can we say that global warmimg will result with more photorespiration in c3 plants if precautions are not taken?

I'm not sure about this, because CO2 levels in the atmosphere are increasing... which might indicate that there would actually be LESS photorespiration because of increased CO2 levels. Curious to hear what others think.

In the last paragraph. How can photorespiration support plant immune defenses?

Plant defense mechanisms include different kinds of cell signaling pathways and cascades. Certain membrane-spanning receptors react to pathogens and activate gene expression. However, in order to proceed with those mechanisms, photosynthesis has to be disrupted. As we know, photorespiration is that 'salvage' way which occurs once photosynthesis is disrupted.

what are plant pigments?

There are many types such as Chlorophyll A, Chlorophyll B, Xanthophyll, Carotenoids, etc. They function to lengthen the absorption spectrum. Some, like the last two pigments listed, also function to increase photoprotection. The Chlorophyll A is what is most prevalent in the leaf, and therefore, gives the leaf its color.

Why do the numbers of carbon in the diagram for Photorespiration not match up

They do, There are 6 5-carbon RuBP molecules (30C), which are broken into 6 3-carbon PGA molecules (18 C) and 6 2-carbon phosphoglycolate molecules (12C). These 2-carbon phosphoglycolate molecules are further broken up into 3 3-carbon PGA molecules (9C) and 3 1-carbon CO2 molecules (3C). The CO2 is released (3C), the 9 total PGA (9x3=27C) are used to regenerate some, but not all of the RuBP. Total product being 9 PGA and 3 CO2 (27C+3C=30C) which is the same amount as we started with in the 6 RuBP

If alternative systems exist to solve this problem, why don't all plants use those systems? Is it less efficient?

It isn't really such a big enough deal to completely wipe out RuBisCo. Remember, back when plants were first starting, there was WAY more CO2 than oxygen. Plus, scientists are beginning to research if there are hidden benefits that haven't been identified yet.

When C3 plans are in a hot environment what do they first die of? Because their ability to produce glucose is significantly reduced and they will eventually use up all their H2O ?

I think of take in CO2 during day whicc CAM plants doesn't and en up losing (not use up) H2O.

Concerning the last part of the text above... How exactly can plants get light-induced damage, how does this damage the plant and how does the redox balance help against this (Does this have something to do with reactive oxygen species?)?

Yes, exactly! It has to do with reactive oxygen species! It was also mentioned in the videos prior to this. Photorespiration is some kind of 'salvage' and protective pathway which avoids the accumulation of unnecessary 02 which could potentially elicit great damage in cells in the form of reactive oxygen species.

why is photorespiration taking place in three different places chloroplasts, leaf peroxisomes and mitochondria?

This is because the different enzymes needed for amination and oxidation of different intermediates are present in the above said 3 organelles. The detailed diagram of the cycle ought to clear your doubt.

Main content

Course: AP®︎ Biology (2018) > Unit 10

Lesson 4: Photorespiration: C3, C4, and CAM plants

Photorespiration

Google Classroom

Photorespiration is a wasteful pathway that competes with the Calvin cycle. It begins when rubisco acts on oxygen instead of carbon dioxide.

Introduction

Do you have any friends who are awesome people, but who also have some kind of bad habit? Maybe they procrastinate a lot, forget your birthday, or never remember to brush their teeth. You wouldn't stop being friends with them for these reasons, yet from time to time, you might find yourself wishing they would clean up their act.

RuBP oxygenase-carboxylase (rubisco), a key enzyme in photosynthesis, is the molecular equivalent of a good friend with a bad habit. In the process of carbon fixation, rubisco incorporates carbon dioxide (

{CO}_{2}

) into an organic molecule during the first stage of the Calvin cycle. Rubisco is so important to plants that it makes up

30 %

or more of the soluble protein in a typical plant leaf

^{1}

. But rubisco also has a major flaw: instead of always using

{CO}_{2}

as a substrate, it sometimes picks up

O_{2}

instead.

This side reaction initiates a pathway called photorespiration, which, rather than fixing carbon, actually leads to the loss of already-fixed carbon as

{CO}_{2}

. Photorespiration wastes energy and decreases sugar synthesis, so when rubisco initiates this pathway, it's committing a serious molecular faux pas.

In this article, we'll explore why photorespiration happens, when it's most likely to take place (hint: think hot and dry conditions), and how it actually works.

Rubisco binds to either ${CO}_{2}$ ‍ or $O_{2}$ ‍

As we saw in the introduction, the enzyme rubisco can use either

{CO}_{2}

O_{2}

as a substrate. Rubisco adds whichever molecule it binds to a five-carbon compound called ribulose-1,5-bisphosphate (RuBP). The reaction that uses

{CO}_{2}

is the first step of the Calvin cycle and leads to the production of sugar. The reaction that uses

O_{2}

is the first step of the photorespiration pathway, which wastes energy and "undoes" the work of the Calvin cycle

^{2}

What determines how frequently each substrate gets "chosen"? Two key factors are the relative concentrations of

O_{2}

and

{CO}_{2}

and the temperature.

When a plant has its stomata, or leaf pores, open

{CO}_{2}

diffuses in,

O_{2}

and water vapor diffuse out, and photorespiration is minimized. However, when a plant closes its stomata—for instance, to reduce water loss by evaporation—

O_{2}

from photosynthesis builds up inside the leaf. Under these conditions, photorespiration increases due to the higher ratio of

O_{2}

{CO}_{2}

In addition, Rubisco has a higher affinity for

O_{2}

when temperatures increase. At mild temperatures, rubisco's affinity for (tendency to bind to)

{CO}_{2}

is about

80

times higher than its affinity for

O_{2}

^{3}

At high temperatures, however, rubisco is less able to tell the molecules apart and grabs oxygen more often

^{4}

The bottom line is that hot, dry conditions tend to cause more photorespiration—unless plants have special features to minimize the problem. You can learn more about plant "workarounds" in the videos on C4 plants and CAM plants.

Photorespiration wastes energy and steals carbon

Photorespiration begins in the chloroplast, when rubisco attaches

O_{2}

to RuBP in its oxygenase reaction. Two molecules are produced: a three-carbon compound, 3-PGA, and a two-carbon compound, phosphoglycolate. 3-PGA is a normal intermediate of the Calvin cycle, but phosphoglycolate cannot enter the cycle, so its two carbons are removed, or "stolen," from the cycle

^{5}

To recover some of the lost carbon, plants put phosphoglycolate through a series of reactions that involve transport between various organelles. Three-fourths of the carbon that enters this pathway as phosphoglycolate is recovered, while one-fourth is lost as

{CO}_{2}

^{5}

How does the photorespiration pathway actually work? To answer this question, let's follow the path of phosphoglycolate, starting when it's just been made in the chloroplast via rubisco's oxygenase reaction

^{5, 6, 7}

Phosphoglycolate is first converted to glycolate inside of the chloroplast. Glycolate then travels to the peroxisome, where it's converted to the amino acid glycine.
Glycine travels from the peroxisome to a mitochondrion. There, two glycine molecules (e.g., from two iterations of the pathway) are converted to serine, a three-carbon amino acid. This releases one ${CO}_{2}$ ‍ molecule.
Serine returns to the peroxisome, where it's converted to glycerate. In the chloroplast, glycerate is turned into 3-PGA and can thus enter the Calvin cycle.

In the diagram below, you can see a comparison between photorespiration and the normal Calvin cycle, showing how many fixed carbons are gained or lost when either

6

{CO}_{2}

6

O_{2}

molecules are captured by rubisco. Photorespiration results in a loss of

3

fixed carbon atoms under these conditions, while the Calvin cycle results in a gain of

6

fixed carbon atoms.

Photorespiration is definitely not a win from a carbon fixation standpoint. However, it may have other benefits for plants. There's some evidence that photorespiration can have photoprotective effects (preventing light-induced damage to the molecules involved in photosynthesis), help maintain redox balance in cells, and support plant immune defenses

^{8}

Attribution:

This article is a modified derivative of "Photosynthetic pathways," by Robert Bear and David Rintoul, OpenStax CNX, CC BY 4.0. Download the original article for free at http://cnx.org/contents/d0b6df3d-22b7-411f-8f28-5eeed0e1c82d@9.

The modified article is licensed under a CC BY-NC-SA 4.0 license.

Works cited:

Percent of Rubisco out of total soluble leaf protein. (2014, January 11). In BioNumbers. Accessed July 22, 2016. Retrieved from http://bionumbers.hms.harvard.edu/bionumber.aspx?id=110003.
Koning, R. E. (1994). Photorespiration. In Plant physiology information website. Retrieved from http://plantphys.info/plant_physiology/photoresp.shtml.
Vu, J. C. V. (2005). Rising atmospheric CO $_{2}$ ‍ and C $_{4}$ ‍ photosynthesis. In Pessarakli, M. (Ed.), Handbook of photosynthesis (2nd ed., p. 320). New York, NY: Taylor and Francis.
Berg, J. M., Tymoczko, J. L., and Stryer, L. (2002). The Calvin cycle synthesizes hexoses from carbon dioxide and water. In Biochemistry (5th ed., section 20.1). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK22344/#_A2795_.
Buchanan, B. B., Gruissem, W., and Jones, R. L. (2000). Biochemistry and Molecular Biology of Plants. Am. Soc. Plant Phys. Rockville. Retrieved from https://en.wikipedia.org/wiki/Photorespiration#/media/File:Photorespiration_eng.png.
Purves, W.K., Sadava, D., Orians, G.H., and Heller, H.C. (2003). Photosynthesis: energy from the sun. In Life: the science of biology (7th ed.). Sunderland, MA: Sinauer Associates, 156-157.
Peterhansel, C., Horst, I., Niessen, M., Blume, C. Kebeish, R., Kürkcüoglu, S., and Kreuzaler, F. (2010). Photorespiration. In The Arabidopsis Book, 8, e0130. http://dx.doi.org/10.1199/tab.0130.
Eisenhut M., Bräutigam A., Timm S., Florian A., Tohge T., Fernie A.R., Bauwe H., and Weber A.P.M. (2016). Photorespiration is crucial to the dynamic response of photosynthetic metabolism and stomatal movement to altered CO2 availability. Mol. Plant. doi: 10.1016/ j.molp.2016.09.011.

References:

Bareja, B. (2015). Plant types: II. In C4 plants, examples, and C4 families. Retrieved from http://www.cropsreview.com/c4-plants.html.

Berg, J. M., Tymoczko, J. L., and Stryer, L. (2002). The Calvin cycle synthesizes hexoses from carbon dioxide and water. In Biochemistry (5th ed., section 20.1). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK22344/.

Bowsher, C., Steer, M., and Tobin, A. (2008). Photosynthetic carbon assimilation. In Plant biochemistry (pp. 93-141). New York, NY: Garland Science.

Buchanan, B. B., Gruissem, W., and Jones, R. L. (2000). Biochemistry and Molecular Biology of Plants. Am. Soc. Plant Phys. Rockville. Retrieved from https://en.wikipedia.org/wiki/Photorespiration#/media/File:Photorespiration_eng.png.

Koning, R. E. (1994). Photorespiration. In Plant physiology information website. Retrieved from http://plantphys.info/plant_physiology/photoresp.shtml.

Percent of Rubisco out of total soluble leaf protein. (2014, January 11). In BioNumbers. Accessed July 22, 2016. Retrieved from http://bionumbers.hms.harvard.edu/bionumber.aspx?id=110003.

Peterhansel, C., Horst, I., Niessen, M., Blume, C. Kebeish, R., Kürkcüoglu, S., and Kreuzaler, F. (2010). Photorespiration. In The Arabidopsis Book, 8, e0130. http://dx.doi.org/10.1199/tab.0130.

Photorespiration. (2015, September 4). Retrieved October 26, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Photorespiration.

Photosynthesis - an overview. (n.d.) In Biomes. Retrieved fromhttp://w3.marietta.edu/~biol/biomes/photosynthesis.htm.

Purves, W.K., Sadava, D., Orians, G.H., and Heller, H.C. (2003). Photosynthesis: energy from the sun. In Life: the science of biology (7th ed., pp. 145-162). Sunderland, MA: Sinauer Associates, Inc.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Alternative mechanisms of carbon fixation have evolved in hot, arid climates. In Campbell biology (10th ed., pp. 201-204). San Francisco, CA: Pearson.

Vu, J. C. V. (2005). Rising atmospheric CO

_{2}

and C

_{4}

photosynthesis. In Pessarakli, M. (Ed.), Handbook of photosynthesis (2nd ed., p. 320). New York, NY: Taylor and Francis.

RuBisCO. (n.d.) In Combining algal and plant photosynthesis. Retrieved from https://cambridgecapp.wordpress.com/improving-photosynthesis/rubisco/.

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  Plant defense mechanisms include different kinds of cell signaling pathways and cascades. Certain membrane-spanning receptors react to pathogens and activate gene expression. However, in order to proceed with those mechanisms, photosynthesis has to be disrupted.
  
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  They do, There are 6 5-carbon RuBP molecules (30C), which are broken into 6 3-carbon PGA molecules (18 C) and 6 2-carbon phosphoglycolate molecules (12C). These 2-carbon phosphoglycolate molecules are further broken up into 3 3-carbon PGA molecules (9C) and 3 1-carbon CO2 molecules (3C). The CO2 is released (3C), the 9 total PGA (9x3=27C) are used to regenerate some, but not all of the RuBP. Total product being 9 PGA and 3 CO2 (27C+3C=30C) which is the same amount as we started with in the 6 RuBP
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  Yes, exactly! It has to do with reactive oxygen species! It was also mentioned in the videos prior to this.
  
  Photorespiration is some kind of 'salvage' and protective pathway which avoids the accumulation of unnecessary 02 which could potentially elicit great damage in cells in the form of reactive oxygen species.
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AP®︎ Biology (2018)

Course: AP®︎ Biology (2018) > Unit 10

Introduction

Rubisco binds to either CO2‍ or O2‍

Photorespiration wastes energy and steals carbon

Want to join the conversation?

Rubisco binds to either ${CO}_{2}$ ‍ or $O_{2}$ ‍