UF Researchers Putting Scents Back Into Flowers

February 13, 2003

GAINESVILLE, Fla. — Stop and smell the roses – that is if you can find any that still have scents.

If you are among the millions who receive flowers on Valentine’s Day, you likely will put your nose to a rose, only to find you can’t catch a whiff of your favorite floral aroma.

And it isn’t because your sense of smell has diminished. Plant breeding has led to bigger, longer-lasting blooms, but in the process many flowers have lost their scents – a trend University of Florida researchers hope to reverse.

“Scent is such an important characteristic of flowers,” said David Clark, an associate professor of environmental horticulture in UF’s Institute of Food and Agricultural Sciences. “Just go to a florist and observe the customers. The first thing they do is attempt to smell the flowers. They’re often frustrated when they discover they can’t.”

Clark and other UF researchers are investigating ways to put scent back in, either through genetic engineering or by developing chemical formulations that might be used through a spray application.

That may be positive news for the consumers in the United States who spent approximately $7.5 billion on cut flowers in 2002. Much of that was spent for Valentine’s Day, the No. 1 holiday for florists and cut flowers, according to Jennifer Sparks, a spokeswoman for the Society of American Florists. The society estimates consumers will purchase 130 million roses this Valentine’s Day.

Researchers do not know exactly why roses and other flowers are losing their scents, but they suspect that in trying to develop more-attractive blossoms with longer vase lives, plant breeders have focused on selecting genes that produce those traits rather than genes responsible for fragrance, Clark said.

Seven years ago, Clark began genetic studies with petunias. What started as a quest for longer-lasting flowers turned into a search for scent.

One of the first genes he worked with was the ethylene receptor. Ethylene is a ripening hormone and gas that causes flowers to wilt.

“We were able to knock out the function of the ethylene receptor so the plants could produce longer-lasting flowers,” Clark said. “We made the flowers insensitive to ethylene gas, but also found that some of the genes involved in making flower scent are regulated by ethylene.”

Different genes trigger production of volatile compounds, which are molecules in plant cells that generate a flower’s scent when they evaporate. Each flower species has a unique scent due to its own combination of volatile compounds.

“Some chemicals that are used to make volatile compounds are chemicals that have been shown to be detrimental to vase life – chemicals that interact with hormones like ethylene,” Clark said.

As breeders selected plants that made less of those chemicals in order to achieve long-lasting flowers, they also may have removed the plants’ abilities to produce floral scent.

So far, Clark and his colleagues have cloned 4,000 petunia genes and are working to identify the ones responsible for making the chemicals that produce volatile compounds responsible for scent. Those genes – or even others from different plant species – could be manipulated and placed in petunia plants to bring back scent. It is possible that petunia genes could be used to help return scents to other flowers.

Scientists frequently place genes from one species of plant into another to attain desired traits. For example, UF researchers have cloned rose scent genes from an unlikely source: tomatoes. A couple chemicals that make up the flavor of a tomato also are components of scent in roses.

Clark also is developing an application technique to add scent to flowers after they have blossomed. Scientists use scientific instruments to analyze the volatile compounds of a flower, then they can mix the appropriate chemicals in proportions that a plant would produce them to recreate a particular scent.

UF researchers have recreated the petunia scent in the lab and are working on formulating rose scent.

“If a rose doesn’t have scent, we have the ability to make it smell like a rose, or we could make it smell like a petunia or a lily or even a pine tree as long as we know what the components of the volatile mixture are,” Clark said. “We manufacture the scent, then add it to the flower with a spray application.”

Whether fragrance is returned to flowers through genetic engineering or other techniques, UF researchers want to do so without sacrificing other qualities consumers and florists have come to value – appearance and longevity.

“I think consumers of the future are going to have a choice,” Clark said. “They will be able to have a scented flower, or they will be able to buy one that’s standard and not scented. It will be like buying hand lotion and deciding between scented and unscented. There are going to be new approaches to floral scent, whether it’s through molecular genetics or biochemistry.”