Document Type

Dissertation - Open Access

Award Date

1964

Degree Name

Doctor of Philosophy (PhD)

Department

Agronomy

Abstract

In order to obtain plant material for in vitro bud formation studies, many preliminary experiments involving germination and seedling growth were conducted. Anatomical studies were conducted to establish the identity of underground parts. Cyclic temperature changes from 20 0C and 30 0C (12 hours each) provided 97, 80, and 21% germination for mottled, grey, and purple seeds in 12 days. Mottled seeds require only 2 cycles of alternating temperature to approach or equal the germination percent obtained with 10 additional temperature alternations. Two cyclic temperature changes provided that one-fourth of the maximum germination percent of grey and purple seeds obtained with 10 additional cycles. Hot water extracts of seeds inhibit seedling growth. Inhibition was less from extracts of more mature seeds (mottled) than from less mature seeds (grey and purple). Maximum growth of isolated root tips was obtained under alternating temperature conditions, when 20 mg per liter adenine sulfate had been added to the media. The greatest portion of the increase was due to the cyclic temperature changes. Kinetin was a potent inhibitor of seedling and isolated root tip growth, in culture, at concentrations as low as 10-4 mg per liter. Root segments from a plant grown on sucrose-based media were induced to maximum lateral root initiation by 1 mg per liter IAA. This same concentration of IAA allowed no buds to form. Maximum stimulation of bud formation was observed at 10-1 mg per liter kinetin. On root segments from a plant grown on sucrose-based media supplemented with adenine sulfate, IAA only induced callus. Bud formation was negligible or non-existent in both kinetin-treated and untreated segments. Maximum stimulation of bud formation on hypocotyl segments occurred at 10-2 mg per liter kinetin, and this effect was removed by 10-4 mg per liter IAA. The callus formation observed on the basipetal ends of untreated segments or segments treated with 10-4 mg per liter IAA was diminished as the concentration of included kinetin increased. The main axis of a mature plant of leafy spurge was composed of aboveground stem(s), a hypocotyl region, varying from a few millimeters to a few centimeters, a transition zone, and the primary root. This vertical primary root produced lateral roots, feeder roots, and adventitious buds. The lateral roots, and roots of other orders, produced additional lateral roots, feeder roots, and adventitious buds. The adventitious buds extended, forming vertical, underground, and aboveground shoots. In established patches of leafy spurge, about 90% of the aboveground shoots arose from adventitious buds on lateral roots. Crowns of buds, at and just below the soil surface, were formed both from vertical stems and from the collect or hypocotyl region of the main axis. The transition zone was found in the collect (lower hypocotylary swelling). The transition from exarch, radial stele of the root to endarch, collateral stele of the upper collet was complete in approximately 2500 microns. All root primordia and endogenous origin from pericycle or pericyclic tissues. Buds arose endogenously in roots but exogenously in the region of the hypocotyl with endarch protoxylem. In many cases, primordia were identified as roots or shoots prior to their emergence from the main axes.

Library of Congress Subject Headings

Germination
Leafy spurge

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

112

Publisher

South Dakota State University

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