Origin of the thiazole ring of camalexin, a phytoalexin from Arabidopsis thaliana.
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.
Zook
M
M
Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, USA. zook@pilot.msu.edu
Hammerschmidt
R
R
D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents / Q000378:metabolism*; D017360:Arabidopsis / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000378:metabolism; D007211:Indoles / Q000378:metabolism*; D013058:Mass Spectrometry; D010935:Plant Diseases; D013844:Thiazoles / Q000378:metabolism*; D062367:ortho-Aminobenzoates / Q000378:metabolism; D000094162:Phytoalexins
D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D003545:Cysteine; D007211:Indoles; D013844:Thiazoles; D062367:ortho-Aminobenzoates; C102405:camalexin; D000094162:Phytoalexins; C031385:anthranilic acid