Transcript Effect of Supplemental Green Light on Seedling Development Aaron

Effect of Supplemental Green Light on Seedling Development
Aaron White, Derick Jiwan, Jake Abel, Artemis Harper, Kenneth Webb and Amit Dhingra
Department of Horticulture and Landscape Architecture, Washington State University, Pullman WA
Results
Introduction
Light is an essential element for plant growth and development. Light is
made of a spectrum of wavelengths. Plants have developed unique photo
absorption systems which can filter out different wavelengths. To date the
effects of red, far red and blue light have been well documented. This has
been successful due to the identification of photoreceptors which perceive
each wavelength. Amongst the spectrum of photosynthetically active
radiation, green light is used the least by plants for photosynthesis. There are
no known green light photoreceptors in plants, but green light is known to
have physiological effects on plants (1). Green light signals have been
shown to reverse blue light-induced stomatal opening (2), stimulate early
stem elongation (3) and inhibit plastid gene expression (4). Plant’s ability to
respond to green light suggests the existence of a green light receptor(s).
Identification of an easily scorable phenotypic response in germinating
seedlings under green light is the first step towards finding a green light
specific photoreceptor(s). Identification and characterizing of such a
receptor(s) can potentially help in controlling plant growth and development.
Characterization of such a receptor can also help in understanding
physiological process in different plants growing in different regions of the
world.
Effect of RB and RBG Light
A
One of the custom-built LED light boxes used in this study
B
A: Arabidopsis germinating under RBG light
B: Arabidopsis germinating under RB light
Seedlings Without Sucrose
RB Tobacco
1.4
RBG Tobacco
RB Arabidopsis
1.2
RBG Arabidopsis
1
Seedlings With Sucrose
2.5
1.6
Root Length (cm)
1.8
Root Length (cm)
3
RB Tobacco
RBG Tobacco
2
0.6
0.4
RBG Arabidopsis
Conclusion and Future Work
1
0.5
0.2
0
0
Percent of Seeds Germinated in
One Week
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2
3
4
Days
5
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7
1
2
3
4
5
Days
Germination Rate of Tobacco Seeds
100%
Supplemental green light exhibited some effect on root length. However,
under these experimental conditions these differences were not
statistically significant. The removal of a carbon source from the growth
media seemed to enhance the phenotypic difference between the two
seedling groups. However no effect was scorable within the same
seedling group.
RB Arabidopsis
1.5
0.8
A:Seedlings grown on carbonless media under RBG
B:Seedlings grown on carbon containing media under RBG
Results
Effect of RB and RGB on root length
90%
80%
70%
60%
6
 The hypothesis tests true as supplemental green light at the given
fluence rates does not generate a scorable phenotype for the parameters
tested in this study.
 A difference in chlorophyll and anthocyanin content was observed in
the seedling grown under different conditions. Future work could
incorporate measurement of relative amounts of anthocyanin and
chlorophyll.
 Light and hormone are known to interact with each other during early
seedling development. Similar experiments could be conducted in
conjunction with presence of plant hormones such as GA, BAP, IAA.
50%
40%
References
30%
20%
10%
0%
RBG + Sucrose
RB + Sucrose
RBG
RB
Germination Rate of Arabidopsis Seeds
Percent of Seeds Germinated in
One Week
The experiment was carried out on seeds from Arabidopsis thaliana
(‘Columbia’ ecotype) and Nicotiana tabacum cv. “Samsun”. Seeds were
sterilized with ethanol and bleach, and then plated on a nutrient rich media
for germination. The first set of trials were carried out on media with
sucrose as a carbon source. The second set of trials were carried out on
media in absence of any carbon source. The plates were wrapped in foil
and placed in 4oC for four days for stratification. After dark and cold
treatment two plates of Arabidopsis seeds and two plates of tobacco seeds
were placed vertically inside one of two LED-light boxes. One of the light
boxes was set to emit only red and blue light, each at 15 mmol m-2s-1. The
other light box was set to emit red, blue, and green light, each at 10 mmol
m-2s-1. The light intensity were measured using a quantum sensor. The
light boxes used were custom-built in the Dhingra lab. The plated seeds
were kept in the light boxes for a week. The germinating seedlings were
photographed everyday at the same time. Data was collected on
germination rates and overall root area. Measurements were done using
Image J.
1.5
1
0cm
Methods
Red Blue Green
Red Blue
Hypothesis
Supplemental green light will have no effect on seed germination,
hypocotyl length or root length.
Effect of different light spectra and carbon source on seed
germination and plant morphology
100%
90%
80%
70%
60%
50%
40%
1. Lin. C., Ahmad. A., Gordon. D., Cashmore. A. S. (1995) Expression of
Arabidopsis cryptochrome gene in transgenic tobacco results in hypersensitivity
to blue, UV-A, and green light. PNAS 92(18): 8423-8427.
2. Frechilla.S., Talbott. L.D., Bogomolni. R.A., Zeiger. E. (2000) Reversal of Blue
Light-Stimulated Stomatal Opening by Green Light. Plant Cell Physiology.
41(2):171-176.
3. Folta. K (2004) Green Light Stimulates Early Stem Elongation, Antagonizing
Light-Mediated Growth Inhibition. Plant Physiology 135:1407-1416
4. Dhingra, A., Bies, D.H., Lehner, K.R., and Folta, K.M. (2006) Green light adjusts
the plastid transcriptome during early photomorphogenic development. Plant
Physiology, 142(3):1256-1266.
30%
Acknowledgements
20%
10%
0%
RBG + Sucrose
RB + Sucrose
RBG
RB
This study was supported by the CAHNRS Undergraduate Research and Creative
Projects Fellowship, The Auvil fellowship and start-up funds to AD.