Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Germination”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed1993

In situ studies of the primary immune response to (4-hydroxy-3-nitrophenyl)acetyl. III. The kinetics of V region mutation and selection in germinal center B cells.

In the murine spleen, germinal centers are the anatomic sites for antigen-driven hypermutation and selection of immunoglobulin (Ig) genes. To detail the kinetics of Ig mutation and selection, 178 VDJ sequences from 16 antigen-induced germinal centers were analyzed. Although germinal centers appeared by day 4, mutation was not observed in germinal center B cells until day 8 postimmunization; thereafter, point mutations favoring asymmetrical transversions accumulated until day 14. During this period, strong phenotypic selection on the mutant B lymphocytes was inferred from progressively biased distributions of mutations within the Ig variable region, the loss of crippling mutations, decreased relative clonal diversity, and increasingly restricted use of canonical gene segments. The period of most intense selection on germinal center B cell populations preceded significant levels of mutation and may represent a physiologically determined restriction on B cells permitted to enter the memory pathway. Noncanonical Ig genes recovered from germinal centers were mostly unmutated although they probably came from antigen-reactive cells. Together, these observations demonstrate that the germinal center microenvironment is rich and temporally complex but may not be constitutive for somatic hypermutation.

Animals↗
PubMed1999

The Effects of Temperature and Seasonal Change on the Germination of Two Salt Marsh Species, Atriplex prostrata and Salicornia europaea, along a Salinity Gradient.

The purpose of this study was to determine whether seasonal temperature changes interact with salinity concentration to inhibit germination. Flooding of a marsh may also influence the size of the seed bank. Soil cores (6.0 cm diameterx7.5 cm deep) were collected from four salt marsh zones in Rittman, Ohio. Salt was most concentrated at the innermost zone, which contained almost exclusively Salicornia europaea, and least concentrated at the outermost zone, which contained mainly Hordeum jubatum and Atriplex prostrata. Soil cores were collected during April, June, and October 1996 and were placed in temperature treatments of 5 degrees /15 degrees C, 5 degrees /25 degrees C, 15 degrees /25 degrees C, and 25 degrees /35 degrees C (dark/light). Seeds were germinated for 8-10 wk, and the seeds that did not germinate were counted from a 2.2-cm-diameter subsample. Results demonstrated that for both S. europaea and A. prostrata, the total number of seeds that germinated decreased throughout the growing season. The number of ungerminated seeds decreased throughout the year for A. prostrata, but for S. europaea, the number of ungerminated seeds increased from April to June and then decreased from June to October. For both species, the ratio of germinated to total seeds decreased from April to June and increased from June to October. Over the growing season and in all salinity zones, the 5 degrees /25 degrees C temperature treatment was the most stimulatory to seed germination. We suspect that a flooding event in June that killed the standing vegetation may have reduced soil salinity and allowed more seeds than usual to germinate, thus effectively eliminating the S. europaea seed bank. Thus, seed banks play a significant role in these salt marsh habitats by providing a new source of seeds for the establishment of later cohorts after flooding or salt stress eliminates an early cohort of seedlings.

Journal Article↗
PubMed1992

Effects of acidity and detergent on in vitro pollen germination and tube growth in forest tree species.

The presence of 1 to 3 mg 1(-1) sodium dodecylbenzensulfonate detergent, or a growth medium pH of 4.0-5.0, inhibited pollen germination and pollen tube elongation more in broad-leaved trees than in conifers. In the broad-leaved species, pollen germination and pollen tube elongation showed similar sensitivities to detergent and acidity, whereas in the conifers, pollen tube elongation was more sensitive than pollen germination to detergent and acidity. Although the germination percentage was low, conifer pollen germinated in the presence of detergent concentrations up to 15 mg l(-1) and at acidities as low as pH 2.5 or 3.0. Pollen germination of most broad-leaved species was completely inhibited in the presence of detergent concentrations of more than 3-5 mg l(-1); the only exceptions were some entomophilous species (e.g., Salix caprea L.) in which the ability of the pollen to germinate in high pollutant concentrations could be related to the presence of tryphyne.

Journal Article↗
PubMed1977

Sterol metabolism during germination of conidia of Aspergillus fumigatus.

The sterol content of germinating conidia of the opportunistic pathogenic fungus Aspergillus fumigatus has been correlated with germination phase and sensitivity to polyene antibiotics. The sterol and sterol ester contents of walls did not change during germination. The sterol ester content of membranes and cell sap remained constant during germination, whereas the sterol content increased during the outgrowth of germ tubes. On the basis of differential extraction studies it was concluded that the loss of resistance to polyenes that occurred in the early stages of swelling of conidia during germination was not due to a movement of sterol or sterol ester out of the wall. Radioactive-labelling experiments demonstrated that, although the amounts of conidial wall sterol and sterol ester did not change during germination, they were metabolically active. Changes in the turnover rate of wall and membrane sterol and sterol ester during germination were investigated and their relationship to a possible mechanism for the change from resistance to sensitivity to polyene antibiotics is discussed.

Antifungal Agents↗
PubMed1981

Involvement of adenosine 3':5'-cyclic monophosphate in the germination of blastospores of Candida albicans.

The germination of blastospores of Candida albicans is accompanied by a rise in the intracellular concentration of adenosine 3':5'-cyclic monophosphate (cyclic AMP). Germination was induced either by peptides isolated from seminal plasma or by an amino acid mixture, and both germination and the rise in cyclic AMP required a temperature of 37 degrees C. The rise occurred during the first hour of incubation, but full germination required a temperature of 37 degrees C for 4 h. Germination and the rise in cyclic AMP, in the presence of suboptimal concentrations of inducers, were stimulated by theophylline. Pre-incubation of cells with dithiothreitol in the absence of inducers inhibited subsequent germination but not the rise in cyclic AMP. Germination and the rise in cyclic AMP were inhibited if dithiothreitol or N-succinimidyl-3-(4-hydroxyphenyl)propionate was present during the induction period.

Bucladesine↗
PubMed1991

The possible involvement of trypsin-like enzymes in germination of spores of Bacillus cereus T and Bacillus subtilis 168.

Germination of spores of Bacillus cereus T and Bacillus subtilis 168 was inhibited by the trypsin inhibitors leupeptin and tosyllysine chloromethyl ketone (TLCK) and by the substrates tosylarginine methyl ester (TAME), benzoyl-L-arginine-p-nitroanilide (L-BAPNA) and D-BAPNA. Potencies of these inhibitory compounds were estimated by finding the concentration which inhibited 50% germination (ID50), as measured by events occurring early (loss of heat resistance), at an intermediate stage [dipicolinic acid (DPA) release], and late in germination (decrease in optical density). In B. cereus T, all the compounds inhibited early and late events with the same ID50. In B. subtilis, TAME inhibited early and late events at the same ID50, but all other inhibitors had a lower ID50 for late events than for early events. This suggests that a trypsin-like enzyme activity is involved at two sequential stages in the germination of B. subtilis spores, one occurring at or before the loss of heat resistance and one at or before the decrease in optical density. Different trypsin-like activities were detected in broken dormant spores and germinated spores of B. cereus T and in germinated spores of B. subtilis by means of three chromogenic substrates: benzoyl-L-phenylalanyl-L-valyl-L-arginine-p-nitroanilide (L-PheVA), L-BAPNA and D-BAPNA. Separation of extracts of germinated spores on non-denaturing polyacrylamide gels showed that in both species the substrates were hydrolysed by three distinct enzymes with different electrophoretic mobilities. The three enzymes had different Ki values for the above inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine↗
PubMed1999

Real-time monitoring of Bacillus subtilis endospore components by attenuated total reflection Fourier-transform infrared spectroscopy during germination.

Chemical changes of particular Bacillus subtilis spore components were monitored by attenuated total reflection Fourier-transform infrared spectroscopy (ATR/FTIR) during spore germination on a ZnSe internal reflection element. Within minutes of the initiation of spore germination, significant changes in the amount of calcium dipicolinate (DPA-Ca) and proteins were noted in the wild-type strain. The changes in a germination mutant (strain 1G9, gerD) were similar to those in the wild-type strain, but the rates of change were slower. The changes in another germination mutant (strain 1G7, gerA) were very different from those in the first two strains: germination was slow and incomplete, and proteins and DPA-Ca remained unaltered throughout the course of the germination study. This technique thus offers a sensitive and non-destructive method for real-time monitoring of various cellular components during spore germination.

Bacillus subtilis↗
PubMed1992

The Effect of 5OH-1,4-Naphthoquinone on Norway Spruce Seeds during Germination.

The effect of 5-OH-1,4-naphthoquinone (5OH-NQ), a known inhibitor of germination and growth and an inducer of oxidative stress, on seeds from Norway spruce (Picea abies) during germination was studied. 5OH-NQ was activated by homogenate from seeds to reactive species that reduce oxygen to superoxide radicals in vitro. Increasing concentrations of 5OH-NQ increased lipid peroxidation during this activation. Small effects of 5OH-NQ on germination of seeds were observed at concentrations up to 200 mum. However, higher concentrations, e.g. 500 and 1000 mum, exerted more pronounced effects on seeds. These results suggest that the effect of 5OH-NQ was a delay rather than an inhibition of germination. However, the effect of 5OH-NQ on postgerminative growth was more potent than that on germination, and higher concentrations inhibited growth >97%. These results suggest that the seeds have a very effective defense system against quinone and reactive oxygen species, since the small effects of 5OH-NQ on germination and postgermination at concentrations up to 200 mum can be explained by the formation of a metabolite of 5OH-NQ that is not as reactive with oxygen as the original quinone. The 5OH-NQ metabolite collected during germination experiments showed differences in its absorption spectrum in comparison with 5OH-NQ, which suggest changes in structure. This metabolite was reduced by quinone reductase, but reduction of oxygen to superoxide radicals was not detected during its activation with homogenate from seeds. This metabolite may arise via a conjugation reaction, since the addition of 500 mum uridine 5'-diphosphoglucuronic acid or 3'-phosphoadenosine-5'-phosphosulfate to the incubation mixture during activation of this metabolite by homogenate from seeds in vitro inhibited reduction of oxygen to superoxide radicals by 50 and 64%, respectively. The constitutive levels of superoxide dismutase and catalase were sufficient to prevent oxygen toxicity during activation of 5OH-NQ, since these enzymes were not induced when the seeds were treated with 200 mum 5OH-NQ.

Journal Article↗
PubMed1972

Phytochrome Control of Germination of Rumex crispus L. Seeds Induced by Temperature Shifts.

High germination of curly dock (Rumex crispus L.) seeds is evident after suitable imbibition and temperature shift treatment, but germination at constant temperatures fails without an input of far red-absorbing form of phytochrome. Preliminary imbibitions at high temperatures (30 C) sharply reduce germination induced by temperature shifts. High germination may be restored by low energies of red radiation, or by brief far red adequate for the photosteady state. Prolonged far red during imbibition also nullifies temperature shift-induced germination. After prolonged far red, high germination may be restored by red radiation of an energy dependent upon the duration of the far red treatment. The evidence supports the conclusion that dark germination induced by temperature shifts arises from the interaction of pre-existent far red-absorbing form of phytochrome in the mature seeds with the temperature shift.

Journal Article↗
PubMed1976

Respiratory Transition during Seed Germination.

Experiments with germinating seeds of Wayne soybean (Glycine max Merr.) show that between the 4th and the 8th hour of germination, respiration experiences a transition from predominantly "alternate" respiration, which is sensitive to salicylhydroxamic acid, to a cyanide-sensitive respiration. The dependence of early germination stages on alternate respiration is reflected in several types of seed functions, including subsequent root growth rate, chlorophyll synthesis, and germination itself. The early period of germination is shown to require a normal O(2) tension, which is no longer a requirement at later stages. The changing sensitivity to cyanide and to salicylhydroxamic acid is found to be common to seven different types of germinating seeds. It is proposed that the alternate pathway of respiration provides something essential for the completion of the earliest stages of seed germination.

Journal Article↗
PubMed1976

Promotive effects of organic solvents and kinetin on dark germination of lettuce seeds.

Significant promotion in dark germination was observed when Grand Rapids lettuce (Lactuca sativa L.) seeds were soaked in acetone or dichloromethane, vacuum-dried, and imbibed at 25 C. Permeation of kinetin via these organic solvents further enhanced the dark germination. Those seeds that were affected by acetone and acetone-kinetin treatments and germinated in the dark escaped red-far red photocontrol of germination. Although abscisic acid was not detected in the organic solvent leachates, they did contain other inhibitory substances affecting lettuce seedling growth. In the light, acetone and acetone-kinetin treatments also enhanced the rate of germination and the increased germination by acetone-kinetin treatment was correlated with increased polyribosome formation. The possible mechanisms involved in promotion of lettuce seed germination by organic solvents and kinetin are discussed.

Journal Article↗
PubMed1980

Studies of the Mechanism of Enhancement of Phytochrome-dependent Lettuce Seed Germination by Prechilling.

Temperature and kinetic studies were performed to examine the mechanism by which prechilling stimulates phytochrome-dependent seed germination in lettuce, Lactuca sativa, L. cv. Grand Rapids. Imbibed seeds were given a short far red irradiation and one day of dark incubation at 20 C to establish very low levels of the far red-absorbing form of phytochrome-(Pfr). Germination was greatly stimulated by subsequent prechilling treatments when they were followed by a second short far red irradiation. Prechilling therefore increased germination sensitivity to the low, normally inhibitory Pfr levels established by far red irradiation. This sensitivity increased with lowered prechilling temperature to a maximum near 4 C. It was linearly dependent upon duration of prechilling at 4 C up to a near maximal response at 10 hours, and it decayed in a converse manner when seeds were returned to 20 C after 10 hours at 4 C. Prechilling also increased germination responses to subsequent periods of high levels of Pfr which were initiated by red and terminated by far red irradiations. High Pfr periods adequate to promote the germination of unchilled seeds produced sharp inflections at 18 C in the dependence of germination on prechilling temperature. Rates of phytochrome potentiation of germination were not affected by prechilling. The response to prechilling fit a mechanism involving homeoviscous adaptation of membrane lipids to temperature.

Journal Article↗
PubMed1984

Precocious Germination during In Vitro Growth of Soybean Seeds.

Immature Glycine max (L.) Merrill seeds were grown and matured in liquid medium at 25 degrees C under fluorescent light. In standard medium containing minerals, 146 millimolar sucrose and 62.5 millimolar glutamine (osmolality 0.24), precocious germination seldom occurred with a starting seed size of less than 300 milligrams fresh weight. Frequency of precocious germination increased with increased starting seed size. Sucrose concentration strongly affected precocious germination while glutamine concentration had no effect. Starting with 300 to 350 milligrams fresh weight seeds, treatments which reduced the sucrose concentration or lowered the osmolality of the culture medium stimulated precocious germination, and increased the fresh weight growth but not the dry weight growth of seeds. Increasing the osmolality to 0.38 with sucrose or mannitol prevented precocious germination without reducing dry weight accumulation in seeds. In medium with initially low osmolality, precocious germination was inhibited by addition of 1 to 100 micromolar abscisic acid to the medium without a reduction in seed growth. During growth and maturation of large soybean seeds in vitro, precocious germination and other abnormal tissue growth can be prevented by high sucrose or mannitol concentrations in the medium or by addition of abscisic acid.

Journal Article↗
PubMed1987

Photoinduced Seed Germination of Oenothera biennis L: II. Analysis of the Photoinduction Period.

The photoinduction period of Oenothera biennis L. seed germination was analyzed by varying the photoinduction temperature and by substituting red light pulses for continuous red light. At 24 degrees C, seeds require 36 hours of continuous red light for maximal percent germination. The optimal photoinduction temperature is 32 degrees C, with higher and lower temperatures being strongly inhibitory. A 30 minute exposure to far-red light, given immediately after a red light period of 1 to 36 hours, reduces germination by about 25%. Seeds escape from far-red inhibition with a half-time of 5 to 10 hours, depending on the length of the red exposure that precedes the far-red light. Periodic 15 minute pulses of red light can substitute for continuous red light in stimulating germination. Ted red light pulses, with 6 hours of darkness between successive pulses, cause maximal germination. The response to periodic red light is fully reversible by far-red light. Probit analysis of the periodic light response shows that as the length of the dark periods between successive pulses increases, less incident light is needed to induce germination but the population variance in light sensitivity remains constant. Probit analysis of the temperature response shows that as the photoinduction temperature increases from 16 to 32 degrees C, less incident light is needed to induce germination and the population variance in light sensitivity also increases.

Journal Article↗
PubMed1988

Synergistic enhancement of ethylene production and germination with kinetin and 1-aminocyclopropane-1-carboxylic Acid in lettuce seeds exposed to salinity stress.

Relief of salt (0.1 molar NaCl) stress on germination of lettuce (Lactuca sativa L., cv Mesa 659) seeds occurred with applications of 0.05 millimolar kinetin (KIN) and 1 to 10 millimolar 1-aminocyclopropane 1-carboxylic acid (ACC). Treatment with KIN enhanced the pregermination ethylene production under saline condition. A synergistic or an additive enhancement of pregermination ethylene production and germination occurred under saline condition in the presence of KIN and a saturating dose (10 millimolar) of ACC. No KIN-ACC synergism was noted in ethylene production or germination under nonsaline condition. Addition of 1 millimolar aminoethoxyvinylglycine (AVG) inhibited the KIN-enhanced pregermination ethylene production (85 to 89%) and germination (58%) under saline condition but not the synergistic effect of KIN + ACC on ethylene production. Under nonsaline condition, AVG had no effect on germination even though ethylene production was strongly inhibited. Alleviation of salt stress by KIN was inhibited in a competitive manner by 2,5-norbornadiene (NBD) (0.02-0.2 milliliter per liter), and the addition of ACC and/or ethylene reduced this inhibition. An increase in the pregermination ethylene production and germination occurred also by cotylenin E (CN) under saline condition. However, neither AVG (1 millimolar) nor NBD (0.02 to 0.2 milliliter per liter) prevented the relief of salt stress by CN. Thus, KIN may alleviate salt stress on germination by promoting both ACC production and its conversion to ethylene. Rapid utilization of ACC may be the basis for the synergistic or the additive effect of KIN plus ACC. The need for ethylene production and action for the relief of salt stress is circumvented by a treatment with CN.

Journal Article↗
PubMed1989

Control processes in the induction and relief of thermoinhibition of lettuce seed germination : actions of phytochrome and endogenous ethylene.

Germination of lettuce seeds (Lactuca sativa L. cv Grand Rapids) in the dark was nearly 100% at 20 degrees C but was inhibited at 27 degrees C and higher temperatures (thermoinhibition). A single 5-minute exposure to red light completely overcame the inhibition at temperatures up to 28 degrees C, above which the effectiveness of single light exposures gradually declined to reach a negligible level at 32 degrees C. However, the promotive effect of light could be extended to 34 degrees C by repeated irradiations. At any one temperature, increased frequency of irradiations increased germination percentage, and with each degree increase in temperature, increasingly frequent irradiations were necessary to elicit maximal germination. Loss of the effectiveness of single irradiations with increase in temperature may result either from acceleration of the thermal reversion of the far red-absorbing form of phytochrome or decrease in seed sensitivity toward a given percentage of the far red-absorbing form of phytochrome. Using continuous red light to induce germination, the role of endogenous C(2)H(4) in germination at 32 degrees C was studied. Ethylene evolution from irradiated seeds began to increase 2 hours prior to radicle protrusion, whereas the dark-incubated (nongerminating) seeds produced a low, constant amount of C(2)H(4) throughout the 24 hour incubation period. Inhibition of C(2)H(4) synthesis with 2-aminoethoxyvinyl glycine and/or inhibition of C(2)H(4) action with 2,5-norbornadiene blocked the promotive effect of light. Exogenous C(2)H(4) overcame these blockages. The results showed that participation by endogenous C(2)H(4) was essential for the light-induced relief of thermoinhibition of lettuce seed germination. However, light did not act exclusively via C(2)H(4) since exogenous C(2)H(4) alone in darkness did not promote germination.

Journal Article↗
PubMed1990

Seed Development in Phaseolus vulgaris L. cv Seminole: II. Precocious Germination in Late Maturation.

Seeds of Phaseolus vulgaris L. cv Seminole in late maturation phase germinated precociously in vitro. Germination occurred in the absence of free water after 5 days but within 24 to 48 hours in contact with water. Excised axes germinated within 12 hours and embryos by 48 hours only if supplied with water. Ethylene accelerated the germination of seeds and embryos irrespective of water availability. There was no effect of ethylene on the rate of axis germination. Ethylene was equally effective within the range 0.5 to 1000 parts per million and 1 hour exposure was fully effective. Induction of precocious germination in vivo was observed by manipulating water content inside pods or by ethylene injection, whether pods were attached to the parent plant or not. These results demonstrate the importance of endogenous regulation of water supply in suppressing precocious germination. Ethylene is identified as a powerful antagonist to the natural control.

Journal Article↗
PubMed1990

A water relations analysis of seed germination rates.

Seed germination culminates in the initiation of embryo growth and the resumption of water uptake after imbibition. Previous applications of cell growth models to describe seed germination have focused on the inhibition of radicle growth rates at reduced water potential (Psi). An alternative approach is presented, based upon the timing of radicle emergence, to characterize the relationship of seed germination rates to Psi. Using only three parameters, a ;hydrotime constant' and the mean and standard deviation in minimum or base Psi among seeds in the population, germination time courses can be predicted at any Psi, or normalized to a common time scale equal to that of seeds germinating in water. The rate of germination of lettuce (Lactuca sativa L. cv Empire) seeds, either intact or with the endosperm envelope cut, increased linearly with embryo turgor. The endosperm presented little physical resistance to radicle growth at the time of radicle emergence, but its presence markedly delayed germination. The length of the lag period after imbibition before radicle emergence is related to the time required for weakening of the endosperm, and not to the generation of additional turgor in the embryo. The rate of endosperm weakening is sensitive to Psi or turgor.

Journal Article↗