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Title: Role of calcium in zoospore biology of Phytophthora and Pythium species
Author: Warburton, Adrian John
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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The work in this thesis was designed to study the role of Ca2+ in zoospore biology, and extends previous findings by comparing effects of Ca2+ and Ca2+ -modulating treatments in zoospores and zoospore cysts of Pythium spp., Phytophthora spp. and Aphanomyces euteiches. Zoospore motility was studied by videomicroscopy to compare the behaviour of Phytophthora infestans, Ph. parasiticia and Ph. plamivora aphanidermatum, Py. dissotocum, Py. catenulatum and A. euteiches. Zoospores of all fungi swam in an extended helix, but the Phytophthora spp. and A. euteiches made frequent changes of direction when swimming in water or buffer, whereas the Pythium spp. did not do so. Chelation of external Ca2+ with EGTA or BAPTA buffer caused zoospores of all fungi to swim in a straight path, reduced random turning, and prevented the spores from flanging direction when they collided with obstacles. Phytophthora zoospores accumulated at the surface of suspensions, but this was abolished in the presence of EGTA, whereas Pythium zoospores always accumulated at the base of suspensions. Isotropic backgrounds of some amino acids (e.g. L-glutamic acid) induced an irregular motility pattern; this was overridden by EGTA but restored by subsequent addition of Ca2+. These findings are discussed in relation to host-location behaviour by zoospores. A role of Ca2+ in germination of cysts, induced by agitation of zoospores of Py. aphanidermatum and Ph. parasitica, was demonstrated by reduced or suppressed germination in the presence of Ca2+ -uptake inhibitors (La3+, verapamil), Ca2+ chelators (BAPTA), calmodulin-antagonists (trifluoperazine, calmidazolium) or compounds that affect intracellular Ca2+ stores (caffeine, TMB-8). The critical concentrations and times of application of these treatments were determined, and some divalent cations and organic nutrients (sugars, amino acids) were shown partly to reverse the suppression of germination. A link was demonstrated between Ca2+ fluxes and zoospore development into cysts.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available