Night blooms

Plants change flowering traits to mark friend from foe  

By Tiasa Adhya
Published: Wednesday 31 March 2010

imageDeciding  between a friend and foe can become challenging. In plants, this dilemma takes a worse dimension because both the friend and foe are the same sometimes.

Scientists from the Max Planck Institute of Chemical Ecology in Germany demonstrated how tobacco plants resolve this conflict with a novel change in flowering traits. When national forests in the southwestern US catch fire, the nearby tobacco plantations get affected too. Night-flowering tobacco blooms only after fires. The opening buds release benzyl acetone (BA) to attract hawkmoth pollinators.

Adult moths lay eggs on the leaves. The larvae hatch out on the leaves which they devour while letting loose a burst of jasmonic acid, a plant hormone. This initiates a chain of defence mechanisms: the plants are stimulated to produce flowers with reduced BA emissions that open in the morning and are pollinated by day-active hummingbirds. The plant can, thus, escape further attack while being pollinated.

In 2007 there was an outbreak of hawkmoth larvae in a native tobacco population. The authors of the study observed heavily infested tobacco plants produced an unusual number of flowers at dawn. To prove caterpillar damage was responsible for this shift, they infected another batch of plants. After eight days, 35 per cent of the buds opened in the morning. The scientists then genetically manipulated the plants and stopped BA emissions.

“Decreased BA emissions reduced hawkmoth visitation,” said Ian Baldwin, who led the study published in Current Biology on January 21, 2010. Nor did the dawn see more flowers bloom. “Production of morning flowers requires methyl-jasmonate signalling caused by elicitors present in the caterpillar’s saliva,” explained Danny Kessler, lead author.

Although the experiment proves the plant’s ability to recognize the pollinator for what it is worth, it does not explain the why in it.
Why flower at night if morning bloom reduces chances of attack and attracts good pollinators like hummingbirds? Said plant scientist Nathan Brown from the University of Oxford: “Hummingbirds may not be as reliable as hawkmoths. The moths are attracted by the flowers’ scent over great distances. The birds are restricted by requirements like location of nest sites.” So can crop plants use this to ward off pests? “Experiments are on. If we decide to incorporate genes into a plant to strengthen its defences, we must study possible negative consequences,” said Rebecca Irwin, plant scientist from Dartmouth University in USA.

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