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Archive for the ‘Secondary Compounds’ Category

wicked_plantsToxic? Yes!….. But wicked?

Wicked (wik’id) adj. [Middle English wikke, evil, akin to Old English wicce, witch] “1. morally bad or wrong; acting or done with evil intent; depraved; iniquitous.” – Webster’s New World Dictionary

A wonderful new book Wicked Plants: The Weed That Killed Lincoln’s Mother and Other Botanical Atrocities by Amy Stewart, which I just finished reading, describes the myriad of chemical compounds found in some plant species that are toxic to animals – especially humans. Of course, such toxic plants aren’t evil or “wicked”. They’re just passively defending themselves against herbivores.

But calling them “wicked” certainly attracts more attention and sells more books, no? And isn’t it a good thing that more people would then learn about plants? So, fair enough.

Perhaps an interesting question to consider is why these plants have come to produce such toxic chemicals.

belladonnaThese “Wicked” Toxic Chemicals are Plant Secondary Compounds

It may come as a surprise to you that most of the basic metabolic pathways found in your cells – glycolysis, respiration, protein synthesis, etc. – are also found in most plant cells. Plant and animal cells likely share a common ancestor – a primitive eukaryotic cell. Thus, both plants and animals have many of the same so-called primary (a.k.a., “housekeeping”) metabolic pathways.

But, since plants don’t eat stuff, they have to make all the specialty organic compounds, such as amino acids, vitamins, pigments, etc., that they need to function well.

Therefore, plants not only have the “primary” metabolic pathways, but also so-called “secondary” metabolic pathways. That is, plants have special (secondary) metabolic pathways to achieve special functions, such as protecting themselves from UV light, chemically attracting pollinators, surviving periods of drought, etc.

Plants Can’t Pee, So They Have to Recycle or Store Their Secondary Metabolic Byproducts

If you ever took an organic chemistry class, you make recall that in chemically synthesizing an organic compound, you would sometimes generate chemical byproducts. Plants do this, too. But how do they get rid of them?

smokerOften, they store these byproducts of secondary metabolism or “secondary compounds” in the vacuole of plant cells. The vacuole sometimes functions as the plant cell’s “garage”.

If one such secondary compound turns out to be nicotine, for example, which just so happens to be toxic to some insect herbivores, then it’s a lucky break for the plant. By chance, an evolutionary selective advantage for the plant has occurred.

And if this compound also turns out to affect humans, then this also may be a lucky break for the plant. (Nice to be cultivated.)

So most, if not all, of the toxic compounds mentioned in “Wicked Plants” are secondary plant metabolties stored in the vacuoles of plant cells. When the plant is eaten, or if trichomes on the plant surface are crushed by contact, the toxic compounds are released, which deter (or, in some cases, inter) potential herbivores.

All just by chance.

No evil or “wicked” intent involved.

HowPlantsWork © 2008-2011 All Rights Reserved.

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Bee_eye.jpgThe eye of a honey bee (photo credits).

Flowers look very different to insect pollinators, such as honey bees, compared to what we mammals see.

As the photo on the left shows, bees have compound eyes.

How a bee sees patterns as a result of its compound eyes is wonderfully illustrated at Andy Giger’s B-Eye website.

Like humans, bees can perceive different colors. (This has been know for over 100 years.)

Unlike humans, however, bees can perceive ultraviolet (UV) light.

Thus, the pigments in flower petals that absorb UV light create patterns visible to bees, but that may be invisible to humans. (see photos below)

These patterns are sometimes referred to as “honey guides” or “nectar guides” that presumably serve to direct the pollinators toward the center of flowers.merge

Flowers in Ultraviolet is a fantastic website that illustrates this in dozens of flowers categorized by plant families.

It was Thompson and co-researchers in 1972 that first published a connection between chemicals called flavonols and patterns on flower petals that may attract insect pollinators.

Plant flavonoids may be the UV-absorbing pigments mostly responsible for the patterns that attract insect pollinators as discussed here.

Taking Photos of Flowers in UV

If you are interested in taking such UV photographs of flowers this is an excellent website to learn how and to see what you need to get started.

For another website on the science and practice of photographing the “invisible” please visit beyondvisible.com.

Flowers Use Several Strategies to Attract Pollinators

It’s clear that some plants have the petal equivalent to “landing lights” at airports to guide airborne pollinators such as bees to the flowers.

Plants also use nectaries and floral scents to attract pollinators. (Bees have odor receptors at the base of their antennae.)

Recent research has provided clues regarding how moths key into the scent of a flower, for example.

Bees apparently have pretty short (5 to 10 seconds) memories and, thus, use a combination of visual and chemical (volatiles) cues to locate flowers.

More on this subject can be found in an excellent review (PDF) of how pollinators recognize flowers.

These just in:

Flowers may also facilitate pollination by using a sort of petal “velcro”.

Video of bee landing.

Bees Recognize Human Faces Using Feature Configuration

“Landing Lights for Bumblebees”

Bees can solve complex mathematical problem.

Leaked Memo Shows EPA Doubts About Bee-Killing Pesticide

For further reading, here are some books about bees:
The Buzz about Bees: Biology of a Superorganism

The Life and Times of the Honeybee

Plan Bee: Everything You Ever Wanted to Know About the Hardest-Working Creatures on the Planet

Bottom Line: Many plant species have flower petals containing pigments that absorb UV light, producing patterns presumably visible to – and providing guidance to – insect pollinators, but not to humans (normally, non-pollinators).

HowPlantsWork © 2008-2011 All Rights Reserved.

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