studia universitatis babeş-bolyai biologia 2

C. I. SICORA, M. DRĂGAN-BULARDA, I. VASS
F i g . 4 . Influence of different concentrations of benzyl alcohol (BA) on the growth of
Synechocystis PCC 6803.
Concerning the UV-B damage and recovery, the BA had an inhibitory
effect on recovery at 10 mM (Fig.5) or at higher concentrations (data not shown).
Starting from a value of 30% of the initial oxygen evolution activity, the sample
without BA recovered fully in a 2-hour period. The sample which contained 10
mM BA recovered to 45% starting from a 20% value in the same period of time
(Fig.5). In the case of using a 5 mM BA concentration, the BA-treated sample was,
after an initial drop, more resistant to UV-B damage and recovered faster (Fig.6).
Using a mutant strain of Synechocystis which contains the luciferase gene under the
psbA 2 promoter, we studied the expression of the gene in the presence of BA.
Exposing the cells to 45 µEm -2 s -1 visible light, at 25°C, we observed, in about 2
hours, a 23-fold increase of the bioluminescence emission (Fig.7). When we added
10 mM BA to the cells, the extent of the increase was only 3.5-fold. This shows a
clear inhibitory effect of the BA at the level of luciferase production.
Conclusions. 1. The photosynthetic cyanobacterium Synechocystis sp. PCC 6803
is, under visible light conditions, capable of full recovery from severe (about 50%)
damages caused by UV-B radiation.
2. The change in the temperature during the recovery phase induced the
modification of the rate of recovery. This effect was, probably, caused by the
modification of the membrane fluidity which influences the turnover of membrane
protein subunits of the PS II, especially D1 and D2.
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