Journal of Plant Physiology 169 (2012) 753–759 Contents lists available at SciVerse ScienceDirect Journal of Plant Physiology jou rn al h o mepage: www.elsevier.de/jplph Differential degradation of photosystem I subunits under iron deficiency in rice Venkateswarlu Yadavalli a , Satyabala Neelam a , Akiri S.V.C. Rao b , Attipalli R. Reddy b , Rajagopal Subramanyam b,∗ a Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad 500046, India b Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500046, India a r t i c l e i n f o Article history: Received 22 October 2011 Received in revised form 22 February 2012 Accepted 23 February 2012 Keywords: Iron deficiency OJIP transients Photosystems Superoxide dismutase a b s t r a c t Rice (Oryza sativa) is one of the staple foods of the world. Iron (Fe) deficiency is a major abiotic stress factor that contributes world-wide to losses in crop yield and decline in nutritional quality. As cofactor for many enzymes and proteins, iron is an essential element. It plays a pivotal role in chlorophyll (Chl) biosynthesis, and iron deficiency may result in decreased Chl production and, thus, reduced photosynthetic capacity. Photosystem I (PSI) is a prime target of iron deficiency because of its high iron content (12 Fe per PS). To understand the protein level changes in the light-harvesting complex (LHC) of PSI (LHCI) under iron deficiency, rice seedlings were grown in Hoagland’s nutrient medium with and without Fe. Chlorophyll content and photosynthetic efficiency decreased under iron deficiency. Protein gel blots probed with antibodies against the PSI core and Lhca 1–4 proteins revealed that the core subunits PsaA and PsaB remained stable under iron deficiency, whereas PsaC and PsaD decreased by about 50%, and PsaE was completely degraded. Among the LHCI subunits, Lhca1 and Lhca2 decreased by 40 and 50%, respectively, whereas Lhca3 and Lhca4 were completely degraded. We propose that the dissociation of LHCI subunits may be due to increased levels of reactive oxygen species, which is suggested by the increased activity of superoxide dismutase. © 2012 Elsevier GmbH. All rights reserved. Introduction Iron (Fe) is an essential element for almost all organisms. In humans, the occurrence of Fe-deficiency is estimated at about 30% of the world population (Lucca et al., 2002). As a transition metal, its ability to gain or lose an electron makes iron an important component of redox reactions taking place in proteins essential for photosynthesis, respiration and many other cellular functions, including DNA synthesis and hormone production. Although iron is abundant in soil, it is mainly present in the oxidized (Fe 3+ ) state, which is poorly soluble in neutral-to-alkaline soils and in water- logged conditions. Fe-deficiency is a serious nutritional problem for virtually all forms of life. In higher plants, it causes a decrease in the abundance of photosynthetic proteins (Pushnik and Miller, 1982), reduction of electron transport chain components (Andaluz et al., 2006), decrease in photosystem (PS) I levels (Timperio et al., 2007), and Abbreviations: Chl, chlorophyll; Cyt, cytochrome; HRP, horseradish peroxidase; LHC, light harvesting complex; PEA, plant efficiency analyzer; PI abs , performance index on an absorption basis; PQ, plastoquinone; PS, photosystem; ROS, reactive oxygen species; SOD, superoxide dismutase. ∗ Corresponding author. Tel.: +91 40 2313 4572; fax: +91 40 2301 0120. E-mail addresses: srgsl@uohyd.ernet.in, psrajagopal@yahoo.com (R. Subramanyam). decrease in the quantum yield of PSII (Samir, 2007; Msilini et al., 2011). Cyanobacteria respond to Fe deficiency via the degradation of light-harvesting phycobilisomes (Guikema and Sherman, 1984) and the expression of the “iron-stress-induced” operon isiAB. Fe deficiency results in decreased PSI antenna size in Chlamydomonas reinhardtii (Moseley et al., 2002). Roots of Fe-deficient plants show morphological and physiological changes. In dicots and non-grass monocots, Fe-deficiency is associated with inhibition of root elon- gation, increase in root tip diameter and abundant formation of root hairs (Schmidt et al., 2000). Young rice plants were shown to be highly susceptible to low Fe supply, being different from other cul- tivated grass species, such as oats, due to lower phytosiderophore production (Mori et al., 1991; Takahashi et al., 2001). Severe Fe defi- ciencies can lead to diminished productivity and even may lead to plant death, resulting in complete crop failure (Guerinot and Yi, 1994). The photosynthetic machinery of higher plants contains two large membrane protein complexes, PSI and PSII, that harness inci- dent light energy to initiate a series of electron transfer reactions across the thylakoid membrane in a coordinated manner. Each PSI core contains subunits designated PsaA to L or to N, respectively, in which PsaA and PsaB are highly conserved and forming the core of the PSI reaction centre. PsaD and PsaE are exposed to the stroma region of thylakoid membranes, where PsaD interacts strongly with Fd, and PsaE channels the electrons coming from PsaD to the rest 0176-1617/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. doi:10.1016/j.jplph.2012.02.008