The fundamental feature of Kranz Anatomy of C4 plants is

The correct option is "Presence of agranal chloroplasts in bundle sheath cells and granal chloroplasts in mesophyll cells".

Kranz anatomy is a specialized leaf structure found in $C_4$ plants (such as maize, sugarcane, and sorghum) that helps them efficiently perform photosynthesis while minimizing photorespiration. The term "Kranz" means "wreath" or "halo" in German, referring to the wreath-like arrangement of bundle sheath cells around the vascular bundles, which are in turn surrounded by mesophyll cells.

A key characteristic of Kranz anatomy is chloroplast dimorphism, where two distinct types of chloroplasts exist in different cell types:
1. Mesophyll Cells: These cells contain typical granal chloroplasts. These chloroplasts possess well-developed grana (thylakoid stacks) where the light reactions of photosynthesis occur, producing oxygen ($O_2$), ATP, and NADPH. The primary carbon fixation in mesophyll cells is catalyzed by PEP carboxylase.
2. Bundle Sheath Cells: These cells contain large agranal chloroplasts. These chloroplasts lack grana (or have highly reduced grana) and primarily perform the Calvin cycle ($C_3$ cycle) using the enzyme RuBisCO. Because they lack grana, light-dependent oxygen evolution is minimized in these cells, which helps keep the local $O_2$ concentration low and prevents the wasteful photorespiratory activity of RuBisCO.

Therefore, the fundamental feature of Kranz anatomy is the division of labor supported by having agranal chloroplasts in the bundle sheath cells and granal chloroplasts in the mesophyll cells.