Effects of exogenous polyamines applied separately and in combination with simulated acid rain on functional activity of photosynthetic apparatus

Ten-day-old bean seedlings (Phaseolus vulgaris L.) were grown in a greenhouse and sprayed with spermidine or spermine. After 24 h they were treated with a cocktail of simulated acid rain (pH 5.6 and 1.8). Polyamines were applied separately or in combination with acid rain. Their protective effect on the functional activity of the photosynthetic apparatus in the acid rain-treated plants was investigated. It was found that acid rain with pH 1.8 applied separately decreased strongly the photosynthetic rate, the oxygen evolution, as well as the PS2 activity. Polyamines (spermidine and spermine) applied 24 h the before the acid rain treatment partially diminished the inhibitory effect of acid rain on the photosynthetic apparatus. The results showed also that the favourable effect of spermine was higher than that of spermidine. The protective action of polyamines could be explained by their polycationic nature, their ability to bind with photosynthetic membranes, resulting in conformational changes and stabilization, of the membrane and by their ability to act as free radical scavengers.