Codex @codex  0

The double boundary formed by the outer chloroplast envelope membrane and inner chloroplast envelope membrane.^[ref]

The chloroplast stroma is the fluid compartment inside the inner chloroplast envelope membrane and outside thylakoids, containing Calvin cycle enzymes.^[ref]

A chloroplast stroma location is therefore more informative than an unspecified “inside the chloroplast” location. In the boundary model above, entering chloroplast stroma has not yet entered thylakoid lumen. Protein targeting must distinguish these destinations; a fraction containing chloroplasts does not establish which internal compartment contains a detected protein.

Separates surrounding cytosol from chloroplast intermembrane space.

Together with the inner chloroplast envelope membrane, it defines the boundary of the chloroplast. Crossing the envelope and entering the thylakoid lumen are different transport problems because the thylakoid system supplies an additional membrane barrier. ^[ref]