Induction Of Secondary Dormancy Research Articles

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).

Anesthetic Effects on Secondary Dormancy and Phytochrome Responses in Setaria faberi Seeds

Seeds of giant foxtail (Setaria faberi Herm.) entered secondary dormancy after pretreatment in H(2)O at 35 degrees C. Pretreatment in 0.1 m ethanol, or several other substances with anesthetic properties, prevented secondary dormancy induction. Pretreatment in 0.5 m ethanol inhibited germination in darkness, but germination could be stimulated by a red irradiation. Germination was initially insensitive to light. Two separate responses are indicated. The first, affected by a variety of substances and low (0.1 m or less) concentrations of ethanol, is related to anesthetic effects and prevention of secondary dormancy. The second, induction of response to red irradiation, is caused by 0.5 m ethanol and some closely related substances. The anesthetic effect is accomplished within the first 8 hours of imbibition while the phytochrome induction effect required treatment for more than 24 hours. Both responses were lost if the 35 degrees C imbibition began in H(2)O. Involvement of cell membranes is suggested in the prevention of secondary dormancy by anesthetics.

Indirect effect of abscisic acid on the induction of secondary dormancy in lettuce seeds

During temporary incubation at 25°C in buffered solutions (pH 4.0) of abscisic acid (ABA) seeds of lettuce (Lactuca sativa L. cv. Olof) lost the red‐light initiated ability to germinate in buffer. The development of secondary dormancy required an inhibitory ABA content in the seeds during a number of days. A temporary incubation in ABA during 24 h met these requirements only if the solution was about 100‐fold more concentrated than during continuous incubation. Studies with 2‐14C‐ABA showed that the amount of ABA which had penetrated in 24 h was reduced by a factor 100 within 3 to 4 days during subsequent incubation in buffer. Both leaching and metabolic changes were involved in the reduction process. The nature of the metabolic products remained obscure. A shift to 2°C after incubation in ABA prevented the induction of secondary dormancy, but inhibited ABA metabolism. ABA did not interfere with the induction rate of secondary dormancy, and it was not required to maintain the state of dormancy. The sole function of ABA was the non‐specific inhibition of germination, which indirectly facilitated the development of an ABA independent secondary dormancy. – The level of endogenous ABA was compared to the amount of ABA found in the embryo during and after incubation in ABA solutions marked with 2‐14C‐ABA. The level of endogenous ABA in air‐dry seeds (0.11 ng/mg dry weight) corresponded to the minimal level at which penetrated ABA inhibited germination. This level had to be present at least during 4 to 5 days to inhibit the effect of red light. Since endogenous ABA was quickly reduced upon imbibition, a regulatory function of endogenous ABA in the inhibition of red light induced germination can be ruled out. A function in the temporary inhibition of dark germination and, consequently, in the development of secondary light irresponsiveness cannot be excluded, however.

Factors Affecting the Induction of Secondary Dormancy in Lettuce

The relationship between the temperature at which germination of 50% of the seeds is inhibited in the light (GT(50) Light) and secondary dormancy was investigated in three cultivars of Lactuca sativa L. Seeds were incubated for varying periods under non-germinating conditions and subsequent germination in response to red light (R) was determined over a wide range of temperatures. Dark incubation at 32 C reduced the GT(50) Light of cv. New York but did not affect germination at temperatures below 24 C. Dark, 32 C incubation had no effect on the GT(50) Light of cv. Great Lakes. In cv. Grand Rapids, dark incubation at 15, 24, 32, or 35 C initially reduced the GT(50) Light. However, longer incubations induced a secondary dormancy, i.e., the seeds became unable to germinate at all temperatures in response to R given after the high temperature incubation. A single exposure to R at the beginning of a 32 C incubation slowed the induction of secondary dormancy. Repeated exposures to R prevented the induction of secondary dormancy, but did not prevent a decline in the GT(50) Light. GA(3) mimicked the effect of repeated R.The differences in the germination behavior of the three cultivars suggest that there may be qualitative differences in the germination mechanism of these cultivars. This research demonstrates the significance of monitoring germination at a range of temperatures to avoid misinterpretation of the data.

Induction of Secondary Dormancy in Chenopodium bonus-henricus L. Seeds by Osmotic and High Temperature Treatments and Its Prevention by Light and Growth Regulators

Factors controlling the establishment and removal of secondary dormancy in Chenopodium bonus-henricus L. seeds were investigated. Unchilled seeds required light for germination. A moist-chilling treatment at 4 C for 28 to 30 days removed this primary dormancy. Chilled seeds now germinated in the dark. When chilled seeds were held in the dark in -8.6 bars polyethylene glycol 6000 solution at 15 C or in water at 29 C a secondary dormancy was induced which increased progressively with time as determined by subsequent germination. These seeds now failed to germinate under the condition (darkness) which previously allowed their germination. Continuous light or daily brief red light irradiations during prolonged imbibition in polyethylene glycol solution at 15 C or in water at 29 C prevented the establishment of the secondary dormancy and caused an advancement of subsequent germination. Far red irradiations immediately following red irradiation reestablished the secondary dormancy indicating phytochrome participation in "pregerminative" processes. The growth regulator combination, kinetin + ethephon + gibberellin A(4)+A(7) (GA(4+7)), and to a relatively lesser extent GA(4+7), was effective in preventing the establishment of the secondary dormancy and in advancing the germination or emergence time. Following the establishment of the secondary dormancy by osmotic or high temperature treatments the regulator combination was relatively more active than light or GA(4+7) in removing the dormancy. Prolonged dark treatment at 29 C seemed to induce changes that were partially independent of light or GA(4+7) control. The data presented here indicate that changes during germination preventing dark treatment determine whether the seed will germinate, show an advancement effect, or will become secondarily dormant. These changes appear to be modulated by light and hormones.

Ecophysiology of Secondary Dormancy in Seeds of Ambrosia Artemisiifolia

As buried seeds of Ambrosia artemisiifolia came out of primary and secondary dormancy, they showed similar germination responses. In early spring at simulated habitat temperatures, seeds germinated well in light but not in darkness, but they germinated well in darkness at temperatures characteristic of the habitat in late spring and summer. By late spring, seeds had entered secondary dormancy and did not germinate at any temperature in light (14—h daily photoperiod) or darkness. Prolonged exposure to 5°C in darkness did not decrease germination in either light or darkness at a 12—h alternating temperature regime of 30°/15°C, but seeds subsequently kept at 15°/6°C in darkness for 1 mo required light for germination. Seeds then lost the ability to germinate in light as they were exposed sequentially to 20°/10°, 25°C/15°C, and 30°C/15°C in darkness. Thus, upon exposure to the sequence of natural temperature regimes in spring, induction of secondary dormancy of seeds in darkness occurs in two physiological stages. While buried seeds are at low marginal temperatures for germination they lose the ability to germinate in darkness, and then at higher temperatures they lose the ability to germinate in light.

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.

Abscisic Acid and Apple Seed Dormancy1

Abstract c,t-Abscisic acid (ABA) was identified in methanol extracts of mature apple (Malus domestica Borkh.) seeds by gas chromatography-mass spectrometry, and concentrations of both free and base-hydrolyzable (bound) ABA in immature and mature seeds were quantified by electron capture gas chromatography. Immature embryos failed to germinate regardless of time of sampling unless seed coats were removed. Germination of excised embryos reached a maximum in early August, then gradually declined to nil in mid-September. Although ABA content of the embryonic axes rose sharply at maturity, the rise occurred only after germination capacity declined. Premature defoliation reduced ABA content of the axes, but did not prevent the induction of embryo dormancy. ABA content of mature seeds declined during stratification at both 5° and 20°C, with maximum differences occurring in the embryonic axis, but dormancy was broken only at 5°. Induction of secondary dormancy by high temperature (27°) was accompanied by a slight decline in ABA content of whole seeds.

DORMANCY AND GERMINATION OF COMMON RAGWEED SEEDS IN THE FIELD

Common ragweed (Ambrosia artemisiifolia) seeds were stored under natural environmental conditions by placing them at three soil levels (surface, 5 cm, and 15 cm) in the field on November 1, 1972. Germination tests at 4‐week intervals indicated that dormancy was broken by the end of January. Germination was initially greater at high temperatures, but this difference decreased with increasing time in the field. Secondary dormancy was evident in surface seeds by March 21 but not until April 18 at 5 cm and June 13 at 15 cm. Germination in the field was greatest at the surface but was observed at all soil levels by March 21. Seedling survival was 68% at the surface and 0% at 5 and 15 cm on June 13. Maximum and minimum soil temperatures were recorded at each soil level during the experiment and were correlated with the results. Greater germination and survival at the surface supports the evidence for ragweed's dependence on soil disturbance for germination, and the induction of secondary dormancy explains why ragweed does not constitute a dominant part of the vegetation when disturbance occurs after the soil warms to a critical point in the summer.

Dormancy and Germination of Common Ragweed Seeds in the Field

Common ragweed (Ambrosia artemisiifolia) seeds were stored under natural environmental conditions by placing them at three soil levels (surface, 5 cm, and 15 cm) in the field on November 1, 1972. Germination tests at 4-week intervals indicated that dormancy was broken by the end of January. Germination was initially greater at high temperatures, but this difference decreased with increasing time in the field. Secondary dormancy was evident in surface seeds by March 21 but not until April 18 at 5 cm and June 13 at 15 cm. Germination in the field was greatest at the surface but was observed at all soil levels by March 21. Seedling survival was 68% at the surface and 0% at 5 and 15 cm on June 13. Maximum and minimum soil temperatures were recorded at each soil level during the experiment and were correlated with the results. Greater germination and survival at the surface supports the evidence for ragweed's dependence on soil disturbance for germination, and the induction of secondary dormancy explains why ragweed does not constitute a dominant part of the vegetation when disturbance occurs after the soil warms to a critical point in the summer.

Effect of Stratification Temperature and Germination Temperature on Germination and the Induction of Secondary Dormancy in Common Ragweed Seeds

Stratification of common ragweed (Ambrosia artemisiifolia) seeds at 4 C was most successful for breaking dormancy, whereas -5 C was least effective and 10 C was intermediate. Germination in the light exceeded that in the dark at all stratification and germination temperatures. The optimum temperatures for germination in the light were 10/20, 15/25, and 20/30. Maximum germination in the dark occurred at 20/30 C for seeds stratified at 4 and 10 C but the optimum temperatures for seeds stratified at -5 C were 10/20, 15/25, and 20/30. Seeds stratified at -5 and 10 C germinated best after 15 weeks of stratification, whereas 12 weeks of stratification at 4 C resulted in maximum germination. Secondary dormancy was induced in seeds which did not germinate in the dark. This was affected by stratification temperature and duration and germination temperature. The ecological significance of these germination characteristics is discussed.

Relationship between endogenous levels of malic acid and dormancy in grain of Avena fatua L.

The endogenous level of malic acid in grain of Avena fatua L. is inversely correlated with the dormancy of the population. Induction of secondary dormancy by anaerobiosis results in a decrease in the level of malic acid. Imbibing seed incorporate 14CO 2 into malic acid before showing visible signs of germination. Inhibition of germination by continuous white light decreases such 14CO 2 fixation.

THE DORMANCY BEHAVIOR OF AVENA FATUA L. IN CULTIVATED SOIL

Recovery of dormant, non-dormant and dead wild oat seeds and seedling emergence from naturally-infested Regina heavy clay soil was used as a measure of viability during 5 years of consecutive summerfallow subsequent to 13 years of continuous cropping.Percentage viability and dormancy corresponded closely throughout the first summerfallow period. By season’s end 33 per cent of the seeds were viable but mostly dormant. It was concluded that persistence was due primarily to seed dormancy and not lack of germinative conditions.Numerous seedlings emerged the following spring until early June when viability averaged 4 per cent. The potential value of delayed seeding methods of control was indicated clearly at this time. Persistence of seeds in the soil in the second and two succeeding summerfallow years was attributed largely to primary seed dormancy. Lack of moisture and oxygen contributed temporarily. There was little or no evidence of secondary dormancy induction under field conditions. Neither moisture nor oxygen supply appeared to seriously reduce total emergence in adjoining cropland. It was concluded that wild oats could be "grown out" equally well in a 2-year rotation of alternate crop and summerfallow as by means of 2 years of consecutive summerfallow if re-infestation was prevented during the crop year.Inhibition of germination of surface seeds, presumably by light, did not markedly prolong persistence of viable seeds in the soil. No viable seeds were found on the surface after June of the third summerfallow year.Results indicated that a minimum of 5 years is needed to elminate wild oats from heavy clay soils under cultivation.

DORMANCY STUDIES IN SEED OF AVENA FATUA: I. THE POSSIBLE ROLE OF GERMINATION INHIBITORS

When aqueous extracts of hull and caryopsis of Avena fatua are chromatographed, two inhibitory regions can be detected. These two inhibitors appear to be present in the hull and caryopsis in approximately equal amounts per unit weight of tissue. Evidence has been brought forward to show that the inhibitory effect of the hull in intact dormant seeds cannot be ascribed solely to the inhibitors present in the hull, nor does interference with gaseous exchange by this tissue account for its effect. Experiments have shown that isolated caryopses from dormant seeds germinate only when in contact with liquid water. Evidence from several experiments indicates that the hull may prevent leaching of inhibitors from the caryopsis which then allows of germination. It has been shown that inhibitors very readily diffuse out of the caryopsis on moist filter paper and that this process is retarded by the hull. Treatment with high oxygen concentrations, which promotes germination of very dormant seeds, appears to result in a reduction of inhibitor level before visible germination. In the induction of secondary dormancy under anaerobic conditions there is a marked increase in the total inhibitor level of the caryopses.