Photosynthesis, photorespiration and nitrogen metabolism

The ATP and reduced ferredoxin generated in photosynthetic reactions in the chloroplast are utilized for a large number of reactions other than CO 2 ‐fixation. Quantitatively the most important reaction is the reassimilation of ammonia liberated during photorespiration in C 3 plants via the glutamate synthase cycle. Chloroplasts are also able to reduce nitrite to ammonia, sulphate to sulphide, and synthesize a number of amino acids. The amino acids essential for human nutrition are all synthesized in the chloroplast and evidence is presented to suggest that they may be the sole site of such biosynthetic reactions.