370 



K. V. Thiynann and N. Takahashi 



The failure of the first internode to respond suggested that the 

 chelating agents are not acting as weak auxins but in some other 

 way. This was tested by studying their action in presence of a strong 

 auxin, namely lAA. It was then found that in presence of lAA, 

 EDTA at 2.5 X lO-^M could increase growth by up to 50 per cent 

 (Figure 3). The action could be exerted in all growth solutions and 

 in presence or absence of sucrose, though without sucrose the in- 

 crement is only 5 to 10 per cent. At optimum sucrose, the increment 

 caused by EDTA is largest when the lAA concentration is from 0.1 

 to 1 p. p.m., but at low sucrose it is best at from 1 to 10 p. p.m. It is 

 clear, therefore, that the action is not simply that of a weak auxin. 

 Comparable results were obtained with 8-HOQ, though the increment 

 was smaller; for example, in 3 experiments with lAA 0.1 p. p.m. 8-HOQ 

 at the optimum level (10-^M) gave an average increment of 13.0 per 

 cent. 



With this knowledge a return was made to the first internode 

 sections and it was found that in presence of lAA these sections did 

 respond to EDTA. In Table 2 representative data are compared 

 ^vith those from coleoptile sections in the same experiment. Though 

 more sensitive to low lAA concentrations than the coleoptile, the 

 first internode gives a response to EDTA only one-quarter as great. 



For further comparison, internode sections from etiolated 'Alaska' 

 peas were used. Again the effect of EDTA was best in presence of 

 auxin, but even at the optimal lAA level, namely 1 mg/1, the incre- 

 ment due to EDTA was only an additional 11 per cent. Addition of 

 sucrose could increase the EDTA effect somewhat, but the response 

 of these sections is still considerably smaller than that of coleoptiles. 

 The effectiveness of EDTA, therefore, is a function of the tissue 

 used, as well as of the amount of auxin present. 



Although the action of EDTA is thus exerted mainly in combin- 

 ation with lAA, this is not a general interaction with auxins since. 



Table 2. Effects of EDTA on sections from Avena coleoptile and first internode 

 under the same conditions. All solutions contain sucrose 2 per cent and KCl 0.005A/; 

 24 hours. 



