T HE C P ATHWAY Plants that are adapted to dry tropical regions have the C pathway mentioned earlier. Though these plants have the C oxaloacetic acid as the first CO fixation product they use the C pathway or the Calvin cycle as the main biosynthetic pathway. Then, in what way are they different from C plants? This is a question that you may reasonably ask.
C plants are special: They have a special type of leaf anatomy, they tolerate higher temperatures, they show a response to high light intensities, they lack a process called photorespiration and have greater productivity of biomass. Let us understand these one by one. Study vertical sections of leaves, one of a C plant and the other of a C plant. Do you notice the differences?
Do both have the same types of mesophylls? Do they have similar cells around the vascular bundle sheath? The particularly large cells around the vascular bundles of the C plants are called bundle sheath cells , and the leaves which have such anatomy are said to have ‘Kranz’ anatomy . ‘Kranz’ means ‘wreath’ and is a reflection of the arrangement of cells.
The bundle sheath cells may form several layers around the vascular bundles; they are characterised by having a large number of chloroplasts, thick walls impervious to gaseous exchange and no intercellular spaces. You may like to cut a section of the leaves of C plants – maize or sorghum – to observe the Kranz anatomy and the distribution of mesophyll cells. It would be interesting for you to collect leaves of diverse species of plants around you and cut vertical sections of the leaves. Observe under the microscope – look for the bundle sheath around the vascular bundles.
The presence of the bundle sheath would help you identify the C plants. Now study the pathway shown in Figure . . This pathway that has been named the Hatch and Slack Pathway, is again a cyclic process.
Let us study the pathway by listing the steps.