Induction of paraquat tolerance in Dunaliella by using some pre-treatments

The effect of paraquat as a pestiside, inducer of oxidative stress, has been investigated on a unicellular green alga Dunalilella during 24 h, pretreated with 14ºC temperature, Buthionine sulfoximine (BSO) and L-galactonic acid -lactone (GAL). High decrease in pigment contents (chlorophylls and β-carotene), fresh weight of the cells and depletion of ascorbate and glutathione pools that was followed by bleaching and dying the cells, were seen after treatment with paraquat under control temperature. Cold pretreatment caused an increase in the fresh weight of the cells and also Chlorophyll a and b contents. In addition, staying high β-carotene content, β-carotene/chl and no depletion of ascorbate and glutathione pools after paraquat treatment were seen. No bleaching was observed in the cold pretreated samples and all suspensions remained green. However, pretreated sample with GAL (ascorbate precursor substrate) in control temperature, showed a big increase in Chl a, b and a small amount of remained reduced ascorbate in a few alive cells, after papraquat treatment, but the complete depletion in glutathione pool, a great increase in oxidized ascorbate and the decrease of cell numbers basically, have been observed and resulted in the bleaching of cell suspension. Pretreatment with BSO (inhibitor of glutathione synthesis) caused bleaching and dying the cells under control temperature after paraquat addition, but it inhibited glutathione increase in cold pretreated cells before adding the paraquat. This pretreatment resulted in keeping the glutathione in low level after adding the paraquat however, this sample remained green. It seems that, cold pretreatment basically and pretreatment with GAL nearly, could induce antioxidant system but the green cell suspensions were seen just in cold pretreated samples under papraquat treatment.