Question

Give the importance of ${ C }_{ 4 }$ plants.

Answer 1

The ${ C }_{ 4 }$ plants are highly efficient in hot and dry climates and can produce a lot of energy. These plants cycle carbon dioxide into four- carbon sugar compounds to enter into the Calvin cycle.

Correct step by step answer:
The importance of ${ C }_{ 4 }$ plants is that they have adapted to the hot environments and also can tolerate saline conditions due to the abundant occurrence of organic acids (malic and oxaloacetic acid) in them which lowers their water potential more than that of soil.
They can perform photosynthesis, but it is a modified form known as ${ C }_{ 4 }$ photosynthesis even when their stomata is closed to prevent the water loss through transpiration. In this type of modified photosynthesis environment ${ CO }_{ 2 }$ is first incorporated into 4- carbon acids in the mesophyll cells. These acids are then transported to the bundle sheath cells. In these bundle sheath cells, the reaction is reversed, ${ CO }_{ 2 }$ is released and subsequently used in the normal (${ C }_{ 3 }$) photosynthetic pathway. To bypass the photorespiration pathway in which the enzyme RuBisCo attaches with the ${ O }_{ 2 }$ and utilizes the energy produced, the ${ C }_{ 4 }$ plants have developed a mechanism to efficiently deliver $CO_2$ to the enzyme RuBisCO. In this specific mechanism, the ${ C }_{ 4 }$ plants use their specific leaf anatomy where chloroplasts exist not only in the mesophyll cells in the outer part of their leaves but in the bundle sheath cells as well, so that $CO_2$ is directly incorporated into a four- carbon organic acid (either malate or aspartate). The organic acid produced in the mesophyll cells is then transported through plasmodesmata into the bundle sheath cells, where it is decarboxylated to regenerate $CO_2$. The above mentioned specific mechanism is known as the ${ C }_{ 4 }$ cycle. Examples of ${ C }_{ 4 }$ plants include sugarcane, maize, sorghum, pineapple amaranth, etc.

Note:
- The ${ C }_{ 4 }$ cycle is commonly known as the Hatch and Slack pathway as it was first elucidated by Marshall Davidson Hatch and C. R. Slack.
- In ${ C }_{ 4 }$ plants, RuBisCO is more active as a carboxylase enzyme rather than as an oxygenase.
- In the incorporation of $CO_2$ into 3- carbon compounds, the enzyme used as a catalyst is Rubisco.