Zook M, Hammerschmidt R
Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824, USA.
Plant Physiol. 1997 Feb;113(2):463-8. doi: 10.1104/pp.113.2.463.
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.
拟南芥在被真菌或细菌感染后积累的主要植保素是3-噻唑-2'-基吲哚（camalexin）。给拟南芥未接种的离体叶片以及接种了真菌玉米小斑病菌（Cochliobolus carbonum）的叶片饲喂[35S]半胱氨酸（Cys）和[35S]甲硫氨酸。与未接种的叶片相比，接种的叶片将来自[35S]Cys的放射性掺入camalexin中的量要多200倍以上。来自接种的拟南芥叶片的[35S]Cys掺入camalexin中的放射性量比来自[35S]甲硫氨酸掺入camalexin中的放射性量高10倍。进行了额外的标记实验以确定Cys的其他原子是否掺入camalexin中。[14C]Cys和[35S]Cys以大致相同的效率掺入camalexin中。用氘（D3-Cys[2,3,3]）或13C和15N（[U-13C,15N]Cys）标记的Cys也被饲喂给接种的拟南芥叶片；通过质谱分析对camalexin进行分析。[U-13C,15N]Cys标记的camalexin的分子离子强度平均比值203/200为4.22，而未标记的camalexin的平均203/200比值为0.607。与未标记的camalexin相比，[U-13C,15N]Cys标记的camalexin的质量碎片离子强度比值60/58（噻唑环离子碎片）和143/142也更高。与未标记的camalexin相比，D3-Cys标记的camalexin的59/58和201/200比值更高。这些数据与预测的由Cys形成camalexin的噻唑环一致。
