ROS-Ca2+ signalling interplay is associated with cobalt-enhanced dendrobine-type total alkaloid production in Trichoderma longibrachiatum UN32.

Cobalt stress can promote the accumulation of dendrobine-type total alkaloids (DTTAs) in Trichoderma longibrachiatum UN32; however, the signalling mechanisms underlying this response remain unclear. In this study, we examined whether changes in Ca2+ and nitric oxide (NO) signalling were associated with ROS-related responses and cobalt-enhanced DTTAs production under cobalt stress. Co2+ treatment increased DTTAs accumulation together with intracellular hydrogen peroxide (H2O2), Ca2+ and NO levels. Among Ca2+ signalling inhibitors, neomycin (Neo) showed the strongest effect: 6 mM Neo reduced intracellular Ca2+ by 59.86%, DTTAs production by 33.70% and H2O2 levels by 25.50% compared with CoCl2 treatment. Time-course analysis further showed coordinated changes in H2O2, Ca2+ and DTTAs accumulation during fermentation. In contrast, L-NAME-mediated inhibition of NO synthesis did not significantly affect DTTAs production. These findings suggest that ROS-Ca2+ interplay is associated with cobalt-enhanced DTTAs accumulation in T. longibrachiatum UN32, whereas NO has a limited role under the tested conditions.