No abstract

Fusarium infection in wheat causes Fusarium head blight, resulting in yield losses and contamination of grains with trichothecenes. Some plant secondary metabolites inhibit accumulation of trichothecenes. Eighteen Fusarium infected wheat cultivars were harvested at five time points and analyzed for the trichothecene deoxynivalenol (DON) and 38 wheat secondary metabolites (benzoxazinoids, phenolic acids, carotenoids, and flavonoids). Multivariate analysis showed that harvest time strongly impacted the content of secondary metabolites, more distinctly for winter wheat than spring wheat. The benzoxazinoid 2-β-glucopyranoside-2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA-glc), α-tocopherol, and the flavonoids homoorientin and orientin were identified as potential inhibitors of DON accumulation. Several phenolic acids, lutein and β-carotene also affected DON accumulation, but the effect varied for the two wheat types. The results could form a basis for choosing wheat cultivars using metabolite profiling as a marker for selecting wheat cultivars with improved resistance against Fusarium head blight and accumulation of trichothecene toxins in wheat heads.

Benzoxazinoids are highly studied compounds due to their biological activity and presence in several cereals. They include compound classes such as hydroxamic acids and lactams and usually occur as inactive glucosides in unstressed plants. Injury to the plant causes enzymatic hydrolysis of the inactive glucosides to the biologically active hydroxamic acid and lactam aglucones. The hydroxamic acids further undergo spontaneous hydrolysis to benzoxazolinones in aqueous solution. Extraction methods that do not cause immediate inactivation of enzymes result in accumulation of aglucones in samples. Using HPLC-MS to profile benzoxazinoids in maize seedlings subjected to several sample preparation techniques, we have found that hydroxamic acid aglucones and benzoxazolinones are present in uninjured maize seedlings, but that the benxozazinoid profile varies depending on sample treatment, potentially underrepresenting the glucoside content and overrepresenting the aglucone and benzoxazolinone content.

Hydroxamic acids are important defense compounds in cereals and have been subject to extensive research. Two important hydroxamic acids in maize are 2-β-D-glucopyranosyloxy-4-hydroxy-7-methoxy-2 H-1,4-benzoxazin-3(4 H)-one (DIMBOA-glc) and its 8-methoxylated derivative (DIM2BOA-glc). The compounds are typically reported as resolved by mass spectrometry rather than chromatography, with DIM2BOA-glc quantified relative to DIMBOA-glc. Biphenyl HPLC columns, however, allow good separation of the two compounds at both the analytical and semi-preparative scale, enabling both isolation and absolute quantitation of both compounds. In combination with established sample treatment and chromatographic methods, biphenyl chromatography thus promises new possibilities for resolving benzoxazinoid glucosides.

From the study it can be concluded that, depending on their properties, surfactants can enhance or reduce the mobility of bentazone. By choosing a non-ionic surfactant, bentazone mobility can be reduced, giving time for degradation and thereby reducing the risk of groundwater pollution.