ABSTRACT. Diploid Thinopyrum elongatum, a wild relative of wheat, contains many agronomically desirable traits and has potential for increasing genetic variability and introducing desirable characters in this crop. Few molecular markers are available for rapid screening of T. elongatum genome segments in the wheat genetic background. We used 36 RAPD primers and 33 ISSR primers to screen for polymorphisms in the common wheat variety Chinese Spring and in T. elongatum. Two RAPD markers and one ISSR marker, designated OPF03 1407 , LW10 1487 and UBC841 701 , were identified and were specific for the T. elongatum E genome. Three pairs of primers flanking these specific sequences were designed to produce SCAR markers. All three SCAR markers were T. elongatum E genome-specific. Two of these SCAR markers, SCAR 807 and SCAR 577 , were present in all seven T. elongatum chromosomes, while SCAR 839 was specific for T. elongatum chromosomes 2E and 3E. These newly developed SCAR markers should be useful for detecting alien genome chromatin or chromosome segments in the genetic background of common wheat.

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Nitrobenzene, although widely used in industry, is a highly toxic environmental pollutant. To evaluate the toxicity of nitrobenzene to tobacco seedlings, seedlings were exposed to varying concentrations of nitrobenzene (0-100 mg/L) for 24 h. The contents of reactive oxygen species (hydrogen peroxide [H(2)O(2)] and superoxide anion [O2(-)]) and the activities of antioxidative enzymes (superoxide dismutase [SOD], guaiacol peroxidase [POD], and catalase [CAT]) were measured in leaf cells. Damage to DNA was assessed by single-cell gel electrophoresis (comet assay). Compared with the control, the contents of H(2) O(2) increased significantly with nitrobenzene concentrations ranging from 5 to 100 mg/L. Activity of SOD was induced by 50 to 100 mg/L of nitrobenzene but not by 10 to 25 mg/L. Activity of POD was stimulated by nitrobenzene at 10 to 50 mg/L but inhibited at 100 mg/L. Activity of CAT was increased significantly only by 100 mg/L. Lipid peroxidation increased with 50 to 100 mg/L, which indicated that nitrobenzene induced oxidative stress in tobacco leaf cells. Comet assay of the leaf cells showed a significant enhancement of the head DNA (H-DNA), tail DNA (T-DNA), and olive tail moment (OTM) with increasing doses of nitrobenzene. The values of H-DNA, T-DNA, and OTM exhibited significant differences from the control when stress concentrations were higher than 10 mg/L. The results indicated that nitrobenzene caused oxidative stress, which may be one of the mechanisms through which nitrobenzene induces DNA damage.

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