Hydroxamic acid content and toxicity of rye at selected growth stages

• Published in: Journal of chemical ecology 2005-08, Vol.31 (8), p.1887-1905
• Main Authors: Rice, C.P, Park, Y.B, Adam, F, Abdul-Baki, A.A, Teasdale, J.R
• Format: Article
• Language: English
• Subjects: Acids; Agricultural practices; allelopathy; Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; Autoecology; Biological and medical sciences; Boa; Cover crops; Cropping systems; Detection limits; Ecotoxicology, biological effects of pollution; Fundamental and applied biological sciences. Psychology; General aspects; Herbicides - chemistry; Herbicides - metabolism; hydroxamic acids; Hydroxamic Acids - metabolism; Hydroxamic Acids - toxicity; Lactuca - drug effects; Lactuca sativa; liquid chromatography; Lycopersicon esculentum; mass spectrometry; Phytotoxicity; Plant Roots - chemistry; Plant Shoots - chemistry; Plant tissues; root growth; rye; Secale - chemistry; Secale - growth & development; Secale - metabolism; Secale cereale; seedling growth; Seedlings; Solanum lycopersicum - drug effects; Tomatoes
• ISSN: 0098-0331; 1573-1561
• DOI: 10.1007/s10886-005-5933-6

Rye (Secale cereale L.) is an important cover crop that provides many benefits to cropping systems including weed and pest suppression resulting from allelopathic substances. Hydroxamic acids have been identified as allelopathic compounds in rye. This research was conducted to improve the methodology for quantifying hydroxamic acids and to determine the relationship between hydroxamic acid content and phytotoxicity of extracts of rye root and shoot tissue harvested at selected growth stages. Detection limits for an LC/MS-MS method for analysis of hydroxamic acids from crude aqueous extracts were better than have been reported previously. (2R)-2-β-d-Glucopyranosyloxy-4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA-G), 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA), benzoxazolin-2(3H)-one (BOA), and the methoxy-substituted form of these compounds, (2R)-2-β-d-glucopyranosyloxy-4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA glucose), 2,4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), and 6-methoxy-benzoxazolin-2(3H)-one (MBOA), were all detected in rye tissue. DIBOA and BOA were prevalent in shoot tissue, whereas the methoxy-substituted compounds, DIMBOA glucose and MBOA, were prevalent in root tissue. Total hydroxamic acid concentration in rye tissue generally declined with age. Aqueous crude extracts of rye shoot tissue were more toxic than extracts of root tissue to lettuce (Lactuca sativa L.) and tomato (Lycopersicon esculentum Mill.) root length. Extracts of rye seedlings (Feekes growth stage 2) were most phytotoxic, but there was no pattern to the phytotoxicity of extracts of rye sampled at growth stages 4 to 10.5.4, and no correlation of hydroxamic acid content and phytotoxicity (I50 values). Analysis of dose-response model slope coefficients indicated a lack of parallelism among models for rye extracts from different growth stages, suggesting that phytotoxicity may be attributed to compounds with different modes of action at different stages. Hydroxamic acids may account for the phytoxicity of extracts derived from rye at early growth stages, but other compounds are probably responsible in later growth stages.