Secret to rose scent surprises scientists

Flowers' Square

Secret to rose scent surprises scientists

Knowing how the flowers make (and lose) their smell could help breeders grow sweeter blooms

Not all roses are sweetly scented. By comparing one that isn’t to this — the Papa Meilland rose (shown) — researchers discovered a surprising enzyme behind the bloom's signature “rose” scent.

Stopping to smell the roses might be a letdown — and now researchers know why.

The sweet-smelling flowers create their scent using a surprising tool. It’s an enzyme — a hardworking molecule — that was thought to help clean up DNA. This enzyme is missing in many roses. And that seems to explain why their blooms also lack a sweet floral aroma. The new finding could help scientists solve the thorny problem of why some rose varieties bred for dazzling color and long-lasting blooms have lost their scent.

“Usually, the first thing that people do when they get [a rose] is smell it,” says Philippe Hugueney. He studies plant biochemistry at the National Institute for Agricultural Research (INRA) in Colmar, France. “Most of the time it’s not scented and it’s very disappointing,” he says.

When roses do smell like roses, it’s because they give off a distinct mix of chemicals, he says. Called monoterpenes, these chemicals can be found in many odorous plants. Monoterpenes come in different shapes and scents, but all have 10 atoms of the element carbon. In roses, these chemicals usually are floral and citrusy. But it was unknown how roses make — or lose — their scent.

Other plants make fragrance chemicals using specialized chemicals. Called enzymes, these molecules speed up chemical reactions without taking part in them. In flowers, these enzymes tend to snip two pieces off an unscented monoterpene to create a scented one.

But when Hugueney’s team compared smelly and smell-free roses, they discovered a different enzyme at work. Called RhNUDX1, It was active in the sweet-smelling roses but mysteriously shut down in the bland blooms. The scientists shared this discovery July 3 in Science.

RhNUDX1 is similar to enzymes in bacteria that remove toxic compounds from DNA. But in roses, the enzyme trims a single piece from an unscented monoterpene. Other enzymes in rose petals then finish the job by chopping off the last piece.

The discovery makes scientists wonder why roses use this unusual method, says Dorothea Tholl. She is a plant biochemist at Virginia Tech in Blacksburg. It may be because RhNUDX1 is more efficient than other enzymes, she says.

Hugueney hopes his team's finding helps future roses come up smelling like — well, roses.