Plants Communicate in Surprising Ways

Hi guys! So by now, most of the scientific community has accepted that plants communicate with one another. This process has best been illustrated through VOC (volatile organic compounds) that plants release into the air during times of danger, but there are a couple other really cool ways that plants communicate besides what chemicals they release into the air. First, I stumbled upon one article with some adorable illustrations that explains how plants use "ultrasonic clicking" sounds to communicate with one another.

Here is the link to that article, if you wanted to understand the mechanism in detail (the clicking is mentioned towards the end):  https://www.npr.org/sections/krulwich/2014/04/29/307981803/plants-talk-plants-listen-here-s-how

Additionally, plants communicate beneath the soil as well. This article explains how plants use those mycorrhizal fungi that we learned about to communicate. The fungi form a network among the roots beneath the soil, facilitating plant-to-plant communication. https://www.the-scientist.com/?articles.view/articleNo/38727/title/Plant-Talk/

Take a look at the articles if they interest you! Or, at least look at the drawings in the first article because they are pretty the most adorable depiction of plants that I have ever seen :)

Pando

When I talked about the Bristlecone Pines being the oldest known single organisms I mentioned that some clonal organisms were much older.

Here's a nice little slideshow about Pando, an 80,000 year old (give or take a few) grove of Quaking Aspen trees in Utah.

The grove which  has about 47,000 stems connected by a single root system  has spread over about 106 acres. The average age of the individual stems is about 130 years.

There's a link to an older article in Discover magazine which has more details on the clone, aging techniques used and some amusing stories:

Since my colleagues and I nominated Pando as the world’s largest organism, he has captured the attention of dozens of newspapers and radio stations across North America, and some of the reactions have been quite funny. Some see Pando as a threat: I received a call from someone asking, Does this giant clone, spreading vegetatively, pose a threat to the people living in southern Utah? 

Plant physiology

One of the leading plant physiology textbooks, called, not surprisingly, Plant Pysiology, by Taiz and Zeiger, has quite a bit of material online including supplementary essays that are perfect for this class. Take a moment to read one, or more...


Essay 4.1, A Brief History of the Study of Water Movement in the Xylem - Hanno Richter, University of Agricultural Sciences, Vienna, and Pierre Cruiziat, PIAF-INRA-UBP, France
(August 2002)

Essay 4.2, The Cohesion–Tension Theory at Work - Pierre Cruiziat, PIAF-INRA-UBP, France, and Hanno Richter, University of Agricultural Sciences, Vienna
(May 2006)

Essay 4.3, How Water Climbs to the Top of a 112 Meter-Tall Tree - George Koch, Northern Arizona University; Stephen Sillett and Gregg Jennings, Humboldt State University; Stephen Davis, Pepperdine University
(May 2006)

Essay 4.4, Cavitation and Refilling - James K. Wheeler and N. Michele Holbrook, Department of Organismic and Evolutionary Biology, Harvard University
(March 2007)

Watermelon

I mentioned that there were several ways to get seedless fruit. There's the 'trick the plant with auxin method' I mentioned in class. There's the 'find a genetic mutant' in the orange example below and when you look into seedless watermelons you find yet another method - create a mule.

The watermelon, or Citrullus lanatus, belongs to a family of climbing vines that include cucumbers and gourds. And like all fruits, they naturally have seeds. The seedless versions are not genetically modified, as some might assume, but are hybrids that have been grown in the United States since the middle of the 20th century. Breeders match the pollen from a diploid plant, one that contains 22 chromosomes per cell, and the flower of a tetraploid plant, which contains 44 chromosomes per cell. The result is a triploid with 33 chromosomes that is incapable of producing seeds. (The tiny white ones you sometimes find are seed coats, where a seed did not mature.) Breeders call it the mule of the watermelon world.

From a Washington Post article, Watermelons: What happened to the seeds?

Etymology

File this under 'more than you wanted to know' but since somebody asked and because I needed to get it straight in my own head here is the answer to whether plant cytokinins are the same as animal cytokines.

Cytokinins are a class of plant growth substances that promote cell division, or cytokinesis from the Greek cyto- (cell) and kinesis (motion, movement), in plants. Kinetin is an example and so is zeatin (pictured, found in maize).

whereas

Cytokines from the Greek cyto-, (cell); and -kinos, (movement) are small cell-signaling protein molecules that are secreted by numerous cells of animal immune systems and are a category of signaling molecules used extensively in intercellular communication. Although they have a rather wide variety of effects they do sometimes trigger differentiation of cells. The most widely known cytokines are the various interferons.

So both animals and plants use signalling molecules to stimulate cell division. In animals the term 'Cytokine' is now used more broadly and encompasses compounds that don't just lead to cell division. As far as I am aware the specific compounds used by animals and plants are completely different - the name Cytokinin/Cytokine describes a function rather than a specific molecular structure so I suppose its possible there is a compound that acts as both a cytokinin in plants and a cytokine in animals. There are about 200 compounds classified as Cytokinins and, I think, a somewhat larger number of Cytokines.

Private life of plants

It's shocking to realize that David Attenborough's Private Life of Plants is now 17 years old but it is still one of the most captivating documentaries on plant growth, morphology, ecology and evolution. Time-lapse photography is used extensively throughout the series and reveals plants as much more complex organisms than we generally think.

There are six episodes in total and they are well worth watching but for the condensed version there are a number of clips available online.

Host sanctions

How do you keep your mutualists 'honest' and prevent them from cheating? If you are a plant and provide Rhizobium bacteria with a nice home and everything it needs what will you do if the Rhizobium turns out to be a deadbeat and doesn't fix enough Nitrogen?  The plant starts turning off the amenities starting with the oxygen...

Explaining mutualistic cooperation between species remains one of the greatest problems for evolutionary biology. Why do symbionts provide costly services to a host, indirectly benefiting
competitors sharing the same individual host? Host monitoring of symbiont performance and the imposition of sanctions on ‘cheats’ could stabilize mutualism. Here we show that soybeans
penalize rhizobia that fail to fix N2 inside their root nodules. We prevented a normally mutualistic rhizobium strain from cooperating (fixing N2) by replacing air with an N2-free atmosphere. A series of experiments at three spatial scales (whole plants, half root systems and individual nodules) demonstrated that forcing non-cooperation (analogous to cheating) decreased the reproductive success of rhizobia by about 50%. Non-invasive monitoring implicated decreased O2 supply as a possible mechanism
for sanctions against cheating rhizobia. More generally, such sanctions by one or both partners may be important in stabilizing a wide range of mutualistic symbioses.

From Host sanctions and the legume–rhizobium mutualism

Seed mega-dormancy

In the news today was the story of Russian scientists who have grown a plant from seeds regenerated from 30,000-year-old frozen fruits, buried by ancient squirrels. This extends the record for seed longevity from a mere 2,000 years to over 30,000 years.

Of course if bad novels have taught me anything about reviving things frozen in ice they've probably also unleashed some ancient evil or at least called down the wrath of ancient squirrels. We all knew the world was going to end in 2012 we just didn't expect ancient squirrels to be involved.

Conifer reproduction videos

Anything that happens in 3-d is just crying out for a video. I showed the second one in class. The first one is very short and a little obvious but I liked the second and third ones a lot. I thought they really helped in visualizing what is going on.

Dessication tolerance

I really like the way that Google helps you to find anything even if you are spectacularly uninspired in finding the right search terms. It took only a single search on 'dry moss' to find I should have been searching on 'dessication tolerance in bryophytes'. Click over to Google Scholar and within 10 seconds of starting the search I've found an interesting, and relatively recent, paper: Desiccation Tolerance in Bryophytes: A Reflection of the Primitive Strategy for Plant Survival in Dehydrating Habitats?
We postulate that desiccation tolerance is a primitive trait, thus mechanisms by which the first land plants achieved tolerance may be reflected in how extant desiccation-tolerant bryophytes survive drying. Evidence is consistent with extant bryophytes employing a tolerance strategy of constitutive cellular protection coupled with induction of a recovery/repair mechanism upon rehydration. 
...
A new phylogenetic analysis suggests that: (i) the basic mechanisms of tolerance seen in modern day bryophytes have changed little from the earliest manifestations of desiccation tolerance in land plants, and (ii) vegetative desiccation tolerance in the early land plants may have evolved from a mechanism present first in spores.

Bog butter

How can you resist an article with the title: Bogosphere: The Strangest Things Pulled Out of Peat Bogs. Don't miss the reference to bog butter.

Sphagnum moss doesn't just live in acidic, nutrient-poor and anoxic  environments it creates acidic, nutrient-poor and anoxic environments thereby shutting out its competitors. From How Sphagnum bogs down other plants, Trends in Ecology and Evolution, 10 270-275:

Recent research on the organo-chemical composition of Sphagnum and on the fate of its litter has further clarified how this plant builds acidic, nutrient-poor, cold and anoxic peat bogs. The bog environment helps Sphagnum to outcompete other plants for light. Its morphology, anatomy, physiology and composition make it an effective ecosystem engineer and at the same time benefit the plant in the short term. This may have facilitated the evolution of the genus.

Competing sinks?

Just because two plants are sufficiently closely related to graft them together doesn't necessarily mean it's a good idea to graft them together.

I must confess that, beyond the novelty value, I don't quite get the amazing tomato-potato.

It seems more sensible from a plant physiology point of view to just plant a tomato next to a potato and have two sets of leaves each providing for one sink rather than have two large sinks competing for the same resources. I initially wondered if maybe the potatoes ripened first and then maybe the tomatoes but the inset photograph seems to show them both ripe together.

Given that tobacco is also in the Solanaceae family I wonder how long it will be before we see tomacco for real? Oh wait someone already did that.

Angel's trumpet poisoning

I looked up some information on the toxic compounds in Brugmansia. The plant contains an unhealthy brew of the alkaloids atropine, scopolamine and hyoscyamine.

Because these can cause hallucinogenic effects they are often ingested by those seeking just such an effect. When combined with alcohol the effects can be rapid. Although the plant can be eaten or smoked the most popular method of ingestion is to prepare a tea from the flowers and seeds.

Unfortunately because the levels of the alkaloids vary widely from season to season it is very easy to overdose and it is estimated that 'teas prepared from as few as 10 flowers could be extremely toxic if not fatal'. Angel's trumpet ingestion produces the classic symptoms of anticholinergic poisoning, so classic that they have their own mnemonic: 'hot as a hare, dry as a bone, blind as a bat, red as a beet and mad as a hatter.'

This paper, Ingestion of Angel's Trumpet: An increasingly Common Source of Toxicity, reports a ten fold increase in Brugmanisa poisoning in Florida in 1994. They failed to locate a particular reason for this (ie reference to Brugmania use in a movie) and suggest the idea was simply spread by word of mouth. And then the internet came along...

The Birds and the Bees and the Flowers and the Trees

Given that about 5% of angiosperms are dioecious but only a few cases of sex chromosomes have been discovered this raises the question of how sex is determined in the rest of these species. I found this nice review in the journal Genetics last year:
The Birds and the Bees and the Flowers and the Trees: Lessons from Genetic Mapping of Sex Determination in Plants and Animals

Sex determination is an important area of study in developmental and evolutionary biology, as well as ecology. Its importance for organisms might suggest that sex determination is highly conserved. However, genetic studies have shown that sex determination mechanisms, and the genes involved, are surprisingly labile.

Trees, photosynthesis and weasels

Any questions?

The Evolution of Sex Chromosomes

Sex chromosomes have arisen independently in many taxonomic groups. It is an interesting question whether the same mechanisms were involved each time.

Sex chromosomes are an oddity in flowering plants. They are limited to dioecious species and only a few examples are known. The genus Silene, which includes the White Campion, includes both dioecious and hermaphrodite species and three of the dioecious species, Silene dioica, S. latifolia, and S. diclinis,  have an X-Y sex-determination system where Y specifies maleness.
Although the X-Y system evolved quite recently in Silene (less than 10 million years ago) compared to mammals (about 320 million years ago), our results suggest that similar processes have been at work in the evolution of sex chromosomes in plants and mammals, and shed some light on the molecular mechanisms suppressing recombination between X and Y chromosomes.

Ref:  Nicolas M, Marais G, Hykelova V, Janousek B, Laporte V, et al. (2005) A Gradual Process of Recombination Restriction in the Evolutionary History of the Sex Chromosomes in Dioecious Plants. PLoS Biol 3(1).

There's a synopsis of the article in the same issue: Evolution of Sex Chromosomes: The Case of the White Campion.

The plant in you (and vice versa)

 From: Double-fertilization, from myths to reality, a review from 2007 -

It is becoming gradually clear that although plant and animal kingdoms diverged more than 1 billion years ago, similar mechanisms govern sexual reproduction in both kingdoms. The review by Márton and Dresselhaus (2008) outlines some of these parallels. The current idiosyncratic nomenclature used to designate plant reproduction has obscured the parallels that now become apparent between plants and animals. It is likely to be the time to rethink the designation of each actor of the reproductive process such that the literature in the field becomes relevant to a broader readership working in the field of reproductive biology.
The  Márton and Dresselhauspaper referred to is A comparison of early molecular fertilization mechanisms in animals and flowering plants.

Why did the tumbleweed cross the road?

Apart from the cool galloping mosses below one of the few examples of a mobile adult plant is the tumbleweed. A number of plants in dry and windy environments have evolved a similar strategy of disengaging from their roots when mature and then, although the mature plant is dead, using the large tumbling plant body as a mechanism of seed dispersal. Seeds may be dispersed as the plant tumbles along or in other species it actually requires the presence of moisture to cause the seed pods to open and release the seeds.

NASA have even used the tumbleweed as inspiration for a low cost (well, relatively low cost, it IS NASA) Mars Rover.

Transpirational Pull

Maria-Cristina linked to David Attenborough's Private Life of Plants series below but I thought I'd add this clip about plant water transport. He makes an obvious point that I'd never thought of before - plants move all this water silently! I also realize that like David Attenborough I forgot to point out that this entire process ('pulling' up very long thin tubes of water) only works because of the extraordinary properties of water - in this case its hydrogen bonding which gives the tube of water great strength.

Sex crazed suitors and more moth