Re: Seeing more red

[Thomas Barr <tcbiii at earthlink_net>]

James quoted:
> 
> "In addition to promoting energy transfer to or from chlorophyll,
> carotenoids play an important role in protecting photosynthetic organisms
> from damage resulting from the photochemical generation of oxygen radicals
> (Sandmann et al. 1993)."

The "caroteniods" in question here are ones that deal with excess light.
The Xanthophyll cycle and other compounds involved in the light havesting
complex. It gives the excess light off as heat through rapid de-epoxidation,
sort a lighting rod starting with Violaxanthin + excess light=>
Antheraxanthin + excess light=> goes to zeaxanthin.
This process produces heat and is one step that preserves/protects the Mn O2
evolving enzyme in PS II from  excess light.
Under low light, the opposite occurs. Zeaxanthin + low light=> reverts back
to Vioaxanthin. 
Those free radicals will build up in excess light raising the H+
concentrations in the lumen(acidification) and destroys this Mn evolving
enzyme. Lipid bi-layers (membranes) start "leaking" when this happens. The
MnO2 evolving molecule is an "expensive" molecule to make and build and once
altered, the plant cell has to rebuild it from scratch, it cannot simply do
a quick repair if too much light energy is added, even a small change in
conformation will mess it up.

This cycle can be slowed a great deal N is limited. It is also dependent on
plant species, growth conditions etc, ambient temps etc.
(Demmig-Adams and Adams 1996)-see "sunflecks". Also in Both text I refer to
later.

Caroteniods are linear, anthocyanins are 3 ringers with a sugar group
attached to one side. The Xano's have a ring at each end of the linear chain
etc.
Other caroteniods besides those of the Xanthopyll cycle also dissipate heat
if the Chl molecule is "full".
There are several other methods plants have to deal with excess light. See
the table I sent about adaptations to high/low light leaves a few weeks
back. Fluorescence is a neat way the plants give off excess light energy.
 
  
> 
> Further on in the text, in a discussion on UV-b inhibition on page 295, they
> discuss some of the possible ideas for why and how UV can damage plant
> cells. They do say that the plant is often capable of repairing itself at
> the same rate that it is bring damaged and quote Cullen, Neal 1993 for the
> statement. They continue:

Plants have many adaptations to high and low light.
I gave a detailed listing of the many ways plants adapt to high and low
light, last month or two or so ago.
Some methods are fast, within 10-^15 sec some much slower, days, months etc.
Anthocyanin is not a caroteniod.
 
> "Numerous strategies to screen UV-b radiation have evolved in photosynthetic
> organisms. One of the most common is the production of pigments which absorb
> the radiation and screen it from the photosynthetic apparatus. Some
> carotenoids, such as beta-carotene, serve this purpose (Dohler, Haas 1995)."

Doesn't say why a plant is red. I can have lots of Beta Carotene without
being red in color.
Why would a carrot have all that beta carotene in the root and not in the
green leaf? Neil pointed out that if there's not chl to mask the other
pigments, they will show themselves more.

But that's a fine line to walk, too much, kills the plants, too little, no
color. 
 
There are many ways, not just this way to deal with high light. High light
doesn't guarantee red color.
Your giving ref's here but it is not relevant to the issue of why a plant
turns red. I can give way too many examples to prove a generalization that
you are trying to support here invalid. You may find specific plants, but I
can find more examples of the opposite I would venture to counter this
notion.
 
> In the 6th edition of Photosynthesis, by Hall and Rao (1999), in section 3.2
> Chloroplast Pigments, they state:

Hey.......
Anthocyanins are not in Chloroplast. Caroteniods like Beta carotene etc are.
Anthocyanins are in the vacuole and cytoplasim.
You can see this clearly with a microscope.

Anthocyanins are colored flavionds that attract critters for pollination and
seed dispersal. That's their main function for plants.

Caroteniods are another group of colored pigments.

Now *Flavones* and *Flavonols* absorb the shorter wavelengths(UV-b) etc but
consider what sees in the UV ranges.........bees. Pollinators.

But they are present is other parts of the plants and can protect against
UV-B. That has been proven(Li et al 1993).

But ..........these ain't anthocyanins.........
 
> "The carotenoids are yellow or orange pigments found in most
> photosynthesizing cells. Their color in the leaves is normally masked by
> chlorophyll,... They have a triple-banded absorption spectra in the region
> from about 400 to 550 nm. The carotenoids are situated in the chloroplast
> lamella, bound to proteins, in close proximity to the chlorophyll. The
> energy absorbed by the carotenoids may be transferred to the chlorophyll a
> for photosynthesis. In addition, the carotenoids protect the chlorophyll
> molecules from too much photo-oxidation in excessive light."

Caroteniods do the protecting and collecting of the light etc. Doesn't say
why red or not. Taste good though, Carrots, mmmuumm.

These light harvesting accessory pigments are sort of set up like a
satellite dish, with P680 or P700 in the middle. Stuff, photo chemistry,
happens very fast there.
 
> From these, and from what both you and Karen have added, I am left with a
> number of questions -
> 
> Does your statement above (regarding Anthocyanins) also apply to
> Carotenoids, thus thowing out what was written in Aquatic Photosynthesis?

What they wrote is accurate, how you interpreted it and applied may not be.
Specifically which caroteniod? Flavones and Flavonols etc, yes right on the
money. Anthocyanins? Nope.
 
> Can you please let the rest of us know what sources you base your dismissals
> upon?

Certainly, Lambers, Chapin and Pons, Plant Physiological Ecology(1998), a
much used botany book with many of the top people in the field today adding
to the book, and considered one of the better/best text for bridging ecology
and Physiology. Look to page 367. There are list of ref's in the back of
each section.
You'd like that book I'd say.
There are others, more focused on the molecular aspects. Taiz and Zeiger
Plant Physiology (1998) is also good, pg 363-367.

Both of these books are used for Plant Physio and Physio Plant Ecology from
FL to CA at the top schools by the top prof's. Both States have BIG
agricultural plant programs.
   
> Has knowledge progressed THAT fast that a book published in 1999 is
> hopelessly out of date in 2002?

Nope. It's a good book, I don't have one but I've thumbed through it.
 
> Are you saying or implying that the non-green colors seen in some aquatic
> plants are totally unrelated to the photosynthetic pigments that are in the
> plants? Are we chasing the wrong rabbit? Which bunny do you chase?

The fat lazy one that is the easiest to catch.
Well it could be totally unrelated to light, but everything is related to
light to a certain degree.
I just think it's much more complex than simply an issue of light, strong vs
weak etc.
It takes light, AND CO2 AND NUTRIENTS to grow plants, not just one of these.
Within a range, things do pretty well. NO3 limitation for example.
Now if you do the test here, use a red Rotala or a Ludwigia sp, keep the
light the same, CO2, good nutrients all around and move the NO3 from 15ppm
and let it drop down to 2ppm and keep it low in the 5 or less range without
bottoming out for more than a day etc, you'll certainly see intense reds.
Most red variable color plants will show this pattern and we can see this
with our own eyes pretty well.
So that's one reason not related to light if we kept light constant with the
NO3 limitation being the dependent variable vs coloration.
But you could play with light and also play with NO3 and PO4.
I'd mess with these in the water column.
Fe I'd add both in the water column and the substrate.
IME, lighting does bring out different growth patterns, some differences in
color etc. But I think a much greater pattern exist with macro nutrient
manipulations. I have had more healthy growth at lower color temps and nicer
color at high color temps. A balance of both seems ideal to me.
How high? How low?
I think 4000K-5000K for the low and 6500-8800K for the high seems fine.
I'm going to try the 8800 K PC bulbs + a 5000K coming up in a week or two.
 
> Or are you saying that aquatic plants, on their way back into the pond,
> picked up some tricks that their land plant ancestors didn't need and the
> rest of us haven't figured out yet?

Possibly, being an antifungal, antiherbivore(?) pigment or to attract a
pollinator.
 
> It can get bewildering for the rest of us when someone dismisses an idea out
> of hand without offering an alternative hypothesis, either of your own or
> from someone else.

I cannot always back up every possible statement but if folks have question,
they can ask. I'll respond. There's simply no way to explain much in one
post, who the heck would read a 20 page rant?
May seem like hair splitting but much in this world seems to go down that
path. 
Regards, 
Tom Barr
 
> James Purchase
> Toronto