A molecular-genetic approach to studying source-sink interactions in Arabidopsis thaliana. Final report, April 1, 1995--March 31, 1998 Page: 4 of 5
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Principal Investigator: Susan I. Gibson
which have currently been fulfilled. The first of these goals was to develop a
faster and more reliable technique for measuring sugar levels in plant tissues.
The second of these goals was to examine the roles of light intensity, soil
nitrogen levels, photoperiod, developmental stage and ability to synthesize
starch in determining fumaric acid levels. The final goal of this part of our
work was to measure soluble sugar and fumaric acid levels in Arabidopsis
In our initial experiments we measured soluble sugar levels in plant
tissues using a standard protocol that involves extracting the sugars into
ethanol, drying down the ethanol, resuspending the sugars in water and then
using a chemical assay to measure sugar concentrations. This procedure is
time consuming to use for large numbers of samples due to the significant
amounts of time needed to dry down the ethanol fractions and then
completely resuspend the sugars. We therefore worked out a different method
for measuring sugar levels that eliminates the need to dry down and then
resuspend each sugar sample. This stream-lined protocol has allowed us to
measure sugar concentrations in many more samples than was previously
During the last three years, we have measured fumaric acid levels in
literally thousands of plant tissue samples. The results of these experiments
indicate that, in Arabidopsis, fumaric acid levels rise with plant age and with
increasing light intensity. We have also determined that fumaric acid levels
are far higher in tissues capable of carrying out photosynthesis than in non-
photosynthetic tissues, and that fumaric acid levels are higher at the end of
the day than at the end of the night. In addition, Arabidopsis plants that can
not make starch accumulate relatively high levels of fumaric acid, indicating
that, in these plants, some of the photosynthate that would normally be used
to synthesize starch is instead being used to make fumaric acid. We also
determined that some, but not all, other plant species accumulate fumaric
acid to high levels. In particular, hollyhock accumulates fumaric acid at levels
up to 10 mg/gram fresh weight. Also, at least one agriculturally important
plant species, soybean, accumulates substantial quantities of fumaric acid
(approximately 0.5 mg/gram fresh weight). Finally, we have determined that
phloem sap from both Arabidopsis and hollyhock contains high concentrations
of fumaric acid, raising the intriguing possibility that significant amounts of
fumaric acid are being transported from what part of the plant to the other
through the phloem.
Characterization of Mutants in Sugar-Regulated Gene
Expression from Arabidopsis. To identify the factors involved in
controlling sugar-regulated gene expression in plants, and to determine the
effects of disrupting this type of regulation, we have isolated and characterized
mutants of Arabidopsis that are defective in the sugar induced expression of
the gene encoding beta-amylase. Prior to the start of the work funded by this
grant, we screened several thousand EMS-mutagenized Arabidopsis plants for
those that fail to regulate beta-amylase production in response to sugar. This
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Gibson, S. I. A molecular-genetic approach to studying source-sink interactions in Arabidopsis thaliana. Final report, April 1, 1995--March 31, 1998, report, November 1998; United States. (digital.library.unt.edu/ark:/67531/metadc710499/m1/4/: accessed February 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.