J. VAN OVERBEEK 



and 



L. D O W D I N G 



Shell Development Co. 

 Modesto, California 



Inhibition of Gibber ellin Action by Auxin 



In 1956 we started a search for a simple, yet specific, test for gib- 

 berellins; something comparable to the section test for auxins. We 

 found it in the Avena leaf base section test and first reported on it at 

 the Stanford AIBS meetings (3). In this test, a section of the basal 

 portion of the coleoptile which includes the enclosed embryonic shoot 

 is taken. It is this shoot which emerges from the coleoptile as a re- 

 sponse specific to gibberellin. We have repeated this test more than 

 100 times, always with the same general results: gibberellin promotes 

 growth, auxins inhibit the growth of this shoot, while kinetins pro- 

 mote it very slightly. In the beginning the variability of the growth of 

 the individual sections was considerable, but gradually we have 

 learned to reduce this to a minimum. 



TECHNIQUE OF THE LEAF BASE SECTION TEST 



Planting and Preparation 



Wooden flats such as are used in nurseries are filled with approxi- 

 mately 2 inches of rather coarse Vermiculite, covered with a tin lid, 

 and steam sterilized at 100° C. for at least 3 hrs. One-half pint of 'Ka- 

 nota' oat seeds are placed in a one-quart jar, 5 to 10 mg. of Ceresan 

 is added, and the jar is filled with water. The seeds are soaked for 1 

 hr. The oats are drained and spread on the sterile Vermiculite. The 

 flat is then soaked with water, covered with the tin lid, drained, and 

 put to germinate at 30° C. for 24 hrs. After germination, the seeds 

 are covered with 0.5 inch sterile Vermiculite, saturated with water, 

 the lid replaced, and the flat drained. With the lid still on, the flat of 

 oats is taken to a physiological darkroom (27° C. and 80 to 90 per cent 

 relative humidity). Here the lid is removed and the flat placed in a 



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