Does Auxin Move in a Stream

Newman s observations, and the reports on oscillations in the transport of auxin in coleoptiles (Hertel and Flory 1968, Shen-Miller 1973 a, b) point to the operation of feedback loops... in the establishment of the stable pH and electical gradients that are associated with the new cellular auxin concentration and an increased cellular flux of auxin (Goldsmith 1977, p 449 see also Scott 1967). Clearly, these processes are oxygen-dependent since no potentials develop in cases even where there is an asymmetric auxin distribution in corn coleoptiles which have been geostimulated under anaerobic conditions (De-DOLPH et al. 1965, Naqvi et al. 1965). 

3 Evaluation of Estimation and Interpretation of Hormone Movement 3.3.3.1 Does Auxin Move in a Stream  

Measurements and calculations of velocities, densities, and intensities of transport to characterize hormone translocation usually imply that these quantities be constant and that the hormone moves in a stream. They do not, however, allow for degradation and/or immobilization, i.e., leakage of molecules out of the stream, to take place. Yet such phenomena do take place, and do vary with time and distance from the hormone source. Variations in the density of mobile auxin have been demonstrated even within short transport sections (e.g., Kaldewey 1963 in Fritillaria axes Newman 1965, 1970 in Avena coleoptiles Kaldewey and Kraus 1972 in Gossypium seedlings Kaldewey etal. 1974 in Pisum internodes Kaldewey 1976 in Tulipa axes). The commonly observed decline of mobile auxin as a function of distance from the auxin source indicates that not all auxin molecules move with the same velocity. The same conclusion may be drawn from the tpyical initial gradual increase of hormone flux into basal receivers which occurs before linearity of the time course is reached (e.g., Hertel 1962, Hertel and Leopold 1963, de la Fuente and Leopold 1973 in Helianthus hypocotyls McCready and Jacobs 1963 a, b, in petioles and Smith and Jacobs 1968 in hypocotyls of Phaseolus de la Fuente and Leopold 1966 in Coleus internodes Thornton and Thimann 1967 in Avena coleoptiles Greenwood and Goldsmith 1970 in Pinus embryonic hypocotyls Wilkins and Cane 1970, Wilkins etal. 1972 and Shaw and Wilkins 1974 in Zea roots Kaldewey et al. 1974 in Pisum internodes Tsurumi and Ohwaki 1978 in Vida roots). 

A further complication is evident in that there exist different transport channels with different properties. The auxin stream seems to contain a fast fraction of low density which is separate from a main and slower fraction (e.g., Vardar 1964, Newman 1965, Rayle etal. 1969, de la Fuente and Leopold 1972, Kaldewey and Kraus 1972, Patrick and Woodley 1973, Krul 1977, Sheldrake 1979, see also Goldsmith 1977, p452ff.). The fast and slow transport fractions may be associated with different compartments of the cells, possibly the cytoplasm and the vacuole, respectively. This possibility is based on the multiphasic efflux and elution profiles of plant sections supplied with labeled auxin (de la Fuente and Leopold 1970 b, 1972, Davies 1974 see also Goldsmith 1977, p 453 f.). 

3 Transport and Other Modes of Movement of Hormones (Mainly Auxins) 

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