The interaction of auxin and ethylene in the maintenance of leaf blade form in Phaseolus vulgaris L. var. Pinto

Auxin treatment results in hyponastic curvature of the primary leaves of Phaseolus vulgaris L. var pinto. Ethylene production by hyponastic leaves is detected within 1 hr after treatment with IAA in concentrations at or above 1 /,M. The amount of ethylene detected is proportional to the concentration of auxin applied. Untreated control leaves and leaves treated with 2,3,5tri-iodobenzoic acid or gibberellic acid did not produce ethylene detectable by our equipment. The hyponastic curvature induced by auxin treatment can be inhibited by exogenous application of ethylene or ethylene-generating compounds, and these treatments produce epinasty in auxintreated leaves. Treatment with inhibitors of ethylene synthesis or action, such as aminoethoxyvinylglycine, carbon dioxide, or heat treatment, prolong hyponasty. The planar form, therefore, appears to be affected by both hyponastic auxin effect and an epinastic ethylene effect. THE BLADE of dicotyledonous leaves is typically flat or planar. Loss of the planar form occurs when some groups of cells divide or expand at a different rate than that of other cells. These differential growth effects produce alterations of form described variously as rolling, curling, cupping, or puckering. If the direction of growth is determined by the organ itself rather than by an external stimulus, the differential growth is defined as being nastic. Upward curvatures, resulting from differential enhancement of growth of the lower side of the blade, are called hyponastic curvatures, and downward curvatures, resulting from differentially enhanced growth of the upper side of the blade, are called epinastic curvatures. Because some authors use the general term "leaf epinasty" when they actually mean epinasty of the petiole, it should be emphasized that in this paper the part of the leaf studied is the blade. Epinastic curvatures of the petiole in response to auxin treatment of the blade, and nyctinastic curvatures of the pulvinus in response to circadian rhythms or dark treatment, are also produced, but should not be confused with the curvatures of the blade discussed in 1 Received for publication 24 September 1979; revision accepted 16 February 1981. This work was supported by a Loyola University Faculty Research grant. The technical advice of Dr. David Crumrine of the Department of Chemistry, Loyola University of Chicago, and the technical assistance of Mr. Michael Mora, are gratefully acknowledged. AVG was a gift of Dr. Arthur Stempel, Research Division, Hoffman-LaRoche, Inc. CESA was obtained from General Research Chemicals; Ethrel from AmChem Products, and all other growth regulators from Nutritional Biochemical Company. this paper. The leaf blade shows a hyponastic response to auxin whether the leaf is in the day or night position and whether the petiole is epinastic or not. Leaf blades of Phaseolus vulgaris L. var pinto treated on the upper, lower, or both surfaces with indoleacetic acid or related compounds within the concentration range of 1 M to 1 mm show hyponastic curvatures that reach a maximum 2 to 4 hr after treatment. The amount of curvature produced shows a linear relationship to the log of the auxin concentration applied (Lippincott and Lippincott, 1971). Within the next 24 hr, the blade returns to the normal planar form. The hyponastic curvature produced can be shown to be associated with a measurable differential auxin-induced growth in the lower portion of the leaf (Hayes and Lippincott, 1976). Leaf blade curvature occurs without exogenous auxin treatment in intact organs under certain environmental conditions. Spontaneous curvatures can be observed in heattreated leaf blades (Hayes and Lippincott, 1981), and in blades maintained in the dark (Lippincott and Lippincott, 1971), indicating that these curvatures are natural responses to environmental change. Auxin treatment amplifies these responses, however, allowing study of the role of growth regulators in this phenomenon. The mechanism that regulates restoration of the planar form has not yet been elucidated. Studies reported here suggest that ethylene may be a component of the system. The normal persistence and rapid recovery of the flat planar form requires a careful system of coordination of the growth of cell layers as different