studies With CJ'>-labeled Ethylene Ibl 



width were the exception. The number two leaves contained ap- 

 proximately three times more activity than the oldest leaves (No. 6). 



Coleus plants with four leaf pairs were treated with the ethylene 

 recovered from the previous experiment with cotton. The experi- 

 mental conditions were the same as used for cotton except 25 g. of 

 sodium hydroxide pellets were placed in the chamber to absorb res- 

 piratory carbon dioxide and moisture. The youngest (No. 1 leaf 

 pairs) and the oldest (No. 4 leaf pairs) fixed the most activity, while 

 the intermediate aged leaves (No. 2 and 3) fixed the least, indicating 

 a species difference from cotton. 



Influence of Plant Age on Ethylene Fixation 



Two cotton plants of three different age groups (early-fruiting the 

 oldest) were treated with 6.20 ml. of ethylene-Ci^ to give about 350 

 p.p.m. of ethylene in the treatment chamber. The plants were main- 

 tained in the dark for 17 hrs. After treatment the leaves and stems 

 of each plant were harvested separately and assayed for radioactivity. 



The results (Figure 2C) indicate that the older plants absorbed 

 more ethylene per unit dry weight and that the foliage contained 

 higher levels than the stems. 



METABOLISM OF EXOGENOUS ETHYLENE-C^^ 



"Fresh" Versus "Aged" Ethylene 



In the absorption and translocation experiments as well as in 

 other metabolite experiments it was noted that greater amounts of 

 Ci^ were incorporated when "aged" ethylene was used compared to 

 "fresh," pure ethylene, or the gas used immediately after releasing 

 it from a light-proof, sealed vial. "Aged" ethylene denotes ethylene 

 that had been recovered after experiments by mercuric-perchlorate 

 absorption and regenerated from the complex for use (21), or ethy- 

 lene that had been stored for a considerable period and then ex- 

 posed to light, high humidity and temperature. The regenerated 

 ethylene, which appears to be the most active, has been studied in 

 some detail. The difference in absorption and fixation is illustrated 

 by the following experiments. 



Cotton plants were exposed to 10 ml. of "fresh" ethylene contain- 

 ing 0.4 mc. of ethylene-Ci4 (1,000 p.p.m.) for 15 hrs. in July, 1958. The 

 leaves of the treated plants contained about 4 cpm/mg of C^^. Im- 

 mediately following the experiment the unused ethylene was evacu- 

 ated into mercuric-perchlorate and the complex stored in the dark at 

 0° C. for one month. The radio-ethylene was liberated from the com- 

 plex (21) into a chamber containing cotton plants of the same age 

 used in the July experiment. The plants were allowed to absorb the 



