When Plants Are Cut, They Bleed, Sort Of
Find out what happens when a plant is cut. It's some crazy stuff. →
When humans suffer a cut, our blood coagulates into a gel, attempting to create a semi-solid blockage so that we don't lose more blood than necessary.
The field of plant "intelligence," that word being a not-really-correct shorthand for how plants interpret and respond to their environments, has lately been exploding. We understand more and more about the intricate, efficient ways plants react to the world - did you know that plants can tell when they're being eaten? And that they don't much like it?
Plants also have a version of blood clotting, but the specifics of how it works have long been a mystery. When a plant is cut, it seems able to direct nutrients and minerals around the cut, sealing the cut area off and protecting healthier parts of the plant. It's not quite the self-healing mechanism that animals have, but more like a cauterization: it stops the bleeding.
On the other hand ... plants don't have blood, and don't bleed.
What they do instead, according to a new study from researchers at the University of Delaware, is open and close channels between cells. Animal cells are highly mobile; blood flows, skin cells grow and move towards the surface to replace older cells, that kind of thing. Plant cells, not so much: They're more like coral, glued onto each other to form a structure and then remaining motionless.
So given that plant cells can't move, there has to be some way to transmit all kinds of stuff from one part of the plant to another: nutrients to make the plant grow, minerals to keep it healthy, various communications to let it know if it's in trouble. That stuff moves from cell to cell through little passages in the cell walls known as plasmodesmata. (The singular, confusingly, is plasmodesma.)
The University of Delaware researchers looked hard at the way these plasmodesmata are guarded. The guards of these little passages is a substance called callose, a glucose-like deposit the plant manufactures. Callose levels can go up and down, a process not previously very well understood: Basically, if there's a lot of callose, the plasmodesmata passages are blocked, and nothing can get through. If there's not very much callose, the plasmodesmata are open.
The researchers discovered that the amount of callose at any given part of the plant can be controlled by a few enzymes in response to all kinds of stimuli. If a plant is infected with some sort of bacteria, it knows that bacteria can travel through the plasmodesmata passages: quick, callose, deploy! Block the bacteria!
And if there's a physical problem, like, say, a cut, the callose also builds up to keep the plant from trying to fire off nutrients into a part of the plant that won't survive. Interestingly, the callose immediately adjacent to a plant's cut, but in a healthy part of the plant, will drop significantly, allowing that part of the plant to grow faster.
Understanding the surprisingly dynamic ways plants respond to stress is fun and interesting, but also potentially very valuable to farmers. The plant has a natural defense when it's sick, and also a natural boosting ability. Could that be used to keep plants healthy and maybe even grow them faster, by reducing callose levels to certain parts of the plant? Who knows. But it's certainly a possibility.
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Seen here close-up under a dissecting microscope, the flowering plant
is the oldest known existing species of petal-bearing plants on Earth. Now in a series of reports published today in the journal Science, molecular geneticists have unlocked the genomic secrets of
, and with it clues as to why flowers display such successful genetic diversity.
's genes were distinct from those of non-flowering plants. In its mitochondrial DNA, which tends to change less than nuclear DNA,
showed a shared affiliation with mosses and green algae. Biologist Danny W. Rice of Indiana University and his team hypothesize that wounded
plants obtained the shared mitochondrial genomes as a result of horizontal gene transfer between these other organisms it was living in close proximity with millions of years ago. Here,
genomic DNA is shown in blue, chloroplast DNA in green, and mitochondrial DNA in red.
Indeed, the team discovered that
's mitochondrial genome provides the largest example of horizontal gene transfer – the acquisition of foreign genes from other species – in any organism. Shown here are male flowers of
The Indiana University team -- working with biologists from the U.S. Department of Energy, Penn State University, and the Institute of Research for Development in New Caledonia -- showed for the first time that an organelle genome has captured an entire foreign genome, in this case, four of them: three green algae and one moss. It is also the first description of a land plant acquiring genes from green algae. Shown here are female flowers of
mitochondrial genome is like the old lady in the song who swallows a fly, and then a spider, a bird, a cat, and so on, all the way to a horse, at which point, finally, "she's dead of course," said co-author of the study Jeff Palmer, a Distinguished Professor in the Indiana University Bloomington College of Arts and Sciences' Department of Biology. Shown here are
female flowers and fruits.
genome has swallowed whole mitochondrial genomes, of varying sizes, from a broad range of land plants and green algae. But instead of bursting from all this extra, mostly useless DNA, or purging the DNA, it's held on to it for tens of millions of years. So you can think of this genome as a constipated glutton, that is, a glutton that has swallowed whole genomes from other plants and algae and also retained them in remarkably intact form for eons," said Palmer in a press release. Shown here are
View from the summit of Mt. Aoupine, New Caledonia. The flowering
, whose mitochondrial genome is amazingly rich in foreign genes and even genomes, is endemic to the island of New Caledonia. The research on
shows "compelling evidence that mitochondrial fusion is the driving force for mitochondrial gene transfer and that incompatibility in the mechanism of mitochondrial fusion between different phyla – plants versus animals or fungi – provides the major barrier to unconstrained mitochondrial 'sex' across the evolutionary tree of life," said Palmer.
The southwest-Australian Christmas tree,
, which parasitizes the roots of grasses to obtain water and minerals. This parasite belongs to the group of parasitic plants (Santalales) from which the
mitochondrial genome has captured many foreign genes by horizontal gene transfer.
A parasitic flowering plant (
) blooming in New Caledonia from its epicortical roots, which, like mistletoe, grow along the branch of its host tree. This parasite belongs to the same group of parasitic plants (Santalales) from which the
mitochondrial genome has captured many foreign genes.
A parasitic flowering plant (
) emerging from the ground to flower. This plant parasitizes the roots of other flowering plants and belongs to the group of parasitic plants (Santalales) from which the
mitochondrial genome has captured many foreign genes. Picture taken in New Caledonia, the South Pacific island on which both