Journal of Plant Physiology 169 (2012) 577–585 Contents lists available at SciVerse ScienceDirect Journal of Plant Physiology jou rn al h o mepage: www.elsevier.de/jplph Interaction of proline, sugars, and anthocyanins during photosynthetic acclimation of Arabidopsis thaliana to drought stress Ilektra Sperdouli, Michael Moustakas ∗ Department of Botany, School of Biology, Aristotle University of Thessaloniki, University Campus, 54124 Thessaloniki, Greece a r t i c l e i n f o Article history: Received 31 August 2011 Received in revised form 28 October 2011 Accepted 1 December 2011 Keywords: Anthocyanins Drought stress Metabolic adjustment Proline Soluble sugars Oxidative stress Arabidopsis thaliana a b s t r a c t The relationships among photosynthetic acclimation, proline (Pro), soluble sugar (SS), and anthocyanin (An) accumulation in Arabidopsis thaliana leaves to the onset of drought stress (OnDS), mild (MiDS) and moderate drought stress (MoDS), were evaluated. As leaf water content (LWC) decreased, metabolic concentrations (Pro, SS, and An) increased and were negatively and significantly correlated with LWC. Thus, these metabolites may have an important role in the acclimation process to drought stress (DS). No correlations among Pro, SS and An accumulation with the quantum efficiency of PSII photochemistry (˚ PSII ) and the excitation pressure (1 - q P ) were observed under DS. This implies that, while metabolites increased in a drought-dependent way, PSII activity did not decrease in the same pattern. Our results indicated that, under MoDS, A. thaliana leaves were able to maintain oxidative compounds such as mal- ondialdeyde, an end product of lipid peroxidation, within the range of control leaves, and to cope with oxidative damage, as was evident by the decreased excitation pressure (1 - q P ) and similar (ns difference) ˚ PSII to that of control leaves. In addition, a statistically significant increased accumulation of Pro, SS and An was recorded only under MoDS compared to controls. The better PSII functioning of MoDS Arabidopsis leaves may reflect the greater capacity of these leaves to undertake key metabolic adjustments, including increased Pro, SS and An accumulation, to maintain a higher antioxidant protection and a better balance between light capture and energy use. © 2012 Elsevier GmbH. All rights reserved. Introduction Abiotic stresses, which cause depletion of cellular water (drought, high soil salinity and temperature extremes) are the pri- mary causes of crop loss worldwide, reducing average yields for most major crop plants by more than 50% (Boyer, 1982). Increasing plant resistance to drought stress (DS) would be the most econom- ical approach to improving agricultural productivity and reducing agricultural use of fresh water resources (Xiong et al., 2006). As the key process of primary metabolism, photosynthesis plays a central role in plant performance under DS (Chaves et al., 2003, 2009; Flexas et al., 2004, 2009; Lawlor and Tezara, 2009; Pinheiro and Chaves, 2011). The balance between light capture and energy use are of great relevance to studies concerning the responsive- ness of the photosynthetic apparatus to DS (Cornic and Briantais, 1991; Chaves et al., 2009; Lawlor and Tezara, 2009; Aranjuelo et al., 2011). When photosynthesis decreases, the excess excitation energy in photosystem II (PSII) leads to an impairment of photo- synthetic function and to accumulation of reactive oxygen species ∗ Corresponding author. Tel.: +30 2310 998335; fax: +30 2310 998389. E-mail address: moustak@bio.auth.gr (M. Moustakas). (ROS), thereby resulting in oxidative stress (Aranjuelo et al., 2011; Wilhelm and Selmar, 2011). Although impressive advances have been made in the last decade with respect to the nature of events occurring in plants subjected to DS, an integrative picture of the metabolic regulation that takes place is still lacking (Rolland et al., 2006; Shinozaki and Yamaguchi-Shinozaki, 2007; Pinheiro and Chaves, 2011). Several metabolic adjustments occur prior to alteration of the plant water status, implying that DS is perceived before changes in plant water status (Pinheiro et al., 2011). Early responses of plants to DS usu- ally help the plant to survive for some time, while the acclimation of the plant subjected to drought is indicated by the accumulation of certain metabolites associated with the structural capabilities to improve plant functioning under DS (Pinheiro et al., 2001; Reddy et al., 2004). General metabolic adaptation, which enables plants to cope with water or osmotic stress, involves an increased synthesis of osmoprotectants, such as proline (Pro) (Hare et al., 1998; Dobrá et al., 2011). This osmolyte is considered to protect plant cells by osmotic adjustment or by stabilizing membranes (Hare and Cress, 1997; Kavi Kishor et al., 2005; Verbruggen and Hermans, 2008; Szabados and Savouré, 2010). The level of free Pro is reg- ulated by the ratio of the rates of its biosynthesis and degradation (Hare and Cress, 1997; Verbruggen and Hermans, 2008; Szabados 0176-1617/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. doi:10.1016/j.jplph.2011.12.015