chlorophyll fluorescence; Hordeum vulgare; photodamage.

The resistance of photosynthetic apparatus of barley (Hordeum vulgare L.cv. Akcent) grown at low light (50 umol.m-2.s-1) to short-term exposure (10 min) to different degree of excess irradiance was studied using the measurements of the 77K chlorophyll a (Chl a) fluorescence spectra and room temperature Chl a fluorescence quenching. The protective down-regulation of the light-harvesting of photosystem II (PS II) as well photosystem I (PSI) was saturated at 850 umol.m-2.s-1 and progressive PS II photodamage was induced at higher irradiances. After exposure of segments to excess irradiance (2410 umol.m-2.s-1) a pronounced maximum at 700 nm appeared in emission spectrum of 77K Chl a fluorescence. We suggest that this maximum reflects agregation of LHC II with part of inner PS II antenna during progressive PS II photodamage.

The resistance of photosynthetic apparatus of barley (Hordeum vulgare L.cv. Akcent) grown at low light (50 umol.m-2.s-1) to short-term exposure (10 min) to different degree of excess irradiance was studied using the measurements of the 77K chlorophyll a (Chl a) fluorescence spectra and room temperature Chl a fluorescence quenching. The protective down-regulation of the light-harvesting of photosystem II (PS II) as well photosystem I (PSI) was saturated at 850 umol.m-2.s-1 and progressive PS II photodamage was induced at higher irradiances. After exposure of segments to excess irradiance (2410 umol.m-2.s-1) a pronounced maximum at 700 nm appeared in emission spectrum of 77K Chl a fluorescence. We suggest that this maximum reflects agregation of LHC II with part of inner PS II antenna during progressive PS II photodamage.