Auxin basipetal efflux

Oscillatory phenomena associated v ith polar transport of synthetic auxin have also been reported in Avena and Zea coleoptiles (Newman 1963, Hertel and Flory 1968, Shen-Miller 1973 a, b), thus the oscillations of basipetal efflux of endogenous auxin found in our experiments may reflect a more general property of the mechanism involved in polar transport of auxin. 

The effects of ABA upon the wave-like pattern of the basipetal efflux of auxin were also observed when the inhibitor was applied for 100 min to the basal ends of tissue blocks (66 mm long). In these tests, however, suppression of the wave amplitudes was observed only at distances up to about 40 mm from the basal end to which ABA was applied (Fig. 7.2 B). This implies that the supracellular oscillatory system, in spite of its polarity, is capable of transmitting signals in both the basipetal and the acropetal direction. The velocity of signal transmission in the acropetal direction, however, appears to be slower. 

Application of zeatin in agar gels to the apical ends of stem segments before sectioning them produced some increase of the auxin efflux. The most interesting action of both cytokinin and gibberellic acid, however, was prevention of the depressive effect of abscisic acid upon the wave-like pattern of the basipetal efflux of auxin (Fig. 7.2 C, D). 

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