In vitro and in situ inhibition of carotenoid biosynthesis in Capsicum annuum by bleaching herbicides

Pepper leaves treated with the herbicide J852 show an accumulation of phyto ene and zeta -carotene, whereas treatment with norflurazon led to an accumu lation of only phytoene. The effects of these herbicides were examined in v itro after the expression of carotenoid desaturases in Escherichia coli. Wh ereas norflurazon is a potent inhibitor of phytoene desaturase (PDS) (I-50 = 0.12 muM) but not of zeta -carotene desaturase (ZDS) (I-50 = 144 muM), 58 52 inhibits both PDS (I-50 = 23 muM) and ZDS (I-50 = 49 muM) The influence of PDS/ZDS inhibition on gene expression was examined by comparative RT-PCR . None of the examined genes, namely, encoding phytoene synthase, PDS, ZDS, or the terminal oxidase associated with phytoene desaturation, were induce d upon herbicide treatment in pepper leaves or seedlings. This was unexpect ed because inhibition of carotene desaturation led to an up-regulation of t he carotenoid biosynthetic capacity (higher amounts of accumulating precurs ors plus remaining colored carotenoids are present in treated tissues versu s control).