Fw: New Discovery Resolves Century Old Scientific Mystery
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Karla Goldstein, (314) 587-1231 kgoldstein@danforthcenter.org
For Immediate Release
New Discovery Resolves Century Old Scientific Mystery
Results to be published in prominent journal
ST. LOUIS, MO June 22, 2010—Researchers from the Donald Danforth Plant Science Center, UC Davis, and Imperial College London have addressed a longstanding mystery which has confused scientists for more than a century. Their discovery will be published in the June 21, 2010 issue of the Proceedings of the National Academy of Sciences of the United States of America, www.pnas.org/cgi/doi/10.1073/pnas.0910558107
The research team demonstrated that cucurbits - a plant family including melons, gourds, cucumbers, squash, and pumpkin - actually have two functionally distinct phloem systems as opposed to one. Phloem is the living tissue that distributes nutrients to various parts of the plant as needed. This discovery is against a popular notion in plant biology under the "structure and function" framework that a similar structure usually indicates similar function and raises questions regarding conclusions made in the past, as the vast majority of research in phloem transport studies use cucurbits as model species and utilize the old dogma as an assumed known.
In vascular plants, phloem systems distribute nutrients, including trillions of tons of sugars produced in leaves each year, to all parts of the plant as needed. These sugars are stored in seeds, wood, and fruits that are critically important in the sustenance of ecosystems and for utilization and consumption by humankind. Sampling phloem sap for research has been difficult because of its small size and very rapid sealing system. Cucurbitaceae have been long been used as model species for studying phloem transport because of the ease of sampling large quantity of phloem exudates by simply incising the stem, petioles and fruits.
Ever since the first extensive study of phloem transport in cucurbits in the 1930s by AS Crafts, a puzzling question remained until recently: why are the contents of phloem exudates in cucurbits so different from what was predicted. According to the current understanding of phloem transport, up to 600 grams per liter of sugar should exist in the phloem exudates of cucurbits in order to sustain their fast fruit growth. The well-known phloem structural proteins (designated as PP1 and PP2 in pumpkin) that are supposed to block extensive bleeding from phloem tissue after wounding do not seem to work in cucurbits, whereas rapid sealing mechanisms block phloem bleeding instantaneously in other plant species, thus preventing sap sampling.
The commonly sampled cucurbit phloem exudates are actually from the extrafascicular phloem system, which is peripheral to the usual fascicular phloem (sugar transporting phloem located in vascular tissue) that is blocked immediately upon wounding. Phloem exudates in the past have been mistakenly assigned to originate from both systems, and particularly to the fascicular system. The conclusions for this work are supported by tracer experiments and the analysis of the metabolome and proteome contents of the two-phloem systems. RFO sugars were detected in abundance fascicular phloem, and the previously proposed phloem structural proteins PP1 and PP2 were totally missing from the fascicular phloem tissues.
The research was conducted by Danforth Center scientists, Drs. Baichen Zhang and Leslie Hicks. "This new discovery will catalyze an exciting start to a new era in phloem transport research using cucurbits as model species, particularly in combination with the recently released cucumber genome information," said Hicks, director of the Proteomics & Mass Spectrometry Facility at the Danforth Plant Science Center.
About The Donald Danforth Plant Science Center
Founded in 1998, the Donald Danforth Plant Science Center is a not-for-profit research institute with a mission to improve the human condition through plant science. Research at the Danforth Center will feed the hungry and improve human health, preserve and renew the environment, and enhance the St. Louis region and Missouri as a world center for plant science. Please visit www.danforthcenter.org for additional information.
Karla R. Goldstein
Vice President of Public and Government Affairs
Donald Danforth Plant Science Center
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Improving the Human Condition through Plant Science
posted by Tom Karst @ 11:54 AM
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