Application of Pulse-Amplitude Modulated Fluorometry to Estimate the Effect of Volatile Organic Compounds and Benzo[a]Pyrene on the Functional Activity of Photosystem II in Leaves of Reed Fescue Festuca arundinacea Schreb.

The mechanisms of action of toxic organic compounds (OC) (pentane, hexane, benzene, o-xylene, butyl acetate, and benzopyrene) on the reed fescue Festuca arundinacea Schreb., which is a common plant in urban environments, were studied using pulse-amplitude modulated (PAM) fluorometry, which allowed the photochemical activity of photosystem II (PS II) to be evaluated from the parameters of the kinetic curve of chlorophyll a (Chla) fluorescence induction in vivo. A dose- and time-dependent reduction in the content of hydrophobic membrane-bound chlorophyll pigments was found along with simultaneous accumulation in the leaves of chlorophyllide (Chlde), a phytol-free product of chlorophyll degradation. It was shown that the effective quantum yield [Y(II)] of PS II photochemical reactions decreased mainly at high doses of toxic compounds while the level of photochemical fluorescence quenching (qP) did not change significantly and the coefficient of nonphotochemical quenching (qN) increased significantly to different degrees depending on the type of toxicant and the time of its exposure. A high negative correlation was observed between changes in qN, which characterized the thermal dissipation of absorbed energy, and the content of membrane-bound phytol chlorophyll pigments and carotenoids. On the other hand, changes in qN correlated positively with the content of Chlde formed during treatment with OC. The demand for thermal dissipation of absorbed energy resulting from the action of OC was proportional to the degree of destruction of the chloroplast pigment apparatus. This was confirmed by the positive correlation between qN and the content of Chlde, which possessed a photodynamic effect. Thus, parameter qN can serve as a reliable test for the damaging effect of toxic techogenic OC.

Automated summary

The study revealed that toxic organic compounds can cause a reduction in chlorophyll pigment content and an increase in Chlde content in reed fescue plants. The effective quantum yield of PS II photochemical reactions decreases at high doses of toxic compounds, while nonphotochemical quenching increases significantly. Changes in qN are negatively correlated with chlorophyll pigments and carotenoids, and positively correlated with Chlde content, making it a reliable indicator of the damaging effect of toxic compounds.