Summary
The role of indolylacetic acid (IAA) in influencing the movement of radiophosphorus from a remote locus has been investigated in the decapitated stems of Pisum sativum (var. Meteor) and disbudded shoots of Populus robusta. It has been shown after only a few hours that the radioisotope accumulates at the region where the auxin was applied. By steam-girdling experiments with pea, it was established that auxin-induced transport occurs via the phloem and other obserbations suggest that this effect may be independent of growth. When tri-iodobenzoic acid was applied together with IAA at the stump or to the surface of the stem between the IAA source and the injection point of the tracer, the transport of 32P along the stem was greatly reduced. Of a number of auxin-type substances tested, only naphthoxyacetic acid gave a comparable response to that obtained with IAA, whilst other growth regulators such as kinetin or gibberellic acid did not stimulate 32P transport.
Studies with isolated poplar cuttings showed that auxin-induced transport could only be demonstrated by completely disbudded shoots. Again, phloem transport seemed to be involved and the movement of 32P could be more readily induced in an acropetal direction.
The results are discussed in relation to some recently proposed theories concerning the mechanism of translocation in the phloem.
Zusammenfassung
Der Einfluß der Indolylessigsäure (IES) auf die Wanderung von radioaktivem Phosphor wurde an dekapitierten Sprossen von Populus robusta nach Entfernung ihrer Knospen und an dekapitierten Stengeln von Pisum sativum (var. Meteor) untersucht. Bereits nach wenigen Stunden war eine Anhäufung von 32P am Ort der Auxinzufuhr zu erkennen. Durch Dampf-Ringelungsversuche ließ sich bei Pisum zeigen, daß der Auxin-induzierte Transport über das Phloem erfolgt; weitere Beobachtungen lassen darauf schließen, daß dieser Effekt unabhängig vom Wachstum sein dürfte. Wenn man gleichzeitig mit IES Trijodbenzoesäure (TIBA) auf die apikale Schnittfläche aufbringt oder in einer Zone zwischen Auxinquelle und Injektionsstelle des 32P als Paste auf die Oberfläche des Sprosses aufträgt, so wird der Längstransport des markierten Phosphors erheblich gehemmt.
Es wurden auch noch einige andere Verbindungen von Wuchsstoffcharakter geprüft. Von ihnen führte nur Naphthyloxyessigsäure zu einem ähnlichen Effekt wie IES; andere Wachstumsregulatoren wie Kinetin oder Gibberellinsäure förderten den 32P-Transport nicht.
Untersuchungen an isolierten Pappelsprossen zeigten, daß der auxininduzierte Stofftransport nur in solchen Sprossen zu beobachten ist, deren Knospen vollständig entfernt worden waren. Auch hier scheint es sich um einen Transport im Phloem zu handeln. Die Wanderung von 32P ließ sich stets leichter in akropetaler Richtung induzieren.
Die geschilderten Ergebnisse werden in Beziehung zu einigen neuerdings vorgeschlagenen Theorien des Transportmechanismus im Phloem diskutiert.
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Davies, C.R., Wareing, P.F. Auxin-directed transport of radiophosphorus in stems. Planta 65, 139–156 (1965). https://doi.org/10.1007/BF00384993
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DOI: https://doi.org/10.1007/BF00384993