Photoprotective function of chloroplast avoidance movement: In vivo chlorophyll fluorescence study Olga Sztatelman a , Andrzej Waloszek b , Agnieszka Katarzyna Banas ´ a , Halina Gabrys ´ a,n a Department of Plant Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krako ´w, Poland b Department of Plant Physiology and Biochemistry, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Krako ´w, Poland article info Article history: Received 8 October 2009 Received in revised form 8 December 2009 Accepted 13 December 2009 Keywords: Arabidopsis thaliana Avoidance response Chlorophyll fluorescence Chloroplast movement Photoprotection abstract Light-induced chloroplast avoidance movement has long been considered to be a photoprotective mechanism. Here, we present an experimental model in which this function can be shown for wild type Arabidopsis thaliana. We used blue light of different fluence rates for chloroplast positioning, and strong red light inactive in chloroplast positioning as a stressing light. The performance of photosystem II was measured by means of chlorophyll fluorescence. After stressing light treatment, a smaller decrease in photosystem II quantum yield was observed for leaves with chloroplasts in profile position as compared with leaves with chloroplasts in face position. Three Arabidopsis mutants, phot2 (no avoidance response), npq1 (impaired zeaxanhtin accumulation) and stn7 (no state transition), were examined for their chloroplast positioning and chlorophyll fluorescence parameters under identical experimental conditions. The results obtained for these mutants revealed additional stressing effects of blue light as compared with red light. & 2010 Elsevier GmbH. All rights reserved. Introduction Light-induced chloroplast movements occur in many plant species, especially in those that have the potential to adapt to different light environments (Augustynowicz and Gabrys, 1999). In dark-adapted leaves, chloroplasts are located along all cell walls; their distribution is not uniform and depends on light conditions during growth (Trojan and Gabrys, 1996). Under weak irradiation, chloroplasts gather at the cell walls perpendicular to the light direction in a so-called accumulation response; this chloroplast arrangement is called face position. Under strong irradiation, chloroplasts redistribute toward the cell walls parallel to the light direction in an avoidance response; this is known as profile position of chloroplasts. In Arabidopsis thaliana, as in most angiosperms, only the blue part of the spectrum is responsible for chloroplast positioning, and phototropins are the photoreceptors involved in light perception (Briggs and Christie, 2002; Sakai et al., 2001). Phototropin1 controls only the accumulation response, while phototropin2 takes part in both accumulation and avoid- ance responses. Therefore, phot2 mutant plants, devoid of phototropin2, show accumulation under blue light irrespective of its intensity (Jarillo et al., 2001). Chloroplast movements are considered to be a part of a plant’s photosynthetic adaptation mechanism. The accumulation response maximizes light harvest- ing in weak light (Takemiya et al., 2005; Zurzycki, 1955), whereas the avoidance response is suggested to be a photoprotective mechanism (Zurzycki, 1955). The chromatophore arrangement was first shown to influence the level of photodamage in the brown alga Dictyota dichotoma (Hanelt and Nultsch, 1991). Experimental evidence for the photoprotective function of chloroplast movement in higher plants was provided by the observation that Tradescantia albiflora was less prone to high light damage than Pisum sativum (Park et al., 1996). The mesophyll cells of these two plants are quite similar at the biochemical level, but only T. albiflora shows light-directed chloroplast relocations. After the identification of A. thaliana photoreceptor mutants in 2000, it was possible to investigate their light stress susceptibility. Such an experiment demonstrated the photoprotective function of chloroplast relocations (Kasahara et al., 2002). However, the authors attributed all the observed differences between phot2 and ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.de/jplph Journal of Plant Physiology 0176-1617/$ - see front matter & 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.jplph.2009.12.015 Abbreviations: F v /F m , maximum quantum yield of PSII; F 0 , initial fluorescence; F m , maximum fluorescence; LHCII, light harvesting complex II; NPQ, non- photochemical quenching; NPQ SB , non-photochemical quenching elicited by strong blue light (100 mmol m 2 s 1 ); NPQ wB , non-photochemical quenching elicited by weak blue (2 mmol m 2 s 1 ) with compensating red light (100 mmol m 2 s 1 ); PSI, photosystem I; PSII, photosystem II; qE, energy quenching; qI, photoinhibition; qP, photochemical quenching; qP wB , photochemical quenching in weak blue (2 mmol m 2 s 1 ) with compensating red light (100 mmol m 2 s 1 ); qT, state transitions; Y, quantum yield of PSII; Y SB , quantum yield of PSII in strong blue light (100 mmol m 2 s 1 ) n Corresponding author. Tel.: + 48 12 664 63 40; fax: + 48 12 664 69 02. E-mail address: halina.gabrys@uj.edu.pl (H. Gabrys ´). Journal of Plant Physiology 167 (2010) 709–716