Lecture 10 – February 17

Readings: See syllabus.  Familiarize yourself with Fig. 8.7 before lecture.

Rubisco – Oxygenation and Photorespiration CONTINUED (from Lecture 9)

 

Photorespiration (Fig. 8.7, see Fig. 1.21)

Compartments:

1.

2.

3.

Inputs:

1.

2.  

3.

Outputs:

1.

2.

 

 

Oxygenation:  An historical artifact?

1. Rubisco evolved

 

2. Photorespiration –

 

Photosynthetic Carbon Fixation Types

1.

2.

3.

4.

1. C3 Plants

a.

b.

c.

d.

 

CO₂ Concentrating Mechanisms

2.

3.

4.

a.

b.

c.

 

2. C4 Plants

a.

b.

c.

d.

e.

Kranz anatomy

C4 Cycle –

a.

b.

c.

d.

e.

 

 

Biochemical Advantage for C4

a.

b.

c.

Crassulaceian Acid Metabolism

1.

2.

3.

4.

 

CAM Cycle (Fig. 8.12)

 

 

CAM Physiology (see Fig. 9.21)

Durnal patterns 

a.

b.

 

QUESTIONS

1. What are the substrates and products of the oxygenase activity catalyzed by rubisco?  Why is this reaction thought to be detrimental to a plant’s carbon balance?

2. In general, what is the relationship between oxygenation and photorespiration in a plant?  In what cell compartments does photorespiration occur? What are the inputs and outputs of photorespiration overall and for each compartment? Briefly, what are the series of reactions that occur in photorespiration?  Why is it thought that the oxygenase activity of rubisco and photorespiration occur in plants?

3. What are the photosynthetic characteristics of a C3 plant?  Give some examples of C3 plants. Why are C3 plants at a disadvantage under hot and dry conditions?

4. What is Kranz anatomy and how does it contrast to leaf anatomy in C3 plants? 

5. Draw a cross section of a C4 leaf and show the locations of the mesophyll and bundle sheath cells.  Summarize the general reactions found in mesophyll and bundle sheath cells of C4 plants.  How does this contrast to photosynthesis in C3 plants?  How is rubisco activity altered in a C4 plant?

6. What are some examples of C4 plants?  How common are C4 plants relative to the numbers of C3 plants?  C4 plants can be described as “obligate”.  What does that mean?  

7. The relationship between photosynthesis (assimilation) rate and intercellular CO₂ concentration is illustrated in Fig. 9.20.  Describe how the data for such a figure were determined.  What is a CO₂ compensation point?  Why do the C3 and C4 plants have different CO₂ compensation points.  What would be approximate points on the curves that would represent photosynthetic performance for the C3 and C4 plants under well-watered conditions in the natural environment?  Under natural conditions, photosynthesis rate in the C4 species is close to maximum but in the C3 species it is not.  What is the biochemical basis of this difference?

8. Describe diurnal patterns of stomatal opening, carbon fixation and tissue acidity changes in plants with CAM .  What are the major reactions involved in CAM metabolism, and how do these reactions relate to plant structure?