Effect of Environment on, and Analysis of, Allelopathic Natural Products in Rye (Secale cereale L.)

Abstract

This research examined the effects of environmental factors such as temperature, fertility, and water status, on the production of a class of allelopathic natural products in rye. These compounds, the benzoxazinones, were first identified and studied in the 1960's as fungal resistance factors in cereal crops. The primary phytotoxic compounds are: 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), its corresponding glucoside (DIBOA-glu), and 2-benzoxazolinone (BOA). Nutrient availability was found to have the greatest overall effect on the production of allelochemicals in rye. Plants grown under a higher fertility regime had significantly greater concentrations of allelopathic compounds in their tissue. Plants grown with low water availability also had elevated levels of allelopathic compounds in their tissue in comparison with those plants grown with adequate moisture. Subjecting rye to elevated growing temperatures also led to a significant increase in allelochemical content. All results were weighed against the established theories of plant defense, optimal defense theory and carbon / nutrient theory. Results did not conform to one particular theory, but were supported by portions of each.

This work also describes the development of a new method for analysis of these compounds as well as other allelopathic agents found in rye tissue, b-hydroxybutyric acid, and b-phenyl lactic acid. Sample preparation consists of extraction of freeze-dried rye vegetative tissue with aqueous ethanol (50%) followed by partitioning of the allelochemicals into an ethyl acetate, evaporation, and derivatization using the trimethyl silylating reagent MSTFA. GC analysis of the silylated mixture was performed using a 20M DB-5 megabore capillary column and a temperature program increasing from 100 to 300 C at 5 C/ min with detection by FID. Injector temperature was 250 C and detector temperature was 325 C. Identities of all compounds were confirmed by GC/MS analysis.