Investigation of the porphyrins accumulation in barley leaves incubated with Mn2+ cations and δ-aminolevulinic acid

In greening etiolated primary leaves of barley (Hordeum vulgare L.), Mn2+ ions have been shown to inhibit chlorophyll (Chl) accumulation in a dose dependent manner and to lead to an accumulation of protoporphyrin IX (Proto) and Mg-protoporphyrin IX monomethyl ester (MgPE). The amount of MgPE that accumulated, was 2 times higher than Proto. In the dark, Proto and MgPE were observed to have accumulated to high levels in seven-day old green and etiolated leaves in the presence of 5 mmol/L Mn2+, but only if 5 mmol/L δ-aminolevulinic acid (ALA) was present. The 24 hours of irradiation of the green barley leaves treated in this way, resulted in a photodynamic destruction of Proto and MgPE as well as of Chl and carotenoids (Car). The observed porphyrin accumulation caused by the Mn2+ ions was reversed in the presence of active iron (Fe2+). This effect was observed when the iron concentration in incubation solutions was half the Mn2+ concentration, most effective for porphyrin synthesis, i.e. 5 mmol/L. The action of Mn2+ on porphyrin accumulation is also discussed.