Changes of polyamines content under osmotic and UV-radiation stresses in cyanobacterium Synechocystis sp. PCC 6803

Abstract

Effect of salt and sorbitol at various concentrations and combined with UV radiations, including UV-A (365 nm; 11-13 w/m2), UV-B ( 302 nm; 1.2-1.3 w/m2) and UV-C (254 nm; 1.0-1.3 w/m2), for 3 hours on cell growth, intracellular pigments (chlorophyll a and carotenoids) and polyamine contents were investigated in a unicellular cyanobacterium Synechocystis sp. PCC 6803. Long-term stress (6-7 days) of Synechocystis cells grown in media up to 650 mM NaCl or 500 mM sorbitol did not severely affect growth, chlorophyll-a and carotenoids content of cells under normal growth light. Salt and sorbitol stresses stimulated the chlorophyll a and carotenoids accumulation. However, the response of cell growths showed different patterns after exposing to UV radiations. Under UV-A alone, growth was slightly decreased but was greatly decreased after combining with high concentration of salt or sorbitol. UV-B affected growth after co-treating with NaCl or sorbitol and UV-C showed the effect only when co-stress with sorbitol. The levels of chlorophyll a were constant under the combined stresses of both UV-ionic and UV-osmotic whereas those levels of carotenoids were slightly increased during the last 3 hours under UV-A both alone and in combination with salt stress and UV-B plus sorbitol treatments when compared to untreated cells. PCA-soluble polyamines were found as major forms and spermidine was present dominantly in all conditions. Short-term stress (1 hour) of UV radiations significantly increased their polyamine contents, especially salt stress combined with either UV-B or UV-C while long-time stress (3 hours) of UV radiations decreased polyamines content, especially under osmotic treatments. Two different genes (adc1 and adc2) encoding ADC, the first enzyme for putrescine synthesis. The transcription and protein levels of ADC were analyzed by RT-PCR and Western blot, respectively. The results showed that adc1 mRNA level was up-regulated higher than adc2 mRNA level under salt stress while osmotic stress seemed to have no effect on adc1 and adc2 mRNA levels. For the protein levels, ADC1 was slightly increased under high concentrations of salt, salt combined with UV-A or UV-B. However, osmotic stress did not have much effect on both transcription and protein levels. In addition, osmotic stress seemed to abolish a tight correlation of both levels when combined osmotic stress with UV radiation. Both transcription and protein levels of ADC were connected by salt and osmotic, as well as salt treatment combined with UV-A and UV-B. On the other hand, UV-C alone or combined with salt or sorbitol had influence on the transcription and protein levels in Synechocystis cells under short-term stress (1 hour)