"Ballistic seed dispersal" is not something you see often in plants – and for good reason, perhaps, when you see just what the affectionately called squirting cucumber is capable of. Shunning external helping hands like wind or animals, this cucumber gets it done on its own, shooting a rapid-fire watery jet of liquid and seeds into the air from one end of its elongated, prickly form. And now we know just how it does it.
Oxford University and The University of Manchester researchers have unraveled one of plant life's most curious feats of nature, painstakingly studying this squirting cucumber, scientifically known as Ecballium elaterium. Each cucumber is capable of shooting its pressurized package more than 10 meters (33 ft) from its sessile parent plant.
Mechanical analysis showed that E. elaterium is able to disperse its seeds over a distance of about 250 times the length of the fruit itself.
In nature, most seed dispersal techniques are due to external factors – wind, animals, fire, gravity – but this remarkable little prickly go-getter native to the Mediterranean has found its own way of getting the job done. You have to respect its bodily autonomy.
“Seed dispersal is incredibly important for plant survival and population, and we see a wide range of dispersal strategies across the plant kingdom, each adapted to different ecological needs," said lead researcher Finn Box from The University of Manchester. “This research is the first comprehensive mechanical explanation for how the cucumber plant launches its seeds with remarkable speed and precision – a process almost unheard of in the plant world."
Using high-speed videography, image analysis, lab experiments and mathematical models, the researchers were able to paint a clear picture of how this fascinating explosion occurs. Until now, the driving force behind this unusual and dramatic method of reproduction hasn't been fully understood.
Essentially, as the fruit ripens, fluid is pushed into the stem connecting it to the plant, which results in a stiffening and straightening of the stem. The position of the usually drooping cucumber changes and, combined with intense pressure within the fruit, triggers the forceful explosion as it splits from the stem and spews liquid and seeds over the impressive distance.
The team was able to capture the moment the magic happens by slowing video footage a massive 400 times – or 10,000 frames per second – giving us a glimpse of E. elaterium that we'd never see with our own eyes in nature.
“The explosive launch of the cucumber plant has evolved over generations to help it survive," said Box. "The way that the stem is able to re-position itself to the perfect angle and build enough pressure to maximize spread has been key to help regulate the plant’s population. These mechanisms allow the plant to disperse seeds over a wide area and reduce overcrowding and competition among offspring and other neighboring plants, ensuring a better chance of survival for the next generation.”
However, you wouldn't want to be in the firing line of this watery jet stream – the fruit is packed with poisonous cucurbitacins, as is the plant itself, and can be fatal if it's ingested.
But there's more to this research than just curiosity. It offers a window into the world of plant adaptation, particularly in a time of great change in environments, and has the potential for medical and biotechnology uses, such as helping drug delivery vectors better reach a specific target in the body.
"Uncovering physical mechanisms of seed dispersal is a crucial component in predicting ecological dynamics e.g., the potential for invasive migratory species in a given ecology; in understanding the effects of environmental changes due e.g., to climate change; and, in some cases, in inspiring technologies," the team noted in the study.
The study was published in the journal The Proceedings of the National Academy of Sciences.
Source: University of Manchester