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Science Forum Index » Environment Forum » Low Temperature Tolerance -- Summary
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| David Naugler |
 Posted: Mon Dec 22, 2003 10:35 am |
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From:
http://www.co2science.org/subject/f/summaries/frosthardiness.htm
Low Temperature Tolerance -- Summary
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Only a handful of studies have attempted to determine what
relationship, if any, exists between atmospheric CO2 enrichment and
the ability of plants to withstand the rigors of cold temperatures.
Nevertheless, some tantalizing things have been learned.
Loik et al. (2000) grew three Yucca species (brevifolia, schidigera,
and whipplei) in pots placed within glasshouses maintained at
atmospheric CO2 concentrations of 360 and 700 ppm and day/night air
temperatures of 40/24°C for seven months, after which some of the
plants were subjected to a two-week day/night air temperature
treatment of 20/5°C. In addition, leaves from each Yucca species were
removed and placed in a freezer that was cooled at a rate of 3°C per
hour until a minimum temperature of -15°C was reached. These
manipulations indicated that elevated CO2 lowered the air temperature
at which 50% low-temperature-induced cell mortality occurred by 1.6,
1.4 and 0.8°C in brevifolia, schidigera and whipplei, respectively.
And on the basis of the result obtained for Y. brevifolia, Dole et al.
(2003) estimated that "the increase in freezing tolerance caused by
doubled CO2 would increase the potential habitat of this species by
14%."
In contrast to these positive results, Obrist et al. (2001) observed
just the opposite response. In an open-top chamber study of a
temperate grass ecosystem growing on a nutrient-poor calcareous soil
in northwest Switzerland, portions of which had been exposed to
atmospheric CO2 concentrations of 360 and 600 ppm for a period of six
years, they determined that the average temperature at which 50%
low-temperature-induced leaf mortality occurred in five prominent
species actually rose by an average of 0.7°C in response to the extra
240 ppm of CO2 employed in their experiment.
Most relevant investigations, however, have produced evidence of
positive CO2 effects on plant low temperature tolerance. Sigurdsson
(2001), for example, grew black cottonwood seedlings near Gunnarsholt,
Iceland within closed-top chambers maintained at ambient and
twice-ambient atmospheric CO2 concentrations for a period of three
years, finding that elevated CO2 tended to hasten the end of the
growing season. This effect was interpreted as enabling the seedlings
to better avoid the severe cold-induced dieback of newly-produced
tissues that often occurs with the approach of winter in this region.
Likewise, Wayne et al. (1998) found that yellow birch seedlings grown
at an atmospheric CO2 concentration of 800 ppm exhibited greater
dormant bud survivorship at low air temperatures than did seedlings
grown at 400 ppm CO2.
Schwanz and Polle (2001) investigated the effects of elevated CO2 on
chilling stress in micropropagated hybrid poplar clones that were
subsequently potted and transferred to growth chambers maintained at
either ambient (360 ppm) or elevated (700 ppm) CO2 for a period of
three months. They determined that "photosynthesis was less
diminished and electrolyte leakage was lower in stressed leaves from
poplar trees grown under elevated CO2 as compared with those from
ambient CO2." Although severe chilling did cause pigment and protein
degradation in all stressed leaves, the damage was expressed to a
lower extent in leaves from the elevated CO2 treatment. This
CO2-induced chilling protection was determined to be accompanied by a
rapid induction of superoxide dismutase activity, as well as by
slightly higher stabilities of other antioxidative enzymes.
Another means by which chilling-induced injury may be reduced in
CO2-enriched air is suggested by the study of Sgherri et al. (1998),
who reported that raising the air's CO2 concentration from 340 to 600
ppm increased lipid concentrations in alfalfa thylakoid membranes
while simultaneously inducing a higher degree of unsaturation in the
most prominent of those lipids. Under well-watered conditions, for
example, the 76% increase in atmospheric CO2 enhanced overall
thylakoid lipid concentration by about 25%, while it increased the
degree of unsaturation of the two main lipids by approximately 17% and
24%. Under conditions of water stress, these responses were found to
be even greater, as thylakoid lipid concentration rose by
approximately 92%, while the degree of unsaturation of the two main
lipids rose by about 22% and 53%.
What do these observations have to do with a plant's susceptibility to
chilling injury? According to a number of studies conducted over the
past decade, a lot.
Working with wild-type Arabidopsis thaliana and two mutants deficient
in thylakoid lipid unsaturation, Hugly and Somerville (1992) found
that "chloroplast membrane lipid polyunsaturation contributes to the
low-temperature fitness of the organism," and that it "is required for
some aspect of chloroplast biogenesis." When lipid polyunsaturation
was low, for example, they observed "dramatic reductions in
chloroplast size, membrane content, and organization in developing
leaves." Furthermore, there was a positive correlation "between the
severity of chlorosis in the two mutants at low temperatures and the
degree of reduction in polyunsaturated chloroplast lipid composition."
Working with tobacco, Kodama et al. (1994) demonstrated that the
low-temperature-induced suppression of leaf growth and concomitant
induction of chlorosis observed in wild-type plants was much less
evident in transgenic plants containing a gene that allowed for
greater expression of unsaturation in the fatty acids of leaf lipids.
This observation and others led them to conclude that substantially
unsaturated fatty acids "are undoubtedly an important factor
contributing to cold tolerance."
In a closely related study, Moon et al. (1995) found that heightened
unsaturation of the membrane lipids of chloroplasts stabilized the
photosynthetic machinery of transgenic tobacco plaints against
low-temperature photoinibition "by accelerating the recovery of the
photosystem II protein complex." Likewise, Kodama et al. (1995), also
working with transgenic tobacco plants, showed that increased fatty
acid desaturation is one of the prerequisites for normal leaf
development at low, nonfreezing temperatures; and Ishizaki-Nishizawa
et al. (1996) demonstrated that transgenic tobacco plants with a
reduced level of saturated fatty acids in most membrane lipids
"exhibited a significant increase in chilling resistance."
These observations are laden with significance for earth's
agro-ecosystems. Many economically important crops, such as rice,
maize and soybeans, are classified as chilling-sensitive; and they
experience injury or death at temperatures between 0 and 15°C (Lyons,
1973). If atmospheric CO2 enrichment enhances their production and
degree-of-unsaturation of thylakoid lipids, as it does in alfalfa, a
continuation of the ongoing rise in the air's CO2 content could
increase the abilities of these critically important agricultural
species to withstand periodic exposure to debilitating low
temperatures; and this phenomenon could provide the extra boost in
food production that will be needed to sustain our increasing numbers
in the years and decades ahead.
Earth's natural ecosystems would also benefit from a CO2-induced
increase in thylakoid lipids containing more-highly-unsaturated fatty
acids. Many plants of tropical origin, for example, suffer cold
damage when temperatures fall below 20°C (Graham and Patterson, 1982);
and with improved lipid characteristics provided by the ongoing rise
in the air's CO2 content, such plants would be able to expand their
ranges both poleward and upward in a higher-CO2 world.
Clearly, more research remains to be done before we can accurately
assess the extent of these potential biological benefits. In
particular, we must conduct more studies of the effects of atmospheric
CO2 enrichment on the properties of thylakoid lipids in a greater
variety of plants; and, in the same experiments, we must assess the
efficacy of these lipid property changes in enhancing plant tolerance
of low temperatures. Such studies should rank high on the to-do list
of relevant funding agencies.
References
Dole, K.P., Loik, M.E. and Sloan, L.C. 2003. The relative importance
of climate change and the physiological effects of CO2 on freezing
tolerance for the future distribution of Yucca brevifolia. Global and
Planetary Change 36: 137-146.
Graham, D. and Patterson, B.D. 1982. Responses of plants to low,
non-freezing temperatures: proteins, metabolism, and acclimation.
Annual Review of Plant Physiology 33: 347-372.
Hugly, S. and Somerville, C. 1992. A role for membrane lipid
polyunsaturation in chloroplast biogenesis at low temperature. Plant
Physiology 99: 197-202.
Ishizaki-Nishizawa, O., Fujii, T., Azuma, M., Sekiguchi, K., Murata,
N., Ohtani, T. and Toguri T. 1996. Low-temperature resistance of
higher plants is significantly enhanced by a nonspecific
cyanobacterial desaturase. Nature Biotechnology 14: 1003-1006.
Kodama, H., Hamada, T., Horiguchi, G., Nishimura, M. and Iba, K.
1994. Genetic enhancement of cold tolerance by expression of a gene
for chloroplast w-3 fatty acid desaturase in transgenic tobacco.
Plant Physiology 105: 601-605.
Kodama, H., Horiguchi, G., Nishiuchi, T., Nishimura, M. and Iba, K.
1995. Fatty acid desaturation during chilling acclimation is one of
the factors involved in conferring low-temperature tolerance to young
tobacco leaves. Plant Physiology 107: 1177-1185.
Loik, M.E., Huxman, T.E., Hamerlynck, E.P. and Smith, S.D. 2000. Low
temperature tolerance and cold acclimation for seedlings of three
Mojave Desert Yucca species exposed to elevated CO2. Journal of Arid
Environments 46: 43-56.
Lyons, J.M. 1973. Chilling injury in plants. Annual Review of Plant
Physiology 24: 445-466.
Moon, B.Y., Higashi, S.-I., Gombos, Z. and Murata, N. 1995.
Unsaturation of the membrane lipids of chloroplasts stabilizes the
photosynthetic machinery against low-temperature photoinhibition in
transgenic tobacco plants. Proceedings of the National Academy of
Sciences, USA 92: 6219-6223.
Obrist, D., Arnone III, J.A. and Korner, C. 2001. In situ effects of
elevated atmospheric CO2 on leaf freezing resistance and carbohydrates
in a native temperate grassland. Annals of Botany 87: 839-844.
Schwanz, P. and Polle, A. 2001. Growth under elevated CO2
ameliorates defenses against photo-oxidative stress in poplar (Populus
alba x tremula). Environmental and Experimental Botany 45: 43-53.
Sgherri, C.L.M., Quartacci, M.F., Menconi, M., Raschi, A. and
Navari-Izzo, F. 1998. Interactions between drought and elevated CO2
on alfalfa plants. Journal of Plant Physiology 152: 118-124.
Sigurdsson, B.D. 2001. Elevated [CO2] and nutrient status modified
leaf phenology and growth rhythm of young Populus trichocarpa trees in
a 3-year field study. Trees 15: 403-413.
Wayne, P.M., Reekie, E.G. and Bazzaz, F.A. 1998. Elevated CO2
ameliorates birch response to high temperature and frost stress:
implications for modeling climate-induced geographic range shifts.
Oecologia 114: 335-342.
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Last updated 17 December 2003
Center for the Study of Carbon Dioxide and Global Change
(www.co2science.org). |
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