Developmental variation in aspartate-family amino acid biosynthesis by isolated chloroplasts

In the last decade, it has become clear that the chloroplast is the main site, if not the sole site, for the biosynthesis of the nutritionally essential aspartate-derived amino acids (Fig. 1) in plant leaves [1,2]. For example, isolated intact chloroplasts carry out the light-driven synthesis of lysine, threonine, and isoleucine from labeled aspartic acid and malic acid [3]. This can be considered a photosynthetic process since ATP and NADPH produced in light are thought to be used directly (Fig. 1) to drive the synthetic reactions [3].