Epiphylly in a Variant ofHelianthus annuus×H. tuberosusInduced byIn VitroTissue Culture

• Published in: International journal of plant sciences 2000-01, Vol.161 (1), p.13-22
• Main Authors: Fambrini, Marco, Cionini, Giuliano, Bianchi, Roberto, Pugliesi, Claudio
• Format: Article
• Language: English
• Subjects: Embryonic cells; Embryonic stem cells; Embryos; Epidermal cells; Leaves; Meristems; Mesophyll cells; Plantlets; Plants; Totipotent stem cells
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/314235

A variant clone (EMB‐2) derived byin vitrotissue culture of the interspecific hybridHelianthus annuus×Helianthus tuberosusshows a particular deviation from the usual pattern of plant development in that it produces, bothin vitroandin vivo, epiphyllous embryos and/or shootlike structures. Ectopic structures, which are usually arranged in clusters or rows along preexisting veins, originate asynchronously from epidermal cells of the adaxial surface of the leaf blade. Sometimes embryos and buds are also detected on the adaxial plane of the petioles and at the nodes of the stem. EMB‐2 individual plants differ greatly in terms of the timing and extent of phenotypic expression of epiphylly. Leaves precociously affected by ectopic structures show a more drastic alteration in the differentiation process. Growth is arrested, the spongy parenchyma and air spaces are absent, and the mesophyll cells do not enlarge. Excluding the veins and epidermis, the leaves are wholly composed of isodiametric cells that are regularly arranged in parallel rows that have dense cytoplasm and prominent nuclei. Ectopic structures isolated from leaves and culturedin vitromostly produce plantlets with the same phenotype as the original clones.In vivo, the EMB‐2 plants are propagated by tubers. Often, the shoot‐meristems that originate from tubers exhibit a teratological appearance and die without further development. However, several normal shoots grow and produce plants that display epiphyllous structures like those of the parent plants. Alterations of the endogenous hormonal levels or mutations in genes involved in the switch from indeterminate to determinate cell fate may be responsible for the ectopic development of shoots and embryos on leaves of EMB‐2 variant.