Immature and mature nonstratified seeds of white ash (Fraxinus americana L.) were dissected transversely and 2/3 of each seed was placed onto agar-solidified Murashige and Skoog medium. Adventitious buds, shoots, and somatic embryos formed on callus, cotyledons, and hypocotyls of the resulting seedlings. Shoot organogenesis was induced on explants cultured on medium with 10 txM thidiazuron but not on explants on media with benzyladenine (BA) or isopentenyladenine. Not all seed sources were equally capable of shoot organogenesis and embryogenesis. Atypical of adventitious regeneration of other woody plants, mature seed explants of white ash were more organogenic with shoots that elongated better than explants from immature seeds. Somatic embryogenesis was observed in cultures where mature seeds were first cultured for 4 weeks on a medium containing 10 I~M adenine 2,4-dichlorophenoxyacetic acid in combination with 0.1 and 1.0 IxM thidiazuron, followed by transfer to a medium containing 0.05 ~M 6-benzyladenine and 0.5 IxM naphthaleneacetic acid. Adventitious shoots and epicotyls from both seedlings and germinated somatic embryos were rooted under intermittent mist and acclimatized to the greenhouse.
Damaging representative plants from five angiosperm families by heating or crushing a small portion of a single leaf results in an electrical change which may spread throughout the shoot. In Mimosa, similar changes have previously been identified as variation potentials.Except in one of the five plants, a variation potential is often accompanied by brief fluctuations which may propagate either basipetally or acropetally and which have many of the properties of action potentials.The spread of a variation potential as described in Mimosa is due to the concommitant spread of a chemical substance in the transpiration stream. In this paper, it is shown that the spread of the purported variation potential is compatible with movement of material in the transpiration stream. In the next paper causation by a substance or group of substances, at present called Ricca's factor, is demonstrated.
An extract of Lycopersicon leaf tissue applied to the base of an excised Lycopersicon leaf causes a variation potential to spread through the leaf. This spread of an electrical wave is closely dependent on the spread of the extract via the transpiration stream, and the amplitude of the variation potential depends on the concentration of extract applied. Extract from 5–10 mg fresh leaves diluted to 1 ml elicits threshold response, and saturation is accomplished with a concentration about 40 times greater. Evidently, the active factor or factors are effective at very low concentrations. A variety of substances cause electrical disturbances when applied to the excised leaf, but plant extract is the only tested material which under the given conditions desensitizes the leaf to an application of saturating extract 5 min after the initial application.The active factor or set of factors has been extracted from plants in several families and appears to be closely related to the substance implicated by Ricca in 1916 in trauma-induced closure of Mimosa leaves. In recognition of this early discovery, the material is at present called Ricca's factor.
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