Observations on the Mechanism of Auxin Formation in Plant Tissues.

Auxin physiologists often have attempted to establish correlations between the amount of auxin in a plant tissue and the manifestation of auxin activity such as growth, rooting, parthenocarpy, bud inhibition, etc. With Avena coleoptiles and tomato stem tips, to use specific examples, it is possible to demonstrate a correlation between growth and the amount of auxin which can be diffused from the tissue into agar. Many tissues produce too little diffusible auxin or are too cumbersome to lend themselves to this type of auxin analysis and resort must be made to more convenient methods of auxin extraction. Ether extraction has been used extensively in correlation studies, particularly since ether was considered to remove the free auxin. It soon became evident, however, that auxin was liberated during the extraction and that many months of successive ether extractions were required before auxin production disappeared. While there often appeared to be a correlation between the amount of auxin obtained in the first ether extraction and the growth process under consideration, the correlation usually disappeared as the extraction process was prolonged. THIMANN and SKOOG (8) made an extensive study of the continued production of auxin during the extraction of fresh, green tissues with ether and came to the following conclusions: 1) Many successive ether extractions spaced over several months were required to extract all of the potentially ether soluble auxin contained in Lemna tissue. 2) Water was necessary for auxin production during ether extraction since oven-dried tissue failed to give off auxin when extracted with anhydrous ether. 3) Drying not only prevented auxin production but appeared to fix added auxin in some form not extractable with ether. 4) Addition of proteolytic enzymes to the tissue prior to ether extraction greatly increased the total amount of auxin which could be extracted but did not shorten the time appreciably nor the number of extractions required for total auxin extraction. They concluded that the continued production of auxin in ether was caused by the slow, enzymatic liberation of aux'in from an inactive form, presumably a protein. GUSTAFSON (4) has developed a method for the extraction of "free" auxin, or auxin which is present in the tissue as such but does not arise by liberation during the extraction process. The tissue is frozen, ground and then boiled with water before extraction with ether. Boiling prevents the continued production of auxin encountered in previous methods. While