364 K. V. Thimann and N. Takahashi 



the growth promotion caused by lAA was also very small and no 

 larger than that caused by EDTA. But with lupine (Lttpinus) hypo- 

 cotyls, Weinstein et nl. (25) found grow^th increments of 30 to 50 per 

 cent with lAA, and EDTA was just about as effective. Under appropri- 

 ate conditions elongation of 100 per cent is easily produced in oat 

 (Avena) coleoptile sections, while it will be shown below that EDTA 

 causes in them only a relatively small elongation. It is true that 

 Cohen et al. (5) have demonstrated some chelation of both lAA and 

 NAA with Cu+2 jons, but this took place in 50 per cent ethanol and 

 in 0.02 M solution, and they found no chelation with Ca^^ q^ Mg*^. 

 AVhen Recaldin and Heath (17) examined the reaction with ferric 

 ions, what they observed was a slow development of color accom- 

 panied by Oo uptake and lAA breakdown, in other w^ords, a chem- 

 ical reaction akin to the Salkowski reaction. Nakazawa (13) could 

 find no evidence that lAA chelates with iron in pea seedlings. Thus, 

 evidence that appreciable real chelation takes place under physiological 

 conditions is lacking, and even if it did take place, there are as yet 

 no indications of a causal relationship to growth. 



However, in favor of some relationship between growth and chela- 

 tion is the increasing evidence mentioned above that metallic ions 

 strongly influence growth. Recently it has been suggested, indeed, 

 that calcium specifically controls growth through its linkage to pectic 

 acid groups in the cell wall (1), and it has been shown that calcium 

 raises the osmotic content of Avena coleoptile cells w^hile at the same 

 time lowering tlie suction pressure — an effect interpreted as due 

 to "tightening" of the cell walls (6). Experiments relating auxin 

 action to pectin meihylesterase (3, 7, 8, 16) are interconnected with 

 this concept, though the effect does not appear to be a simple one. 

 In any event, chelating agents might indeed promote growth by re- 

 moving some of the hypothetical wall-bound calcium. The fact that 

 the ferric-EDTA complex does not promote growth, under conditions 

 where free EDTA does, supports this idea (25). 



The whole phenomenon seemed to warrant restudy of the action 

 both of chelating agents and of some metal ions on growth. 



MATERIALS AND METHODS 



The EDTA used was a three times recrystallized sample of the 

 sodium salt sold as Sequestrene AAA, and kindly supplied by the 

 Alrose Company of Providence, R.I. The stock solution was atljusted 

 to pH 5.6. The 8-hydroxyquinolinc (8-HOQ), and other chelating 

 agents were CP chemicals. Avena coleoptile sections 10 mm. long were 

 cut in the usual manner about 3 mm. below the tip from seedlings 

 of 'Victory' oats 74 hrs. old, grown in water at 25° C. after receiving 



