Phloem transport of D,L-glufosinate and acetyl-L-glufosinate in glufosinate-resistant and -susceptible Brassica napus

Phloem transport of D,L-[C-14]glufosinate, D-[C-14]glufosinate, and acetyl- L-[C-14]glufosinate was examined in the susceptible Brassica napus cv Excel and a glufosinate-resistant genotype (HCN27) derived by transformation of cv Excel with the phosphinothricin-N-acetyltransferase (pat) gene. Consider ably more C-14 was exported from an expanded leaf in HCN27 than in cv Excel following application of D,L-[C-14]glufosinate (25% versus 6.3% of applied , respectively, 72 h after treatment). The inactive isomer, D-glufosinate, was much more phloem mobile in cv Excel than racemic D,L-glufosinate. Folia r or root supplementation with 1 mM glutamine increased D,L-[C-14]glufosina te translocation in cv Excel but only transiently, suggesting that glutamin e depletion is not the major cause of the limited phloem transport. Acetyl- L-[C-14]glufosinate (applied as such or derived from L-glufosinate in pat t ransformants) was translocated extensively in the phloem of both genotypes. Acetyl-L-[C-14]glufosinate was readily transported into the floral buds an d flowers, and accumulated in the anthers in both genotypes. These results suggest that phloem transport of D,L-glufosinate is limited by rapid physio logical effects of the L-isomer in source leaf tissue. The accumulation of acetyl-L-glufosinate in the anthers indicates that it is sufficiently phloe m mobile to act as a foliar-applied chemical inducer of male sterility in p lants expressing a deacetylase gene in the tapetum, generating toxic concen trations of L-glufosinate in pollen-producing tissues.