Chilling Sensitivity Research Articles

Prior temperature exposure affects subsequent chilling sensitivity

The chilling sensitivity of small discs or segments of tissue excised from chillingsensitive species was significantly altered by prior temperature exposure subsequent to holding the tissue at chilling temperatures as measured by a number of physiological processes sensitive to chilling. This temperature conditioning was reversible by an additional temperature exposure before chilling, and mature‐green and red‐ripe tomato tissue exhibit similar chilling sensitivities.Exposing pericarp discs excised from tomato fruit (Lycopersicon esculentum Mill. cv. Castelmart), a chilling‐sensitive species, to temperatures from 0 to 37°C for 6 h before chilling the discs at 2.5°C for 4 days significantly altered the rate of ion leakage from the discs, but had no effect on the rate of ion leakage before chilling and only a minimal effect on discs held at a non‐chilling temperature of 12°C. Exposing chillingsensitive tissue to temperatures below that required to induce heat‐shock proteins but above 20°C significantly increased chilling sensitivity as compared to tissue exposed to temperatures between 10 and 20°C. Rates of ion leakage after 4 days of chilling at 2.5°C were higher from fruit and vegetative tissue of chilling‐sensitive species (Cucumis sativus L. cv. Poinsett 76, and Cucurbita pepo L. cv. Young Beauty) that were previously exposed for 6 h to 32°C than from similar tissue exposed to 12°C. Exposure to 32 and 12°C had no effect on the rate of ion leakage from fruit tissue of chilling tolerant species (Malus domestica Borkh. cv. Golden Delicious, Pyrus communis L. cv. Bartlett). Ethylene and CO2 production were higher and lycopene synthesis was lower in chilled tomato pericarp discs that were previously exposed for 6 h to 32°C than the values from tissue exposed to 12°C for 6 h before chilling. Increased chilling sensitivity induced by a 6 h exposure to 32°C could be reversed by subsequent exposure to 12°C for 6 h.

Prior temperature exposure affects subsequent chilling sensitivity

Prior temperature exposure affects subsequent chilling sensitivity

Surface Color Changes of Tomato and Other Solanaceous Fruit during Chilling

Chilling of mature-green (MG) tomato fruit (Lycopersicon esculentum Mill. and related species) was investigated to determine the effect of chilling stress on surface color during low-temperature storage. Color measurements were made with a tristimulus calorimeter (L, a, b values), and data were analyzed by multivariate analysis of variance and canonical variates analysis. Changes in surface color of MG fruit during chilling were not correlated overall with relative chilling sensitivity of cultivars/lines; however, within standard and cherry types, chilling-tolerant fruit changed surface color more during chilling than chilling-sensitive fruit when fruit were picked early in the season. Early harvests were less chilling-sensitive than late harvests. The number of hours below 15.6C in the 200 hours before harvest was positively correlated with postharvest chilling sensitivity. A high vs. ambient relative humidity during storage did not affect chilling-induced percent change in color. Tobacco mosaic virus resistance led to less and Verticillium albo-strum Reinke & Berthier resistance led to more chilling-induced color change. There was no effect from resistances to Fusarium oxysporum Schlechtend f. sp. lycopersici (Sacc.) W.C. Snyder & H.N. Hans, alternaria stem canker (Alternaria solani Sorauer), anthracnose [Colletotrichun coccodes (Wallr.) S.J. Hughes], root-knot nematode (Meloidogyne hapla Chitwood), Phytophthora infestans (Mont.) deBary, or Stemphylium botryosum f. sp. lycopersici Rotem, Cohen, & Wahl. Our results show harvest date had an effect on chilling-induced changes in surface-color in MG fruit.

Effect of Temperature Conditioning on Chilling Injury of Cucumber Cotyledons

Endogenous abscisic acid levels and induced heat shock proteins were measured in tissue exposed for 6 hours to temperatures that reduced their subsequent chilling sensitivity. One-centimeter discs excised from fully expanded cotyledons of 11-day-old seedlings of cucumber (Cucumis sativus L., cv Poinsett 76) were exposed to 12.5 or 37 degrees C for 6 hours followed by 4 days at 2.5 or 12.5 degrees C. Ion leakage, a qualitative indicator of chilling injury, increased after 2 to 3 day exposure to 2.5 degrees C, but not to 12.5 degrees C, a nonchilling temperature. Exposure to 37 degrees C before chilling significantly reduced the rate of ion leakage by about 60% compared to tissue exposed to 12.5 degrees C before chilling, but slightly increased leakage compared to tissue exposed to 12.5 or 37 degrees C and held at the nonchilling temperature of 12.5 degrees C. There was no relationship between abscisic acid content following exposure to 12.5 or 37 degrees C and chilling tolerance. Five heat shock proteins, with apparent molecular mass of 25, 38, 50, 70, and 80 kilodaltons, were induced by exposure to 37 or 42 degrees C for 6 hours, and their appearance coincided with increased chilling resistance. Heat shock treatments reduced the synthesis of three proteins with apparent molecular mass of 14, 17, and 43 kilodaltons. Induction of heat shock proteins could be a possible cause of reduced chilling injury in tissue exposed to 37 or 42 degrees C.

Lipid-protein interactions in thylakoid membranes of chilling-resistant and -sensitive plants studied by spin label electron spin resonance spectroscopy.

Lipid-protein interactions in thylakoid membranes from lettuce, pea, tomato, and cucumber have been studied using spin-labeled analogues of the thylakoid membrane lipid components, monogalactosyl diglyceride and phosphatidylglycerol. The electron spin resonance spectra of the spin-labeled lipids all consist of two components, one corresponding to the fluid lipid environment in the membranes and the other to the motionally restricted lipids interacting with the integral membrane proteins. Comparison of the spectra from the same spin label in thylakoid membranes from different plants shows that the overall lipid fluidity in the membranes decreases with chilling sensitivity. Spectral subtraction has been used to quantitate the fraction of the membrane lipids in contact with integral membrane proteins. Thylakoid membranes of cucumber, a typical chilling-sensitive plant, have been found to have a higher proportion of motionally restricted lipids and a different lipid selectivity for lipid-protein interaction, as compared with those of pea, a typical chilling-resistant plant. This correlation with chilling sensitivity holds generally for the different plants studied. It seems likely that the chilling sensitivity in thylakoid membranes is not determined by lipid fluidity alone, but also by the lipid-protein interactions which could affect protein function in a more direct manner.

CHANGE IN THE FATTY ACID COMPOSITION OF AVOCADO FRUIT DURING ONTOGENY, COLD STORAGE AND RIPENING

The ratio of saturated fatty acids to unsaturated fatty acids has been implicated in the sensitivity of plant materials to chilling injury. Chilling sensitive plant materials have been reported to have a higher mole percent of saturated fatty acids than plant materials not sensitive to chilling injury. Changes in the fatty acid composition have also been reported for chilling sensitive crops during and following exposure to chilling temperatures and that these changes may be related to chilling sensitivity. The fatty acid composition of ‘Fuerte' and 'Hass' avocados was determined during ontogeny, cold storage, and ripening. During ontogeny, oleic acid increased, linoleic and linolenic acids decreased and palmitic and palmitoleic remained essentially constant relative to the percentage of total fatty acids. The fatty acid composition did not change significantly during 2, 4 and 6 weeks storage at 0°, 5° and 10°C or after ripening at 20°C subsequent to the cold storage treatments.

CULTIVAR RESPONSE OF OKRA TO CHILLING AND PACKAGING

Okra pods are highly perishable due to a high respiration rate and chilling sensitivity. The purpose of this experiment was to evaluate okra cultivar response to package and storage temperature. Freshly harvested `Annie Oakley', `Blondy', `Burgundy', `Clemson Spineless' and `Emerald' okra pods were placed in plastic boxes and shrink-wrap bags. Pods were evaluated for weight loss, chilling injury and electrolyte leakage during 8 days of storage at 12.5 and 3°C. Weight loss was similar for all cultivars at both temperatures, but it was much less when pods were stored in bags compared to boxes. Percent electrolyte leakage was similar for all cultivars before storage. `Blondy' displayed the most severe chilling injury after 8 days of storage at 3C while `Emerald' had few symptoms of chilling injury. After 8 days of storage, all cultivars except `Emerald' had increased electrolyte leakage. These results indicate that okra pods have increased membrane permeability with chilling injury, and the degree of chilling injury may differ with cultivar.

A Chilling Sensitive Mutant of Arabidopsis with Altered Steryl-Ester Metabolism

A chilling-sensitive mutant of Arabidopsis thaliana was isolated and subjected to genetic, physiological, and biochemical analysis. The chilling-sensitive nature of the mutant line is due to a single recessive nuclear mutation at a locus designated chs1. In contrast to wild-type plants, which are not adversely affected by low temperatures, the chs1 mutant is killed by several days of exposure to temperatures below 18 degrees C. Following exposure to chilling temperatures, the mutant displays two common symptoms of chilling injury-leaf chlorosis and electrolyte leakage. In these respects, the physiological response of the mutant to low temperatures mimics the response observed in some naturally occurring chilling sensitive species. The biochemical basis of chilling sensitivity was explored by examining the pattern of incorporation of (14)CO(2) into soluble metabolites and lipids in wild-type and mutant plants. The only difference observed between the mutant and wild type was that following low temperature treatment, the mutant accumulated 10-fold more radioactivity in a specific class of neutral lipids which were identified by a variety of criteria to be steryl-esters. The accumulation of radioactivity in the steryl-ester fraction occurs 24 hours before there is any visible evidence of chilling injury. These results suggest one of two possible explanations: either the mutation directly affects sterol metabolism, which in turn leads to chilling sensitivity, or the mutation affects another unidentified function and the accumulation of radioactivity in steryl-esters is a secondary consequence of chilling injury.

Simultaneous measurements of heat, water vapour and CO 2 fluxes above alfalfa and maize

The objective of this study was to measure the short-term biophysical responses of alfalfa and maize crops growing in unmodified field environments. Flux densities of heat (H), water vapour ( LE) and CO 2 ( Fc) between the crop surface and the atmosphere were obtained using a Bowen ratio-energy balance (BREB) method. Two BREB systems were designed and used to provide simultaneously the fluxes above adjacent fields of unirrigated alfalfa ( Medicago saliva L.) and maize ( Zea mays L.) in southern Ontario (Koppen's climate classification Dfb). Differences in fluxes between alfalfa and maize were characteristic of their C3 and C4 metabolism, respectively, as indicated by higher rates of Fc above maize, higher rates of LE above alfalfa and chilling sensitivity in maize, but not alfalfa. Bowen ratios were larger above the alfalfa crop following harvest, but were highest for maize when both crops were fully grown.

リンゴ‘千秋’果実の収穫熟度による低温障害感受性, 呼吸活性一びにエチレン生成の差異

Changes in respiratory rate and ethylene production in ‘Sensyu’ apple fruit, and electrolyte leakage from flesh tissue during storage were investigated in relation to fruit maturity and chilling sensitivity. Fruits were harvested at early maturity (pre-climacteric), standard maturity (climacteric) and late maturity (post-climacteric).1. During storage, the rates of respiration and ethylene production were greatly reduced at -1°, 0° or 5°C compared to 20°C. After transfer from the chilling temperature (-1° to 5°C) to 20°C, fruits harvested at the same maturity showed nearly the same pattern of changes in respiratory rate and ethylene production.2. When apple fruits were stored at 20°, 5°, 0° or -1°C, ethylene-forming enzyme (EFE) activity increased rapidly in proportion to the increase in storage temperature, excepting for the early-harvested fruits. In these fruits, the increase of EFE activity of fruits stored at 0°C was faster than in fruits stored at 5°C.3. During storage at 20°C, fruit softening and rotting were markedly observed in the fruits of standard and late harvest as compared with the early-harvested ones. On the other hand, the development of chilling injury symptoms was severe in the early-harvested fruits, while slight pitting occurred in the fruits of standard and late harvest during storage at 0° or -1°C. It could be suggested that storage temperature at 5°C would be available for the early-harvested fruits, while for the fruits of standard and late harvest it would be -1°C.4. The rate of electrolyte leakage from flesh tissue on the first inspection of the fruits just harvested was low in the early-maturity fruits, which showed high chilling sensitivity. On the other hand, a marked increase in the rate of electrolyte leakage occurred in the early-harvested fruits during storage at 0° or -1°C, while almost no change was observed in the fruits of standard and late harvest.

Proline and Polyamine Involvement in Chilling Tolerance of Maize Suspension Cultures

We have assessed the effect of various medium supplements in promoting the ability of maize (Zea mays L.) inbred FR27rhm suspension cultures to grow following a period of 4 °C chilling stress. Following a 4 week exposure to 4 °C in culture medium without proline, no cell growth occurred upon subsequent incubation at 28°C for 2 weeks. This inhibition was reversed when 3 to 48 mol m−3 proline or 0.1 mol m−3 putrescine or 0.01 mol m−3 spermidine were present in the medium during the chilling stress. On the other hand, suspensions were made more sensitive to 4°C by blocking polyamine biosynthesis with 1.0 mol m−3 methylglyoxal bis (guanylhydrazone) (MGBG) or a combination of 1.0 mol m−3 difluoromethylornithine (DFMO) and 1.0 mol m−3 difluoromethylarginine (DFMA). The addition of 10 mol m−3 putrescine to the suspension containing DFMO and DFMA prevented the increased chilling sensitivity. Electrolyte leakage studies conducted to assess membrane integrity after 4 weeks at 4°C and a 2 week regrowth period showed that cells treated with no polyamines (control), 0.01 mol m−3 spermidine, 1.0 mol m−3 putrescine, or 1.0 mol m−3 MGBG lost 43, 32, 14, and 100% of the total electrolyte pool, respectively. These results suggest that proline and polyamines are beneficial for inducing chilling tolerance in FR27rhm suspension.

Fatty Acid Composition of Phosphatidylglycerols in Relation to Chilling Sensitivity of Woody Plants

In the present study, we analyzed the fatty acids of PG from leaves of temperate-zone evergreens, tropical evergreens and temperate-zone deciduous plants. The results are discussed in terms of estimated levels of various molecular species of the PG. It appears that the sum of the levels of saturated and trans-monounsaturated molecular species, as a proportion of the total in the PG in leaves of evergreens, is correlated with the chilling sensitivity of leaves, as previously demonstrated in herbaceous plants

Photoinhibition at Low Temperature in Chilling-Sensitive and -Resistant Plants

Photoinhibition resulting from exposure at 7 degrees C to a moderate photon flux density (300 micromoles per square meter per second, 400-700 nanometers) for 20 hours was measured in leaves of annual crops differing widely in chilling tolerance. The incidence of photoinhibition, determined as the decrease in the ratio of induced to total chlorophyll fluorescence emission at 693 nanometers (F(v)/F(max)) measured at 77 Kelvin, was not confined to chilling-sensitive species. The extent of photoinhibition in leaves of all chilling-resistant plants tested (barley [Hordeum vulgare L.], broad bean [Vicia faba L.], pea [Pisum sativum L.], and wheat [Triticum aestivum L.]) was about half of that measured in chilling-sensitive plants (bean [Phaseolus vulgaris L.], cucumber [Cucumis sativus L.], lablab [Lablab purpureus L.], maize [Zea mays L.], pearl millet [Pennisetum typhoides (Burm. f.) Stapf & Hubbard], pigeon pea [Cajanus cajun (L.) Millsp.], sesame [Sesamum indicum L.], sorghum [Sorghum bicolor L. Moench], and tomato [Lycopersicon esculentum Mill.]). Rice (Oryza sativa L.) leaves of the indica type were more susceptible to photoinhibition at 7 degrees C than leaves of the japonica type. Photoinhibition was dependent both on temperature and light, increasing nonlinearly with decreasing temperature and linearly with increasing light intensity. In contrast to photoinhibition during chilling, large differences, up to 166-fold, were found in the relative susceptibility of the different species to chilling injury in the dark. It was concluded that chilling temperatures increased the likelihood of photoinhibition in leaves of both chilling-sensitive and -resistant plants. Further, while the photoinhibition during chilling generally occurred more rapidly in chilling-sensitive plants, this was not related directly to chilling sensitivity.

Maturation and chilling sensitivity of ‘Fuyu’ persimmon fruit in New Zealand

Abstract Seasonal changes in fruit growth, soluble tannins, soluble solids concentration, colour, fruit firmness, and chilling sensitivity were recorded during fruit maturation of the persimmon cultivar, Fuyu. Comparisons were made between fruit growing in Auckland and Gisborne in two seasons. There were major variations between seasons in soluble solids concentrations, soluble tannins, and colour as fruit matured. Chilling sensitivity was also greater in one year than another. Tannin content and chilling sensitivity of fruit varied between sites within a season. These results confirm observations that maturation of persimmon fruit in New Zealand does not follow the same pattern as it does in Japan.

Galactolipase activity and free fatty acid levels in chloroplasts of domestic and wild tomatoes with different chilling tolerance

In order to establish differences in the chilling sensitivity of domestic and wild Lycopersicon species, galactolipase (EC 3.1.1.26) activity, free fatty acid (FFA) level and Hill reaction activity were measured in chloroplasts isolated from control and cold treated leaves of L. esculentum Mill., cv. Norton, L. hirsutum Humb. and Bonpl., L. peruvianum var. glandulosum Mill. Galactolipase activity was higher in chloroplasts from Lycopersicon species with high chilling sensitivity than in chloroplasts of more chilling‐resistant ones. A similar relationship was observed for FFA level in chloroplasts from both cold‐stored and control leaves. Decrease in Hill reaction activity due to cold stress was greater in chloroplasts of more chilling‐sensitive species. The changes are accompanied by a decline of photochemical activity. Considering the changes in the three parameters noted above, an increasing order of chilling tolerance was established: L. esculentum < L. hirsutum (700 m) < L. hirsutum (3100 m) < L. peruvianum (3400 m). It is suggested that measurements of galactolipase activity and FFA may be useful in an evaluation of differences in resistance to chilling injury of closely related species.

Role of Carbohydrates in Diurnal Chilling Sensitivity of Tomato Seedlings

Tomato seedlings (Lycopersicon esculentum Mill.) chilled starting at different times during the light/dark cycle were most chilling-sensitive at the end of the dark period (AI King, MS Reid, BD Patterson 1982 Plant Physiol 70: 211-214). Low-temperature tolerance was regained with as little as 10 minutes of light exposure. Low light intensities were less effective than high light intensities in reducing sensitivity, and the length of exposure to light directly influenced sensitivity. Seedlings kept at low night temperatures prior to chilling were also less injured following chilling. Light also restored chilling tolerance to seedlings whose roots were removed. Supplying cut shoots with sucrose, glucose, or fructose reduced chilling sensitivity and largely eliminated the diurnal difference in sensitivity. Endogenous carbohydrate content was correlated with changes in chilling sensitivity; starch and sugar content fell markedly during the dark period. Increased concentrations of sugars were detected 15 minutes after the start of the light period. This evidence all suggests that changes in chilling sensitivity over the diurnal period are regulated by the light cycle. It also suggests that increased sensitivity at the end of the dark period could be due to carbohydrate depletion, and that chilling tolerance following light exposure is likely due to carbohydrate accumulation or closely related events.

ウメ果実の収穫熟度による低温障害感受性の差異とリン脂質成分及び膜透過性との関連について

In our previous paper, it was reported that mume fruits became chilling-insensitive when they were harvested at a late period, and that the surface color of the stone may be a useful criterion of harvest time. This paper deals with the changes in stone color, K+ leakage rate, and phospholipid composition with reference to fruit maturity and chilling sensitivity.1. ‘Ohshuku’ mume fruits were harvested at weekly intervals from May 16 to June 13 and investigated for the relation between surface color of the stone and fruit maturity. The stone was white in fruits harvested before May 30, and the embryos were not yet matured. Stone color changed to light brown in fruits harvested on June 6 and the embryos were mature.2. HCl-soluble pectin content decreased rapidly after June 6 and water-soluble pectin content increased concomitantly. Citric acid content increased and malic acid content decreased during maturation; especially, a marked decrease of malic acid content was found after June 6.3. The number of days from harvest to the beginning of rapid increase of CO2 and C2H4 production, and peel yellowing, decreased during maturation. A marked decrease was found between May 23 and June 6.4. As an index of membrane permeability, the rate of K+ leakage was measured at 3, 6, 8°C on the harvest day, and its relation to chilling sensitivity was investigated. The rate of K+ leakage was low in fruits harvested from May 23 to June 6; these fruits showed high chilling sensitivity.5. As an index of membrane flexibility, the phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio was investigated in relation to harvest maturity. Theratio was very low in fruits harvested from May 23 to June 6, which showed high chilling sensitivity. Fruits harvested on June 13 showed a high ratio and low chilling sensitivity.From these results it was concluded that the time of stone-color change from white to light brown or brown coincides with a physiological turning point of fruits, and that mume fruits acquire chilling resistance after that.

The Influence of Dark Adaptation Temperature on the Reappearance of Variable Fluorescence following Illumination

The effect of chilling temperatures (5 degrees C) on chlorophyll fluorescence transients was used to study chilling-induced inhibition of photosynthesis in plant species with differing chilling sensitivities. A Brancker SF-20 fluorometer was used to measure induced fluorescence transients from both attached and detached leaves of chilling-sensitive cucumber (Cucumis sativus L. cv Ashley) and chilling-resistant pea (Pisum sativum L. cv Alaska). The rate of reappearance of the variable component of fluorescence (F(v)), following a period of illumination at 25 degrees C, was dependent on the temperature at which the leaf was allowed to dark adapt in chilling-sensitive cucumber, but not in chilling-resistant pea. In cucumber, dark adaptation at 25 degrees C following illumination resulted in a much faster return of F(v) than dark adaptation at 5 degrees C following illumination. However, F(v) reappearance during the dark adaptation period in chilling-resistant pea was temperature independent. The difference in the temperature response of F(v) following illumination correlated with temperature sensitivity of these two species. The process responsible for the difference in F(v) may represent a site of chilling sensitivity in the photosynthetic apparatus.

Photoinhibition at Chilling Temperatures

Relative susceptibilities of chilled leaves to photoinhibition were determined for 15 species of crop annuals showing a wide range of chilling tolerance. Leaf tissue at 7°C was exposed to a moderate photon irradiance of 300 �mol m-2 s-1 and photoinhibition was measured by the decrease in chlorophyll fluorescence (Fv/Fm) measured at 77K. All chilling-resistant plants surveyed (barley, broad bean, oat, pea and wheat) were photoinhibited at chilling temperatures. The chilling-sensitive plants (bean, cucumber, lablab, maize, pearl millet, pigeon pea, sesame, sorghum and tomato) were more susceptible, the mean of values for susceptibility to photoinhibition being twice that of the chilling-resistant plants. Rice, however, showed a tolerance to photoinhibition at 7°C comparable to that of some of the chilling- resistant plants. Indica rices were more susceptible than japonica rices. Photoinhibition increased with decreasing temperature and with increasing photon irradiance in both the chilling-resistant and sensitive plants. In pea and cucumber, photoinhibition at 7°C was correlated linearly with the decrease in photosystem II activity assayed in chloroplast thylakoids isolated from similarly treated tissue. Relative tolerances of leaves of the same 15 species to chilling injury in the dark were also measured. No linear correlation was found between susceptibility of chilled leaves to photoinhibition and susceptibility to dark chilling injury. The pattern of differences between species for photoinhibition at 7°C was largely preserved when photoinhibitory treatments were given at a non-chilling temperature (21°C) by increasing the photon irradiance to 900 �mol m-2 s-1. We conclude that, while the chilling-sensitive plants were generally more susceptible than the chilling-resistant ones to photoinhibition at low temperatures, this arose from a greater sensitivity to the irradiance rather than from the chilling sensitivity. Photoinhibition associated with low temperatures was also demonstrated in the tropical fruit species, banana, pawpaw and Monstera. Low values of Fv/Fm recorded in leaves exposed to full sunlight during the winter month of July (range 0.39-0.56 compared with 0.70-0.79 in January) indicated that photoinhibition could adversely affect some tropical perennial fruit species cultivated in semitropical or warm temperate areas experiencing recurrent cool to cold winters.

A Comparison of the Effects of Chilling on Leaf Gas Exchange in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.)

The effects of chilling on the photosynthesis of a chilling-resistant species, pea (Pisum sativum L. cv Alaska) and a chilling-sensitive species, cucumber (Cucumis sativus L. cv Ashley) were compared in order to determine the differences in the photosynthetic chilling sensitivity of these two species. For these experiments, plants were chilled (5 degrees C) for different lengths of time in the dark or light. Following a 1 hour recovery period at 25 degrees C, photosynthetic activity was measured by gas exchange (CO(2) uptake and H(2)O release), quantum yield, and induced chlorophyll fluorescence. The results show that pea photosynthesis was largely unaffected by two consecutive nights of chilling in the dark, or by chilling during a complete light and dark cycle (15 hours/9 hours). Cucumber gas exchange was reduced by one night of chilling, but its quantum yield and variable fluorescence were unaffected by dark chilling. However, chilling cucumber in the light led to reduced CO(2) fixation, increased internal leaf CO(2) concentration, decreased quantum yield, and loss of variable fluorescence. These results indicate that chilling temperatures in conjunction with light damaged the light reactions of photosynthesis, while chilling in the dark did not.