21 



Paleg, 1965; Varga and Humphries, 1974; Maheshwari et al . , 1980). 

 However, others have reported that observed synergistic interactions 

 were due to an auxin-sparing reaction wherein applied gibberellins inhi- 

 bited or reduced the concentration of auxin degrading enzymes such as 

 IAA oxidase (Brian and Hemming, 1958; Kogl and Elema, 1960, cited in 

 Weaver, 1972; Galston and Purves, 1960; Sarma, 1979). 



Ashton (1959) postulated that the reason 2,4-D was more effective as 

 a herbicide in plants that were actively growing was due to an increase 

 in translocation; therefore, the growth promoting properties of GA might 

 increase the effectiveness of 2,4-D. To test this hypothesis red kidney 

 bean plants were pretreated with 100 mg/1 of the potassium salt of GAo 

 prior to the treatment of a single primary leaf with radioactively 

 labeled 2,4-D. Twenty-four hours after 2,4-D treatment the amount of 

 2,4-D in the whole plant was higher than plants not receiving GA 3 

 treatment. This effect disappeared after 72 hours and was shown not to 

 be due to a reduction in the breakdown of 2,4-D by GA3. Similar results 

 were reported with 2,4-D by Basler (1959) and 2,4,5-T by Basler (1974) 

 utilizing Phaseolus vulgaris. Pi let (1965) reported pretreatment of 

 Lens culinaris epicotyl segments with GAo increased the uptake and velo- 

 city of movement of applied IAA out of apical growing regions. Basler 

 (1974) demonstrated that increased translocation of 2,4,5-T by 



GA 3 appeared to be specific to 2,4-5-T, since the translocation of 



3 14 



labeled sucrose- H and glycine- C were relatively unaffected by 



GA3 after 4 to 24 hours post treatment. Pieterse and Roorda (1982) also 

 hypothesized that increased sensitivity-of waterhyaci nths to 2,4-D 

 when combined with GA 3 was due to increased translocation. The only 



