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Medicinal plants (PG 101) Level 1 Clinical Pharmacy-PharmD

Therefore, the mesophyll cells act to minimize photorespiration by supplying a

steady flow of CO 2 to the Calvin cycle even when stomatal conductance is low.

III. Crassulacean Acid Metabolism (CAM pathway)

In: - desert plants of Crassulaceae.

- some monocot & dicot families.

- some gymnosperms.

❑ Stomata remain closed during the day, this helps the plant prevent water loss, but

prevent CO 2 from entering the leaves. Therefore, CAM plants assimilate CO2 at

night when their stomata are open.

✓ Night time (Stomata opened): Initial fixation of CO2

(1) Like C4, the initial product of carboxylation is a 4C acid:

CO 2 + PEP (phosphoenolpyruvate) → oxaloacetate (OAA)

(2) OAA is converted to malic acid which is stored in the vacuoles.

(3) Internal p ↓ at night due to malic acid formation.

✓ Day time (Stomata closed):

(1) "de-acidification" occurs.

(2) Malate is decarboxylated & the resulting CO2 enter Calvin cycle.

Remember:

▪ Both C4 and CAM pathways include Calvin cycle (C3 pathway); the difference

is where CO 2 is fixed initially.

▪ CAM plants conserves water better than C4 plants but fix little carbon & grow

slowly.
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