Ecophysiology of Plants
Resources: abiotic and biotic environmental factors that vary over time and space (limiting),
and that are consumed by organisms
Resources for plants: space, carbon, light, water, nutrients
Carbon: CO2, primary building block
C3: temperate areas
C4: savannah or tropical rainforest; hot but wet periods of time – temperature is the
important factor here; not how dry it is: sufficient precipitation
CAM: hot and dry conditions: little precipitation
(glandular) trichomes: surface hairs – defense mechanism and retain water by reducing
airflow/evaporation
Leaf
Top: palisade parenchyma layer, below: spongy parenchyma
Stem
Pit parenchyma in the middle
Red: xylem
Phloem around the xylem
Bumps on the outside: sclerenchyma cells to fortify the stem (sturdy extra support for the stem)
1
,Root
C3 photosynthesis:
Palisade and spongy parenchyma
CO2 fixation during light period
Fixation of CO2 via Calvin cycle
Relatively high photorespiration by Rubisco
Rubisco = ribulose biphosphate carboxylase/oxygenase
Need ATP and NADH from the light reaction (H2O O2)
Carboxylation, reduction and regeneration!
Photorespiration (oxygenation)
2
, Mainly at high O2/CO2 ratios and higher temperatures: so not many C3 plants in for example
the savannah
Competition with carboxylation: in normal conditions higher affinity to CO2 (more oxygen in
the air than CO2)
Evolutionary relict or overflow mechanism? In the past there was a much higher CO2
concentration
Role in nitrate metabolism
C4 photosynthesis
Krantz or bundle sheath anatomy
CO2 fixation during light period
First fixation of CO2 via PEP carboxylase
PEP = phosphoenolpyruvate
Almost no photorespiration
Low Km for CO2 fixation (fast), but not for the Rubisco reaction (slower than C3)
Energetically less efficient (recycling PEP costs ATP)
Sensitive for low temperatures instead of high temperatures: low temperatures affect the
activity of pyruvate Pi dikinase (PEP formation) – less C4 species in colder places, such as the
Netherlands
3
, C4 plants have developed several tim during evolution
Dark inflated (!) cells contain lots of chloroplasts: bundle sheath cells containing high CO2
concentrations – carboxylation will take place
Maize is a C4 species
Mesophyll cells contain atmospheric concentrations of CO2
Bundle sheath cells contain high concentrations of CO2 to prevent oxygenation or
photorespiration
Pyruvate will be transported back from the bundle sheath cells to the mesophyll cells to be
reconverted into PEP so that the cycle will continue – this process costs ATP (2 ATP to fix 1 C) –
4
Resources: abiotic and biotic environmental factors that vary over time and space (limiting),
and that are consumed by organisms
Resources for plants: space, carbon, light, water, nutrients
Carbon: CO2, primary building block
C3: temperate areas
C4: savannah or tropical rainforest; hot but wet periods of time – temperature is the
important factor here; not how dry it is: sufficient precipitation
CAM: hot and dry conditions: little precipitation
(glandular) trichomes: surface hairs – defense mechanism and retain water by reducing
airflow/evaporation
Leaf
Top: palisade parenchyma layer, below: spongy parenchyma
Stem
Pit parenchyma in the middle
Red: xylem
Phloem around the xylem
Bumps on the outside: sclerenchyma cells to fortify the stem (sturdy extra support for the stem)
1
,Root
C3 photosynthesis:
Palisade and spongy parenchyma
CO2 fixation during light period
Fixation of CO2 via Calvin cycle
Relatively high photorespiration by Rubisco
Rubisco = ribulose biphosphate carboxylase/oxygenase
Need ATP and NADH from the light reaction (H2O O2)
Carboxylation, reduction and regeneration!
Photorespiration (oxygenation)
2
, Mainly at high O2/CO2 ratios and higher temperatures: so not many C3 plants in for example
the savannah
Competition with carboxylation: in normal conditions higher affinity to CO2 (more oxygen in
the air than CO2)
Evolutionary relict or overflow mechanism? In the past there was a much higher CO2
concentration
Role in nitrate metabolism
C4 photosynthesis
Krantz or bundle sheath anatomy
CO2 fixation during light period
First fixation of CO2 via PEP carboxylase
PEP = phosphoenolpyruvate
Almost no photorespiration
Low Km for CO2 fixation (fast), but not for the Rubisco reaction (slower than C3)
Energetically less efficient (recycling PEP costs ATP)
Sensitive for low temperatures instead of high temperatures: low temperatures affect the
activity of pyruvate Pi dikinase (PEP formation) – less C4 species in colder places, such as the
Netherlands
3
, C4 plants have developed several tim during evolution
Dark inflated (!) cells contain lots of chloroplasts: bundle sheath cells containing high CO2
concentrations – carboxylation will take place
Maize is a C4 species
Mesophyll cells contain atmospheric concentrations of CO2
Bundle sheath cells contain high concentrations of CO2 to prevent oxygenation or
photorespiration
Pyruvate will be transported back from the bundle sheath cells to the mesophyll cells to be
reconverted into PEP so that the cycle will continue – this process costs ATP (2 ATP to fix 1 C) –
4
