~ Pergamon 0306-4565(93)E0008-R J. therm. Biol. Vol. 19, No. 3, pp. 171-176, 1994 Copyright © 1994 ElsevierScienceLtd Printed in Great Britain. All rights reserved 0306-4565/94 $7.00 + 0.00 THE LONG-TERM EFFECT OF COLD ON THE METABOLISM OF WINTER WHEAT SEEDLINGS. II. COMPOSITION OF FATTY ACIDS OF PHOSPHOLIPIDS A. SKOCZOWSKI, M. FILEK and F. DUBERT Polish Academy of Sciences, The Franciszek Grrski Dev_trtment of Plant Physiology, ul. Pod|u~na 3, 30-239 Krak6w, Poland (Received 8 August 1993; accepted in revised form 18 December 1993) Abstract--l. In seedlings of winter and spring (controls) wheat the changes in the composition of phospholipid fatty acids induced by long-term cold treatment and by subsequent adaptation to 20°C are examined. 2. In both genotypes grown at 2°C, as compared to 20°C, linolenic acid (18:3) was increased and oleic (18:1) and linoleic acids (18:2) decreased in content, and the ratio of 18:3/18:2 also increased. 3. In the winter variety, during growth at 20°C, changes in 18:3/18:2 ratio were small but at 2°C, after a cold treatment sufficient for vernalization (56 days), rapid decrease in the ratio was observed. This change however, did not influence the double bond index (DBI). 4. After 4 days adaptation to 20°C winter wheat seedlings, subjected to prior cold treatment, retained a fatty acid composition resembling that formed in the cold. In the spring variety 2 days adaptation to 20°C caused changes in fatty acid composition characteristic for seedlings grown at 20°C. Key Word Index: Adaptation to temperature; cold; fatty acids; phospholipids; Triticum vulgare; vernalization; wheat INTRODUCTION The effect of long-term exposure to low temperatures on the composition of membrane lipids (Grenier and Willemont, 1974; Horvath et al., 1983; Smolefiska and Kuiper, 1977; Thompson and Zalik, 1973) and the degree of unsaturation of their fatty acids (Harris and James, 1969a, b; Huber and Zalik, 1963; Kuiper, 1985; Lyons et al., 1979; Willemont, 1979) has been investigated many times, mainly in connection with the frost hardening of plants. However, there are few studies dealing with the rate of change in mem- brane composition in plants grown in the cold, to an increase in temperature. Rivera and Penner (1978) demonstrated that a change in plant growth temperature caused rapid (observable after 24h) reversible shifts in membrane lipid fatty acid compo- sition. These investigations were carried out in the Abbreviations: < 16, fatty acids with carbon chains shorter than 16 C; 16: 0, palmitic acid; 18 : 0, stearic acid; 18:1, oleic acid; 18:2, linoleic acid; 18:3, linolenic acid; 18:3/18:2, ratio of linolenic to linoleic acid content; DBI, double bond index = Z(% of fatty acid con- tent x #of double bonds) x 100-1; PL, phospholipids. temperature range 15-30°C, i.e. not at typical cold temperature. Skoczowski et al. (1992) have demonstrated that the seedlings of winter wheat, grown on the light for 35 days at 5°C showed, even after 8 days adap- tation to 25°C, higher fatty acid unsaturation than the non-chilled controls. These results confirm the opinion that low temperature induced desaturation of fatty acids is not mainly controlled by higher oxygen concentration in cytosol (Skriver and Thomp- son, 1976). This is true specially in photosynthetic tissues where oxygen levels are apparently too high, due to endogenous production of the gas, to be rate limiting in the desaturation process. It is for this reason that we have investigated the influence of long-term cold and subsequent adaptation to 20°C of the plants, grown in darkness, on the fatty acid composition of their membranes. The experiments were carried out on a winter wheat variety, which, under field conditions in autumn and spring, is subjected to prolongated exposure of cold. A spring variety was also used as controls, this variety experiences only temporary periods of cold in field conditions. 171