Copyright © Physiologia Plantarum 2000 PHYSIOLOGIA PLANTARUM 108: 87 – 93. 2000 Printed in Ireland —all rights resered ISSN 0031-9317 Growth in excess copper induces changes in the lipid composition and fluidity of PSII-enriched membranes in wheat Mike F. Quartacci a , Calogero Pinzino b , Cristina L. M. Sgherri a , Francesca Dalla Vecchia c and Flavia Navari-Izzo a, * a Dipartimento di Chimica e Biotecnologie Agrarie, Uniersita ` di Pisa, Via del Borghetto, 80, I -56124 Pisa, Italy b Istituto di Chimica Quantistica ed Energetica Molecolare, CNR, Via Risorgimento, 35, I -56126 Pisa, Italy c Dipartimento di Biologia, Uniersita ` di Padoa, Via Trieste, 75, I -35121 Padoa, Italy *Corresponding author, e -mail: fnaari@agr.unipi.it Received 6 April 1999; revised 6 August 1999 decreased, whereas the degradation of the polar lipids caused Changes in the lipid composition and fluidity of PSII-enriched thylakoids were studied in seedlings of wheat (Triticum du - an accumulation of free fatty acids (FFA). The total amount of unsaturated lipids associated with the PSII-enriched mem- rum Desf. cv. Adamello) grown in nutrient solution supple- mented with CuSO 4 to achieve a final concentration of 10 branes of wheat was not affected by excess copper supplies, even though changes in the individual fatty acids occurred. and 50 M Cu. Metal content increased in the chloroplasts of the 50 M Cu-grown plants. PSII isolated from wheat sup- The effect of copper on the fluidity of PSII membranes was evaluated by electron paramagnetic resonance (EPR) mea- plied with 10 M Cu did not show any alteration in the lipid composition or in the lipid and protein levels of the mem- surements, using spin-probed fatty acids as probes. The PSII membranes, spin probed by means of 5- and 16-doxylstearic branes, nor was any change in the ultrastructure of the membranes detected. The 50 M Cu-grown plants showed acids, showed that only the fluidity of the surface region of thylakoid swelling, particularly in the stroma and terminal the bilayer close to the polar head group was reduced follow- ing the 50 M Cu supply. In contrast, the fluidity of the inner grana thylakoids. Furthermore, an alteration in the lipid composition of PSII preparations was observed together with membrane region of the bilayer did not show any change. The a decrease in the lipid content, which resulted in a reduction implications of changes in the lipid composition and lipid- protein interactions on the fluidity of specific transversal in the lipid to protein ratio. The monogalactosyldiacylglycerol membrane regions are discussed. (MGDG) to digalactosyldiacylglycerol (DGDG) molar ratio under excess copper supply the production of harmful oxy- gen species, such as hydroxyl radicals arising from superox- ide, has been demonstrated (Navari-Izzo et al. 1998, 1999). In addition to a direct toxic action, the accumulation of high levels of reactive oxygen species may also be responsi- ble for an indirect action of copper on the photosynthetic apparatus of plants (Stohs and Bagchi 1995, Navari-Izzo et al. 1999). The thylakoid intrinsic pigment-protein complexes of higher plants are distributed within the lipid bilayer so that any change in the lipid composition and fluidity may alter the conformation, the orientation and the function of Introduction Copper is known to be an essential micronutrient for higher plants, however, when present in excess, copper causes severe damage to plant organelles through inhibitory effects to photosynthetic electron transport and degradation of the chloroplast inner structure and pigment content (Ouzou- nidou 1996, Ciscato et al. 1997). Studies on the inhibitory effects of copper on photosynthetic activity have shown that PSII is more sensitive to copper than PSI (Jegerscho ¨ld et al. 1995, Horva ´th et al. 1998). Copper-mediated damage to the photosynthetic apparatus may be the result of a direct toxic action, both on the oxidising and on the reducing sides of PSII (Baro ´ n et al. 1995). In PSII isolated from wheat grown Abbreiations – DGDG, digalactosyldiacylglycerol; EPR, electron paramagnetic resonance; FFA, free fatty acids; MGDG, monogalactosyl- diacylglycerol; PC, phosphatidylcholine; PG, phosphatidylglycerol; SASL, doxylstearic acid spin probe; SQDG, sulfoquinovosyldiacylglyc- erol. Physiol. Plant. 108, 2000 87