Plant Chemical Out Posts

Flower of Garden Strawberry (Fragaria ×ananassa)
Image via Wikipedia

The search for chemical mediators in plant root rhizosphere interactions with symbiotic and pathogenic organisms found in the soil continues to generate interesting research. Martha Hawes group at the University of Arizona reported on the role of sugars, proteins and small molecules found in root cap secretions – a mucilaginous mixture that covers the growing root tip and “converses” with the surrounding matrix of living organisms. The cap is rich in root border cells, which detach from the growing root tip. Curlango-Rivera et al (2010) provides us a bit more detail about which metabolites are biologically active. Neither sugars nor amino acids triggered root growth or border cell production. Transient exposure to biologically active concentration levels of the isoflavonoid pisatin, a phytoalexin, stimulated root border cell production but not root tip growth. I wonder if inhibition of root elongation may “reset” plant growth patterns as root border cells, acting as chemical sense organs, define the nature of the environment?

A second paper used histochemcial methods to profile root metabolites in plants from the Rose family (Hoffman et al., 2010). They found flavan-3-ol molecules in the root tip and border cells. Their findings suggest that the distribution of flavan-3-ols in Fragaria and Malus is under tight developmental control. These molecules are found in plants as catechin and epicatechin derivatives and in long chain (polymeric) form. They influence the taste and medicinal potential of green tea and wine, to name a few well-known plants. Previous researchers summarized their role in chelating toxic cations (metals) in the soil, establishing mycorrhizal interactions and priming plant root defense. This paper suggests a role in the transport of the long distance plant hormone auxin, which would link the chemical cross talk at root border cells with responses that occur in tissue distal to root tips. Hoffman’s research lacked a clear distinction of whether the monomeric or polymeric flavan-3-ol forms where the active species. This has plagued plant research for some time, since the analytical methods for detecting the polymeric forms have been crude and ineffective. All of their samples were from a botanical garden. I wonder if the flavan-3-ol profile would differ compared to native wild grown species?

References:

  1. Curlango-Rivera, G. et al. (2010) Plant Soil 332:267-275
  2. Hoffmann, T. et al. (2011) Plant Biology, 13: no. doi: 10.1111/j.1438-8677.2011.00462.x

Mining the World of Science for Ideas and Language to Expand Your Poetry

This is based on a talk I’m giving at the 2019 Bay to Ocean Writers conference Saturday, March 9th.

Much like ekphrasis, which uses visual art as a jump off point, science articles offer both unique phenomena and highly specific vocabulary to build the scaffolding of poetry.  And the substructure of ideas provides space for more esoteric, even spiritual explorations that link questions about grand design with the granularity of a narrator’s voice.

In general, science articles provide examples of deep, underlying, non-linear patterns found in nature that can be mined for the bones of ideas that allow space for authentic emotional voice to emerge. And the observational phenomena appeals to the Imagist Poet in me. Scientific vocabulary and the specificity of meaning can be a barrier and a benefit. There’s a fine line between expecting readers to look up words and to learn ideas as part of their engagement with the poem, and locking them out with material that does not invite them into the poem.

During the rewriting and shaping process, I keep returning to the question of accessibility. I often turn to intelligent lay readers for feedback on whether they felt left out of or included in  the poem. I look for unique language and phenomena to weave interesting lines and phrases.

The poem in the example below, published in the The Syzygy Poetry Journal 2015, was sourced from several articles about the science of weather in the upper atmospheric layers. We live with our head down or lack awareness of events beyond the cloud layer. The poem asks what if we were creatures of air? And what does it mean to return to being human by falling to earth? The question has been asked before without the aid of scientific knowledge. The lineation and rhythmic structure supports the sense of being airborne and falling:

A Theory of Air

Gaia’s magnetic field snaps back
displeased at being rubbed
the wrong way.
An aurora borealis pungent
and teeming spills over
the invisible edge.

We are all creatures of air.

Hurricane speed currents plunge
ice crystals down to earth’s surface
as electrostatic discharge
organized in previously unexplored
directions, seeding nimbus dust
with reproducing bacteria
on the troposphere mist.

Our cellular progenitors, we carry
their imprint of sky, engulf
other ephemeral bodies
in symbiont desperation, a reverse
sublimation into mutlicellularity,
Gaia intending our existence
to be a lighter resurfacing
less of the organized, arrogant
tissue we now drag through air.

Another example, published in The Broadkill Review 2015, originated as an investigation into the developmental pattern found in Boneseed lilac (Osteospermum spp.) flowers, and how the elaboration of biological function was tied to a Fibonacci sequence (each number is the sum of the previous two numbers, geometrically creating a nautilus-like shape).

It became a bit of a rabbit hole, pursuing Fibonacci, the mathematician and his effort to popularize Hindu–Arabic numeral system in West, which advocates numeration using digits 0–9 and place value. The math in those cultures had far surpassed western thinkers. Adoption of the new numbering system was transformational.

The worm hole eventually took me into researching Pascal’s contribution to probability theory, specifically, Pascal’s wager – An infinite gain will always outweigh even a finite loss or gain. Therefore, it’s always more rational to bet that God exists.

At some point the poem forced me to pull back so I could understand what I was actually seeing and to create the physical phenomena that would become the structure for the personal narrative to unfold.

Bone Seed Lilac

Poised on this final cusp
of summer, florets settle
into opposing spirals,
tenderly
bleed magenta.

A Fibonacci sequence floats
outward from the zero point,
self-similar
and counting itself into existence.

Osteospermum,
one of the smaller daisy tribes,
reminds us of how
Hindu numbering emerged
elegant and bathed in spectral
light, its wind sway
establishing resonance,
a field pattern negative
of wrens in flight.
The hard decay of its seed
will hint at dark matter,
Pascal’s wager of infinite
loss, our reliance on small
gods of fixed dimension, ignoring
the rhythm of deeply
repeated patterns,
fractal emanations
altering topography so life
might begin again.

At the end of the day, the creative process allowed me to push away from ensuring that everything was scientifically accurate. The song found in the structure and rhythm of the language, the sense of entering into new and potentially sacred space, all this needed to be present, to invite the reader into the adventure of finding out what poem was waiting to emerge.

 

Both of these poems can be found in my book, The Acoustic Properties of Ancient People, published by Finishing Line Press.

Ecological Rational for Multiple, Plant Secondary Compounds

(Gossypium L.)
Image via Wikipedia

As I’ve studied medicinal plants, one intriguing question keeps cropping up – what is the biological rationale for plants investing in several classes of structurally varied plant secondary metabolites?. Certainly this question drives a number of researchers in the field of plant chemical ecology. Edwards et al (2008) provided some striking evidence from their study of bacteria resistant cotton (Gossypium hirsutum).

They detected flavonoid pigments, chrysanthemin and isoquercitin, at unusually high levels in epidermal tissue of young leaves in response to Xanthomonas infection. These cells clustered around infected cells that had died because of the plant’s hypersensitive resistance response.

A very different chemical, a  sesquiterpene, 2,7-dihyroxycadalene, acted as a light activated phytoalexin, destroying both bacteria and the infected plant cell. So what were the flavanoids doing to help out? The presence of the flavanoids in surrounding cells appeared to filter sunlight, limiting the generation of free radicals resulting from light activation of 2,7-dihyroxycadaline. How’s that for compartmentalizing your response to friends and enemies?

Good Wine, Good Fungi

A study of organic soils found that the those associated with organic gardening compared to conventional methods or native grasslands, was very similar in types and diversity of mycorrhizal fungal taxa to that of the native soils. Increasingly, viticulturalists have been promoting the sustainability of using organic techniques over the fungicide heavy approaches of conventional wine management practices, and that this fundamental investment in “terroir” makes better wine. One method is to restore the density and diversity of beneficial, symbiotic fungi in the vineyard soil. These fungi are seriously depleted in soils that have had extensive chemical fertilizers, fungicides or pesticides applied.

Mycorrhizal inoculum applied to new vines plantings and as a dressing to cover crop used to improve nitrogen availability in vineyard soils, associates with the vine roots and  increases both the available levels of organic carbon and the water holding capacity of the surrounding soils. And with healthy vines, and a biological approach to vineyard management in place, the rhizosphere community rich in mycorrhizal fungi can influence the quality of wine produced. 

Gabriele et al. (2016) investigated the effect of mycorrhizal inoculation of various Sangiovese wine grapes. The symbiotic relationships improved the oxidative stability, thus the potential ability of the wine to age, and increased 14 polyphenols compared to un-inoculated plants. The later effect may improve the structure and the flavor profile of the wine.

I’ve asked to join the downstream portion of the research team to investigate the impact of these changes on the consumers experience.

What’s the Best Way to Flirt with Mycorrhizal Fungi?

Signaling molecules from either plant or fungi are perceived by the other using receptors. Many plants monitor their ecosystem for bacteria or fungi using receptor-kinases, which as cell surface proteins activate a signaling cascade in the cell to change it’s function in some way. Research groups continue to unearth various themes on this mechanisms for plant/mycorrhizal communication.

One model, identified Lipochitooligosaccharides (LCO) as signal molecules used by nitrogen fixing bacteria (rhizobia) to alter how plant roots form a symbiotic relationship. Communication using LCOs allows plants to gain nitrogen from soil bacteria and bacteria to gain carbon in the form of plant sugars. Similar molecules are excreted by arbuscular mycorrhizal (AM) fungi. This research noted that a mixture of sulphated and non-sulphated lipochitooligosaccharides (LCOs) secreted from the AM fungi, Glomus intraradices, stimulated root branching and growth in the legume Medicago truncatula. Apparently, the diffusible chemicals activated plant root genes that code for a series of receptor kinase. In M. truncatula, rhizobium LCO secretions also stimulate the same symbiotic pathway. The researchers found this signaling effect active in diverse plant species.

In other experiments, scientists found a hydrolase protein (D14L), which functions deep within the cell, modulating plant communication with AM fungi. This receptor had originally been characterized as a receptor for Karrikin, a plant hormone produced when plant material is burned. In species such as eucalyptus and the tobacco family, this hormone detects smoke and stimulates seed germination after fire has decimated an ecosystem. It allows those plants, known as fire chasers, to outcompete in the newly altered environmentWhat is particularly interesting – the same protein is part of early plant developmental interaction with light, and may have played an evolutionary role in plant emergence on to land.

So burn a little incense, light a candle, offer up something sweet and see if your mycorrhizal fungus responds. You don’t need to burn down the entire house!

Outpost Communication

Dr.  Martha Hawes has been a pioneering researcher on plant root border cells. I became fascinated with their role while researching the fungal/plant communication in the rhizosphere of goldenseal (Hydrastis canadendis) during my doctorate. I called her lab hoping someone might speak with me. She answered and spent an hour pointing out important research papers and suggesting approaches I might take to incorporate root border cell research. She was always open to helping anyone with a curious mind and passion for the subject into which she’d immersed her career efforts. I’m grateful to her for showing me generosity and kindness.

Plant root border cells are formed at the root tip where physical and biological interactions occur with the soil and microbe communities. The cells are genetically programmed to separate from the rest of the root structure and from each other. Cell-wall degrading enzymes dissolve cell wall matrix material that holds plant cells together. These “outpost” remain biologically active, excreting proteins and smaller molecules into the surrounding environment. Both types of molecules act as signals turning on/off gene expression to stimulate or prevent the growth of soil-borne bacteria and fungi. One important role appears to be in establishing a symbiotic relationship with mycorrhizal fungi (see previous post).

Few plants such as the Arabidopsis thaliana, which do not produce root border cells, also do not form mycorrhizal associations. In most plants, the content of border cells are accessible only to microorganisms able to recognize and respond to specific root signals. Among the compounds located in root border cells of various plants, medicinally valuable isoflavonoids modulate stable ecological relationships between mycorrhizal fungi and plant root tissue. These fungi stimulate the production of isoflavonoid in plant root tissue, while simultaneously the isoflavonoids increase mycorrhizal spore germination. The spores are an important survival mechanism used by the fungi. Measuring the activity in root border cells in “real time” as they interact with fungi is one of the great challenges to plant biologists.

Here’s a short video showing the release of border cells from a plant root cap:

More in-depth readings:
Harrison, M. and Dixon, R. (1993) Isoflavonoid accumulation and expression of defense gene transcripts during establishment of vesicular-arbuscular mycorrhizal associations in roots of Medicago truncatula. Mol. Plant Microbe Interact. 6:643-654
Hawes, M,C. et al (1998) Function of root border cells in plant health: Pioneers in the Rhizosphere, Annual Review of Phytopathology, 36:311-327.
Hawes, M.C. et al (2003) Root Caps and Rhizosphere. J. Plant Growth Reg. 21:353.
Kape, R. et al (1992) Legume root metabolites and VA-mycorrhiza development. J. Plant Physiol. 141:54-60.
Phillips D.A. et al (2004) Microbial products trigger amino acid exudation from plant roots. Plant Phys. 136: 2887-2894

The Real Gumbo Recipe

I wanted to follow up requests in response to my post on Spices, and share the gumbo recipe I mentioned. 

It’s my mom’s from her mom, Nannie (Louise P. Curtis)

I’ve used Nannie’s original language

Start with 1 large TBS bacon, ham or sausage drippings in heavy saucepan

Chop 1 pound of okra, 1 large onion, 1 large bell pepper and 5 cloves of garlic

Fry in oil until wilted. Okra will lose stringiness.

Add 1-2 TBS of flour. Cook slowly about 30-45 minutes until okra gets drier.

Add 1 can tomato paste

Add hot seafood water, about 4 cups

Add seafood 1  lb crabmeat and 1 lb peeled shrimp

Add seasonings:

  • 2 drops Tabasco or cayenne pepper
  • salt and pepper to taste
  • a couple of bay leaves
  • chopped celery (1/4 cup)
  • green onions and parsley (optional)

Simmer for about 1 hour over very low fire

Serve over rice

 

Note: I always added olive oil and Louisiana Crystal Hot Sauce and opened a bottle of Jax or two.