Effects of ambient ozone pretreatment on transpiration and susceptibility to ozone injury

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Abstract
The effects of daily pretreatment with low levels of ozone (0.02 μl litre−1) on the susceptibility of primary bean leaves to acute ozone injury involve several stages. Plants subjected daily to low ozone from the time of sowing exhibit an early resistance to acute injury which decreases with time. When the low ozone pretreatments begin about 10 days after sowing, there is no change in susceptibility for 2–3 days, then it increases to a level which remains constant. At the start of this period of greater susceptibility, such pretreated plants are more susceptible than controls in filtered air; after about 8 days, they are less susceptible because of the marked increase insusceptibility of the controls with time. In contrast, daily pretreatments with higher (0.05 μl litre−1) levels, beginning 8 days after sowing, cause an initial decrease in susceptibility followed by a marked increase, leading to predisposition to acute injury.The early increase in susceptibility of plants transferred from filtered air to 0.02 μl ozone litre−1appears to be the result of the decreased ability of stomates to close in response to high ozone levels. The later stage of decreased relative susceptibility is associated with a dampening of stomatal activity, which is independent of the presence of high ozone levels.

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