Stress response in two strains of the aquatic hyphomycete Heliscus lugdunensis after exposure to cadmium and copper ions

Abstract

Biochemical responses to cadmium (Cd2+) and copper (Cu2+) exposure were compared in two strains of the aquatic hyphomycete (AQH) Heliscus lugdunensis. One strain (H4-2-4) had been isolated from a heavy metal polluted site, the other (H8-2-1) from a moderately polluted habitat. Conidia of the two strains differed in shape and size. Intracellular accumulation of Cd2+ and Cu2+ was lower in H4-2-4 than in H8-2-1. Both strains synthesized significantly more glutathione (GSH), cysteine (Cys) and gamma-glutamylcysteine (gamma-EC) in the presence of 25 and 50 microM Cd2+, but quantities and rates of synthesis were different. In H4-2-4, exposure to 50 microM Cd2+ increased GSH levels to 262% of the control; in H8-2-1 it increased to 156%. Mycelia of the two strains were analysed for peroxidase, dehydroascorbate reductase, glutathione reductase and glucose-6-phosphate dehydrogenase. With Cd2+ exposure, peroxidase activity increased in both strains. Cu2+ stress increased dehydroascorbate reductase activity in H4-2-4 but not in H8-2-1. Dehydroascorbate reductase and glucose-6-phosphate dehydrogenase activities progressively declined in the presence of Cd2+, indicating a correlation with Cd2+ accumulation in both strains. Cd2+ and Cu2+ exposure decreased glutathione reductase activity.

Cadmium and copper induction of oxidative stress and antioxidative response in tomato (Solanum lycopersicon) leaves

“…In barley plants, Finkemeier et al (2003) observed a 50% reduction of glutathione reductase activity under cadmium exposure depending on external N availability. Decline in GR activity after heavy metals treatment was also reported by Braha et al (2007);Tripathi et al (2006). GR did not respond to heavy metal exposure could be explained by the fact that its constitutive activity was sufficient to maintain glutathione in a reduced state (Sharma et al 2004) and/or through metal binding to SH-groups at the active site of the enzyme (Nagalakshmi and Prasad 2001).…”

“…GR did not respond to heavy metal exposure could be explained by the fact that its constitutive activity was sufficient to maintain glutathione in a reduced state (Sharma et al 2004) and/or through metal binding to SH-groups at the active site of the enzyme (Nagalakshmi and Prasad 2001). Later idea seems to be rejected by some authors who concluded that direct interference by the metals can be excluded, since adding Cd or Cu to the test tube did not affect enzyme activities (Braha et al 2007). Another reason for decreased glutathione reductase activity could be a lack of redox equivalents such as NADPH.…”

“…Another reason for decreased glutathione reductase activity could be a lack of redox equivalents such as NADPH. NADPH deficiency can be due to the inhibition of some enzymes producing redox equivalents such as the glucose-6-phosphate dehydrogenase (Braha et al 2007).…”

Effects of Zn, Fe and Mn on Leaf Litter Breakdown by Aquatic Fungi: a Microcosm Study

“…Given that microbial decomposition is mainly governed by fungi PASCOAL et al, 2005a), and fungi may canalize part of their energy towards defence mechanisms against metal stress (AZEVEDO et al, 2007(AZEVEDO et al, , 2009BRAHA et al, 2007;GUIMARÃES-SOARES et al, 2007), it is plausible that fungal biomass and/or reproduction could be affected with possible impacts to leaf litter decomposition.…”

Reproduction of aquatic hyphomycetes at low concentrations of Ca2+, Zn2+, Cu2+, and Cd2+

“…Aquatic hyphomycetes respond to metal exposure or other forms of stress by synthesizing various thiol-containing proteins/peptides, phytochelatins, heat shock proteins, and antioxidiants [33][34][35][36]. Type and magnitude of these counteradaptations are generally species specific.…”