The cytokinin 2-isopentenyladenine causes partial reversion to skotomorphogenesis and induces formation of prolamellar bodies and protochlorophyllide(657) in the lip1 mutant of pea

When grown in darkness the photomorphogenic lip1 mutant of pea (Pisum sativ um L.) has a slender stem, expanded leaves, prolamellar body (PLB) lacking plastids with the size of chloroplasts and a low level of phytochrome A. Th e lack of PLBs in a dark-grown material (lip1) created a possibility to fur ther study the regulation of their formation in relation to plant developme nt, Inclusion of a cytokinin, 2-isopentenyladenine (2iP), in a medium suppo rting growth of the pea seedlings in darkness was found to reduce epicotyl length in the wild type. In lip1 the formation of a slender stem was inhibi ted and a short epicotyl developed. Furthermore, leaf expansion was inhibit ed, the plastid size reduced and the formation of PLBs induced. The PLB for mation in lip1 was not accompanied by an increase in the amount of protochl orophyllide (Pchlide) or Pchilde oxidoreductase (POR), In the presence of 2 iP the level of phytochrome A protein was increased in lip1 and the FOR mRN A levels decreased in both lip1 and wild-type plants. The chloroplast chara cteristic trans-3-hexadecenoate acyl group of phosphatidylglycerol, present in the plastids of dark-grown lip1, was not influenced by 2iP, Thus, not a ll photomorphogenic processes reacted similarly in the lip1 mutant, but lea f expansion and plastid differentiation, including PLB formation, seemed to be regulated by the same signal transduction chain, Exogenously applied br assinolide could rescue neither dark- nor light-grown defects of the lip1 m utant. Thus, cytokinins but not brassinolides seem to be involved in the re gulation of certain characteristic traits of skotomorphogenesis in pea, inc luding plastid development and PLB formation.