Published online 19 October 2005
Published in Agron J 97:1564-1569 (2005)
DOI: 10.2134/agronj2005.0073
© 2005 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Freezing Point Temperatures of Corn Seed Structures during Seed Development
James M. Woltza,
Dennis B. Eglib and
Dennis M. TeKronyb,*
a Syngenta Crop Protection AG, Basel, Switzerland
b Dep. of Plant and Soil Sci., 1405 Veterans Drive, Univ. of Kentucky, Lexington, KY, USA 40546-0312
* Corresponding author (dtekrony{at}uky.edu)
Received for publication March 10, 2005.
 |
ABSTRACT
|
|---|
Seed in hybrid corn (Zea mays L.) production can be exposed to freezing temperatures before harvest, which may reduce quality. This study examined changes in freezing point temperature (FPT) in seed, embryo, and endosperm tissue from ears of three F1 hybrids and one F2 hybrid harvested at various stages of development and exposed to temperatures of –6 or –11°C. Seed FPT decreased in a curvilinear manner from –0.5°C for immature seed (>500 g kg–1 seed moisture concentrations, SMC) to below –4°C when freezing was last detectable in mature seed (SMC 
300 g kg–1). There were no differences in FPT when seeds were frozen at –6 or –11°C or at different rates (rapid vs. gradual) of temperature change. Seeds froze at the same FPT across all hybrids and years, except for one F1 hybrid in 1999. As seeds matured (SMC < 400 g kg–1), the embryo tissue had higher moisture levels than the endosperm, which resulted in the embryo freezing at warmer temperatures (–4.5°C) than the endosperm (–9.2°C). Immature seeds can freeze at temperatures ranging from –1.0 to –2.0°C (typical of the first freeze of autumn); however, if seed has reached or exceeded physiological maturity (SMC 360 g kg–1), it is unlikely that injury will occur.
Abbreviations: DAP, days after planting • FPT, freezing point temperature • PM, physiological maturity • SMC, seed moisture concentration (fresh weight basis)
|
INTRODUCTION
|
|---|
CORN SEED produced in the midwestern United States is usually planted between mid-April and mid-May and harvested when the seed reaches physiological maturity (PM, moisture content near 350 g kg–1) (Wych, 1988). Variation in the weather may cause the seed crop to encounter freezing temperatures before PM. During a 21-yr period, Rossman (1949) reported that there were 8 yr where more than 10% of the U.S. corn crop was immature at the time of a freeze. When freezing temperatures during seed maturation are predicted, a seed producer must decide whether to harvest the seed prematurely or allow it to be exposed to freezing temperatures, which may reduce seed germination and vigor. A lack of information concerning the temperatures required to freeze seeds during development makes such decisions difficult.
Freezing in any living tissue occurs in a sequential manner (Mazur, 1970). The initial step is the supercooling of the solution (i.e., the solution cools below its freezing point without ice formation) within and surrounding the cells, which predisposes the solution to freezing on ice nucleation (Steponkus, 1984). Once ice nucleation occurs, the water in solution crystallizes, and heat (latent heat of fusion) is released. The temperature peak following the release of heat is the FPT and depends, in part, on the amount of free water available to freeze (Vertucci, 1993), solute concentrations (Lineberger and Steponkus, 1980), and presence of ice-nucleating agents (Wisniewski et al., 1997).
Early studies (Kiesselbach and Ratcliff, 1920) demonstrated that the germination of corn seeds with SMC > 371 g kg–1 exposed to –2°C for 24 h was lower than unfrozen seed. When the temperature was reduced to –6.7°C, loss of germination occurred in seeds with SMC as low as 283 g kg–1. Further reductions in temperature caused injury in seeds with SMC below 283 g kg–1. Rossman (1949) found that germination of seed from unhusked ears was reduced as much as 48 percentage points when seeds at 500 and 400 g kg–1 SMC were exposed to –6.7°C for 8 and 16 h, respectively. When seeds with the same moisture levels were exposed to –3.3°C for up to 16 h, germination was not reduced. Goodsell (1948), however, reported no difference in germination between corn seeds with moisture contents of 340 and 510 g kg–1 after 8 h at –12.2°C.
While all of these studies involved the determination of seed quality after the seeds were exposed to low temperatures, other researchers tried to determine the FPT. Roberts and Ellis (1989) reported that the FPT for immature barley (Hordeum vulgare L.) seeds was above –5°C between SMC of 350 and 500 g kg–1. Freezing point temperature declined as moisture content dropped below 350 g kg–1. A similar pattern was found for lettuce (Lactuca sativa L.) seeds, except that FPT remained above –5°C until the moisture was below 200 g kg–1. Fick (1989) found a significant difference in FPT between corn seed harvested at 610 g kg–1 (–1.2°C) and 480 g kg–1 (–1.6°C). Judd et al. (1982) reported a curvilinear decrease in FPT of soybean [Glycine max (L.) Merr.)] seed as seed moisture decreased with FPT ranging from –2.5°C at 600 g kg–1 SMC to –20°C at 300 g kg–1. The ice–liquid phase transition temperatures in mature, rehydrated soybean cotyledons exhibited a linear decline from –36°C at 300 g kg–1 to –43°C at 50 g kg–1 using differential scanning calorimetry (Vertucci, 1989).
Fick (1989) examined the dynamics of freezing corn seeds on the ear. In two separate experiments, FPT from seeds on the same ear ranged from –0.2 to –7.1°C compared with between –0.1 and –5.0°C for seeds on a second ear. The seeds on the ear froze in an asynchronous manner as heat released by the freezing event (heat of fusion) warmed adjacent seeds by as much as 0.7°C. The warming of the adjacent seeds resulted in variation in the time of seed freezing by as much as 223 min on one ear and by 82 min on the second ear.
Most freezing studies subjected seeds to specific subzero temperatures for a given time period then examined them for evidence of freezing injury. While this technique describes the effects of freezing on seed function and survival, it does not provide any information regarding the temperature necessary to cause freezing or if the initial temperature varies among seed structures. Therefore, the objective of this experiment was to determine the FPT of intact corn seed, embryo, and endosperm tissue exposed to freezing temperatures at various stages during seed development for several hybrid cultivars.
|
MATERIALS AND METHODS
|
|---|
Seed of six corn hybrids was produced at the Spindletop Research Farm near Lexington, KY (38°02' N lat) from 1998 to 2000. Production and harvest information are shown in Table 1. The maternal inbred lines used to produce seed of F1 Hybrids A, C, and F were chosen to represent commonly used field corn inbreds derived from the B73 (Hybrid A) and Mo17 (Hybrid C) or public breeding (Hybrid F) backgrounds but are not identified at the request of the companies providing the seed. The same paternal parent was used for F1 Hybrids A, C, E, and F and was a widely used inbred (Mo17 type) used throughout the Corn Belt. The F2 seed produced by Hybrid B was derived by planting F1 seed of Pioneer 3394, which was a widely used commercial field corn hybrid adapted to Kentucky. The female parent of Hybrids D and E was produced by planting seed from the su sweet corn ‘Silver Queen’, which was crossed to a sugary (Hybrid D) or starchy (Hybrid E) male parent line. One to five ears (depending on the total number of ears pollinated) were harvested at frequent intervals throughout seed development (Table 1), so the seeds ranged from very immature (SMC > 600 g kg–1) to mature (<250 g kg–1).
View this table:
[in this window]
[in a new window]
|
Table 1. Planting, pollinating, harvest dates, and days after pollination (DAP) for six hybrids used in 1998–2000.
|
|
To standardize temperature before freezing, all harvested ears (with husk and shank attached) were cooled to 10 ± 1°C in a walk-in chamber for at least 3 h. Each ear constituted an experimental unit with each seed representing one replication. All seeds were frozen on the ear at –6 or –11°C with the husks attached. Freezing point temperature was measured by cutting a small opening in the husk to expose a small section of seeds. A hole was bored through the crown of the seeds into the endosperm using a hand drill with a 0.48-mm bit. Thirty-gauge copper-constantan thermocouples were inserted into the holes, and the husk leaves were folded over the seeds and taped to cover the opening. Freezing point temperatures were measured on three to five seeds per ear during freezing exposures of 9 h in 1998 and 7 h in 1999 and 2000. Temperature from each thermocouple was recorded at 30-s intervals using a 21X Micrologger (Campbell Scientific, Inc., Logan, UT) and then graphed vs. time, and the resulting curve was examined for the presence of an exotherm indicating that freezing had occurred. In 1998, SMC was based on the mean concentration of seeds of the control ears from each harvest while in 1999 and 2000, the individual seeds in which temperature was measured were removed from the ear after freezing, and SMC (fwb) was determined by drying the individual seeds at 105°C for 72 h.
Freezing Rate
This experiment was conducted to determine if the rate of change in air temperature during freezing altered seed FPT. Seeds from F1 Hybrids A (2000) and F (1999) were subjected to two rates of temperature decline: (i) a gradual decrease from 10 to –6°C over a 4-h period (–4°C/h) in a programmable growth chamber and (ii) directly transferring the ears from the 10°C chamber to –6°C. After the air temperature reached –6°C, sets of ears in both treatments were held at that temperature for 6 h before thawing.
Air Temperature
The relationship of temperature (–6 vs. –11°C) to seed FPT was examined using four seeds per temperature in each of five ears of Hybrid B in 1998 and 1999.
Genotype
Freezing point temperatures were measured in three to five ears of F1 Hybrid A and F2 Hybrid B (1998), F1 Hybrids A and C and F2 Hybrid B (1999), and F1 Hybrids A and C (2000) with sampling as described in Table 1.
Endosperm Composition
In 1999 and 2000, the effect of endosperm composition on FPT was determined using a su sweet corn hybrid ‘Silver Queen’, which was (i) sib-mated to produce F2 seed with sugary endosperm (Hybrid D) and (ii) mated with a dent corn pollinator to produce F2 seed with starchy endosperm (Hybrid E). Seed temperature was maintained at –11°C (7-h duration) in one or two ears per hybrid.
Embryo vs. Endosperm
Embryo and endosperm FPTs were evaluated throughout seed development for the F1 single-cross Hybrids F (1999) and C and F (2000). Ears of Hybrid F were harvested at 2- to 3-d intervals starting at 35 (506 g kg–1 SMC) d after pollination (DAP) in 1999 and 2000 and finishing at 65 DAP (212 g kg–1 SMC). Hybrid C was harvested from 28 DAP (614 g kg–1) to 58 DAP (245 g kg–1). Four seeds were randomly selected in the middle portions of each ear, and FPTs were measured in the embryo and the endosperm of each seed. Holes were bored into the endosperm (depth of approximately 5 mm) and the embryo of the same seed using a hand drill with a 0.48-mm bit. The tip of 30-gauge copper-constantan thermocouple was inserted into the embryo and endosperm of the four seeds for a total of eight measurements per ear. The ear with husks attached as described previously was preconditioned at 10°C and placed in a –18°C freezer for at least 12 h after which it was thawed at 10°C for at least 6 h. After thawing, the seeds with thermocouples were removed from the ear, and the embryo was excised from the endosperm. Moisture concentration of each structure was determined by drying at 105°C for 72 h. Whole-seed moisture content was determined by combining the wet and dry weights of the embryo and endosperm for each seed. Temperature changes within the seeds during exposure to freezing temperature were recorded with a 23X Micrologger at 5-s intervals. Each data set was examined for the presence of an exotherm.
Data Analysis
The experiments were designed with each ear as an experimental unit with each seed as a replication. Means and standard errors for moisture and freezing point data were calculated for each ear. Regression analysis was performed using the PROC REG procedure of SAS Statistical Program (SAS Inst., Cary, NC). Models (linear, quadratic, or higher orders) were selected by evaluating the coefficient of determination and the significance of the additional terms in the higher-order models. Mean FPT data were plotted against the mean seed moisture for each ear, and 95% confidence intervals around the regression line were used to compare data from different hybrids and years.
|
RESULTS
|
|---|
The seeds of all hybrids (except Hybrid D) reached PM (maximum dry seed weight) at SMCs ranging from 304 to 422 g kg–1 (mean 366 g kg–1) across the 3 yr (Table 1). As expected, Hybrid D with sugary endosperm in both inbred parents reached PM at much higher moisture concentrations (501 and 608 g kg–1).
Freezing Point Temperature
During the early stages (0 to 60 min) of seed exposure to –11°C, the temperature decreased rapidly from 10 to <0°C (Fig. 1) . This was followed by a slower decline as the seed solution supercooled until the seed froze (an exotherm was formed—the temperature increased to the FPT) after which the temperature continued to decline. Each set of temperature data (–6 and –11°C) was graphed, and the FPT was determined from the exotherm (if present). Seed freezing occurred at any time after the seed was exposed to subzero temperatures. If freezing did not occur, the seed eventually equilibrated with ambient temperature.
View larger version (33K):
[in this window]
[in a new window]
|
Fig. 1. Seed temperature of Hybrid B exposed to –11°C for 420 min (upper curve). Data were averaged over 15-s intervals. The seeds supercooled until an exotherm formed (temperature increased to the freezing point temperature, and the seeds froze) at 225 min. The lower curve plots the changes in temperature in the chamber with peaks occurring when door was opened.
|
|
Freezing Rate
When seeds were frozen at –6°C using the slow (–4°C/h) rate, there was a significant linear (P < 0.01) relationship between moisture concentration and FPT for Hybrids A and F (Fig. 2A, 2B) . As the seed developed (i.e., seed moisture declined from 500 to 270 g kg–1), FPT decreased from –0.8 to –4.7°C. Fast-freezing the ears (placed directly into –6°C) resulted in a linear trend for Hybrid F but a quadratic relationship (P < 0.05) for Hybrid A. The 95% confidence intervals (CI) around the regression models overlapped throughout the common moisture content intervals for Hybrid A. Thus, the rate of freezing had no effect on FPT.
View larger version (23K):
[in this window]
[in a new window]
|
Fig. 2. The relationship between freezing point temperature (mean ± standard error) and mean seed moisture concentration when ears from (A) Hybrid F (1999) and (B) Hybrid A (2000) were frozen at two rates (fast, slow gradual) at –6°C and when (C) ears of Hybrid B were frozen at two temperatures (1999). Regression (solid and dashed) and 95% confidence intervals (dotted lines) compared changes in seed freezing point temperatures during development.
|
|
Temperature
Seeds of Hybrid B froze at –6°C and –11°C when SMC was 
400 g kg–1, but freezing occurred only at –11°C when SMC was between 400 and 320 g kg–1 (Fig. 1C). There was a linear (P < 0.01) relationship between SMC and FPT when seeds were frozen at –6°C while a cubic (P < 0.01) relationship was shown for seeds frozen at –11°C. The freezing temperature did not affect the FPTs for this hybrid.
Genotype
As seeds of the three hybrid genotypes matured and the SMC declined, there was a significant reduction in FPT across 3 yr (Fig. 3A, 3B, 3C) . The FPT of immature seeds (SMC > 450 g kg–1) was –2.0°C while more-mature seeds (300 to 350 g kg–1) had a wider range (–3.0 to –7.0°C). The trends in FPT among genotypes were consistent across years, except for Hybrid C. In 1999, the FPTs were consistently lower for Hybrid C than in 2000, ranging from nonsignificant differences (0.2°C) between years at the highest SMCs (450 and 500 g kg–1) to nearly 2°C colder at lower SMC (350 g kg–1).
View larger version (29K):
[in this window]
[in a new window]
|
Fig. 3. The relationship between freezing point temperature (mean ± standard error) and mean seed moisture concentration for Hybrids A (1998–2000), B (1998–1999), and C (1999–2000) when frozen at –6 and –11°C. Regression (solid and dashed) and 95% confidence intervals (dotted lines) compared differences among years. (There were not enough data points to plot regression for Hybrid A in 1999.)
|
|
Endosperm Composition
Seeds with sugary endosperm froze at approximately 2°C colder temperatures in both years than seed with starchy endosperm when the SMC was similar (Fig. 4)
. As SMC decreased from 600 to 400 g kg–1, there was a significant linear decline in FPT for both the sugary and starchy endosperm seeds, except for the sugary endosperm in 2000.
View larger version (26K):
[in this window]
[in a new window]
|
Fig. 4. The relationship between freezing point temperature (mean ± standard error) and mean seed moisture concentration for seeds with starchy and sugary endosperm when froze at –11°C in 1999 and 2000. Regression was not significant for sugary endosperm in 2000. Regression (solid and dashed) and 95% confidence intervals (dotted lines) compared differences between years and phenotypes.
|
|
Embryo and Endosperm Comparison
In immature seeds (SMC > 500 g kg–1), the moisture concentration of embryo and endosperm tissue was the same (Fig. 5A)
, but as seeds matured, endosperm moisture concentration decreased faster than the embryo. Embryo moisture was 100 g kg–1 higher than endosperm moisture concentration in mature seeds (<200 g kg–1 SMC). The regression lines and 95% confidence intervals for the FPT of each hybrid overlapped over years, so the data for each structure were pooled across hybrids for regression analysis shown in Fig. 5B. Early in seed development (SMC > 450 g kg–1), there were no differences in FPT between embryo and endosperm. As the seed matured (SMC decreased below 400 g kg–1), the endosperm gradually froze at colder temperatures than the embryo.
View larger version (31K):
[in this window]
[in a new window]
|
Fig. 5. The relationship between (A) embryo and endosperm moisture concentration or (B) freezing point temperature when exposed to –18°C (mean ± standard error) and mean whole-seed moisture concentration during development for Hybrids C (2000) and F (1999 and 2000). Regression (solid and dashed) and 95% confidence intervals (dotted lines) compared in embryo (solid line) and endosperm (dashed line) tissue.
|
|
|
DISCUSSION
|
|---|
A consistent relationship was shown throughout these experiments between stage of seed development (as measured by SMC) and FPT (Fig. 2 and 3). Immature seeds (high SMC > 500 g kg –1) readily froze at FPT 
–2.0°C. These temperatures can be encountered before corn seed harvest in many production areas. As seeds matured (moisture concentration decreased), the FPT decreased to about –3.0°C at PM (360 g kg–1 SMC), and the decrease continued until there was inadequate moisture concentration (<300 g kg–1) for ice nucleation in seed tissue. Thus, it would take a severe freeze in the field for freezing to occur if the seed had reached PM.
A curvilinear change in FPT occurred in both the embryo and endosperm tissue as seeds matured (Fig. 5B), which was similar to the pattern reported for soybean (Judd et al., 1982). Our data also are supported by the results of Fick (1989), who reported that corn embryo and endosperm FPT declined substantially as seed moisture decreased from 340 to 300 g kg–1. However, he evaluated only a very narrow range in SMC, which contributed little to our understanding of the FPT changes that occur throughout corn seed development. When we evaluated a wider range in seed moisture of the embryo and endosperm tissue (Fig. 5A and 5B), the FPT of the two tissues were the same (–2.0°C) at high SMCs (500 g kg–1). As the whole-SMC declined below 350 g kg–1, the embryos (which had higher moisture levels, >400 g kg–1) froze while the endosperms remained unfrozen due to a lack of available water (Fig. 5B). Since the embryo is the structure responsible for seedling development during germination, its freezing point may be more critical than that of the endosperm. Even at SMCs as low as 250 g kg–1, embryo freezing occurred at temperatures as warm as –4°C. Thus, the higher moisture concentration of the embryo may lead to increased susceptibility to freezing injury in a field environment.
Vertucci (1993) classified the changes in seed water status into five hydration levels. At high moisture contents (>500 g kg–1), a large amount of free water is available for cell expansion, and solute concentrations are low (Hydration Level 5). As the seeds mature, the amount of solutes increase while moisture concentrations decrease, producing a concentrated solution (Hydration Level 4), which depresses the freezing point depending on the amount of dissolved solute. Finally, the seeds desiccate to the point where there is not enough available water to freeze and freezing is no longer detected (Hydration Level 2). The quadratic and linear relationships shown in our experiments (Fig. 2, 3, and 5) would be expected if FPTs were monitored when the seeds are frozen at Hydration Levels 3 and 4.
Previous freezing studies with corn were conducted by harvesting ears at various stages of maturity and placing them directly into constant freezing temperatures (Kiesselbach and Ratcliff, 1920; Goodsell, 1948; Rossman, 1949; Fick, 1989). Under field conditions, the temperatures do not change abruptly; rather, the changes are gradual. Thus, in 1999 and 2000, the freezing environment was modified by either altering the rate of temperature change or by changing air temperature. When ears were frozen with the same air temperature, but at two rates of temperature change, freezing occurred at similar temperatures (Fig. 2A and 2B); however, some seeds could freeze as much as 120 min sooner using the slow rate than the fast rate (data not shown). The differences in time to seed freezing were due to the seeds reaching their FPT during the gradual temperature decline to –6°C rather than freezing occurring when the air temperature reached –6°C. When two freezing temperatures were used (i.e.,–6 vs. –11°C, Fig. 2C), the seeds supercooled more extensively at the lower temperature but froze at similar times and temperatures. Thus, the exposure temperature influenced the degree of supercooling, and the rate influenced the timing of the freeze, but the FPT was controlled by the seed.
One possible seed characteristic that can influence FPTs is the carbohydrate composition of the endosperm. This possibility was examined by sib-mating a su sweet corn mutant to produce a sugary endosperm compared with mating the sweet corn with a dent corn pollinator to produce a kernel with starchy endosperm. Both crosses had the same maternal parent, but the endosperms were different. The FPT of the sugary endosperm was approximately 2°C colder than the starchy endosperm when similar SMCs were compared (Fig. 4). This result is consistent with the observations of Rossman (1949), who reported that seeds of two sweet corn inbreds had higher germination after freezing (–6.7°C) than several dent corn inbreds with the same moisture concentration. Thus, the sweet corn used in our study and the inbreds used by Rossman would likely be classified as more freezing tolerant than the dent corn due to the endosperm composition. Lineberger and Steponkus (1980) also showed that freezing point depression increased as the concentrations of glucose, sucrose, and raffinose in chloroplast thylakoids increased.
The four field corn hybrids in this study were chosen to represent germplasm derived from the B73 or Mo 17 background commonly used in Corn Belt of the USA. We compared the freezing patterns of two or more of these hybrids within 1 yr and one or more hybrids across 2 yr. Interestingly, the confidence intervals around the FPT regression lines for Hybrids A (F1) and B (F2) overlapped throughout the entire range of harvests measured, indicating that there were no differences in FPT (Fig. 3A and 3B). Similar quadratic relationships between seed moisture and FPT were shown for the same two hybrids when seed was produced in different years. The similarity of FPT between ears frozen at two temperatures for Hybrid B and at different freezing rates for Hybrids A and F with similar SMC is consistent with the idea that seeds with similar endosperm compositions should freeze at the same temperatures, which was supported by similar FPT for Hybrid C in 2000. However, the 1999 results for Hybrid C (Fig. 3C) did not support this preliminary hypothesis, as the FPTs were lower than for Hybrids A and B in 1999. This suggests that there may be a genotypic x environment interaction, independent of moisture concentration that may influence seed freezing; however, this assumption cannot be confirmed until more genotypes and environments are evaluated.
There was a consistent relationship in these experiments between the stage of seed development that seeds froze and the FPT. Immature seeds (SMC > 500 g kg–1) froze at much higher FPT (–2.0°C) while the FPT was always <–2.0°C for more mature seed (SMC < 400 g kg–1) across all hybrids and the three production years. Thus, if a seed has reached PM (SMC 360 g kg–1) or later, it is unlikely that a light freeze (typical of the first freeze of autumn) will result in ice nucleation and freezing. Freezing point temperatures differed only slightly among the hybrids examined, which suggests that the freezing point is regulated by seed characteristics rather than the environment. The similarity of freezing points among the hybrids tested is important because it suggests that the data presented here may be extrapolated to a wider range of hybrids to provide information regarding the likelihood that corn seed will freeze during a frost event. Thus, a seed producer who has monitored the development of their seed crop can make decisions to prioritize the harvesting of hybrid corn seeds with moisture concentrations that are likely to freeze to avoid injury and reductions in quality.
|
NOTES
|
|---|
Contribution of Kentucky Agricultural Experiment Station no. 05-06-032, Univ. of Kentucky, Lexington, KY 40546-0091.
|
REFERENCES
|
|---|
- Fick, V. 1989. Ice nucleation in maturing seed corn and conductivity testing for freezing injury. Ph.D. diss. Iowa State Univ., Ames (Diss. Abstr. 89–20131) (Diss. Abstr. Int. 06B 2212).
- Goodsell, S.F. 1948. Triphenyltetrazolium chloride for viability determination in frozen corn seed. Agron. J. 40:432–442.[Free Full Text]
- Judd, R., D.M. TeKrony, D.B. Egli, and G.M. White. 1982. Effect of freezing temperatures during soybean seed maturation on seed quality. Agron. J. 74:645–650.[Abstract/Free Full Text]
- Kiesselbach, T., and J. Ratcliff. 1920. Freezing injury of seed corn. Bull. 16. Nebraska Agric. Exp. Stn. Res., Lincoln.
- Lineberger, R.D., and P.L. Steponkus. 1980. Cryoprotection by glucose, sucrose and raffinose to chloroplast thylakoids. Plant Physiol. 65:298–304.[Abstract/Free Full Text]
- Mazur, P. 1970. Cryobiology: The freezing of biological systems. Science (Washington, DC) 168(22):939–949.[Free Full Text]
- Roberts, E.H., and R.H. Ellis. 1989. Water and seed survival. Ann. Bot. (London) 63:39–52.[Abstract/Free Full Text]
- Rossman, E.C. 1949. Freezing injury of maize seed. Plant Physiol. 24:629–656.[Free Full Text]
- Steponkus, P.L. 1984. Role of the plasma membrane in freezing injury and cold acclimation. Annu. Rev. Plant Physiol. 35:543–584.[CrossRef][ISI]
- Vertucci, C.W. 1989. Relationship between thermal transitions and freezing injury in pea and soybean seeds. Plant Physiol. 90:1121–1128.[Abstract/Free Full Text]
- Vertucci, C.W. 1993. Predicting optimum storage conditions for seeds using thermodynamic principles. J. Seed Technol. 17(2):41–52.
- Wisniewski, M., S.E. Lindow, and E.N. Ashworth. 1997. Observations of ice nucleation and propagation in plants using infrared video thermography. Plant Physiol. 113:327–334.[Abstract]
- Wych, R.D. 1988. Production of hybrid seed corn. p. 565–605. In G.F. Sprague and J.W. Dudley (ed.) Corn and corn improvement. 3rd ed. Agron. Monogr. 18. ASA, CSSA, and SSSA, Madison, WI.
This article has been cited by other articles:
|
|
|
|
 
J. Woltz, D. M. TeKrony, and D. B. Egli
Corn Seed Germination and Vigor Following Freezing during Seed Development
Crop Sci.,
May 18, 2006;
46(4):
1526 - 1535.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
