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Beni Meier with his 2323.7 pound world record pumpkin in 2014.

Beni Meier and his world record pumpkin (2014).

Size Does Matter (If You’re Growing Giant Pumpkins)

Question: What does a 1968 Volkswagen Beetle and the current World Record Giant Pumpkin have in common?

Answer: They each weigh about 1 ton (US) or about 2000 pounds (907 kilograms).

Indeed, the current world record heaviest pumpkin (see the photo on the left) weighed in at a massive 2,323 pounds (1,054 kilograms).

Of course, the obvious question is: How are these pumpkins able to grow so huge?

First, it’s important to note that a pumpkin is NOT a vegetable. It’s a fruit.

So, basically, what we’re talking about here is unfettered fruit growth. Seemingly, as long as the pumpkin is provided with sufficient water and resources (primarily in the form of carbohydrates from the leaves), it will continue to grow – until winter sets in.

I found that good basic resource about the physiology and genetics of giant pumpkins has been provided by Prof. Jules Janick of Purdue University. (See Ref. 1 below)

From this article (and references therein): “The accumulation of fruit size is a combination of physiology, environment, and genetics. The water content of pumpkin is about 88% and may be as high as 91 to 94% in giant pumpkins (Culpepper and Moon, 1945). The fruit acts as a physiological sink and the combination of cell size and cell number determines final fruit size. In large-fruited pumpkin as compared to fruits of smaller cucurbits there is a more extended period of cell division and greater cells expansion after cell division ceases (Sinnott, 1939).

As noted by Prof. Janice, there has not been very much research done on giant pumpkins. I did, however, find a few recent papers (listed below) regarding giant pumpkins, which have shed a bit more light on their nature.

Nakata, et al. (Ref. 2 below) “…found that both the cell number and cell sizes were increased in a large fruit while DNA content of the cell did not change significantly.” Interestingly, giant pumpkins apparently do not exhibit higher ploidy in their vegetative material or fruit, as do many large agricultural fruits. These researchers do, however, provide some evidence for enhanced photosynthesis in the leaves of giant pumpkins.

Several investigators in Prof. Holbrook’s lab at Harvard University have also recently been investigating the growth of giant pumpkins. Briefly, they found that “There was no evidence that changes in leaf area or photosynthetic capacity impacted fruit size. Instead, giant varieties differed in their ovary morphology and contained more phloem on a cross-sectional area basis in their petioles and pedicels than the ancestral variety. These results suggest that sink activity is important in determining fruit size and that giant pumpkins have an enhanced capacity to transport carbon.” (from Ref. 3 below)

Finally, even some mechanical engineers have been fascinated by giant pumpkins. Hu, et al. (Ref. 4 below) reported: “Using time-lapse photography and measurements collected by volunteer farmers, we show that as pumpkins grow, they morph from spherical to pancake shapes, flattening up to 50% in height-to-width aspect ratio.” From these observations, as well as theoretical calculations, they concluded that “The observed growth plasticity allows the fruit to redistribute internal stresses, thereby growing to extreme sizes without breaking.


1. Janick, J. (2008) “Giant pumpkins: genetic and cultural breakthroughs.” Chronica Horticulturae, Vol. 48, pp. 16-17. (Full Text – PDF)

2. Nakata, Y. et al. (2012) “Comparative analysis of cells and proteins of pumpkin plants for the control of fruit size.” Journal of Bioscience and Bioengineering, Vol. 114, pp. 334–341. (Abstract)

3. Savage, J. A., D. F. Haines, and N. M. Holbrook (2015) “The making of giant pumpkins: how selective breeding changed the phloem of Cucurbita maxima from source to sink.” Plant, Cell & Environment, Vol. 38, pp. 1543–1554. (Abstract)

4. Hu, D. L., P. Richards, and A. Alexeeva (2011) “The growth of giant pumpkins: How extreme weight influences shape.” International Journal of Non-Linear Mechanics, Vol. 46, pp. 637-647. (Abstract)

“BIG Time” by Peter Gabriel (1986)

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Spraying RNAi To Silence Target Genes In Crops (And Insect Pests)…

Many object to GMO crop plants, at least in part, because they contain foreign genes artificially – and permanently – inserted into the plant’s genome.

But what if you could TEMPORARILY modifY plants (and even their insect pests) by simply spraying little bits of genetic material on the leaves?

These aren’t really GMO crop plants….are they? If they aren’t, then one of the main reasons that governments and the public object to GMO’s would be eliminated. And this may be why such technology has recently attracted the attention of the plant biotech community, especially Monsanto.

According to Dr. Robert Fraley, Monsanto Chief Technology Officer, Monsanto’s so-called BioDirect™ technology (see Ref. 1 below) “…has the potential to be one of the most exciting advancements for agriculture that I’ve seen in my career”. And since Fraley has been at Monsanto for over 30 years, if what he says is true, then this is a pretty big deal, and we should understand how it works.

A good place to start is a recent article published in the MIT Technology Review (please see Ref. 2 below). And several other excellent articles that’ll help bring you up to speed on the subject are Refs. 3, 4 & 5 below.

But if you don’t want to wade in so deep right now, please allow me to present the basic story…

…very simply put, the idea is to spray on plants relatively small bits of genetic material (in this case, small, distinct strands of RNA) that very specifically turn off the production of certain gene products (mainly, proteins). This may be potentially lethal in some cases, for example, if a critical enzyme is turned off in insect pests on the plants (for example, see YouTube video below), or if an enzyme that confers herbicide tolerance is turned off in noxious weeds.

This technology is based on a number of genetic discoveries that were first made about 20 years ago, now collectively referred to as “RNA interference”.

RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression, typically by causing the destruction of specific mRNA molecules. Historically, it was known by other names, including co-suppression, post transcriptional gene silencing (PTGS), and quelling. Only after these apparently unrelated processes were fully understood did it become clear that they all described the RNAi phenomenon. Andrew Fire and Craig C. Mello shared the 2006 Nobel Prize in Physiology or Medicine for their work on RNA interference in the nematode worm Caenorhabditis elegans, which they published in 1998.” (from Wikipedia)

Brief aside: Some felt that the Nobel committee ignored vital groundwork on RNAi in plants and that at least one plant biologist should have shared the 2006 Nobel. (Please see previous post on why few plant scientists have won the Nobel Prize.)

Anyway, back to the subject at hand… spraying RNA on plants…

To me (and others), it’s quite remarkable that this actually works, for several reasons. The first reason has to do with the fact that RNA is very unstable. Chemically and biologically, RNA is significantly more labile than DNA. And RNA is very expensive to synthesize in the quantities that would be required for this proposed technology.

Another reason, as pointed out by Monsanto’s Dr. Fraley “…no one yet understands exactly how to get RNA inside a plant’s cells using a field sprayer—at least not with the sort of inexpensive, works-every-time efficiency farmers would be looking for. Many insects are also not easily affected. Monsanto has been spending millions to crack these problems, collaborating with biotech companies specializing in drug delivery. “We’re still a few breakthroughs away,” he says.” (from Ref. 2 below)

One such drug delivery company is Apse, Inc. (see Ref. 6 below), which, according to their website, “…has developed technology that will allow the cost efficient production of RNA for broad acre topical RNAi uses in agriculture.

But overcoming these technological issues is not the only problem faced by spraying RNA on plants.

…And Praying That This Technology Is Approved (And Accepted By The Public)

In the past couple of years, both the US Environmental Protection Agency (EPA) and the European Food Safety Authority (EFSA) have published reports dealing with the possible risks to the environment and human health from agricultural RNAi technology.

“The EPA’s advisors, in their report last year, agreed that there was little evidence of a risk to people from eating RNA. But is there some kind of ecological risk? This question they found harder to answer. Monsanto paints RNA as safe and quick to disappear, yet the aim is to make it lethal to insects and weeds, and the company wants to develop longer-lasting formulations. How long? In Hunter’s trees [see YouTube video below] the molecules persisted for months. What’s more, Monsanto’s own discoveries have underscored the surprising ways in which double-stranded RNA can move between species.
These unfolding discoveries suggest that complex biology is at work, leading the EPA’s advisors to say that the “potential scale” of RNA used in agriculture “warrants exploration of the potential for unintended ecological effects.” RNA may be natural. But introducing large amounts of targeted RNA molecules into the environment is not. The advisory panel concluded that “knowledge gaps make it difficult to predict” exactly what problems might arise.”
(from Ref. 2 below)

From the 2014 EFSA workshop report: “Genetically modified plants intended for market release can be designed to induce silencing of target genes in planta or in insect pests through RNA interference. As part of the pre-market risk assessment, the European Food Safety Authority evaluates any risks that genetically modified plants may pose to animal and human health and the environment. To discuss potential risks associated with RNA interference-based genetically modified plants and to identify issues unique to their risk assessment, the European Food Safety Authority organised an international scientific workshop on 4-5 June 2014 in Brussels (Belgium), bringing together experts from academia, risk assessment bodies, non- governmental organisations and the private sector. The workshop considered the molecular biology underlying the RNA interference mechanism, current and future applications of RNA interference- based genetically modified plants, and risk assessment aspects. During the workshop, risk assessment aspects were discussed in three separate break-out sessions, each focusing on one of the three main areas of genetically modified plant risk assessment: molecular characterisation; food/feed safety assessment; and environmental risk assessment. The objective of the workshop was to solicit scientific expertise for the problem formulation phase of the risk assessment of RNA interference-based genetically modified plants. An overview of the presentations given, remarks made and discussion points put forward during the workshop are presented and summarised in this report.” (Please see Ref. 7 below)

A lot of money is resting on the approval and acceptance of this technology: “Both Monsanto and Syngenta have invested heavily in RNAi technology over the last couple years. Monsanto acquired an Israeli company that uses RNAi to improve plant traits, as well as a pharmaceutical company with major intellectual property in RNAi research. Meanwhile, Syngenta purchased Devgen, a leader in RNAi crop protection.” (from Ref. 3 below)

Bottom Line: Agricultural spraying of RNAi has many significant challenges to overcome, not the least of which is governmental and public acceptance.

Online References

1. BioDirect™ – Monsanto

2. Antonio Regalad, “The Next Great GMO Debate.” MIT Technology Review (online) August 11, 2015. (Full Text)

3. Jackie Robin “RNA interference: Big potential for agriculture.” Ag-WestBio (online) April 17, 2015. (Full Text)

4. Narender Nehra and Nigel Taylor “Improving Crops with RNAi.” The Scientist (online) June 1, 2015. (Full Text)

5. Andrew Pollack “Genetic Weapon Against Insects Raises Hope and Fear in Farming.” The New York Times (online) January 27, 2014. (Full Text)

6. Apse

7. European Food Safety Authority (2014) “International scientific workshop ‘Risk assessment considerations for RNAi-
based GM plants
’.” Full Text (PDF)

YouTube Video of Dr. Wayne Hunter briefly explaining how RNAi technology can be manipulated to kill psyllids in citrus groves.

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Slurping Sugars

The main reason for pruning plants is to stimulate the growth of axillary buds, a.k.a., lateral buds. (Please see previous post.)

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

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

In the previous post regarding the biology of pruning, “new” scientific evidence (well, it was new in 2010) was presented about how apical dominance works on the cellular level.

Fast forward to 2015….

Currently there are new reports of scientific experiments that may significantly alter the way we explain the cellular mechanisms of apical dominance.

In 2014, a paper published in PNAS (see Ref. 1 below) claimed that sugars may indeed be more important than plant hormones in stimulating the growth of axillary buds in plants after removal of the apical buds.

Basically, here’s the story: “It is commonly accepted that the plant hormone auxin mediates apical dominance. However, we have discovered that apical dominance strongly correlates with sugar availability and not apically supplied auxin. We have revealed that apical dominance is predominantly controlled by the shoot tip’s intense demand for sugars, which limits sugar availability to the axillary buds. These findings overturn a long-standing hypothesis on apical dominance and encourage us to reevaluate the relationship between hormones and sugars in this and other aspects of plant development.” (from Ref. 1 below)

Increasingly, over the past few years, sugars – sucrose, and in particular trehalose 6-phosphate (T6P) – have been implicated in the regulation of plant growth and development (e.g., see Ref. 2 below), especially in the case of apical dominance.

But apical dominance is a complex process, and it’s likely that both sugars and plant hormones are involved in the story (see Ref. 3 below).


1. Mason, M. M., et al. (2014) “Sugar demand, not auxin, is the initial regulator of apical dominance.” Proc. Natl. Acad. Sci. (USA), Vol. 111, pp. 6092–6097. (Full Text)

2. Van den Ende, W. (2014) “Sugars take a central position in plant growth, development and, stress responses. A focus on apical dominance.” Frontiers in Plant Science, Vol. 5, p. 313.(Full Text)

3. Rameau, C., et al. (2015) “Multiple pathways regulate shoot branching.” Frontiers in Plant Science, p. 741 (Full Text)

For More Information: Here is a 40-minute YouTube video of a seminar about Ref. 1:

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Another Take On The Term “Rewilding”?

In the previous post, we explored the concept of crop “rewilding” as it pertains to genetically resurrecting “wild” plant genes by reintroducing or by re-activating them in some modern crop plants.

One of the main justifications for doing so is to develop new crop plants to help feed and clothe the Earth’s growing human population, especially since we may be soon running out of food (see As Global Population Grows, Is The Earth Reaching The ‘End Of Plenty’?, for instance).

With all of this freshly in mind, I was interested to discover a couple of recent stories (Refs. 1 & 2 below) that are sort of about crop “rewilding”.

But, in these cases, genetic engineering is NOT involved.

Instead of the resurrection of plant genes, these stories are about the resurrection of so-called “lost crops”. That is, native or traditional crop plants that may have been displaced by modern crop plants, such as GMO crops.

African Super Veggies

The idea of using indigenous crop plants as a basis for African agricultural development is not new.

In the 1990s, the US National Research Council (NRC) in Washington DC convened a panel to examine the potential of Africa’s ‘lost crops’, including grains, fruits and vegetables. Chaired by renowned agricultural researcher Norman Borlaug, the panel concluded that native plants held tremendous potential for improving food security and nutritional intake across Africa, and should be a greater focus for researchers.” (From Ref. 1 below)

It may have taken twenty years, but “Scientists in Africa and elsewhere are now ramping up studies of indigenous vegetables to tap their health benefits and improve them through breeding experiments. The hope is that such efforts can make traditional varieties even more popular with farmers and consumers.” (from Ref. 1 below)

Asiatic Cotton Versus GMO Cotton

The authors concluded that under rain-fed conditions, the benefits traditionally associated with growing Bt American cotton are not necessarily realised. They recommend that a range of factors – including yields and profits but also irrigation and alternative cotton varieties – should be taken into account when planning strategies to improve cotton farming in India.” (from: Oxford University News)


1. Cernansky, R. (2015) “The rise of Africa’s super vegetables”. Nature, Vol. 522, pp. 146-148. (Full Text)

2. Romeu-Dalmau, C., et al. (2015) “Asiatic cotton can generate similar economic benefits to Bt cotton under rainfed conditions.” Nature Plants, Article Number 15072. (Abstract)

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A Blast From The Past?

Is it just me, or does there seem to be a lot about the so-called “rewilding” of crop plants in the news lately? (Please see here, for example.)

I think I first heard the term “rewilding” about 20 years ago in a Biology Department seminar at Montana State University. In this case, the term “rewilding” was used in the context of conservation biology.

Simply put, rewilding, as a means of ecological restoration, has to do with reintroducing apex predators or keystone species into an environment. (Think wolf reintroduction into Yellowstone National Park, for example.)

But the recently-newsworthy “rewilding” of crop plants refers to something quite different. Instead of physically reintroducing “wild” species into “domesticated” ecosystems, crop plant rewilding has to do with genetically reintroducing “wild” genes back into the “domesticated” genomes of crop plants.

Of course, this can be done via traditional plant breeding techniques such as crossing a crop plant species with a wild relative.

But the main reason for the recent increased interest in the rewilding of crop plants is the emergence of new plant breeding techniques (NBTs) that are more precise and much faster than traditional “introgression” plant breeding.

“Introgression breeding is the standard method used to introduce genes and traits from wild plants into domesticated crops. This method uses an initial cross between the crop and the wild relative of interest followed by repeated backcrossing to the domesticated crop to erase as much genetic material from the wild relative as possible while keeping the trait of interest. Molecular markers can be used to track the trait of interest through the crosses, a process called ‘marker-assisted breeding’. However, introgression breeding is time consuming and technically challenging when more than one gene is being selected for, and it is often difficult to get rid of closely linked undesired genes.” (from Ref. 1 below)

Some of these new plant breeding techniques rely on powerful new ways to edit DNA (more about this later on).

Some of these NBTs involve methods of genetic engineering that allow for “rewilding” in such a way that the final crop can’t be distinguished from a crop bred by traditional means. Therefore, some scientists see a natural place for ‘rewilded’ plants in organic farming.

Because no “foreign” genes (from another species) are present in genetically-engineered, rewilded crop plants, will that render these GMO’s more socially acceptable?

More on this fascinating topic to come….


1. Andersen, M. M., et al. (2015) “Feasibility of new breeding techniques for organic farming.” Trends in Plant Science, http://dx.doi.org/10.1016/j.tplants.2015.04.011. (Full Text)

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The “Inside” Story?

An article in Science magazine (see Ref. 1 below) reports evidence supporting the hypothesis that leaf-dwelling, nitrogen-fixing bacteria may provide host plants with significant amounts of nitrogen.

In the past, we briefly explored the microbial phyllosphere, that is, the microbes – including nitrogen-fixing cyanobacteria – that dwell on the surfaces of plant leaves.

However, the bacteria in today’s story don’t dwell ON the leaves, but INSIDE the leaves.

Yes, there are bacteria (and fungi) that actually live in the spaces between the plant cells, inside the leaves. These microbes are collectively known as endophytes (as opposed to the surface-dwelling “epiphytes”).

And there is no question that most plants – even cultivated crop plants – likely serve as hosts for some endophytes.

The BIG question is: Do these endophytes affect the physiology (function) of the host plants? And, if so, how?

Presumably, the endophytes benefit, at least, from the solar-powered donut factory (i.e., photosynthesis) provided by the leaves. If the endophytes use some of the carbs (sugars) made by the plants, they are somewhat of a drain on the plant’s resources.

Then, another good question is: Why do the plants put up with these microbial “moochers”?

The likely answer is that the plants are somehow benefiting from these microbial endophytes. And, indeed, there are lots of studies showing that plants with certain endophytes may grow better (and may even survive harsh conditions better) compared to plants without these endophytes.

If this is true, then what are these microbial endophytes doing that benefits the host plant?

In other words.…

How Do Endophytes Work?

Despite all the studies showing that endophytes can improve plant growth (and may even be responsible for plant survival in extreme physical environments), precise reasons to explain HOW such endophytes do this have remained elusive.

At least a partial answer to this fundamental question may be provided by results reported in this Science magazine article (Ref. 1 below).

According to this article, at a recent scientific meeting, two separate researchers – Prof. Sharon Doty and Prof. A. Carolin Frank – presented evidence supporting the notion that that some leaf-dwelling bacterial endophytes can convert atmospheric nitrogen gas (N2) into a more biologically usable form (NH4+), which is then used by the host plants.

These results provide evidence that one reason that some bacterial endophytes benefit their hosts is by providing the plant with a source of nitrogen. Plants are often deficient in this essential mineral nutrient, especially in nutrient-poor soils.

Simply put, some of the bacteria living inside plant leaves may actually be fertilizing the plant with nitrogen.

However, this is a controversial hypothesis, and it has met with skepticism from some in the scientific community.

“That’s a radical notion, because nitrogen fixation is generally thought to happen primarily in bacteria-rich nodules on the roots of legumes and a few other plants, and not in the treetops. “We are completely fighting dogma,” says Doty, a plant microbiologist at the University of Washington, Seattle.” (from Ref. 1 below)

One reason for this skepticism is that the bacterial enzyme (nitrogenase) that converts N2 into NH4+ is significantly inhibited by oxygen gas (O2), which, of course, is quite abundant in photosynthesizing leaves.

Despite such objections some scientists “…are now cautiously embracing the idea. “There’s a change in attitude, not from skepticism to believing but from skepticism to cautious questioning,” says Gerald Tuskan, a plant geneticist at Oak Ridge National Laboratory in Tennessee. Tuskan and his colleagues have isolated about 3000 microbes from poplar, many of which are equipped with nitrogenase. Some sequester themselves in biofilms with oxygen-limited compartments, where nitrogenase could function even in the leaf’s oxygen-rich environment.” (from Ref. 1 below)

Why is this important?

Frank and Doty suspect that nitrogen-fixing leaf bacteria may be widespread, and, if transferred to crops, could help boost yields on marginal soil.” (from Ref. 1 below)

“Other plant biologists, although far from convinced, are paying attention. “If there’s an unrecognized set of nitrogen fixers in a wide number of [tree] species, that’s a big deal,” says Douglas Cook, a plant and microbial biologist at UC Davis.” (from Ref. 1 below)


1. Pennisi, E. (2015) “Leaf bacteria fertilize leaves, researchers claim.” Science, Vol. 348, pp. 844-845. (Abstract).

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You Talkin’ To Me?

Dodder (genus Cuscuta) is an example of a parasitic plant. That is, it derives some or all of its nutritional requirements from another living plant.

In a previous post, we saw how dodder seedlings may “sniff out” their victims.

But dodder seedlings may do much more than use volatile chemicals to find their plant hosts. Dodder may also “genetically communicate” with its host plant using small bits of RNA, specifically mRNA.

A paper published in the journal Science (see Ref. 1 below) has provided evidence that “When dodder attacks a host plant, it opens up a conduit through which messenger [RNAs] and perhaps other regulatory RNAs are exchanged between parasite and host. Because a single dodder plant can attack multiple hosts, such exchanges may underlie instances of genes transferring between species.” (from Editor’s Summary Ref. 1 below).

You can read a brief report regarding these findings HERE and watch a video below (thanks to Virginia Tech for both).

This is not the first report of small bits of RNA acting as a potential means of communication within an organism and between different organisms.

The ability of messenger RNAs (mRNAs) to move long distances in plants is well known. This mobility is thought to be controlled by the specific interactions between mRNAs and proteins that produce complexes capable of traversing plasmodesmatal pores into the phloem stream where they can be carried throughout the plant. Our understanding of this process has been limited by challenges in tracking specific mRNAs. In this issue of Nature Plants Thieme et al. [Ref. 2 below] describe a substantial step forward in characterizing mRNA mobility, revealing patterns of movement that suggest a broad scope and sophisticated regulation.” (from Ref. 3 below)

Of course, the main question about all of this is that, if small bits of RNA serve as a “language” among plants (and also among plants and fungi), then what are these organisms actually saying to each other?

There is some evidence that pathogenic fungi may use small bits of RNA to compromise the immune system of host plants (see for example small things considered).

It’s not unreasonable to expect that parasitic plants such as dodder use RNA trafficking to their advantage. For example, “…it is interesting to speculate whether RNAs from the parasite could be used as pathogenic factors in establishing and maintaining host connections.” (from Ref. 4 below).

Perhaps the greatest implication of all of this mobile RNA has to do with horizontal gene transfer.

As noted by the authors of Ref. 1 below:
This widespread exchange of mRNA raises the possibility of horizontal gene transfer (HGT). Given what appears to be a constant exchange of mRNA between Cuscuta and its hosts, the relative prevalence of cases of HGT involving Cuscuta is not surprising. Although most documented cases of HGT in parasitic plants suggest a mechanism involving direct transfer of DNA, at least one case of HGT into a parasitic plant (Striga hermonthica) exhibits evidence of an RNA intermediate in the mechanism.


1. Kim, G., et al. (2014) “Genomic-scale exchange of mRNA between a parasitic plant and its hosts.” Science, Vol. 345, pp. 808-811. (Abstract).

2. Thieme, C. J. , et al. (2015) “Endogenous Arabidopsis messenger RNAs transported to distant tissues.” Nature Plants, Article number: 15025 (Abstract).

3. Westwood, J. H. (2015) “RNA transport: Delivering the message.” Nature Plants, Article number: 15038.

4. LeBlanc, M., G. Kim and J. H. Westwood (2012) “RNA trafficking in parasitic plant systems.” Frontiers in Plant Science, Vol. 3, p. 203. (Full Text).

Parasitic Plant Time lapse – Virginia Tech from VirginiaTech on Vimeo.

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Dandelions Redux

Dandelions – Much Maligned.

Yes, it’s that time of year again in the upper left-hand corner of the USA when the dandelions are making themselves highly visible (by flowering). This prompted me to to consolidate and update a couple of previous dandelion-related posts.

A lot of people are pissed off by dandelions. Few plants generate such annoyance among suburban homeowners with immaculate lawnscapes as the common dandelion (in North America, they are most likely Taraxacum officinale).

What 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) and to kill crops (some of which were used as the enemy’s food source).

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.)

How Does 2,4-D Kill Dandelions…?

First produced in the 1940’s, the herbicide 2,4-D is one of many so-called phenoxy herbicides. These herbicides all are both structural and functional analogs of the plant hormone auxin, more precisely, indole-3-acetic acid (IAA). Such synthetic auxins as 2,4-D are not only structurally similar to IAA, but they are also biologically active as auxins in most 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.

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 kill the plant because ” it grows itself to death”, and I’ve read that 2,4-D “…simply confuses the plant to death”.


At 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 Ref. 1 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.)

Is Sex Necessary? – For The Common Dandelion, Apparently Not

Despite efforts to eradicate them using chemical warfare, the dandelions exhibit a remarkable ability to proliferate.

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.

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

Dandelions – Highly Underrated?

Perhaps to the chagrin of suburban “lawnscapers” who spend so much time and effort and money in eradicating dandelions, did you know that dandelions are actually commercially cultivated in many places in the United States? Vineland, New Jersey, may indeed be the “dandelion capital of the world”. See here and here for why.

Also, did you know that dandelions can be a significant source of latex for the manufacture of tires (or tyres, if you’re outside the USA or Canada)?

It’s true! See here and here, for just two links.

Yes, and because of this, dandelions are plants of interest to biotechnologists in the USA, Germany, and the Netherlands.

So, despite the fact that millions of pounds of herbicides are used every year to kill them in lawns throughout the USA, dandelions can be used for food and as herbs, to make wine (“mellow yellow”), and even to make tires (or tyres).

And, There’s More!

If you’d like more information about these plants that are seemingly ubiquitous this time of year because of their bright yellow flowers, here are some online resources:

  • Dandelions in folklore, in literature, and much more can be found here and here.


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

2. Grossmann, K. (2010) “Auxin herbicides: current status of mechanism and mode of action.” Pest Management Science, Vol. 66, pp. 113–120, (Abstract)

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Flowers That Change Color Over The Course Of A Day

Are transgenic plants a curse or a blessing?

Many people in the industrialized countries believe the former, despite ample scientific evidence to the contrary.

But I really don’t want to get into this thorny issue here, mainly because it’s been so well discussed elsewhere. (Please see, for example, Ref. 1 below.)

I would, however, like to tell you about some recent examples of genetically-engineered plants that may lead to greater social acceptance of plant GMO’s – starting with Petunia Circadia.

How would you like to grow plants with flowers that change color continuously throughout the day, from pink to blue and back again?

Well, the folks at Revolution Bioengineering are genetically modifying common petunias to do just that.

Here’s a YouTube video summarizing their story:

How do they do it? A good explanation can be found at: the science of color changing flowers.

For More Information: A list of stories about Revolution Bioengineering

If you’d like to grow some color-changing petunias, here’s your chance to help make it so:

Currently, Revolution Bioengineering is seeking financial support at INDIEGOGO, and you can see their latest updates here.


1. Raven, Peter H. (2014) “Transgenic Plants and the Natural World: Curse or Blessing?” (Full Text)

HowPlantsWork © 2008-2015 All Rights Reserved.

P1000980Where Does The Daffodil Flower’s “Trumpet” Come From?

An answer to this question can be found in a 2013 report published in The Plant Journal (please see Ref. 1 below). The full text of this article is now available online (thanks to the Wiley Online Library), and I’ve read it (so that you don’t have to). Here’s my take on this story:

Maybe we should we should start by taking a closer look at the flower of the daffodil.

Starting from the outside working in, the six petals are actually “tepals”, which are a kind of developmental combination of sepals and petals.

Next up is the famous trumpet-shaped part of the daffodil flower called the corona (“crown”) that is the main subject of this blog post.

The central part of the daffodil flower consists of the six stamens that encircle the carpel (gynoecium). In the photo above, you can barely see the anthers (produce pollen) of the stamens, and also you can only see the top of the carpel called the stigma (receives pollen).

When And How Is A Daffodil Flower Made?

You maybe surprised to find out that a miniature version of the daffodil flower actually develops not in the spring just before it blooms, but at the end of the previous growth season. Thus, a floral bud is fully formed, and over-winters, within the dormant bulb.

This means that plant scientists investigating daffodil flower formation (see Ref. 1 below) have to dissect out flower buds from the developing bulbs. Whew! (Thank goodness for grad students: nearly the ultimate in cheap labor. Ultimate = undergrads!)

Anyway, as a result of such efforts, Waters, et al. (Ref. 1 below) discovered that the daffodil corona forms relatively late in the flower-development program.

As described in a previous post, the flower-development program can be described like a play with several acts.

In the first act, the plant genetically shifts from a vegetative state to a flowering state.

In the second stage, which I call “arranging the chairs”, the spatial arrangement of the flower is determined.

In the third act, which I call “seating the guests”, the different flower parts (in this case, tepals, stamens and carpel) are seated in their appropriate “chairs”.

In daffodils (and perhaps other species within the Amaryllis plant family that have trumpet-shaped flowers) there apparently is an additional fourth act.

In this final act of daffodil flower development, new “chairs” are provided and arranged in a circle between the rings of the tepals and the stamens. These “late” guests are then seated.

The question was: to which of the four basic flower parts (sepals, petals, stamens, carpels) are these “late” guests most related? Turns out they are genetically related to stamens.

But, of course, an obvious question is: How does the daffodil make something that looks like petals by starting with the genetic “blueprints” for stamens?

The honest answer is we simply don’t know at the present time. It should be mentioned, however, that some of the results of Ref. 1 show that there is a late burst of coronal growth in the spring, so a great deal of elaboration of the “stamen” program is happening to result in a petal-like structure. This and other evidence suggest that petal-like structures “…can be produced by different genetic pathways even within the same flower.” (from Ref 1 below)

Why Do Daffodils Have Trumpet-Shaped Flowers?

Most explanations from botanists involve attracting pollinators. But who pollinates domesticated daffodils? Mostly likely, it’s people!

Most of the showy daffodils that we see in the spring in parks and around homes and businesses are a product of plant breeding, i.e., artificial selection, not natural selection. (You can read more about this here.)

That is, such daffodil flowers are a product of what has looked good to humans (daffodil breeders especially), not insects. Indeed, most of the domesticated daffodils that we see in the spring may not be especially attractive to bees, and thus the daffodils may not even be pollinated (unless the bees are desperate).

What about the origin and evolution of trumpet-shaped flowers (before humans got involved)?

No one can be absolutely certain of an answer, but the long narrow corona of the genus Narcissus may have evolved to accommodate pollination by bees over butterflies or moths, which can’t easily enter the tall narrow corona to access the pollen. (from Ref. 2 below)

In Summary:

If all of the above was a bit much, it might help to listen to a brief (4 min) audio clip about the daffodil’s mysterious trumpet courtesy of The Science Show on Australian Broadcasting Corporation’s RadioNational.

OK, if you’ve listened to this audio clip, then you’ve heard that the “trumpet” or “corona” of the daffodil flower is probably not an extension of the petals, as previously thought, but is a distinct organ – sharing genetic identity with stamens.

If you haven’t listened (and even if you have), you can read brief summaries of Ref. 1 (below) here and here.


1. Waters, M. T., A. M. M. Tiley, E. M. Kramer, A. W. Meerow, J. A. Langdale, and R. W. Scotland (2013) “The corona of the daffodil Narcissus bulbocodium shares stamen-like identity and is distinct from the orthodox floral whorls.” The Plant Journal, Vol. 74, pp. 615-625. (Full Text)

2. Graham, S. W. and S. C. H. Barrett (2004) “Phylogenetic reconstruction of the evolution of styler polymorphisms in Narcissus (Amaryllidaceae).” American Journal of Botany, Vol. 91, pp. 1007–1021. (PDF)

Question: Doesn’t the scientific study of flower development ruin people’s appreciation of the aesthetic beauty of flowers?

Answer: Here’s the best answer to this question that I know of, provided by Nobel Laureate (Physics, 1965) Prof. Richard Feynman:

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