Do polyamines alter the sensitivity of lichens to nitrogen stress?

The sensitivity of lichens measuring photosynthetic efficiency and polyamines as modulator of nitrogen stress tolerance was investigated. Two lichen species with a markedly different tolerance to nitrogen compounds, namely Evernia prunastri (L.) Ach. and Xanthoria parietina (L.) Th.Fr., were incubated with deionized water (control) and solutions of KNO 3, NH 4NO 3 and (NH 4) 2SO 4 and then exposed to different light conditions. The F v/ F m parameter (maximum quantum efficiency of photosystem II) was used as stress indicator. The results showed that F v/ F m values, in the produced experimental conditions, were independent from the light gradient. Photosynthetic efficiency of E. prunastri was impaired by high ammonium concentrations, while nitrate had no effect; X. parietina was hardly influenced by nitrogen compounds. External supply of polyamines reduced the sensitivity of E. prunastri, while polyamine inhibitors reduced the tolerance of X. parietina to NH 4 +, suggesting that polyamines play an important role in modulating the sensitivity/tolerance to nitrogen stress.