DOI: 10.1007/s11099-015-0156-8 PHOTOSYNTHETICA 54 (1): 47-55, 2016 47 Kaolin-based, foliar reflective film protects photosystem II structure and function in grapevine leaves exposed to heat and high solar radiation L.-T. DINIS * , H. FERREIRA * , G. PINTO ** , S. BERNARDO *** , C.M. CORREIA * , and J. MOUTINHO-PEREIRA *,+ Centre for the Research and Technology of Agro-Environmental and Biological Sciences (CITAB), Universidade de Trás-os-Montes e Alto Douro, Apt. 1013, 5001-801 Vila Real, Portugal * Department of Biology & CESAM – Centre for Environmental and Marine Studies, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal ** School of Agriculture and Veterinary Sciences (ECAV), Universidade de Trás-os-Montes e Alto Douro, Apt. 1013, 5001-801 Vila Real, Portugal *** Abstract Extreme conditions, such as drought, high temperature, and solar irradiance intensity, are major factors limiting growth and productivity of grapevines. In a field experiment, kaolin particle film application on grapevine leaves was examined during two different summer conditions (in 2012 and 2013) with the aim to evaluate benefits of this practice against stressful conditions hindering photochemical processes. We used chlorophyll a fluorescence to investigate attached leaves. Two months after the application, during the hottest midday, the kaolin-treated plants showed by the JIP test significantly higher quantum yield of PSII photochemistry, flux ratios, maximum trapped excitation flux of PSI, absorption flux, electron transport flux, maximum trapped energy flux per cross section, and performance index than plants under control conditions in the warmer year. On the contrary, the treated plants showed a lower initial slope of relative variable fluorescence and a decrease in the absorption and electron transport per cross section. The JIP test showed higher efficiency of PSII in the plants treated with kaolin mainly in 2013 (higher temperature and drought). Our results supported the hypothesis that the accumulation of active PSII reaction centres was associated with decreased susceptibility to photoinhibition in the kaolin-treated plants and with more efficient photochemical quenching. Grapevines in the Douro Region seems to profit from the kaolin application. Additional key words: chlorophyll a fluorescence transient; energy flux; Vitis vinifera. Introduction Winemaking has a large social, environmental, and eco- nomic relevance in Europe and it is responsible for nearly 60% of Vitis vinifera L. area under cultivation worldwide (OIV 2006). Grapevine production in Mediterranean ——— Received 7 January 2014, accepted 15 May 2015, published as online-first 24 June 2015. + Corresponding author; e-mail: moutinho@utad.pt Abbreviations: ABS/CS0 – absorption flux per cross section; ABS/RC – average absorbed photon flux per PSII reaction centre; Car – carotenoids; Chl – chlorophyll; DFABS or log (PIABS) – driving force on absorption basis; DI0/RC – dissipated energy flux at time zero per PSII; ET0/ABS – relative yield of electron transport; ET0/CS0 – electron transport flux per cross section; ET0/RC – electron transport flux at time zero per PSII; Fv/Fm – quantum yield of PSII photochemistry; M0 – the relative QA reduction; PIABS – performance index; RCs – QA – reducing PSII reaction centres; Sm – normalized area above the OJIP transient; TR0/CS0 – maximum trapped energy flux per cross section; TR0/RC – maximum trapped excitation flux at time zero per PSI; φE0 – quantum yield of the electron transport (at t = 0) flux from QA to QB; φP0 – maximum quantum yield of primary PSII photochemistry (at t = 0); ψ0 – efficiency/probability (at t = 0) with which a PSII trapped electron is transferred from QA to QB. Acknowledgements: The study was undertaken under the PTDC/AGR-ALI/110877/2009 and European Union Funds (Enoexcel – Norte – 07-0124-FEDER-000032) financed by ‘Fundação para a Ciência e a Tecnologia’ (FCT, Portugal). The postdoctoral fellowship (SFRH/BPD/84676/2012) awarded to the first author is appreciated. We would also like to thank “Quinta Do Vallado” for the collaboration and efforts in making the vineyard's facilities available for the research and particularly to Engineer António Pinto. G. Pinto is hired under the programme Ciência 2008 (FCT, Portugal), co-funded by the Human Potential Operational Programme (National Strategic Reference Framework 2007-2013) and European Social Fund (EU).