PHYSIOLOGIA PLANTARUM 114: 559–565. 2002 Copyright C Physiologia Plantarum 2002 Printed in Denmark – all rights reserved ISSN 0031-9317 Increased anthocyanin accumulation in aster flowers at elevated temperatures due to magnesium treatment Liat Shaked-Sachray a , David Weiss b , Moshe Reuveni a Ada Nissim-Levi a and Michal Oren-Shamir a, * a Department of Ornamental Horticulture, Agricultural Research Organization, The Volcani Center, Bet-Dagan 50250, PO Box 6, Israel b Department of Horticulture, Faculty of Agriculture, The Hebrew University of Jerusalem, PO Box 12, 76100, Rehovot, Israel *Corresponding author, e-mail: lporen/wicc.weizmann.ac.il Received 19 July 2001; revised 9 November 2001 Temperature is one of the main external factors affecting anthocyanin accumulation in plant tissues: low temperatures cause an increase and elevated temperatures cause a decrease in anthocyanin concentration. Several metals have been shown to increase the half-life time of anthocyanins, by forming com- plexes with them. We studied the combined effect of elevated temperatures and increased metal concentrations on the ac- cumulation of anthocyanins in aster ‘Sungal’ flowers. It has been found that magnesium treatment of aster plants or de- tached flower buds, partially prevents colour fading at elevated temperatures. Anthocyanin concentration of aster ‘Sungal’ flowers grown at 29æC/21æC day/night, respectively, was about half that of flowers grown at 17æC/9æC. The activity of phenyl- alanine ammonia-lyase (PAL) and chalcone isomerase (CHI) Introduction Anthocyanins are the group of pigments ranging from red to violet and blue, which are primarily responsible for flower colour (van Tunen and Mol 1991). These pig- ments accumulate in the epidermal cell vacuoles, and both their intensity and hue are dependent on external conditions, as well as on the microenvironment con- ditions in the vacuoles (Harborne and Grayer 1988). Temperature is one of the main external factors affect- ing anthocyanin accumulation in plant tissues: Low tem- peratures increase and elevated temperatures decrease anthocyanin concentration (Christie et al. 1994, Leyva et al. 1995, Oren-Shamir and Nissim-Levi 1997, 1999, Zhang et al. 1997 and Zhong and Yoshida 1993). Fur- thermore, in several plant systems, such as maize seed- lings (Christie et al. 1994), Arabidopsis (Leyva et al. 1995) and petunia (Shvarts et al. 1997) temperature has been shown to have a significant effect on the expression Abbreviations – PAL, phenylalanine ammonia-lyase; CHI, chalcone isomerase; SD, short day; LD, long day; ICP, inductively coupled plasma atomic emission. Physiol. Plant. 114, 2002 559 decreased as the temperature increased. Treatment of both whole plants and detached flower buds grown at elevated tem- peratures in the presence of magnesium salts, increased flower anthocyanin concentration by up to 80%. Measurement of magnesium following these treatments revealed an increased level of the metal in the petals, suggesting a direct effect. Mag- nesium treatment does not seem to cause increased synthesis of anthocyanin through a stress-related reaction, since the activ- ities of both PAL and CHI did not increase due to this treat- ment. The results of this study show that increasing magnesium levels in aster petals prevents the deleterious effect of elevated temperatures on anthocyanin accumulation, thus enhancing flower colour. of anthocyanin genes: low temperature conditions were accompanied by a several fold increase in transcript levels of genes, whose products are either key enzymes in the general phenylpropanoid pathway such as phenyl- alanine ammonia lyase (PAL), or genes whose products catalyse reactions committed to the flavonoids and anthocyanin biosynthesis, such as chalcone synthase (CHS), chalcone isomerase (CHI) and dihydroflavonol reductase (DFR). Clearly, one of the factors responsible for the lower anthocyanin concentrations in plants at elevated temperatures is a decreased rate of synthesis (Shvarts et al. 1997). However, temperatures may affect not only the synthesis, but also the stability of antho- cyanins. Therefore, the decrease in anthocyanin concen- tration at elevated temperatures may result from both a decrease in synthesis and an increase in degradation. Several studies have examined the effect of different