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 of 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. aphanidermatum could be maintained in five distinct swimming modes (normal, and four perturbed modes) by addition or chelation of divalent cations or treatment with Ca2+-modulating drugs. The divalent cations (Ca2+, Ba2+, Mg2+, Mn2+, Sr2+; up to 500 mum) and Ca2+ channel-blockers (La3+, verapamil) caused perpetual circular swimming. EGTA (Ca2+ chelator) caused perpetual straight swimming. A23187 (Ca2+ ionophore) and amiloride (membrane ion flux inhibitor) caused irregular, jerky swimming. Dibucaine and trifluoperazine (calmodulin antagonists) caused slow, spiral 'skidding'. Spores with circular or straight swimming perturbations did not show chemotaxis to an attractant amino acid nor avoidance responses during collisions, indicating override of receptor-mediated functions. Spores with perturbed swimming were highly prone to encyst. Ca2+ evidently mediates zoospore motility, relevant to the motility changes that ensure host-location by Pythium.