Question

Do both C3 and C4 plants have a PEPCase?

Answer 1

Hint: Phosphoenolpyruvate carboxylase or PEPCase is an enzyme that is most commonly found in plants and some bacteria. The function of PEPCase is the addition of bicarbonate to phosphoenolpyruvate to form four carbon oxaloacetate and inorganic phosphate.

Complete answer:
C3 plants are those plants that utilise the C3 carbon fixation pathway for the fixation of carbon into sugars. In the C3 fixation pathway carbon dioxide and ribulose bisphosphate are converted into two molecules of 3-phosphoglycerate using the enzyme ribulose bisphosphate carboxylase oxygenase or RuBisCO. C3 plants are unable to grow in very hot regions because RuBisCO is known to incorporate more oxygen into ribulose bisphosphate which in turn leads to photorespiration. This causes loss of nitrogen and carbon from the plant and hinders the growth of the plant. C4 plants are the ones which use the C4 fixation pathway also known as the Hatch-Slack pathway. C4 plants are known to reduce photorespiration by concentrating carbon dioxide around RuBisCO so that the enzyme works in an environment having much higher carbon dioxide and much less oxygen. To make the environment rich in carbon dioxide, the carbon dioxide is fixed in the mesophyll cells using the enzyme PEPCase that reacts with phosphoenolpyruvate to give oxaloacetic acid. The oxaloacetic acid can be chemically transformed into malate or aspartate and diffused to the bundle sheath followed by decarboxylation to give a carbon dioxide rich environment. Thus only C4 plants possess PEPCase and not C3 plants.

Note:
The possession of PEPCase is of advantage to the C4 plants because as a result of high carbon dioxide environment less photorespiration takes place and thus the growth of these plants are also not hindered, unlike C3 plants.