Ethylene produced by the lichen Cladina stellaris exposed to sulphur and heavy-metal-containing solutions under acidic conditions

Abstract

Podetia of the terricolous lichen Cladina stellaris (Opiz) Brodo, collected in an unpolluted rural area in N. Finland, were wetted with either H₂O, diluted acidic solutions of H₂SO₄, HNO₃ and NaHSO₃, simulating acidic rain, or the following salts: K₂SO₄, KCl, CuSO₄, CuCl₂, Cu(NO₃)₃, ZnSO₄, ZnCl₂, Zn(NO₃)₂, FeSO₄, FeCl₂, Fe₂(SO₄)₃, FeCl₃ and Fe(NO₃)₃. The samples were further exposed to combined treatments in both acidic solutions, simulating acidic rain, and heavy metal salts in solution. Lichen samples wetted with H₂O at pH 6·8, diluted solutions of H₂SO₄, HNO₃ or a mixture of these two acids produced low concentrations of endogenous ethylene. The application of NaHSO₃ greatly increased the production of ethylene. The application of KCl induced a higher rate of ethylene production than the application of K₂SO₄ solutions. The application of Cu-containing solutions enhanced the production of ethylene. The influence of Zn was smaller than that of Cu. Iron was the most effective heavy metal to promote the production of ethylene: very high ethylene concentrations were detected upon the application of FeCl₂. Combined treatments in H₂SO₄ or H₂SO₄+HNO₃ followed by either FeCl₂ or FeSO₄, yielded higher concentrations of ethylene than the same treatments in a reversed order. The role of Fe ions in the production of ethylene is discussed in reference to previous works dealing with ethylene production in higher plants, fungi and algae.