Forcing blooms goes high tech

Thursday, November 3, 2005

When leaves begin changing from green to yellow and brown and falling off trees, many Texans begin looking ahead to holiday cheer. Chrysanthemums grace football corsages. Poinsettias will soon adorn tables. As Texans gather for Thanksgiving and other holiday feasts, food will take center stage.

Thanks to research being conducted at the University of North Texas, florists and farmers are getting help to produce yearlong yields for both flowers and food.

Scientists are within reach of this possibility because of genetic plant studies conducted by a UNT researcher and his colleague. Brian Ayre, UNT professor of biology, and his collaborator, Robert Turgeon, a Cornell University professor of biology, have demonstrated that introducing a specific gene (out of the 25,000 or so genes in a plant) to a leaf can cause a plant to flower outside of its normal growing season.

Scientists have been working to understand the chemical nature of the flowering process for more than 75 years, and now Ayre and Turgeon are one step closer to finding the answer. Their discovery could make it possible for farmers to increase food production by producing crops from several planting cycles. The research could also lead to florists saving the money they would normally spend to force plants to bloom out of season.

"Understanding what stimulant causes a plant to flower could be the key to increasing crop and flower production," Ayre says. "Plants that typically only bud in the summer could also bud in the spring. Crops could be stimulated to have a double harvest."

Ayre and Turgeon conducted research for two years to learn more about what causes plants to flower. They started with a blueprint based on what scientists already know about plants.

"Plants can tell the season and the length of day," Turgeon says. "And what was found a long time ago is that this perception takes place in a plant's leaves, but it's not the leaves that flower."

Research shows that the transition to reproductive growth occurs far from the leaves, at the tip of the plant known as the meristem.

"A signal must be transmitted from the leaves to the meristem," Ayre says. "This signal has a name, florigen, but the problem in identifying it has been so perplexing that scientists refer to it as the Holy Grail of plant biology."

Knowing that the perception of light in one part of a plant causes a response in another part, Ayre and Turgeon studied which signals were transported through the veins of a plant, causing it to flower.

"We manipulated the phloem -- the plumbing system of the plant -- at a molecular level," Turgeon says.

Their research focused on a single gene called CONSTANS (CO). Scientists knew that CO played a role in the flowering process, but the role was unclear. It was thought to be a product of florigen, functioning at the plant's tip.

To discover more about how the gene works, Ayre and Turgeon increased the amount of CO in a plant called Arabidopsis, which is similar to a mustard plant.

For one day, the two placed the plant under conditions that would normally delay its flowering, but the plant still flowered. Ayre and Turgeon then grafted portions of Arabidopsis to vegetative tips from plants that had no CO. As a result, the plants that had been grafted began to flower immediately after the graft junctions healed.

"With this experiment, we demonstrated that a CO-derived signal in a leaf is transported to the plant's tip," Ayre says. "Our work suggests that CO is a precursor to florigen, rather than a product of it."

He adds that at the molecular level, the CO gene can switch the florigen signal on or off, depending on day length.

"The discovery of the role of CO in the florigen process could mean that certain plants will not be dependent upon the prevailing environmental conditions in order to reproduce," Ayre says.

Typically, short-day plants such as strawberry, rice, soybean, sorghum and cotton flower in late fall, winter or early spring. Long-day plants such as oats, peas and canola flower in late spring and summer. Ayre says introducing CO into short-day plants as well as long-day plants could increase production.

In addition, flower producers may no longer have to mask their greenhouses to force short-day plants like zinnia, dahlia and African marigolds to bloom in the summer, or depend on expensive lighting systems to artificially extend winter days for summer plants like fuschia and begonia.

"The role of CO in generating flowering brings us closer to having an abundance of affordable vegetables and flowers all year round," Ayre says.

UNT News Service Phone Number: (940) 565-2108