. Auxins and plant growth. Auxin; Plant growth promoting substances. 112 Fundamentals of Auxin Action The first of these is the actual auxin content of the organ which may be abscissed, particularly with respect to the gradient of auxin levels between the organ and the stem to which it is attached. The impor- tance of the auxin gradient was established by Shoji et al (1951). They found that abscission of leaves occurred when auxin production be- came low and the gradient of auxin across the abscission layer became small. This gradient is a function of the rate of auxin production in the organ
. Auxins and plant growth. Auxin; Plant growth promoting substances. 112 Fundamentals of Auxin Action The first of these is the actual auxin content of the organ which may be abscissed, particularly with respect to the gradient of auxin levels between the organ and the stem to which it is attached. The impor- tance of the auxin gradient was established by Shoji et al (1951). They found that abscission of leaves occurred when auxin production be- came low and the gradient of auxin across the abscission layer became small. This gradient is a function of the rate of auxin production in the organ and the auxin level in the stem. Either of these can be altered by the addition of auxins or materials modifying auxin action. 100. 5 DAYS TIME AFTER TREATMENT Fig. 51. The dual effects of auxin on abscission of excised bean leaf petioles. The addition of auxin (105 of indoleacetic acid) to the distal end of the petiole prevents abscission, whereas addition to the proximal end forces more rapid abscis- sion (Addicott and Lynch, 1951). A general demonstration of the role of auxin production in the prevention of leaf abscission was made by Myers (1940). His measure- ments of auxin levels revealed that coleus leaves produced relatively small amounts of auxin in the winter season and much larger amounts in the spring. Applications of auxins to prevent abscission were much more effective in the winter during the period of relatively low auxin production. Many workers have reported that removal of leaf blades caused subsequent petiole abscission. The ability of auxins to substi- tute for the leaf blade in preventing that abscission has clearly dem-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Leopold, A. Carl (Aldo Carl), 1919-. Berkeley, University of California Press
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