More on Plants: BGR #34

You may be wondering why, all of a sudden, plant posts finally started reappearing here at Foothills Fancies. It's a puzzle best solved by noting that the latest Berry-Go-Round plant carnival is now posted over at Watching the World Wake Up.
After months of dereliction, we are trying to recoup our reputation as a plant blog by submitting these last couple posts on plants and their activities.

Pity the green ash, a sample here of the indignities discussed below in Plants Die. We've all observed that, in any encounter with power lines, the tree loses. It might be fun to make a series of these, something like RPL's ecology of shopping carts. What do you think?

As usual, the Watcher has rounded up a nice collection of plant goodies, taking us from cotton T-shirts to favorite malts and brews by way of tropical paradises and temperate berries. Drop in and check out some great plant blogging!

Stuff Plants Do

We know plants sleep through the long season; some (especially annuals) will never awaken. But plants also move through diurnal cycles most of us tend to ignore; some wake and sleep so obviously that we all notice. Explore these delightful time lapse photographic sequences from Indiana to see plants sleep, and waken, and dance, and grow, and thrash about hunting for something to grow upon.

Photo above of Mimosa pudica, Sensitive Plant (leaves open), from native habitat in Goa India. Photo by J.M. Garg, from Wikipedia. This plant also displays reaction to touch, thigmonasty.

We don’t know whether sleeping plants dream. That link takes you to an essay I wrote 14 years ago; I commented then that, although plant responses to light and darkness (nyctinasty) had been known for centuries, scientists these days had “mostly ignored” this line of research. That’s no longer true, it seems, so the story needs an update, as some puzzles are slowly being unraveled. Darwin would be proud.

Mimosa pudica, leaves closed, Photo from Wikipedia, by “Bluemoose.”

Darwin was right
Indeed, as with so many topics, Darwin was the original researcher, the observer and experimenter who explored the esoteric. The Power of Movement in Plants, published in 1880, was his next-to-last book, and he despaired at times of ever finishing it!

Darwin to Sir Joseph Hooker, March 25, 1878:
I think we have proved that the sleep of plants is to lessen the injury to the leaves from radiation. This has interested me much, and has cost us great labor, as it has been a problem since the time of Linnaeus. But we have killed or badly injured a multitude of plants.

Darwin to Asa Gray, Oct 24, 1879:
I have written a rather big book—more is the pity—on the movements of plants, and I am now just beginning to go over the MS. for the second time, which is a horrid bore.

Darwin to DeCandolle, May 28, 1880:
My MS. relates to the movements of plants, and I think that I have succeeded in showing that all the more important great classes of movements are due to the modification of a kind of movement common to all parts of all plants from their earliest youth.

I just happen to have a handy copy of The Life and Letters of Charles Darwin, compiled and edited by his son Francis, but Darwin's letters are now also available online where we all can explore at will.

Modern Science Jumps In
Some plants, such as Maranta, are equipped with specialized joints that control their daily movements. These structures, called pulvini (sing. pulvinus), occur where the leaf blade joins the petiole, functionally somewhat like the wrist joint connecting your hand and forearm. Rapid movements should be suspected in plants that have obvious pulvini—e.g., in Spathiphyllum, which wilts dramatically in an attempt to remind you to water it, then recovers with equal alacrity when you do.

Don’t you just love scientific writing? I was going to entertain you with terrific information about phytochrome and potassium fluxes and glucosidase, but I'd rather stick to what I can see and understand (sometimes) and appreciate (always!)... I can offer a picture (you'll have to click to be able to read it):


I’m so out of practice that, even when I understand the individual words and phrases, it can be tough to extract meaning from some passages (try your skill with samples at the end of this post). As Alice said to the Caterpillar:

I’m afraid I can’t put it more clearly, for I can’t understand it myself to begin with.

However, science is like a foreign language, where sometimes you can get the general sense of things without exactly being able to translate it word for word. Here goes with a few gleanings.

• Light hitting leaf blades does nothing, but if it hits the pulvinus, the leaf reacts.
  
• Ergo, the pulvinus is the photoreceptor and reacts independently of other pulvini.
  
• Phytochrome is the pigment that keeps leaves from opening when it’s dark.
  
• Phytochrome controls the direction of potassium movement, which controls water movement and hence cell turgor.

Ueda et al. do the best job of explaining all this in an article that almost reads like English, in parts:

One of these is a leaf-opening factor that “awakens” plant leaves, and the other is a leaf-closing factor that reverses this process such that the plant leaves “sleep”. …significant changes in the concentration of the ratio between leaf-closing and -opening factors in the plant are responsible for leaf movement. And this is a universal mechanism in five nyctinastic plants. …

The motor cells in the pulvini of nyctinastic plants consist of two types: extensors and flexors. Leaflets move upward during closure and downward during opening due to the actions of the extensors located on the upper side of a leaf and the flexors on the lower side. …

So these findings represent an important advance in the bioorganic study of nyctinasty and provide important clues regarding the molecular mechanism of nyctinasty, which has been a historical mystery since the era of Darwin.

To me, the fun thing about this article is that, while the mechanism is universal, the pairs of leaf-opening and leaf-closing factors were discovered to be different chemicals in each of the five species studied! How cool is that? (For extra cool, note that Ueda et al. also address the question of memory in plants, specifically Venus Fly-traps and their mechanism for leaf closure.)

In the case of sleeping leaves that rise, as in Maranta and most others, it seems logical that the sleep position is a tense one, and the leaf relaxes into its daytime posture. If so, then raised leaves are actively holding a position, and wilting must occur through some other process. In Maranta, it does; the leaves relax even more, and leaf margins roll inward as turgor is lost.

So far so good. But these articles tend to use Albizia julibrissin or other leguminous species. What about species whose leaves adopt a drooping posture in sleep (e.g., Oxalis)? Are the "extensors" and "flexors" reversed, or do they respond to different signals? In Oxalis, wilting and sleeping postures may be difficult to distinguish. The upper surfaces are relatively exposed, and covering the lower surfaces may help reduce transpiration, reducing further water loss.

With all that we know about plants, it's nice to know a few mysteries remain. It seems no one has answered the ultimate question: If sleeping is so advantageous, why don't more plants do it?

C. Darwin. The Power of Movement in Plants, John Murray, London (1880).
C. Darwin. Insectivorous Plants, John Murray, London (1875).

—References—

Find lots more references by searching nyctinasty at Google Scholar. Here are a few excerpts from just a few samples over the decades to get you started...

Illumination of pinnule tissue alone induced no response, while illumination of an area as narrow as 1 mm, including only the tertiary pulvini and adjacent portions of rachilla and pinnules, was sufficient for a full response. This suggests that the pulvini themselves, the sites of the response, act as photoreceptors. In experiments with various shielding devices, pinnules on the same rachilla responded independently to local illumination, suggesting the absence of any translocatable effects.

Koukkari, Willard L. and William S. Hillman 1968 Pulvini as the Photoreceptors in the Phytochrome Effect on Nyctinasty in Albizzia julibrissin Plant Physiology 43:698-704.

————

Prolonged irradiation during appropriate parts of the diurnal cycle promotes the opening of Albizzia sic julibrissin leaflets. Leaflets also open without illumination, but such opening starts later and is slower and less complete. Opening in the dark is accompanied by lower potassium efflux from dorsal pulvinule motor cells but equal or greater potassium movement into ventral motor cells than occurs during opening in the light. Far red-absorbing phytochrome inhibits opening in the dark… i.e., a high far red absorbing phytochrome level is associated with low potassium content in ventral motor cells, high potassium content in dorsal motor cells, and a small angle between leaflets.

Satter, Ruth L. and Arthur W. Galston 1971. Phytochrome-controlled Nyctinasty in Albizzia julibrissin: III. Interactions between an Endogenous Rhythm and Phytochrome in Control of Potassium Flux and Leaflet Movement. Plant Physiology 48:740-746.

————

The nyctinastic leaf movement is induced by a pair of leaf-movement factors, and one of each pair is a glucoside. There are two key proteins that are involved in the control of nyctinasty. One is -glucosidase: a biological clock regulates the activity of -glucosidase, which deactivates the glucoside-type leaf-movement factor, controlling the balance in the concentrations of the leaf-closing and -opening factors. The other is the specific receptor for each leaf-movement factor: the genuine target cell for each leaf-movement factor is confirmed to be a motor cell from leaflet pulvini, and the specific receptors that regulate the turgor of motor cells are localized in the membrane fraction. (Ueda et al., 2007.)

Ueda, Minoru, Yoko Nakamura, and Masahiro Okada. 2007. Endogenous factors involved in the regulation of movement and “memory” in plants. Pure Appl. Chem., Vol. 79, No. 4, pp. 519–527, 2007.

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Plants Die

As I wander around marveling at the wonders of Nature, I can’t help also wondering at my fellow human beings. Time and again, I notice that many of them act as if plants are not alive. This is especially true for trees, who exude a sense of eternity that we more transient beings lack. Their relative permanence apparently makes humans think of them as indestructible features of the nonliving landscape, kind of like rocks. (The humans who read Berry-Go-Round are naturally not in this category of humans.)

That phenomenon, a form of plant blindness surely, causes humans to visit all kinds of indignities on these supremely dignified lifeforms, strangling them with wire fences, lopping off limbs, crippling them in countless ways. Even blithely nailing signs to them as if they had no greater purpose in life than to advise us of money-making opportunities or lost pets.

So, for the record: Plants are ALIVE. Trees included, but plants of all sizes and shapes live, and breathe, and grow, and reproduce, and even, after their fashion, move. They do stuff. (Left, a grape ivy looking for something to climb on.) They eat (some more dramatically than others). If you cut them, they will bleed. If you hit a tree with a lawnmower, it will bruise. Each of those verbs could easily be an entire post in itself, but let’s expand just this one example.

“A tree is much more than a chunk of dead wood,” says Alex Shigo, a career plant pathologist with the Forest Service. “Trees are alive; they live all year ‘round, not just for a short time in the summer.” Dissecting trees with a chainsaw, Shigo revolutionized our understanding because he didn’t rest on what “everyone” knew.

“I could either go with the book or go with what I saw in the tree. Either the books were wrong or the trees were wrong. I chose to go with the trees.”

“I started to see trees in a different way because a tree is a living thing. When you hit a living thing, it reacts. When you hit a tree, it does something. When a tree is threatened, it doesn’t just stand there. It establishes boundaries.”

Citing Shigo, a profile in Irrigation and Green Industry (May 2004) adds that humans put new cells in the same old places throughout their lives, but trees put new cells in new places. A tree doesn’t heal, because it doesn’t replace injured cells with new ones; it just creates a wall, or boundary, between the injured wood and the functional tissue. And that lawnmower “bruise” will remain in the wood indefinitely.

Photo courtesy Wikimedia commons by Max Wahrhaftig June 2005: Alex Shigo (far right) explaining markings on an Oak section during one of his last symposia.

Shigo’s work changed how professionals prune trees by demonstrating that some methods actually promoted rot. Sadly, most tree-trimmers have probably not been exposed to these newer methods, and go about blithely disfiguring trees and shrubs right and left. My most pained memory of this is from Arizona, where trees (I think mulberries) are routinely "pruned" back almost to the trunks on a regular basis; they never develop normal branching patterns but become permanent lollipops.

This post topic was inspired by an outdoor planter I saw recently, full of scented geraniums left to wither and freeze. These plants are perennials, houseplants that thrive inside and add wondrous scents to our indoor air! And they’re favorites of mine. It was all I could do to resist attempting to rescue them, but having already brought all my geraniums indoors to crowd the house, I had to walk away. (I also suspected they were already too far gone to recover. May the devas of scented geraniums forgive me…)

As we head into the season of disposable plants* (or one of them), I part company with the so-called green industry, which creates so much life just to send it out into careless hands who think these living beings are mere decoration.

* Yes, poinsettias too are alive, and, in their native haunts or in greenhouses, capable of growing into mature trees of considerable height.

Confessions: I have, of course, killed my share of plants, perhaps, because of my interest in them and attempts to have them share my life, more than my share. Some, no doubt, were killed with neglect. But not willfully, not with premeditation or malice. (Okay, there are exceptions; certainly there are some plants we prefer to see dead.)

So, yes, plants die. Sometimes on their own, and too often with our help.

In the spirit of Thanksgiving, I offer a deep formal curtsy to any and all who treat these amazing, phenomenal lifeforms with all the respect they clearly deserve.

For Berry-Go-Round #34

p.s. Don't forget to observe Buy Nothing Day this Friday!! Eschew the hype...

The Heart of the Monster

Those who look forward to seeking out goblins, demons, monsters, and other scary critters during this spooky season need look no further than the skyscape that is displayed during these long nights. Last week, my early morning stargazing* taught me a new monstrous constellation.

I'd been scanning the dark gulf between Procyon and Regulus, in hopes of figuring out Cancer, the Crab. A very faint constellation with no star brighter than 4th magnitude, Cancer isn't easily seen this close to "civilization," or with a lightening dawn to compound the challenge. I got a bonus—even spookier than the pale Crab was the critter below.

My eye is always captured, it seems, by the red or orange stars, and just below Cancer, alone in the field, was Alphard, the Solitary One. Alphard, a mid-2nd magnitude star, is also known as Cor Hydrae, the heart of the Hydra, a vast sea monster that stretches across the otherwise quiet space between Cancer and Virgo, ending far east below Spica. The brightest star in a dim constellation, Alphard is more impressive than it looks from here: 175 light-years away, 40 times the Sun's diameter, and burning 400 times brighter. Alphard is an orange giant nearing the end of its life.


Although most of the Hydra was invisible, Spica itself is easy to find, being south of Arcturus, another of my favorite red stars, who was just rising. In fact, Arcturus and Spica were about the only stars visible in that lightening part of the sky. (And, of course, we get to Arcturus by "arcing" along the handle of the Big Dipper and following the arc on to Spica.)

Harry Potter fans might prefer to think of Hydra as the giant and evil basilisk; the resemblance is certainly compelling for a latter-day mythology. Other constellations have been translated to modern times (still looking for that link), so why not Hydra? As the largest constellation, the Water Serpent stretches one-quarter of the way around the sky.

* Please note: Early morning stargazing throws me off schedule with more "normal" evening observers, who should look for the Hydra crossing southern skies February through April.

Hydra may be the largest, but it is not the only, monster up there. There is, to name one example, another sea monster, Cetus, off on the other side of the sky just below the raging bull, Taurus. The story of that monster is well displayed in Watcher's most-thorough post on Andromeda (and almost everything else), which takes in the mythology of Perseus and Cetus and the entire cast of characters in this part of the sky. Here's Perseus as it appears in the east on a fall evening.

Speaking of Perseus (nice seque, eh?), another demon appears in that constellation— as Watcher will explain, the hero Perseus is carrying the severed head of Medusa the Gorgon, she of the serpentine coif. The star Algol represents Medusa's head or eye, and glares in our direction with great malevolence. The name Algol, in fact, is from Arabic for "the ghoul" or demon, and she is an appropriate visitor for the Halloween season.

Algol's gaze, like Medusa's, is considered unlucky. The system is actually a double star, with a bright blue primary and a yellow secondary. As the two stars circle, one eclipses the other every three days, causing the brightness we see to dip from magnitude 2.1 to about 3.4. This eerie blinking of the demon's eye gives the star its unsavory reputation, although it happens so quickly I've yet to catch it in action (or, likely, my ability to judge its relative brightness is underdeveloped). No matter, it gives me something to watch for...