Plant Physiol, October 1999, Vol. 121, pp. 619-628

Phloem Transport of D,L-Glufosinate and Acetyl-L-Glufosinate in Glufosinate-Resistant and -Susceptible Brassica napus¹

Department of Plant Sciences, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A8

Phloem transport of D,L-[¹⁴C]glufosinate, D-[¹⁴C]glufosinate, and acetyl-L-[¹⁴C]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 ¹⁴C was exported from an expanded leaf in HCN27 than in cv Excel following application of D,L-[¹⁴C]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-[¹⁴C]glufosinate translocation in cv Excel but only transiently, suggesting that glutamine depletion is not the major cause of the limited phloem transport. Acetyl-L-[¹⁴C]glufosinate (applied as such or derived from L-glufosinate in pat transformants) was translocated extensively in the phloem of both genotypes. Acetyl-L-[¹⁴C]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.