ORIGINAL ARTICLE Alexander G. Ivanov Æ Marianna Krol Dimitri Sveshnikov Æ Gunilla Malmberg Per Gardestro¨m Æ Vaughan Hurry Æ Gunnar O ¨ quist Norman P. A. Huner Characterization of the photosynthetic apparatus in cortical bark chlorenchyma of Scots pine Received: 27 January 2005 / Accepted: 18 October 2005 / Published online: 7 December 2005 Ó Springer-Verlag 2005 Abstract Winter-induced inhibition of photosynthesis in Scots pine (Pinus sylvestris L.) needles is accompanied by a 65% reduction of the maximum photochemical efficiency of photosystem II (PSII), measured as F v /F m , but relatively stable photosystem I (PSI) activity. In contrast, the photochemical efficiency of PSII in bark chlorenchyma of Scots pine twigs was shown to be well preserved, while PSI capacity was severely decreased. Low-temperature (77 K) chlorophyll fluorescence mea- surements also revealed lower relative fluorescence intensity emitted from PSI in bark chlorenchyma com- pared to needles regardless of the growing season. Nondenaturating SDS-PAGE analysis of the chloro- phyll–protein complexes also revealed much lower abundance of LHCI and the CPI band related to light harvesting and the core complex of PSI, respectively, in bark chlorenchyma. These changes were associated with a 38% reduction in the total amount of chlorophyll in the bark chlorenchyma relative to winter needles, but the Chl a/b ratio and carotenoid composition were similar in the two tissues. As distinct from winter pine needles exhibiting ATP/ADP ratio of 11.3, the total adenylate content in winter bark chlorenchyma was 2.5-fold higher and the estimated ATP/ADP ratio was 20.7. The pho- tochemical efficiency of PSII in needles attached to the twig recovered significantly faster (28–30 h) then in de- tached needles. Fluorescence quenching analysis re- vealed a high reduction state of Q A and the PQ-pool in the green bark tissue. The role of bark chlorenchyma and its photochemical performance during the recovery of photosynthesis from winter stress in Scots pine is discussed. Keywords Bark chlorenchyma Æ Chlorophyll fluorescence Æ Energy partitioning P700 Æ Pinus needles Æ Recovery of photosynthesis Abbreviations AL: Actinic light Æ Chl: Chlorophyll Æ EPS: Epoxidation state of the xanthophyll cycle pigments Æ F o : Instantaneous (dark) chlorophyll fluorescence at open PSII centers in dark-adapted samples Æ F o¢ : Minimal fluorescence at open PSII centers immediately after illumination Æ F m : Maximal fluorescence at closed PSII centers Æ F m¢ : Maximal fluorescence at closed PSII centers under actinic light Æ F v : Variable fluorescence Æ F v¢ : Variable fluorescence under actinic light Æ F v /F m =(F m À F o )/ F m : The maximal photochemical efficiency of PSII Æ F v¢ / F m¢ =(F m¢ À F o¢ )/F m¢ : The efficiency of open PSII units under illumination Æ LHCII: The major Chl a/b pigment–protein complex associated with photosystem II Æ qN, NPQ: Nonphotochemical quenching Æ P700: Reaction center pigment of PSI Æ P700 + : Oxidized form of the reaction center of PSI Æ PSI, PSII: Photosystem I and photosystem II, respectively Æ PQ: Plastoquinone Æ Q A : Primary electron-accepting quinone in PSII Æ Q B : Secondary electron-accepting quinone in PSII Æ qP: Photochemical quenching Æ SN: Summer needles Æ WN: Winter needles Introduction Following the initial report of photosynthesis by bark chlorenchymes (Pearson and Lawrence 1958), photo- synthetic activity in chlorophyll-containing stem and bark tissues has been reported in a wide variety of woody species (Adams and Strain 1969; Kriedemann and Buttrose 1971; Foote and Schaedle 1976; Pilarski 1995; Pfanz 1999; Schmidt et al. 2000; Wittmann et al. A. G. Ivanov Æ M. Krol Æ N. P. A. Huner (&) Department of Biology and the Biotron, University of Western Ontario, 1151 Richmond Str. N, London, ON, Canada N6A 5B7 E-mail: nhuner@uwo.ca Tel.: +1-519-6792111 Fax: +1-519-6613935 A. G. Ivanov Æ D. Sveshnikov Æ G. Malmberg Æ P. Gardestro¨m V. Hurry Æ G. O ¨ quist Umea˚ Plant Science Centre, Department of Plant Physiology, Umea˚ University, 90187 Umea, Sweden Planta (2006) 223: 1165–1177 DOI 10.1007/s00425-005-0164-1