CAM photosynthesis allows plants to take up carbon dioxide at night and store it as malic acid. During the day, the plant's stomata are closed to reduce water loss through transpiration, and the stored malic acid is broken down to release carbon dioxide for the Calvin cycle. Key aspects of CAM include nocturnal stomatal opening and CO2 fixation, storage of fixed carbon as malic acid, and daytime decarboxylation of malic acid to release CO2. CAM provides an advantage over C3 and C4 pathways in arid conditions by minimizing water loss.

1. CAM
CRASSULACEAN ACID METABOLISM
PHOTOSYNTHESIS IN PLANTS

2. The C4 pathway overcomes Photorespiration and high evaporation /
transpiration .with the CO2 being initially captured as HCO3 by
phosphoenolpyruvate carboxylase (PEPCase) and then fixed via the
C3 pathway by Ribulose bisphosphate carboxylase oxidase(Rubisco).
 C4 plants have a spatial separation of the C4 and C3 pathways
occurring within two different cell types in the leaf.
The C4 pathway, located in the palisade mesophyll cells, is radially
arranged around the C3 pathway located in the bundle sheath cells,
which surround the vascular tissue. This is typically referred to as
Kranz anatomy
A Quick RECAP

3. CAM
Defination
 Crassulacean Acid metabolism CAM is a
metabolic and anatomical adaptation that is
characterised by net noctunal Carbon dioxide
uptake with a temporal separation of the C4 and
C3 pathway resulting in decreased transpiration
rates and water loss

4. CAM is a cyclic reaction occurring in the dark phase of photosynthesis
in the plants of Crassulaceae. The cycle occurs in mesophyll cells.
Malic acid the first CO2 fixation product .
Examples of CAM plants are Bryophyllum, Kalanchoe, Crassula,
certain plants of Cactus e.g. Opuntia, Orchid and Pine apple families.
The mesophyll cells have larger number of chloroplasts and the
vascular bundles are not surrounded by well defined bundle sheath cells.
The CAM plants close stomata during the day and open them during
the night when the humidity is high to survive under adverse Xeric
conditions and are best suited for conditions of extreme dessication.
CAM

5. CAM plants typically have a mesophyll anatomy with
primarily spongy parenchyma cells with a large central
vacuole, which has the ability to store the increasing
accumulation of malic acid during the nocturnal period.
CAM plants anatomycally have very low mesophyll
airspace so when stomata are closed the CO2
concentrations inside the leaf are high enough to
supress photorespiration.
CAM cycle involves two major steps:1.
Acidification
2.
CAM

6. CAM

7. In darkness, the stored carbohydrates are converted into phophoenol
pyruvic acid by the process of Glycolysis.
The stomata in CAM plants are open in dark and they allow free
diffusion of CO2 from the atmosphere into the leaf.
Now, the phosphoenolpyruvic acid is carboxylated by the enzyme
phosphoenol pyruvic acid carboxylase and is converted in to oxalaoacetic
acid.
Phosphoenol Pyruvate + CO2 + H2O  Oxaloacetic acid + H3PO4
 The oxaloacetic acid is then reduced to malic acid in the presence of
the enzyme malic dehydrogenase.
The reaction requires NADPH2 produced in Glycolysis.
Oxaloacetic acid + NADPH2  Malic acid + NADP+
The malic acid produced in dark is stored in the vacuole and it increases
the acidity of the tissues.
CAM
Acidification

8. Deacidification
CAM
The stomata are closed during the day, the malic acid is
decarboxylated to produce pyruvic acid and evolve carbon dioxide
in the presence of the malic enzyme.
When the malic acid is removed, the acidity decreases in the cells.
Malic acid + NADP+ Malic enzyme  Pyruvic acid + NADPH2 +
CO2
The pyruvic acid may be oxidized to CO2 by the pathway of
Kreb’s cycle or it may be reconverted to phosphoenol pyruvic acid
and synthesize sugar by C3 cycle.
The CO2 released by deacidification of malic acid is accepted by
ribulose diphosphate and is fixed to carbohydrate by C3 cycle..

9. CAM
Major enzymes are highlighted in yellow. During the night PEP is synthesised from carbohydrate
pools (hexagon) pyruvate OAA-oxaloacetate acid) and carbon dioxide is carboxylated (orange
pathway) resulting in malate and is transported and decarboxylated blue arrows. MDH – Malate
Dehydrogenase/ ME- Malic enzyme/ PEP- phosphoenol pyruvate/PEPC- PEP Carboxylase/PEPCK -

11. COST OF CAM AND EFFICIENCY.
• FOR TERRESTRIAL PLANTS, THE GREATEST BENEFIT OF CAM IS CONSIDERED
TO BE INCREASED WATER USE EFFICIENCY (WUE) BECAUSE STOMATAL
OPENING DURING THE DARK PERIOD CAUSES MUCH LESS TRANSPIRATIONAL
LOSS OF WATER THAN OPENING DURING THE LIGHT PERIOD.
• CAM PLANTS CAN PERFORM NET CO2 FIXATION 15% MORE EFFICIENTLY THAN
C3 , PLANTS, ALTHOUGH 10% LESS EFFICIENTLY THAN C4 PLANTS.

12. Significance of CAM Cycle
1. It is advantageous for succulent plants to obtain CO2 from malic
acid when stomata are closed.
2. During day time stomata are closed and CO2 is not taken but
continue their photosynthesis.
3. Stomata are closed during the day time and help the plants to avoid
transpiration and water loss.