The osmotic responses of Penicillium ochro-chloron: Changes in internal solute levels in response to copper and salt stress

The marked copper tolerance of Penicillium ochro-chloron has been confirmed as has its ability to grow in solutions of high salinity. The major low molecular weight organic solutes present in P. ochro-chloron were glycerol, erythritol, arabitol, mannitol, sorbitol and trehalose. Of these, glycerol increased significantly during growth in high concentrations of Na⁺ or Cu²⁺, a 15-fold increase, relative to the control, occurring in concentrations of 0.5 M. Cell K⁺ increased with elevated external Na⁺ but decreased slightly with elevated external Cu²⁺. With high external Cu²⁺ mycelium maintained a constant level of Cu²⁺, with low levels of Na⁺ in all treatments. It is concluded that the high concentrations of glycerol induced by high external Na⁺ or Cu²⁺ had a significant osmotic effect, allowing growth in media of high osmolality. The exclusion of ions may have a gratuitous role in the copper tolerance of P. ochro-chloron.