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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 3699

Jeff A. Zeikus and Richard C. Starr; The Genetics and Physiology of Non-inducibility in Volvox carteri f. nagariensis Iygengar. Arch.Protistenk 123:127-161, 1980

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In Volvox carteri f. nagariensis addition of the sex hormone produced by male strains to asexual populations of either the standard male (69-1b) of female (HK10) strains results in 100% induction of sexual spheroids in the next generation. A mutant strain has been found in which sexual spheroid formation is impaired, such that 100% induction is not achieved in any concentration of the sex inducer. The factor effecting this non-inducibility phenotype is inherited at a single gene locus, but the different degrees of induction given among strains carrying non-inducibility suggests more than one locus is involved. Genetic analysis indicates suppressor factors carried in parental strains recombine randomly with the non-inducibility locus and, as a consequence, produce diverse expressions of non-inducibility among the siblings strains. Induction in strains carrying non-inducibility is related to light intensity and CO2 concentration in a way that suggests non-inducibility may be the result of a photosynthetic defect. However, a comparison of photosynthetic [14]CO2 fixation in female strains carrying non-inducibility and the standard female strain shows that photosynthesis is not altered by the non-inducibility locus. Furthermore, studies of induction influenced by the photosynthetic inhibitor DCMU suggest that the effect of CO2 concentration on induction (CO2 enhancement) is not entirely related to photosynthetic CO2 uptake. These results indicate maximum induction in strains carrying non-inducibility 1) requires a metabolic rate substantially higher than that needed for 100% induction in the standard strains and 2) involves at least one process not needed for induction in the standard strains. The efficiency by which sexual developmental processes are accomplished is discussed as a function on the non-inducibility locus.