Xanthoxin, a New Naturally Occurring Plant Growth Inhibitor

Abstract

WE have extracted a neutral growth inhibitor from the seedlings of dwarf bean (Phaseolus vulgaris cultivar ‘Canadian Wonder’) and wheat (Triticum vulgare cultivar ‘Hybrid’ 46). Comparison of chemical, chromatographic and bioassay data has shown it to be a mixture of two isomeric compounds which we have characterized as products of the photo-oxidation of violaxanthin¹, a common plant xanthophyll. They are the highly active 5-(1′,2′-epoxy-4′-hydroxy-2′,6′,6′-trimethyl-l′-cyclohexyl) 3-methyl-cis,trans-2,4-pentadienal (I) and the less active trans,trans isomer (II). The name xanthoxin is now proposed for the inhibitor, the activity of which in the cis, trans configuration is comparable with the known naturally occurring inhibitor abscisic acid (ABA) in several tests.