J. Dixon et al., OZONE POLLUTION MODIFIES THE RESPONSE OF SUGAR-BEET TO THE HERBICIDE PHENMEDIPHAM, Water, air and soil pollution, 85(3), 1995, pp. 1443-1448
Experiments were conducted in which sugarbeet plants (Beta vulgaris L.
cv. Saxon) with 2 to 3 leaves were exposed to a simulated 2 day ozone
episode (100 nl l(-1), 7 h d(-1)). Three days later; the plants were
sprayed with field rate phenmedipham (1.14 kg a.i. ha(-1)) and growth
analysis conducted 7 days later indicated an antagonistic interaction
was occurring Physiological and biochemical studies were undertaken to
determine the nature of this antagonism. Treatment with phenmedipham
increased the ratio of transpiration to photosynthetic rates within 2
days of spraying, whilst exposure to ozone had no effect. When die two
treatments were combined, water use efficiency was not significantly
different from that when phenmedipham was applied alone. In contrast,
trends in the membrane permeability after treatment, indicated that th
e response of plants exposed to ozone followed by treatment with the h
erbicide, was intermediate between that of the herbicide (high pamrabi
lity) and ozone (low permeability). Furthermore, when the two treatmen
ts were combined the results of antioxidant enzyme assays indicated gr
eater than expected activities of enzymes which am mainly cytosolic, e
g. guaiacol peroxidase, as well as a similar increase in the activity
of the mainly chloroplastic superoxide dismutase. Treatment with ozone
alone and phenmedipham alone only slightly increased superoxide dismu
tase. Ozone may therefore induce the activities of these protective en
zymes. Thus, when another oxidative stress,such as the photosystem II
inhibitor phenmedipham was applied the plants could then respond more
quickly and showed less herbicide visible damage.