Physiology of oil seeds: I. Regulation of dormancy in virginia-type peanut seeds

The germination and ethylene production by dormant Virginia-type peanut seeds were observed in relation to phytohormone treatments that could conceivably release the dormancy of these seeds. A comparison was made between the effects of these treatments on the less dormant apical seeds and the more dormant basal seeds. Indole-3-acetic acid did not stimulate ethylene production by, or germination of, the dormant seeds to any extent. Gibberellic acid at 5 × 10⁻⁴ M stimulated ethylene production by apical seeds to 17 millimicroliters per hour and germination to only 40% above the control. The more dormant basal seeds were affected even less by gibberellic acid than the seeds. Ethylene gas at 8 microliters per liter stimulated germination to 85% above the control for both apical and basal seeds. At this ethylene concentration the physiology of the more dormant basal seeds was altered, so that they behaved in a manner similar to the inherently less dormant apical seeds. 2-Chloroethylphosphonic acid at 10⁻³ and 5 × 10⁻⁴ M provided results similar to ethylene gas. Both apical and basal seeds germinated 100% at 48 hours. Among the phytohormones tested in this study, ethylene gas produced the greatest germination at low concentrations, and it appears must directly related to initiating the reactions required for converting the quiescent cells to an active state of growth.     

Carbon Dioxide and Ethylene Control of Spore Germination in Onoclea sensibilis L

Regulation of spore germination in the fern Onoclea sensibilis L. was investigated by applying CO₂ alone and in combination with ethylene. Sterile spores were sown aseptically on Knops solution in loosely capped culture tubes, enclosed individually in 2-liter chambers, and grown under continuous white light. When maintained in enclosed containers with the ethylene-absorbent mercuric perchlorate and with atmospheres enriched up to 2% CO₂ (v/v), spores germinated without any inhibition. Higher levels of applied CO₂ were progressively inhibitory. Inhibition by CO₂ was reversible. When CO₂ was permitted to escape and spores were exposed subsequently to ambient laboratory air, recovery from inhibition occurred within 48 hours. Also, inhibition by CO₂ was specific, since the same degree of inhibition resulted regardless of whether spores were treated with exogenous CO₂ for 48, 72, or 96 hours. The effect on germination of 1 μl/l added ethylene depended upon the amount of applied CO₂. When containers of KOH were enclosed and ambient CO₂ was absorbed, inhibition of germination by 1 μl/l exogenous ethylene was 90%. When CO₂ was applied in concentrations from 0.25 to 1.0% (v/v), CO₂ increasingly antagonized the inhibitory action of 1 μl/l added ethylene. Thus, photoinduced germination of spores was regulated by competitively interacting levels of CO₂ and ethylene.     

Abscisic Acid and Precocious Germination in Soybeans

Immature embryos of soybeans (Glycine max L. Merr.) can be inducedto germinate precociously by depleting the endogenous pool ofabscisic acid (ABA). Washing the embryos or allowing the embryosto dry slowly within or out of detached pods causes a gradualdecline in ABA content. The extent of germination is correlatedwith the length of washing or drying treatments, which in turn,affects the level of endogenous ABA. Providing embryos are threeweeks of age or older, maturation and precocious germinationcan be induced by treating embryos in a way that causes a reductionin embryo ABA content. Drying is not an obligatory requirementfor soybean seed maturation or germination. Key words: ABA, Germination, Embryos     

Effects of ethylene and some other environmental factors on different stages of germination in red root pigweed (Amaranthus retroflexus L.) seeds*

Abstract. Ethylene was found to promote two distinct processes during germination of redroot pigweed (Amarantus retroflexus L.) seeds: embryo expansion that splits the seed coat (incomplete germination), and radicle penetration through the more elastic endosperm (complete germination). The two events can be separated in time by subjecting seeds to low water potential or low CO₂ levels, which arrest germination of some seeds at the incomplete stage. Ethylene applications to incompletely germinated seeds promote complete germination, with a response threshold near 0.02 cm³ m^?3 and saturation near 0.5 cm³ m^?3. Higher ethylene concentrations (0.5 to 50 cm³ m^?3) given during the first day of seed imbibition also increase the percentage of seeds which initiate embryo expansion and split the seed coat. Light and elevated CO₂ also promote radicle penetration of the endosperm in seeds incubated under water stress. The results support the view that the germination pause at the incomplete stage is an adaptation to environmental stresses that can be overcome with exogenous ethylene or certain other stimuli.     

Somatic embryogenesis of holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L.): ethylene production and polyamine content

The production of ethylene and the endogenous content of polyamines (PAs) have been recorded during the early development, maturation and germination of holm oak (Quercus ilex L.) somatic embryos. Ethylene production was high in embryogenic callus, immature somatic embryos and in explants showing secondary embryogenesis, while it was lower in mature and germinating somatic embryos. A higher ethylene production was also associated to the process of secondary embryogenesis. The exogenous application of 1-amino-1-cyclohexane carboxylic acid was not significantly effective on the production of ethylene by holm oak somatic embryos. Total PAs were more abundant in embryogenic callus and in both somatic and zygotic immature embryos, decreasing later on in the mature and germination phases. Immature somatic embryos of holm oak and immature zygotic embryos contain high levels of spermidine (Spd), which decreased during maturation and germination. Spermine (Spm) concentration was lower than that of Spd. Spm was more abundant in embryogenic callus and immature zygotic embryos than in mature embryos. Ethylene production did not seem to interfere with PA metabolism.     

Involvement of ethylene in the action of the cotton defoliant thidiazuron

The effect of the defoliant thidiazuron (N-phenyl-N′-1,2,3-thiadiazol-5-ylurea) on endogenous ethylene evolution and the role of endogenous ethylene in thidiazuron-mediated leaf abscission were examined in cotton (Gossypium hirsutum L. cv Stoneville 519) seedlings. Treatment of 20- to 30-day-old seedlings with thidiazuron at concentrations equal to or greater than 10 micromolar resulted in leaf abscission. At a treatment concentration of 100 micromolar, nearly total abscission of the youngest leaves was observed. Following treatment, abscission of the younger leaves commenced within 48 hours and was complete by 120 hours. A large increase in ethylene evolution from leaf blades and abscission zone explants was readily detectable within 24 hours of treatment and persisted until leaf fall. Ethylene evolution from treated leaf blades was greatest 1 day posttreatment and reached levels in excess of 600 nanoliters per gram fresh weight per hour (26.7 nanomoles per gram fresh weight per hour). The increase in ethylene evolution occurred in the absence of increased ethane evolution, altered leaf water potential, or decreased chlorophyll levels. Treatment of seedlings with inhibitors of ethylene action (silver thiosulfate, hypobaric pressure) or ethylene synthesis (aminoethoxyvinylglycine) resulted in an inhibition of thidiazuron-induced defoliation. Application of exogenous ethylene or 1-aminocyclopropane-1-carboxylic acid largely restored the thidiazuron response. The results indicate that thidiazuron-induced leaf abscission is mediated, at least in part, by an increase in endogenous ethylene evolution. However, alterations of other phytohormone systems thought to be involved in regulating leaf abscission are not excluded by these studies.     

Ethylene-induced Phenylalanine Ammonia-Lyase Activity in Carrot Roots

Ethylene enhanced the activity of phenylalanine ammonialyase in carrot (Daucus carota L., var. “Nauty”) root tissue. Slight increase in enzyme activity was exhibited by root discs incubated in ethylene-free air. It was probably due to the ethylene formed within the sliced tissue. Addition of ethylene to the air stream increased phenylalanine ammonia-lyase activity and the total protein content of the discs until maximum activity was reached after 36 to 48 hours of incubation. The continuous presence of ethylene was required to maintain high level of activity. Ethylene, at a concentration of 10 microliter per liter induced higher activity than at lower or higher concentrations. CO₂ partially inhibited the ethylene-induced activity. Cycloheximide or actinomycin D effectively inhibited the ethylene-induced activity in discs that had not previously been exposed to ethylene. The results appear to support the hypothesis that the mode of action of ethylene may involve both de novo synthesis of the enzyme protein and protection or regulation of activity of the induced enzyme.     

Requirement for the action of endogenous ethylene during germination of non-dormant seeds of Amaranthus caudatus

The role of endogenous ethylene during germination of non-dormant seeds of Amaranthus caudatus L. was investigated. The seeds readily germinated in water and darkness at 24°C. Application of ethylene or of its precursor I-aminocyclopropane-I-carboxylic acid (ACC) slightly increased the rate of germination. Both compounds effectively antagonized osmotic inhibition by polyethyleneglycol. Application of aminoethoxyvinylglycine (AVG) reduced ethylene production by 90% but did not inhibit germination. However, germination was inhibited by 2,5-norbornadiene, a competitive inhibitor of ethylene action. This inhibition was counteracted by ethylene, ethephon or ACC and enforced by AVG. It is concluded that the action of endogenous ethylene is an indispensable factor during germination of non-dormant seeds of A. caudatus. Ethylene action is required from the start of imbibition on. In water, low levels of endogenous ethylene are sufficient for this action. PEG increased the ethylene requirement considerably.     

Regulation of Senescence in Carnation (Dianthus caryophyllus) by Ethylene: Mode of Action

Carnation (Dianthus caryophyllus) flowers were exposed to 2 μl/l ethylene and examined at intervals to determine the time course of wilting, decrease in water uptake, and increase in ionic leakage in response to ethylene. A rapid decrease in water uptake was observed about 4 hours after initiating treatment with ethylene. This was followed by wilting (in-rolling of petals) about 2 hours later. Carbon dioxide inhibited the decline in water uptake and wilting and this is typical of most ethylene-induced responses. Ethylene did not affect closure of stomates. Ethylene enhanced ionic leakage, as measured by efflux of ³⁶Cl from the vacuole. This was judged to coincide with the decrease in water uptake. Gassing flowers with propylene initiated autocatalytic ethylene production within 2.4 hours. Since the increase in ethylene production by carnations preceded the increase in ionic leakage and the decline in water uptake by several hours, it is apparent that the change in ionic leakage does not lead to the initial increase in ethylene production as reported (Hanson and Kende 1975 Plant Physiol 55:663-669) in morning glory but may explain the autocatalytic phase of ethylene production.     

Temperature and water requirements for germination and effects of discontinuous hydration on germinated seed survival in Tillandsia recurvata L.

Tillandsia recurvata is an epiphytic bromeliad with a wide distribution in the Americas; however, little is known about the development of its post-seminal adaptations for survival in epiphytic environments. The purpose of this study was to define the temperature and water requirements for the germination of T. recurvata seeds. The absence of radicle emergence in T. recurvata seeds resulted in 2?stages of germination: swollen with broken seed coat (stage-1) and chlorophyllic embryos (stage-2). The effects of partial or discontinuous hydration on germinated seed survival were also assessed. The seeds were collected in a semi-arid shrubland of Mexico City. We explored: (1) whether water vapour can provide a sufficient water source for germination; (2) the temperature required for germination stage-1 and the optimal and critical osmotic potentials for germination in both germination stages; (3) the effect of seed incubation at different osmotic potentials that undergo subsequent dehydration on their survival in stage-2; and (4) the loss of dehydration tolerance during early post-seminal development. In addition, an image of T. recurvata seed anatomy was obtained to illustrate its structures. Germination stage-1 of T. recurvata seeds is rather similar across the tested temperature range. The seeds required to be in contact with liquid water to germinate. The interval of osmotic potential facilitating both germination stages was from 0 to ?0.6?MPa. Although germinated seeds displayed dehydration tolerance, this tolerance decreased in germination stage-2. The osmotic potential during germination affected the tolerance of the chlorophyllic embryos (stage-2) to subsequent dehydration.     

Characterization of ethylene/gibberellic acid control of germination in Lactuca sativa L.

Ethylene production during germination of lettuce seeds (Lactucasativa L., cv. Premier Great Lakes) occurred at two distinctlydifferent rates. A very low rate of ethylene release was observedprior to the 12th hour of incubation at 22?C. The rate of ethyleneproduction, however, increased 100 fold between the 12th and16th hour of incubation. This high rate of ethylene productiononly occurred in the presence of seeds which exhibited a visibleprotrusion of the radicle. The duration of exposure to a supraoptimaltemperature (32?C) was inversely proportional to the percentgermination at 32?C. Ethylene production and growth were notblocked by incubating visibly germinated seeds at 32?C. Exogenous ethylene partially restored germination at 32?C, butonly in the light. Gibberellic acid partially substituted forthe induced light requirement but not for ethylene. It was concludedthat the supraoptimal temperature raised the threshold concentrationof ethylene required for germination. This threshold requirementwas satisfied in the presence of exogenous ethylene. Germinationat 32?C was abo dependent upon the presence of GA. With exogenousethylene present, the GA-mediated system was presumably reinstatedor bypassed by exposing the seeds to either light or GA. Theinitial low rate of ethylene production apparently regulatessubsequent germination but only when present at a minimum thresholdconcentration. Those events initiating germination have obviouslyoccurred prior to the time of radicle emergence. Post-germinationethylene production, therefore, did not break thermodormancy,but occurred simultaneously with radicle emergence. (Received November 29, 1976; )     

Onset of deoxyribonucleic Acid synthesis in germinating wheat embryos

Germinating wheat embryos (Triticum vulgare var. Florence) synthesize proteins before the onset of DNA synthesis. The onset of DNA replication occurs at about 15 hours of germination and was shown to depend on proteins synthesized before 9 hours of germination with the use of blasticidin S, a specific inhibitor of protein synthesis. A 10-fold increase in the activity of DNA-dependent DNA polymerase was found in extracts derived from germinated embryos, as compared to the activity found in extracts from ungerminated embryos.     

Dormancy removal in apple embryos by nitric oxide or cyanide involves modifications in ethylene biosynthetic pathway

The connection between classical phytohormone-ethylene and two signaling molecules, nitric oxide (NO) and hydrogen cyanide (HCN), was investigated in dormancy removal and germination “sensu stricto” of apple (Malus domestica Borkh.) embryos. Deep dormancy of apple embryos was removed by short-term (3–6 h) pre-treatment with NO or HCN. NO- or HCN-mediated stimulation of germination was associated with enhanced emission of ethylene by the embryos, coupled with transient increase in ROS concentration in embryos. Ethylene vapors stimulated germination of dormant apple embryos and eliminated morphological anomalies characteristic for young seedlings developed from dormant embryos. Inhibitors of ethylene receptors completely impeded beneficial effect of NO and HCN on embryo germination. NO- and HCN-induced ethylene emission by apple embryo was only slightly reduced by inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity during first 4 days of germination. Short-term pre-treatment of the embryos with NO and HCN modified activity of both key enzymes of ethylene biosynthetic pathway: ACC synthase and ACC oxidase. Activity of ACC synthase declined during first 4 days of germination, while activity of ACC oxidase increased markedly at that time. Additional experiments point to non-enzymatic conversion of ACC to ethylene in the presence of ROS (H₂O₂). The results indicate that NO and HCN may alleviate dormancy of apple embryos “via” transient accumulation of ROS, leading to enhanced ethylene emission which is required to terminate germination “sensu stricto”. Therefore, ethylene seems to be a trigger factor in control of apple embryo dormancy removal and germination.     

Seed germination in Chenopodium album L.: further evidence for the dependence of the effects of growth regulators on nitrate availability

Abstract Chenopodium album L. plants, grown under controlled environmental conditions on different levels of soil nitrate, produced seeds with proportionately different NO^?₃ contents. Regardless of the endogenous NO^?₃ content, few seeds germinated in water or upon treatment with KNO₃. Ethylene promoted germination, and the extent of germination was positively correlated with the endogenous seed NO^?₃ content. Combined application of ethylene and KNO₃ in the dark had a synergistic effect on NO^?₃ -deficient seed. The synergism between ethylene and KNO₃ was attributable to the NO^?₃ moiety of the nitrate salt. Ethylene and light showed moderate synergism in seeds with low or high endogenous nitrate. Addition of nitrate, however, masked the interaction between ethylene and light. Gibberellic acid₄₊₇ (GA₄₊₇) or red light, each alone or combined with KNO₃, had little effect on germination. When applied together in the dark, ethylene and GA₄₊₇ synergistically enhanced the germination of NO^?₃-deficient seed. The combined effects of the two hormones on this seed were further enhanced by the addition of KNO₃. There was no synergism between ethylene and GA₄₊₇ in NO^?₃-rich seed. These interactions among GA₄₊₇, ethylene and KNO₃ were not affected by light. The results confirm and further elaborate our earlier finding that the sensitivity of C. album seeds to ethylene may depend on nitrate availability.     

Phase-sequence of redroot pigweed seed germination responses to ethylene and other stimuli

Phase-sequence studies showed that light, ethylene, and high temperature each enhanced germination of redroot pigweed (Amaranthus retroflexus L.) seeds when given during the first 24 hours of seed imbibition. Responses were maximal during the first 12 hours. After 48 hours all three stimuli given together caused 75% germination but each alone was ineffective. The main influence of water potential on seed germination occurred at about 24 hours, but the influence of CO₂ extended into the second and third days. Germination was reduced by water stress (−4 bars) or CO₂-free air, but ethylene reversed the reduction even when administered after several days incubation. This suggested that environmental and hormonal factors affected redroot pigweed seeds at two distinct stages in the sequence of germination events.     

De novo synthesis of 3'-nucleotidase in germinating wheat embryo

The enzyme 3′-AMP nucleotidase was purified 2,500- to 5,000-fold from extracts of an acetone powder of wheat (Triticum aestivum) embryonic axes germinated for 40 hours. Sodium dodecyl sulfate acrylamide gel electrophoresis and chromatography on Biogel-P100 indicate that the enzyme is monomeric with a molecular weight of 39,000. Extracts of embryos germinated up to 6 hours have only 1% of the 40-hour level of enzyme activity. To see if the increase to 40 hours represents de novo synthesis, extracts were compared for their ability to react with a rabbit antibody prepared against the enzyme. In immunodiffusion tests, 40-hour extracts showed a strong precipitin line coincident with that of the purified enzyme, whereas no precipitation was observed with 1-hour extracts. When the enzyme present in 40-hour extracts was partially inactivated by EDTA, it still blocked the ability of the antibody to inhibit enzyme activity. Extracts of 1-hour embryos, in contrast, were not able to block the inhibitory activity of the antibody. Embryos allowed to take up ³⁵SO₄ between 40 and 46 hours of germination synthesized ³⁵S-labeled 3′-nucleotidase. In contrast, no radioactive protein synthesized by embryos during the first 6 hours of germination coincided on gel electrophoresis with the enzyme. These results indicate that the increase in 3′-nucleotidase activity is a consequence of de novo synthesis of the enzyme.     

Ethylene Inhibition of Phytochrome-Induced Germination in Potentilla norvegica L. Seeds

Germination of Potentilla norvegica L. (rough cinquefoil) seeds stimulated by fluorescent irradiations of nearly 24 hours was inhibited by ethylene at <1 microliter per liter. Sensitivity to ethylene inhibition was highest during and immediately after the irradiation. By delaying ethylene treatment until about a day after the light potentiation, seeds escaped the inhibition. Ethylene inhibition may be readily reversed upon release of the gas and reirradiation of the seeds. Imbibition of seeds at 10 or 15°C, or at high temperatures of 35 and 40°C, partially prevented subsequent inhibition by ethylene. Alternating temperatures during germination nearly overcame the inhibition from 1 microliter per liter ethylene, but not higher doses. With brief red-irradiation and alternating temperatures, 0.1 microliter per liter ethylene promoted germination about 2-fold. These data suggest that ethylene may loosely associate on a site required for phytochrome action. The effect of temperature that opposed the inhibition may be to deny the association of ethylene with the site. Loose association is supported by the reversal of inhibition by gas release and increased temperature during germination. A blocking effect was shown by the failure of phytochrome to act when ethylene was present.     

Ethylene, seed germination, and epinasty

Ethylene activity in lettuce seed (Lactuca satina) germination and tomato (Lycopersicon esculentum) petiole epinasty has been characterized by using heat to inhibit ethylene synthesis. This procedure enabled a separation of the production of ethylene from the effect of ethylene. Ethylene was required in tomato petioles to produce the epinastic response and auxin was found to be active in producing epinasty through a stimulation of ethylene synthesis with the resulting ethylene being responsible for the epinasty. In the same manner, it was shown that gibberellic acid stimulated ethylene synthesis in lettuce seeds. The ethylene produced then in turn stimulated the seeds to germinate. It was hypothesized that ethylene was the intermediate which caused epinasty or seed germination. Auxin and gibberellin primarily induced their response by stimulating ethylene production.     

GROWTH REGULATION BY ETHYLENE IN FERN GAMETOPHYTES. V. ETHYLENE AND THE EARLY EVENTS OF SPORE GERMINATION

Early events during the germination of spores of the fern Onoclea sensibilis were studied to determine the time during germination when ethylene had its greatest inhibiting effect. Water imbibition by dry spores was rapid and did not appear to be inhibited by ethylene. During normal germination DNA synthesis occurred about four hours before the nucleus moved from a central position to the spore periphery. Following nuclear movement, mitosis and cell division occurred, partitioning the spore into a small rhizoid cell and a large protonemal cell. Cell division was complete approximately six hours after nuclear movement. Ethylene treatment of the spores blocked DNA synthesis, nuclear movement, and cell division. The earliest DNA replication in uninhibited spores was observed after 14 hours of germination, and the maximal rate of spore labeling with ³H-thymidine was between 16 and 20 hours. Spores were most sensitive to ethylene, however, during the stages of germination prior to DNA synthesis, and it was concluded that ethylene did not directly inhibit DNA replication but blocked germination at some earlier fundamental step. The effects of ethylene were reversible. since complete recovery from inhibition of germination was possible if ethylene was released and the spores were kept in light. Recovery was much slower in darkness. It was hypothesized that light acted photosynthetically to overcome the ethylene inhibition of germination. Consistent with this, it was shown that spores exhibit net photosynthesis after only two hours of germination.     

Asymbiotic seed germination and in vitro seedling development of Cymbidium aloifolium (L.) Sw.: a multipurpose orchid

Cymbidium aloifolium is a multipurpose economically important epiphytic orchid grows on tree trunk in the primary forests. Its population in natural habitat is downsized due to different anthropogenic activities. A successful attempt was made for asymbiotic immature embryo culture and in vitro mass scale production of plantlets. For successful culture initiation seed pods of various developmental ages, various nutrient media, sucrose concentrations, different quality and quantity of plant growth regulators were surveyed. Immature embryos of 9 months after pollination was successfully germinated on MS medium containing sucrose (2%) (w/v) and α-naphthalene acetic acid (NAA) and benzyl adenine (BA) (3 and 6 μM respectively in combination) within 45 days of culture where 90% germination was recorded. The germinated seeds formed PLBs on the optimum germination medium within two passages. The protocorm like bodies (PLBs) differentiated into rooted plantlets within 3 weeks on regeneration medium containing sucrose (3%), casein-hydrolysate (0.1 gl^?1) and BA 3 μM. Amongst the three media studied, optimum regeneration was registered on MS medium where as many as 12 shoot buds developed per explants per subculture of 4 weeks duration. The well rooted plantlets of 6–7 cm long with 3–4 roots were hardened in vitro 3–4 weeks before they were transferred to potting mix. The potted plants were exposed to full sunlight periodically and watered at regular interval. About 70–80% transplants survived after 2 months of potting.