camalexin and anthranilic-acid

Camalexin (3-thiazol-2'-yl-indole) is the principal phytoalexin that accumulates in Arabidopsis after infection by fungi or bacteria. Camalexin accumulation was detectable in Arabidopsis cell-suspension cultures 3 to 5 h after inoculation with Cochliobolus carbonum (Race 1), and then increased rapidly from 7 to 24 h after inoculation. Levels of radioactivity incorporated into camalexin during a 1.5-h pulse labeling with [14C]anthranilate also increased with time after fungal inoculation. The levels of radioactive incorporation into camalexin increased rapidly between 7 and 18 h after inoculation, and then decreased along with camalexin accumulation. Relatively low levels of radioactivity from [14C]anthranilate incorporated into camalexin in the noninoculated controls. Autoradiographic analysis of the accumulation of chloroform-extractable metabolites labeled with [14C]anthranilate revealed a transient increase in the incorporation of radioactivity into indole in fungus-inoculated Arabidopsis cell cultures. The time-course measurement of radioactive incorporation into camalexin during a 1.5-h pulse labeling with [14C]indole was similar to that with [14C]anthranilate. These data suggest that indole destined for camalexin synthesis is produced by a separate enzymatic reaction that does not involve tryptophan synthase.

Topics: Arabidopsis; Ascomycota; Cells, Cultured; Indoles; Kinetics; ortho-Aminobenzoates; Plant Diseases; Thiazoles; Tryptophan

The principal phytoalexin that accumulates in Arabidopsis thaliana after infection by fungi or bacteria is 3-thiazol-2'-yl-indole (camalexin). Detached noninoculated leaves of Arabidopsis and leaves inoculated with the fungus Cochliobolus carbonum were fed [35S]cysteine (Cys) and [35S]methionine. Inoculated leaves incorporated more than a 200-fold greater amount of radioactivity from [35S]Cys into camalexin, as compared with noninoculated leaves. The amount of radioactivity from [35S]Cys that was incorporated into camalexin from inoculated Arabidopsis leaves was 10-fold greater than the amount of radioactivity that was incorporated into camalexin from [35S]methionine. Additional labeling experiments were performed to determine whether other atoms of Cys are incorporated into camalexin. [14C]Cys and [35S]Cys were incorporated into camalexin with approximately the same efficiency. Cys labeled either with deuterium (D3-Cys[2,3,3]) or 13C and 15N ([U-13C,15N]Cys) was also fed to inoculated leaves of Arabidopsis; camalexin was analyzed by mass spectroscopic analysis. The average ratio of molecular ion intensities of 203/200 for [U-13C,15N]Cys-labeled camalexin was 4.22, as compared with 0.607 for the average 203/200 ratio for unlabeled camalexin. The mass fragment-ion intensity ratios of 60/58 (thiazole ring ion fragment) and 143/142 were also higher for [U-13C,15N]Cys-labeled camalexin, as compared with unlabeled camalexin. The 59/58 and 201/200 ratios were higher for D3-Cys-labeled camalexin as compared with unlabeled camalexin. These data are consistent with the predicted formation of the thiazole ring of camalexin from Cys.

Topics: Anti-Bacterial Agents; Anti-Infective Agents; Arabidopsis; Chromatography, High Pressure Liquid; Cysteine; Indoles; Mass Spectrometry; ortho-Aminobenzoates; Plant Diseases; Thiazoles