Changes in cytokinin levels of Phalaenopsis leaves at high temperature

The effect of high temperatures on cytokinin levels in Phalaenopsis hybrida leaves was investigated. Endogenous cytokinins were identified and quantif ied in Phalaenopsis leaves grown under high temperature conditions (30/25 d egrees C day/night) using high performance liquid chromatography, bioassay and gas chromatography-selected ion monitoring-mass spectrometry. After 5 a nd 20 d of low temperature (25/20 degrees C day/night), zeatin, zeatin ribo side and dihydrozeatin levels in the leaves were higher than that in leaves subjected to high temperature treatments. When Phalaenopsis leaves were ex posed to low temperatures, about 76% of the free cytokinins detected were o f the zeatin-type. Glucoside cytokinins in the leaves increased significant ly 5 d following high temperatures, and the rate of increase in glucoside c ytokinins corresponded to the duration of high temperatures. At the same ti me, zeatin riboside and dihydrozeatin declined significantly following high temperature application. A significant accumulation of glucoside cytokinin s. zeatin-9-glucoside, zeatin-O-glucoside, zeatin riboside-O-glucoside, and dihydrozeatin-O-glucoside was observed 20 d following high temperatures. T hese results suggest that high temperatures lead to an accumulation of gluc oside cytokinins and a reduction of free base and riboside cytokinins. (C) 2000 Editions scientifiques et medicales Elsevier SAS.