Degree Of Dormancy Research Articles

ABA Content and Levels of GA-like Substances in Asparagus Buds and Roots in Relation to Bud Dormancy and Growth1

Abstract A high concentration of inhibitors which were as high as that of gibberellin (GA)-like substances was found in young asparagus (Asparagus officinalis L.) spears using the rice seedling bioassay, and one of inhibitors was identified as abscisic acid (ABA) by gas chromatography. Endogenous ABA was extracted more thoroughly from the lyophilized materials than from frozen tissue. ABA level was the highest in tops including growing points of spears, and was always higher in the distal half than in the proximal, and higher in the cortex than in the pith. Free ABA levels tended to increase with the development of spears, while bound ABA levels remained the same irrespective of age. Three peaks of ABA were found in crown buds and root tips in March or April, August and December. Presumably asparagus crowns were in the deepest dormancy around the middle of December. Clearly the degree of dormancy from October to January paralleled ABA levels in crown buds and root tips. Endogenous levels of ABA in buds at developing stages was found highest in the resting buds.

Germination tests on thirty‐two East African weed species

Summary:The seeds of thirty‐two species of common East African weeds were set to germinate in the light and in the dark. Eighteen species with more than 40% germination in the light were also germinated in leaf shade and in neutural shade of equal intensity. Germination of fifteen of these was inhibited by darkness, and of sixteen by leaf shade, with complete inhibition in six species. A high degree of dormancy was found in fourteen species. Only one species in this group responded to alternate wetting and drying of the seeds. In eight species dormancy was less in older seeds.The ecological implications of the results are briefly discussed, and comparisons made with temperate weeds.

Endogenous hormones in afterripening wild oat (Avena fatua) seed

Levels of gibberellins and cytokinins in dormant Avena fatua L. seeds were measured by bioassay during the afterripening process. Little change in the level of either hormone was detected in the dry seed. Following imbibition of fully afterripened seed, however, gibberellin levels increased while cytokinin levels declined. Seed strains varying in their degree of dormancy were also analysed for hormone levels; a significantly higher level of cytokinin activity was found in the most dormant strain compared with the least dormant strain. Low levels of bound hormones, including cytokinin ribotides and gibberellin glucose conjugates, were detected following enzyme hydrolysis but neither class of compounds varied greatly in level during afterripening.The major cytokinins detected in Avena fatua seeds cochromatographed with zeatin-9-glucoside, zeatin riboside, and zeatin on both HPLC columns and chromatography paper. The major gibberellin activity cochromatographed with GA4/GA7 on silica gel partition columns and thin-layer plates.Germination studies demonstrated that GA4/7 is significantly more active than GA3 in promoting the germination of dormant Avena fatua seeds. External applications of cytokinins were not found to affect the germination of dormant seed, but did promote germination in partially afterripened material.

Dormancy of Kentucky Bluegrass Seed in Relation to the Color of Spikelets and Panicle Branches at Harvest1

One of the most important factors affecting germination of Kentucky bluegrass (Poa pratensis L.) seed is maturity at harvest. This study evaluated degrees of seed dormancy in 10 cultivars and selections of Kentucky bluegrass harvested at various stages of change in color of spikelet and panicle branches from green to brown.Significant differences in the degree of dormancy at different stages of change in color of panicle branches existed among the entries. ‘Merion’ exhibited the most prolonged dormancy of seed during this period of change in color. The reduction in dormancy was generally accompanied by changes in color, of the panicle branches in particular, from green to brown. A color index was, therefore, proposed to determine the right time for harvesting Kentucky bluegrass seed to obtain maximum germination.

Seed dormancy of Emex australis and E. spinosa

Seed dormancy in Emex australis and E. spinosa was investigated by the application of light, gibberellic acid (GA3) or kinetin (KT) and by scarification of the fruits. Results from these experiments suggested that dormancy was controlled by the balance between promotive hormones and inhibitors and that a semipermeable barrier prevented leaching of inhibitors and/or uptake of exogenously applied GA3 or KT, and/or restricted oxygen diffusion. Storage of seed at alternating temperatures in the laboratory or the field reduced the level of dormancy, the reduction being more rapid for E. australis than for E. spinosa. The degree of dormancy also varied between populations within E. australis. Burial of non-dormant seeds of E. australis did not induce secondary dormancy even though dormancy was enforced by burial at a temperature regime of 25/20°C. Partly dormant (light-requiring) seeds of E. spinosa attained a degree of secondary dormancy following burial for 4 weeks at 25/20° and 9/9°. The results are discussed with reference to cultural control practices.

The fluctuations in the level of endogenous growth regulators in seeds ofAcer pseudoplatanus L. in the course of stratification

In the course of cold stratification ofAcer pseudoplatanus L. fruits a statistically significant alternation occurs in their seeds of a rise and fall in the level of endogenous growth regulators. In the initial weeks the inhibitory effect slightly declines, or, on the contrary, the stimulatory effect slightly increases; in the middle phase of stratification a marked increase in inhibitions and reduction of stimulations appears, and towards the end of stratification the stimulatory effect of isolated substances in the individual biotests rises again, or their inhibition effect is decreased. No direct dependence was found between the decrease of the degree of dormancy and the drop of inhibitor, or increase of promotor levels. However, a certain analogy was observed between the time course of fluctuations in the level of growth regulators and the germination energy of the seeds investigated. An enhancement of the growth activity of the substances isolated (e.g. those of a gibberellin-like nature) in the last weeks of stratification can already be considered as the result of the release of fruits from dormancy.

Physiology of Oil Seeds. VI. A Means to Break Dormancy of Peanut (Arachis hypogaea L.) Seeds in the Field1,2

Abstract Peanut seedling emergence is not uniform in some years. Lack of uniformity is most prevalent among the large-seeded peanut types (Virginia and Runner). Variations in the degree of dormancy of the large-seeded peanuts are a contributing factor. A procedure is described that will aid in increasing uniformity of large-seeded peanut seedling emergence by overcoming the dormancy factor. A dust formulation of Ethrel (15%/W) was diluted with fungicide (Orthocide/Botran, 60-20 S.P. dust PN 5213) and applied to dry, Virginia-type ‘NC-13’ peanut seeds by shaking in a plastic bag. Concentrations of 0.5, 1, 3 and 5% Ethrel were tested for their effects on rate and total emergence of dormant seeds from vermiculite/sand potting mixtures and from 3 different soils. Also, seeds were stored after treatment and then planted at monthly intervals in soil to test the stability of the Ethrel-fungicide mixture, as indicated by the emergence of the initially dormant seeds. All concentrations of Ethrel released the seeds from dormancy and achieved at least 90% emergence, except at the 0.5% concentration. Compared to the other concentrations, 1% Ethrel provided the most rapid rate of emergence. Growth of the hypocotyl-radicle of afterripened, NC-13 seed samples treated with the 1% concentration was initially slower than that of the controls, but recovery had occurred by the 5th day from planting. However, emeregnce of nondormant ‘Starr’, Spanish-type seedlings was retarded by 1%, but not by 0.5% Ethrel. The Ethrel-fungicide mixture remained stable in storage for 6 months. Field plantings at two locations of dormant, 1% Ethrel-treated seeds resulted in greater than 95% emergence, but the rate of emergence was slower at one location. The data suggest that the Ethrel dust could be combined with the usual fungicide treatment of peanut seeds to stimulate germination of dormant seeds in the field.

An experimental study of water dispersal in Polygonum spp.

The annual smartweeds Polygonum lapathifolium L., P. pensylvanicum L., and P. persicaria L. grow on alluvial river bars during the summer and autumn when their substrate is free of flood waters and physical disturbance. They are dependent upon dispersal for the annual recolonization of this habitat. Achenes are the only diaspores (dispersal units), and hydrochory (water dispersal) appears to be a major dispersal method.An experimental study of water dispersal of these species revealed several adaptive features. The coordination of fruit fall with the availability of the agent (flood water) ensures that the achenes are picked up. The duration of buoyancy is adequate for successful transport downstream. The presence and condition of the perianth, degree of water turbulence, and achene size are factors which determine the duration of buoyancy. Alteration of the degree of dormancy but no loss of viability occurs as a result of water transport. After deposition the achenes may remain dormant or germinate rapidly depending on environmental conditions. The deposition stage (and therefore, hydrochory) is unsuccessful for most achenes of P. persicaria, which rapidly lose viability in sites where deposition is likely to occur. The presence of this species on alluvial bars must be due to other means of dispersal.

Environmental and Hormonal Control of Turion Germination in Myriophyllum verticillatum

Germination, or outgrowth, of Myriophyllum verticillatum turions involves a series of visible changes starting with reflexing of leaves followed by extension and curving of the axis, and then by root formation. Before abscission, turions grow out in response to long days (16 hr) but not short days (8 hr). After abscission, turions show maximal dormancy which can be fully broken by a cold treatment (4 C). Turions are heterogeneous in degree of dormancy and ability to respond to less complete dormancy-breaking treatments, e.g., long days at 20 C. Cytokinins (10-6 m) break dormancy of non-cold-treated turions, whereas gibberellic acid (GA3) is ineffective except at high concentrations (10-3 m). Continuous treatment with cytokinins causes abnormal development after germination. GA3, on the other hand, induces apparently normal development even at high concentration. Indoleacetic acid (IAA) induces outgrowth only at high concentrations (10-3 - 10-4 m), but these concentrations also produce abnormal development. Abscisic acid (ABA, 10-5 m) retards outgrowth of cold-treated turions and can completely suppress it in non-cold-treated turions. The activity of ABA-like substances in turions remains about the same before and during germination, whereas other (unidentified) acidic inhibitors decrease markedly. The cytokinin activity changes in a complex pattern.

ENVIRONMENTAL AND HORMONAL CONTROL OF TURION GERMINATION IN MYRIOPHYLLUM VERTICILLATUM

Germination, or outgrowth, of Myriophyllum verticillatum turions involves a series of visible changes starting with reflexing of leaves followed by extension and curving of the axis, and then by root formation. Before abscission, turions grow out in response to long days (16 hr) but not short days (8 hr). After abscission, turions show maximal dormancy which can be fully broken by a cold treatment (4 C). Turions are heterogeneous in degree of dormancy and ability to respond to less complete dormancy‐breaking treatments, e.g., long days at 20 C. Cytokinins (10‐6 m) break dormancy of non‐cold‐treated turions, whereas gibberellic acid (GA3) is ineffective except at high concentrations (10‐3 m). Continuous treatment with cytokinins causes abnormal development after germination. GA3, on the other hand, induces apparently normal development even at high concentration. Indoleacetic acid (IAA) induces outgrowth only at high concentrations (10‐3 ‐ 10‐4 m), but these concentrations also produce abnormal development. Abscisic acid (ABA, 10‐5 m) retards outgrowth of cold‐treated turions and can completely suppress it in non‐cold‐treated turions. The activity of ABA‐like substances in turions remains about the same before and during germination, whereas other (unidentified) acidic inhibitors decrease markedly. The cytokinin activity changes in a complex pattern.

Correlative Aspects of Imposition of Dormancy in Caryopses of Aegilops kotschyi

Caryopses of Aegilops kotschyi Boiss. from different positions within the same spikelet differ greatly in their degree of dormancy. Imposition of this dormancy pattern is a correlative phenomenon within the spikelet, inasmuch as the uppermost developing caryopsis is least dormant and its development is associated with the dormancy status imposed on the lower (one or two) caryopses. Differences in pigmentation of the caryopses follow a corresponding pattern.

Uptake and Effect of Abscisic Acid during Induction and Progress of Radicle Growth in Seeds of Chenopodium album

AbstractIn the seeds of Chenopodium album L. visible phenomena preceding the final protrusion of the radicle enable a clear distinction between the induction and the progress of growth inside the covering structures. The light‐dependent induction of radicle growth is not inhibited by exogenously applied abscisic acid (ABA). Experiments with 1‐14C‐ABA ruled out a lack of penetration of the hormone.However, ABA does inhibit the growth of the radicle before final protrusion. This inhibition and the uptake of 1‐14C‐ABA are enhanced at lower pH values, indicating absorption of the undissociated molecule. The uptake of labeled hormone strongly increases during the growth of the radicle. This increase is not merely a reflection of extra water uptake.Seeds of different degrees of dormancy contain equallly low levels of endogenous ABA. Much higher levels of ABA in the seeds were obtained by exogenous application of the hormone but these levels stills do not prevent the breaking the dormancy by light. It is concluded that ABA has no function in the regulation of dormancy in C. album seeds.

Influence of Bulb Harvest Date and Temperature on Growth and Flowering of Lilium longiflorum1

Abstract Lilium longiflorum Thunb. cv. Nellie White bulbs were shipped in 1969, 1970, and 1971 from the west coast to St. Paul by air freight from July to October at 15 day intervals. Bulbs were given 0 or 2 weeks of 10°C, 15.5°C or 21 °C followed by 0 or 6 weeks of 4.5°C. Two weeks exposure to 10°C enhanced shoot emergence and flowering of late-harvested non-cooled bulbs and enhanced flowering of cooled bulbs. Treatments of 15.5°C or 21°C had little influence on shoot emergence and flowering of non-cooled bulbs and delayed flowering of early harvested cooled bulbs. With time and with increased bulb growth the degree of dormancy (delay of emergence) decreased and degree of maturity (enhancement of early flowering by 4.5°) increased.

Dormancy Variations in Common Purslane Seeds

Common purslane (Portulaca oleraceaL.) seeds, produced by the same plants, had different degrees of dormancy. The dormancy variations were caused neither by low seed viability nor by location on the plant where seeds were produced. Seed water content and seed age at time of collection contributed to, but were not solely responsible for, the dormancy variations. Immature, brown seeds of high water content were less dormant than the more mature, black seeds of low water content. The immature seeds germinated better in the dark than did the more mature seeds. A puncture in the seed, over the radicle, broke purslane dormancy. Dormancy was not caused by blockage of water imbibition by seeds. Purslane dormancy developed during later stages of seed maturation on the mother plant.

Biochemical and physiological studies on dormancy release in tree buds. I. Changes in degree of dormancy, respiratory capacity, and major cell constituents in overwintering vegetative buds of Populus balsamifera

Changes in the degree of dormancy, rate of growth, respiratory capacity, and in the amounts of several major cell constituents (sugars, protein, amino acids, cell wall materials, starch, and chlorophyll) were examined in vegetative buds of Populus balsamifera L. as they developed from midwinter dormancy to the spring flush of growth in 1972. A significant decrease in the dormancy status of buds occurred during the period March 17 to April 3, and this was accompanied by an increased level of catabolic metabolism of carbohydrates and protein. A further change to anabolic metabolism at the end of April, nearly 2 weeks before bud burst, resulted in a net synthesis of cellular constituents in preparation for bud burst.

Effect of Temparature Preconditioning and Cultivar on Ryegrass (Lolium sp.) Seed Dormancy1

This study was conducted to determine if cultivar differences in seed dormancy existed in ryegrass (Lolium sp.), and whether seasonal differences in dormancy could be related to temperature during the seed development period.Field‐grown ryegrass cultivars differed in degree of seed dormancy when grown under the same field environment. ‘Gulf,’ ‘Florida Rust‐Resistant,’ and ‘Magnolia’ annual and ‘NK‐100,’ ‘Manhattan,’ ‘Atempo,’ ‘Petra,’ and ‘Pelo’ perennial ryegrass cultivars were considered dormant. ‘Obahikari’ annual and ‘Verna Pajdjerg’ and ‘Linn’ perennial ryegrass cultivars were nearly nondormant.Temperature preconditioning during seed development and maturation affected the degree of dormany present in freshly harvested seed. These studies were conducted using a detached culm technique in growth chamber and greenhouse facilities. The dormancy response of Gulf seed produced on detached culms was similar to that of seeds from intact plants, lending validity to the use of this technique. Gulf seeds developed at low temperatures were dormant, but those developed at high temperatures were nondormant. The duration of exposure to different temperatures and the stage of development at which the seeds were exposed to high or low temperature also influenced the degree of dormancy. Exposure to 1 week of low temperature during ripening increased seed dormancy, but at anthesis reduced dormancy. Extended periods of low temperature during seed development increased seed weight. Seed weight was reduced when seeds were exposed to high temperatures during the 2nd week of seed development.A multi‐temperature technique was used to characterize the degree of dormancy present in the seeds.

Dormancy studies in seed of Avena fatua. 7. The effects of light and variation in water regime on germination

Light can regulate the germination of seeds of Avena fatua L. In low volumes of water, seeds are inhibited by white light and in high volumes they are promoted, when compared to seeds in darkness. Blue, red, and far-red light also inhibited germination of seeds in low volumes of water; in high volumes of water there were no differences between these three bands of light and darkness. Degree of dormancy and presence or absence of hulls and of gibberellin all interacted with water status of the caryopsis and light to modify germination. Suppression of germination by white light induced a concomitant reduction in the rate of increase of water potential in these seeds compared with similar seeds germinated in darkness.

High Yielding Groundnut Bunch Cultures with Seed Dormancy

Bunch variety of groundnut is non-dormant in nature and pods sprout in the field if wet weather prevails at the time of maturity. Seed dormancy in groundnut is governed by multiple factors (John et al., 1948). As result a of hybridisation work a partially dormant selection, 'A. h. 6481 (progeny of a cross between 'Gudiyatham Bunch' and 'Native Tanganyika') was evolved in Madras State (Seshadri, 1962). Recently a new bunch strain TMV7 was evolved by pureline selection from "Tennessee White" variety which has seed dormancy besides high yield (Varisai Muhammad et al., unpubl.). Certain promising hybrids were isolated by Ramachandran et al (1967) which possess seed dormancy and this character was observed to be partially dominant over non-dormancy. Six out of 206 bunch varieties maintained at Bhavanisagar possess high degree of dormancy (Varisai Muhammad and Stephen Durairai, 1968). High yielding bunch cultures which have seed dormancy were evolved by hybridisation at the Regional Research Station, Tindivanam. An account of the yield performance, dormancy and economic attributes of the promising cultures is presented in this paper.

Conseguenze e Significato del Prolungamento Nella Durata della Dormienza inTriticum DurumDesf

Abstract Consequences and significance of dormancy Prolongation in «Triticum durum» Desf. — Different environment conditions have effect on the dormancy duration: this has been ascertained also for durum wheat Cappelli. Starting from this acquisition, the author does the embryo exchange between seeds of Cappelli different for dormancy degree. It is demonstrated that there is a direct relation between dormancy degree and inhibition power of endosperm.

Título en español.

Las selecciones de las especies Dioscorea composita y D. floribunda pueden propagarse vegetativamente por medio de pedazos del rizoma tuberoso. El estado de reposo del rizoma tuberoso retarda la formación y el desarrollo de las yemas en los pedazos, de manera que la germinación no es uniforme y se pierde un gran número de los pedazos que tardan en germinar debido a la podredumbre. Tal parece que el grado de reposo del rizoma tuberoso es afectado por la constitución genética de la planta y por el estado de crecimiento en que se encuentre la planta madre, ya sea en pleno crecimiento o en reposo. El grado de reposo aumenta de la corona hacia el ápice del rizoma. La germinación de los pedazos de rizoma de las selecciones de D. floribunda a una temperatura de 31° C., estimuló la formación y el desarrollo de yemas adventicias. El tratamiento de los pedazos de rizoma de las especies D. composita y D. floribunda con dosis de 0.06 a 0.12 ml. de chlorhidrina de etileno, por litro de espacio en el envase, estimuló significativamente la formación de yemas adventicias. Relativamente, tanto la germinación como el desarrollo acelerado de las yemas adventicias pudieron lograrse experimentalmente mediante el uso de rizomas de plantas en crecimiento activo, de los cuales se utilizaron segmentos de sus áreas intermedias y también mediante la suspensión del período de reposo de los rizomas.