Photosynthesis as a Tool for Indicating Temperature Stress Events
13.4 Photosynthetic Function as a Criterion
for Screening Chilling Susceptibility
267
Exposure to low temperatures brings about phase transitions in the biomembranes of chilling-susceptible plants (Lyons 1973), with consequent
metabolic disorders, especially of photosynthetic function. Only in very rare
cases does acute damage occur; in most cases necroses develop during the
process of decay following irreversible impairment. The progress of chilling
damage depends not only on the degree and duration of cooling, but also on
the age of the leaves, the ontogenetic stage of the individual plant, its state
of acclimatization, and numerous boundary conditions (e.g., speed of temperature change, soil temperature, air humidity, incoming light during and
after chilling). Especially in agriculture and plant breeding there is great
interest in an early warning and in quantitative criteria for grading plant
species and varieties according to their chilling susceptibility.
A useful method for the recognition of critical threshold temperatures for
stress-induced functional deviations and for the onset of pathological processes is provided by the determination of abnormalities in respiration and
photosynthetic CO 2 or O2 exchange rates at low but nonfreezing temperatures. An important criterion for chilling susceptibility is a depression of
photosynthesis continuing for hours or even days. In addition to the effect of
cold on chloroplast functioning, stomatal closure is also involved in the
reduction of CO2 uptake. The latter cannot only be evoked by an increased
internal CO2 partial pressure, but also by altered water relations (Bauer et
al. 1985) and, probably, by hormonal signals. A direct insight into chilling
disturbances in chloroplast functioning under non-destructive conditions is
provided by biophysical methods, such as leaf absorbance changes, prompt
and delayed chlorophyll fluorescence, and photoacoustic signals (Havaux
and Lannoye 1985).
In chilling-sensitive plants the thermotropic properties of the biomembranes change at higher temperatures than in chilling-tolerant species.
Lateral phase separation and segregation of chlorophyll-protein complexes
occur (Berry and Raison 1981; Maenpaa et al. 1988), the water-splitting
side of PS II becomes inhibited (Havaux and Lannoye 1984; Shen et al.
1990) and reoxidation of QA is drastically depressed (Havaux 1987). Such
thylakoid impairments are reflected in changes of chlorophyll fluorescence
during cooling by an increasing delay in peak fluorescence (Melcarek and
Brown 1977; Smillie and Hetherington 1983), a decrease in the variable
fluorescence decay following the peak (Havaux and Lannoye 1984; Larcher
and Bodner 1987; Lichtenthaler 1988), and a lowering of the photochemical
quenching coefficient at steady state (Havaux 1987; Neuner and Larcher
1990).
Employing photosynthetic parameters as stress indicators, the temperature thresholds for chilling damage were determined on related plant
13.4 Photosynthetic Function as a Criterion
for Screening Chilling Susceptibility
267
Exposure to low temperatures brings about phase transitions in the biomembranes of chilling-susceptible plants (Lyons 1973), with consequent
metabolic disorders, especially of photosynthetic function. Only in very rare
cases does acute damage occur; in most cases necroses develop during the
process of decay following irreversible impairment. The progress of chilling
damage depends not only on the degree and duration of cooling, but also on
the age of the leaves, the ontogenetic stage of the individual plant, its state
of acclimatization, and numerous boundary conditions (e.g., speed of temperature change, soil temperature, air humidity, incoming light during and
after chilling). Especially in agriculture and plant breeding there is great
interest in an early warning and in quantitative criteria for grading plant
species and varieties according to their chilling susceptibility.
A useful method for the recognition of critical threshold temperatures for
stress-induced functional deviations and for the onset of pathological processes is provided by the determination of abnormalities in respiration and
photosynthetic CO 2 or O2 exchange rates at low but nonfreezing temperatures. An important criterion for chilling susceptibility is a depression of
photosynthesis continuing for hours or even days. In addition to the effect of
cold on chloroplast functioning, stomatal closure is also involved in the
reduction of CO2 uptake. The latter cannot only be evoked by an increased
internal CO2 partial pressure, but also by altered water relations (Bauer et
al. 1985) and, probably, by hormonal signals. A direct insight into chilling
disturbances in chloroplast functioning under non-destructive conditions is
provided by biophysical methods, such as leaf absorbance changes, prompt
and delayed chlorophyll fluorescence, and photoacoustic signals (Havaux
and Lannoye 1985).
In chilling-sensitive plants the thermotropic properties of the biomembranes change at higher temperatures than in chilling-tolerant species.
Lateral phase separation and segregation of chlorophyll-protein complexes
occur (Berry and Raison 1981; Maenpaa et al. 1988), the water-splitting
side of PS II becomes inhibited (Havaux and Lannoye 1984; Shen et al.
1990) and reoxidation of QA is drastically depressed (Havaux 1987). Such
thylakoid impairments are reflected in changes of chlorophyll fluorescence
during cooling by an increasing delay in peak fluorescence (Melcarek and
Brown 1977; Smillie and Hetherington 1983), a decrease in the variable
fluorescence decay following the peak (Havaux and Lannoye 1984; Larcher
and Bodner 1987; Lichtenthaler 1988), and a lowering of the photochemical
quenching coefficient at steady state (Havaux 1987; Neuner and Larcher
1990).
Employing photosynthetic parameters as stress indicators, the temperature thresholds for chilling damage were determined on related plant