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Plant Physiology 59:636-640 (1977)
© 1977 American Society of Plant Biologists

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Articles

Effects of Increased Gravity Force on Nutations of Sunflower Hypocotyls 1

Allan H. Brown2 and David K. Chapman

a Plant Centrifuge Laboratory, University City Science Center and Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19174

A centrifuge was used to provide sustained acceleration in order to study the hypocotyl nutation of 6-day-old Helianthus annuus L. over a range of g-forces, up to 20 times normal g. At the upper end of this g-range, nutation was impeded and at times was erratic evidently because the weight of the cotyledons exceeded the supportive abilities of the hypocotyls.

Over the range 1 to 9 g, the period of nutation was independent of the resultant force vector. Over the same g-range, the amplitude of nutation was nearly independent of the chronic g-force.

If nutation in sunflower seedlings is an oscillation caused by a succession of geotropic responses which continue to overshoot the equilibrium position (plumb line), we might expect its amplitude to be more sensitive to changes in magnitude of the sustained g-force. In order to preserve the geotropic model of nutation-viz. that it is a sustained oscillation driven by geotropic reactions, it is necessary to assume that geotropic response must increase with increasing g most rapidly in the region of the g-parameter below the terrestrial value of 1 g.

2 Correspondence concerning this paper should be addressed to Allan H. Brown, Biology Department, G5, University of Pennsylvania, Philadelphia, Pa. 19174.

1 This work was supported by NASA Grants NGR 39-010-104 and NGR 39-010-149 to the University of Pennsylvania and by Grant NGR 39-030-010 to the University City Science Center. It also was supported by NASA Contracts NAS 2-2432 and NAS 2-7730 to the University of Pennsylvania and NASW-2208 to the University City Science Center.






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ASPB Publications PLANT PHYSIOLOGY® THE PLANT CELL
Copyright © 1977 by the American Society of Plant Biologists