Identification of the active component in the papilla-regulating extract from barley leaves

Abstract

A partially purified extract from barley seedlings, referred to as the papilla-regulating extract (PRE), has been reported to induce both the formation of oversize papillae and resistance to penetration by the powdery mildew fungus in inoculated, susceptible barley coleoptiles. Purification and identification of the active component in the PRE were accomplished in this study. Biological activity was monitored by bioassay. The extract, obtained from barley seedlings through autoclaving, was first passed through a C18 reverse phase column. The eluent, in which activity was detected, was next passed through a gel permeation chromatography column packed with Sephadex LH-20 in 50% methanol. The active fractions were chromatographed on a Bio-Gel P-2 column in water. Although xylonate was a major organic component in the active fractions from the P-2 column, authentic xylonate was not biologically active by itself. After rechromatography in the P-2 column, it was determined by ion chromatography and inductively coupled argon plasma atomic emission spectroscopy that the active compound was potassium phosphate. Bioassays using authentic potassium phosphates confirmed this conclusion. The effects of the PRE were also found to be Ca 2+ -mediated. Potassium phosphates in plants may be important in regulating papilla formation and induced resistance.