Loss Of Dormancy Research Articles

Patterns of change in seed dormancy and persistence of Bromus diandrus Roth. (great brome) in the field

Mature seeds of great brome (Bromus diandrus Roth;.) from Western Australia were dormant when freshly harvested. This dormancy was lost progressively over summer. The rate of loss of dormancy was more rapid in the northern than in the southern accessions. Compared with bare soil, a wheat stubble microenvironment favoured the relief of dormancy during the initial period of dormancy breakdown. Shallow burial of newly shed dormant seeds also accelerated the after-ripening process. Germination of non-dormant seeds during summer was minimised by high temperatures and low soil moisture content. By autumn/winter, almost all the seeds became germinable. At 20/10�C, the temperature regime corresponding to late autumn, 95-99% germination occurred under constant darkness, but in the light germination varied from 55 to 95%. In the field, complete mass germination did not occur but germination was a well-defined event. There was little germination following this pulse until the succeeding autumn/winter. The seed bank of great brome appears to be essentially a transient one, but this is the subject of further work. The concentration of germination at a single time of year, and the very small carryover of seeds to successive years, suggest that good control should be achieved by a single, timely cultivation or spraying.

Interactions Among Ethephon, Nitrate, and After-Ripening in the Release of Dormancy of Wild Oat (Avena fatua) Seed

Germination of dormant wild oat (Avena fatuaL. # AVEFA) seed was examined in response to various concentrations of ethephon (2-chloroethylphosphonic acid), KNO3, or both together in the dark at temperatures ranging from 7 to 32 C. Both chemicals significantly (P = 0.05) promoted germination and their effects were additive. Maximum stimulation of germination in response to all treatments occurred at 7 C, with a gradual decrease in reponse as temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon also occurred during storage of mature seed at 3 to 32 C. The rate and extent of this dormancy loss increased with an increase in storage temperature. Regardless of the temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon and KNO3treatments. Suitable combinations of after-ripening, ethephon, and KNO3induced over 90% germination of seed that was dormant at maturity. Experimental evidence has been obtained that suggests that this percentage may represent the total number of viable seed in the population. While ethephon promoted seed germination, it severely stunted root and shoot growth of the resulting seedlings. It appears that strategies could be developed to combine the use of ethephon and nitrate with the natural process of after-ripening to enhance and synchronize wild oat germination.

GERMINATION RESPONSES TO LIGHT AND ALTERNATING TEMPERATURES IN EUROPEAN POPULATIONS OF DACTYLIS GLOMERATA L.: IV. THE EFFECTS OF STORAGE.

A direct linear relationship between germination responses to light and alternating temperatures and storage period was recorded when seeds of three populations of Dactylis glomerata L. of contrasting origin were stored under cool dry laboratory conditions (15°C, 15% r.h.). Under these conditions the rate of after-ripening in two batches of a Mediterranean population were independent of original dormancy level but lower than in populations originating from southern England and Western France. The effects of storage on germination responses were additive in all cases. In contrast, when seeds of a population from southern England were stored under natural conditions of temperature and humidity from August to April germination behaviour was dependent on the conditions used in germination tests. Evidence is presented that the rate of loss of primary dormancy under natural conditions exceeded that which occurred during controlled storage in the laboratory. An apparent simultaneous loss of primary dormancy and induction of secondary dormancy observed when seeds were stored under natural conditions is discussed. Dry storage at -75°C effectively arrested after-ripening over a period of 110 weeks.

LIGHT AND DRY STORAGE INFLUENCES ON THE RESPIRATION OF GERMINATING SEEDS OF FIVE SPECIES

SummaryIn an attempt to study the influence of light on early metabolic events in seed germination, the rates of oxygen uptake of germinating seeds of five species were measured in relation to their germination response to light and to their loss of primary dormancy during dry storage. No significant effects of light on oxygen uptake prior to germination (i.e. prior to radicle protrusion) were detected. A difference m the initial rates of oxygen uptake prior to germination was observed when seeds were stored at low (8%) moisture contents suggesting that significant changes in their respiratory capacity occurred under these conditions.

Imbibition conditions and seed dormancy of Arabidopsis thaliana

The optimal combinations of temperature in the range of 0 to 20°C and duration (1 to 14 days) of imbibition for the induction of germination of Arabidopsis thaliana (L) Heynh., ecotype “Landsberg‐erecta”, by red light were investigated. At 2°C, 10 days of imbibition are needed tor loss of dormancy, whereas at higher temperatures, e.g 15°C, it is already lost after 1 or 2 days. It is proposed that the development of light‐inducible germination is governed by two temperature‐dependent processes‐the loss of primary or innate dormancy and the simultaneous induction of secondary dormancy. Data are discussed in terms of the availability of phytochrome, the availability of an unknown factor X and changes in sensitivity of the process of germination induction by the far‐red absorbing form of phytochrome (Pfr).

A study of the relationship between seed dormancy and pentose phosphate pathway activity in Avena fatua

The hypothesis that loss of seed dormancy is associated with an increased activity of the pentose phosphate pathway (PPP) relative to glycolysis and the Krebs cycle was tested. The PPP activity was monitored by measuring the C6/C1 ratio in embryos excised from incubated caryopses of two genetically pure nondormant (ND) lines and in three dormant (D) lines of Avena fatua L., the wild oat. The C6/C1 ratios of all lines were similar at the commencement of incubation. In the two ND lines the ratio increased steadily prior to and during emergence of the radicle. In the three D lines the ratio increased during the first 24 h and then remained almost constant; there was no germination. When gibberellin treatment was used to overcome dormancy in the D lines, the C6/C1 ratio increased during the first 24 h in two of the lines and continued to increase parallel to germination in a manner similar to normal germination in ND lines. In the third D line, despite loss of dormancy from gibberellin treatment, the ratio did not increase after 24 h. Loss of dormancy during dry storage of seeds of a D-type pure line was accompanied by an increase in the C6/C1 ratio, as measured in freshly imbibed seeds. This indicates a decreased activity of the PPP relative to glycolysis and the Krebs cycle. These findings are contrary to Roberts's hypothesis that loss of dormancy in wild oats is associated with a relative decrease in the C6/C1 ratio.

The germination of watercress (Rorippa nasturtium- aquaticum)seeds. I. The effects of age, storage, temperature, light and hormones on germination

SummaryThe upper temperature limit for germination of watercress seeds was higher in the light than in the dark. Seeds became progressively less dormant following harvest, the upper temperature limit for germination in both light and dark becoming higher and the rate of germination increasing. Earlier-ripening seeds were more dormant than later-ripening ones. High humidity or a short period at high temperature during storage hastened dormancy loss. Germination at 20 °C in the dark could be induced by treatment with a combination of GA4, GA7 and benzyladenine. The promotion of germination by red light was nullified by immediate exposure to far-red light, indicating that the effect of light was mediated through phytochrome. The practical relevance of the results is discussed.

Dormancy and Germination of Seed of Eight Populations of Themeda australis

Seed of eight populations of Themeda australis (R.Br.) Stapf from sites nith the widest range of climates in Australia and Papua New Guinea (P.N.G.) was tested for its dormancy status and germination responses to different temperature and moisture regimes. The populations were from Lae. P.N.G.. Katherine. N.T.. Mundubbera. Qld. Alice Springs. N.T.. Tantangara. N.S.W.. Adelaide Hills. S.A.. Bunbury, W.A. and Hobart. Tas. Dormancy of fresh seed was negligible in Lae and Mundubbera populations. considerable in the Alice Springs population and intermediate in populations from Katherine and all temperate sites. Addition of gibberellic acid hastened the release from dormancy of seed from Katherine and Bunbury. Exposure of plants to three different temperature regimes during seed formation had an effect on dormancy of the Katherine population. Stratification at 4°C and high alternating daily temperatures (45 20°C) hastened the loss of dormancy of fresh seeds of some populations. Germination of non-dormant seed of the different populations was relatively unaffected b) temperatures between 20 and 40°C. Germination of the Alice Springs population was the most sensitive to increasing water stress and that from Lae the least sensitive. Radicle elongation of seedlings from Alice Springs was significantly greater than that of most other populations at a water potential of - I .0 MPa. The differences reported for seed dormancy and germination characteristics of T. australis populations do not reflect a strong physiological adaptation to the climatic characteristics of the sites from which they were collected.

The interaction of environmental factors controlling loss of dormancy in seeds

The interaction of environmental factors controlling loss of dormancy in seeds

Changes in phenolic acids and abscisic acid in sugar pine embryos and megagametophytes during stratification

The phenolic acids and abscisic acid (ABA) of sugar pine (Pinus lambertiana Dougl.) embryos and megagametophytes, separated by high‐pressure liquid chromatography, were analyzed during 90 days stratification of the seeds. The phenolic acids occurred mainly as glycosides. Following hydrolysis, the majority of phenolics present could be identified as common benzoic and ciranamic acid derivatives. Levels of phenolic acids were relatively low in dormant seeds, but increased substantially in the embryos during stratification at 5°C, particularly cinnamic acid, p‐coumaric acid, ferulic acid, and one unknown. This active synthesis during stratification did not support an inhibitory function for phenolic acids. During stratification at 5°C, changes in ABA levels in both tissues followed a triphasic pattern, with no loss during the first 30 days, a significant decrease the second 30 days, and a lesser decrease the last 30 days. Loss of ABA from moist seeds at 25°C occurred three times as rapidly, so that by 30 days the ABA level of these seeds was equivalent to that of seeds stratified 90 days at 5°C; however, dormancy was not alleviated at 25°C. Application of exogenous ABA (10−7 to 10−4M) to stratified seeds did not significantly reduce germination. Together, the above results did not support a primary role for ABA in the maintenance of dormancy in sugar pines.A correlated increase in phenylpropanoid metabolism and respiratory capacity with increased germinability during stratification suggests that loss of dormancy may be more closely dependent on increased levels of growth promoters or shifts in metabolic pathways.

Changes in phenolic acids and abscisic acid in sugar pine seed coats during stratification

The phenolic acids and abscisic acid (ABA) of sugar pine (Pinus lambertiana Dougl.) seeds coats, separated by high‐pressure liquid chromatography, were analyzed during 90 days stratification of the seeds. Although levels of seed coat phenolic acids and ABA declined significantly during, stratification, this decrease did not appear to be responsible for the loss of dormancy due to stratification. Lack of improved germination following washing, cracking, or removal of the seed coats, plus additional evidence, did not support a significant role for the seed coat in the dormancy of sugar pine seeds.

Studies in Wild Oat Seed Dormancy

Seed of Avena fatua were shown to exhibit a characteristic loss of dormancy during dry storage at 25 C, whereas similar seed stored at 5 C maintained dormancy. 2-Chloroethylphosphonic acid was shown to increase germination of partly dormant seed imbibed under certain temperature regimes; a similar effect could not be established for fully dormant or fully nondormant seed. Using gas-liquid chromatography, natural ethylene levels were followed during imbibition of fully dormant and nondormant seed. A large peak in production was observed in the period prior to radicle emergence in the case of the nondormant seed. Measurements of ethylene production taken at 15 C, following periods of after-ripening in moist soil at either 5 or 25 C, indicated that endogenous production was unlikely to be a main cause of dormancy breakage in this species. The possibility that endogenous ethylene could play a role in natural dormancy breakage in aged seeds is discussed. The practical possibilities of 2-chloroethylphosphonic acid as a dormancy breaking agent in a field situation are outlined.

Pentose phosphate metabolism during dormancy breakage in Corylus avellana L.

Commercially obtained fruits of Corylus avellana exhibit the characteristic loss of dormancy of this seed following chilling under moist conditions. The activities of cytosolic and organellar enzymes of pentose phosphate pathway in cotyledonary tissue were assayed throughout stratification and over a similar period in damp vermiculite at 20° C. Glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconic acid dehydrogenase (6PGDH) were both found in cytosolic extracts in all treatments; only 6PGDH was present in the organellar fraction.The enzyme activities monitored in seeds at 20° C remained relatively constant over the course of the investigation except in the case of cytosolic 6PGDH where it is suggested an inhibitor of the enzyme accumulated. This inhibitor was removed by the partial purification procedure. Increases in the activities of the enzymes occurred during stratification, the major increase coinciding exactly with dormancy breakage but prior to the initiation of germination. The marked increase in G6PDH and 6PGDH concurrent with the change in germination potential of the chilled seed may have considerable biochemical significance in breaking down the dormant state.

Characteristics of alternating temperatures which stimulate loss of dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

Characteristics of alternating temperatures which stimulate loss of dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

Characteristics of alternating temperatures which stimulate loss of dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

Abstract. Alternating temperatures stimulate the germination of Rumex crispus L. and Rumex obtusifolius L. The optimum period spent at the lower temperature in a diurnal cycle is greater than that spent at the higher temperature. Under most conditions the optimum period at the upper temperatures is about 8 h but, as the upper temperature of a cycle is increased, the optimum period at the upper temperature becomes shorter and more critical. Thus when it is 35°C the optimum period is 2.5–4 h in the light, or about 1 h in the dark. The effect of alternating temperatures is much less in the dark than in the light and in general only extreme alternations with short periods at the higher temperature are effective in the dark. In the light any temperature alternation within the range 1–35°C is effective to at least some extent, providing the temperature difference is 5°C or more and providing the alternation includes one temperature which is above approximately 15°C and one which is below approximately 25°C. The optimum temperature difference is about 15°C. In the light, 4 to 10 cycles saturate the response, but in the dark, where the effect is much less, the response may not be saturated even by 16 cycles. KNO3 at 10−3 M has little effect on the response to alternating temperatures either in the light or the dark. The response to alternating temperature regimes does not appear to vary in quality, i.e., in terms of which particular treatments are best, but it varies in magnitude with site and year of seed collection; and it increases slowly during dry storage, even when stored at a temperature as low as 1.5°C.

Effects of low temperatures on the loss of innate dormancy and the development of induced dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

Abstract It is possible to remove the innate dormancy of seeds of Rumex crispus L and Rumex obtusifolius L. by an initial period of low‐temperature stratification, providing the seeds are then transferred to a higher temperature. The lower the initial temperature within the range 1.5°‐15°C, the greater the germination; there is no stratification effect at 20°C. Although 10°C and 15°C were shown to be suitable for both stratification and for the process of germination itself, neither temperature results in any germination if given constantly: a change from a lower to a higher temperature is essential.The optimum period for stratification depends on two separate processes which occur during the treatment–a rapid loss of innate or primary dormancy and a slower development of induced or secondary dormancy. Within the range 1.5°‐15°C the rate of loss of innate dormancy appears to be independent of light and is probably independent of temperature. In contrast, the rate of induction of secondary dormancy increases with increase in temperature, and is more rapid in the dark than the light. The rate of induction of secondary dormancy during stratification is greater in R. crispus than in R. obtusifolius. As a consequence, maximum germination was obtained in both species after stratification at 1.5°C in the light, the optimum period of treatment being about 4 weeks in R. Obtusifolius and 6 weeks in R. crispus, while the maximum germination obtained and the optimal period of stratification decrease in both species with increase in stratification temperature.

The long term decline of a population of Avena fatua L., with different cultivations associated with spring barley cropping

Summary:The decline of a population of A. fatua established in September 1971, and not allowed to seed thereafter, was monitored in three successive barley crops Numbers of viable seeds in the son in June fell from 159 m2 in 1972 to 1 m2 in 1974 declining by 83° in the first, and by 96° in the second year. Seedling numbers fell from 138 m2 in 1972 to 9 m2 in 1974, declining by 32° in their first and by 89° in the second year. The slower decline of seedling numbers in the first year was attributed to loss of dormancy of seed reserves giving proportionally more seedlings in the second spring.Cultivations had no major influence on the pattern of seedling emergence in the spring, but they did affect population level. Where the stubble was cultivated immediately after seeding in September 1971, twice as many seedlings and three times as many seeds in the soil were present in 1972 compared with delayed autumn cultivations in 1971. From this greater reserve of seeds in the soil more seedlings arose in 1973 and in 1974. Time cultivation in the winter of 1971 resulted in slightly more seedlings in 1972 than did ploughing; this greater population declined more rapidly with line cultivation in 1973 and 1974. It is suggested that with no herbicidal control annual line cultivation will lead to a more rapid build up than ploughing: where A. fatua is controlled, the decline should be more rapid with tne cultivation. Persistence of A. fatua as a weed in arable situations seems related more to survivors shedding seeds than to the persistence of seeds on the soil. Factors which may influence the persistence of seeds in the soil are discussed.

Seasonal periodicity of the loss of dormancy of imbibed seeds in Brassica vegetables

The present study deals with the mode of loss of dormancy of imbibed seeds in Brassica japonica and B. cernua. Mature seeds were sown in petri dishes immediately after harvest and were placed either at room temperature or at a constant temperature of 25°C. After the first flush of germination of non-dormant seeds, most seeds continued to be in a non-germinating state, suggesting that they were dormant. The germination of such dormant seeds occurred sporadically during several years. Under constant 25°C, the germination behaviour of the imbibed seeds was “quasi-simultaneous” in B. japonica and “continuous” in B. cernua. Both species showed a unimodal distribution of germination in time. Under fluctuating room temperature, the distribution of seed germination in each species was characterized by 3 peaks which occurred in summer. In B. japonica the 3 peaks were the same in height, but in B. cernua the middle peak was much higher than the other 2. Such seasonal periodicity of germination was caused by environmental factors of which temperature was the most important.

The Shrubs of Poplar Box (Eucalyptus populnea) Lands and their Biology.

Of the 25 species of shrubs common in poplar box lands, 17 are considered to have reached the status of being a "woody weed" in New South Wales and/or Queensland. Thickening up of scrub in pastoral areas appears to have been episodic after periods of above-average rainfall. Germination of seed may occur at most times of the year if soil moisture is high. Fire promotes germination of species with hard seeds (some Acacia, Cassia and Dodonaea spp.). Increased shrub density usually follows soil disturbance if seed is present, and once established, the individuals of most apecies appear to be long-lived. Productivity of shrub communities is commensurate with rainfall. The species are well adapted to tolerate drought and they retain leaves under extreme water stress. Most species flower and set seed each year in the spring and summer period but in more arid parts of poplar box lands some species reproduce opportunistically after good rainfall. In favourable conditions most species produce copious quantities of seed. Dormancy is common in seed recently shed and loss of dormancy may occur within months or up to 3 years after seed shed. All species are subject to invertebrate and vertebrate predation and death of individuals or whole populations may sometimes result. A few species are moderately palatable to domestic livestock and native herbivores; the majority are rarely eaten even by starving animals. The regenerative ability of shrubs following fire or grazing differs amongst species and is affected by shrub size.

Grain dormancy, peroxidase activity and oxygen uptake in Oryza sativa

In developing grains of rice ( Oryza sativa L.) of the dormant variety H4, peroxidase activity decreased sharply about a week before grain maturity without any change in grain dormancy and oxygen uptake of intact grain. During storage or after-ripening of mature dormant intact grains of four varieties (H4, H6, Mayang Ebos and Seraup 27) at 25–30°, the critical range in peroxidase activity was 1·0–1·4 μmol purpurogallin/hr/grain above which rice grains were almost completely dormant and below which the grains were almost completely nondormant. The oxygen uptake of intact H4 grain tended to decrease during the loss of dormancy. The decrease in both the peroxidase activity and oxygen uptake could be attributed mainly to the lower activities of the hull. Dehulling of developing and mature H4 grains reduced dormancy and increased the oxygen uptake of the grain. Thus, reduction by the hull of the level of oxygen available to the dehulled grain (embryo) was mainly responsible for grain dormancy in rice.