Photosynthetic performance and fluorescence in relation to antenna size and absorption cross-sections in rye and barley grown under normal and intermittent light conditions

The size of the Photosystem II light harvesting antenna and the absorption cross-sections of PS I (_PSI) and PS II (_PSII) were examined in relation to photosynthetic performance fluorescence. Wild-type (WT) rye (Secale cereale) and barley (Hordeurn vulgare) as well as the barley chlorophyllb-less chlorina F2 mutant were grown under control and intermittent light (IML) conditions. (_PSII) in control barley F2 was similar to IML grown WT rye and barley, which, in turn was 2.5 to 3.5 times smaller than for control WT plants. In contrast, _PSI was similar for all control plants. This was 2.5 to 4 times larger than for IML-grown WT plants. IML-grown barley mutant plants had the smallest absorption cross-sections. Photosynthetic light response curves revealed that the barley chlorina F2-mutant had rates of oxygen evolution on a per leaf area basis that were only slightly lower than control WT rye and barley while IML-grown plants had strongly reduced photosynthetic performance. Convexity () for control barley chlorina F2-mutants was equal to the WT controls (0.6–0.7), while all IML-grown plants had a of 0. This indicates that, in contrast to control barley mutants, IML-plants were limited by PS II turn-over rates at all irradiances. However, on a per leaf Chl-basis the IML-grown plants exhibited the highest photosynthetic rates. Thus, the comparatively poor photosynthetic rates for IML-grown plants on a per leaf area basis were not due to less efficient photosynthetic reaction centers, but may rather be due to an increased limitation from PS II turn-over and a reduction in the number of reaction centers per leaf area.