[Transport of [(14)C] auxin from young pods of Vicia faba L]

Seasonal variations in the polar-transport pathways and retention sites of [(3)H]indole-3-acetic acid in young branches ofFagus sylvatica L

Branches were cut from young beeches (Fagus sylvatica L.) at various stages of the annual cycle and [(3)H]indole-3-acetic acid (0.35 nmol) was applied to the whole surface of the apical section of each branch, just below the apical bud. The labelled pulse (moving auxin) and the following weakly radioactive zone (auxin and metabolites retained by the tissues) were localized by counting: microautoradiographss were made using cross sections from these two regions. During the second fortnight of April, auxin was transported by nearly all the cells of the young primary shoot, but the label was more concentrated in the vascular bundles. Auxin transport became the more localized: the cortical parenchyma appeared to lose its ability to transport the hormone (end of April), followed in turn by the pith parenchyma (May). Polar auxin movement at that time was limited to the outer part of the bundle (cambial zone and phloem) and to the inner part (protoxylem parenchyma). Later protoxylem parenchyma ceased to carry auxin. During the whole period of cambial activity, auxin was transported and retained mainly by the cambial zone and its recent derivatives. In September, before the onset of dormancy, and in February, at the end of the resting period, the transport pathways and retention sites for auxin were mainly in the phloem, where sieve tubes often completely lacked radiolabel. When cambial reactivation occurred in the one-year shoot, auxin was mainly carried and retained again in the cambial zone and differentiating derivatives.

[Transport, distribution and metabolism of auxin in Vicia faba L. roots after application of [(14)C]IAA or [ (3)H]IAA to the apical bud]

After application of [2-(14)C]IAA or [(3)H]IAA to the apical bud of intact young broad-beans, the movement of labelled auxin into the roots was followed by liquid scintillation counting and by autoradiographic analyses. Its metabolism was studied by chromatography, and its pathways by autoradiographic analyses coupled with ringing experiments or removal of the stele.The movement of [(14)C]IAA or [(3)H]IAA was characterized by a high retention of radioactivity in tissues, particularly in very young plants. The speed, which did not exceed 9 mm·h(-1) in old roots, appeared the slower the younger the plants were. However, it seemed possible that small quantities of IAA or its derivates went into sieve tubes in which they moved downwards faster. In the apical part of the root the labelled IAA was more quickly transformed than in the other parts of this organ. 24 h after the application of the IAA, the labelled molecules gathered more densely in the cap itself than in apical meristem.At least 2/3 of the applied auxin moved within the stele, which in a crosssection represents only 1/7 of the whole area. In the older part of the root, the cambial zone located between mature phloem and mature xylem was the preferred pathway of IAA transport, although it is a zone where the hormone is immobilized, used and metabolised. In the younger part of the root, the whole stele was the preferred pathway. Therefore, the auxin is in a privileged situation to take part in the regulation of various processes, especially in the development of secondary vascular tissue, more particularly of xylem.