Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)



First Advisor

C. Dean Dybing


The flowering pattern of flax (Linum usitatissimum, L.) is cyclic in nature with periods of blossoming separated by periods of rest. To study the regulation of flowering cycles, four experiments were conducted. The first two dealt with nutritional aspects of cyclic flowering by imposing environmental stresses which conceivably might regulate flowering pattern nutritionally. The third and fourth experiments dealt with regulation from hormonal systems and included in vitro regulation of bud growth by growth regulators as well as characterization of endogenous hormonal systems by fluorimetry and bioassays. In the first experiment, the effects of light intensity, temperature, nitrogen and defoliation treatments were studied. As light intensity increased from 14,300 to 25,500 lux, boll production, seed yield, and seed weight were all increased. Further increase to 31,900 lux, however, provided no additional yield increment. Low temperature favored the growth of plant while high temperature treatment reduced boll and seed production. Nitrogen did not appear limiting since no significant difference was obtained in any characteristic measured at 50, 100, and 300 ppm levels of N. Defoliation reduced the number of bolls and seeds produced during the first and second flowering cycles but did not affect seed weight. CO2 enrichment studies showed that effects on plants were greater if plants were exposed to treatments at an early age. CO2 treatments (1270 ppm) produced marked effects regardless of duration of CO2 exposure as long as plants were no more than 37 days of age at the time exposure commenced. Maximum effects of CO2 treatment were observed at high light intensity. An increase in CO2 from the normal level (325 ppm) to 1270 ppm under a light intensity of 29,500 lux significantly increased number and weight of mature bolls, total number of seeds, and seeds per boll but at the same time decreased the number of immature bolls remaining at harvest. Isolation of 3 different types of buds which normally do not flower in intact plants during the resting period between flowering cycles was conducted to determine whether or not these nonflowering buds could be brought to flower by chemical treatments. Terminal buds were the first ones to produce flowers even when no growth substance was added to the basal medium. Maximum flowering response was observed in buds treated with 3-indoleacetic acid (IAA), especially when treated during the early and postbloom stages of plant development. All buds that were brought to flower showed, at first, a certain degree of elongation before flowers appeared. While buds could still tolerate a 10 ppm concentration of IAA in the growing medium, naphthaleneacetic acid (NAA), gibberellic acid (GA), and kinetin appeared toxic even at a 5 ppm level. Terminal buds demonstrated greater readiness to flower than alternate buds from panicle branches on main stem buds. The NAA-treated buds exhibited callus formation from 5 ppm and above. GA treatment stimulated shoot elongation at 1 ppm but reduced elongation at greater concentrations. None of the GA-treated buds developed root systems. Kinetin stimulated vegetative growth of senescing buds to a greater degree than the other regulators. Finally, quantitative analyses of plant extracts to determine endogenous growth substances were also conducted. Fluorimetric procedures and the Avena coleoptile test were used to determine the amount of endogenous IAA, while for GA determination the lettuce hypocotyl bioassay was used. Plants in early bloom stage had a high endogoncus IAA content. IAA level declined during the first flowering stage but increased to a new peak level during the resting period between flowering cycles. GA levels were high during the early bloom and postbloom stages of growth.

Library of Congress Subject Headings

Plant growth promoting substances



Number of Pages



South Dakota State University