores with circular or straight swimming perturba tions did not show chemotaxis to an attractant amino acid nor avoidanc e responses during collisions, indicating override of receptor-mediate d functions. Spores with perturbed swimming were highly prone to encys t. Ca2+ evidently mediates zoospore motility, relevant to the motility changes that ensure host-location by Pythium.