Fusicoccin-induced growth and hydrogen ion excretion of Avena coleoptiles: Relation to auxin responses.

The fungal toxin fusicoccin (FC) induces both rapid cell elongation and H(+)-excretion in Avena coleoptiles. The rates for both responses are greater with FC than with optimal auxin, and in both cases the lag after addition of the hormone is less with FC. This provides additional support for the acid-growth theory. The FC responses resemble the auxin responses in that they are inhibited by a range of metabolic inhibitors, but the responses differ in three ways. First auxin, but not FC, requires continual protein synthesis for its action. The auxin-induced H(+)-excretion is inhibited by water stress or by low external pH, while the FC-induced H(+)-excretion is much less sensitive to either. It is concluded that auxin-induced and FC-induced H(+)-excretion may occur via different mechanisms.