@Kaylap23 Plant Physiology First Half of Semester

Combo of @kaylap23 Plant Physiology Quiz 1, Quiz 2, and Midterm Sets EEB 2250

Purposes of CO2 concentration

Make rubisco run at Vmax, minimize photorespiration, increase WUE and NUE

Where do plants concentrate CO2?

In the stroma of the chloroplast

What is the C4 cycle?

PEP Carboxylase produces a four-carbon compound to elevate CO2 concentration at the site of Rubisco

What are the most productive crops?

C4 grasses (maize, sorghum, and sugar cane)

How much of our caloric intake is C4 plants?

25%

How much of the world’s plants are C4 crops?

8/10

Difference in C3 and C4 plant structure?

Kranz anatomy says that there’s a big vascular tissue surrounded by bundle sheath and mesophyll cells

What does PEP carboxylase do better than Rubisco?

Fix CO2 faster

How is Rubisco running in C4?

At Vmax and with no photorespiration

How does C4 photosynthesis work?

Atmospheric CO2 enters mesophyll cells and is converted to bicarbonate which is then carboxylated to PEP and produces OAA, which is then transported to the bundle sheath cell and decarboxylated, releasing CO2 at Rubisco, which initiates the Calvin-Benson cycle. A three-carbon compound returns to the mesophyll cell.

Where does carboxylase saturation and oxygenase-inhibiting CO2 occur?

The bundle sheath

What step requires energy in C4 photosynthesis?

Regenerating PEP requires 2ATP per CO2 fixed

Total energy per CO2 fixed by Rubisco in C4

5ATP + 2NADPH

Why did C4 photosynthesis evolve?

When atmospheric CO2 decreased

What water advantage do C4 plants have over C3 plants?

PEPC fixes CO2 effectively even when CO2 is low, reducing stomata opening and losing water

Ratio of water loss to carbon gain during photosynthesis C4

C4: 300 H2O / 1 CO2

What type of plants do CAM photosynthesis?

Desert plants, big plants in rainforests

Economically important CAM plants?

Vanilla, pineapple, aloe vera, agave

How does CAM cycle work?

CO2 uptake occurs at night (less water loss), CO2 is fixed by PEP Carboxylase, CO2 is stored as C4 acids in the vacoule, CO2 is released in the daytime, Rubisco fixes CO2 during the day even though stomata are closed, bc there is light energy

CAM leaf anatomy?

CAM leaves are very thick and densely packed, creates succulent leaf due to vacuoles

CAM Cycle simplified

Night - open & PEPC, Day - closed & Rubisco

WUE in CAM Plants

100 H2O / 1 CO2

Origins of CAM

Declines in CO2 (origins are older, but expansion related to more recent declines in CO2)

Which carbon is radioactive

C14

What is PDB standard from?

Carbon-13 work sampling shells of a squid, had a high C13:C12 ratio and was established as the standard value of zero

What does Rubisco favor?

C12

Why is the fixation of 12CO2 more rapid?

Because C12 is lighter and processed faster

Why has C13 decreased since start of Industrial Revolution?

Fossil fuels increase 12CO2 faster than 13CO2, driving C13 downward in “The Suess Effect”

PEPC discriminates blank

Less strongly against C13 than Rubisco

What does the amount of C13:C12 mean in a plant

Indicates contribution of photosynthetic PEPC carboxylation

Discrimination against 13C order

C3<CAM<C4

When was the global expansion of C4 ecosystems?

6-8 Ma years ago

What drove emergence of genus Homo?

C4 grasslands expanded, woods decreases, couldn’t live in trees anymore

How much has atmospheric CO2 concentration increased since the start of the industrial revolution?

50%

What are the four representative concentration pathways?

2.6 - peak between 2010 and 2020, 4.5 - peak between 2040, 6 - peak around 2080, 8.5 - rise throughout 21st century

What happens to stomata with more CO2?

Less stomata

What plants will benefit more from elevated CO2?

C3 plants

What plants will benefit more from rising temperatures?

C4 plants because they do not do photorespiration

What do plants do overtime with elevated CO2?

Make biochemical changes in response to elevated CO2 that reduces the fertilization effect.

What ends up decreasing with elevated CO2?

N (protein) and macro and micro nutrients

what is principal photoreceptor in plants?

chlorophyll

What is the primary function of the photosynthetic reaction center and its specialized chlorophyll pair?

To emit an electron for photosynthetic electron transport.

What happens to the energy of a blue photon compared to a red photon when it is absorbed by chlorophyll?

It is lost as heat.

What term refers to light damage of PSII

Photoinhibition

How many substrate carbons are involved in the carboxylation reaction of Rubisco?

6

What do shade plants do to increase antennae size?

Add more light harvesting chlorophyll protein complexes

Describe a sun leaf

More cells layers and more vertical chloroplasts

Describe a shade leaf

Flat with larger surface area per unit weight

What do chloroplasts do to minimize or maximize light interception?

Move

Diaheliotropic vs Paraheliotropic leaves

Increase vs reduce light absorbtion

What is photoprotection

Dissipation of light energy as heat

What is quenching

Dissipation of energy by photochemistry to reduce fluorescence

Xanthophyll Cycle, how is it reversible

Decreases deficiency of light-harvesting complexes, conversion of zeaxanthin to violaxanthin and vice versa

Photoinhibition

Damage to core D1 protein , can be repaired

Site of CO2 fixation

Chloroplast stroma (insides)

What does it mean to the plant that there are large CO2 resistances?

Large drop in CO2 from the atmosphere to site of carboxylation in the chloroplast

Stomatal resistance

Resistance to CO2 diffusion through stomates (cell doesn’t wanna lose water)

What is the ratio of water loss to carbon gain

600 H2O to 1 CO2

Carboxylation

RuBP (5 carbon) + Co2 —(rubisco)> 2 PGA (3 carbon)

How many active/catalytic sites does rubisco have

8

How is Rubisco coded in higher plants

Small subunity is encoded on nuclear genome, larger subunity encoded on chloroplast genome

How is Rubisco activated

Increase in stromal pH and Mg2+ concentration

How does the reduction phase of the calvin cycle work

Three turns CO2 molecules (3 turns) are required to generate GAP

What is GAP?

Can be made into starch and sucrose

Reduction phase

PGA—>GAP

What is being regenerated in the Calvin Cycle?

RuBP

What is the energy-requiring step of the regeneration phase of the Calvin-Benson cycle.

Final step of RuBP regeneration

Discovery of Calvin-Benson Cycle

Algae, C14 labeled CO2, paper chromatography at different times

What is carbon assimilated as during the day?

Triose phosphate to make starch or sucore

What does sucrose move through

Phloem

What are examples of sources and sinks?

Potatoes/leaf, flower/fruit

What makes primary xylem and phloem

Apical meristem

What makes secondary xylem and phloem

Vascular cambium

What layer of phloem is functional in a woody plant?

Secondary

Describe phloem movement?

Sugars are loaded into the phloem by active transport (creates pressure gradient), move through sieves, water moves by osmosis and follows.

What does carboxylation vs oxygenation make?

3-PGA vs 2-PG

What do CO2 and O2 act as respectively?

Competitive inhibitors

Rubisco has a higher affinity for …? BUT!

CO2, there is less CO2 in the atmosphere

How much faster is carboxylation then oxygenation?

3 times

What does PEP Carboxylase do?

Bin HCO3 to avoid competition by O2

How does photorespiration work?

O2 + RuBP in Chloroplast become glycolate, then glycine in the peroxisome, then co2 + serine in the mitochondria, then glycerate in the peroxisome, then into PGA

How much carbon gets lost and recovered in photorespiration

25% loss, 75% recovery

Photorespiration accounts for decrease in what two crops and by how much?

20% in wheat, 36% in soybeans

3 consequences of photorespiration in C3 plants?

Radiation use efficiency (RUE is reduced) because ATP is required, Water use efficiency (WUE is reduced) because water is lost through transpiration, Nitrogen use efficiency (NUE is reduced)

Bad news with photorespiration and CO2 concentration and temperature

Oxygenation increases with temperature faster than rate of carboxylation - thus Photorespiration becomes more important than photosynthesis at higher temperatures

General overview of photosynthesis

Electromagnetic energy is absorbed and converted to chemical energy + CO2 for biosynthesis

How much CO2 does photosynthesis take from the environment?

Uptake of CO2 by photosynthesis = 1/2 annual CO2 produced from fossil fuels

Wavelength

Measure of distance between peaks

Frequency

Number of complete wave cycles per second

Energy in radiation is inverse to blank and directly proportional to blank

Wavelength, frequency

Long wave length means blank energy

Low

Visible light nm

400-700

Which has more energy, a blue or red photon, and which can a plant use more?

Blue has more energy, but a plant will use the same amount of energy from each and release excess energy as heat.

How much energy content of solar radiation is visible light?

1/2

Why do different bodies emit different radiation?

They are different temperatures

What radiation does the sun and earth give off?

Visible, infrared

What do greenhouse gases absorb?

Infrared radiation

What type of tail does chlorophyll have and why?

Hydrophobic, to sit in membrane

Why is chlorophyll good at absorbing visible light?

Alternating single and double bonds

What can special chlorophyll a do?

Transfer excited electrons to other molecules