[Plant-education] Re: Phytochrome lab exercises?

David R. Hershey dh321 at excite.com
Tue Jul 26 20:28:14 EST 2005

Here's some possibilities and ideas.

1. I've seen or conducted photoperiodism labs mainly in horticulture
classes. Bringing poinsettias into flower in the fall semester is a
nice lab because students get to take a blooming poinsettia home at
Christmas. It does take about ten weeks and require greenhouse space
with blackcloth to control the photoperiod. You can also do other
experiments, such as growth regulator effects, at the same time. At
least a short day and a long day treatment are needed. You can also
have a control of natural daylengths and other treatments such as an
hour of incandescent light in the middle of a long night.
Chrysanthemums are another commercially grown short day plant that can
be used. Japanese morning glory (Pharbitis nil 'Violet'), which
requires only one short day to induce flowering, is faster but not as
attractive or relevant to the real world. Some big propagators used to
provide free poinsettia and chrysanthemum cuttings to universities for
teaching and research use. I'm not sure if they still do.

For a multi-week experiment like this students may be required to
observe or measure their plant(s) once a week and write a report. If
space is limited, it can be more of a demonstration with fewer plants.

Another option might be to take a field trip to a commercial greenhouse
that uses photoperiod control to produce flower crops. Students might
also be able to see real world applications of some other plant
physiology concepts such as plant nutrition, irrigation/transpiration,
adventitious rooting of cuttings, seed germination, apical dominance
(e.g. pinching of chrysanthemums to promote branching and axillary
flower bud development), application of hormones and chemical growth
regulators, carbon dioxide enrichment, use of electric lights to
increase photosynthesis, etc.

Famous botanist/horticulturist Liberty Hyde Bailey (1903) wrote, "A few
days ago I saw a professor of botany in a commercial greenhouse, asking
the florist many questions about the growth and behavior of plants. I
asked him why. He replied, "Those men know more real plant physiology
than we do." Those men were horticulturists."

Bailey, L.H. 1903. What is horticulture? Proceedings American Society
for Horticultural Science 2: 53-60.

2. Adventitious plantlet formation on leaves of the houseplant, devil's
backbone or mother of thousands (Kalanchoe daigremontiana), is a long
day response and is faster than flowering. Students can also be
challenged to determine why plantlet formation is no longer
photoperiodic after leaves are removed from the plant. Students can
take some plantlets home to grow as houseplants. Some of the plants
could be recycled for other experiments. K. daigremontiana is a model
research plant for CAM photosynthesis. It is also long-short day plant
for flowering but the long day requirement can be satisfied with a
gibberellin spray.

Hershey, D.R. 2002. Using the Kalanchoe daigremontiana plant to show
the effects of photoperiodism on plantlet formation. Science Activities

3. Witham et al. (1971) has labs on "Photoperiodism in Cocklebur" and
"Photoreversible control of Avena coleoptile elongation". Kaufman et
al. (1975) has a similar cocklerbur lab on "Photoperiodic control of
flower initiation in Chenopodium rubrum" and one on "Light-mediated
increase in the rate of chlorophyll synthesis under saturating white
light in mustard seedling cotyledons."

Kaufman, P.B., Labavitch, J., Anderson-Prouty, A. and Ghosheh, N.S.
1975. Laboratory Experiments in Plant Physiology. New York: Macmillan.

Witham, F.H., D.F. Blaydes and R.M. Devlin. 1971. Experiments in Plant
Physiology. NY: Van Nostrand Reinhold.

4. Ross (1974) has a lab on "Effects of phytochrome upon night-closure
movements of pinnules from Albizzia julibrissin leaves." Reiss (1994)
has a similar lab, "Phytochrome control of leaflet movement in

Reiss, C. 1994. Experiments in Plant Physiology. Englewood Cliffs, NJ:
Prentice Hall.

Ross, C.W. 1974. Plant Physiology Laboratory Manual. Belmont, CA:

5. Reiss (1994) has a lab on "De-etiolation and Phytochrome" with bean
and pea plants treated with red and far-red light combinations. There
is an online lab on De-etiolation of pea seedlings:


6. Sun plants elongate their leaves or stems greatly when exposed to
incandescent landscape footlamps at night; shade plants generally
don't. It's been termed the end-of-day light response. It could make a
practical lab to compare different types of landscape footlamps
(incandescent, LED and fluorescent) or end-of-day incandescent light
effects on sun versus shade plants. You could try to answer a practical
question such as does your houseplant grow taller because it receives
incandescent light before you go to bed?

Gorton, H.L. and Winslow R. Briggs. 1980. Phytochrome Responses to
End-of-Day Irradiations in Light-grown Corn Grown in the Presence and
Absence of Sandoz 9789. Plant Physiology 66(6): 1024-1026.

Peer, Wendy A., Winslow R. Briggs and Jean H. Langenheim. 1999.
Shade-avoidance responses in two common coastal redwood forest species,
Sequoia sempervirens (Taxodiaceae) and Satureja douglasii (Lamiaceae),
occurring in various light quality environments. American Journal of
Botany 86:640-645.

7. Plant density experiments have a phytochrome aspect; the greater the
plant density, the taller the plants due to etiolation. Such
experiments can also feature other concepts such as LAI and decline in
individual plant size but rise in overall productivity.

8. Plants could be grown under two or more different red to far-red
(R/FR) ratios with the same PAR and determine R/FR ratio effect on
plant growth. If you had sensors to measure R and FR light or R/FR
ratio, students could measure the R/FR ratio in the treatments and
correlate it with plant morphology differences such as stem length and
leaf area. The lab could be shortened by growing the plants in advance
and just have the students measure the plants and the R/FR ratios.

Ch. Robin, M. J.M. Hay, P. C.D. Newton and D. H. Greer. 1994. Effect of
Light Quality (Red:Far-red Ratio) at the Apical Bud of the Main Stolon
on Morphogenesis of Trifolium repens L. Annals of Botany 74: 119-123.

9. Photoperiod effects on tree domancy might make an interesting lab.
If given long days and kept in a greenhouse, many temperate zone
deciduous trees keep growing rather going dormant. Hanover (1975) used
long photoperiods as part of his Accelerated Optimal Growth (AOG)
method for rapid production of tree seedlings.

Hanover, J. et al. 1975. Accelerated-Optimal Growth: A New Concept in
Tree Production. Michigan State University Research Report 317. 16 pp.

Wood, B.W. and Hanover, J.W. 1981. Accelerating the growth of black
walnut seedlings. Tree Planters' Notes 32(2):35-38.

10. This page had some interesting open-ended phytochrome lab ideas:

David R. Hershey

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