Photosynthesis Research 70: 207–220, 2001. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 207 Regular paper Iron deficiency interrupts energy transfer from a disconnected part of the antenna to the rest of Photosystem II Ferm´ın Morales 1,∗ , Nicolae Moise 2,3 , Rebeca Qu´ılez 1 , Anunciaci ´ on Abad´ıa 1 , Javier Abad´ıa 1 & Ismael Moya 2 1 Department of Plant Nutrition, Aula Dei Experimental Station, Consejo Superior de Investigaciones Cient´ıficas, Apartado 202, E-50080 Zaragoza, Spain; 2 Groupe Photosynth` ese et T´ el´ ed´ et´ ection, LURE/CNRS, Bat 203, Centre Universitaire Paris-Sud, B.P. 34, 91898, Orsay cedex, France; 3 Permanent address: The National Institute for Lasers, Plasma and Radiation Physics, Lasers Department, 76900 Bucharest-Magurele, Romania; ∗ Author for correspondence (e-mail: fmorales@eead.csic.es; fax: +34-976-716145) Received 13 February 2001; accepted in revised form 5 July 2001 Key words: Chl fluorescence induction, energy transfer, iron deficiency, phase fluorometry, Photosystem II efficiency, sugar beet, time-resolved chlorophyll fluorescence Abstract Iron deficiency changed markedly the shape of the leaf chlorophyll fluorescence induction kinetics during a dark– light transition, the so-called Kautsky effect. Changes in chlorophyll fluorescence lifetime and yield were observed, increasing largely the minimal and the intermediate chlorophyll fluorescence levels, with a marked dip between the intermediate and the maximum levels and loss of the secondary peak after the maximum. During the slow changes, the lifetime–yield relationship was found to be linear and curvilinear (towards positive lifetime values) in control and Fe-deficient leaves, respectively. These results suggested that part of the Photosystem II antenna in Fe-deficient leaves emits fluorescence with a long lifetime. In dark-adapted Fe-deficient leaves, measurements in the picosecond–nanosecond time domain confirmed the presence of a 3.3-ns component, contributing to 15% of the total fluorescence. Computer simulations revealed that upon illumination such contribution is also present and remains constant, indicating that energy transfer is partially interrupted in Fe-deficient leaves. Photosystem II-enriched membrane fractions containing different pigment–protein complexes were isolated from control and Fe-deficient leaves and characterized spectrophotometrically. The photosynthetic pigment composition of the fractions was also determined. Data revealed the presence of a novel pigment–protein complex induced by Fe deficiency and an enrichment of internal relative to peripheral antenna complexes. The data suggest a partial disconnection between internal Photosystem II antenna complexes and the reaction center, which could lead to an underestimation of the Photosystem II efficiency in dark-adapted, low chlorophyll Fe-deficient leaves, using chlorophyll fluorescence. Abbreviations: BSA – bovine serum albumin; Chl – chlorophyll; DDM – n-dodecyl-β -D-maltoside; F  m – maximal Chl fluorescence yield (or lifetime) during energization; F o and O – minimal Chl fluorescence yield (or lifetime) in the dark; F p and P – maximal Chl fluorescence yield (or lifetime) during the Kautsky effect; F pl and I – intermediate Chl fluorescence yield (or lifetime) plateau during the Kautsky effect; F s and T – steady-state Chl fluorescence yield (or lifetime) during the Kautsky effect; F v /F m – optimal quantum yield of PS II photochemistry; ϕ – phase shift; FWHM – full width at half maximum; OIDPSMT – levels of Chl fluorescence during the Kautsky effect;  – Chl fluorescence yield;  PSII =F/F  m – effective PS II quantum yield; τ – Chl fluorescence lifetime; LHC – light- harvesting complexes; m – demodulation factor; PAR – photosynthetic active radiation; PPFD – photosynthetic photon flux density; PS I and PS II – Photosystem I and II, respectively; PS IIm – Photosystem II-enriched membranes; SPAD – portable Chl meter; V + A + Z – violaxanthin (V) + antheraxanthin (A) + zeaxanthin (Z)