The transport of abscisic acid in cotyledonary petiole sections of cotton seedlings was investigated using (2-14C)-ABA in a donor-receiver system. Using the intercept technique, a transport velocity of 22.4 mm/hr was determined. This velocity was found to be independent of the length of the petiole or of the concentration of ABA applied. In a 24-hr period 70%of the applied ABA moved through the tissue sections. No polarity was found in any of the studies.The capacity of the transport system decreased with increasing age of the tissue and with increasing time of pre-exposure to ABA. When metabolism of the tissue was restricted by cold temperature, low-O2tension or DNP treatment, transport was inhibited 80 to 98%.The distribution of ABA in the petiole during transport was also investigated. The results are discussed in relation to the well-studied transport of IAA and in relation to the physiologicalrole of ABA.
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