Effect of Auxin and Gibberellin on Conidial Germination inNeurospora crassaII.“Conidial Density Effect”and Auxin

摘要

Conidial germination in liquid shake culture ofNeurospora crassawas affected by the number of conidia in the medium (conidial density effect) with the optimum density being around 2×106conidia/ml. The conidial density effect at 2×104and 2×105conidia/ml was eliminated by the addition of auxin, IAA or 2,4-D with the optimum concentrations of IAA and 2,4-D being around 10−6M. IAA and 2,4-D had no effect on the effect at 2×107conidia/ml. An active substance(s) for conidial germination which was related to the conidial density effect was detected in the cell-free filtrate of the germination medium, and was found to be non-dialyzable and thermolabile. At the early stage of germination, the concentration of active substance(s) in the medium increased in proportion to the conidial density and reached a supraoptimum amount for germination at 2×107conidia/ml. IAA (10−6M) enhanced the concentration. Endogenous auxin concentrations in filtrates of the germination media containing 2×105, 2×106and 2×107conidia/ml were 5.8×10−12, 4.6×10−11and 1.7×10−10M IAA equivalent, respectively. The conclusion reached was that auxin may control conidial germination with mediation by the