(Arboricultural-styled) 'Fact of the Day'

[Kveldssanger]

22/09/15. Fact #38.

 

Photosynthesis requires both carbon dioxide and water for operations to function. Carbon dioxide is taken up via stomata, which are small openings in the leaf surface (usually on the underside in most abundance, but not always). However, for the leaf to uptake carbon dioxide, water will evaporate via the very same stomata.

 

Guard cells therefore exist, surrounding the cell, to control water loss and carbon dioxide uptake. Such cells, to operate efficiently, rely on numerous 'signals' both internal and external to the plant.

 

One main one is light intensity.

 

Blue light receptors (called phototropins) will respond to light intensity (blue light is utilised by the plant principally to assess light quality and quantity) and, increasing in-tandem with light intensity (to a point!), 'pump' positively-charged hydrogen ions out of the guard cells via the plasma membrane. As these ions move out of the cell, the intra-cellular negative electrical charge facilitates the inflow of positively-charged potassium ions.

 

As these potassium ions are drawn into the cell, water is also brought in via diffusion (water will move across a gradient and into a more 'concentrated' solution - in this case, K+ ions are causing the higher concentration). This water makes the guard cells 'stiff' (or turgid) and keeps them open, thereby facilitating carbon dioxide uptake and water evaporation.

 

Receptors of the guard cells will also respond to internal carbon dioxide levels. Elevated internal levels will cause guard cells to close, and vice versa. This is important, as the guard cells must respond to the needs of the leaf in regards to photosynthesis (interesting fact - respiration 'at dark' leads to high internal levels of carbon dioxide). As the process uses carbon dioxide, the guard cells will therefore continually be opening and closing, providing the needed levels of carbon dioxide, and controlling water loss also through responding to plant and atmospheric water (relative humidity) status.

 

I could go on...

 

Source: Karban, R. (2015) Plant Sensing & Communication. USA: The University of Chicago Press.

[daltontrees]

22/09/15. Fact #38.

 

Photosynthesis requires both carbon dioxide and water for operations to function. Carbon dioxide is taken up via stomata, which are small openings in the leaf surface (usually on the underside in most abundance, but not always). However, for the leaf to uptake carbon dioxide, water will evaporate via the very same stomata.

 

Guard cells therefore exist, surrounding the cell, to control water loss and carbon dioxide uptake. Such cells, to operate efficiently, rely on numerous 'signals' both internal and external to the plant.

 

One main one is light intensity.

 

Blue light receptors (called phototropins) will respond to light intensity (blue light is utilised by the plant principally to assess light quality and quantity) and, increasing in-tandem with light intensity (to a point!), 'pump' positively-charged hydrogen ions out of the guard cells via the plasma membrane. As these ions move out of the cell, the intra-cellular negative electrical charge facilitates the inflow of positively-charged potassium ions.

 

As these potassium ions are drawn into the cell, water is also brought in via diffusion (water will move across a gradient and into a more 'concentrated' solution - in this case, K+ ions are causing the higher concentration). This water makes the guard cells 'stiff' (or turgid) and keeps them open, thereby facilitating carbon dioxide uptake and water evaporation.

 

Receptors of the guard cells will also respond to internal carbon dioxide levels. Elevated internal levels will cause guard cells to close, and vice versa. This is important, as the guard cells must respond to the needs of the leaf in regards to photosynthesis (interesting fact - respiration 'at dark' leads to high internal levels of carbon dioxide). As the process uses carbon dioxide, the guard cells will therefore continually be opening and closing, providing the needed levels of carbon dioxide, and controlling water loss also through responding to plant and atmospheric water (relative humidity) status.

 

I could go on...

 

Source: Karban, R. (2015) Plant Sensing & Communication. USA: The University of Chicago Press.

 

I borrowed this nifty graph off the 'net, It is usefyul to appreciate that since photosynthesis uses CO2 and respiration produces it, and since it is unthinkable that a leaf wouldn't recycle CO2 wherever possible within the spingy mesophyll layer, what matters is the net CO2 demand at any time. Twice a day they might balance out to a net zero demand. I wonder if plants in the arctic circle that experience 24 hour daylight even bother to pump it.

[Kveldssanger]

Interesting addition there! Have you trawled Google Scholar for articles?

 

23/09/15. Fact #39.

 

Plants can respond to touch, or other form of mechanical stress, and subsequently adapt their form so that their growth is 'optimal'. But how does the plant actually achieve this - what signals are present, and how does the plant interpret that it needs to allocate growth to particular positions in response to mechanical forces?

 

Simply put, the reaction induces a response at the interface of the cell wall and plasma membrane. Within (quite literally) seconds of the interface being 'stressed', simply via mechanical stimulation (the plant's own growth) or via the plasma membrane being strecthed (external forces), the electrical resistance and 'action potential' changes. These processes stimulate ion channels that flow within the plasma membrane, causing positively-charged Ca2 (calcium) ions to move into the cells within the vicinity.

 

This localised influx in calcium ions upregulates genes in the 10-30 minute following stimulation, inducing adaptive growth. Particular species, such as Arabidopsis spp., may see at least 2.5% of the entire genome being 'upregulated' following such stimulation. In many other species, it is however likely to be less.

 

Sources:

 

Braam, J. (2005) In touch: plant responses to mechanical stimuli. New Phytologist. 165 (2). p373-389.

 

Chehab, E., Eich, E., & Braam, J. (2009) Thigmomorphogenesis: a complex plant response to mechano-stimulation. Journal of Experimental Botany. 60 (1). p43-56.

 

Karban, R. (2015) Plant Sensing & Communication. USA: The University of Chicago Press.

 

Lee, D., Polisensky, D., & Braam, J. (2005) Genome‐wide identification of touch‐and darkness‐regulated Arabidopsis genes: a focus on calmodulin‐like and XTH genes. New Phytologist. 165 (2). p429-444.

 

Telewski, F. (2006) A unified hypothesis of mechanoperception in plants. American Journal of Botany. 93 (10). p1466-1476.

Edited September 23, 2015 by Kveldssanger

[Kveldssanger]

To add to the above point, the book continues to suggest that recent advances have identified jasmonic acid being implicated in the overall process to touch response. Interestingly, where certain plants studied were unable to 'produce' jasmonic acid, mechanostimulant responses were non-existent.

 

There really is so much to this Plant Sensing & Communication book. It is truly fascinating. Get it if you can! It's good value, for such a comprehensive book.

Edited September 23, 2015 by Kveldssanger

[Kveldssanger]

23/09/15. Fact #40.

 

Gravitropism causes shoots to grow against gravity (up) and roots to grow with gravity (down). Simple enough. Though how does the tree 'know' how gravity is impacting its structure?

 

Via statolith cells, found within the interface of the cell wall and plasma membrane (the interface is pretty much the 'control panel' for the plant in terms of response to stimuli).

 

Rich in starch granules, these granules within the cells are subject to gravity and thus apply pressure on the cell's lower side, which 'informs' the interface of the direction of gravity.

 

Strain / stimulus / stretching of the plasma mebrane occurs, calcium ions are accumulated within cells locally (in the roots statoliths are found in the root cap, and in shoots within the endodermal layer), and a "biochemical cascade" (sounds cool) ultimately leads to asymmetrical auxin (growth regulator) distribution and, subsequently, directed growth.

 

Did I say this book was good?

 

Sources:

 

Karban, R. (2015) Plant Sensing & Communication. USA: The University of Chicago Press.

 

Morita, M. T. (2010). Directional gravity sensing in gravitropism. Annual Review of Plant Biology. 61. p705-720.

Edited September 23, 2015 by Kveldssanger

[Kveldssanger]

23/09/15. Fact #41.

 

I bet this'll throw you all! I shall quote.

 

"More carefully conducted experiments also suggest that plants use senses other than those that are currently well understood. For example in one study, proximity to a neighbouring plant influenced seed germination and growth of seedlings even when cues associated with light, chemicals, or touch were blocked."

 

Interesting...

 

Sources:

 

Gagliano, M., Renton, M., Duvdevani, N., Timmins, M., & Mancuso, S. (2012) Out of sight but not out of mind: alternative means of communication in plants. PLoS One. 7 (5). e37382.

 

Karban, R. (2015) Plant Sensing & Communication. USA: The University of Chicago Press.

[daltontrees]

Interesting addition there! Have you trawled Google Scholar for articles?

 

23/09/15. Fact #39.

This localised influx in calcium ions upregulates genes in the 10-30 minute following stimulation, inducing adaptive growth. Particular species, such as Arabidopsis spp., may see at least 2.5% of the entire genome being 'upregulated' following such stimulation. In many other species, it is however likely to be less.

 

Sources:

 

Braam, J. (2005) In touch: plant responses to mechanical stimuli. New Phytologist. 165 (2). p373-389.

 

Chehab, E., Eich, E., & Braam, J. (2009) Thigmomorphogenesis: a complex plant response to mechano-stimulation. Journal of Experimental Botany. 60 (1). p43-56.

 

Karban, R. (2015) Plant Sensing & Communication. USA: The University of Chicago Press.

 

Lee, D., Polisensky, D., & Braam, J. (2005) Genome‐wide identification of touch‐and darkness‐regulated Arabidopsis genes: a focus on calmodulin‐like and XTH genes. New Phytologist. 165 (2). p429-444.

 

Telewski, F. (2006) A unified hypothesis of mechanoperception in plants. American Journal of Botany. 93 (10). p1466-1476.

 

I am following this thread with an almost religious regularity, but I am dismayed by talk of upregulation. Why, because I don't know what it means. If it's in a dictionary at all, I suspect it's still in nappies (or more likely, diapers). Did the sources use the word? I'm old-fashioned about facts, and refuse to take them in unless they are unassailably true, but if I can't understand the lingo what chance have I? I shall slink back to the 20th century, clutching a printed dictionary with whitened and anxious knuckles.

Edited September 23, 2015 by daltontrees

[Kveldssanger]

Upregulation is used by the author of the book. When I read it I interpreted it as becoming more acutely sensitive. Guess I was partially right, as...

 

...the definition is quite good here.

 

Oh look, they're talking about nappies there (almost). Hah!

[daltontrees]

Upregulation is used by the author of the book. When I read it I interpreted it as becoming more acutely sensitive. Guess I was partially right, as...

 

...the definition is quite good here.

 

Oh look, they're talking about nappies there (almost). Hah!

 

Thanks for taking the trouble to find a reference, and for the dleightfully tenous link to diapers, but upregulating still sounds like a made-up americanism. They do it all the time over there, often as a means of impressing without informing. Like the incidences of 'misspeaking' which Obama used in self-deprecation, I'm still not sure what it means but seems to be somewhere between getting caught lying and getting caught not knowing what you are unmisspeaking about.

 

So I'll take the localised influx of Ca ions at face value, but the rest is beyond my comprehension.

 

But keep going, I'm all ... eyes.

[Kveldssanger]

I do understand where you are coming from. If I am honest, the author of the book has a good way of explaining things. Only a few things thus far have gone 'over my head', so to speak.

 

If I were to paraphrase this:

 

"This localised influx in calcium ions upregulates genes in the 10-30 minute following stimulation, inducing adaptive growth. Particular species, such as Arabidopsis spp., may see at least 2.5% of the entire genome being 'upregulated' following such stimulation. In many other species, it is however likely to be less."

 

I would say:

 

Cellular increases in calcium ions local to the stimulated area induce (through a far more complex series of events) a heightened sensitivity and thereby initiate adaptive growth responses (through the creation and distribution of hormones such as auxin), in the 10-30 minutes following on from initial stimulation.

 

Yes, I am paraphrasing my own parahrase!