CHEMICAL CONFIGURATION AND ACTION OF 



DIFFERENT GROWTH SUBSTANCES AND 



GROWTH INHIBITORS: 



NEW EXPERIMENTS WITH THE PASTE METHOD 



H. LiNSER 

 Biologisches Laboratorium der Osterreichische Stickstoffwerke A.G., Linz, Austria 



In 1953 at Lund, Sweden, I reported on my paste method, and on the 

 difference between the types of concentration-action curves obtained with 

 two types of chemicals, which may be called growth substances and growth 

 inhibitors. Although we commonly use these two words, we are not certain 

 if all the compounds we usually call growth substances would give the 

 typical curve for growth substances in the paste test. There may be some 

 compounds, classed as growth substances, which give a concentration-action 

 curve of the growth-inhibitor type. We could show that every concentration- 

 action curve of a cell-elongating growth substance is composed of two 

 components, one promoting, and one inhibiting. Our paste method, which 

 uses an intact coleoptile, is able to reveal both growth-promoting and growth- 

 inhibiting activity in the same experiment. The two components, the pro- 

 moting one and the inhibiting one, can be of different magnitudes. In 

 some special cases, the promoting activity of a growth substance can be 

 reduced to zero. Therefore we may say that a growth inhibitor is a growth 

 substance with a promoting component of zero. In the same way we can 

 define a growth substance as a growth inhibitor with a growth-promoting 

 component (larger than zero). 



Some experiments with mixtures of a promoting and an inhibiting 

 substance were described at Lund, and I reported in Paris (Linser, 1954a) 

 on further similar experiments. Dr. Kaindl's paper at this Symposium is 

 concerned with the results of these experiments and a mathematical examina- 

 tion of them. Experiments have recently been carried out using mixtures of 

 different growth substances with one another and different inhibitors with 

 one another. The results obtained will be published at a later date. The 

 earlier experiments provided evidence that there is competition between 

 growth substances and growth inhibitors in filling a space, which we call the 

 'gap', which exists in the living system. The probability of filling this gap is 

 determined by the affinity between the molecule of the active substance and 

 the gap (Linser, 1954b,c). We know that this affinity depends mainly on 

 the chemical nature of the compound, or on the physical properties of the 

 atoms of which the molecule is composed and on its electronic configuration. 

 It also depends, though to a lesser extent, on the size and form of the molecule, 

 i.e. its space-filling capacity. 



In view of the above considerations, we compared our results with the 



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