The herbicide 2,4-D has had a sound crop safety record since its introduction in 1945, gaining health and safety regulatory approval in more than 100 countries.
However, a recent study threatens to tarnish that reputation if accepted by the wider agricultural science community.
Angus Murphy, a horticulture department professor from Perdue University, discovered during a study on plant transporter proteins that 2,4-D can cause excessive accumulations of the plant protein auxin when absorbed by plants.
The herbicide is a synthetic form of auxin.
Murphy said auxin can accumulate at dangerous levels in cereals, and possibly kill them because 2,4- D cannot be exported out of plant cells as naturally occurring auxin.
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He said ABCB4 is a protein that acts as a transporter within plants to regulate the amount of auxin in their root hairs.
When the amount of auxin is high, the ABCB4 protein switches from its auxin uptake mode and transports the excess auxin out of the plant.
ABCB4 absorbs the 2,4-D when it is used to control broadleaf weeds in cereal crops. The herbicide binds to the ABCB4 protein in a way that does not allow the protein to transport the auxin out of the plant, even when the level of auxin is high, said Murphy.
The problem is that the auxin accumulation takes place in the outer layer of a plant’s root cell, while the deactivation mechanism, which would allow ABCB4 to switch to transport mode and move out the excess auxin, is on the inner layer of the root cell.
Murphy said cell damage will occur if the ABCB4’s transport mode doesn’t change.
Small amounts of the herbicide can cause these accumulations in the root hair cells and affect their length. Murphy said it could also cause the root hair cells to die.
Seventy to 90 percent of a plant’s absorption of water and mineral nutrients takes place in its root hairs, he added.
Murphy said ABCB4 is not absolutely necessary for plant survival, but does assist in improving plant growth.
It is possible to get rid of the ABCB4 protein through selection, which would make plants more 2,4-D resistant, but crop productivity may suffer as a result.
He said the findings of the study are timely because of plans to promote the use of crop varieties that are 2,4-D resistant.
The findings, which were published inPlant Journallate last month, are the first time a connection has been made between 2,4-D, ABCB4 and auxin.
