Observations on the physiological basis for the selectivity of morfamquat to graminaceous plants

Abstract

AbstractThe bipyridylium herbicide morfamquat damages dicotyledon plants in a similar way to paraquat but unlike paraquat, has little activity on Gramineae such as cocksfoot, wheat and maize.Results are presented which show that this selective action is not due to differences in the amounts of chemical taken up by treated leaves of susceptible and resistant plants or to differences in the degree of movement in plants.Freeze‐thaw experiments show that the plasmalemma and tonoplast membranes of sensitive and resistant weeds are less permeable to morfamquat than to paraquat. Whilst this could account for differences in activity of the two herbicides on cocksfoot, further evidence is given which shows that selectivity is not due to differences in morfamquat movement from free space to cytoplasm. Differential movement from cytoplasm into the chloroplasts of resistant and susceptible species may be the basis of the selective action, but several other mechanisms of selectivity are also mentioned.