Dela, G., Dept. of Ornamental Hort. Science, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Or, E., Department of Tree Breeding, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Ovadia, R., Dept. of Ornamental Hort. Science, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Nissim-Levi, A., Dept. of Ornamental Hort. Science, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Weiss, D., Department of Horticulture, Fac. Agric., Food/Environ. Qual. S., Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
Oren-Shamir, M., Dept. of Ornamental Hort. Science, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

Temperature plays a key role in affecting anthocyanin accumulation in plant tissue. In this study, we describe the impact of transient high temperature on the concentration and composition of anthocyanins in 'Jaguar' rose flowers. We show that a 1-day heat treatment of 39/18°C day/night has no effect on pigmentation but a 3-day treatment has a substantial effect. The effect on anthocyanin concentration was most pronounced when the high-temperature conditions were applied at stages 3 and 4 of bud development, and the effect was long term. An extended recovery period was observed before accumulation resumed. The plant's response to high temperature by decreasing pigmentation occurred only in the bud, independent of the heat conditions inflicted on the rest of the plant. Transcript levels of chalcone synthase (CHS) and dihydroflavonol reductase (DFR), two key enzymes in the anthocyanin synthesis pathway, decreased by 50% after heat treatment, suggesting that the decreased anthocyanin concentration is due in part to reduced transcription. The composition of anthocyanin underwent a significant change due to heat stress: the two anthocyanidins making up 'Jaguar' color, pelargonidin and cyanidin, which are at equal concentrations in mature buds under normal conditions, showed a ratio of 2:1 in flowers subjected to heat shock at an early growth stage. However, the level the enzyme determining the shift in the anthocyanin pathway from pelargonidin to cyanidin synthesis, F3′H, did not manifest a significant effect due to heat shock. © 2003 Elsevier Science Ireland Ltd. All rights reserved.