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1.
J Agric Food Chem ; 48(10): 4676-80, 2000 Oct.
Article in English | MEDLINE | ID: mdl-11052718

ABSTRACT

Pepper leaves treated with the herbicide J852 show an accumulation of phytoene and zeta-carotene, whereas treatment with norflurazon led to an accumulation of only phytoene. The effects of these herbicides were examined in vitro after the expression of carotenoid desaturases in Escherichia coli. Whereas norflurazon is a potent inhibitor of phytoene desaturase (PDS) (I(50) = 0.12 microM) but not of zeta-carotene desaturase (ZDS) (I(50) = 144 microM), J852 inhibits both PDS (I(50) = 23 microM) and ZDS (I(50) = 49 microM). 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 induced upon herbicide treatment in pepper leaves or seedlings. This was unexpected because inhibition of carotene desaturation led to an up-regulation of the carotenoid biosynthetic capacity (higher amounts of accumulating precursors plus remaining colored carotenoids are present in treated tissues versus control).


Subject(s)
Capsicum/metabolism , Carotenoids/biosynthesis , Herbicides/pharmacology , Plants, Medicinal , Capsicum/chemistry , Capsicum/drug effects , Depression, Chemical , Oxidoreductases/metabolism , RNA, Messenger/biosynthesis , Reverse Transcriptase Polymerase Chain Reaction
2.
Plant Physiol ; 123(4): 1427-36, 2000 Aug.
Article in English | MEDLINE | ID: mdl-10938359

ABSTRACT

The Arabidopsis IMMUTANS gene encodes a plastid homolog of the mitochondrial alternative oxidase, which is associated with phytoene desaturation. Upon expression in Escherichia coli, this protein confers a detectable cyanide-resistant electron transport to isolated membranes. In this assay this activity is sensitive to n-propyl-gallate, an inhibitor of the alternative oxidase. This protein appears to be a plastid terminal oxidase (PTOX) that is functionally equivalent to a quinol:oxygen oxidoreductase. This protein was immunodetected in achlorophyllous pepper (Capsicum annuum) chromoplast membranes, and a corresponding cDNA was cloned from pepper and tomato (Lycopersicum esculentum) fruits. Genomic analysis suggests the presence of a single gene in these organisms, the expression of which parallels phytoene desaturase and zeta-carotene desaturase gene expression during fruit ripening. Furthermore, this PTOX gene is impaired in the tomato ghost mutant, which accumulates phytoene in leaves and fruits. These data show that PTOX also participates in carotenoid desaturation in chromoplasts in addition to its role during early chloroplast development.


Subject(s)
Arabidopsis Proteins , Carotenoids/biosynthesis , Nuclear Proteins/genetics , Plants/genetics , Plastids/metabolism , Amino Acid Sequence , Arabidopsis/genetics , Arabidopsis/metabolism , Base Sequence , Blotting, Southern , Capsicum/genetics , Capsicum/metabolism , Carotenoids/metabolism , Chloroplasts/metabolism , Escherichia coli/genetics , Escherichia coli/metabolism , Immunoblotting , Solanum lycopersicum/genetics , Solanum lycopersicum/metabolism , Molecular Sequence Data , Mutation , Nuclear Proteins/metabolism , Plants/metabolism , Plants, Medicinal , RNA, Messenger/analysis , Reverse Transcriptase Polymerase Chain Reaction , Sequence Homology, Amino Acid
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