How crafty is your plant?

Allelopathy is the release of organic chemicals that help or harm plants growing nearby by a plant. What is really interesting is that these allelochemicals are not used by the plant except to influence other plants.

One of the best known cases of this happens with walnut trees. Walnut trees produce hydojuglone. When hydrojuglone is exposed to oxygen it causes anything from wilting to death in plants near the walnut tree.

While digging around the net learning about allelopathy I started to wonder just how smart plants might be and stumbled upon: Aspects of Plant Intelligence a paper published in the Annals of Botany in 2003

The more we learn about plants and the chemical signaling inside and sent out from the plant, the less like vegetables they appear to be.

The paper is very readable, you won’t need a science degree to dig through it and worth a read. You’ll not look at your plants the same way again.

See also:
The secret language of plants
Chemical war: How plants starve bugs

Blue is for leaves, red is for flowers

The tip of the leaf of a plant senses blue light and signals the plant to grow in the direction of the blue light.

The red glow of a sunset is what signals the plant when it is time to bloom. A plant kept in a dark closet can be signaled to flower with just a short flash of red light.

Plants use both blue and red light to feed themselves but slightly favor red.

Plants appear mostly green because they are reflecting most of the green light that hits them, it doesn’t get used by the plant.

If your plant is not growing well, try adding more blue light. If you’re not getting flowers try more red light.

Plants release scents to warn other plants of insect attacks

Plants release hundreds of volatile chemicals ( scents ) to both attract and repel insects.

Cabbage butterflies lay their eggs in cabbage. In response the cabbage plants release a scent that attracts two species of moths that feed on cabbage butterflies.

When insects lay eggs in the plant they damage the plant, this damage triggers the plant to release chemicals to protect it from the insects about to hatch and feed on the plant. Some chemicals kill the plant tissue around the egg causing the egg to fall off the plant. Other chemicals attract predators of the insect eggs.

Cabbage family plants make glucosinolate from sugar giving them their well known bitter flavor. This is what acts to fight cancer in people who eat these plants.

Plants containing glucosinolate can be used keep pests away from other crops.Some insects have adapted to be able to deflect the toxins and use these plants for feeding and egg laying.

Plants cry for help when attack expected
PLOS One, Plant volatiles induced by herbivore egg deposition affect insects of different trophic levels

Why do plants with too little light get leggy?

In short: Plants measure the amount of red and blue light reaching their leaves. When that light falls to too low of a level the plant releases hormones which allow it to shoot up past the plants around it so it may get more light.


Plants grow in dense vegetations at the risk of being out-competed by neighbors. To increase their competitive power, plants display adaptive responses, such as rapid shoot elongation (shade avoidance) to consolidate light capture.

These responses are induced upon detection of proximate neighbors through perception of the reduced ratio between red (R) and far-red (FR) light that is typical for dense vegetations. The plant hormone auxin is a central regulator of plant development and plasticity, but until now it has been unknown how auxin transport is controlled to regulate shade-avoidance responses.

Here, we show that low R:FR detection changes the cellular location of the PIN-FORMED 3 (PIN3) protein, a regulator of auxin efflux, in Arabidopsis seedlings. As a result, auxin levels in the elongating hypocotyls are increased under low R:FR. Seedlings of the pin3-3 mutant lack this low R:FR-induced increase of endogenous auxin in the hypocotyl and, accordingly, have no elongation response to low R:FR.

We hypothesize that low R:FR-induced stimulation of auxin biosynthesis drives the regulation of PIN3, thus allowing shade avoidance to occur. The adaptive significance of PIN3-mediated control of shade-avoidance is shown in plant competition studies. It was found that pin3 mutants are outcompeted by wild-type neighbors who suppress fitness of pin3-3 by 40%. We conclude that low R:FR modulates the auxin distribution by a change in the cellular location of PIN3, and that this control can be of great importance for plants growing in dense vegetations. paper

Tricky lily lures flies

Scientists from the Max Planck Institute for Chemical Ecology in Jena, Germany, have solved a case of fraud that has been pending for 40 million years. Arum palaestinum, also called the Solomon’s lily, attracts drosophilids (vinegar flies) as pollinators by emitting odor molecules that resemble those produced during alcoholic fermentation of rotting fruit initiated by yeast. The plant accomplishes the illusion of yeast simply by producing six chemicals that – together in a specific mix – create the impression of fermentation in the fly brain. The produced volatiles include two chemicals which are very rarely encountered in plants but are typical of wine and vinegar – actually byproducts of yeast activity. The scientists showed that the lily’s fragrance targets a deeply conserved neuronal pathway specifically tuned to yeast odors. Thus, the Solomon’s Lily is exploiting a million-year-old instinct in flies for its own purposes. (Current Biology, DOI 10.1016/j.cub.2010.09.033, October 7, 2010)

The genus Drosophila – vinegar flies – consists of many species that feed on a variety of sources ranging from fruit to bacterial layers on certain tropical land crab species. For most drosophilids, yeast is the main food. Their antennae and antennal lobes, the
first brain region that receives input from the olfactory sensory neurons, are accordingly specialized in perceiving odor molecules typically emitted by growing yeast. The smallest concentrations are sufficient to lead vinegar flies to their food source.

Many flowering plants depend on insect pollinators; they ensure that offspring are produced and guarantee genetic variability. Flowers use colorful petals and odor bouquets to attract them. Although often pollination service is rewarded with sweet nectar, Arum palaestinum tricks its pollinators. The plant, also called the Solomon’s Lily, produces an odor in its violet-black flowers that to a human nose is most similar to a fruity wine. It was obvious that the plant attracts pollinators with this odor, namely vinegar flies. But unlike other flowers, Arum palaestinum does not give a reward in form of nectar; in fact, flies are trapped in the flower overnight and not released until the next day.

Johannes Stökl and Marcus Stensmyr have not only collected and analyzed this odor, but also examined and identified the drosophilid species trapped in the plant. Together with behavioral biologist Markus Knaden, they studied the reactions of the insects to different odor molecules. In addition, their colleagues Silke Sachse and Antonia Strutz performed neurophysiological measurements on the flies. The studies provided interesting results: Arum palaestinum attracts an average of 140 flies per plant, mainly flies from eight different Drosophila species including the well-known laboratory work horse and kitchen nuisance Drosophila melanogaster. Fourteen chemical compounds that caused the flies’ antennae to respond were emitted by the plant. To test these reactions, Johannes Stökl measured and recorded the action potentials in the antennae of the insects. Chemical analysis of the odor compounds released by the plants showed that most were esters.

“The most remarkable odors of the bouquet were 2,3-butandiol acetate and acetoin acetate,” explains Marcus Stensmyr, leader of the study. Interestingly, these molecules are not contained in the bouquets of flowering plants, but are characteristic of vinegar, especially aceto balsamico, and wine – or, in other words: yeast fermentation products. Those two compounds as well as four more that also emerge during yeast fermentation showed the strongest and most stable signals in the electroantennograms.

In neurophysiological experiments, the flies were exposed to natural odor bouquets, such as the smells of rotting peaches or bananas as well as Lambrusco (red wine) and aceto balsamico (vinegar). The respective electroantennograms strikingly resembled the recordings from flies that had been exposed to the lily odor, suggesting that to a fly, these odors have a most similar smell.
“The flies are unable to distinguish the lily from rotting fruit – they are deceived by the lily because it imitates the yeasty odor although it does not offer yeast as food,” says Johannes Stökl. The insects’ involuntary pollination service is not even rewarded; in fact, just the opposite is true: the flies are trapped in the flower until it opens again after 24 hours – and they stay hungry.

Using transgenic flies expressing a calcium sensitive activity reporter, Silke Sachse, leader of the Functional Imaging Group, and her PhD student Antonia Strutz, were able to trace the activity of the yeast odor stimulants in the brains of the flies. This functional imaging technology helped to demonstrate that eleven different odorant receptors were activated. Because different drosophilid species were deceived by the Solomon’s Lily, it seemed likely that evolutionary ancient odorant receptors were among the activated ones, and this turned out to be the case. “The sequence of two of the odorant receptors, namely Or42b and Or92a, is highly conserved. These genes
are likely to have a critical function as “yeast detectors” across most, if not all drosophilid flies,” explains Bill Hansson, director at the institute.

Is keeping a Solomon’s lily now the ultimate solution to rid your kitchen of flies? “Well, since they only flower once per year, and then only for a few hours, a cup of vinegar is still a better option. However, during the hours it flowers, I can assure you there will be no flies left in your kitchen!” says Marcus Stensmyr. [JWK, AO]

Original Publication:
Johannes Stökl, Antonia Strutz, Amots Dafni, Ales Svatos, Jan Doubsky, Markus Knaden, Silke Sachse, Bill S. Hansson, Marcus C. Stensmyr: A deceptive pollination system targeting drosophilids through olfactory mimicry of yeast. Current Biology, October 7, 2010, DOI 10.1016/j.cub.2010.09.033.

Anise flowers heat up to attract insects

Could a “hot” flower attract pollinators by serving as a reward in a plant-pollinator mutualism? Many flowering plants produce nectar and pollen as rewards in exchange for pollination services by insects and other animals. Interestingly, however, a few plants have flowers that also produce heat metabolically — so what is the adaptive function of this flower heating?

Susanne Renner from the University of Munich, Germany and Shi-Xiao Luo from the South China Botanical Garden, along with collaborators from China and Taiwan, were interested in determining whether there was a connection between the heating of flowers and the pollination services of flies in an ancient Chinese family, Schisandraceae. Although this family is quite widespread, including Asia and the Americas, its center of diversity is in China, which is one reason Renner and colleagues chose to examine this question in two Chinese Illicium species. Their novel findings are published in the July issue of the American Journal of Botany.

“A few flowers, usually ones pollinated by beetles or flies, produce heat to help scent emission or to create especially attractive egg laying sites for their pollinators,” Renner commented. “Usually such heating occurs only during flowering, simultaneous with the release of pollen and stigma receptivity. We discovered that in an Asian Illicium species, flowers reach their highest temperatures during early fruit development, and experiments revealed that this is for the exclusive benefit of the pollinator’s larvae, which develop in the spent flowers.” Read more, When flowers turn up the heat

Trees retaliate when their fig wasps don’t service them

It would seem trees are not as dumb as they first appear. When wasps try to lay eggs from outside the flower with out pollinating the flower, instead of inside the flower while spreading pollen the trees drop the fruit containing the baby wasps to death.

While trees often drop unpollinated flowers, they will often hold onto the galls containing the wasps and provide themselves with a future generation of pollinators.

Figs and fig wasps have evolved to help each other out: Fig wasps lay their eggs inside the fruit where the wasp larvae can safely develop, and in return, the wasps pollinate the figs.

But what happens when a wasp lays its eggs but fails to pollinate the fig?

The trees get even by dropping those figs to the ground, killing the baby wasps inside, reports a Cornell University and Smithsonian Tropical Research Institute study published in the Proceedings of the Royal Society B (published online Jan. 13). ( read more read more about tree retaliation )

More information
Download the paper (pdf)