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3554315659_58ffc0bbda.jpg“Apple, Peaches, Pumpkin Pie….”

After the initial reports in 1983 of successful genetic transformation of tobacco, petunia and sunflower plants using Agrobacterium to mediate gene transfer, this technique was tried on many other crop plants.

By 1989, a colleague at the time summarized a “Plant Gene Transfer” meeting he’d attended by singing the line “Apple, Peaches, Pumpkin Pie….” from the 1967 hit song by Jay & The Techniques.

It was almost easier to name the crop plants NOT reported as being genetically modified using Agrobacterium.

There were, however, a very important group of crop plants not amenable to this transformation technique. The cereals.

Corn (maize), wheat, barley, oats, etc., all resisted efforts at genetic transformation using the Agrobacterium-based technology. The reasons are complex, but suffice it to say here that it was mainly due to the fact that they are all monocots. The cereals not only don’t serve as good hosts for Agrobacterium, but also can’t be regenerated very easily via tissue culture, which is a critical step in Agrobacterium-mediated genetic transformation.

So, what were the poor cereal breeders to do?

Shotgunning DNA

In 1988, it was reported (see ref. 1 below) that maize could be genetically transformed by bombarding maize embryos (isolated from seeds) with extremely small tungsten micro-projectiles (0.6 or 2.4 microns in diameter) coated with DNA. Thus, these researchers avoided having to use Agrobacterium to deliver the foreign DNA into plant cells and, by using maize embryos, the necessity of generating plants from somatic cells.

And so the gene gun was born.

Information about the Biolistic®-PDS-1000/He Particle Delivery System, e.g., can be found here. (And you may even be able to buy a used one for $100!)

So, by 1990, there were multiple ways to genetically transform plants. And the race was on to develop commercially available (and profitable) GMOs.

genengcrops.gif

The first GMO approved by the USDA for human consumption was the “Flavr Savr” tomato in 1992. And by 1996, Roundup Ready® soybeans were sold by Monsanto. As indicated in the graph above, both herbicide-tolerant (HT) and insect-resistant (Bt) genetically engineered (GE) crops have been widely adopted by U.S. farmers. (For more info click on figure.)

Though their GE crops have sold well, biotech companies want to protect their investments by limiting or preventing the ability of growers to save seeds from GE crops. One way is through litigation. Another way is through technology.

“Terminating” Seed Germinationthe-terminator.jpg

Officially called the Technology Protection System (TPS), a way was found to block the germination of seed produced by GE plants.

Briefly, this so-called “terminator” technology incorporates genes into GE plants that, when expressed, are lethal to seed embryos. (see ref. 2 below for more information)

T-GURTs Are “Traitors”

Another technological way to prevent farmers from saving and replanting seeds from GE crop plants would be to incorporate traits into the GE plants that would require a special chemical for second-generation seeds to germinate. Sort of like a special key for the lock.

Officially known as Trait-specific Genetic Use Restriction Technology or T-Gurt (a.k.a., “Traitor” technology), this method incorporates a genetic control mechanism that requires yearly applications of a proprietary chemical to activate desirable traits. (see ref. 2 below for more information)

Bottom Line: These days, the genetic transformation of plants, even cereals, has become routine. And there are even ways to insert “locks and keys” into your GE plants.

References

1. Klein, T.M., Fromm, M.E., Weissinger, A., Tomes, D., Schaaf, S., Sleeten, M. & Sanford, J.C. (1988) “Transfer of foreign genes into intact maize cells with high-velocity microprojectiles.” Proceedings of the National Academy of Sciences (USA) Vol. 85, pp. 4305-4309. (PDF)

2. “Terminator” Technology, Department of Soil and Crop Sciences, Colorado State University.

HowPlantsWork © 2008-2011 All Rights Reserved.

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joker-card-01.jpgHow To Screw Organic Farmers

In a recent issue of our local paper, there was a tragic story about how several organic farmers in the region had unknowingly purchased manure which turned out to be contaminated with a powerful herbicide. Consequently, they lost most of their crops. And they certainly lost their organic seal of approval.

How did this happen? And how common is it for organic growers to be screwed in this way?

This story led me to investigate instances of herbicide contamination in so-called “organic” manure.

It turns out that instances of this problem have been reported for several years. Cases were well documented in England in 2008 and 2009. ( Map of contaminated manure UK 2008/2009 ) Indeed, the herbicide in question was banned in the UK, at least, for time. (UK ban petition) It was reinstated in April, 2010.

Here’s the story.

As described in a previous posting, many herbicides work by interfering with the plant hormone auxin. These so-called auxinic herbicides have been around for long time. So long that some plant species targeted by these herbicides have developed resistance to them.

Chemical companies such as Dow Chemical have overcome this resistance by making chemical modifications to these herbicides in order to create new versions. An example of this is the herbicide aminopyralid.

This herbicide was introduced several years ago and is proven to be a problem because of its resistance to biological breakdown. It persists in hay, manure, compost, and grass clippings (also, see refs below).

From the makers of this product: DOW Agrosciences UK and DOW Agrosciences USA

Does your manure contain herbicides?

Bioassay for herbicides in manure – Mother Earth News

And, finally, a personal story – Persephone Farms.

References

1. Aminopyralid Residues in Compost and other Organic Amendments – Whatcom County Extension

2. Persistent Pesticide As Organics Recycling Foe

3. Davis, J., S.E. Johnson, and K. Jennings (2010) “Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings: Caution to Hay Producers, Livestock Owners, Farmers, and Home Gardeners”, North Carolina Cooperative Extension. (PDF)

4. Aminopyralid Family of Herbicides, Dow AgroSciences (2010) (PDF)

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Can Chemically Inducing Dormancy Help Plants Cope With Stress?

sleepyhead.jpgThis was a very bad year for wheat in Russia because of an extraordinarily hot and dry summer. And many climatologists believe this may be only a glimpse of the not-too-distant future in many parts of the world. If so, then it is of critical importance to find ways to make crop plants more drought and heat tolerant.

One way to do this, of course, is to develop new varieties of crops that can better withstand hot, dry summers. Unfortunately, using conventional plant breeding, this typically takes a very long time, sometimes decades.

But what if it was possible to spray plants with a chemical that induces them to become more tolerant of heat and drought?

Some scientists believe that research reported in the last couple of years have brought us steps closer to such a scenario.

Abscisic Acid = The Plant’s “Sleeping Pill”?

green_pills.jpgAs mentioned in a previous post, the plant hormone Abscisic Acid (ABA) triggers the closing of stomata in plant leaves in response to water stress. It also is well known in promoting dormancy in seeds of many plant species. (ABA may also play a role in maintaining a state of dormancy in other parts of plants, but scientific evidence for this is equivocal.)

In a way, plant dormancy is somewhat analogous to sleep in that it may induce a sort of near inactive metabolic state in plants.

In such a state, plant cells and tissues are usually better able to withstand extremes of cold, heat, and drought. Briefly, this is due to the expression of protective proteins, such as dehydrins, and to changes in the cellular structures, such as the composition of cell membranes.

What ABA does is trigger the cellular processes involved in such changes. The question that has confounded scientists for many years is exactly how ABA does this.

Targets and messengers.

It turns out that 2009 and 2010 have been very good years for research on the mode of action of the plant hormone ABA.

In 2009, several laboratories, including Sean Cutler’s lab at UC Riverside, identified ABA receptors, that is, cellular proteins that specifically bind to ABA.

And this year, much more was learned about the docking site for ABA on these proteins and about what these proteins do. (See here and here for more about this.)

Briefly, these proteins function as phosphatases, which often function to regulate the activity of other enzymes. In this way, they act as an army of messengers, greatly amplifying and elaborating the ABA signal.

Artificially Inducing Dormancy?

Information about the ABA docking site may allow scientists to develop chemicals, such as pyrabactin, that can mimic the action of ABA, but that are way more stable and cheaper than the natural plant hormone ABA itself.
Some scientists envision the use of such chemicals as a way to artificially induce a transient dormancy-like state in growing crop plants, such as wheat for example, in order for them to survive episodes of extreme heat and drought.

For example, Dr. Mike Sussman, from a recent article regarding his work on ABA puts it this way: “”Since they cannot walk or run, plants have developed an interesting and complicated system for sensing and responding very quickly to dehydration and other stresses,” says Sussman, noting that, on average, a plant is composed of 95 percent water. “Most plants have what’s called a permanent wilting point, where if water content goes below 90 percent or so, they don’t just dehydrate and go dormant, they dehydrate and die.”

Figuring out how to trigger a dormant state, such as exists naturally in seeds, which are 10 percent water and can in some cases remain viable for hundreds of years, could be key to creating plants that survive drought in the field, Sussman explains.

It’s possible that someday farmers will spray their wheat fields with such chemicals, which will induce the plants to “sleep through” an unusually hot, dry period.

HowPlantsWork © 2008-2011 All Rights Reserved.

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apical_dom.jpgPlant Cut-Backs

Pruning is one of the most important cultural practices for maintaining woody plants, including ornamental trees and shrubs, fruits and nuts. It involves both art and science: art in making the pruning cuts properly, and science in knowing how and when to prune for maximum benefits.” (from ref. 1 below)

Briefly, the main effect of pruning a plant is to stimulate the growth of axillary buds (a.k.a., lateral buds).

But why is the growth of axillary buds stimulated by cutting off the terminal (or apical) bud?

The most common explanation to this question, dear readers, is the long-known, and somewhat confounding, phenomenon called “apical dominance”.

The Curious Case of Apical Dominance

Apical dominance is defined as the control exerted by the shoot tip on the outgrowth of axillary buds, whereas correlative inhibition includes the suppression of growth by other growing buds or shoots. The level, signaling, and/or flow of the plant hormone auxin in stems and buds is thought to be involved in these processes.” (from ref. 2 below)

But hold on a second, I thought auxin stimulated plant growth.

Apical_Dominance.jpgThis contradiction was noted way back in 1933 by the eminent plant physiologists Kenneth Thimann and Folke Skoog – “…it seems paradoxical that a substance promoting cell extension can also act as an inhibitor….” (from ref. 3 below)

New Evidence

In a previous post back in the fall of 2008, I reported on the discovery of proposed new class of plant hormones called strigolactones.

These compounds, derived from carotenoids, were shown to inhibit shoot branching.

Since then, research on strigolactones, especially as they relate to apical dominance, has yielded evidence that auxin may indirectly stimulate the production of strigolactones (see ref 4 below).

So, does reducing auxin in the plant by removing the apex via pruning also reduce the levels of strigolactones, which, in turn, may increase the growth of axillary buds?

It’s likely not that simple an answer. Other factors such as the plant hormone cytokinin are also involved.

Bottom Line: Pruning works by disrupting a natural process we call apical dominance, which is likely the result of complex interactions among two classic plant hormones (auxin and cytokinin) and one new one (strigolactones).

References

1. Wade, G.L. and R.R. Westerfield “Basic Principles of Pruning Woody Plants” The University of Georgia Cooperative Extension.

2. Ferguson, B. J. and C. A. Beveridge (2009) “Roles for Auxin, Cytokinin, and Strigolactone in Regulating Shoot Branching” Plant Physiology vol. 149, pp. 1929-1944.

3. Thimann, K. V. and F. Skoog (1933) “Studies on the Growth Hormone of Plants III. The Inhibiting Action of the Growth Substance on Bud Development” Proc Natl Acad Sci (USA) vol.19 pp.714–716.

4. Hayward, A., P. Stirnberg, C. Beveridge, and O. Leyser (2009) “Interactions between Auxin and Strigolactone in Shoot Branching Control” Plant Physiology vol. 151, pp. 400-412.

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witchazel.jpgThe End of Winter?

We experienced a relatively warm January here in western Washington (record-setting, in fact). Some daffodils are already coming up and the witch hazels are blooming.

But most of the trees haven’t started to leaf out because they haven’t yet emerged from winter dormancy.

Most woody perennial plants (mainly trees and shrubs) that must survive winter in the temperate latitudes do so by becoming dormant in the fall.

The deepest state of this dormancy called “endodormancy” – often referred to in horticulture as “rest” – allows them to survive cold temperatures, sometimes well below -30o F. (This adds new meaning to the phrase “chilling out”.)

Cold Acclimation (a.k.a., Cold Hardening)

Some plants, but not all, can become more cold tolerant or cold hardy simply by being exposed to near freezing temperatures. This is sometimes called cold hardening or cold acclimation. Interestingly, plants that are more cold hardy are generally also more tolerant to cellular desiccation. Indeed, improved cold hardiness may also be induced by mild drought. So, it appears that some of the cellular things the plant does to become cold hardy are the same as it does to become more drought tolerant. Icy_Tree.jpg

What happens at the cellular level during cold acclimation to make the plants more cold tolerant was described in a previous post. Briefly, the plants may synthesize new proteins that inhibit ice crystal formation or stabilize cellular structures against the cold.

For some plants, it may take only a few days to become cold-hardened. For other plants, especially those entering endodormancy, it may take weeks to become fully cold-hardened.

Of course, the degree of cold hardiness varies greatly among plant species. (USDA Plant Hardiness Zone Map) “So-called chilling-sensitive plants, such as the tropical banana and the semitropical avocado, can be severely injured or even killed by long-term exposure to temperatures (50 degrees Fahrenheit, for example) that are well above freezing. By contrast, chilling-resistant plants, such as garden peas and potatoes, survive brief periods of frost but are killed when freezing conditions continue for more than about four hours. Cold-hardy plants, on the other hand, tolerate extended periods of freezing, and laboratory tests indicate that cold hardness in some of these plants permits them to survive at temperatures as low as minus 75 degrees Fahrenheit.” (from Ref. 1 below)

pussy_willow.jpgThe Big Chill

Plants that exhibit the greatest cold hardiness are those that become dormant. When these plants make the transition to dormancy, one of the first stages in this process is similar to cold acclimation. This actually may be triggered in many plants by longer nights and reinforced by cooler temperatures.

But these plants go beyond chilling tolerance into a so-called “resting state” (endo-dormancy or mid-winter hardiness) that renders them extremely cold hardy. This resting state is characterized by a temporary suspension of growth and a lower rate of metabolism.

Dormancy is broken after exposure to long periods (weeks to months) of cool temperatures (typically below 40o F) and shorter nights (among other factors), though cold deacclimation and reacclimation may take place. (see Ref. 3 below)

How global warming may affect the complex process of tree winter dormancy has certainly been on the minds of some plant scientists (e.g., see Ref. 4 below).

The plant hormone ABA is generally thought to be a chemical signal that induces cold acclimation and dormancy in many plants. (Lots of new information about how ABA works has been published in the past few months, so maybe that would be a good subject for next time.)

References

1. John W. Einset “What Determines a Plant’s Cold Hardiness?” Arnold Arboretum, Harvard University (PDF)

2. Mark Longstroth Dormancy and Cold Hardiness in Fruit Crops

3. Kalberer, S.R., M. Wisniewski and R. Arora. (2006) “Deacclimation and reacclimation of cold-hardy plants: Current understanding and emerging concepts.” Plant Science vol. 171, pp.3-16. (PDF)

4. Legave, J.M., I. Farrera, T. Almeras and M. Calleja. (2008) “Selecting models of apple flowering time and understanding how global warming has had an impact on this trait.” Journal of Horticultural Science & Biotechnology vol. 83 pp. 76–84. (PDF)

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frosty_leaves.jpgPlants Can’t Come In From The Cold

Imagine for a moment that you had to stand outside your house or apartment, without moving, all winter long…and that you were naked.

How long do you think you could last?

Not long, especially if the temperature went below freezing. And certainly not if the temperature went below 0o F (-18o C).

In temperate zones on Earth that’s what perennial plants must be able to do to survive. And even annual plants may have to withstand an early or late frost in order to complete their life cycles.

But, you may reply, plants are not warm-blooded organisms like mammals. What difference is it to them whether it’s cold or not?

How Cold Kills Plants

What happens if water freezes inside at plant?

At least a couple of things can happen…both bad for the plant.

The first, and likely lethal for the plant, is ice crystal formation inside cells. This has just about the same effect on a plant cell as the little alien chestburster did on the actor John Hurt in the movie Alien. (Sorry, but it’s an effective analogy.) It’s lethal.

If, however, the water freezes outside the cells, in the intercellular spaces, this may lead to the extreme desiccation of the plant. That is, it’s sort of the same as if the plant was drying out.

Other cold-temperature effects on plants include (1) decrease in enzyme activity and (2) changes in the fluidity of cellular membranes, both of which could severely harm plant cells, and, thus, the plant as a whole.

How Do Plants Cope With the Cold?frosty_tree.jpg

To answer this question we have to consider plants at the cellular level.

How do the cells of cold-tolerant plants survive sub-freezing temperatures, i.e., withstand dehydration and, more importantly at very low temperatures (below 0o F or -18o C) , avoid the formation of ice crystals in the cell?

1. Accumulation of solutes (sucrose, mainly, but also other organic compounds such as proline) by the cells to depress the freezing point of water (think salting ice on the sidewalk) and to stabilize membranes. (But this can only be effective at temperatures from 32o F to 20o F.)

2. So-called “antifreeze” proteins help prevent ice crystals from forming in the extracellular spaces (outside cell); plant cells that make these proteins typically secrete them into cell wall region (intercellular spaces).

3. The plant cells may synthesize proteins called “dehydrins”, which are inside the cell (cytoplasm), may bind water molecules and alter the collective structure of water in the cell to stabilize membranes.

4. Plant cells can alter lipid composition of cellular membranes in order to adjust the fluidity (functionality) to colder temperatures.

red_leaf.jpgCan Plants Generate Their Own Heat?

A silly question? I think not.

Some unusual plants, by partially uncoupling their cellular mitochondria, can generate small amounts of heat. (Please see ref #1 below for more information) But this is likely not very significant with regard to cold tolerance, however. (More on this interesting topic here.)

Bottom Line: Plant cells survive sub-freezing temperatures by adjusting their solutes, proteins, and membrane lipids in order to withstand desiccation and to avoid ice crystal formation.

Reference

1. Seymour, Roger S. (1997) “Plants That Warm Themselves.” Scientific American, March 1997, pp. 104-109. (Summary)

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King_Tut.jpgA Truly Ancient Grain?

The wheat variety called Kamut® has a fascinating history.

According to “Kamut®: Ancient Grain, New Cereal”, one of the original growers, and one of the trademark holders, of Kamut®, Robert M. Quinn recounts the story of this unusual wheat variety.

“Following WWII, a US airman claimed to have taken a handful of this grain from a stone box in a tomb near Dashare, Egypt. Thirty-six kernels of the grain were given to a friend who mailed them to his father, a Montana wheat farmer. The farmer planted and harvested a small crop and displayed the grain as a novelty at the local fair. Believing the legend that the giant grain kernels were taken from an Egyptian tomb, the grain was dubbed “King Tut’s Wheat.”

This is certainly not the only story of germinating seeds that are thousands of years old, which were collected from Egyptian tombs. (Please see here and here, for examples.)

The Mummy’s Curse?

On p. 55 of Seeds: The Definitive Guide to Growing, History, and Lore, the author dismisses such claims as being “Right up there with the mummy’s curse that supposedly led to the death of Lord Carnarvon, the archaeologist who uncovered King Tutankhamen’s tomb…”

Arctic_lupine.jpgThe oldest claim for longevity (> 10,000 years) cited in this book (published in 2005) is for arctic lupine (Lupinus arcticus) seeds frozen and buried in the Canadian Yukon. The author is skeptical of the claim, and, indeed, a recent scientific report (see ref. 2 below) confirms that the seeds were from modern times.

Seed Longevity: The Facts

Thanks to scores of scientific studies, we now have a pretty good idea of how long most seeds remain viable, that is, able to germinate. Under normal conditions (dry and cool), most seeds will remain viable for only a few years, and anything over 50 to 100 years is quite remarkable. (The reason, of course, is that some, if not most, of the seed is alive and respiring, and, thus, is using up its food supply, albeit very slowly.)

For reference: Table of garden seed longevity and How to test seeds for viability.

To extend the time of seed viability, seed banks may use special storage conditions, such as liquid nitrogen temperatures. (But this will be a subject for another time.)

And coming back around full-circle to the story of Kamut®, Robert M. Quinn admits that“…most scientists believe it probably survived the years as an obscure grain kept alive by the diversity of crops common to small peasant farmers perhaps in Egypt or Asia Minor.”

More mythbusting?: Mummy DNA: History or hype?

References

1. SEEDS by Peter Loewer

2. Radiocarbon dates reveal that Lupinus arcticus plants were grown from modern not Pleistocene seeds. (New Phytologist)

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