Mineral Toxicity Stress Laboratoire de Biologie et Physiologie Cellulaires Ve´ge´tales, Faculte ´ des Sciences de Bizerte, Zarzouna, Bizerte, Tunisia Altered Fatty Acid Profile of Polar Lipids in Maize Seedlings in Response to Excess Copper R. Chaffai, M. A. Elhammadi, T. N. Seybou, A. Tekitek, B. Marzouk, and E. El Ferjani AuthorsÕ addresses: Dr. R. Chaffai (corresponding author; e-mail: radhouanec2002@yahoo.fr), Dr. M. A. Elhammadi, Dr. T. N. Seybou, and Dr. E. E. Ferjani, Laboratoire de Bio-Physiologie Cellulaires Ve´ge´tales, Faculte´ des Sciences de Bizerte, 7021 Zarzouna, Tunisia; Dr. A. Tekitek, Laboratoire de Biochimie et de Biologie Mole´culaire, Faculte´ des Sciences de Bizerte, 7021 Zarzouna, Tunisia; Dr. B. Marzouk, Laboratoire des Ame´liorations et Adaptations des Plantes, Institut National de la Recherche Scientifique et Technique (INRST), BP 95-2050 Hammam-Lif, Tunisia With 5 figures and 5 tables Received May 15, 2006; accepted November 15, 2006 Abstract A wide range of cellular responses occur when plants are exposed to heavy metal stress, including changes in the membrane fatty acid composition. In this study, we examined the effect of excess copper (100 lm) on the degree of unsaturation [double bond index (DBI) of 18-C fatty acids] and the polar lipid profiles in maize (Zea mays L.). The level of unsaturation of total fatty acids decreased from 1.42 to 1.28 in maize roots. However, copper-induced compositional changes of polar fatty acid composition show a general trend of increasing DBI. These responses suggest that individual 18-C fatty acid classes may have specific roles in maintaining optimal membrane function, enabling plant growth under copper stress. The results also reveal key changes including marked decrease in total root phospholipid levels and consistent increase in the steryl lipid/phospholipid (SL/ PL) ratio, as well as a decrease in monogalactosyldiacyl- glycerol/digalactosyldiacylglycerol (MGDG/DGDG) ra- tio, reflecting alteration of membrane permeability and fluidity. In shoots, the DBI obtained from phosphatidyl- choline (PC), sulphoquinovosyldiacylglycerol (SQDG) and monogalactosyldiacylglycerol (MGDG) was in- creased. In contrast, these indices were decreased in phosphatidylinositol (PI) and phosphatidylglycerol (PG). However, the PI, PC, PG, MGDG and DGDG contents in shoots were significantly decreased, suggesting altera- tions in the photosynthetic membranes. Key words: copper stress — glycolipids — lipid peroxidation — phospholipids — polar lipids — steryl lipids — Zea mays L. Introduction Exposure to heavy metals is one of the most prevalent environmental stresses encountered by plants. In the natural environment, an increase in the concentrations of heavy metals can occur, mainly as a result of agricultural, manufacturing, mining and waste-disposal practices. Heavy metals such as copper (Cu), nickel (Ni) and zinc (Zn) are essential to plant nutrition and act as the active centres of enzymes. Marked increase in the level of essential or non-essential heavy metals in plants, induced impairments at various levels of cell organization; heavy metals particularly affect the integrity of the plasma membrane by inducing an oxidative damage (De Vos et al. 1989, 1991). Three possible mecha- nisms of induction of metal stress toxicity were suggested: (i) production of reactive oxygen species by autoxidation and Fenton reaction, (ii) blocking of essential functional groups in biomolecules, and (iii) displacement of essential metal ions from biomolecules (Schu¨ tzendu¨ bel and Polle 2002). Plants respond to heavy metal toxicity in a variety of ways by the induction of general stress responses, which in part include the immediate changes in the membrane lipid composition (Jones and Harwood 1993). Thus, the regulation of fatty acid (FA) synthesis is significant to maintain functional mem- branes and as a mechanism of plant adaptation to J. Agronomy & Crop Science 193, 207—217 (2007) doi:10.1111/j.1439-037X.2007.00252.x Ó 2007 The Authors Journal compilation Ó 2007 Blackwell Verlag, Berlin ISSN 0931-2250 U.S. Copyright Clearance Centre Code Statement: 0931–2250/2007/9303–0207 $15.00/0 www.blackwell-synergy.com