Functioning of the photosynthetic apparatus under low and high light conditions in chlorotic spruce needles as evaluated by in vivo chlorophyll fluorescence

The photosynthetic apparatus rapidly responds to the environmental influences. In vivo chlorophyll fluorescence was applied for the evaluation of photosystem II (PSII) and electron-transport chain functioning and for determination of photochemical and nonphotochemical quenching in chlorotic spruce needles exposed to urban pollution. More injured needles had lower content of chloroplast pigments and changed chloroplast ultrastructure, in comparison with less injured needles. The maximum PSII efficiency was measured in dark-adapted samples, whereas other parameters were measured under low and high light conditions (125 and 1400 µmol photons/(m2s), respectively). The PSII efficiency and relative electron transport rate (rel. ETR) were lowered at both irradiance levels while the photochemical quenching was significantly lower only in high light. Nonphotochemical quenching coefficients (qN) values were higher at both light levels in more injured needles, however, the difference was insignificant. High nonphotochemical quenching in both needle groups probably made possible the photosynthetic apparatus to function at the high light level. Our results suggested that the lowering of the chlorophyll content could be considered as a protecting event rather than just the consequence of the stress.

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