Vessel element formation in cultured carrot-root phloem slices

Abstract

The effects of light, auxin and cytokinin on vessel element formation in phloem slices of carrot root were examined. When slices of carrot cultivars, ‘Nakamura-senko-futo’ and ‘Yamada-hyakunichisenk6- naga’, precultured in the dark on modified Murashige and Skoog's medium for two days were cultured on a medium containing 5×10−6 M 2,4-D in the dark, no vessel element formation occurred. When precultured slices were cultured in the light with 5×10−6M 2,4-D, vessel element formation was remarkable. But when 5×10−7M kinetin, benzyladenine or zeatin was added, vessel elements were readily formed even in the dark. When slices were cultured in the light, a cytokinin-like substance(s) that causes vessel element formation was produced in the slices, then was released to the medium. The substance(s) was fairly stable to heat. In slices of carrot cultivars, kuroda-gosun, ‘Kintoki’ and ‘Kokubu-senk6-6naga’, a different result for vessel element formation was obtained. When slices of these cultivars were cultured on a medium containing 5×10−6M 2,4-D in the dark, vessel element formation was remarkable. It seemed, therefore, that these cultivars contain enough of a cytokinin-like substance(s) to form vessel elements. In fact, vessel element forming activity was found in the alcohol extract of carrot root phloem from these cultivars.