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One way to increase the smell is to simply suppress the color

Botany / In the Petal Genome Project, Israeli researchers locate the genes responsible for the scent of the flowers

By Marit Selvin

Photographs: The Hebrew University

With the help of two rose varieties - a pink variety with a strong smell and a yellow variety with no smell (below) - the researchers identified for the first time genes involved in the creation of the smell in roses

The flowers of today do not smell like the flowers of the past. Years of repeated cross-breeding, with the aim of obtaining flowers with special colors, attractive shapes and above all a long shelf life, meant that the roses, carnations and many other flowers, whose scent extracts were used to create perfumes, today smell like plastic flowers.

A flower's unique scent signature is a mixture of substances that evaporate into the air from the petals. Orchids, for example, produce about a hundred different volatile substances. Ari's mouth flowers, on the other hand, produce between seven and ten scent substances only. The mixture of smells attracts insects that pollinate the plant; Other combinations of the same scents attract the enemies of the insects that feed on the leaves of the plants. Another defense strategy has developed in tobacco plants, which are damaged by caterpillars or beetles that bite them: the plants release three odorous substances into their environment that paralyze up to 90% of the enemy's activity.

The strategy of spreading the scent by the flowers has been perfected during evolution and adjusted to the agenda of the insects. Last year, the plant researcher Natalya Dodereva from Purdue University in Indiana found that marigold plants have a biological clock that directs the release of odorous substances so that during the day, the hours of activity of the bees that pollinate the plant, four times more substance is released than during the night. Petunia and tobacco flowers, on the other hand, release large amounts of fragrances precisely at night - the time of activity of the moths that pollinate them. These and these stop the scent secretion after pollination.

For hundreds of years, the scent essences were extracted from the flowers using different techniques. The art of extracting the smell and turning it into a perfume was a unique profession that few practiced because it required a developed sense of smell which was the only tool for testing the nature of the smell. Despite the many technical skills required of the perfumer, a thorough knowledge of how fragrances are formed was not required. And so, until recently no one tried to understand how the flowers produce their scent; What are the biochemical processes that lead to the creation of fragrances.

The first to research the subject was Prof. Eran Picharsky from the University of Michigan, a former Israeli. Picharsky wondered why certain plants developed the ability to produce a smell while other plants, close to them in structure and composition, do not produce a smell at all. He searched the professional literature for clues to this, and discovered that scientists have no idea how the smell is created in flowers.

In 1994, Picharski and his team began researching the Clarkia, a fragrant wild plant that grows in California. The researchers trapped in a tank the volatile substances that the flower emits, did a chemical analysis on them and found 12 different substances. Following the chemical identification, they were able to isolate and characterize for the first time an enzyme that participates in the creation of the smell and creates the volatile substance linalool - one of the smelling substances of the flowers. The researchers were also able to isolate the gene encoding the enzyme. Since then, three more genes have been found that code for enzymes involved in the creation of fragrances in Clarkia flowers. In addition, Picharsky discovered that the process of creating the smell takes place in the outer layer of cells of the petals, from where the path to the free air is short. In a similar way, another enzyme involved in the creation of one of the main odor substances in the lion's mouth was identified by the researcher Dodarva and the gene coding for it was isolated.

These methods of searching for enzymes involved in the formation of odorants are slow. An alternative, faster method was developed in Israel. Dr. David Weiss from the Institute of Plant Sciences and Genetics in the Faculty of Agriculture of the Hebrew University decided to identify the genes participating in the production of fragrances using modern tools developed in the Human Genome Project. Weiss heads the petal genome project, which was established three years ago with the assistance of the Ministry of Science. As part of the project, they scan DNA from the plant tissue and look for genes that seem to have a role in the creation of the odor molecules.

Together with a team of researchers, which included Professors Alexander Weinstein, Danny Zamir and Tzach Adam from the Faculty of Agriculture, Dr. Ephraim Levinson from the Agricultural Research Administration at Beit Dagan and Prof. Eran Picharsky, Weiss succeeded in building a DNA database that runs the titles of roses To this end, the researchers used two varieties of roses: a variety that is pink in color and has a strong smell and a second, yellow, odorless variety. When they compared petals from these two strains they found completely different volatile substances in them. They were able to isolate and characterize more than 3,000 genes that function in the petals of roses, at least 20 of which have a putative role in creating different fragrances.

In order to check if these genes are indeed involved in the creation of the smell, they were injected into bacteria that produced proteins that the genes code for. The activity of the proteins was tested using devices that detect odorants. So far, researchers have identified and characterized four genes encoding such enzymes; This is the first time that genes involved in the creation of the scent have been found in roses. Some of the research results are published this month in the journal
;” "Plant Physiology another part will be published in three months in the journal." "Plant Cell" We hope to use genomic methods to find out the molecular mechanism responsible for the creation of the smell", says Weiss. "At the same time, we are trying to use these genes to return the flowers to their lost scent."

A first step in this direction has already been taken. In the work published this month in the journal "Breeding Molecular", Weiss and his group presented carnation flowers that had been injected with a gene that naturally participates in the creation of the scent in Clarkia flowers and roses. "Although we created a new odorant in the nail, as found in chemical analyses, we were unable to detect it in smell tests. It was therefore necessary to increase the smell," says Weiss. A substantial change in nail smell was obtained using an alternative approach. The assumption was that creating color and smell are the two main strategies of the plant to attract insects. Indeed, biochemical tests carried out by the team members revealed that some of the naturally occurring scents in carnation flowers originate from the same biochemical pathway that leads to the creation of the color. Team member Amir Zucker showed in his doctoral thesis, a part of which was published two months ago in the journal "Molecular Breeding" that it is possible to increase the creation of the scent in the petals of a clove by blocking the pigment creation pathway.

"In the future, we aim to create new, more attractive scents," says Weiss, "even though we still lack a lot of knowledge in understanding the complex biochemical pathways and how they are controlled and activated."

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