HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Massardo, F. Articles by Alberdi, M. Search for Related Content PubMed Articles by Massardo, F. Articles by Alberdi, M. Agricola Articles by Massardo, F. Articles by Alberdi, M.

SEED PHYSIOLOGY, PRODUCTION & TECHNOLOGY

Embryo Physiological Responses to Cold by Two Cultivars of Oat during Germination

^a Dep. of Ecology and Evolutionary Biology, Univ. of Connecticut, 75 North Eagleville Road, Storrs, CT 06269-3043 USA
^b Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 2407, Concepción, Chile
^c Instituto de Botánica, Universidad Austral de Chile, Austral, Chile

fmassardo{at}eudoramail.com

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 
Physiological responses and mechanisms triggered by cold are known for seedlings and mature plants, but are poorly understood for early developmental stages. Previous research on seedlings of two oat (Avena sativa L.) cultivars, `Ot220xOmihi' (Ot220) and `America', characterized them as cold tolerant and cold sensitive, respectively. This study investigates if cold responses during seed germination, at the phases of coleorhiza (1–2 mm elongation) and radicle (10 mm elongation) emergence, are similar to those described for these same cultivars at later developmental stages. Accumulation of cryoprotective solutes, degree of fatty acid unsaturation, oxygen consumption, and oxidative damage were evaluated. From imbibition until coleorhiza or radicle protrusion, seeds were maintained in darkness at constant temperatures of 17°C (control) or 3°C (low temperature treatment). Number of days to initiate germination (Di), days to reach 50% germination (D₅₀), and lethal temperature for 50% of the population (LT₅₀) were determined. At 3°C, Di and D₅₀ occurred significantly earlier in Ot220. LT₅₀ values, however, did not differ significantly. At the coleorhiza stage, embryos of both cultivars at 3°C accumulated soluble sugars; fructans accumulated only in Ot220. At the radicle stage, proline and fructans accumulated in both cultivars. No clear differences between cultivars were detected with regard to the relative composition or degree of unsaturation of fatty acids at low temperatures. However, at 3°C, Ot220 exhibited greater oxygen consumption and catalase activity than did America. Significant lipoperoxidative damage occurred only in America. As for the seedling stage, Ot220 can be characterized as cold tolerant and America as cold sensitive during germination. Responses to low temperature at this early development stage, however, were indicative of higher metabolic rates and less oxidative damage, rather than an accumulation of cryoprotective solutes.

Abbreviations: AO, alternative oxidase • BHT, butylated hydroxy-toluene • Cyt c, cytochrome c oxidase • Di, time in days to the initiation of germination • D₅₀, time in days to reach 50 total germination • FW, fresh weight • LT₅₀, temperature at which 50 of the population survives

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 
LOW TEMPERATURES during seed germination can reduce the percentage and timing of radicle protrusion in diverse species or cultivars (Scott et al., 1984; Roberts, 1988), but the physiological mechanisms involved in those germination variations, are still poorly understood (Hallgreen and Öquist, 1990; Dell'Aquila and Spada, 1994; Dahal et al., 1996). Physiological mechanisms triggered by low temperatures are better understood for later developmental stages of plant growth, i.e., seedlings or mature plants (Alberdi and Corcuera, 1991; Nilsen and Orcutt, 1996). At later developmental stages, "cold tolerant" cultivars of mono- and dicotyledoneous species can exhibit (i) accumulation of cryoprotective solutes such as sugars and proline (Alberdi and Corcuera, 1991; Nilsen and Orcutt, 1996); (ii) quantitative and qualitative changes in membrane fluidity (Leborgne et al., 1992; Alberdi et al., 1993; Thomas and James, 1993); (iii) synthesis of cold-induced cryoprotective peptides and proteins (Guy, 1990); (iv) higher metabolic rates (van der Venter, 1985); and (v) less oxidative injury because of more efficient antioxidant mechanisms (Purvis and Shewfelt, 1993). Although not all of these physiological and biochemical changes are correlated with cold tolerance in every species (Murelli et al., 1995; Nilsen and Orcutt, 1996), some of them can influence metabolism at low temperatures and may help to explain the lower lethal temperatures (LT₅₀) observed for "cold tolerant" genotypes (Alberdi and Corcuera, 1991; Nilsen and Orcutt, 1996). In addition, some of the changes correlated with cold tolerance at later development stages could also be responsible for cold tolerance at early developmental stages. This study examines if cold responses reported for seedling and adult stages of oat cultivars also work during seed germination of those cultivars.

Oat is considered a cold-tolerant species during germination because its minimal germination temperature is between 3 and 5°C (Mayer and Poljakoff-Mayber, 1989). But as for other species, almost nothing is known about the mechanisms of cold tolerance in oat embryos. Previous research on seedlings of Chilean oat cultivars, characterized Ot220xOmihi (Ot220) as cold tolerant and America as cold sensitive (Alberdi et al., 1993). At low temperatures, Ot220 exhibited lower LT₅₀, greater accumulation of cryoprotective solutes at the seedling stage, and better growth and yield parameters at mature stages.

This study investigates cold responses of Ot220 and America during seed germination, at the phases of coleorhiza (1–2 mm elongation) and radicle (10 mm elongation) emergence, and compares these responses with those reported for later developmental stages of these cultivars. Associated with a better understanding of cold responses during germination, this investigation can provide valuable practical information for the selection of cultivars at early developmental stages (Mayer and Poljakoff-Mayber, 1989; Hallgreen and Öquist, 1990). Ot220 and America are among the most commonly grown oat cultivars in southern Chile (38–40°S) where mean minimal winter temperatures are less than 5°C (di Castri and Hajek, 1976).

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 
Seed Source and Temperature Treatments
Seeds of Ot220 and America were obtained from the Instituto de Investigaciones Agropecuarias (INIA, Chile). Seeds were collected by INIA from plants growing in Temuco region of Chile (39°S) under similar field conditions in 1992. The seeds were then stored in a dry chamber at 15°C. Each seed lot was characterized for dried weight, and viability by TTC (2,3,5-triphenyl tetrazolium chloride) test (ISTA, 1987). Surface sterilized (commercial hypochlorite 67.2 mmol kg^-1 and Tween-20 for 10 min) seeds were sown in Petri dishes (100 by 20 mm) on absorbent paper. Seed imbibition was initiated by adding 8 mL of distilled water, and seeds were maintained in the dark at constant temperature regimes (0, 3, 6, 10, or 17°C) until embryo elongation (radicle or coleorhiza). A seed with a visible coleorhiza was considered germinated. Embryos (embryonic axis and scutellum) were dissected for analyses at two stages: the coleorhiza stage (coleorhiza emerged 1–2 mm elongation), and the radicle stage (radicle 10 mm long). Experiments with intact seeds were performed at these same stages of development.

Cold Tolerance during Germination
Sensitivity to low temperatures was evaluated by the following parameters: (i) the number of days to the initiation of coleorhiza emergence (Di), (i) the number of days for 50% of the seed population to germinate (D₅₀), and (iii) the final percentage of germinated seeds after 15 d. Similar criteria to evaluate tolerance to low temperature has been used previously (Scott and Jones, 1982; Martin et al., 1988). Evaluations were conducted on eight replicates of 30 seeds at five temperatures (0, 3, 6, 10, and 17°C) to distinguish low temperature sensitivity from vigor characteristics of Ot220 and America. If differences in germination parameters were explained by vigor only, then similar differences would be expected over the entire range of temperatures. If differences in germination between cultivars were associated with differential sensitivity to low temperatures, however, then larger differences in germination would be expected at lower temperatures.

Freezing Tolerance
Freezing tolerance was evaluated as the lethal temperature for 50% of the population (LT₅₀). Groups of 30 seeds were grown at 3 or 17°C until they reached the coleorhiza or radicle stage of development; then they were exposed to freezing treatments (0, -3, -6, or -10°C) for 2 h. After the freezing period, the temperature was increased at 6°C/h and all groups were maintained at 17°C until growth resumed. The LT₅₀ values were estimated by extrapolation of the survival curves 10 d after the freezing period.

Cryoprotective Solutes
Proline content was measured by extracting 0.5 g from embryos (coleorhiza and radicle stages) into 118.0 mmol kg^-1 sulphosalicylic acid, using the acid ninhydrin reaction method (Bates et al., 1973). To quantify soluble sugars and fructans, 0.5 g of embryo material were extracted into 800 g kg^-1 ethanol for 24 h. The extract was centrifuged (12 000 x g for 2 min), and soluble sugar in the supernatant were determined by means of anthrone reagent (Riazi et al., 1985). For fructans, after embryo extraction and centrifugation (12 000 x g for 2 min), the extract was precipitated with absolute ethanol (24 h at 5°C), centrifuged at (12 000 x g for 10 min), and the precipitated fraction was resuspended in 800 g kg^-1 ethanol (Livingston, 1990; Vieira and Figueiredo-Ribeiro, 1993). Fructans were evaluated colorimetrically by means of anthrone reagent, and the fructan content was expressed as inulin equivalents (Alberdi, 1996, personal communication).

Fatty Acid Isolation
Polar lipid fractions were obtained from 1 g of intact embryos (coleorhiza and radicle stages), treated with boiling isopropanol for 1 min immediately after dissection, and maintained at -20°C until extraction. Embryonic tissue was extracted at 0°C three times in 2:1 (v/v) chloroform:methanol containing 2.3 mmol kg^-1 BHT. The pooled extract was filtered and, after the addition of distilled water, the samples were stirred and centrifuged (Sorvall SS-34 5 000 rpm for 5 min). Water was eliminated with a separatory funnel and organic solvents were removed with a rotary evaporator. Total lipids were resuspended in 2 mL chloroform:acetic acid (10:1 v/v). Polar lipids were obtained after silica-gel column chromatography that was eluted with 20 mL absolute methanol. Methanol was evaporated and polar lipids were resuspended in chloroform and dried under N₂(g) prior to fatty acid analysis. Fatty acids were derivatized as methyl esters and analyzed via gas chromatography using a Perkin-Elmer spectrometer (Autosystem 9000 semicapillary column RTX-2330, PerkinElmer Instruments, Norwalk, CT, 30 m x 0.53 mm and 0.20 µm) as described in AOAC (1984). The degree of unsaturation (UD) of fatty acids was calculated as UD = (De Man, 1985).

Oxygen Consumption
Oxygen consumption of intact embryos germinated at 3°C was measured polarographically at 20°C with a Clark-type electrode at the coleorhiza and radicle stages. To register consumption rates before visible tissue elongation, oxygen consumption also was measured 48 h before coleorhiza emergence. The 10 to 15 embryos were incubated within 20 min, immediately after their dissection in 6 mL of fully aerated 10 mM MES-KOH buffer (pH 6.9) (Leprince et al., 1992). After the initial respiration measurements, 0.5 mM KCN was added to inhibit cytochrome c oxidase (Cyt c); then 15 mM salicylhydroxamic acid (SHAM) was added to inhibit alternative oxidase (AO).

Oxidative Reactions
Lipoperoxidative damage was quantified as malonaldehyde (MDA) production by the thiobarbituric acid (TBA) method at A₅₃₂ to A₆₀₀ (Zhang et al., 1995). Soluble proteins were extracted by grinding embryos from surface sterilized seeds growing in a sterile Petri dish (100 by 20 mm) system (with double Whatman N°1 paper) with 8 mL sterilized water containing 10 µg/mL chloramphenicol. Catalase activity was estimated from the disappearance rate of 13.2 x 10^-3 mmol kg^-1 H₂O₂ at 240 nm in 50 mM potassium phosphate buffer pH 7.4 (Worthington, 1988). The extraction of catalase was performed in the presence of a mix of protease inhibitors (5 µg mL^-1) phenylmethylsulfonyl fluoride (PMSF), antipain, leupeptin, pepstatin A, and chymostatin (Sigma Chem. Co., St. Louis, MO).

Statistical Analysis
Non-parametric statistics (Kruskal-Wallis and Mann-Whitney tests) were used because most data did not fit normal distributions required for parametric tests (Sokal and Rohlf, 1981). Each experiment, except when indicated, included three to five replicates per cultivar and treatment.

	Results

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 
Germination Dynamics
At 17°C, the cultivars did not differ with respect to Di or D₅₀ (Fig. 1A,B) . At 10°C, 6°C, and 3°C, however, Di and D₅₀ occurred significantly earlier for Ot220. Therefore, lower temperatures delayed significantly more the germination of America than Ot220. For this reason, Ot220 was classified as the "cold tolerant" cultivar and America was classified as the "cold sensitive" cultivar. Neither cultivar germinated at 0°C.

View larger version (20K): [in this window] [in a new window]   Fig. 1 Days to the initiation (Di) and to 50% germination (D50) at four temperature regimes. Asterisks indicate significant differences between Ot220 and America oat seeds at P 0.01. Data are mean ± SD of eight replicates of 30 seeds

View larger version (16K): [in this window] [in a new window]   Fig. 2 Final germination percentage of the two oat cultivars at four temperature regimes. Asterisks indicate significant differences between Ot220 and America cultivars at P 0.05. Data are mean ± SD eight replicates of 30 seeds

Cryoprotective Solutes
Proline, soluble sugars, and fructans accumulated in embryos at the coleorhiza and the radicle stage when seeds were exposed to 3°C (Table 2) . Proline accumulation at 3°C occurred only during the radicle stage, and was greater in America than in Ot220 embryos. In contrast, significant accumulation of total soluble sugars at 3°C occurred only at the coleorhiza stage, and sugar levels were higher in Ot220 than in America. Cold treatment had no effect on the soluble sugar content at the radicle stage, and there was no difference between cultivars. Fructan accumulation at 3°C was significantly greater in Ot220 than in America. For Ot220, fructan contents were 2.2 and 1.7 times higher at 3°C than at 17°C at the coleorhiza and radicle stages, respectively. No significant accumulation of fructans occurred in America, in response to cold treatment at the coleorhiza stage, and the increase at the radicle stage was less than for Ot220.

View larger version (37K): [in this window] [in a new window]   Fig. 3 Total oxygen consumption of intact embryos of Ot220 and America grown at 3°C at three stages of development. Error bars are standard deviation. Asterisks indicate significant differences between Ot220 and America at P 0.05

View larger version (45K): [in this window] [in a new window]   Fig. 4 Relative oxygen consumption as the percentage contribution of cytochrome c oxidase (Cyt c) (15 mM SHAM resistant) and the alternative oxidase (AO) (0.5 mM KCN resistant) pathways of two oat cultivars grown at 3°C at three developmental stages. Error bars are standard deviation of 10 to 15 embryos. Asterisks indicate significant differences between Ot220 and America cultivars at P 0.05

	Discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

Freezing tolerance during seed germination is still poorly understood because the seedling stage is usually the earliest stage used to screen genotypes for cold tolerance by LT₅₀ (Roberts and Grant, 1968; Cloutier and Andrews, 1984; Rizza et al., 1994; Bridger et al., 1995). Differential low temperature sensitivity is maintained throughout development in Ot220 and America, but associated physiological responses vary during germination and seedling stages. Greater sensitivity to cold may also explain the higher susceptibility of America seedlings to fungal attack after exposition to 3°C (Massardo, 1997). A similarity in LT₅₀ at early stages of development could be related to a lack of differences in accumulation patterns of cryoprotective solutes. At the seedling stage accumulation patterns of cryoprotective solutes differ significantly between America and Ot220, which could explain their differences in LT₅₀ (Alberdi et al., 1993). Metabolic differences during germination, expressed as higher rates of oxygen consumption, could contribute to explain marked differences in germination dynamics. The similarity in LT₅₀ at early stages of development, in these two particular cultivars, renders the use of embryo tissue to select cold tolerant oat cultivars questionable. Cold tolerance classification based on the germination parameters Di and D₅₀ is probably a better alternative at early stages of development. Differences in LT₅₀ are more marked at later stages of development, and can be applied to discriminate adequately cold sensitivity (Andrews et al., 1960; Roberts and Grant, 1968; Cary, 1975; Alberdi and Ríos, 1983; Sakai and Larcher, 1987).

At the seedling stage, LT₅₀ was -5°C in America and -7°C for Ot220 after 4 d at 4°C (Alberdi et al., 1993). These temperatures are lower than those reported here, of -2.4°C and -1.9°C for the coleorhiza and radicle stages, respectively. The radicle phase has been described as the most sensitive developmental stage to low temperature (Cary, 1975; Fuller and Eagles, 1978; Alberdi and Ríos, 1983; Sakai and Larcher, 1987). Here, both oat cultivars increased LT₅₀ by approximately 0.5°C at the radicle stage, relative to the coleorhiza stage. The greater sensitivity at the radicle stage is probably related to a higher water potential, which raises freezing temperature closer to 0°C (Massardo, 1997).

Higher final germination percentages at 10°C compared to 17°C could be a consequence of thermodormancy, which is broken at lower temperatures. Germination of recently harvested oat seeds is inhibited at relatively high temperatures. Corbineau et al. (1991) suggested that this inhibition is due to the synthesis of inhibitors, which are absent at lower temperatures (5–10°C).

Cryoprotective Solutes
Accumulation of cryoprotective solutes has been proposed to increase cold tolerance by osmotic effects or through the protection of macromolecules (Alberdi and Corcuera, 1991; Thomas and James, 1993). At the radicle stage, proline accumulation was greater in America than in Ot220, and followed a similar pattern to that described previously for seedlings of these cultivars (Alberdi et al., 1993). Although greater accumulation of this cryoprotectant in the sensitive cultivar may seem contradictory, it has been suggested that proline is a nonspecific stress indicator rather than a cryoprotectant (Larcher, 1995; Murelli et al., 1995). There is evidence of proline accumulation in embryos under saline stress, but proline metabolism in embryos at low temperature has not been thoroughly investigated (Poljakoff-Mayber et al., 1994).

Differences in accumulation of soluble sugars at 3°C relative to 17°C in embryos of Ot220 and America were less marked than differences between seedlings of these cultivars. Following exposure to 4°C, Ot220 seedlings doubled their total sugar content but no accumulation occurred in America seedlings (Alberdi et al., 1993). Although sugar accumulation is one of the best-documented responses to cold stress during the later stages of oat development (Livingston et al., 1989; Alberdi and Corcuera, 1991; Livingston, 1991), it appears to be less important at earlier stages of growth.

Among cryoprotective solutes, differences in fructan content in response to low temperature were the most noticeable between Ot220 and America embryos. In addition, fructan compartmentation may also play an important role in protecting tissue (Livingston, 1991; Thomas and James, 1993; Livingston and Henson, 1998). But it is important to note that fructans accounted only for 10 to 25% of the total soluble sugars accumulated in Ot220 and America.

Fatty Acid Composition
Significant changes in fatty acid composition have been found in Ot220 seedlings in response to cold treatment (Alberdi et al., 1993). Uemura and Steponkus (1994) reported slight differences in fatty acid composition between spring and winter cultivars of oat but not between cold and non-cold treated oat seedlings. In embryos, there was no significant difference in fatty acid composition or membrane fluidity between cultivars or associated with low temperature treatments. The only significant variations occurred between the coleorhiza and radicle stage. In addition, the distribution of fatty acid reported here for oat embryos is markedly different from that described by Alberdi et al. (1993) for oat leaves, which had higher proportions of linolenic acid (18:3) and lower proportions of oleic (18:1) and linoleic (18:1) acids. These results agree with the review of Nishida and Murata (1996), who found that the stage of development has a significant effect on the fatty acid composition.

Oxygen Consumption
Oxygen consumption on a dry weight basis was significantly greater in Ot220 embryos germinated at low temperatures through all germination stages (Fig. 3). Greater metabolic rates in Ot220 may explain the faster germination rates compared to America. Greater oxygen consumption by Ot220 compared with America, also may indicate the higher production of energy rich compounds or heat, which could facilitate the germination of tolerant embryos under cold conditions. Although both Cyt c and AO pathways produce heat, it has been suggested that the AO pathway increased heat evolution under cold stress in several species (van der Venter, 1985; Moynihan et al., 1995). Although inhibition with SHAM may underestimate electron transport through this pathway (Lambers et al., 1998), the AO pathway accounted for 15 to 20% of the electron transport for both cultivars in this study (Fig. 4). Therefore, the metabolic differences between Ot220 and America did not depend upon the relative contribution of the two electron transport pathways.

Assuming that 1 mL of O₂ generates 21.1 J (Seymour and Schultze-Motel, 1996) and 1 cal °C^-1 g^-1 water (embryos have 740 g kg^-1 water at precoleorhiza stage and 890 g kg^-1 water at radicle stage), we estimate the heat production of Ot220 embryos to be 2.4 x 10^-6 J min^-1 at the precoleorhiza and 2.7 x 10^-5 J min^-1 at the radicle stage. The same estimation for America embryos provides values of 1.0475 x 10^-6 and 1.4 x 10^-5 J min^-1 for the pre-coleorhiza and radicle stages. Therefore, Ot220 embryos generated twofold greater heat than America. This heat is probably negligible in terms of the amount needed to play a role in cold tolerance (Lambers et al., 1998), but could be important in a localized way within the embryos (Moynihan et al., 1995). Plants are poikilotherms and most do not produce sufficient heat to raise the temperature of bulk tissue. Moynihan et al. (1995) have suggested, however, that the heat generated by respiration could counteract deleterious effects of low temperatures on the fluidity of mitochondrial membranes and mitochondrial enzyme activity.

Oxidative Damage
Low temperatures can stimulate the generation of active oxygen species by perturbing the metabolism involved in electron transfer, which can lead to damage of cellular membranes and accumulation of thiobarbituric acid-reactive substances associated with lipid peroxidation. Hence, cold tolerance in plants has been associated with minimizing these deleterious effects (Purvis and Shewfelt, 1993). Lipoperoxidative injury in embryos can be estimated through MDA augmentation, and in the seedling stage of corn (Zea mays), MDA production only increases in cold sensitive cultivars at low temperatures (Zhang et al., 1995). Interestingly, among the oat cultivars studied here, only the cold sensitive America increased the initial levels of MDA with low temperature treatment, suggesting greater lipoperoxidative injury in the embryo.

One mechanism to reduce oxidative injury due to cold stress would be to increase the activity of oxygen scavenging enzymes, such as catalase (Purvis and Shewfelt, 1993). Zhang et al. (1995) demonstrated an increase of catalase activity after cold treatment in a cold tolerant line of corn, compared with a reduction in catalase activity in a cold sensitive one. In Ot220 embryos, greater catalase activity at 17°C and increased catalase activity following exposure to cold could counteract the increased production of reactive oxygen species caused by cold, and confer greater cold tolerance. The cold sensitive America did not exhibit an increase in catalase activity at 3°C compared with 17°C. Together the lower degree of lipoperoxidation, and higher activities of protective enzyme systems may be responsible for the greater cold tolerance of Ot220 embryos compared with those of America.

In summary, higher catalase activity, lower lipoperoxidation, higher total oxygen consumption at 3°C (before coleorhiza emergence and through radicle protrusion), and a twofold increase in fructan content are correlated with and could contribute to the higher cold tolerance of Ot220 during germination compared with America.1984

	ACKNOWLEDGMENTS

 
C. Anderson, P. Arce, J. Armesto, R. Bible, L. Cardemil, Z. Cardon, R. Dunn, P. Gogarten, E. Lissi, R. Mercier, R. Rozzi, C. Vargas, E. Vergara, and three anonymous reviewers made valuable comments on the manuscript. F. Massardo specially thanks the support of Dr. G. Anderson's Laboratory at the Department of Ecology & Evolutionary Biology, University of Connecticut, and the Inter-American Foundation Fellowship for final preparation of this article. The authors' research is supported by Fondecyt 1940858 and DID-UACH 5-9317. This publication is also a contribution of the research program of Senda Darwin Biological Station, Chiloé, Chile.

Received for publication June 22, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 

• Alberdi M., Ríos D. Frost resistance of Embothrium coccineum Forst. and Gevuina avellana Mol. during development and aging. Acta Oecol./Oecol. Plant. 1983;4:3-9.
• Alberdi M., Corcuera L.J. Cold acclimation in plants. Phytochemistry 1991;30:3177-3184.
• Alberdi M., Corcuera L.J., Maldonado C., Barrientos M., Fernández J., Henríquez O. Cold acclimation in cultivars of Avena sativa. Phytochemistry 1993;33:57-60.
• Andrews J.E., Horricks J.S., Roberts D.W.A. Interrelationships between plant age, root-rot infection, and cold hardiness in winter wheat. Can. J. Bot. 1960;38:601-611.
• AOAC. 1984. Association of Official Analytical Chemist. 14 (ed). Official Methods of Analysis of the Association of Official Analytical Chemist, Washington, DC.
• Bates L., Waldren R., Teare Y. Rapid determination of free proline for water stress studies. Plant Soil 1973;39:205-207.
• Bridger G.M., Falk D.E., McKersie B.D., Smith D.L. Crown freezing tolerance and field winter survival of winter cereals in Eastern, Canada. Crop Sci. 1995;35:150-157.
• Cary J.W. Factors affecting cold injury of sugarbeet seedlings. Agron. J. 1975;67:258-262.[Abstract/Free Full Text]
• Cloutier Y., Andrews C.J. Efficiency of cold hardiness induction by desiccation stress in four winter cereals. Plant Physiol. 1984;76:595-598.[Abstract/Free Full Text]
• Corbineau F., Poljakoff-Mayber A., Côme D. Responsiveness to abscisic acid of embryos of dormant oat (Avena sativa) seeds. Involvement of ABA-inducible proteins. Physiol. Plant. 1991;83:1-6.
• Dahal P., Kim N.-S., Bradford K.J. Respiration and germination rates of tomato seeds at suboptimal temperatures and reduced water potentials. J. Exp. Bot. 1996;47:941-947.
• Dell'Aquila A., Spada P. Effect of low and high temperature on protein synthesis patterns of germinating wheat embryos. Plant Physiol. Biochem. 1994;32:65-73.
• De Man W. The effect of genotype and environment of the fatty acid content of barley (Hordeum vulgare) grains. Plant Cell Environ. 1985;8:571-577.
• di Castri F., Hajek E. Bioclimatología de Chile. Santiago, Chile: Universidad Católica de Chile, 1976.
• Fuller M.P., Eagles C.F. A seedling test for cold hardiness in Lolium perenne L. J. Agric. Sci. (Cambridge) 1978;91:217-222.
• Guy Ch.L. Cold acclimation and freezing stress tolerance: Role of protein metabolism. Annu. Rev. Plant Physiol. Plant Mol. Biol. 1990;41:187-223.[ISI]
• Hallgreen, J.E., and G. Öquist. 1990. Adaptations to low temperature. p. 265–293. In Stress Responses in Plants: Adaptations and acclimation mechanisms. Wiley-Liss Inc., New York.
• ISTA. Handbook of vigour test methods, 2nd ed Zurich: ISTA, 1987.
• Lambers H., Chapin F.S., III, Pons T.L. Plant Physiological Ecology. New York: Springer-Verlag, 1998.
• Larcher W. Physiological plant ecology, 3th ed Berlin: Springer-Verlag, 1995.
• Leborgne N., Dupou-Cézanne L., Teulières Ch., Canut H., Tocanne J.F., Boudet A.M. Lateral and rotational mobilities of lipids in specific cellular membranes of Eucalyptus gunnii cultivars exhibiting different freezing tolerance. Plant Physiol. 1992;100:246-254.[Abstract/Free Full Text]
• Leprince O., van der Werf A., Deltour R., Lambers H. Respiratory pathways in germinating maize radicles correlated with desiccation tolerance and soluble sugars. Physiol. Plant. 1992;85:581-588.
• Livingston D.P. Fructan precipitation from a water/ethanol extract of oats and barley. Plant Physiol. 1990;92:767-769.[Abstract/Free Full Text]
• Livingston D.P. Nonstructural carbohydrate accumulation in winter oat crowns before and during cold hardening. Crop Sci. 1991;31:751-755.[Abstract/Free Full Text]
• Livingston D.P., Olien C.R., Freed R.D. Sugar composition and freezing tolerance in barley crowns at varying carbohydrate levels. Crop Sci. 1989;29:1266-1270.[Abstract/Free Full Text]
• Livingston D.P., Henson C.A. Apoplastic sugars, fructans, fructan exohydrolase, and invertase in winter oat: responses to second-phase cold hardening. Plant Physiol. 1998;116:403-408.[Abstract/Free Full Text]
• Martin B.A., Smith O.S., O'Neill M. Relationships between laboratory germination tests and field emergence of maize inbreds. Crop Sci. 1988;28:801-805.[Abstract/Free Full Text]
• Massardo F. Efecto del frío sobre la germinación de dos variedades de avena (Avena sativa L.). Santiago, Chile: Ph. D. Dissertation Thesis, Facultad de Ciencias, Universidad de Chile, 1997.
• Mayer A.M., Poljakoff-Mayber A. The germination of seeds, 4th ed Oxford, England: Pergamon Press, 1989.
• Moynihan M.R., Ordentlich A., Raskin I. Chilling-induced heat evolution in plants. Plant Physiol. 1995;108:995-999.[Abstract]
• Murelli C., Rizza F., Marinone F., Dulio A., Terzi V., Cattivelli L. Metabolic changes associated with cold-acclimation in contrasting cultivars of barley. Physiol. Plant. 1995;94:87-93.
• Nilsen E.T., Orcutt D.M. Physiology of plants under stress. Abiotic factors. New York: John Wiley & Sons, Inc., 1996.
• Nishida I., Murata N. Chilling sensitivity in plants and bacteria: the crucial contribution of membrane lipids. Annu. Rev. Plant Physiol. Plant Mol. Biol. 1996;47:541-568.[ISI]
• Poljakoff-Mayber A., Sommers G.F., Werker E., Gallagher J.L. Seeds of Kosteletzkya virginica (Malvaceae): their structure, germination, and salt tolerance. II. Germination and salt tolerance. Am. J. Bot. 1994;81:54-59.[ISI]
• Purvis A.C., Shewfelt R.L. Does the alternative pathway ameliorate chilling injury in sensitive plant tissues?. Physiol. Plant. 1993;88:712-718.
• Riazi A., Matsuda K., Arslan A. Water-stress induced changes in concentrations of proline and other solutes in growing regions of young barley leaves. J. Exp. Bot. 1985;36:1716-1725.[Abstract/Free Full Text]
• Rizza F., Crosatti C., Stanca A.M., Cattivelli L. Studies for assessing the influence of hardening on cold tolerance barley genotypes. Euphytica 1994;75:131-138.
• Roberts, E.H. 1988. Temperature and seed germination. p. 109–132. In S.P. Long and F.I. Woodward (ed.) Plants and temperature. Symposia of the Society of Experimental Biology, Company of Biologist, Ltd. Cambridge, England.
• Roberts D.W.A., Grant M.N. Changes in cold hardiness accompanying development in winter wheat. Can. J. Plant Sci. 1968;48:369-376.
• Sakai A., Larcher W. Frost survival of plants. Responses and adaptation to freezing stress. Ecological Studies 62. Berlin: Springer-Verlag, 1987.
• Scott S.J., Jones R.A. Low temperature seed germination of Lycopersicon species evaluated by survival analysis. Euphytica 1982;31:869-883.
• Scott S.J., Jones R.A., Williams W.A. Review of data analysis methods for seed germination. Crop Sci. 1984;24:1192-1199.[Abstract/Free Full Text]
• Seymour R.S., Schultze-Motel P. Thermoregulating lotus flowers. Nature 1996;383:305.
• Sokal R.R., Rohlf F.J. Biometry, 2nd edition New York: W.H. Freeman and Company, 1981.
• Thomas H., James A.R. Freezing tolerance and solute changes in contrasting genotypes of Lolium perenne L. acclimated to cold and drought. Ann. Bot. (London) 1993;72:249-254.[Abstract/Free Full Text]
• Uemura M., Steponkus P.L. A contrast of the plasma membrane lipid composition of oat and rye leaves in relation to freezing tolerance. Plant Physiol. 1994;104:479-496.[Abstract]
• van der Venter H.A. Cyanide-resistant respiration and cold resistance in seedlings of maize (Zea mays L.). Ann. Bot. (London) 1985;56:561-563.[Abstract/Free Full Text]
• Vieira C.C.J., Figueiredo-Ribeiro Fructose contaning carbohydrates in the tuberous root of Gomphrena macrocephala (Amaranthaceae) at different phenological phases. Plant Cell Environ. 1993;16:919-928.
• Worthington M. 1988. Worthington Biochemical Corporation. Ch. Worthington ed., Freehol, NJ.
• Zhang J., Cuy S., Lee J., Wey J., Kirkham M.B. Protoplasmic factors, antioxidant responses, and chilling resistance in maize. Plant Physiol. Biochem. 1995;33:567-575.

This article has been cited by other articles:

				J. R. Mahan and S. A. Mauget Antioxidant Metabolism in Cotton Seedlings Exposed to Temperature Stress in the Field Crop Sci., September 23, 2005; 45(6): 2337 - 2345. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Massardo, F. Articles by Alberdi, M. Search for Related Content PubMed Articles by Massardo, F. Articles by Alberdi, M. Agricola Articles by Massardo, F. Articles by Alberdi, M.