Ozone plant susceptibility

FIGURE 11-6 Ozone concentration vs. duration of exposure required to produce a S% response in three diffinent plant susceptibility groupings. The curves were generated by developing 95% confidence limits around the equations for all plants in each susceptibility grouping from Table 11-25. Qirves a > sensitive plants, b intermediate ants, c > resistant plants. 

Plant susceptibility to ozone as determined by visible injury may be very closely related to quantities of o-diphenols associated with the chloroplasts and specific requirements for activation of polyphenol oxidase enzymes. There is a significant correlation between ozone injury and concentrations of total phenols expressed as percent caffeic acid equivalents in peanut cultivars. This concept is not intended to underestimate the importance of membranes that separate phenols and enzymes. Perhaps future research will demonstrate that membranes of resistant alfalfa, green bean and other species differ both qualitatively and quantitatively from those of susceptible plants of these species. 

Freebaim noted a decrease in oxygen uptake of plant and bovine liver mitochondria that was reversible by glutathione and ascorbic acid. The activity of some mitochondrial enzymes, including succinic dehydrogenase and cytochrome oxidase, has been found to be susceptible to ozone. 

It seems reasonable that susceptibility and resistance of different plant species and different varieties within a species should depend on concentrations of endi enous antioxidants. The results of such studies do not give a clear picture Hanson et al. concluded that the range of susceptibility in petunia varieties depended on the ascorbic acid concentration, but Menser found that the ascorbic acid content of tobacco varieties was not related to ozone susceptibility. Ozone resistance of plants can be conferred by application of antioxidants. In the... 

Physiologic Effects Leaf age and illumination have been studied as physiologic and physical factors that affect the response of plants to PAN. Leaves of most plants are most susceptible when very young. In primary leaves of pinto bean, the period of maximal susceptibility to PAN precedes that for ozone by several days (about 5-7 days from seed for PAN, as opposed to 9-13 days for ozone). The example of tomato is particularly striking, inasmuch as the terminal leaflet of the compound leaf is the oldest tissue. Thus, the youngest susceptible leaf is affected in the terminal leaflet but, as the leaves become older, the terminal leaflet is resistant and the lateral leaflets are injured. ... 

TABLE 11-24 List of Plant Species and Cultivars by Susceptibility to Acute Ozone Exposures ... 

TABLE 11-25 Concentration, Time, Response Equations for Three Susceptibility Groups and for Selected Plants or Plant Types with Respect to Ozone ... 

Dugger, W. M., Ir., O. C. Taylor, E. Cardiff, and C. R. Thompson. Relationship between carbohydrate content and susceptibility of pinto bean plants to ozone damage. Proc. Amer. Soc. Hort. Sci. 81 304-314, 1962. 

Menser, H. A. Response of plants to air pollutants. III. A relation between ascorbic acid levels and ozone susceptibility of light-preconditioned tobacco plants. Plant Physiol. 39 564-567. 1964. 

Miller, P. R. Susceptibility to ozone of selected western conifers. Abstract 0579. In Abstracts of Papers. Second International Congress of Plant Pathology, University of Minnesota, Minneapolis, Minnesota, U.S.A., September 5-12, 1973. 

Stolzy, L. H., O. C. Taylor, W. M. Dugger, Jr., and J. D. Mersereau. Physiological changes in and ozone susceptibility of the tomato plant after periods of inadequate oxygen diffusion to the roots. Proc. Soil Sci. Soc. Amer. 28 305-308, 1964. 

Ting, I. P., and W. M. Dugger, Jr. Factors affecting ozone sensitivity and susceptibility of cotton plants. J. Air Pollut. Control Assoc. 18 810-813, 19M. 

The direct effects of ozone on plant species constituting the shrub layer in the conifer forest are not yet sufficiently understood to permit any conclusion to be drawn. In many sites where the conifer overstoiy is well developed, the shrub species are excluded completely. In more open pine stands, some shrubs are very common, such as skunk bush iAmorpha califomica) and white horn (Ceanothus cordulatus). Of these two species, only skunk bush shows highly visible chlorotic mottle of leaflets and premature defoliation where ozone dosages are high. A shrub species common to the lower chaparral zone, squaw bush Rhus trilobata), is even more susceptible to ozone injury. In the San Bernardino Moun-... 

Yonkers et al, have tested the ozone susceptibility of 15 species of annuals common to the Mojave Desert just north and east of the Los Angeles basin (and San Bernardino Mountains). Compared with the susceptible pinto bean plants included in the experiment with ozone at 0.35 ppm, Plantago sp., Cercidium sp., and Prosopsis sp. were also sensitive. Further interpretation of these results is complicated by the influences of plant age and pre-exposure conditions. 

Mixtures of Toxicants, Polluted atmospheres are complex mixtures of many toxic and inert materials which may interact to increase or diminish plant injury. Menser and Heggestad (26) reported the first evidence of synergistic response when an ozone-susceptible tobacco strain was exposed to a mixture of ozone and sulfur dioxide. Other researchers have subsequently confirmed this response, but attempts to identify synergistic or antagonistic responses with other pollutants have been unsuccessful, although synergistic effects of NO2 and SO2 are suggested. 

Salt Transport. The effects of ozone on membrane permeability can also be assessed by estimating salt leakage from treated tissue. In one study, susceptible bean plants were allowed to take up RbCl for 24 hr prior to ozone exposure. After exposure, leaf discs were placed in a desorption solution containing 0.5 M CaSOi and 2 mM KCl and the rate of Rb leakage into the desorption solution was determined. The initial loss was indistinguishable between treated and untreated plants and we assume that it represented exchange from free space. Then, for an extended period, treated tissue exhibited a linear loss of... 

Susceptible cultivars of most of these plants develop severe leaf injury when exposed to 2 to 5 pphm of ozone for 1 to 4 hr. This level of ozone is very common in urban areas and so are symptoms of ozone injury. However, such symptoms have also been reported from plants growing in such rural states as Maine and South Dakota. Even when no obvious injury can be seen, plants exposed to low levels of ozone may not grow as well or yield as much as plants growing in air free of ozone. On some plants, e.g., spinach, the symptoms of ozone injury are quite distinctive consequently, plants like these are being used in some places to detect and monitor air pollution. 

In another experiment (J ) we treated ozone-resistant and ozone-susceptible varieties of tobacco with toxic doses of oc-iodoacetic acid, and a-iodoacetamide, both sulfhydryl-binding reagents. The symptoms produced by both compounds were similar to those produced by ozone. The severity of the injury also paralleled ozone resistance (Table II). The degree of injury caused by these two compounds also paralleled the ozone susceptibility of leaves of different ages on the same plant. The uppermost, youngest, leaves appear to be most resistant to both the sulfhydryl-binding reagents and to ozone. 

Figure 1-4. Alfalfa leaves exposed to ambient concentrations of ozone a. From a resistant clone and shows no injury or pigment accumulation. b. From a susceptible plant and shows both leaf injury and pigment accumulation.

One of the earliest indications of ozone injury on several plant species is an upper surface discoloration with a waxy appearance. This symptom often disappears completely a few hours after exposure is terminated. High dosages of ozone cause permanent necrotic lesions on susceptible leaf tissue. Permeability of cell membranes is apparently disrupted, and cell contents are allowed to leak into the intercellular spaces producing a water-soaked appearance. Upon drying, the tissue will totally collapse and turn white or various shades of brown. Lesions which extend through the entire thickness of the leaf are commonly referred to as bifacial... 

High concentrations of ozone in the atmosphere may cause early fall color and leaf drop. This damage can be difficult to diagnose because symptoms mimic many other disease conditions. Check for similar damage on other ozone-susceptible plants growing in the same area. 

Prevention and Control Ozone levels in the air may reach damaging levels during the hot, calm days of mid- to late summer. Automobile exhaust is a major source of ozone pollution. There is no cure for ozone damage. Avoid it in following years by planting less-susceptible plants, including beets, lettuce, and strawberries. 

Ground-level ozone interferes with the ability of plants to produce and store food. This makes them more susceptible to disease, insects, other pollutants,... 

Plant damage with a definite economic significance, because the damages to crops and forests. Some cultivated species are very susceptible to ozone and P.A.N (ex. tobacco and grape). 

---