The effect of zearalenone on PSII photochemical activity and growth in wheat and soybean under salt (NaCl) stress

The effects of mycotoxin zearalenone (ZEN) on the photochemical activity of photosystem II (PSII) in wheat and soybean leaf discs incubated in ZEN solutions as well as the after-effects of pre-sowing soaking of seeds in solutions containing ZEN on the photochemical activity of PSII and on the seedlings growth under salt stress (NaCl solutions were investigated). The incubation of wheat leaf discs in ZEN solutions strongly inhibited the energy flux per cross section (CS) for absorption (ABS/CS), trapping (TRo/CS) and electron transport (ETo/CS), while the effects of ZEN action on soybean discs were opposite and the values of those parameters significantly increased with the increase in ZEN concentration. Incubation of seeds in a ZEN solution resulted in an increase in photochemical efficiency of PSII in soybean seedlings, but did not induce any response of PSII in those of wheat at medium illuminations. Only at the stronger illumination for both species did ZEN induce an increase in efficiency of excitation energy capture by open PSII reaction centers, photochemical quenching of chlorophyll a fluorescence and quantum yield of PSII electron transport. Pre-sowing soaking of seeds in a ZEN solution decreased the photoinhibitory injuries of PSII in wheat and soybean due to safe scattering of the excess excitation energy through an increase in energy-dependent quenching (qE) and state transition quenching (qT). ZEN when added to NaCl solutions during the period of germination contributed to reduction in the growth inhibition of wheat seedlings. The incubation of wheat leaf discs in ZEN solutions strongly inhibited CS, ABS/CS, TRo/CS and ETo/CS. Possible effects of ZEN on some physiological processes in plants have been discussed especially in the context with photochemical activity of PSII and a salt stress.