Investigation of natural auxins and growth inhibitors 



THE BIO-ASSAY 



Since the primary aim of our study is to separate and identify biologically 

 active substances, it is important to have a sensitive, reliable, and easy-to- 

 perform bio-assay. The results of a search for a suitable plant material! l^d 

 us to conclude that the coleoptile and the first internode of the oat seedling 

 were suitable test objects. The variety Brighton:|:, a hulless oat, was used 

 throughout these studies. When coleoptiles were wanted, the seeds were 

 exposed to red light after soaking to prevent the growth of the first internode. 



Figure 8. The physiological 'merry-go-round'' used to rotate the oat first internodes. The 125 c.c. 

 Erlenmeyer flasks are ready to receive the 13 X 100 mm Pyrex tubes containing the sections plus 0-5 c.c. 

 of solution. If the atmosphere of the room is dry, the tubes should be closed with vaccine stoppers. The 

 machine rotates at 1 r.p.m. 



When first internodes were wanted, the seeds were grown in total darkness. 

 All manipulations were performed under green light, at a wavelength 

 (about 546 m^) which has practically no inhibitory effect on the growth of 

 first internodes. 



A difficulty encountered early in this work was that the first internodes 

 curved so much in the auxin solutions that they were difficult to measure. 

 Rotating the sections around a horizontal axis solved this problem, and the 

 sections coming out of the physiological 'merry-go-round' [Figure 8) grew 

 straight. The coleoptiles, on the other hand, were gently shaken on a 



"j" The details of this work can be found in a paper by Nitsch and Nitsch, to appear in 

 Plant Physiol. 31 (1956). 



% Kindly supplied by the Canadian Department of Agriculture, Central Experimental 

 Farm, Ottawa, Canada. 



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