From: Randolph E. Schmid, Associated Press
Published August 12, 2005 12:00 AM

Leaf to Bud: Pssst, It's Time to Flower

WASHINGTON — How does a flower know when to, well, flower? For one thing, it isn't just April showers that do the trick. After all, some forsythia burst forth in early spring, roses enjoy the summertime and there are types of rice that flower in the fall.


Scientists have long known that it is the amount of sunshine that makes the difference. Now they have figured out how the leaves signal the flowers to form.


A series of papers by German, British, Swedish and Japanese researchers details the process in Friday's issue of the journal Science.


A gene called FT in the leaves, discovered in the 1990s, is crucial to the process, but questions remained about how it delivered the message.


The researchers have now found a protein called FD, which occurs in the tips of branches, that causes bunches of plant stem cells to form flower buds.


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"Only when FT and FD join forces in the same cell can they be active," said Detlef Weigel, director at the Max Planck Institute for Developmental Biology in Teubingen, Germany.


The researchers concluded that the protein produced by the FT gene moves from the leaves to the branch tips where it activates FD.


Philip Wigge, who recently moved from the Max Planck Institute to become a group leader at the John Innes Centre in Norwich, England, noted that "the transition to flowering is one of the most important decisions made by plants. It has to be carefully controlled according to the seasons."


"For example, plants that need to be fertilized by pollen from other members of the same species, as is the case for cherry trees, need to make sure that they produce flowers at the same time as their neighbors. Requiring two independent components to come together for activation of flowering is a neat trick. One determines the right time of year and the other specifies the right place for the formation of flowers," Wigge said in a statement.


Miguel A. Blazquez of the Polytechnic University of Valencia, Spain, said the findings fill a gap in knowledge about how such information is delivered. Blazquez was not part of any of the research teams.


Source: Associated Press


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