Participation of GA3, ethylene,NO and HCN in germination of Amaranthus retroflexus L. seeds with various dormancy levels

Amaranthus retroflexus seeds were dormant at 25 °C in the darkness and in the light, and also at 35 °C in the darkness. GA₃ and ethylene partially removed dormancy at 35 °C in the darkness and at 25 °C in the light. Dormancy was removed by 1–5 days of treatment with nitric oxide or cyanide. The effect of NO and HCN was inhibited by cPTIO, thus the effect of HCN was NO dependent. Dry storage for 16 weeks could partially release dormancy only at 35 °C, but not at 25 °C. Dry storage increased the response to light, GA₃ and ethylene. The response to GA₃ and ethylene at 25 °C was enhanced with increasing storage temperature. GA₃, ethylene and nitric oxide could substitute dry storage and stratification in partially dormant seeds.     

Necessity of gibberellin for stimulatory effect of KAR1 on germination of dormant Avena fatua L. caryopses

Avena fatua L. florets (caryopses enclosed by lemma and palea) were partially dormant at 10–20 °C and did not germinate at temperatures outside this range. After-ripening florets at 25 °C for 12 weeks completely removed dormancy. Caryopses (florets without lemma and palea) were able to germinate totally at 20 °C. Karrikinolide (KAR₁) and gibberellic acid (GA₃) applied at 10–25 °C partially or markedly induced germination of dormant florets and caryopses, respectively. Both florets and caryopses were more sensitive to KAR₁ than to GA₃. To obtain similar effects, 1,000 to 10,000 times lower concentrations of KAR₁ than GA₃ were required. After-ripening with time gradually increased sensitivity of caryopses to these regulators. Likewise, after-ripened, non-dormant caryopses were sensitive to KAR₁ and GA₃. Inhibitors of gibberellin biosynthesis, ancymidol, paclobutrazol and flurprimidol inhibited the effect of KAR₁. This inhibition was reversed by GA₃. Caryopses pre-incubated in water with ancymidol or paclobutrazol in the presence or absence of KAR₁ germinated completely but with different rates after transfer to GA₃. KAR₁ probably requires gibberellin biosynthesis to stimulate germination of dormant Avena fatua L. caryopses. Both KAR₁ and GA₃ increased α-amylase, β-amylase and dehydrogenases activities during imbibition before visible germination occurred.     

Responsiveness of Amaranthus retroflexus seeds to ethephon, 1-aminocyclopropane 1-carboxylic acid and gibberellic acid in relation to temperature and dormancy

Dormant Amaranthus retroflexus seeds do not germinate in the dark at temperatures below 35°C. Fully dormant seeds germinate only at 35–40°C whereas non-dormant ones germinate within a wider range of temperatures (15 to 40°C). Germination of non-dormant seeds requires at least 10% oxygen, but the sensitivity of seeds to oxygen deprivation increases with increasing depth of dormancy. 10^–6 to 10^–4 M ethephon, 10^–3 M 1-aminocyclopropane 1-carboxylic acid (ACC) and 10^–3 M gibberellic acid (GA₃) break this dormancy. In the presence of 10^–3 M GA₃ dormant seeds are able to germinate in the same range of temperatures as non-dormant seeds. The stimulatory effect of GA₃ is less dependent on temperature than that of ethephon, while ACC stimulates germination only at relatively high temperatures (25–30°C). The results obtained are discussed in relation to the possible involvement of endogenous ethylene in the regulation of germination of A. retroflexus seeds.Abbreviations ACC 1-aminocyclopropane 1-carboxylic acid - GA₃ gibberellic acid - SD standard deviation     

Tolerance of kikuyu grass to long term salt stress is associated with induction of antioxidant defences

Primary dormancy in A. retroflexus seeds wascompletely broken by dry storage or ethylene treatment and partially removedwith GA₃. Norbornadiene counteracted the dormancy breaking action ofethylene and GA₃. The GA₃ effect was lowered bycobaltous ions. ABA increased the ethylene requirement in primary dormant seeds.Dormant seeds had a similar or different ability to produce ethylene and ACCoxidase in vivo activity than did non-dormant seeds,depending on the period of incubation. Dormant seeds contained less endogenousACC than non-dormant seeds. Thus, ethylene seems to play an essential role inthe release of primary dormancy in A. retroflexus seeds.Ethylene also participates in the release of dormancy achieved by GA₃treatment. The results indicate that both ethylene biosynthesis and action isinvolved in the control of primary dormancy in Amaranthusretroflexus seeds.     

The role of gibberellic acid (GA3) in the removal of dormancy inFraxinus excelsior L. seeds

The seeds ofFraxinus excelsior L. were stratified at 17-20 °C (warm stratification), at 4-6 °C (cold stratification) and at alternating temperature (warm — cold stratification). The seeds subjected to warm stratification only, remained dormant. The seeds stratified only at 4-6 °C germinated gradually during a long period of time. The seeds subjected to warm — cold stratification, however, germinated with great intensity within a relatively short period of time. GA₃ was shown to stimulate the growth of embryos markedly, and its effect on the germination of seeds depended on the temperature of stratification. GA₃ applied during the cold stratification accelerated the removal of dormancy by shortening the period of stratification and by influencing the germination of seeds. The results obtained indicate a similarity between the effect of temperature 17-20 °C during the warm stratification and that of gibberellic acid. Both those factors applied separately affect favourably after-ripening of the embryos and accelerate the germination of seeds.     

Hormonal and temperature regulation of seed dormancy and germination in <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Fluctuating temperature plays a critical role in determining the timing of seed germination in many plant species. However, the physiological and biochemical mechanisms underlying such a response have been paid little attention. The present study investigated the effect of plant growth regulators and cold stratification in regulating Leymus chinensis seed germination and dormancy response to temperature. Results showed that seed germination was less than 2 % at all constant temperatures while fluctuating temperature significantly increased germination percentage. The highest germination was 71 % at 20/30 °C. Removal of the embryo enclosing material of L. chinensis seed germinated to 74 %, and replaced the requirement for fluctuating temperature to germinate, by increasing embryo growth potential. Applications of GA₄₊₇ significantly increased seed germination at constant temperature. Also, inhibition of GA biosynthesis significantly decreased seed germination at fluctuating temperatures depending upon paclobutrazol concentration. This implied GA was necessary for non-dormant seed germination and played an important role in regulating seed germination response to temperature. Inhibition of ABA biosynthesis during imbibition completely released seed dormancy at 20/30 °C, but showed no effect on seed germination at constant temperature, suggesting ABA biosynthesis was important for seed dormancy maintenance but may not involve in seed germination response to temperature. Cold stratification with water or GA₃ induced seed into secondary dormancy, but this effect was reversed by exogenous FL, suggesting ABA biosynthesis during cold stratification was involved in secondary dormancy. Also, cold stratification with FL entirely replaced the requirement of fluctuating temperature for germination with seeds having 73 % germination at constant temperature. This appears to be attributed to inhibition of ABA biosynthesis and an increase of GA biosynthesis during cold stratification, leading to an increased embryo growth potential. We suggest that fluctuating temperature promotes seed germination by increasing embryo growth potential, mainly attributed to GA biosynthesis during imbibitions. ABA is important for seed dormancy maintenance and induction but showed less effect on non-dormant seed germination response to temperature.     

Low-temperature stratification strategies and growth regulators for rapid induction of Paris polyphylla var. yunnanensis seed germination

The seeds of Paris polyphylla var. yunnanensis are deeply dormant, and they remain dormant for 18 months or longer in their natural environment. Periodic exposure of the seeds to a low-temperature of 4 °C broke the dormancy in about 16 weeks (112 days). The most effective temperature stratification scheme was an interval of 14 days at 4 °C and 14 days at 22 °C. Both GA₃ and ethephon significantly enhanced the germination rate during the stratification treatment. The seed coat, particularly the mesophyll outer layer of the seed coat, strongly inhibited the germination. With removal of the seed coat and exposure of the uncoated seeds to 600 mg/l GA₃ for 48 h before the temperature stratification of 14 days at 4 °C and 14 days at 22 °C for 112 days, a germination percentage as high as 95.3% of the seeds was attained in about 160 days.     

Control of seed dormancy in Nicotiana plumbaginifolia: post-imbibition abscisic acid synthesis imposes dormancy maintenance

The physiological characteristics of seed dormancy in Nicotiana plumbaginifolia Viv. are described. The level of seed dormancy is defined by the delay in seed germination (i.e the time required prior to germination) under favourable environmental conditions. A wild-type line shows a clear primary dormancy, which is suppressed by afterripening, whereas an abscisic acid (ABA)-deficient mutant shows a non-dormant phenotype. We have investigated the role of ABA and gibberellic acid (GA₃) in the control of dormancy maintenance or breakage during imbibition in suitable conditions. It was found that fluridone, a carotenoid biosynthesis inhibitor, is almost as efficient as GA₃ in breaking dormancy. Dry dormant seeds contained more ABA than dry afterripened seeds and, during early imbibition, there was an accumulation of ABA in dormant seeds, but not in afterripened seeds. In addition, fluridone and exogenous GA₃ inhibited the accumulation of ABA in imbibed dormant seeds. This reveals an important role for ABA synthesis in dormancy maintenance in imbibed seeds. Received: 31 December 1998 / Accepted: 9 July 1999     

Low temperature, gibberellin and acid lipase activity in removal of apple seed dormancy

The activity of acid lipase and the level of gibberellin A₄ (GA₄) were determined in apple embryos excised from seeds after different time periods of stratification and subsequently cultured in darkness at 4°C or at 25°C. Enzyme activity and GA₄ content were higher at 4°C. Exogenous gibberellin stimulated lipase activity, while AMO-1618, an inhibitor of gibberellin biosynthesis, inhibited, to the same degree, both the enzyme activity and the GA₄ accumulation. The involvement of GA₄ and lipolytic enzymes in cold-mediated removal of embryonal dormancy has been discussed and compared with the role of these two factors in light-stimulated germination of dormant apple embryos, described earlier (Smoleńska and Lewak 1974).     

Triangular interplay between ROS,ABA and GA in dormancy alleviation of <Emphasis Type="Italic">Bunium persicum</Emphasis> seeds by cold stratification

Seeds of Bunium persicum (Boiss.) B. Fedtsch. have complex physiological dormancy that can be released by 15 weeks stratification. The present study revealed that cold stratification enhanced content of H₂O₂, O^{2 -·} and application of GA₃ and ROS donors (Fenton reagent, H₂O₂, methylviologen and menadione) did not affect or only slightly promoted the germination of non-stratified, fully dormant seeds. Dormancy was markedly decreased by ROS-generating reagents, GA₃ and fluridone (an inhibitor of ABA biosynthesis) and was enhanced by ROS-decreasing compounds (DMTU, Tiron, SB and DPI), diniconazole (Dinc, an inhibitor of ABA catabolism) and paclobutrazol (PAC, an inhibitor of GA biosynthesis) when dormancy was partially removed by cold stratification. The response to these compounds reduced with increasing time of stratification. ABA inhibited germination by repressing of NADPH oxidase activity and ROS accumulation and conversely, GA triggered germination by promoting an increase of NADPH oxidase activity and ROS levels. Data in this study, for the first time suggest releasing deep complex physiological dormancy by cold stratification is associated with interplay between ROS and ABA/GA.     

Deep and intermediate complex morphophysiological dormancy in seeds of Ferula gummosa (Apiaceae)

We tested the hypothesis that seeds of the monocarpic perennial Ferula gummosa from the Mediterranean area and central Asia have deep complex morphophysiological dormancy. We determined the water permeability of seeds, embryo morphology, temperature requirements for embryo growth and seed germination and responses of seeds to warm and cold stratification and to different concentrations of GA₃. The embryo has differentiated organs, but it is small (underdeveloped) and must grow inside the seed, reaching a critical embryo length, seed length ratio of 0.65–0.7, before the seed can germinate. Seeds required 9 weeks of cold stratification at <10°C for embryo growth, dormancy break and germination to occur. Thus, seeds have morphophysiological dormancy (MPD). Furthermore, GA₃ improved the germination percentage and rate at 5°C and promoted 20 and 5% germination of seeds incubated at 15 and 20°C, respectively. Thus, about 20% of the seeds had intermediate complex MPD. For the other seeds in the seed lot, cold stratification (5°C) was the only requirement for dormancy break and germination and GA₃ could not substitute for cold stratification. Thus, about 80% of the seeds had deep complex MPD.     

Involvement of phytohormones in germination of dormant and non-dormant oat (Avena sativa L.) seeds

Oat seeds are susceptible to high temperature dormancy. Dormant grainsdo not germinate at 30 °C unless afterripened, dry, for severalweeks. Isolated embryos of dormant grains do germinate, especially ifGA₃ is added to the germination medium. ABA inhibits germinationproportionally to the concentration applied and GA₃ can overcome theABA inhibitory effect. Measurements of endogenous ABA and several GAs revealedthat the initial levels of ABA in dormant and non-dormant grains were quitesimilar. But, endogenous ABA in non-dormant seeds almost disappeared within thefirst 16 h of imbibition, while the amount in dormant grains haddecreased by less than 24%. The level of GA₁₉ in non-dormant seedswas higher, and GA₁₉ appears to be converted to GA₂₀ within the first 16h. The GA₂₀ was converted to GA₁ at leastduring the first 48 h of the germination process. Bothphytohormones thus appear to be involved in the germination process ofnon-dormant seeds. ABA first declines, while GA₁ is producedduring the first 16 h of imbibition to allow proper germination.Indormant grains the level of ABA remained high enough to prevent germinationduring at least a week and precursor GAs were not converted to GA₁.     

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 A₄+A₇ (GA₄₊₇), and to a relatively lesser extent GA₄₊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 GA₄₊₇ in removing the dormancy. Prolonged dark treatment at 29 C seemed to induce changes that were partially independent of light or GA₄₊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.     

Changes in endogenous abscisic acid levels during dormancy release and maintenance of mature seeds: studies with the Cape Verde Islands ecotype,the dormant model of<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

Mature seeds of the Cape Verde Islands (Cvi) ecotype of Arabidopsis thaliana (L.) Heynh. show a very marked dormancy. Dormant (D) seeds completely fail to germinate in conditions that are favourable for germination whereas non-dormant (ND) seeds germinate easily. Cvi seed dormancy is alleviated by after-ripening, stratification, and also by nitrate or fluridone treatment. Addition of gibberellins to D seeds does not suppress dormancy efficiently, suggesting that gibberellins are not directly involved in the breaking of dormancy. Dormancy expression of Cvi seeds is strongly dependent on temperature: D seeds do not germinate at warm temperatures (20–27°C) but do so easily at a low temperature (13°C) or when a fluridone treatment is given to D seeds sown at high temperature. To investigate the role of abscisic acid (ABA) in dormancy release and maintenance, we measured the ABA content in both ND and D seeds imbibed using various dormancy-breaking conditions. It was found that dry D seeds contained higher amounts of ABA than dry ND after-ripened seeds. During early imbibition in standard conditions, there was a decrease in ABA content in both seeds, the rate of which was slower in D seeds. Three days after sowing, the ABA content in D seeds increased specifically and then remained at a high level. When imbibed with fluridone, nitrate or stratified, the ABA content of D seeds decreased and reached a level very near to that of ND seeds. In contrast, gibberellic acid (GA₃) treatment caused a transient increase in ABA content. When D seeds were sown at low optimal temperature their ABA content also decreased to the level observed in ND seeds. The present study indicates that Cvi D and ND seeds can be easily distinguished by their ability to synthesize ABA following imbibition. Treatments used here to break dormancy reduced the ABA level in imbibed D seeds to the level observed in ND seeds, with the exception of GA₃ treatment, which was active in promoting germination only when ABA synthesis was inhibited.Abbreviations ABA Abscisic acid - Cvi Cape Verde Islands - D Dormant - GA Gibberellin - GA₃ Gibberellic acid - ND Non dormant     

Hormonal regulation of tomato seed germination at a supraoptimal temperature

Germination of tomato cv. New Yorker seed is inhibited at 35°C. This thermoinhibition was partially counteracted by application of GA₄₊₇ alone, the compound applied in combination with ACC or ethephon markedly enhancing the process. The latter compound alone was not able to induce germination at 35 °C. Thermoinhibition of seeds at 35 °C was also counteracted by fluridone, an inhibitor of ABA biosynthesis. At 25 °C, an optimal temperature, ABA inhibited germination of New Yorker seeds. Although another known growth inhibitor MeJA, when applied at an optimal temperature (25 °C), had also a slightly inhibitory effect on germination of those seeds and clearly delayed the process, inhibitors of its biosynthetic pathway (ibuprofen, indoprofen, antypiryne and salicylic acid) did not remove thermoinhibition at 35 °C. An increase in endo-β-mannanase activity after 24 hours of incubation at 35 °C was observed in the seeds incubated in the presence of gibberellins, ACC, ethephon, fluridone used alone and in combinations, but it was not clearly correlated with the effects of these compounds on alleviation of seed germination. However, fluridone present in the same incubation medium at 35 °C with ABA was able to counteract the inhibitory effect of ABA on endo-β-mannanase activity. The results of our study suggest that gibberellins, ethylene (produced from ACC or ethephon) and ABA, but not jasmonates, regulate tomato seed germination at supraoptimal temperatures. Alleviation of thermoinhibition of New Yorker seed germination by plant growth regulators and fluridone is partially associated with their controlling endo-β-mannanase activity.     

Germination dimorphism in Suaeda acuminata: A new combination of dormancy types for heteromorphic seeds

Desert annual Suaeda acuminata produces two morphologically distinct types of seeds on the same plant. The main aims of our study were to compare germination characteristics of the dimorphic seeds, ascertain their dormancy types and give the hormonal explanation. The two seed types of S. acuminata absorbed water at different rates with brown seeds imbibing water faster. Germination percentages of brown seeds were significantly higher than those of black seeds in all temperature and light regimes tested. Eight weeks of cold stratification did not break dormancy of black seeds, whereas exogenous GA₃ promoted germination. Excised embryos of untreated black seeds produced normal seedlings. Contents of ZR, GA₃ and ABA of brown seeds were significantly higher than that of black seeds; while contents of IAA of black seeds were significantly higher than that of brown seeds. Brown seeds of S. acuminata are non-dormant, whereas black seeds have intermediate physiological dormancy (PD). Interaction among ZR, ABA and GA₃ may play an important role in dormancy status of both seed types. This is the first report of non-dormancy and intermediate PD in a heteromorphic species.     

Interaction of karrikinolide and ethylene in controlling germination of dormant <Emphasis Type="Italic">Avena fatua</Emphasis> L. caryopses

Caryopses of Avena fatua L. are dormant after harvest and germinate poorly at 20 °C. Dormancy was released by after-ripening the dry caryopses in the dark at 25 °C for 3 months. Karrikinolide (butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one, KAR₁), in contrast to exogenous ethylene and the precursor of ethylene biosynthesis 1-aminocyclopropane-1-carboxylic acid (ACC), completely overcame dormancy. The effect of KAR₁ was not affected by aminoethoxyvinylglycine (AVG), α-aminoisobutyric acid (AIB) and CoCl₂, inhibitors of ACC synthase and oxidase, respectively. 2,5-Norbornadiene (NBD), a reversible inhibitor of ethylene binding to its receptor, counteracted the stimulatory effect of KAR₁. Ethylene, ethephon and ACC counteracted and AVG reinforced inhibition caused by norbornadiene. Inhibition due to norbornadiene, applied during the first 3 days of imbibition in the presence of KAR₁, disappeared after transfer to air or ethylene. The obtained results confirm that KAR₁ breaks dormancy and indicate that ethylene alone plays no role in releasing dormancy of Avena fatua caryopses. KAR₁ probably did not relieve dormancy via the stimulation of ethylene biosynthesis. Some level of endogenous ethylene is probably required for ethylene action, which might be required for releasing dormancy by KAR₁ or for subsequent germination of caryopses after removing dormancy.     

梾木种子低温层积过程中内源激素含量的动态变化特征

应用酶联免疫吸附测定法(ELISA)研究了梾木种子低温层积过程中内源激素含量的动态变化,分析了内源激素与种子休眠与发芽的关系。结果表明:(1)梾木种子中IAA含量在层积处理初期剧烈降低,持续一段时间后又显著升高,但后期下降,且IAA/ABA也出现同样的变化;种子中ABA含量在层积处理前期较高,但随着处理时间的延长趋于下降;种子内GA1/3含量以及GA1/3/ABA均随层积处理时间的延长逐渐增大;种子内ZRs和iPAs含量的变化相对较为平稳,尽管有一定的波动,但整体呈渐趋增高趋势。(2)梾木种子发芽率及发芽势在未经层积处理以及处理时间少于90d的条件下均为0,但随着层积处理时间的延长二者明显上升,层积处理的时间长短对梾木种子萌发有显著影响。(3)相关分析表明,梾木种子内GA1/3含量与种子的发芽率、发芽势均呈显著正相关关系,相关系数分别为0.688、0.662;种子内GA1/3/ABA增大有利于种子休眠解除和萌发。     

Achene germination of the spring ephemeroid species Carex physodes in the Gurbantunggut Desert

Much of the seed germination research on Carex has focused on wetland species, and little is known about the species of arid habitats. Here, we investigated seed dormancy and germination of Carex physodes, which is an important component of the plant community of the Gurbantunggut Desert of the Junggar Basin in Xinjiang, China. Our studies included the effects of mechanical and chemical scarification, dry storage, treatment with GA₃, wet‐cold stratification, and burial in the field. No freshly matured achenes germinated over a range of temperature regimes after treatment with GA₃, 6 months of dry storage or removal of part of the endosperm. The mechanical scarification resulted in < 5% achene germination, however, higher percentage of achene germination occurred after removal of the pericarp (60%), H₂SO₄ scarification (30%) or scarification in 10% NaOH (85%). Six and nine months of wet‐cold stratification promoted < 40% achene germination. The optimal germination temperatures ranged from 25/10°C to 35/20°C. Maximum germination after 9 months of burial at a depth of 3 cm in the field was 36%. These results indicate that the seeds have non‐deep physiological dormancy (PD) and that the pericarp contains germination inhibitors and has strong mechanical resistance to germination.