Red light regulates nectar secretion

Sep 27, 2010
Ants of the genus Crematogaster defend a Lima bean plant (Phaseolus lunatus) against an herbivorous insect. Photo: Christian Kost, MPI Chemical Ecology

Flowering plants produce nectar to attract insect pollinators. Some plant species, such as Lima bean, also secrete nectar from so-called extrafloral nectaries to attract ants which in turn fend off herbivores. Scientists of the Max Planck Institute in Jena, Germany, have discovered that the production of extrafloral nectar is light dependent. They have shown that the plants are able not only to distinguish between day and night, but also to adapt their nectar secretion to current light conditions by using a special photoreceptor, the phytochrome.

Phytochrome probably influences the regulation of a special enzyme that binds the jasmonic acid (JA) to the amino acid isoleucine (Ile). The emerging JA-Ile molecule affects the secretion of extrafloral nectar in such a way that the plant's defense against herbivores is most effective whenever herbivory is most likely - or, more precisely, during the day. (PNAS Early Edition)

Plants have to continuously defend themselves against herbivores to survive and reproduce. They do this directly by producing toxic substances, such as nicotine, or indirectly, by calling their enemies' enemies for help. An example of an indirect defense is the release of volatile substances that attract predatory or parasitoids and guide them to their prey; for example, predatory wasps or bugs are led to a caterpillar that is feeding on a plant.

Another indirect defense is the secretion of extrafloral nectar from special leaf organs. In this way Lima beans attract ants that not only enjoy the sweet nectar but also defend the plant against herbivores. Scientists in the Department of Bioorganic Chemistry study this "sweet" defense mechanism. Radhika Venkatesan, a PhD student from India, completed a series of experiments on this topic and tested whether nectar secretion in Lima beans is light dependent. "After all, nectar consists mainly of sugars, and sugars are primary products in the process of photosynthesis - which depends on light," notes the scientist. In the course of her studies, which were published in the Early Edition of the "Proceedings of the National Academy of Sciences USA" last week, she came across an old acquaintance in plant research - the so-called phytochrome. Plants contain phytochromes as photoreceptors in their leaves, which is the reason why phytochromes are sometimes called "the eye of the plant."

"Not the light intensity, but light quality or composition plays a decisive role in regulating nectar production in Lima bean," says Wilhelm Boland, director of the Max Planck Institute. As he explains, the phytochrome in the plant absorbs that enables the plant to distinguish the diurnal and seasonal variation of sunlight quality. Radhika Venkatesan's experiments are the first to demonstrate that plants also use the phytochrome system to set up their lines of defense effectively and economically.

The hormone jasmonic acid is known as an important signal that plants produce after wounding by herbivores. It also plays a central role in regulating nectar secretion. The scientists have discovered that phytochrome-mediated light regulation has a significant impact on the signaling effect of jasmonic acid: Free jasmonic acid inhibits nectar secretion in the dark but stimulates its production in the light. Radhika Venkatesan found the key to this light-regulated behavior in a reaction that binds jasmonic acid to the amino acid isoleucine. The emerging conjugate JA-Ile is a signal molecule already known from other studies. For the first time, it has been identified as the actual elicitor of nectar secretion. Additional experiments have confirmed that nectar production doesn't increase if binding of JA and isoleucine is prohibited by an inhibitor. If plants are wounded in the dark to stimulate JA production, JA-Ile is produced only in those leaves that were previously exposed to red light.

Explore further: Male monkey filmed caring for dying mate (w/ Video)

More information: Venkatesan Radhika, Christian Kost, Axel Mithöfer, Wilhelm Boland (2010). Regulation of extrafloral nectar secretion by jasmonates in lima bean is light dependent. Proceedings of the National Academy of Sciences USA, Early Edition, 20. September 2010, DOI: 10.1073/pnas.1009007107

Provided by Max Planck Institute

5 /5 (1 vote)

Related Stories

Plant hormone regulates nectar production

Mar 29, 2010

Rapeseed is one of the ten most important agricultural crops worldwide. In spring, the rapeseed fields with their bright yellow flowers are widely visible: this year winter rapeseed is being cultivated on ...

Nectar is not a simple soft drink

Feb 27, 2007

The sugar-containing nectar secreted by plants and consumed by pollinators shares a number of similarities to fitness drinks, including ingredients such as amino acids and vitamins. In addition to these components, nectar ...

Honeybees not fooled by cheating flowers

Apr 15, 2009

(PhysOrg.com) -- Flowers that want to cheat pollinators by not paying them for their services shouldn’t try to lure them in using floral scents, scientists at Newcastle University have shown.

Acacias use ants to guard flowers

Jan 04, 2010

(PhysOrg.com) -- Research by Dr Nigel Raine, Senior Lecturer in Animal Behaviour at Royal Holloway, University of London has revealed how a special plant-ant relationship thrives on give and take for mutual ...

Are bees also addicted to caffeine and nicotine?

Feb 10, 2010

A study carried out at the University of Haifa has found that bees prefer nectar with a small concentration of caffeine and nicotine over nectar that does not comprise these substances at all. "This could ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Skeptic_Heretic
not rated yet Sep 27, 2010
This is something that's been well understood for a long, long time. I'm surprised to find this is the content of the research. Is the abstract wrong?

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.