W. C. HALL 

 C. S. MILLER 

 F. A. HERRERO 



Texas A. and M. College 



Studies With C -labeled Ethylene 



Ethylene is a potent physiologically-active gas affecting plants in 

 many diverse ways. Certain species and responses are affected by con- 

 centrations as low as one part per billion in the atmosphere (8). The 

 earlier work on the effects of ethylene upon plants and its specific roles 

 in plant metabolism has been reviewed by Crocker (8). The more 

 recent research, particularly that centering around the possible role of 

 ethylene in abscission and the physiology of ripening fruits has been 

 reviewed by others (1, 5, 13, 20). Several of the responses (epinasty of 

 leaves, proliferation of tissues, stimulation of rooting, coloring and 

 ripening of fruits, and acceleration of flowering in pineapple and 

 other species) and the levels of ethylene necessary to induce these are 

 similar to those caused by the auxins. The effect on other responses 

 (abscission of organs, apical dominance and inhibition of lateral buds, 

 and breaking of dormancy) appears to be the opposite of those pro- 

 duced by the auxins. 



Quantitative proof has been obtained for the biological produc- 

 tion of ethylene by aerobically respiring fruits (5) and from excised 

 and intact leaves (14, 19), and indirect evidence exists that other tissues 

 produce the gas (8). 



Although many data have been accumulated to suggest that ethyl- 

 ene plays an important role in plant metabolism, the exact mecha- 

 nism of its mode of action or production is still unknown. Because of 

 its natural production by plants, often in sufficient concentrations to 

 affect physiological processes and to modify development, Crocker (8) 

 considered ethylene to be a phytohormone. Other workers, however, 

 have questioned the validity of this classification. Biale et al. (5) and 

 Addicott and Lynch (1) doubt whether ethylene has regulatory func- 



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