Active Absorption Summary
In summary, examples for active absorption of herbicides across plant membranes are limited. Evidence accumulated to date supports the transport of the cationic herbicide, paraquat, and the anionic herbicides, 2,4-D and glyphosate. In each example, the herbicide appears to be transported by a carrier that recognizes herbicide molecules with structures similar to the endogenous molecules transported by that carrier. The overall importance of active transport to phytotoxicity and herbicide effectiveness is unknown.
Why are there so few herbicides that require active transport to enter a plant cell?
ANSWER: Currently, three are known and these herbicides enter the cell via a carrier which recognizes that structure because it shares key characteristics which the natural product possesses.