Document Type


Date of Award



Plants, Effect of light on Plants, Flowering of, Plant photoperiodism, Flowering time, Duckweeds

Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

Herbert B. Posner

Second Advisor

James D. Grierson

Third Advisor

Alan H. Haber


Lemna perpusilla 6746, a short day plant on Hutner's medium, is induced to flower by a single long night. Resulting flower primordia develop normally in short days but regress in unfavorable photoperiods such as long days or continuous white light. Flower development following a single long night is approximately proportional to the number of long nights given in the post-inductive treatment. The critical night length for flower development is approximately one hour shorter than that for flower initiation. Unfavorable photoperiods arrest the growth and differentiation of flower primordia. These primordia eventually break down and the adjacent axillary fronds enlarge.

Flower primordia develop in continuous blue light but regress in continuous red light. Development in combined red-blue light decreases as the proportion of red is increased. Regression also occurs with post-inductive treatment of red-interrupted long nights. This regression is partially prevented if the red interruption is followed by a far-red interruption, suggesting similar requirements in phytochrome (Pfr) levels for the two phases of flowering.

Partial flower development occurring in continuous white or red light is further inhibited by an increase in light intensity. Photosynthetic inhibitors, including 3,(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), partially reverse the inhibition of continuous white light. DCMU also partially reverses the inhibition of red-interrupted long nights, suggesting that photosynthetic pigments, as well as phytochrome, are photoreceptors for the photoperiodic inhibition of flower development.

Photoperiodic inhibition of flower development in continuous white light is partially reversed by eliminating ammonium ion or adding inorganic phosphate to the medium. Inhibition is also partially reversed by cyclic AMP, 5′ AMP, and 5′ ADP on medium supplemented with sucrose. On medium not supplemented with sucrose, inhibition is partially reversed by cyclic AMP, 5′ ADP, and 5′ ATP. These supplements may affect the control of intermediary reactions of flowering. Photoperiodic inhibition of flower development in continuous white light is partially reversed by L-alanine, and amino acid precursors, potassium citrate and glucose-6-phosphate, suggesting that photoperiodic inhibition involves some intermediate reactions including an amino acid utilizing pathway.

Flower development occurs under several light treatments not allowing flower initiation. The medium supplements and photosynthetic inhibitors that partially reversed photoperiodic inhibition of flower development, do not reverse photoperiodic inhibition of flower initiation. These results suggest that some reactions affected by photoperiod in the development phase of flowering are different from those in the initiation phase.