Flagellum Growth and Regeneration in the True Slime Mould Didymium nigripes

Abstract

SUMMARY: The kinetics of flagellum elongation during flagellum morphogenesis were investigated in the slime mould, Didymium nigripes. Growth rate varied at different temperatures. Long and short flagella elongated at independent rates and exhibited their maximum rates of elongation at different times. Limitation on final length did not seem to be a function of the precursors available for flagellum synthesis. Growth kinetics of normally growing and regenerating flagella and of amoebae previously exposed to cycloheximide suggest that control of growth rate is not merely a function of flagellum length or the diffusion of precursors to the assembly site. The effect of cycloheximide and streptomycin on flagellum growth were compared in both morphogenetic and regenerating systems. Addition of cycloheximide to a growing or regenerating system immediately halted flagellum elongation. Amoebae exposed to cycloheximide, washed free of the drug and then incubated under standard conditions showed abnormal growth kinetics and reduced final flagellum length; these observations suggest some residual effect of this drug. Streptomycin delayed the morphogenetic process but did not affect flagellum length once morphogenesis occurred.