Transcript Different Photosynthetic Mechanisms

Chapter 11 - Photosynthesis and Respiration
Different Photosynthetic Mechanisms
• When sufficient water is available, transpiration and
photosynthesis work together.
– In times of drought & high light, the two may conflict.
• In many areas, sufficient rain in the growing season
makes a compromise between CO2 intake & water
loss is a non-issue.
– Plants evolved here are called C3 plants, because CO2
that enters the leaf is directly used to generate the
3-carbon molecule phosphoglycerate.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 11 - Photosynthesis and Respiration
Different Photosynthetic Mechanisms
Plants in more arid regions have
adaptations that help conserve water
—but not inhibit photosynthesis.
These are C4 and crassulacean
acid metabolism (CAM) plants.
The C4 mechanism is found in
tropical grasses such as corn,
sorghum, warm-season turfgrasses, and other species.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 11 - Photosynthesis and Respiration
Different Photosynthetic Mechanisms
• In C4 plants, CO2 temporarily attaches to a 3-carbon
organic acid, making a 4-carbon organic acid.
– The acid shuttles to the bundle sheath cells and the CO2
is released and used to generate glyceraldehyde.
• Due to increased CO2 capture efficiency, not as
much CO2 has to enter the leaf, so stomates can
be more tightly closed to reduce water loss.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 11 - Photosynthesis and Respiration
Different Photosynthetic Mechanisms
• CAM plants are water-storing desert plants such as
succulents and cacti.
– Stored water absorbs heat & keeps plants cool in the day
when the temperatures are hot, but stomates are closed.
CAM attaches CO2 to a three-carbon
organic acid at night when stomates
can open with less water loss.
CO2 is held on the acid until light
is available & released to follow the
normal photosynthetic pathway.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 11 - Photosynthesis and Respiration
Plant Development & the Source–Sink Relationship
• Plant growth significantly influences net & total rate
photosynthesis, in single leaves & the total canopy.
– Provided all other environmental factors are constant.
• As single leaves develop, photosynthetic rates rise
in step with the expansion of the leaf.
– Chlorophyll content & rate of net photosynthesis per
square centimeter of leaf area both rise to maximum
values just after the leaf reaches full expansion.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 11 - Photosynthesis and Respiration
Plant Development & the Source–Sink Relationship
• When the leaf reaches full expansion, it is called a
source leaf because the carbohydrate synthesized
in that leaf is in excess of what the leaf itself needs.
– Excess is exported to parts of the plant that are actively
growing—roots, fruits, seeds—often called sink tissues.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458