Effect of Radiation and Growth Regulators on Leaf Abscission in Seedling Cotton and Bean.

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Abstract
With light-grown seedlings, chemical treatments had a more pronounced effect upon petiole abscission than did darkness, low-intensity room light, red, far-red or fluorescent light. The promoting effect of ultraviolet light upon abscission is believed to be due to injury and to IAA inactivation. Both light quality (wave length) and irradiance were shown to have a significant effect upon abscission. The light-chemical interaction also was significant. High-light intensity significantly reduced abscission of debladed cotton petioles, probably due to rapid dehydration and enzyme inactivation. With dark-grown bean seedlings removal of the apical meristem had no effect upon abscission. The slight abscission-promoting effect of far-red radiation was small compared to the stimulating effect of chemicals. Reversibility of a red-far-red reaction in abscission was not conclusively proven, and it appears that the red-far-red effect is only a part of the total abscission response system. These experiments do not support the belief that abscission is solely an auxin mediated response. Red radiation had a definite stimulating effect upon axillary bud growth in cotton whereas darkness, room light, far-red and ultraviolet prevented or reduced regrowth. The promoting effect of red light upon axillary bud growth of cotton indicated an auxin-light mediated response.