752 Hall, Miller, and Herrero 



tion with particular reference to fruit ripening and abscission. Con- 

 clusive proof, however, that ethylene lacks biological significance in 

 plants remains to be established. 



A limited number of experiments have been conducted with radio- 

 active ethylene (7, 15). Buhler et al. (7) noted that the uptake of 

 carbon-labeled ethylene from the atmosphere surrounding fruits was 

 small and they believed that ethylene is probably a terminal product 

 in fruit and cannot be further metabolized. On the contrary, field 

 observations (13) and the rapid uptake of ethylene-Ci^ (15) suggest 

 absorption and metabolism in young, rapidly growing plants. 



The results given in this paper report some of the findings ob- 

 tained to date in a long-term project designed to elucidate the bio- 

 logical significance of ethylene. It is believed that the radiochemical 

 approach coupled with other techniques should clarify the importance 

 of ethylene in plant metabolism and the labeling of suspected sub- 

 strates should aid in establishing its biological mode of production. 



ABSORPTION AND TRANSLOCATION EXPERIMENTS 



A number of experiments were conducted on the absorption and 

 translocation of ethylene-C^^, some in conjunction with studies to 

 obtain tissue for metabolite investigations. To date Coleus and cot- 

 ton have been the test plants. The plants were grown in the green- 

 house in Vermiculite or quartz sand supplied daily with nutrient 

 solution. 



In an initial experiment ten healthy cotton plants, 'Deltapine 15' 

 at the six true leaf stage and five plants of the green-leaf variety of 

 Coleus blumei (five leaf pair stage), were treated inside a Plexiglass 

 chamber with 1,000 p. p.m. of radioactive ethylene of 1 mc/mA/ spe- 

 cific activity. In addition, ethylene-C^^ recovered from a previous ex- 

 periment was liberated from a mercuric-perchlorate complex inside 

 the chamber according to the method of Young et al. (21). It is esti- 

 mated that a total of 0.8 millicurie of radioactive ethylene was avail- 

 able in the chamber for the plants to absorb. The experiment Avas 

 conducted in subdued light in a fume hood for 15 hrs. The unused 

 ethylene was evacuated from the chamber into mercuric-perchlorate 

 solution. Simple monitoring of the treated plants with a Geiger tube 

 indicated appreciable activity in the leaves. Intact and detached leaves 

 were lyophilized, mounted, and pressed against No-screen X-ray film 

 for 30 days. The radioautograms showed that ethylene was absorbed 

 readily and uniformly over the blades, petioles, and stems. Repre- 

 sentative detached leaves are sho\\ n in Figure 1. It can be noted that 

 the stipules absorb the gas rather heavily. The dilference between the 

 young and old cotton blades in the density of the main veins is prob- 

 ably due to greater self-absorption by the thicker veins of the older 

 lea\cs. 



