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Biomedical subjects

D K Chapman

Publications and source records attributed to D K Chapman.

25 records · Page 2Linked to original sources
PubMed1980

Gravity Functions of Circumnutation by Hypocotyls of Helianthus annuus in Simulated Hypogravity.

For more than a decade research on the botanical mechanism responsible for circumnutation has centered on whether or not these nearly ubiquitous oscillations can be attributed to a hunting process whereby the plant organ continuously responds to the gravity force and, by overshooting each stimulus, initiates a sustained oscillation or, driven by a not yet defined autogenic mechanism, performs oscillatory activities that require no external reinforcement to maintain the observed rhythms of differential growth.We explore here the effects of altered gravity force on parameters of circumnutation. Following our earlier publication on circumnutation in hypergravity we report here an exploration of circumnutation in hypogravity.Parameters of circumnutation are recorded as functions of the axially imposed gravity force. The same method was used (two-axes clinostat rotation) to produce sustained gravity forces referred to as hypergravity (1 < g), hypogravity (0 [unk] g < 1), and negative gravity (-1 < g < 0). In these three regions of the g-parameter nutational frequency and nutational amplitude were influenced in different ways.The results of our tests describe the gravity dependence of circumnutation over the full range of real or simulated gravity levels that are available in an earth laboratory. Our results demonstrated that nutational parameters are indeed gravity-dependent but are not inconsistent with the postulate that circumnutation can proceed in the absence of a significant gravity force.

Journal Article↗
PubMed1979

Importance of temperature control for HEFLEX, a biological experiment for Spacelab 1.

HEFLEX is an experiment in plant gravitational physiology now being developed for the Spacelab 1 Mission. Its object is to measure kinetic properties of plant nutation in a very low g environment. HEFLEX is designed to be scientifically compatible with restrictions imposed by engineering considerations. Among those restrictions one of the more important but one not necessarily well appreciated by mission engineers is the specification for spacelab air temperature. Development of the HEFLEX space experiment has been seriously complicated and the flight hardware significantly increased in cost as a result of the burden of insuring adequate temperature control being shifted from the spacelab module design to the biological experiment itself. The question is raised: Is this the most economical method of implementing biological research in space?

Adaptation, Physiological↗
PubMed1977

Effects of increased gravity force on nutations of sunflower hypocotyls.

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.

Journal Article↗
PubMed1977

Nutations of sunflower seedlings on tilted clinostats.

The kinetics of hypocotyl nutations in Helianthus annuus L. were measured on plants which were rotated on clinostats with axes of rotation inclined at various angles, alpha, away from the vertical. The g-force component acting in the direction of the plant axis was taken as g cos alpha. The average period and average amplitude of nutation were constant for all such axially directed g-forces between 1.0 and 0.2 g (vertical to about 80 degrees inclination). On the horizontal clinostat (90 degrees inclination) nutation was neither initiated nor sustained. The g-force just sufficient fully to activate nutational oscillations should be sought in the range of the g-force parameter, 0 < g < 0.2.

Gravitation↗
PubMed1976

Morphology of Arabidopsis Grown under Chronic Centrifugation and on the Clinostat.

Morphological measurements were made on populations of Arabidopsis thaliana grown from seed for 21 days under essentially constant environmental conditions except for the influence of gravitational or centrifugal accelerations. Growth conditions were what had been proposed for experiments in an artificial satellite. Observations are reported for plants grown at normal 1-g upright or on horizontal clinostats and for plants grown on a centrifuge. Increased g-force, up to 15 times normal, was found to have significant but small effects on some morphological end points. The plants' sensitivity to the magnitude of the g-force was much less than to its vector direction.Data from centrifuge experiments (which determined the g-functions for particular characters) were extrapolated to zero-g to predict a set of morphological characteristics of a plant developing in the satellite environment. As an alternative means of predicting properties of a zero-g plant, characteristics of plants grown on horizontal clinostats were measured. The results of these two predictive methods were not in agreement.Clinostat grown plants were morphologically distinct from upright stationary controls. When plants were grown while rotating in the upright position on vertical clinostats they were similar to stationary plants also grown upright, but there were small differences some of which were statistically significant.

Journal Article↗
PubMed1976

Limitation on the use of the horizontal clinostat as a gravity compensator.

If the horizontal clinostat effectively compensates for the influence of the gravity vector on the rotating plant, it should make the plant unresponsive to whatever chronic acceleration may be applied transverse to the axis of clinostat rotation. This was tested by centrifuging plants while they were growing on clinostats. For a number of morphological end-points of development the results depended on the magnitude of the applied g-force. Therefore, gravity compensation by the clinostat was incomplete. This conclusion is in agreement with results of satellite experiments which are reviewed.

Journal Article↗