Riverside, California
December 9, 2003
Researchers at the
University of California,
Riverside have identified a protein that helps guide sperm
to egg in flowering lily plants, a significant step forward in
the field of plant reproduction.
Elizabeth Lord, professor of plant biology and a member of the
Center for Plant
Cell Biology at UC Riverside, authored the paper titled
“Chemocyanin, a Small, Basic Protein from the Lily Stigma
Induces Pollen Tube Chemotropism.” The paper appears this week
in the Proceedings of the
National Academy of Sciences.
Botanists have long known that, in flowering plants, the
female organs play a role in guiding sperm-laden pollen tubes
to the eggs found in ovules. But until now, they did not know
exactly how. Lord’s team found that chemocyanin, a protein
with a previously unknown function, effectively guided
sperm-laden lily pollen tubes to the plant’s ovules, which
hold the eggs from which come seeds in the lily. The protein
works specifically in lilies. Tobacco pollen tubes were not
similarly guided.
The paper also shows that chemocyanin was more effective when
another protein found in the stigma of the lily, SCA, was
present. Chemocyanin and other proteins such as SCA may unlock
the network of signals involved in plant reproduction.
“The importance of understanding how plants reproduce is
enormous for the future manipulation of crop and nursery
plants,” said Lord. “There is a huge flower industry in
California, and we know little about how seed set occurs in
most flowering plants.”
Lilies are good examples because they cannot produce seed with
their own pollen so they must be cross-pollinated with another
variety, according to Lord. And while the industry grows
Easter lilies from bulbs not seed, whenever they want to
produce new varieties for the flower market or for gardens
they have to produce seed by crossing varieties.
“This research has relevance for all flowering plants because
we do not know yet how pollen tubes, which carry sperm cells,
are guided to the egg cell in the ovary,” said Lord. “Our
discovery of a protein from the pistil which acts to guide
pollen tubes to the egg cell is a first for flowering plants.”
The protein, chemocyanin, is concentrated on the flower
stigma, where pollen grains land on the flower. The pollen
grains germinate on the stigma to form pollen tubes, which
carry sperm cells, then pass through the female tissues
starting from the stigma, ending up in the ovary, which
contain ovules that contain eggs.
“You would be surprised to know that we don't even know the
identity of the molecules that attract human sperm cells to
the egg,” Lord added.
Lord’s research team at UC Riverside included doctoral
students Sunran Kim and Juan Dong; postgraduate researchers
Jean-Claude Mollet and Sang-Youl Park; and academic
coordinator in the Department of Chemistry, Kangling Zhang.
Related Links:
Elizabeth
Lord's Web page
The University of California,
Riverside is a major research institution and a national
center for the humanities. Key areas of research include
nanotechnology, genomics, environmental studies, digital arts
and sustainable growth and development. With a current
undergraduate and graduate enrollment of nearly 17,000, the
campus is projected to grow to 21,000 students by 2010.
Located in the heart of inland Southern California, the nearly
1,200-acre, park-like campus is at the center of the region's
economic development.
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