Metabolism of¹⁴C-labeled epibrassinolide in intact seedlings of cucumber and wheat

Abstract

The metabolism of exogenously applied¹⁴C-24-epibrassinolide (¹⁴C-EBR) in seedlings of cucumber and wheat was examined. Total lipids were extracted with isopropanol and chloroform, and then partitioned with water. More than 80% of radioactivity was distributed to chloroform-phase. Concentrated chloroform-phase was applied to silica gel plate and was developed with chloroform-ethanol (5:1 v/v). Rf value of original¹⁴C-EBR was about 0.6. In cucumber leaves harvested after 2 day-culture, three peaks were detected at Rf 0.11, 0.47 and 0.84. In cucumber petioles of 2 day-culture, however, a major peak was detected at Rf 0.90. But¹⁴C-EBR was hardly metabolized in hypocotyls and roots after 2 days.

In wheat leaves harvested just after pulse labeling, a peak was detected at Rf 0.63. By further analysis of this peak using ODS-HPLC, however, an original peak of¹⁴C-EBR and two metabolites having higher polarity were detected. In wheat leaves harvested after 2 day-culture, the profile of TLC scanning was similar to that just after pulse labeling, although, an original peak of¹⁴C-EBR was no longer detected by ODS-HPLC. In wheat roots,¹⁴C-EBR was hardly metabolized. These results indicate that¹⁴C-EBR occurring in leaves and petioles is metabolized to produce several kinds of metabolites.