776 Hall, Miller, and Herrero 



this might not be a reflection of the different ratio of surface area to 

 mass of the leaf at this particular stage. If the youngest leaf were not 

 spread out and the stomata exposed, the ethylene would not be able 

 to enter. This could possibly explain the difference that you have 

 noted in penetration of ethylene into leaves of different ages. 



Dr. Hall: The youngest leaf you refer to, our No. 1 leaf, was 

 partially expanded. In other words, it had emerged from the apical 

 bud. Based on our work I believe that entrance of ethylene does not 

 depend entirely on the stomata, but it may also penetrate the epi- 

 dermis directly. 



Dr. Forti: I would like to ask Dr. Thimann if he has any explana- 

 tion about the inhibition of oxygen uptake and ethylene production 

 by dinitrophenol at the level of 10-'^ molar. 



Dr. Thimann: The oxidation rate in many tissues is inhibited by 

 dinitrophenol at somewhere near that. Actually apple is a little more 

 sensitive than coleoptile or pea tissue or potato tubers by about a 

 power of 10. 



Dr. Shantz: Dr. Hall, as I understood your remarks with the "aged" 

 ethylene, this was taken up by the plant at many times the rate of 

 fresh ethylene. Have you also found by any method for the quantita- 

 tive estimation of growth effects of ethylene, that the "aged" ethylene 

 induced a correspondingly higher growth response than fresh ethylene? 

 Dr. Hall: The "aged" ethylene acts biologically similar to fresh 

 ethylene. One response that would indicate that it has essentially the 

 same effect as the fresh ethylene is that it induces rapid abscission of 

 leaves, the same as the fresh ethylene. The "aged" ethylene also pro- 

 duces epinasty, chlorosis, and coloring. I might comment briefly 

 about the possible relation of ethylene to smog. We have an air pol- 

 lution problem in Texas where ethylene is being liberated from an 

 industrial plant near the Gulf Coast causing rather serious damage to 

 cotton and other crops in the area. Apparently "aging" of ethylene 

 from this source also takes place in the atmosphere because the ex- 

 tent of the damage to plants depends upon certain atmospheric con- 

 ditions. 



I might add. Dr. Thimann, that we have already conducted ex- 

 periments with castor bean mitochondria. It was thought that our 

 finding that ethylene reacts with a phosphorylated compound and its 

 well known stimulating effect upon respiration might be more than 

 coincidentally related. In other words, it would be attractive to think 

 that ethylene might be uncoupling oxidation from phosphorylation. 

 However, we have not been able to demonstrate this with castor bean 

 mitochondria. In fact, when using radioactive ethylene, we have not 

 been able to demonstrate any measurable radioactivity in the mito- 



