Effect of Imazamethabenz-methyl on Nitrate Uptake in Wheat ( Triticum durum L.)

The effect of the herbicide imazamethabenz-methyl (IMZM), a mixture of the two isomers methyl (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H -imidazol-2-yl]-4-methylbenzoate (para isomer) and methyl (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H -imidazol-2-yl]-5-methylbenzoate (meta isomer), on the uptake of nitrate by wheat grown hydroponically was studied. IMZM stimulates the nitrate uptake in both “induced” (NO 3 - -pretreated) and “uninduced” (NO 3 - -starved) seedlings, most likely as a response to a plant stress. The decrease in acetohydroxy acid synthase (AHAS; EC 4.1.3.18) activity and in protein content of IMZM-treated roots supports this hypothesis. The presence of valine, leucine, isoleucine, and IMZM prevents the effects of the herbicide treatment in both induced and uninduced plants. The addition of IMZM to humic acid enhances the nitrate uptake, although to a lower extent than with the herbicide alone. Possible traces of imazamethabenz acid (IMZA) in growing units do not seem to be responsible for the greater N demand observed.