Phloem Transport of d,l-Glufosinate and Acetyl-l-Glufosinate in Glufosinate-Resistant and -Susceptible Brassica napus

Phloem transport of d,l-[(14)C]glufosinate, d-[(14)C]glufosinate, and acetyl-l-[(14)C]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. Considerably more (14)C was exported from an expanded leaf in HCN27 than in cv Excel following application of d,l-[(14)C]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. Foliar or root supplementation with 1 mm glutamine increased d,l-[(14)C]glufosinate translocation in cv Excel but only transiently, suggesting that glutamine depletion is not the major cause of the limited phloem transport. Acetyl-l-[(14)C]glufosinate (applied as such or derived from l-glufosinate in pat transformants) was translocated extensively in the phloem of both genotypes. Acetyl-l-[(14)C]glufosinate was readily transported into the floral buds and flowers, and accumulated in the anthers in both genotypes. These results suggest that phloem transport of d,l-glufosinate is limited by rapid physiological effects of the l-isomer in source leaf tissue. The accumulation of acetyl-l-glufosinate in the anthers indicates that it is sufficiently phloem mobile to act as a foliar-applied chemical inducer of male sterility in plants expressing a deacetylase gene in the tapetum, generating toxic concentrations of l-glufosinate in pollen-producing tissues.