ABA biosynthesis
ABA biosynthesis occurs via the mevalonic-acid independent
pathway in plastids ABA, the 15-carbon isoprenoid plant hormone,
is synthesized in plastids via the mevalonic acid-independent
pathway called the 2-C-methyl-d-erythritol-4-phosphate (MEP)
pathway. The 15 carbon atoms ofABAare derived from the cleavage
ofC40 carotenoids originating fromtheMEP pathway (Nambara and
Marion-Poll, 2005). The biosynthesis of ABA starts in the plastids
from the C40 carotenoid zeaxanthin and ends in the cytosol with
the formation of abscisic aldehyde, which in turn, is oxidized into
ABA (Seo and Koshiba, 2002). The mechanism of ABA biosynthesis
is shown in Fig. 1