Vessel element formation in cultured carrot-root phloem slices

The effects of light, auxin and cytokinin on vessel elementformation in phloem slices of carrot root were examined. When slices of carrot cultivars, ‘Nakamura-senko-futo’and ‘Yamada-hyakunichisenk6- naga’, preculturedin the dark on modified Murashige and Skoog's medium for twodays were cultured on a medium containing 5x10^–6 M 2,4-Din the dark, no vessel element formation occurred. When preculturedslices were cultured in the light with 5x10^–6M 2,4-D,vessel element formation was remarkable. But when 5x10^–7Mkinetin, benzyladenine or zeatin was added, vessel elementswere 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 fairlystable to heat. In slices of carrot cultivars, kuroda-gosun, ‘Kintoki’and ‘Kokubu-senk6-6naga’, a different result forvessel element formation was obtained. When slices of thesecultivars were cultured on a medium containing 5x10^–6M2,4-D in the dark, vessel element formation was remarkable.It seemed, therefore, that these cultivars contain enough ofa cytokinin-like substance(s) to form vessel elements. In fact,vessel element forming activity was found in the alcohol extractof carrot root phloem from these cultivars. (Received June 8, 1971; )