A Rapid Extraction Method for Free Auxin and Its Application in Geotropic Reactions of Bean Seedlings and Sugar-Cane Nodes

Abstract

1. When tissue of sugar-cane nodes is submerged for a few minutes in boiling water, a substance is released which suppresses the action of indoleacetic acid in the Avena test (fig. 2). The substance is soluble in water and diethyl ether but not in petroleum ether. It is therefore extracted together with auxin, and for this reason heating of such plant material-and perhaps of plant material in general-prior to ether extraction is an undesirable step in auxin extraction technique. 2. In the course of ether extraction, there is during the first half hour a gush of auxin (fig. 3), but soon the rate slows down to a mere trickle, which continues for many months (20). 3. When the auxin of the upper and lower halves of horizontal hypocotyls of bean seedlings is extracted, using only the auxin yielded rapidly during the early part of the extraction, 33% is obtained from the upper side and 67% from the lower (table 2). This is precisely the average auxin distribution found for free auxin as determined by the diffusion method (21). 4. When the auxin of the upper and lower halves of horizontal hypocotyls of bean seedlings is extracted, using only the auxin yielded slowly during the later part of the extraction, no such unequal yields are obtained (table 2). Apparently the auxin yielded during the early part of the extraction is the free auxin of the plant tissues. 5. A rapid-extraction technique for the extraction of free auxin consists in freezing the plant tissue in dry ice (crushing is unnecessary); extracting it in Erlenmeyer flasks in ether for two or three periods of 1/2 hour each at room temperature; taking the extract up in a known amount of agar and using it on the Avena test (plants grown in sand instead of the usual glass holders). 6. When the free auxin content of horizontal stems of sugar cane is compared with stems in the vertical position, after a few days in the horizontal position the auxin concentration in the meristematic region of the node (the growth ring) increases 100% and more (fig. 1; tables 3, 4). This increase is less marked in the root band and is absent in the middle portion of the internodes. 7. The unilateral distribution of free auxin so striking in horizontal bean seedlings is totally absent in sugar cane. In further contrast to bean seedlings, no growth response to applied auxin-other than promotion of root growth and bud inhibition-was found in sugar cane. 8. The auxin extracted from etiolated bean hypocotyls and from sugar cane appears to be of the type of indoleacetic acid rather than auxin-a or auxin-b, in respect to stability to hot alkali and lability to hot acid. Both the auxin yielded during the early part of the extraction and that yielded during the prolonged later part belong to the indoleaceticacid type.