Thesis (M.Sc.)--Chulalongkorn University, 2012

This research studied about the effect of ultraviolet or UV radiations on intracellular pigments and polyamine contents associated to photosynthesis in cyanobacterium Synechocystis sp. PCC 6803. All UV radiations (UV-A, UV-B, and UV-C with intensity of 10, 1.3, and 1.3 w•m-2, respectively) had slight effects on growth but highly significant changes on intracellular pigments within 24 h-treatment. Chl a content was decreased within 24 h about 10 – 40% whereas carotenoid content was decreased about 30 – 80%. All UV radiations reduced the photosynthetic efficiency within 3 h-treatment by 90 -98% decreasing. For total polyamine content, all UV radiations affected decreasingly on polyamine contents in whole cell and polyamines associated with thylakoid membranes within 24 h-treatment. The dominant polyamine responded to UVs was spermidine. Moreover, the polyamines associated with photosystem was determined. The photosynthetic proteins on thylakoid membranes were solubilized from thylakoid membranes and separated those proteins of photosystems using sucrose gradient ultracentrifugation at 144,000xg, 4 ºC for 14 h. Polyamines associated with PSII which located at the boundary of 30 – 40% sucrose layer (F5) and the boundary of 40 – 50% sucrose layer (F6) were significantly changed under UV treatments. However, the level of polyamines associated with PSI which located at 10% sucrose layer (F2) was not changed. Altogether, polyamines had the important response to UV stress and were identified their association with photosynthetic systems.