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ANATOMY OF A ROSE -- EXPLORING THE SECRET LIFE OF FLOWERS |
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FOURTEEN: What We Don't Know WE GET UP EVERY DAY, surrounded by mystery and marvel, enthused by all the things we do not know. Life on earth has had four billion years to get this far. We woke up this morning to try and figure it out. I am meeting Rob Raguso at the Arizona Desert Museum in Tucson to watch the hawkmoths as they appear at twilight among mounds of sacred datura, also called jimsonweed, thorn apple, and moonflower. The sacred datura has large, trumpet-shaped, silky blossoms, creamy white and pale lavender. When eaten, the flowers can cause hallucinations, blindness, and death. Their beauty, as in a myth, has two faces. I have grown up with this gorgeous, sinister flower, and I never take it for granted. Whenever I see it, I want to gasp. In the museum's "moth garden" are also patches of purple verbena, yellow sundrops, rock trumpets, pink four-o'clocks, and white evening primrose. These primroses are delicate. The four heart-shaped petals seem tissue-thin, veined in a slightly darker color, like the veined skin of the very old or very young. The flowers look blown here, on their way to somewhere else. They look uncertain, as though they might blow away again.
Datura In fact, they are busy, pumping out scent, preparing for the hawkmoth. Hawkmoths are a group of species that appear worldwide. Coiled under the moth's head is a strawlike proboscis for sucking nectar. Their stout bodies are equipped with large, stiff, powerful wings boldly patterned. Hawkmoths have good eyesight in dim lighting. They can fly far, and they can fly fast. They can regulate their body temperature. The hawkmoths in this desert, the white-lined sphinx moths, have four brown wings colored in bands of pink and white. Habitually, the larvae rise up like tiny sphinxes, daring you to interfere with their happy lives of eating everything in sight. These caterpillars are lime green with a yellow head, side rows of pale spots bordered by black lines, and a bright yellow or orange rear horn. They are strikingly beautiful. And they seem to know it. As a child, Rob Raguso collected moths and butterflies. As an undergraduate at Yale, he learned about flowers as butterfly food. By the time he began his graduate work in the biology of floral scent, he was looking more at the food than at the butterflies, hoping someday to look at everything, to start with molecules released from a petal and end up in the sky pumping wings. Rob is happy to talk about the relatively obscure wildflower Brewer's clarkia, the subject of his doctoral dissertation, completed in 1995. In the evening primrose family, Clarkia breweri is hot pink, with four petals that divide into a central lobe and two side lobes. The little flower looks gay and excitable. It grows fast and can be used easily for genetic studies. It is the only known scented species in a genus of over forty species. "In the Clarkia genus," Rob says fondly, "we had a group of plants that were ancestrally bee-pollinated, that offered pollen to specialist bees, and that lacked fragrance. In time, Clarkia breweri evolved a long nectar tube, switched to nectar, and added scent. How did that happen?" Rob spent a year learning how to collect and analyze odor molecules. He found that Brewer's clarkia has a relatively simple scent. The flower makes two kinds of chemical compounds: terpenoids, common in citrus and mint, and benzenoids, characteristic of clove and cinnamon. Trace amounts of terpenoids are also in the flower's nearest relative, C. concinna. Brewer's clarkia had amplified these compounds and added another group. Next, Rob and others would determine which parts of the flower produced which odors, which enzymes were involved, and which genes. These are all things we did not know before. By adding scent, the bright pink flower attracted new pollinators, such as night-flying hawkmoths. By making a larger flower, having lots of nectar, and staying open in the day, Brewer's clarkia also began to attract hummingbirds. But that's another story. Rob was interested in whatever the hawkmoths were interested in. What, for example, did they smell? He learned how to record the responses of hawkmoth antennae and found that they smell everything. This was something else we didn't know before. Rob thought it was wonderful news. *** AT THE TUCSON DESERT MUSEUM, Rob and I are joined briefly by his wife and three-month-old son. Rob talks to the baby as all parents do, as though the infant understood every word and might well answer in a complete sentence: "Yes, I do want to be changed right now." "No, I am not tired, although this is what you would like to believe. I am bothered by the setting sun in my eyes." The setting sun drops behind the postcard purple, jagged mountains, and the world turns suddenly blurry. Like airplane pilots on a schedule, the hawkmoths appear, moving invisibly against a lattice of greenish gray leaves and ghostly flowers. "Look, look," Rob says. I try and see only the aftermath of wings, a ripple in the space-time continuum. "Look, look," Rob urges. I cannot see the hawkmoths, but I can smell the flowers and something more, a powdery sweetness I associate with my grandmother's makeup, her voice out of tune in the Methodist church as we sang together, "I Walk through the Garden Alone" and "Glory Be to the Power and to the Son aaand to the Ho-leee Ghost." All the cues of memory blend together in a complex system: the paisley of her dress, the polished wood of the pew, the sound of music. Rob pulls a hawkmoth out of the air and holds it in his hand. I almost clap. That's a magic trick. The sphinx moth is the insect version of the hummingbird, whirring its wings, hovering to drink from a corolla tube. Briefly, the moth struggles. "Look how muscular he is," Rob says admiringly. "This is a strong guy!" The moth as action hero. The air is suffused with scent, with sex, with food, with memory. "What is your question?" I ask Rob. He pauses to let our hero escape. "How does a moth experience a flower?" *** SOME 200,000 YEARS AGO, human beings evolved to think creatively outside. Grass and sun and trees were the natural setting for thought. Carefully, we watched the other animals. Today, we experience delight when we are allowed to do this again. When we feel intelligent in a meadow, we feel right at home. We are still evolving. Our best science now often happens indoors, in the laboratory, where we are surrounded by tools we invented but do not fully understand. In Rob's lab at the University of Arizona, gas chromatography analyzes the compounds produced by a flower. A computer program takes each compound's mass spectrum, its unique fingerprint, and compares it with the thousands of compounds we already know. There are thousands more we do not know. Like a perfume maker, Rob has trained his nose to identify scent. He can equate a smell, a physical experience, with a molecule. Then he can equate that molecule with a mass spectrum. It may be the closest any of us come to living like a hawkmoth. Rob likes playing detective. When he smells a flower, he asks himself, What's in there? Why does it smell like grape or chocolate when it doesn't have any of those molecules? What is making this flower shimmer? What odors are masking other odors? What odors are synergizing to make a new odor? What does this odor mean to a honeybee? One question leads to another and to six thousand more. How does a moth experience a flower? How does a flower experience a moth? There are so many reasons to get out of bed. Since hawkmoths respond to a range of odors, flowers can switch to hawkmoth pollination fairly easily. Flowers do not have to make a specific class of chemicals. They can simply smell good. Some plants amplify the emissions from their sepals and leaves. Some alter their defense compounds. Some use existing nectaries and anthers. Some evolve a new nectary. Now Rob wonders what would happen if he compared three different plant families, all with night-blooming, moth-pollinated flowers: the evening primroses, the potato/tomatoes, and the four-o'clocks. How have these groups changed their strategies through time, losing and gaining fragrance as they evolved in different climates and soils? Is fragrance lost when self-pollination evolves? Can fragrance return? Are there patterns within each family? The evening primrose family contains over 650 species. One of them is Brewer's clarkia. One is the flimsy-looking evening primrose I am watching now being pollinated in the Tucson Desert Museum. One is the tiny white enchanter's nightshade, which the Greek witch Circe used to change men into pigs. We don't know much about these plants. Mostly we study crop plants for which our questions are quite practical. The four-o'clocks are still a mystery. The sacred datura is still a mystery. The white enchanter's nightshade is still a mystery. How did she change those men into pigs? *** AT THE INTERNATIONAL BOTANICAL CONGRESS, in a cavernous convention center, where five thousand scientists gather for seven days to talk about plants, I feel lost. I feel lonely. Suddenly I see Rob. I have been at the conference for one hour, and here is a familiar face. I almost clap. That's a magic trick. These big conferences have a hierarchy. Celebrity scientists give speeches at the plenary lectures. In the symposia, five to six scientists read and present research that is often already published. In the poster exhibition, usually the younger scientists and graduate students describe newer, unpublished work. They do this, unpretentiously, on a sheet of poster board. At this congress, more than a thousand posters have been hung on six-foot-high panels that form rows through which people can walk and browse. Rob has a poster on evening primroses and hawkmoth pollination. He invites me to see him on Wednesday morning, 9-10 A.M., when the authors of even-numbered posters stand in front of their work and explain it to people passing by. Shortly after, the shift changes, for the authors of odd-numbered posters. The exhibition hall is huge, with the ambiance of an airplane hanger. I enter the hall and am immediately beguiled: The place hums. The air hums and thrums. I have entered some kind of hive, a honeycomb of panels and posters, where people murmur and talk about flowers. The hive is busy. The hive is excited. So much work is getting done. It's not all pure science. I roam, gathering phrases: "Relocation." "A very practical field." "He's difficult to work with." "My thesis committee." "A starting salary." People are getting into new schools and finding new jobs and asking about mentors and fitting their lives into the life of the hive, of knowledge built on top of knowledge. I almost expect them to touch heads, smelling each other, exchanging news. Rob's poster attracts a stream of men and women interested in primroses or in hawkmoths. Rob Raguso vibrates with enthusiasm. His dark eyes gleam. He has just gotten a new job at a university where he will teach some but where he will mostly do research, believing that all questions add up to something larger, believing that this is how he is meant to be in the world. A woman stops and reads his poster. She, too, is interested in floral evolution. She, too, has worked with floral scent. She and Rob begin to dance.
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