Smelling nice is a luxury for humans. Skipping deodorant isn’t really going to hurt us, although it may bother whomever we stand next to on the bus. For flowering plants, emitting a pleasant, or maybe just strong, smell isn’t a choice. Beyond helping to attract pollinators and signal growth cycles, researchers have learned that flowers must get their attractive odors into the air, because holding them inside would be fatal. Now a series of experiments has figured out exactly how flowers keep themselves safe from their own delightful fragrances.
The gases that we usually refer to as a flower’s fragrance are technically known as “volatile organic compounds,” or simply volatiles. While volatiles tickle our smell receptors when they enter our nose, they’re toxic to the plant cells that produce them. The realization of this critical fact forced scientists to rethink their original model of how flowers release volatiles so animals can smell them, which stated that the fragrant molecules passively diffused through cell walls into the atmosphere. However, that process would actually be much to slow for the health of the plant, prompting further investigation into how plant cells send their scents into the air.
Isolating petunias’ volatile pump
The first part of the study looked at petunias, as they release very few volatiles as buds, but really pour them out when the flowers have bloomed. The contrast between these two phases allowed researchers to look for genes that were more or less active at either time, revealing which genes and therefore molecular mechanisms were being cranked up to push more volatiles out of the flower’s cells. The answer was a type of ATP-binding cassette transporter, which flowers use to not only move volatiles, but other compounds like a leaf’s wax coating as well. The volatiles were actually moved out of the cell thanks to combinations of hydrophilic, or water-attracting, and hydrophobic, or water-repelling molecules. The volatiles themselves are also hydrophobic, and so the right combination of similar and contrasting molecules could effectively shove the volatiles out of the cell after they were produced.
To test this hypothesis, researchers manipulated the transporter genes in petunias and other plants. In flowers that presumably relied on these genes to eject volatiles, the genes were suppressed, leading to less fragrant blooms and eventually more dead cells thanks to a build-up of volatiles. On the flip side, the transporter genes were added to non-flowering tobacco plants, then dosed those plants with potentially dangerous volatiles. As expected, tobacco that had the volatile transporter genes could keep its cells alive by pumping out volatiles. Normal tobacco plants that lacked this extra mechanism couldn’t cope, and died like the genetically modified petunias mentioned earlier. Thanks to these experiments, scientists now know exactly how flowers survive their own scents, and may be able to further control volatile output in the future.
Source: Stopping to smell the roses? You’re inhaling flower farts by Abrahim El Gamal, Massive Science