Auxin transport in explants of coleus

Abscission: movement and conjugation of auxin

A 1-hour application of indole-3-acetic acid to bean (Phaseolus vulgaris L. cv. Red Kidney) explants inhibited abscission for an 8-hour aging period. Use of indole-3-acetic acid-(14)C showed that the applied indole-3-acetic acid was conjugated within explant tissue and that this conjugation mechanism accounts for loss of effectiveness of indole-3-acetic acid in inhibiting abscission after 8 hours. Reapplication of indole-3-acetic acid to an explant at a later time, before the induced aging requirement was completed reinhibited abscission. 2,4-Dichlorophenoxyacetic acid, which is not destroyed or conjugated by this system, did not lose its ability to inhibit abscission. It was concluded that indole-3-acetic acid destruction is one of the processes involved in the aging stage of abscission in explants.

Movement and metabolism of kinetin-C and of adenine-C in coleus petiole segments of increasing age

To see if polar movement was typical of growth-regulators other than auxins, the movement of adenine-8-(14)C and of kinetin-8-(14)C was studied in segments cut from petioles of increasing age. No polarity was found. In time-course experiments lasting 24 hr, kinetin showed a progressive increase of radioactivity in receiver blocks, while adenine showed a maximum at 8 hr with a decline thereafter. More kinetin moved through older segments than through younger ones. There was no difference in net loss as far as the position of the donor block is concerned. However, the loss of radioactivity from adenine donor blocks was much higher than the loss of radioactivity from kinetin donor blocks.The radioactivity in receiver blocks after 24 hr treatment with kinetin-(14)C was still with kinetin, judging by location on chromatograms. By the same criterion, adenine and a smaller amount of some other compound were in receiver blocks after a 6 hr transport with adenine-(14)C in the donors. By contrast, more zones of radioactivity were extracted from petiole segments to which kinetin or adenine had been added. For both purine derivatives the original compound represented no more than 20% of the total radioactivity extracted from the tissue after a transport period of 24 hr.

Hormonal regulation of leaf abscission

A review is given of the progress made during the last 6 years in elucidating the nature, locus of action, and transport properties of the endogenous hormones that control leaf abscission.

Auxin transport and conjugation in cotton explants

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On the relation between auxin transport and auxin metabolism in explants of Coleus

Transport and metabolism of naphthylacetic acid, labelled with (14)C or with (3)H, were studied by means of the liquid scintillation counting technique in combination with thin layer chromatography.The amounts of radioactivity reaching the receiver blocks as well as the loss from donor blocks greatly depended on the donor concentration. The relative amounts in receiver blocks increased with decreasing auxin concentrations in donor blocks. This phenomenon may be ascribed to the low immobilization capacity of the tissue at very low auxin concentrations.The relative amounts of radioactivity lost from donor blocks increased with decreasing auxin concentrations in donor blocks.Different characteristics of auxin transport can be explained by assuming a movement in symplast or in apoplast. During transport in the symplast the auxin is immobilized. Auxin immobilization governs many characteristics of auxin transport and could have a regulating effect on the free auxin content in plant tissues.