LOW-TEMPERATURE SPECTROSCOPY OF ALGAE AFFECTED BY UV-B STRESS - ABSORPTION FLUORESCENCE AND HOLE-BURNING

Algae have the ability to protect themselves against excess of light e nergy by dissipating the excessive excitation energy. UV-B stress can damage the protecting mechanism. Applied UV-B irradiation causes appro ximate to 50% decrease of photosynthetic activity. It produces an incr ease of low-temperature fluorescence of the antennae and a decrease of the relative fluorescence of the RC due to a decrease of excited ener gy-transfer (EET) efficiency which reflects interruption of the EET be tween CP 43, CP 47 and the RC of PS II. Further information was obtain ed from persistent spectral hole-burning (PSHB) experiments. From the widths of the zero-phonon holes, EET rate constants were determined. T he Value of the Huang-Rhys factor Value (S), which characterizes the e lectron-phonon coupling was approximately 1.5 times higher in UV-B str essed algae (S approximate to 1.2). Broad-band holes with hole widths approximate to 170 cm(-1) were observed in the fluorescence spectra of all samples, these holes were not significantly affected by UV-B.