In C₄ plants, Calvin cycle occurs in

The correct option is: chloroplasts present in the stroma of bundle sheath.

To understand why this is correct, let's break down the anatomy and photosynthetic process of C₄ plants step-by-step:

1. Kranz Anatomy of C₄ Plants:
C₄ plants exhibit a specialized leaf anatomy called Kranz anatomy. In these plants, the vascular bundles are surrounded by a ring of large bundle sheath cells, which are in turn surrounded by mesophyll cells. This separation allows C₄ plants to perform photosynthesis efficiently under high temperatures and dry conditions.

2. Dimorphic Chloroplasts:
C₄ plants possess two distinct types of chloroplasts:
• Mesophyll Chloroplasts: These are granal (contain well-developed grana stackings). They carry out the light reaction to produce ATP and NADPH, and initial carbon fixation where CO₂ is fixed into a 4-carbon acid (malic or aspartic acid) by the enzyme PEP carboxylase.
• Bundle Sheath Chloroplasts: These are agranal (lack grana or have poorly developed grana) but contain a rich stroma with starch grains. They lack the active Photosystem II (PSII) complex, minimizing oxygen evolution and reducing photorespiration.

3. Location of the Calvin Cycle:
The fixed 4-carbon acids are transported from the mesophyll cells to the bundle sheath cells. Inside the bundle sheath cells, these acids are decarboxylated to release CO₂. This released CO₂ is then fixed through the standard Calvin cycle (C₃ cycle) by the enzyme RuBisCO.
Since all the enzymatic reactions of the Calvin cycle (including the activity of RuBisCO) take place in the fluid matrix of the chloroplast, it occurs specifically in the stroma of the bundle sheath chloroplasts.