PHOTORESPIRATIONExercise 10

CHUA, Edbelyn

ABENIDO, Shannen

VALEZA, John Ruben

Group 1 WX-5L

Energy-converting Processes Photosynthesis

light energy -> chemical form (organic compounds)

Respiration energy released: ATP

Photorespiration does not result to ATP

intermediate products: glycine and serine

Photorespiration

light + high temperature

IN: high [O2]

OUT: CO2 Three organelles:

chloroplast

peroxisome

mitochondrion

Figure 10.1. Reactionsoccurring inphotorespiration(Nelson and Cox,2008).

Feature C3 C4 CAM

leaf structure

bundle sheath

cells with no

chloroplasts

bundle sheath

cells with

chloroplasts

mesophyll cells

have large

vacuoles

enzyme

for fixing

atmospheric

CO2

Rubisco PEPCase PEPCase

optimum T 15C 25C 30 40C 35C

Table 10.1. Characteristics of plant groups exhibiting photorespiration.

Feature C3 C4 CAM

other

characteristics

most plants

efficient at

midrange T

where a majority

of plants grow

mesophyll cells fix

CO2 and produce

glucose

more efficient in

hot, dry

environments

PEPCase reduces

photorespiration

because it does

not bind O2

mesophyll cells fix

CO2, bundle

sheath cells

produce glucose

(spatial

separation)

xerophytes

not as efficient as

C3 or C4 but allows

plants to survive in

arid conditions

Temporal

separation of CO2fixation and

glucose

production

C3 C4 CAM

ricetobaccosoybean

cornsugarcane

pineapplekataka-taka

Table 10.2. Plants exhibiting photorespiration.

OBJECTIVES

compare the response of species exhibiting high and low rates ofphotorespiration and relate them to changes in carbon dioxide/oxygenlevels

METHODOLOGY

Figure 10.2. Photorespiration set-up.

RESULTS

DAY

CONTROL PLANT PLANT INSIDE BELL JAR

RICE* CORN+ RICE CORN

0high vigor

green leaveshigh vigor

green leaves

green to yellow green leaves

decresing vigor

high vigorgreen leaves

1high vigor

normal leaveshigh vigor

normal leaveslight yellow leaves

decreased vigorhigh vigor

green leaves

2normal vigorgreen leaves

normal vigorgreen leaves

decreased vigorthinner stem

high vigorgreen to yellowish

leaf parts

* - C3 plant; + - C4 plant

Table 10.3. Observation of the rice (C3) and corn (C4) plants in two separate set-ups for 5 days.

3healthy plantgreen leaves

constant vigorgreen leaves

yellow leavesthin stem

green leaves with yellow tips

4healthy plantgreen leaves

normal vigorgreen leaves

yellow leavesthin stem

wilting of some leaves

decreased vigor

5healthy plantgreen leaves

with some wilted leaves

healthy plantgreen leaves

yellowing of leavesmany leaves wilted

thin stem

wilting leavessome parts healthy

DAY

CONTROL PLANT PLANT INSIDE BELL JAR

RICE* CORN+ RICE CORN

* - C3 plant; + - C4 plant

Table 10.3. Observation of the rice (C3) and corn (C4) plants in two separate set-ups for 5 days. (continued)

RESULTS

Figure 10.3. Rice and corn control set-ups (left) and rice and corninside bell jar for photorespiration set-up (right) at day 5.

DISCUSSION

increased [O2]; decreased [CO2]

presence of sunlight Photosynthesis (PS) O2 produced

inc [O2]: higher photorespiration rate in C3 C3 plants do not exhibit CO2 conc mechanism

high [O2] fixation by ribulose 1,2-bisphosphate oxygenase in C3

no ATP = no Energy for growth and maintenance of plants wilting

DISCUSSION

C4 plants

spatial separation of enzymes

useful when [CO2] is low PEPCase in bundle sheath

fixation of CO2 PS still possible and continued production of ATP

source of energy for plant growth and repair

Answers to Study Questions

1. Will [O2] in the set-up increase or decrease? Whateffect wwould there be on C3 plants for such changein O2 level?

increase, since plant continues to photosynthesize

induce photorespiration since C3 do not exhibitCO2 concentrating mechanism

rubisco will act as oxygenase

O2 fixated, NO ATP = NO Energy

low source of E for growth and maintenance

Answers to Study Questions

2. Define CO2 compensation point and light compensation point. CO2 comp pt: [CO2] in which fixation is ZERO

Light comp pt: reached evident with net CO2 exchange that is ZERO because of rateof PS or CO2 uptake is balanced with Respiration

Additional, CCP is the pt at w/c the light level where CO2 is released duringrespiration is offset by CO2 fixation during PS.

Answers to Study Questions

3. With the decline in [CO2] in the set-up, which species would stillexhibit net photosynthesis after one (1) week? Explain youranswer.

CORN (C4) low CO2 comp pt

photosynthetic efficiency

PS is reduced: efficient use of CO2 due to spatial separation ofenzymes bundle sheath cells CO2 fixation

mesophyll cells PEPCase