Crop Science 43:927-933 (2003)
© 2003 Crop Science Society of America
SEED PHYSIOLOGY, PRODUCTION & TECHNOLOGY
Response of Eastern Gamagrass Seed to Gibberellic Acid Buffered below Its pKa
X. Tiana, A. D. Knapp*,a, L. R. Gibsona, R. Struthersa, K. J. Moorea, E. C. Brummera and T. B. Baileyb
a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
b Dep. of Statistics, Iowa State Univ., Ames, IA 50011
* Corresponding author (adknapp@iastate.edu
)
 |
ABSTRACT |
Eastern gamagrass [
Tripsacum dactyloides (L.) L.] seed are usually
dormant, often causing seedling establishment difficulties.
This study was conducted to assess the effect of gibberellic
acid (GA
3) buffered below its pKa (3.8) on seed germination
of eastern gamagrass. In one experiment, concentrations of 0.001-,
0.005-, and 0.01
M buffered GA
3 solutions were applied to seed
with cupules removed from six commercial seed lots produced
in three different years. After 28 d of germination, GA
3 application
increased total seed germination by 25 to 47 percentage points.
The three GA
3 concentrations were equally effective in promoting
germination in all seed lots except one, where 0.001
M GA
3 was
more effective than 0.01
M GA
3. The germination rate was accelerated
by GA
3 application during the germination process but did not
result in germination of all the viable seeds. An average 10%
of the viable caryopses remained dormant at the end of the germination
test. A second experiment evaluated the germination of intact
cupules after treatment for 24 or 48 h in distilled water, 0.001
M GA
3 solution, buffer solution, or buffered 0.001
M GA
3 solution.
Buffered GA
3 was not effective at enhancing germination of eastern
gamagrass seed when cupules were left intact. These results
suggest that there may be multiple dormancy mechanisms in eastern
gamagrass. At least one mechanism involves the caryopsis and
is affected by GA
3 application. Furthermore, the cupule-mediated
dormancy mechanism(s) and the caryopsis-mediated mechanism(s)
must be addressed to obtain complete germination of dormant
seed.
Abbreviations: TZ, 2,3,5-triphenyl tetrazolium chloride • GA, gibberellic acid
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INTRODUCTION |
E
ASTERN GAMAGRASS is a warm-season perennial grass, native to
the southeastern and central USA (
Hitchcock and Chase, 1950).
It has been identified as an excellent forage crop with high
palatability and productivity (
Polk and Adcock, 1964) and has
great value for wildlife habitat, revegetation of certain lowland
areas, and as a potential silage replacement for corn (
Zea mays L.) on marginal and sloping lands (
Hardin, 1994). The use of
eastern gamagrass has been limited to date because of stand
establishment difficulties partially associated with seed dormancy.
Ahring and Frank (1968) investigated the effect of prechill on seed germination of two eastern gamagrass seed lots. Germination increased with up to 6 wk of prechill at 5 to 10°C and then appeared to decline after longer prechill periods. Prechill has been recommended and used with certain success to reduce dormancy in this species (USDA, 1991); however, to be effective, the seed must have imbibed water near its maximum capacity and must be kept moist throughout the prechill period. Further, a long prechill treatment (6–8 wk) is required, after which the prechilled seeds should be transferred to conditions favorable for germination without being allowed to dry (Gamagrass Seed Company, 1999). Nevertheless, the results are inconsistent and unpredictable (Kindiger, 1994).
In previous work, Tian et al. (2002) tested the roles of the cupule and pericarp on seed dormancy of eastern gamagrass. Cupule removal followed by pericarp scarification resulted in germination of all viable seeds. It was concluded that cupule removal and pericarp scarification overcame the seed dormancy in eastern gamagrass. However, establishing a mechanical system to remove the cupule and scarify the pericarp without damaging the caryopses may be difficult. The difficulty may arise because the cupule shape and size of eastern gamagrass is not uniform, the embryo extends the length of the caryopsis, and the embryo is not recessed relative to the surface of the caryopsis.
A stimulatory effect of GA3 on germination of dormant seed has been reported for many plant species, such as lettuce (Lactuca sativa L.) (Lona, 1956), most cereals (Mott, 1978; Agrawal, 1981; Prasad et al., 1983), and many other grasses (Mott, 1974; Hagon, 1976; Fulbright et al., 1983). Anderson (1985) applied GA3 to eastern gamagrass seed of one seed lot collected near Carbondale, IL. Both nonhulled and dehulled seeds were soaked in 1.0 g L-1 (0.003 M) of GA3 solution for 24 h. Gibberellic acid was somewhat effective at breaking dormancy of dehulled seeds, increasing germination percentage from 40 to 65% after 30 d of germination. The effect of GA3 on germination of seeds with their cupule intact was slight, with germination percentage increasing 5 to 8% when compared with untreated seed.
Nikolaeva (1977) stated that hormonal treatment had little effect if the seeds were in coat-imposed dormancy. Seed germination of wild oats (Avena fatua L.) (Hsiao, 1979a) and wild buckwheat {Polygonum convolvulus L. [= Fallopia convolvulus (L.) A. Love]} (Hsiao, 1979b) was not influenced by GA3 until the seed coat was made more permeable by NaOCl. In a study of the effect of GA3 on the germination of yellow rocket (Barbarea vulgaris R. Br.) seed, Taylorson (1976) demonstrated that seed scarification or buffering the substrate pH at 3.0 increased responsiveness of the seeds to GA3. He suggested that GA3 uptake is a limiting factor in the stimulation of germination in intact seeds.
Toole and Cathey (1961) studied the response of light-requiring seeds lettuce and Virginia peppergrass (Lepidium virginicum L.) to GA3, and observed that a buffered (citrate phosphate, pH 3.2) solution of GA3 was more effective in stimulating seed germination in the dark than unbuffered solutions. Palevitch and Thomas (1976) showed that the stimulation of celery (Apium graveolens L.) seed germination by GA3 was enhanced by decreasing the pH of the incubation solution below the pKa of gibberellin. This was accomplished by adding low-pH compounds such as buffers, weak acids (e.g., citric acid), or by titration with strong acids, such as HCl. Collectively, these previous studies suggest that buffering GA3 below its pKa may enhance its uptake and stimulatory effect of GA3 on germination of eastern gamagrass seeds.
The enhancement of GA3 activity by reducing its pH was explained in two ways (Palevitch and Thomas, 1976). First, lowering the pH of the GA3 solution increased the proportion of the undissociated form of GA3 in the solution, thus facilitating GA3 movement through the lipid membranes of seeds (Toole and Cathey, 1961). Second, under low pH conditions, hydrogen ions might affect the acidic bonds of the cell walls or stimulate the activity of certain cell-wall-degrading enzymes which react more efficiently in an acidic environment, a phenomenon known as the acid effect (Evans, 1974).
The studies reported herein were conducted to assess the influence of GA3 solution buffered below its pKa (3.8) on the germination of decupulated and intact caryopses of eastern gamagrass. The two major named cultivars from several production years were used to assess the variability in response across different seed lots.
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MATERIALS AND METHODS |
Two studies were conducted to assess the value of buffered GA
3 application in breaking eastern gamagrass seed dormancy. In
Experiment 1, caryopses were removed from cupules, treated with
one of five test solutions for 24 h, and then tested for germination.
Test solutions consisted of (i) distilled water, (ii) pH 3.5
citrate phosphate buffer solution, (iii) citrate phosphate buffered
0.001
M GA
3 solution, (iv) citrate phosphate buffered 0.005
M GA
3 solution, and (v) citrate phosphate buffered 0.01M GA
3 solution. These GA
3 concentrations were chosen because unbuffered
0.003
M GA
3 was previously shown to stimulate germination in
eastern gamagrass (
Anderson, 1985). Experiment 2 evaluated the
germination of seed with intact cupules after treatment for
24 or 48 h in one of four test solutions: (i) distilled water,
(ii) 0.001
M GA
3 solution, (iii) pH 3.5 citrate phosphate buffer
solution, or (iv) citrate phosphate buffered 0.001
M GA
3 solution.
The unbuffered GA
3 solution was added to this experiment because
it was difficult to completely wash the buffer solution from
intact cupules. This treatment, in combination with the other
three treatments, allowed for determination of buffer solution
effects on seed germination.
Seed lots of ‘Iuka’ and ‘Pete’ eastern gamagrass used in these studies were produced in 1995, 1996, and 1997 for Experiment 1 and in 1996, 1997, and 1998 for Experiment 2. Seeds were received in November of their year of production and stored at 4.4°C and 46% relative humidity until needed. The first study was initiated in March 1998 and the second study in March 1999. Viability of seeds was determined in January 1998 for 1995, 1996, and 1997 seed used in both experiments and in January 1999 for 1998 seed used in Experiment 2. Tetrazolium (TZ; 2,3,5-triphenyl tetrazolium chloride) tests indicated that viability was between 87 and 97% across the different cultivars and production years of the seed lots (Table 1).
The GA
3 solutions were prepared by continuously agitating GA
3 powder (Fluka Biochemika, Milwaukee, WI) in either heated distilled
water or heated buffer solution. Solutions were allowed to cool
to room temperature before use. The pH 3.5 citrate phosphate
buffer solution was prepared from 0.005
M citric acid (Sigma
Chemical Co., St Louis, MO) and 0.01
M disodium phosphate (Fisher
Scientific Co., Pittsburgh, PA) according to
Dawson et al. (1969).
For Experiment 1, the 0.005 and 0.001
M GA
3 solutions were serially
diluted from a 0.01
M GA
3 solution. Freshly prepared solutions
were used for each replication.
Eastern gamagrass seeds were randomly sampled from each seed lot. In Experiment 1, the cupule (including the lemma and palea) was removed by cutting through it at the juncture of rachis and glume with a razor blade. Care was taken to ensure that the caryopsis was not scarified during this procedure. Twenty-five caryopses were soaked for 24 h at 25 ± 1°C in a 100- by 15-mm plastic Petri dish with two sheets of Whatman No. 1 filter paper (Whatman Chemical Separation, Inc., Clifton, NJ) moistened with 5 mL of the appropriate test solution. A similar procedure was used for Experiment 2 except that 50 seeds were sampled from each lot, the cupules were left intact, 9 mL of treatment solution were used, and soaking was performed for either 24 or 48 h. After the proper exposure time, caryopses or cupules were washed for 60 s under distilled water to remove any remnant treatment solution. The pH of the test solution in treatment dishes was checked using a micro-combination pH electrode (Orion Research Inc., Beverly, MA) to determine that buffering capacity during incubation was sufficient.
Immediately after washing, seeds for each treatment were placed in 13- by 13- by 3.5-cm covered containers with two layers of Anchor Steel blue seed germination paper (Anchor Paper Co., St. Paul, MN) moistened with distilled water. One box, containing 25 randomly sampled seeds for Experiment 1 and 50 seeds for Experiment 2, was considered as an experimental unit. All germination tests were performed at 20/30°C alternating night/day temperature (16-h night/8-h day; Ahring and Frank, 1968). Light was supplied in conjunction with the day temperature period.
Seed from Experiment 1 was germinated in a Percival (Perry, IA) model 1-35 incubator with two 40-W cool-white fluorescent lights set vertically on each the left and right side. Replication for Experiment 1 was done in time. Seed from Experiment 2 was germinated simultaneously with each replication in a different incubator. Seed for two replications were placed in Hoffman (Albany, OR) model SG30 incubators with three 40-W cool-white fluorescent lights oriented vertically in each the front and rear. Seed for the third replication was germinated in a Conviron (Pembina, ND) model G30 germinator with four 40-W cool-white fluorescent lights vertically oriented on each the left and right sides. Temperature of each chamber was measured with a thermograph and was generally within 1°C of the set temperatures. Photon flux density (400–700 nm) was measured in all chambers using a Licor (Lincoln, NE) LI-190SA Quantum Sensor and was 20 ± 5 µmol m2 s-1 when the sensor was held vertically (facing the lights) in the center of the incubators.
Germination counts were made every 7 d for 28 d. Seeds were considered germinated if the coleoptile exceeded the seed in length and the seedling was normal according to the seedling evaluation criteria of the Association of Official Seed Analysts for comparable grasses (Association of Official Seed Analysts, 1992). Normal seedlings were removed as they were counted. Water was added to each germination box as needed to maintain optimum moisture levels. After 28 d of incubation, ungerminated seeds were examined by TZ tests and classified as dormant or dead.
The experimental design for both studies was a randomized complete block and each study was analyzed independently. Treatments in Experiment 1 were factorial combinations of six seed lots by five test solutions replicated four times. Experiment 2 contained factorial combinations of six seed lots by four test solutions by two exposure times with three replications. Germination percentages were collected from each dish and adjusted based on the viability of each seed lot. Germination data from each week were then subjected to analysis of variance according to General Linear Model (GLM) procedure of the Statistical Analysis System (SAS Inst., Cary, NC). Analysis of germination across time, from 7 to 28 d was accomplished using Proc Mixed of SAS with the auto regressive [ar(1)] covariance structure and the Satterthwaite approximation of degrees of freedom. Mean comparisons were performed using LSD or Duncan's Multiple Range tests at P < 0.05. The coefficients of variation for germination was 18 and 102% in Experiments 1 and 2, respectively.
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RESULTS |
Experiment 1During the 24-h seed treatment period, the increase in pH units
of the five test solutions was 1.5 in distilled water, 0.5 in
citrate phosphate buffer solution, 0.3 in both 0.001 and 0.005
M GA
3, and 0.2 in 0.01
M GA
3 solution (
Table 2). Thus, GA
3 solutions
were buffered below the pKa of GA
3 and kept protonated during
the seed treatment period.
Germination of caryopses with their cupules removed increased
significantly when treated with buffered GA
3 solutions compared
with distilled water or buffer alone (
Table 3). Increases in
germination after 28 d ranged from 25 to 47 percentage points,
depending on seed lots and concentrations of GA
3. Concentrations
of 0.001, 0.005, and 0.01
M GA
3 were equally effective in promoting
germination in all seed lots except in Pete 96, where 0.001
M GA
3 was more effective than 0.01
M GA
3. When averaged across
seed lots, germination of buffer-treated caryopses was eight
percentage points higher than those soaked in distilled water.
But, this trend was significant for only one seed lot, Iuka
96.
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Table 3. Germination percentage of eastern gamagrass caryopses as influenced by gibberellic acid (GA3) treatment after 28 d of germination test.
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Generally, GA
3 accelerated germination (
Fig. 1). Seed lots of
Pete 95, Iuka 96, and Pete 96 responded to GA
3 within the first
2 wk. Following the 14-d initial peak, germination was no further
or slightly increased by GA
3 in the remaining testing period.
However, seed lots Iuka 95, Iuka 97, and Pete 97 displayed a
slower response to GA
3 and the maximum germinations were achieved
at the end of the germination test.
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Fig. 1. Influence of GA3 treatment on the germination of six different lots of eastern gamagrass cultivars with cupules removed.
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The GA
3 solutions stimulated germination, but some caryopses
still remained dormant when the experiment terminated. According
to the viability tests at the end of the germination test, average
remaining dormant seeds across seed lots were 9, 10, and 11%
in caryopses treated with 0.001, 0.005, and 0.01
M GA
3 solutions,
respectively.
Experiment 2
A test of pH during soaking of intact cupules found that the pH of the buffer solution and buffered GA3 solution was at or below 3.8 at 24 and 48 h. Thus, the buffered GA3 solution was below the pKa of GA3 and kept protonated during the seed treatment period. The pH of the unbuffered GA3 solution, at 4.3 ± 0.07 and 6.1 ± 0.03 at 24 and 48 h, respectively, rose above the pKa of GA3.
There were no significant differences in germination response to exposure of intact cupules to treatment for 24 and 48 h, therefore data for the two periods were combined (Fig. 2). Treatment with 0.001 M GA3 solution increased germination from 9 to 16% when compared with soaking in water alone. Germination response from treatment with buffered GA3 solution was similar to soaking in water. Treatment with buffer solution alone had a negative impact on germination, decreasing it from 9 to 5% when compared with soaking in water. Tetrazolium tests performed at the end of the 28 d germination period indicated that soaking in the buffer solution did not increase the proportion of dead seeds (data not shown).
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Fig. 2. Influence of GA3 application on germination of eastern gamagrass with cupules intact. Average of six lots produced across three different years.
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Gibberellic acid in water both accelerated germination and resulted
in greater germination after 28 d. The slopes of linear regression
lines fit to these data (
Table 4) indicate that the rate of
germination for seed soaked in GA
3 and water was nearly 60%
greater than the rate for seed soaked in GA
3 and buffer or in
water alone. Soaking seeds in buffer alone decreased the germination
rate to about half that from soaking in GA
3 and buffer or water
alone and one-third the germination rate of seeds soaked in
GA
3 and water.
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Table 4. Slopes of linear regression fit to germination data of eastern gamagrass seed with the cupule intact and soaked in various treatment solutions. Lines were fit through germination data collected at 7, 14, 21, and 28 d of germination time and represent combined data from six seed lots produced across three different years and soaking periods of 24 and 48 h.
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Seed lot
x treatment effects were significant for the 21- and
28-d germination counts. These interactions were created by
a differential response of the lots to GA
3 application in water
(
Fig. 3). Four of the lots, Iuka 98, Pete 96, Pete 97, and Pete
98, exhibited a positive germination response to GA
3 solution.
The level of the response after the 28-d germination period
varied from 6 to 18 percentage points when compared with soaking
in water. Two lots, Iuka 96 and Iuka 97, did not respond to
GA
3.
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Fig. 3. Influence of GA3 application on germination of six different lots of eastern gamagrass cultivars with cupules intact.
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DISCUSSION |
Gibberellic acid application, under buffered (below pKa) conditions,
at concentrations of 0.001, 0.005, and 0.01
M, considerably
improved germination of eastern gamagrass seed when cupules
were removed. The effect was generally consistent across different
commercial seed lots produced in different years and the three
GA
3 concentrations were equally effective in promoting germination.
Only a slight enhancement occurred when GA
3 solutions were applied
to seed with intact cupules. Buffering GA
3 solution below its
pKa did not improve germination of seed with intact cupules
beyond levels obtained with GA
3 in water. These results suggest
that there may be multiple dormancy mechanisms in eastern gamagrass.
At least one mechanism involves the caryopsis and is affected
by GA
3 application. Furthermore, cupule-mediated dormancy mechanism(s)
and caryopsis-mediated mechanism(s) must both be overcome to
obtain complete germination of dormant seed.
Gibberellic acid is important in the promotion and maintenance of germination (Bewley, 1997), while embryos are considered to be the source of GA3, the GA3 requirement for germination in eastern gamagrass could imply inadequate endogenous levels or inadequate GA3 synthesis in the embryos. Mechanisms by which GA3 stimulates seed germination have been suggested. Simpson (1990) proposed that GA3 could promote formation of low molecular weight mono- and disaccharides, which assist the intracellular generation of negative water potentials that aid radicle emergence. However, Welbaum and Bradford (1990) found no increase in turgor pressure before radicle protrusion in muskmelon (Cucumis melo L.) seeds.
Endosperm weakening during tomato (Lycopersicon esculentum Mill.) seed germination has been extensively studied (Groot and Karssen, 1987; Haigh and Barlow, 1987; Groot et al., 1988). Seed germination of GA3–deficient tomato mutants was absolutely dependent on application of GA3 unless the endosperm and testa layers opposing the radicle were removed (Groot and Karssen, 1987). Groot et al. (1988) found that GA3 application increased the activity of galactomannan hydrolyzing enzymes in the mutant seeds. They concluded that the key role of GA3 in seed germination is to induce the synthesis of endosperm cell wall-degrading enzymes to hydrolyze the layers surrounding the radicle until they no longer act as physical barriers to radicle emergence.
Our previous study (Tian et al., 2002) indicated that the outer layers of the embryo restricted germination of eastern gamagrass. Seeds germinated readily when the cupule was removed and the pericarp was scarified. The stimulatory effect of GA3 on seed germination of eastern gamagrass could involve weakening those structures through enzymatic degradation. Also, accumulating osmotic solutes could increase the hydrostatic pressure of embryo tissues and help expanding radicles burst through barrier tissues. In addition, a loosened cell wall would promote water and oxygen uptake needed for expansive growth of the emerging radicle.
It should be noted that GA3 did not break down the dormancy of all caryopses when applied to seeds with cupules removed. Eastern gamagrass has an indeterminate fruiting pattern in that different spikes on a single plant develop during an extended time period. At harvest, seeds are not uniform in age and the dormancy levels could vary due to differences in physiological stage and environmental conditions experienced during seed development.
The stimulatory effect of GA3 is restricted to periods when the seeds are capable of responding to the hormone because of receptor availability or activity. The majority of eastern gamagrass seeds used in this study responded to GA3. The failure of a small portion of the seeds to respond to GA3 could be due to insensitivity or the presence of other factors limiting the processes leading to germination. For example, GA3 application did not improve the seed germination of genetically pure lines of wild oats with very deep seed dormancy unless the seeds were afterripened before GA3 treatment (Upadhyaya et al., 1982). The authors hypothesized that several blocks exist in dormant seeds. Increased sensitivity of seeds to GA3 by afterripening or slow drying has been reported (Evans and Young, 1975; Nicholls, 1979, 1986). This sensitivity of seeds to dormancy-breaking agents is proposed to be related to membrane-bound or membrane-associated receptor proteins within the embryonic cells (Taylorson, 1988; Hooley et al., 1991; Vleeshouwers et al., 1995). It has been hypothesized that receptor proteins move to the membrane surface and become exposed during afterripening.
Our results generally agree with those of Anderson (1985) in that GA3 resulted in significant enhancements in eastern gamagrass germination when cupules were removed from seeds, but made only a slight difference in seeds with intact cupules. However, germination levels obtained from application of GA3 to decupulated seed were higher in the current study than the 65% reported by Anderson. This could be due to the use of buffered GA3 solutions or differences in genotype, production environments, handling and processing, age, and incubation temperature.
Buffering GA3 below its pKa was not effective at breaking dormancy in eastern gamagrass when the cupule remained on the seed. Significant but small increases in germination occurred when cupules were soaked in GA3 dissolved in water. The response to GA3 in water varied considerably among the lots tested. These results suggest that there are one or more cupule (including lemma and palea)-mediated dormancy mechanisms in eastern gamagrass. These mechanisms appear very strong in some lots and prevented the action of GA3. In other lots, the cupule-mediated dormancy was weaker and the GA3 stimulated germination.
Previous research has shown that a cold-moist (4.4°C) stratification period of 40 to 60 d followed by exposure to >25°C was necessary for many eastern gamagrass seeds to germinate when their cupules were intact (Ahring and Frank, 1968; Anderson, 1985). Dormancy mechanisms affected by these prechilling conditions are unknown for this species. Germination of seeds in contact with their removed cupules had greater germination than cold-moist stratified seed or dry seed with the cupule removed, suggesting that there is no chemical inhibitor in the cupule (Anderson, 1985). Soaking cupule-enclosed seed in sodium hypochlorite solution did not stimulate germination, adding further weight to this argument (Anderson, 1985; Ahring and Frank, 1968). Germination was not enhanced by subjecting seeds to ethylene chlorohydrin vapors and solutions or using salt solutions of 0.1 to 0.8% KNO3 as moistening agents (Ahring and Frank, 1968). Lack of evidence for chemical germination inhibitors suggests that the cupule dormancy mechanism is physical. This hypothesis is supported, in some ways, by recent work that suggested that the integrity of the cupule must be reduced before germination will proceed normally (Springer et al., 2001).
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ACKNOWLEDGMENTS |
The authors thank R. Struthers for technical assistance with
the second experiment.
|
NOTES |
Journal Paper No. J-18414 of the Iowa Agric. and Home Economics
Exp. Stn., Ames, IA 50011. Project No. 3244, and supported by
the Hatch Act, State of Iowa, and a grant from the Leopold Center
for Sustainable Agriculture.
Received for publication April 3, 2002.
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REFERENCES |
- Agrawal, P.K. 1981. Genotypic variation in seed dormancy of paddy and simple methods to break it. Seed Res. 9:20–27.
- Ahring, R.M., and H. Frank. 1968. Establishment of eastern gamagrass from seed and vegetative propagation. J. Range Manage. 21:27–30.[ISI]
- Anderson, R.C. 1985. Aspects of the germination ecology and biomass production of eastern gamagrass (Tripsacum dactyloides L.). Bot. Gaz. (Chicago) 146:353–364.[ISI]
- Association of Official Seed Analysts. 1992. Poaceae, grass family V. p. 84–87. In Seedling evaluation handbook. Contrib. No. 35. AOSA, Las Cruces, NM.
- Bewley, J.D. 1997. Seed germination and dormancy. Plant Cell 9:1055–1066.[Free Full Text]
- Dawson, R.M.C., D.C. Elliott, W.H. Elliott, and K.M. Jones. 1969. Data for biochemical research. Clarendon Press, Oxford.
- Evans, M.L. 1974. Rapid responses to plant hormones. Annu. Rev. Plant Physiol. 25:195–223.[ISI]
- Evans, R.A., and J.A. Young. 1975. Enhancing germination of dormant seeds of downy brome. Weed Sci. 23:354–357.[ISI]
- Fulbright, T.E., E.F. Redente, and A.M. Wilson. 1983. Germination requirement of green needlegrass (Stipa viridula). J. Range Manage. 36:390–394.[ISI]
- Gamagrass Seed Company. 1999. The gamagrass grower's guide [Online]. [1 p.] Available at: http://www.gamagrass.com/grwguide.htm [posted 14 May 1999; verified 5 Nov. 2002]. Gamagrass Seed Co., Falls City, NE.
- Groot, S.P.C., and C.M. Karssen. 1987. Gibberellins regulate seed germination in tomato by endosperm weakening: a study with gibberellin-deficient mutants. Planta 171:525–531.[ISI]
- Groot, S.P.C., E. Kieliszewska-Rokicka, E. Vermeer, and C.M. Karssen. 1988. Gibberellin induced hydrolysis of endosperm cell walls in gibberellin-deficient tomato seeds prior to radicle protrusion. Planta 174:500–504.[ISI]
- Hagon, M.W. 1976. Germination and dormancy of Themeda australis Danthonia spp., Stipa bigeniculata and Bothriochloa macra. Aust. J. Bot. 24:319–327.[ISI]
- Haigh, A.M., and E.W.R. Barlow. 1987. Water relations of tomato seed germination. Aust. J. Plant Physiol. 14:485–492.[ISI]
- Hardin, B. 1994. Eastern gamagrass: Corn's comeback cousin. Agric. Res. 4:12–15.
- Hitchcock, A.S., and A. Chase. 1950. Manual of the grasses of the United States. USDA Publ. 200. 2nd ed. U.S. Gov. Print. Office, Washington, DC.
- Hooley, R., M.H. Beale, and S.J. Smith. 1991. Gibberellin perception at the plasma membrane of Avena fatua aleurone protoplasts. Planta 183:274–280.[ISI]
- Hsiao, A.I. 1979a. The effect of sodium hypochlorite and gibberellic acid on seed dormancy and germination of wild oats (Avena fatua). Can. J. Bot. 57:1729–1734.[ISI]
- Hsiao, A.I. 1979b. The effect of sodium hypochlorite, gibberellic acid, and light on seed dormancy and germination of wild buckwheat (Polygonum convolvulus) and cow cockle (Saponaria vaccaria). Can. J. Bot. 57:1735–1739.[ISI]
- Kindiger, B. 1994. A method to enhance germination of eastern gamagrass. Maydica 39:53–56.[ISI]
- Lona, F. 1956. L'acido gibberellico determina la germinationne dei semi di Lactuca scariola in fase di scoto-imbizione. L'Atheneo Parmense 27:641–644.
- Mott, J.J. 1974. Mechanisms controlling dormancy in the arid zone grass Aristida contorta L. 1. Physiology and mechanisms of dormancy. Aust. J. Bot. 22:635–645.[ISI]
- Mott, J.J. 1978. Dormancy and germination in 5 native grass species from savannah woodland communities of the northern territory Australia. Aust. J. Bot. 26:621–632.[ISI]
- Nicholls, P.B. 1979. Induction of sensitivity to gibberellic acid in developing wheat caryopses—Effect of rate of desiccation. Aust. J. Plant Physiol. 6:229–240.[ISI]
- Nicholls, P.B. 1986. Induction of sensitivity to gibberellic acid in wheat and barley caryopses: Effect of rate of dehydration, temperature and the role of the embryo during caryopses maturation. Aust. J. Plant Physiol. 13:785–794.[ISI]
- Nikolaeva, M.G. 1977. Factors controlling the seed dormancy pattern. p. 51–74. In A.A. Khan (ed.) The physiology and biochemistry of seed dormancy and germination. North-Holland Biomedical Press, Amsterdam, The Netherlands.
- Palevitch, D., and T.H. Thomas. 1976. Enhancement by low pH of gibberellin effects on dormant celery seeds and embryoless half-seeds of barley. Physiol. Plant. 37:247–252.[ISI]
- Polk, D.B., and W.L. Adcock. 1964. Eastern gamagrass. Cattleman 50:82–84.
- Prasad, V.N., V.N.P. Gupta, and D. Bajracharya. 1983. Alleviation by gibberellic acid and kinetin of the inhibition of seed germination in maize (Zea mays) under submerged conditions. Ann. Bot. 52:649–652.[Abstract/Free Full Text]
- Simpson, G.M. 1990. Seed dormancy in grasses. Cambridge Univ. Press, Cambridge.
- Springer, T.L., C.L. Dewald, and G.E. Aiken. 2001. Seed germination and dormancy in eastern gamagrass. Crop Sci. 41:1906–1910.[Abstract/Free Full Text]
- Taylorson, R.B. 1976. Responsiveness of intact and scarified seeds of Barbarea vulgaris to gibberellic acid and changes in phytochrome. Physiol. Plant. 38:196–200.[ISI]
- Taylorson, R.B. 1988. Anaesthetic enhancement of Echinochloa crus-galli (L.) Beauv. seed germination: Possible membrane involvement. J. Exp. Bot. 39:50–58.[Abstract/Free Full Text]
- Tian, X., A.D. Knapp, K.J. Moore, E.C. Brummer, and T.B. Bailey. 2002. Cupule removal and caryopsis scarification improves germination of eastern gamagrass seed. Crop Sci. 42:185–189.[Abstract/Free Full Text]
- Toole, V.K., and H.M. Cathey. 1961. Responses to gibberellin of light-requiring seeds of lettuce and Lepidium virgincum. Plant Physiol. 36:663–671.[Free Full Text]
- Upadhyaya, M.K., J.M. Naylor, and G.M. Simpson. 1982. The physiological basis of seed dormancy in Avena fatua. 1. Action of the respiratory inhibitors sodium azide and salicylhydroxamic acid. Physiol. Plant. 54:419–424.[ISI]
- USDA. 1991. Native perennial warm season grasses for forage in southeastern United States (except South Florida). USDA, SCS, Ecological Science and Planning Staff. Fort Worth, TX.
- Vleeshouwers, L.M., H.J. Bouwmeester, and C.M. Karssen. 1995. Redefining seed dormancy: An attempt to integrate physiology and ecology. J. Ecol. 83:1031–1037.[ISI]
- Welbaum, G.E., and K.J. Bradford. 1990. Water relations of seed development and germination in muskmelon (Cucumis melo L.). V. Water relations of imbibition and germination. Plant Physiol. 92:1046–1052.[Abstract/Free Full Text]
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L. R. Gibson, E. Z. Aberle, A. D. Knapp, K. J. Moore, and R. Hintz
Release of Seed Dormancy in Field Plantings of Eastern Gamagrass
Crop Sci., January 31, 2005; 45(2): 494 - 502.
[Abstract] [Full Text] [PDF]
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C. Rogis, L. R. Gibson, A. D. Knapp, and R. Horton
Enhancing Germination of Eastern Gamagrass Seed with Stratification and Gibberellic Acid
Crop Sci., March 1, 2004; 44(2): 549 - 552.
[Abstract] [Full Text] [PDF]
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ABSTRACT
INTRODUCTION
0.05.
], red clover produced intermediate stands (22%), and birdsfoot trefoil and kura clover produced poorer stands (16 and 13%, respectively). This may be, in part, why alfalfa and red clover are the preferred species for interseeding into existing pastures in the North-Central region. However, if kura clover spreads and increases in mixed stands, relatively low establishment may or may not be a critical factor in the usefulness of kura clover in pastures. Birdsfoot trefoil stands, while 33% when sod was suppressed, were lower than alfalfa or red clover (
TOP
ABSTRACT
INTRODUCTION
, total carbohydrates 
, and sucrose 
. Sulfur increased with increasing protein 
, but S/N ratios were constant across protein concentrations. Decreases in carbohydrates with increases in protein would contribute to increased nutritional value of the meal from these breeding lines. The consistent S/N ratio across the range of seed protein concentrations indicates that S-containing amino acids were not sacrificed with increases in seed protein.
that they felt would pose difficulties for the soybean breeder who wanted to reduce stachyose content of the seed while maintaining high seed protein.
, and oil 
, were not significant. In contrast, there was a strong inverse relationship between sucrose and protein 
and a positive relationship between sucrose and oil 
among all lines combined across the two groups. These relationships demonstrated the feasibility of developing soybean germplasm with high seed protein and low stachyose + raffinose in the meal.
70% of total soybean seed protein (
and sucrose 
increased with increases in seed oil (
associated with the decrease in protein with increasing oil content. 
, mg cysteine 
for 13 lines of G. max and G. soja (Sieb. and Zucc.).
. This indicated that the amount of S-containing amino acids was relatively constant regardless of the amount of protein in the seed of these breeding lines. 
among 12 soybean strains that varied from 390 to 480 g kg-1 seed protein.
subunit of soybean ß-conglycinin. Plant Mol. Biol. 15:197–201.
1.25 Mg m-3. The pots, which had small holes in the bottom, were placed in trays containing 5 mm standing water until soil was saturated. Pots were then removed from trays and kept on the greenhouse bench for 48 h until the soil water content was 
80% with 14 d of stratification, if the seeds are moved directly to germination without drying. However, we have found germinability (but not viability) may decrease by half or more if the stratified seeds are first dried and then rehydrated for germination testing. The reappearance of dormancy (secondary dormancy) during poststratification drying is herein called reversion. During poststratification drying, dormancy reversion increased as the degree of desiccation increased. Extended stratification (for 
0.05). The square root of germination percentage was arcsin transformed to normalize germination data. Back-transformed data (sin transformation squared) are reported. Sigmoidal curves were fitted to the cumulative germination time course for the stratification interruption study using Microcal Origin (Microcal Software, Inc., Northampton, MA). Daily germination change by stratification, that is, rate of dormancy breaking, was derived from the sigmoidal curves.
2 of 13.8 (df = 17, P = 0.99), 105 (df = 9, P = 0.31), and (df = 11, P = 0.20) for seeds continuously stratified, dried at Day 7, and dried at Day 14, respectively. The inset shows the daily germination percentage changes (derived from sigmoidal curves and of Gaussian distribution) caused by stratification.
محسن چاوشی 
زم فریب چشماتو خوردمو
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