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Posts Tagged ‘agriculture’

3345231197_4a21b7c54b.jpgWalking on the Moon

On July 20, 1969 Apollo 11 crew members Neil Armstrong and Buzz Aldrin were the first humans to walk on the moon.

With the 40th anniversary of this first moon landing currently in news, I thought it would be interesting to investigate what’s known about the effects, if any, of the moon on plants….so that you don’t have to.

(By the way, if you haven’t seen In the Shadow of the Moon yet, it’s definitely worthwhile viewing.)

Planting and Gardening by the Moon: Legit or Lunacy?

Some people firmly believe that the phases of the moon affect seed germination, plant growth and flowering.

The effect of the moon on planting times is stated as a matter of fact in such popular publications as The Old Farmer’s Almanac and books such as Gardening and Planting by the Moon 2009: Higher Yields in Vegetables and Flowers, and, of course, calendars such as The Biodynamic Sowing and Planting Calendar 2009.

Others, however, consider such notions as prime examples of “New Age freakery”.

497000227_efba4f620d_m.jpgBut is there any scientific evidence to support the idea that the moon elicits such effects on plants?

A few minutes with Google leads to sites such as this, this, and this. Such websites seem to be long on folklore and astrology and short on any scientific evidence, except for occasional vague references to university studies (unfortunately with no specific citations provided).

The Effects of the Moon on Plants webpage does, however, provide numerous explanations for reported lunar effects on plants. Here only the citations are provided, but that’s a start.

Delving into the Scientific Literature

A good place to start turned out to be a brief review on the subject written in 1946 by Dr. C.F.C. Beeson (see ref. 1 below).

Dr. Beeson introduced the subject this way:
The literature on the moon and plants can be assigned to two groups: one comprising reiterations of peasant beliefs, myths and rules, both ancient and modern, and similar unsubstantiated statements; the other comprising experiments supported by numerical data capable of statistical analysis. This second group consists of (a) experiments mainly of the anthroposophical school, which demonstrate the existence of lunar effects on the growth of plants; and (b) experiments of professional horticulturists and foresters, which prove that there are no such effects, or that, if they do exist, they have no value in agricultural practice.

2171728529_1ed93d76e3.jpgThe experiments Beeson reviewed from the so-called “anthroposophical school” (a.k.a., Biodynamics) were primarily those of Lily Kolisko, published in 1936.

More recent examples of work from biodynamic investigators include, for example: Evidence for Lunar-Sidereal Rhythms in Crop Yield: A Review (PDF) and Can lunar cycles affect the taste of wine?.

Obviously, the biodynamic folks have an axe to grind regarding lunar effects on plants. So, I can understand why scientists may be skeptical of their results. (see here, for example)

But is there recent research (since Beesons’ review) from professional plant scientists (non-biodynamic) that have studied the question of the moon’s effects on plants?

Yes!

Next Time: Scientific evidence regarding the effects of moonlight on plants. (The information may surprise some of you skeptics.)

References
1. Beeson, C.F.C. (1946) “The moon and plant growth.” Nature vol. 158, pp. 572-573. (PDF)

HowPlantsWork © 2008-2011 All Rights Reserved.

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veggies.jpgNo Controversy Here

Despite the denials of global warming caused by increased atmospheric CO2 from the scientifically ignorant or from the oil/coal corporations (or from politicians bought or rented by these corporations), there is one thing they can not deny.

The level of atmospheric CO2 on Earth has been steadily increasing for the past century and will continue to increase. Indeed, the rate of increase may actually be accelerating.

Because plants rely on CO2 as their carbon source for photosynthesis, how does/will this increased CO2 affect green plants?

Less Nutritious Plants in a High-CO2 World?

In a previous post, I briefly discussed the possible effects of higher CO2 on plants.

A recent report indicates that under high CO2 conditions some crop plants may produce higher levels of toxins and lower levels of protein, rendering them less nutritious.

The lower levels of protein as a component of plant biomass may be due to a decreased production of the protein RuBisCo in response to higher levels of CO2. RuBisCo may account for up to 40% of the protein in leaf tissue, for example.

Despite early predictions that higher CO2 would lead to increased crop yield more recent information suggests otherwise.

Bottom line: Increasing levels of atmospheric CO2 will be a significant factor affecting plants now and in the future. We need more research into the effects of increased levels of CO2 on crop plants in order to better prepare for a high-CO2 world.

HowPlantsWork © 2008-2011 All Rights Reserved.

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dandy2.jpgSend In The Clones

Few plants generate such annoyance among suburban homeowners with immaculate lawnscapes as the common dandelion (in North America, most likely Taraxacum officinale).

Despite efforts to eradicate them using chemical warfare (see here for info on such herbicides), the dandelions exhibit a remarkable ability to proliferate.

And they do so likely because they produce seeds asexually, that is, without the complications of sexual reproduction, such as pollination.

This is because most dandelions reproduce by a process called apomixis.

Unlike other forms of asexual reproduction in plants such as vegetative plant propagation via cuttings, apomixis is asexual reproduction via seeds.

In the case of most dandelions (i.e., Taraxacum officinale), the embryo in the seed forms without meiosis, thus the offsping are genetically identical to the parent.

Hence, most, if not all, of the dandelions in your neighborhood may be clones.

What are the benefits of apomixis?

Well, despite the lack of the evolutionary benefits of sexual reproduction (lack of diversity), apomixis allows for the “mass production” of seeds, which appears to be an effective strategy for dandelion propagation.

Bottom line: By rapidly producing cloned offspring, sex is certainly not necessary for the common dandelion.

HowPlantsWork © 2008-2011 All Rights Reserved.

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Roundup.jpgThe Last Roundup?

The herbicide that most Americans are likely familiar with is Roundup®.

Unlike the auxin-based herbicides I discussed in the previous post, Roundup® is not a selective herbicide. That is, it usually kills all green plants (except if the plant is Roundup Ready® or if the plant is a naturally Roundup®-resistant “superweed” – see below for more).

Roundup® is the Monsanto brand of the artificial chemical glyphosate, which was first synthesized in the 1970’s by Monsanto as a so-called “broad-spectrum” herbicide (i.e., kills all plants).

Glyphosate kills plants by specifically blocking the action of a key enzyme (5-enolpyruvylshikimate-3-phosphate synthase or EPSPS) that plants use to synthesize three amino acids (tyrosine, tryptophan and phenylalanine) that are essential components of all proteins. Without the ability to synthesize these amino acids, the plants will die.

Why doesn’t glyphosate similarly affect animals?

Humans and most other animals don’t have this enzyme, so glyphosate has no specific target as it does in plants*. (Since they do not have this enzyme, animals do not synthesize these three essential amino acids. They get them from their food.)

*Please note: This is NOT to say, however, that glyphosate is totally non-toxic to animals – more below.

Roundup may be losing its effectiveness, however, due to several factors.

Are Your Plants “Roundup Ready®”?

During the 1980’s there was a revolution going on in the plant sciences. Scientists discovered how to insert genes into the genome of some plants by using the bacterium Agrobacterium tumefaciens (At) as a genetic vector. Here’s how:

Scientists were able to use recombinant DNA technology to load genes into the Agrobacterium. And the bacteria were then able to “infect” susceptible plant tissue and deliver the genes straight into the plant cell’s genome. These foreign genes were actually “hard-wired” (stably inserted) into the plant’s genome. Moreover, these genes were able to be passed along to the plant’s offspring.

Simply put, Agrobacterium was like a taxicab, and the DNA was the passenger.

Using such technology, Monsanto scientists discovered a bacterial version of the enzyme EPSPS (see above) that was not affected by glyphosate, isolated the gene coding for it from the bacteria, and then inserted this bacterial gene into soybeans.

Roundup Ready® soybeans were born. Followed by Roundup Ready® cotton and canola. And when scientists learned how to genetically engineer grasses (Agrobacterium doesn’t work so well on grasses) using the so-called gene gun, along came Roundup Ready® corn. And maybe even Roundup Ready® turfgrass for lawns!

RR_1.jpg

Roundup® Ready crops have certainly contributed to the extensive use of glyphosate, making it the most widely used herbicide in the U.S. This has likely increased the evolutionary selective pressure on “weeds”, leading to the generation of naturally glyphosate-resistant plants, a.k.a., “superweeds”. (Figs. 1 & 2 from Ref. 1 below)

Here Come the Superweeds.

Recent articles, such as this one in, of all places, Business Week have discussed implications of the appearance of so-called “superweeds”.

RR_2.jpg

Examples of more recent reports of Roundup®-resistant weeds can be found here, here, and here. The increase in the number of such glyphosate resistant plant species has elicited warnings from environmental groups such as the Union of Concerned Scientists, as well as the international press.

In addition to naturally occurring gylphosate-tolerant weeds, there also is the risk of the spread of the genes conferring herbicide tolerance from GM (genetically modified) plants to native plants. Such events have recently been reported to have occurred in test plots of Roundup Ready® turfgrass in Oregon.

Briefly, the artificial gene conferring gylphosate-tolerance was discovered to be present in some native grass species growing adjacent to the test plots. (The genes presumably traveled via pollen from the GM plants to pollenate the native grasses.)

Thus, the possibility of the creation of superweeds via the escape of herbicide-resistance-conferring gene constructs is a very real possibility indeed.

May Increased Use of Glyphosate Also Be Toxic to Animals?

Though glyphosate has been considered one of the more benign pesticides, its environmental impacts are being reconsidered in light of some recent evidence to the contrary.

Reference
1. Boerboom, C. and M. Owen (2006) “Facts About Glyphosate Resistant Weeds”, Purdue University Extension, publ. GWC-1. (PDF)

Bottom Line: Though glyphosate kills plants by targeting an enzyme not present in animals, its overuse – due in part to GM Roundup Ready® crops – may be harmful to agriculture, to the environment, and, ultimately, to human health.

HowPlantsWork © 2008-2011 All Rights Reserved.

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dandy1.jpgWhat Do Suburban Lawns and the Vietnam War Have in Common?

Answer: The herbicide 2,4-D.

You may be familiar with this herbicide as an active ingredient in “Weed ‘n Feed®”, “Weed B Gon MAX®”, Turf Builder® With Weed Control”, etc..

During the Vietnam War, it was an active ingredient in Agent Orange.

On lawns it’s used to kill the dandelions, but NOT the grass. (Find out how it does this below).

In the Vietnam War the U.S. military used it to defoliate the trees (so that they could more easily spot the Viet Cong).

You’re likely familiar with the term “Agent Orange” because of the controversy regarding the tragic health problems it caused to U. S. soldiers. (For current info re. this issue see here).

The serious health issues to both Americans and Vietnamese caused by Agent Orange are due to contaminants called dioxins produced during its chemical synthesis. (For more info on this see 2,4-D and dioxins and also here.)

But since this post is about how such herbicides work on the plants, let’s leave dioxin issues aside (for now).

Herbicides Such as 2,4-D are Auxinsdandy3.jpg

Auxin in perhaps the most well-known plant hormone. (I’ve previously discussed auxin in this blog here.)

The herbicide 2,4-D is a synthetic auxin first produced in the 1940’s. It is one of many so-called phenoxy herbicides. These herbicides all are both structural and functional analogs of the natural auxin indole-3-acetic acid (IAA). That is, these synthetic auxins not only are structurally similar to IAA, but they are also biologically active as auxins in plants.

Although they both look and act like auxins, plants can not metabolize these phenoxy herbicides as they can with IAA, the natural auxin.

This turns out to be the key to why phenoxy herbicides such as 2,4 D are able to kill some plants.

How Does 2,4-D Kill Dandelions…?

Auxin-based herbicides are referred to as “selective” herbicides because they kill so-called “broadleaf” plants (a.k.a., dicots) but not grasses, for example. (Hence, that’s why they’re such popular herbicides with both growers of lawns as well as of wheatfields.)

But how exactly does spraying 2,4-D on susceptible plants kill them?

This turns out to be very poorly understood, and it’s also the subject of much misinformation. For example, I’ve heard people say that such herbicides “grow the plant to death” and read that 2,4-D “…simply confuses the plant to death”. Huh?

dandy2.jpgAt the present time nobody really knows precisely how the auxin-like herbicides kill susceptible plants. As with most effects of plant hormones, it probably has a lot to do with the plant species in question.

However, recent findings have provided important clues. And these clues support the idea that plant death may occur as a result of a combination of factors.

Here’s a summary of the story:

First off, one of the well-know effects of excess amounts of auxin on dicots is to cause them to overproduce the plant hormone ethylene. For example, in 1969, Mary Hallaway and Daphne J. Osborne first showed that ethylene is a factor in defoliation caused by 2,4-D.

Because plants can’t break down 2,4-D, it’s action persists. This action includes the excess production of ethylene, which may result in a number of plant responses, including epinasty and senescence.

Another effect of excess ethylene production in response to 2,4-D is to stimulate the production of yet another plant hormone, abscisic acid (ABA). The effects of ABA on the plant may contribute to eventual plant death. (For an illustration of the complex effects of auxin-based herbicides on plants, see Figure 1 in the reference listed below.)

…and why doesn’t 2,4, D Kill the Grass? (and You?)

Perhaps the simplest explanation for both questions has to do with sensitivity to the plant hormone auxin.

In general, grasses are much less sensitive to synthetic auxin herbicides than are dicots. That is, a much higher threshold level of auxin-based herbicide is required to elicit physiological responses in grasses versus the so-called “broadleaf” plants. So, at the doses used to kill dandelions, for example, grasses are largely unaffected. (Higher doses of 2,4-D may kill the grass, too, however.) Grasses may be more resistant to such herbicides because of differences in leaf morphology, translocation of the herbicide inside the plant, and the ability to metabolize (breakdown) synthetic auxins.

Aside from the toxic contaminant dioxin, 2,4-D has no physiological effects on animals at hormonal levels, that is, at the concentrations that affect plants. (Indeed, there is no reputable evidence that any of the five main plant hormones affects animals.)

Reference
Grossmann, K. (2007) “Auxin Herbicide Action: Lifting the Veil Step by Step”, Plant Signaling & Behavior 2:421-423. (PDF)

Bottom Line: The herbicide 2,4-D mimics the plant hormone auxin and sets off a complex series of events – involving two other plant hormones – that eventually lead to the death of susceptible plants. At hormonal levels, auxins affect plants but not people.

Next-Time: More on Herbicides (Is Roundup® Losing Its Punch?)

HowPlantsWork © 2008-2011 All Rights Reserved.

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412791223_79498a7b2f_m.jpgHow Do We Know Plants Can Tell Time?

The daily opening and closing of flowers and the rhythmic leaf movement of some plants suggests, even to the casual observer, that plants have an internal clock.

To more careful observers, such as Carl Linnaeus and Charles Darwin, the evidence was clear that plants can tell time.

For example, in 1751 Linnaeus published Philosophia Botanica in which he noted what time of day flowers of various species open and close.

And also in this book, Linnaeus conceived the idea of a floral clock (“horologium florae“) garden by which one could estimate the time of day by observing which flowers were open and which had closed. (Click on photo of floral clock below for more information.)

Darwin, assisted by his son Francis, studied the diurnal movement of leaves (sometimes called “sleep movements”, a.k.a., nyctinasty). In his book The Power of Movement in Plants Darwin argued that the plants had an internal clock that generated the observed rhythms, rather than them being solely imprinted by the diurnal cycle.

Of course, we now know that these “sleep” movements in plants are manifestations of the circadian rhythm, which is evident in most organisms.

leaves.jpgWhat Sets the Clock?

Think about it…what happens during the course of a typical 24-hr period on Earth? In simplest terms, it cycles between light/warm and dark/cool.

So, what sets (entrains) the biological clock of plants are mainly light/dark transitions, augmented or reinforced by diurnal cycles in temperature. In other words, light (dawn/dusk) acts to reset the clock, but temperature also has an effect, albeit not very well defined.

It turns out that, in most plants, the leaves play a central role in sensing the light that entrains the biological clock. But it’s not chlorophyll that is the light-sensing pigment, but two other non-photosynthetic pigments called phytochrome and cryptochrome. (Much more about these two photoreceptors another time.)

How Does the Clock Work?

Research on the cellular mechanisms of circadian (“about a day”) rhythms in plants has greatly advanced our understanding of how the clock works at the molecular level. (For an excellent review from an historical perspective see here.)

Briefly, the clock works at the individual cell level and consists of three basic components as shown in the diagram below.

oscillator.jpg

It turns out that plants likely have three such mechanisms, all interlocked in a complex system, working inside leaf cells. As mentioned above, phytochrome and cryptochrome are the photoreceptors. These modify other proteins involved in a transcription/translation feedback loop that serves as the central oscillator.

The collective output consists chiefly of proteins, and maybe even RNA, that serve to modify the plant’s metabolism and development. These output signals may even travel from the leaves through the phloem to other parts of the plant.

Some Recent News About Plant Circadian Rhythms

Leaves may have three interlocking clocks, but there may be only one root clock, and it’s apparently a slave of the leaf clocks.

The circadian rhythm also apparently results in the rhythmic growth of plants.

Researchers at the University of Texas at Austin have shown that modifying the internal clock may result in bigger plants.

Much has been learned about clock genes in plants and how they relate to clock genes in animals.

FloralClock_ChCh_gobeirne.jpg

Bottom line: For hundreds of years people have recognized that plants have an internal clock, but only recently have plant molecular biologists discovered the complex inner workings of this timepiece.

Next Time: Why Plants Tell Time

HowPlantsWork © 2008-2011 All Rights Reserved.

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2262636867_a80f7eca8a.jpgThe Power of Movement in Plants

Most of a flowering plant’s development and physiology is regulated by plant hormones.

The first of these chemical signals to be isolated and characterized was auxin.

In the 1930’s, after the initial discovery of auxin by Frits Went in 1928, he, Kenneth Thimann, and Folke Skoog showed that, in addition to causing cell elongation, auxin had developmental effects: it enhanced formation of roots on cuttings and inhibited lateral buds.

But nearly 50 years before this, Charles Darwin, assisted by his son Francis, studying the phenomenon of phototropism in grass seedlings, hypothesized that some sort of internal signal was involved in the bending of the seedlings toward light. (see movie below)

This signal turned out to be the plant hormone auxin, as shown by Went.

The Darwins’ results were published in a book entitled The Power of Movement in Plants. (A copy can also be found online here.)69-1.jpg

How Auxin Grows Plants

Auxin’s most well-known function is to stimulate cell elongation in young dicot stems via the acid growth theory.

It’s within this context of plant growth stimulation that auxin has been shown to mediate both phototropism and gravitropism in plants.

That is, auxin acts as the signal between the perception of light or gravity by the plant and the plant’s response. This response usually is more growth on one side of the stem or root, leading to the observed curvature.

How Auxin Shapes Plants

As in the game Spore, one of the first things to do when building an organism is to decide what’s up/down (forward/back) – in other words, the polarity of the organism.

1mechanism.gifAuxin has been shown to help establish polarity in very young plants (embryos). Click on small photo left for more info.

A recent report in the journal Nature helps explain how this may work at the cellular level.

As previously blogged here, physical stress and strain may affect the fate of plant cells and thus affect the shape/function of a plant stem or leaf.

081214191012.jpgPlant biologists have shown that this may also be involved in determining root patterns and how auxin may be involved.

Finally, we have more new news regarding auxin and root hairs.

Root hairs (see diagram right) are critical conduits for the uptake of water and minerals by plants. Auxin apparently increases the length of root hairs, thus increasing their effective surface area. This would likley have significant implications to agriculture.

A recent report shows that limiting the amount of auxin in localized areas of developing plant tissues may also affect the form of plants.

*A short movie of phototropism in corn seedlings can be viewed here.

Bottom line: As with most plant hormones, auxin plays multiple roles in regulating plant development, far beyond what the Darwins could imagine.

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