Effect of Naphthalene on Photosystem 2 Photochemical Activity of Pea Plants

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A. V. Lankin¹, V. D. Kreslavski^1,2*, A. Yu. Khudyakova³, S. K. Zharmukhamedov^2*, and S. I. Allakhverdiev^1,2*

¹Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, ul. Botanicheskaya 35, 127276 Moscow, Russia; fax: (499) 977-8018

²Institute of Basic Biological Problems, Russian Academy of Sciences, ul. Institutskaya 2, 142290 Pushchino, Moscow Region, Russia; fax: (4967) 330-532; E-mail: vkreslav@rambler.ru; watcher01@rambler.ru; allakhverdiev@gmail.com

³Institute of Biological Engineering, Russian Academy of Sciences, ul. Institutskaya 7, 142290 Pushchino, Moscow Region, Russia; fax: (4967) 330-522

^* To whom correspondence should be addressed.

Received June 20, 2014; Revision received July 29, 2014

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The effect of a typical polyaromatic hydrocarbon, naphthalene (Naph), on photosystem 2 (PS-2) photochemical activity in thylakoid membrane preparations and 20-day-old pea leaves was studied. Samples were incubated in water in the presence of Naph (0.078, 0.21, and 0.78 mM) for 0.5-24 h under white light illumination (15 μmol photons·m^–2·s^–1). The PS-2 activity was determined by studying fast and delayed chlorophyll (Chl) a fluorescence. Incubation of samples in water solutions at Naph  concentrations of 0.21 and 0.78 mM led to a decrease in the maximum PS-2 quantum efficiency (F_v/F_m), noticeable changes in the polyphasic induction kinetics of fluorescence (OJIP), and a decrease in the amplitudes of the fast and slow components of delayed fluorescence of Chl a. The rate of release of electrolytes from leaves that were preliminarily incubated with Naph (0.21 mM) was also increased. Significant decrease in the fluorescence parameters in thylakoid membrane preparations was observed at Naph  concentration of 0.03 mM and 12-min exposure of the samples. Chlorophyll (a and b) and carotenoid content (mg per gram wet mass) was insignificantly changed. The quantum yields of electron transfer from Q_A to Q_B (φ_ET2o) and also to the PS-1 acceptors (φ_RE1o) were reduced. These results are explained by the increase in the number of Q_B-non-reducing centers of PS-2, which increased with increasing Naph concentration and exposure time of leaves in Naph solution. The suppression of PS-2 activity was partly abolished in the presence of the electron donor sodium ascorbate. Based on these results, it is suggested that Naph distorts cell membrane intactness and acts mainly on the PS-2 acceptor and to a lesser degree on the PS-2 donor side.

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KEY WORDS: naphthalene, photosystem 2, variable and delayed fluorescence of chlorophyll, detached pea leaves, thylakoid membranes, photosynthetic pigments

DOI: 10.1134/S0006297914110091

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