Five weird and wonderful types of pollination

There’s more to pollination than bees. Plants are sneaky. They’ll use anyone or anything to get what they want. From treats to treachery and imprisonment, here are some of their most uncommon pollination tricks.

Pollen blast

Axinaea affinis

A flower of Axinaea affinis, showing “bellows” style stamens. Image source: Dellinger et al., 2014, Current Biology.

Birds passing this Axinaea flower are in for a treat. Its stamens (pollen-producing organs) are attached to what looks like a delicious yellow berry. These eye-catching appendages are full of sugar, so the bird hops down to peck off a tasty treat.

Of course, the plant has a reason for producing these energetically expensive snacks. These appendages are made of spongy material, full of air. The black sticks are the anthers where the pollen is produced. In this flower they’re hollow with a pore at the far end.

When a bird’s beak clamps down on the spongy appendages, the air inside is squeezed out through the anther like a bellows, blasting the bird with a face-full of pollen, which is carried to the next plant when the bird moves on.

 

Imprisoning pollinators

The giant Amazon water lily (Victoria amazonica) is an amazing plant. Its leaves can reach over 2.5 metres across and its beautiful flowers are over 30cm wide, but they live for just two days.

On its first evening the magnificent bloom opens, revealing white petals scented like pineapple. Beetles are attracted to the flower not just for its fragrance, but for the heat that the flower provides; around 10°C higher than the surrounding air. The flowers are female on the first night, and as the beetles enter they transfer any pollen they’re carrying onto the stigma.

In the morning the flower gets sneaky, trapping the basking beetles inside.

 

During the day the lily flower turns pink and becomes male, showering the scrabbling beetles inside with pollen. On the second evening, the flower opens once more, this time without scent or heat. The pollen-dusted beetles leave to search for another white flower, and the pollination continues.

 

Cologne for bees

Male_Euglossa_sp

A beautiful male Euglossa bee. Image from Wikipedia

The bucket orchids (Coryanthes sp.) produce aromatic oils for one purpose; it’s cologne for bees. Males euglossid bees collect the esters and other fragrant chemicals from the flower to impress the ladies, but in their excitement and jostling they often fall into the water-filled bucket of the flower. Their wet wings and the slippery sides make their escape almost impossible, except through an escape tunnel with bee-sized footholds. Handy.

You can see the escape spout in this Coryanthes alborosea flower on the left. Image from Wikipedia.

You can see the escape spout in this Coryanthes alborosea flower on the left. Image from Wikipedia.

The escape tunnel of bucket orchids is very narrow. Bees take around 30 minutes to carefully climb out to safety, but not before being adorned with a pollinium, an aggregated mass of pollen grains. On their next dip into a bucket orchid, the pollinium rubs off onto the stigma inside the entrance to the escape tunnel.

The scent droplets produced by the plant dry up by the time the bees have escaped the flower, which encourages the bee to visit another flower the next time it wants to apply cologne.

 

Fatal figs

There are around 750-850 species of figs (Ficus), each with its own species of pollinating fig wasp. Each is totally dependent on the other for successful reproduction. I’ll explain, but first, step away from any fig-based foods you might be eating.

A cross section of a fig

A cross section of a fig. Image from Wikipedia.

A fig fruit is a synconium, a bulbous stem containing hundreds or thousands of flowers, completely enclosed but for a narrow ostiole (hole) that only allows a specific species of fig wasp to enter. Female fig wasps crawl into the ostiole when they are ready to lay their eggs. The passage is so narrow that the wasp usually loses its wings and antennae, so she is doomed to die within.

(Some of the figs we eat come from sterile species that don’t require wasps. Others, however, do have… deceased occupants).

The fig contains three types of flowers; male, short female and long female. The wasp lays its eggs in the short female flowers, but it can’t reach down into the base of the longer females. Instead, these flowers are pollinated with the pollen the adult female carried from her original host fig and develop into seeds.

fig with wasps

A fig with its wasp inhabitants. Image from Wikipedia

When the larvae hatch they feed on their host short female flower until mature, receiving a coating of pollen from the male flowers as they move within the fig. The adult males are wingless and have two important jobs to do. First, they mate with the females. Next, they chew a hole out of the fig through which the females can escape. Then they die.

The females, coated with pollen, then emerge from the fig to find a new place to lay their eggs.

 

Tidal transfers

Zostera_marina

Zostera marina‘s tiny flowers release and capture pollen underwater. Image source: Wikipedia

We’ve seen plants trick-or-treating animals into carrying their pollen, but what happens when a plant spends its entire life underwater?

Zostera (eelgrass) is a seagrass, a true flowering plant. It employs a little known type of pollen dispersal called hydrophily. Its tiny male flowers release streams of pollen into the surrounding water, which have a few special adaptations for life under the sea.

It takes time to find another receptive flower without dedicated pollinator-transport, so eelgrass pollen has the same density as water, allowing it to drift in the current for days without floating or sinking.

Zostera pollen is elongated. While spherical pollen must be directly upstream of the female flower to pollinate it, longer thread-like pollen grains can be caught in the flow and eddies of water around the plant and eventually swirl into place on the female flower.

 

Over to you

Competition for pollinators has led to plants exploiting a huge range of animals, as well as wind and water. Do you know of any weird and wonderful kinds of pollination? Let me know in the comments below, or message me on Twitter @JoseSci!

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Arabidopsis, the darling of plant science

arabidopsis

Arabidopsis thaliana, the lab rat of plants

Plant scientists are obsessed with a little weed called Arabidopsis.

On the surface it’s a strange plant to study; it’s not grown for food nor to feed animals, it’s not ecologically important and its flowers are, frankly, boring. Yet tens of thousands of researchers around the world dedicate their careers to discovering everything there is to know about thale cress, Arabidopsis thaliana.

This little weed is more than it seems. Like rats, E. coli and fruit flies, Arabidopsis is a model organism. Scientists study model organisms to learn their basic biology, which can be extrapolated into other related species. Arabidopsis can tell us a lot about crop plants, many of which are notoriously difficult to study. It’s even given us an insight into human diseases!

What makes Arabidopsis a good model plant?

Arabidopsis is a weed, which is great for research because it’ll pretty much grow anywhere, from soil to Petri dishes to liquid nutrient solutions. The mature plants are only about 5-10cm in diameter, so you can grow hundreds of them in a typical growth chamber. Best of all, it’s fast growing, going from seed to (irritatingly small) seed in just 6 weeks.

arabseeds

Arabidopsis seeds are tiny!

What really separates Arabidopsis from the crowd is its tiny genome. It has around 27,500 genes encoded within a genome of 125 million bases (letters) of DNA. Contrast this with the huge genomes of crop plants like barley (30,000 genes, 5.1 billion bases) and wheat (96,000 genes, 17.1 billion bases) and it’s easy to understand how Arabidopsis was the first plant to have its genome sequenced, way back in 2000 (a year before the Human Genome Project was completed). Since then, fantastic genetic resources have been developed in Arabidopsis, leading to a revolution in plant science.

Arabidopsis’ impact

By deciding to focus on Arabidopsis, scientists around the world were able to share knowledge and rapidly build upon new ideas. Many people, including myself, believe that this had led to a much broader and deeper understanding of plant biology than we could ever have achieved otherwise.

One way to understand the function of a gene is to stop it from working properly and look at the effect on the plant. The Arabidopsis genome sequence has allowed scientists to develop huge libraries of “mutants”, plants deficient in every single known gene. We knew the basic processes of plants from work done on crops over 100 years ago, but didn’t really understand the details. By working backwards from the mutants, we are able to discover which genes are responsible.

dna alignment

Genes from different species have some changes. The less closely related they are, the more different they are likely to be. Image produced in ApE.

The next stage is to translate the knowledge gained in weedy little Arabidopsis into more useful plants, like crop plants. Even though they look so different, almost all the genes you find in Arabidopsis are present in all flowering plants.

barley

Barley in a growth cabinet

Using the new genome sequences of plants like wheat and barley, it’s easy to search for Arabidopsis genes in these crops. It’s a bit like Google. Stick the letters in and it’ll give you the best matches. Different plants usually have a few changes in the sequence of a gene, but the best match is usually the gene you’re looking for.

From there it’s a matter of silencing the gene you have identified in your chosen crop plant to see if it has the same impact as it did in Arabidopsis. If so, you’ve just improved our understanding of an economically important crop species.

The future of Arabidopsis

Genome sequencing is becoming increasingly cheap and easy. Will we still need Arabidopsis in a world of species-specific genomes? I’d argue yes, at least for a decade or two yet. It is still comparatively very difficult to work with crop plants directly. We don’t yet have full libraries of mutants so Arabidopsis plays a vital first step in gene identification. A full understanding of genes in the model plant would make it a lot more easy to investigate their functions in crop species. Future research areas like synthetic plant biology are predicted to be developed in Arabidopsis too.

Arabidopsis thaliana is the backbone of plant science. Its genetic resources have led to great leaps in our understanding of plant biology, focussing research and enabling translation into crop plants.

Weeds are flowers too, once you get to know them – A. A. Milne