Postdoctoral research scientist Adriana Ortiz-Lopez uses a spectrophotometer to
examine the different pigments contained in canola seed extracts while plant
physiologist John Whitmarsh prepares a new sample for analysis.
In the world of plants, green is
usually good . . . except in canola seeds. That's because too much green means
too much chlorophyll has remained in the seedmeaning the seed hasn't
matured. Freezing temperatures can prevent maturation, causing the seed to stay
green. An early frost can cost North American canola growers up to $150
"The freezing interrupts chlorophyll breakdown in canola seeds,"
explains Agricultural Research Service
plant physiologist C. John Whitmarsh. "Seeds can reach maturity and have a
high oil content, but if they're green, their price drops."
Seed crushers remove the green from the oil with bleaching clays, which
produce an added expense and pose an environmental problem.
Canola is an oilseed crop grown mainly in parts of western Canada, with some
acreage in Ontario and the Pacific Northwest, north-central, and southeastern
United States. Its yellow flowers produce pea-shaped pods that contain tiny
seeds harvested for their oil. Canola oil contains omega 3 fatty acids,
acclaimed for improving human immune and vascular systems.
Laser light is used
to analyze material
extracted from canola seeds.
"Ultimately, we may be able
to provide industry with genetically altered canola plants tailor-made to
tolerate freezing temperatures," says Whitmarsh, who is based at Urbana,
Illinois. "Many plants break down chlorophyll even after a freeze. That's
what happens in the fall when chlorophyll disappears and other leaf pigments
become visible, creating spectacular fall foliage."
Whitmarsh works collaboratively with Donald R. Ort, head of the ARS
Photosynthesis Research Unit. Their lab experiments have shown that seed
degreening in Arabidopsisa close relative of canolamimics
canola's freeze sensitivity. Their goal is to identify Arabidopsis
mutants that develop little or no seed chlorophyll, as well as other mutants
that display early chlorophyll breakdown during seed maturation.
To check seed degreening, postdoctoral research scientist Adriana
Ortiz-Lopez puts plants in a growth chamber with freezing air blowing over
them. She also keeps watch over other plants maintained at above-freezing
temperatures. After a few weeks, she notes that seeds from plants exposed to
freezing air are green, while those from plants held at slightly warmer
temperatures are brown.
Ortiz-Lopez uses chlorophyll fluorescence to illuminate the breakdown
products of chlorophyll. She's looking for the stage in the degradation process
that is blocked and is hoping to identify which proteins and genes are involved
in chlorophyll degradation.
The mutant seeds that degreen appear to be more freeze tolerant. The next
step is to identify the modified genes that are responsible for tolerance to
freezing temperatures in selected mutants. This accomplishment will open the
door to cloning the mutated genes and introducing the freeze-tolerance genes
into a wild plant. Ultimately, transgenic canola plants can be developed and
tested for freeze tolerance. If successful, plants will produce seeds without
chlorophyll, even after exposure to freezing temperatures.
"Ten years ago, we did the basic research," says Whitmarsh.
"Now our work demonstrates the possibility of going from basic molecular
research to an applied solution."By
Linda McGraw, Agricultural
Research Service Information Staff.
This research is part of Plant Biological and Molecular Processes, an ARS
National Program (#302) described on the World Wide Web at
C. John Whitmarsh and Adriana
Ortiz-Lopez are in the USDA-ARS Photosynthesis Research Unit,
University of Illinois, 190PABL, 1201 W. Gregory, Urbana, IL 61801-3838; phone
(217) 333-2947, fax (217) 244-4419.