The role of surface wax in susceptibility of plants to air pollutant injury

Abstract

The relationship between quantity of epicuticular wax and plant sensitivity to hydrogen chloride (HCl) gas was investigated using 8-, 12-, and 16-day-old Phaseolus vulgaris L. plants exposed for 20 min to 27.6 2 3.9 mg ~~l . m -~.Twelve-day-old plants were more sensitive than 8-or 16-day-old plants and possessed the lowest mean surface wax quantity. Multiple regression analysis showed that surface wax quantity was negatively linearly related to percent of leaves glazed. Necrotic injury was also negatively correlated with surface wax quantity, but to a lesser degree than glazing. Chamber temperature also affected the amount of necrotic injury incurred. Plant age and HC1 concentration did not contribute to the observed variation in any of the injury variables in the regression analysis.The results of this study support the hypothesis that cuticular resistance, which is influenced by the amount of epicuticular wax, is a major factor influencing leaf glazing due to gaseous HC1. Since necrotic injury was affected by both surface wax quantity and chamber temperature, the incidence and severity of necrotic injury may be controlled by both cuticular and stomata1 resistances. IntroductionThe type and severity of injury incurred when plants are exposed to gaseous air pollutants is influenced by many factors which may be considered under the categories of pollutant, plant, and environment. The interactions of these factors determine the ultimate amount of plant injury produced. As a result of such interactions, it may be difficult to ascertain the effect of any single factor unless the effects of all other factors, known or unknown, are controlled. This is accomplished experimentally by keeping all extraneous variables constant when possible and by partitioning the effects of variables that have fluctuated.Previous reports (Endress et al. 1978(Endress et al. , 1979a indicated that at least some of the injury on Phaseolus vulgaris leaves exposed to gaseous hydrogen chloride (HC1) resulted from diffusion of acid through the cuticle. This suggested that plant injury would exhibit some dependence on cuticular resistance. In preliminary experiments, the quantity of leaf surface waxes on bean plants of equal age was observed to vary significantly over a period of weeks. Presumably, fluctuations in light intensity, relative humidity, and temperature over time in the greenhouse accounted for the observed variation in surface wax development (Skoss 1955;Whitecross and Armstrong 1972;Baker 1974). We have also observed that the relative sensitivity of equally aged plants to gaseous HC1 varies over time (unpublished observations). In addition, the sensitivity of unifoliate bean leaves to gaseous HC1 varies with leaf age (Endress et al. 1979).

The influence of ozone and acid mist on the amount and wettability of the surface waxes in Norway spruce [Picea abies (L.) Karst.]

“…As no significant interaction between ozone and acid mist was shown in the present study, it is concluded that the combined effects of the pollutants on the wettability of the needle surface are no more than additive. Increased wettability of the needle surfaces induced by ozone and/or acid mist may enhance foliar leaching (Tukey, 1971), aid pollutant uptake from the atmosphere (Swiecki, Endress & Taylor, 1982), increase susceptibility to phylloplane pathogens (Rotem, 1978) and exacerbate the physical effects of frost (Barnes et al, 1988a).…”

Effects of Simulated Acid Rain on Production, Morphology and Composition of Epicuticular Wax and on Cuticular Membrane Development

“…(Huttunen & Laine, 1983;Riding & Percy, 1985;Crossley & Fowler, 1986). The amount of epicuticular wax on leaflets of pinto bean {Phaseolus vulgaris L.) exposed to gaseous hydrogen chloride was negatively correlated with the degree of foliar injury (Sweicki, Endress & Taylor, 1982). Fumigation with SOg stimulated wax production in ryegrass (Lolium perenne L.) (Koziol & Cowling, 1981), but such effects were later found to be dependent upon genotype, SOg concentration and season (Shelvey & Koziol, 1986).…”

Cuticular transpiration and epicuticular lipids of primary leaves of barley (Hordeum vulgare)

“…Other investigations, however, schJer 1971), exchange of gases with the atmosphere show no or only poor correJations between cuticular (Jeffree et al 1971), protection against mechanical and transpiration and the quantity of epicuticular lipids pest damage (Martin 1964), and protection against ul- (Denna 1970a,b, Rama Das et al 1979. In addition to traviolet radiation (Clark and Lister 1975) and air pol-the total amount, other properties of the epicuticular Klutants (Swiecki et al 1982). Despite the potential sig-pids, such as different components or different chain nificance of these aspects, experimental evidence for lengths of these, might affect the water loss through the specific functions is tacking.…”