
New Research Explains Signaling System for
Plant NutrientsBy Linda McGraw March 10, 1999New discoveries about how plants
distribute nutrients internally could lead someday to crops that are more
nutritious, can produce higher yields or overcome environmental challenges,
Agricultural Research Service scientists
report. Just like animals have a signaling system between the brain and the stomach
to tell them when to stop or start eating, plants also have a special signaling
system that regulates nutrient distribution. The signaler in the system is sucrose, the major form of sugar
transported in the plants vascular system. The plant responds to
sucroses signal by increasing or decreasing nutrient flow to roots,
seeds, and storage organs--known as sink tissues. These tissues are called sinks because they import sugars and
amino acids to support plant growth and development, according to ARS plant
physiologist Daniel R. Bush. Bush works in the ARS
Photosynthesis Research Unit at
Urbana, Illinois. ARS is the chief scientific research agency of the
USDA. When sucrose exits plant leaves, it flows through elongated structures
called phloem cells, which lie end to end, forming a continuous conduit in the
plants vascular system. A specialized sucrose transport protein loads the
sugar into the phloem. Inside the phloem cells, the concentration of sucrose is
100 times greater than that outside. This attracts water into the cells. The release of sucrose into sink tissues causes the water to
leave the phloem cells, creating a hydraulic pressure difference between the
leaf and the sink phloem that drives long-distance nutrient transport. This is
similar to the pressure-driven flow of blood pumped through the human body. A story about this research is in the March issue of Agricultural
Research magazine, which can be found on the World Wide Web at http://www.ars.usda.gov/is/AR/archive/mar99/sugar0399.htm Scientific contact: Daniel R. Bush, ARS Photosynthesis Research Unit,
Urbana, Ill., phone (217) 333-6109, fax (217) 244-4419,
[email protected] U.S. Department of Agriculture | |