Date of Award:

5-1983

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Frank B. Salisbury

Committee

Frank B. Salisbury

Abstract

Plants rotated about a horizontal axis show certain growth responses. This research was designed to clarify which of the responses of clinostating are caused by gravity compensation and which are caused by mechanical stresses. Plants used were Xanthium strumarium L. (cocklebur) Chicago strain and Lycopersicon esculentum Mill. (tomato) cv. Rutgers. Six automated treatments that ran for five days were used to separate out the effects. Treatments were: 1) controls, 2) horizontal clinostat, 3) intermittent clinostat, 4) inversion (every 10 min), 5) invert and return, and 6) vertical rotation. Plant height and diameter changes were measured at ink dots with a vertical translator microscope (50X) modified with dial indicators. This allowed measurement without stressing the plant. Epinasty was measured using the radius of the circle circumscribing the triangle formed by the stem-petiole junction, petiole-blade junction, and the leaf tip. Clinostating and inversion (both gravity compensators) have different effects on plant growth (varies from species to species). Clinostating stimulated the elongation of partially mature stem tissues, but may inhibit the youngest portions. Ethylene probably does not mediate the stem response as there is no increase in stem diameter. Development of typical leaf epinasty in both clinostating and inversion may be affected in long-term experiments by the "gestalt" of the leaves.

The effects of rotation on the induction of flowering as well as prolonged rotation on fruit development and subsequent germination and growth for cockleburs was also studied. Mechanical stress slows transport of the flowering stimulus, though the effect is slight even with vigorous shaking (floral stage of treated plants is about 1 1/2 stages lower than controls after nine days). Induction of flowering is attenuated by gravity compensation. Treatment during, or just before the inductive dark period had the greatest effect. Prolonged rotation (61 days) with over-induction (33 16-h nights) reduces the height growth, the size of the leaf blades, number of fruits, and average fruit weight. Germination of normally dormant cocklebur seeds appears to be stimulated by either horizontal or vertical rotation. Plants grown from seed that developed on clinostated plants can be induced to flower normally.

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