2,4-D Resistance in a Tobacco Cell Culture Variant: Cross-Resistance to Auxins and Uptake, Efflux and Metabolism of 2,4-D

摘要

A tobacco (Nicotiana tabacumL.) variant selected as a cell line resistant to 2,4-D was found to possess cross-resistance to auxins including IAA, naphthalene-1-acetic acid (NAA), and 4-amino-3,5,6-trichloropicolinic acid (picloram). The uptake of 2,4-D by the variant and two wild-type cell lines was essentially linear in relation to 2,4-D concentration, and the variant took up 2,4-D more rapidly than the wild types. Analysis of the 2,4-D metabolism revealed some diversity in the metabolic pattern among the cell lines but no significant differences which could explain the resistance of the variant. Although the variant possesses a much higher capacity to metabolize 2,4-D than the wild types, this is most likely a result rather than a cause of the resistance. We conclude that neither the uptake nor the metabolism is responsible for the resistance. The variant, on the other hand, exhibited a significantly lower rate of efflux out of the cells, particularly that of free 2,4-D, than the wild types upon washing with and transfer to 2,4-D-free medium. We suggest that immobilization of 2,4-D or auxins within cells by compart mentation may be related to but not solely responsible for the resistance of this tobacco cell culture variant.