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The effect of irradiation on completely covered regions of 7-d-old, light-grown sunflower (Helianthus annuus) cotyledons (A) and on the cotyledons of 7-d-old etiolated sunflower seedlings (B). The 77 K fluorescence emission spectra are normalized at their maxima. Continuous line: samples cooled to 77 K before irradiation, broken line: samples irradiated with a light flash (160 J 2 ms−1) and cooled to 77 K 10 s later. Excitation wavelength = 440 nm.
