Production Practices and Quality Assessment of Food Crops. Vol. 1

Impact of Ozone on Crops 199
technique is rapid, non-invasive, and non-destructive and requires relatively inexpensive
instrumentation. The utility of fluorescence measurements in the field as
an indicator of plant responses to environmental conditions is well established
(Bolhar-Nordenkampf et al., 1989). Fluorescence measurements are mainly used
to determine activities of photosynthetic apparatus, such as the fluxes of absorbed
photons, trapped energy or transported electron. Therefore, fluorescence measurements
can be used before any changes in the visual appearance of leaves have
occurred or even when no changes in their chemical composition can be detected.
The ratio of variable fluorescence to maximal fluorescence is used to estimate
maximum quantum yield of PSII. This parameter, also called photochemical efficiency
estimates any disturbance in electron transfer between PSII and PSI. Ambient
O 3 exposure causes a decrease in the photochemical efficiency (Guidi et al., 1997).
Photochemical and non-photochemical quenching coefficients are also utilized to
detect the primary acceptor of PSII oxidation and heat emission (Reiling and
Davison, 1994). Both parameters are modified by the presence of O 3.
Fluorescence imaging is a newly developed tool (Lichtenthaler and Miehé, 1997;
Oxborough and Baker, 1997). It is used to identify the primary site of damage
and to characterize some features of O 3 damage when leaves are exposed to O 3. High
resolution image of bean leaves exposed to O 3 fumigation showed localized decreases
in PSII. Photochemical efficiencies were accompanied by an increase in minimal
fluorescence level, which is indicative of PSII inactivation (Leipner et al., 2001).
It is expected that the application of chlorophyll fluorescence and chlorophyll
fluorescence imaging will be very successful in detecting the incipient effects of
O 3 stress.
Various other techniques have been used for the assessment of O 3 injury to plants.
The following techniques have been utilized: chlorophyll losses, ethylene emission,
products of lipid peroxidation, ion leakage, antioxidative enzymes and free radical
metabolites (Tingey et al., 1976; Lee et al., 1982; Bors et al., 1989; Floyd et al.,
1989; Langebartels et al., 1991; Pitcher et al., 1991; Yalpani et al., 1994; Glick et
al., 1995; Sharma et al., 1996). These techniques are not specific for O 3 injury,
since other factors (heavy metals, herbicides, high temperature, and UV radiation)
causing oxidative stress induce similar results.
15. OZONE CONTROL
In addition to crop yield loss, damage of forest ecosystems and a reduction of
lung function in healthy people and people with an impaired respiratory system have
been demonstrated (Schmieden and Wild, 1995; Sandermann et al., 1997, 1998;
US EPA, 1998). Because of these serious environmental problems as a result of
the presence of O 3 in the lowest layer of the atmosphere many efforts have been
made to reduce the level of O 3. National and international limits for ambient O 3
exist, but are usually exceeded in North America and Western Europe. Despite
massive and costly efforts, countries in Europe and North America still experience
a severe problem (Photochemical Oxidants Review Group, 1990; National
Research Council, 1991). Ground-level O 3 is the most difficult to control of the