Stomatal Action in Plants as Related to Damage From Photochemical Oxidants

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Abstract
The role of stomates, as a factor in controlling the injury to plants from the photochemically produced pollutants, ozone and peroxyacetyl nitrate (PAN), was investigated. Stomatal action was quantitatively measured by determining the resistance to air flow through the stomates with a Wheatstone bridge resistance porometer. By a combination of measurements involving apparent photosynthesis, transpiration, and degree of leaf damage produced by the air pollutant oxidants it was shown that: stomates open rapidly in the light, even after a long dark period, and close slowly in the dark; transpiration rate from plants transferred from the dark to the light equals the rate of control plants in the light within 30 minutes; the physiological age of bean plants and not the degree of stomatal opening determines the susceptibility to the 2 oxidants. (Five and 6 day old bean plants are not damaged by ozone yet the stomates are functional. Plants of this age are most susceptible to PAN damage); apparent photosynthesis and degree of stomatal opening were not significantly reduced in pinto bean by a 30 minute fumigation with ozone. The length of the pre-fumigation dark period determines the extent of leaf damage from this pollutant. The nature of ozone damage and the protective action of a long pre-fumigation dark period suggest that the level of carbohydrates in the leaves has some role in predisposing plants to damage from this oxidant.