Yeast heaters

Yeast living in the nectar of flowering plants can act as miniature space heaters for winter-blooming flowers, suggesting the microorganisms may be a third player in what scientists have traditionally viewed as a two-part plant-pollinator relationship, according to a study published online today (February 9) in Proceedings of the Royal Society B. Helleborus foetidusImage: Carlos Herrera"It's pretty exciting," said evolutionary microbiologist linkurl:André Lachance;http://www.uwo.ca/biology/Faculty/lachance/index.htm of the University of West Ontario, who was not involved in the research. "Some plants have mechanisms to produce heat on their own," such as harnessing solar radiation, he said, but the finding that "yeasts [are] producing heat in flowers, that's entirely new." Many species of yeast live in the nectar of hundreds of different plant species. By metabolizing the sugar it contains, the yeast drain the value of the nectar that bees and other pollinators receive as a reward for their pollen-dispersal services. The plants and pollinators may also benefit from the squatting yeast, but how yeast affect the plants' physiology and relationship with their pollinators has not been well studied. The heat generated during yeast metabolism, for example, may warm the flowers and attract pollinators, thereby increasing the plants' reproductive success. In addition, heat generated by yeast may boost pollen tube growth, fruit development, and seed size, which can further enhance plant reproduction. To determine if the yeast living inside flowers increase flower temperatures, ecologist Carlos Herrera and Maria Pozo of the linkurl:Doñana Biological Station;http://www.ebd.csic.es/ in Spain measured the temperatures of the winter-blooming Helleborus foetidus in southeastern Spain with and without cultures of yeast living inside their flowers. Because yeast are introduced to the plants by foraging bumblebees, simply preventing pollinator visitation by bagging the flowers kept some flowers yeast-free, while others were inoculated naturally. The researchers also injected some of the bagged flowers with a liquid culture of Metschnikowia reukaufii -- the most commonly found yeast in H. foetidus -- to artificially introduce a single yeast species. Of all the flowers, those with yeast were significantly warmer than those with no yeast in their nectar, and up to 6 or 7 degrees Celsius warmer than the ambient air temperatures. "The results of this study are surprising from an ecologist's viewpoint," plant ecologist Clara de Vega, a postdoc in Herrera's lab who did not participate in the study, wrote in an email to The Scientist. "Yeast could be turning what was thought to be a binary association (plant-pollinator) into an ecological trio (plant-yeast-pollinator)." The warming effect is likely to benefit all three organisms in the trio, said Lachance. "The flower benefits by being pollinated, the insects benefit by increasing their nutrition, and the yeast benefit by reproducing and spreading their genes. It's a three way mutualism." However, the payoffs of these interactions likely depend on the "ecological context," Herrera noted in an email to The Scientist. "Under low ambient temperature conditions, as in cloudy cool days, floral warming will presumably have beneficial effects to plants," he explained. On warmer days, however, the yeast may provide no such benefit, merely exploiting the plant-pollinator mutualism for their own good, he said -- "'eating up' the sugar in nectar that was aimed as a reward to pollinators." Herrera and his team are currently working with captive bumblebee colonies to assess how yeast affect pollinator behavior. One the one hand, bumblebees prefer nectar with higher sugar content, but they also prefer warmer flowers, he said. Furthermore, the yeast may have other effects on the flower, such as altering the smell or taste of the nectar. In addition, "if the yeast [are] a primary agent of heat, how does it do it?" Lachance asked. "The biochemistry is understood" -- having been studied extensively in the classic yeast model, baker's yeast -- "but the actual ecology of it [is not]." Unanswered questions include how much heat is produced by the yeast, and how fast the heat is dissipated by the plant. To further understand the energetics of the system, it will be interesting "to test whether there is some element in the floral architecture of Helleborus foetidus that enhances warming," Herrera added. **__Related stories:__***linkurl:Bee calamity clarified;http://www.the-scientist.com/blog/display/55919/ [24th August 2009]*linkurl:Cross-Pollination;http://www.the-scientist.com/article/display/55720/ [June 2009]*linkurl:Making sense of floral scents;http://www.the-scientist.com/blog/display/54980/ [28th August 2008]

Yeast heaters

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