|MadSci Network: Biochemistry|
I didn't know the answer to this one, so I asked a plant physiologist friend. She said that sucrose is used as an osmotic stabilizer so that the chloroplast doesn't disintegrate. In other words, the buffer just uses sucrose as a convenient large molecule that won't cross the membrane, not for any particular biological activity. Other molecules with the same properties, such as polyethyleneglycol, can be used instead.
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