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 361 records · Page 20Linked to original sources
PubMed2000

Conidial germination in Aspergillus nidulans requires RAS signaling and protein synthesis.

The dormant spores of Aspergillus nidulans become competent for growth and nuclear division in a process called conidial germination. To analyze the molecular details of conidial germination, we developed a genetic screen in which we identified spore germination-deficient mutants that are blocked in this process at the restrictive temperature. These mutants defined eight genes, of which we identified five. Four of the five were directly involved in translation and protein folding, and the fifth showed a high degree of homology to a malonyl CoA synthetase. These results suggest that out of a wide array of processes occurring during conidial germination, translation is essential if germination is to proceed. We also show that conidia containing a mutant-activated form of rasA, the ras homologue in A. nidulans, germinate in the absence of an inducing carbon source, suggesting an important role for rasA signaling in conidial germination. Together these data suggest a model by which a carbon source activates a ras-dependent sensory mechanism, inducing translation and leading to conidial germination. This study shows that conidial germination in A. nidulans requires protein synthesis and that the initiation of translation is linked, through an as yet to be determined signaling cascade that includes rasA, to a carbon-source-sensing apparatus.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1986

Germination of Eucalyptus sieberi L. Johnson seeds. II. Internal water relations.

At 15-20 degrees C, seeds of Eucalyptus sieberi L. Johnson need to maintain a water content equal to 30% or more of dry weight for approximately 60 h in order to germinate. Several shorter periods of imbibition at 30% water content separated by between 6 and 120 h desiccation were as effective as an unintenupted imbibition in bringing seeds to the point of germination. Even after 8 months' desiccation an earlier imbibition shortened the time required for the completion of germination, although it did not hasten the onset of germination. The water potential of seeds sufficiently hydrated to germinate was about -0.6 MPa, whereas that of the embryo was only about -4.5 MPa. The difference was caused by the inhibition of water uptake by the inner integument of the seed coat. During germination, reserve protein in a small group of cells above the collet was hydrolyzed. Subsequent expansion of these cells caused rupture of the inner integument thereby allowing further water uptake by the embryo. The balance of water absorption and evaporative loss by the outer integument was such that most seeds on a moist substrate but exposed to dry air (6.5-8 x 10(-4) MPa) did not maintain the 30% water content necessary for germination. Thus although able to germinate on seedbeds subject to intermittent drying, E. sieberi seeds have the capacity to avoid germination except under humid conditions.

Journal Article↗
PubMed1994

Biology of germinal centers in lymphoid tissue.

Germinal centers in lymphoid tissue are the sites of generation of memory B cells undergoing isotype switching and somatic mutation in their Ig genes. Their formation cannot be induced by stimuli other than immunogenic ones. It seems likely that in the function and possibly also in the formation of germinal centers, one important factor is the localization of immune complexes with fixed complement on the surface of follicular dendritic cells. CD4+ T cells, located primarily in the "apical light zones" of the centers, are necessary for germinal center formation. However, their exact role in the process needs clarification, as both cell to cell contact and cytokine production could be involved at different stages of the germinal center generation. These T cells are usually specific for the antigen inducing the germinal center, but they may sometimes respond to other surface components on the B cell surface. In view of the possible stimulatory role of CD4+ T cells in follicular center-derived lymphomas, the functional significance of these T cells in germinal center proliferation is important to unravel. The B cells in germinal centers proliferate extremely rapidly, especially those located in the "dark zones." Many of them undergo apoptosis, particularly in the "basal light zones." The microenvironment of these centers is well suited to the task of expanding and selecting memory B cells of high affinity for the inducing antigen. The interactions of the proliferating B cells with dendritic cells and T cells, unevenly distributed in the various zones of the germinal center, are thought to determine which cells deserve rescue from apoptosis and induction to differentiation into small resting memory B cells. The memory B cells that emerge from the germinal center bear sIg, usually of "switched" isotype, and exhibit somatic mutations in the variable regions of their rearranged Ig genes.

Aging↗
PubMed1981

Relationship between sporulation medium and germination ability of Mucor racemosus sporangiospores.

Asexual sporangiospores of Mucor racemosus produced on a minimal sporulation medium (M spores) germinated only if glucose, mannose or a complex substrate such as peptone, yeast extract or Casamino acids was present. Once germinated, growth was supported by a wide range of substrates including amino acids, carbohydrates or organic acids. Sporangiospores produced on a nutritionally complex sporulation medium (C-spores) germinated on a wide range of carbon sources. C-spore phenotype was pleiotropic in that sporangiospores capable of germinating on cellobiose could always germinate on glutamate or xylose; but C-spores capable of germinating on xylose or glutamate did not always germinate on cellobiose. There was a hierarchy of substrates capable of initiating germination with glucose = mannose greater than xylose greater than glutamate greater than cellobiose. C-spores also differed from M-spores by initiating germination in the presence of the non-metabolizable glucose analogue 3-O-methylglucose. These results suggest that at least two sporangiospore phenotypes are produced depending upon the concentration and type of ingredients present in the sporulation medium.

3-O-Methylglucose↗
PubMed1984

Stimulation of germination of unactivated Bacillus cereus spores by ammonia.

Inclusion of ammonia in germinant mixtures containing L-alanine and inosine stimulated germination of unactivated Bacillus cereus spores at rates equal to those obtained using heat-activated spores without ammonia. D-Alanine had little effect on germination of heat-activated spores, but severely inhibited germination of unactivated spores in the presence of ammonia. Ammonia did not replace the requirement for either L-alanine or inosine: all three compounds were required for rapid germination. Kinetic analysis suggested that the functions of ammonia and L-alanine were more closely related than the functions of ammonia and inosine. With rate-saturating concentrations of L-alanine and inosine, germination rates showed saturation kinetics for ammonia with a Km for NH4Cl of 5 mM. Comparisons of the effects of salts, amines and pH on germination rates suggested that NH4OH rather than NH+4 was the rate-limiting form of ammonia. In comparisons of various strains of B. cereus, stimulation of germination by ammonia occurred in all cases, although spores of most soil isolates germinated more rapidly than B. cereus T spores in the absence of ammonia.

Alanine↗
PubMed1996

Germin Gene Expression Is Induced in Wheat Leaves by Powdery Mildew Infection.

Germin gene expression is induced in wheat (Triticum aestivum L.) leaves by powdery mildew (Erysiphe graminis f. sp. tritici) infection. Germin is a protein marker for early cereal development and is an oxalate oxidase, an enzyme that catalyzes the conversion of oxalate to CO2 and H2O2. The induction of germin gene expression by powdery mildew infection is consistent with the importance of H2O2 to plant defense and identifies a mechanism for the elevation of H2O2 levels in wheat leaves. Germin mRNA levels increased 2 d after inoculation of seedlings with powdery mildew and continued to increase throughout an 8-d time course. The increase in accumulation of germin mRNA was accompanied by an increase in the germin oligomer, which reached maximal levels by d 6. An increase in oxalate oxidase activity paralleled germin oligomer accumulation. Germin gene expression was induced in a relatively resistant cultivar (Bobwhite) as well as in a susceptible cultivar (Cheyenne), suggesting that the induction of germin gene expression is an indicator of powdery mildew infection rather than cultivar resistance.

Journal Article↗
PubMed1978

Temperature and photocontrol of onoclea spore germination.

Germination of Onoclea sensibilis L. spores is controlled by light and temperature. Temperatures of 30 C can induce maximal germination in the dark to a level of 60 to 95% of that induced by a saturating dose of red light (0.38 joules/square meter) providing the spores are placed at the elevated temperature immediately after being sown. Maximum dark germination occurs with a minimum exposure of 16 to 24 hours at 30 C, suggesting that the temperature treatment is required for the induction of germination rather than for the germination process per se. Interaction of temperature and light for induction of germination shows nonadditive behavior. Germination induced by light and temperature applied consecutively never exceeded that which could be induced by a saturating dose of red light alone. Imbibition of the spores at 25 C in the dark for 12 or more hours prior to incubation at 30 C results in a loss of thermosensitivity. Dose response curves for red light induction of germination after varying times of imbibition at 25 C show no concomitant loss of sensitivity of the spores to red irradiation. This suggests that the mechanism and/or pathway of thermoinduction of germination differs from that of photoinduction. The loss of thermosensitivity as a result of presoaking at 25 C can be prevented if the spores are imbibed at 25 C in osmotic agents such as 0.3 molar mannitol or 0.1 gram per liter of polyethylene glycol 400 or in 0.08% dimethylsulfoxide or 10 micrograms per milliliter of herbicide SAN 9789 (4-chloro-5-(methylamino)-2-(alpha,alpha,alpha-trifluoro-m-tolyl-3-(2H)pyridazinone). The latter two substances are hypothesized to act upon membranes. These results suggest that the degree of hydration and possibly changes in membrane properties play a role in the change in sensitivity of Onoclea spores to temperature.

Journal Article↗
PubMed1978

Effects of ethylene and carbon dioxide on the germination of osmotically inhibited lettuce seed.

Lettuce seeds (Lactuca sativa L.) used in this study germinated 98% at 25 C in light or dark. Their germination was completely inhibited by 0.20 m NaCl, 0.35 m mannitol, or polyethylene glycol 6000 (-7 bars) under continuous light when germination tests were made in Petri dishes. Approximately 50% germination occurred in sealed flasks due to endogenously produced C(2)H(4) and CO(2). Removal of either or both gases prevented germination. In the presence of endogenous CO(2), addition of C(2)H(4) (0.5 to 16 microliters/liter) stimulated 95 to 100% germination (after 5 days) only in the light, but the rate of germination was dependent on C(2)H(4) concentration. At 16 microliters/liter C(2)H(4), full germination occurred within 72 hours. Addition of up to 3.2% CO(2) had no adverse effect on the C(2)H(4) action. Higher concentrations or the complete absence of CO(2) reduced both rate and total germination. CO(2) alone was ineffective.Under these osmotic conditions the promotive effect of C(2)H(4) was under the control of phytochrome.

Journal Article↗
PubMed1988

Dual Effect of Light on the Gibberellin- and Nitrate-Stimulated Seed Germination of Sisymbrium officinale and Arabidopsis thaliana.

Red light (R) has a dual effect on the seed germination of the two related species Arabidopsis thaliana and Sisymbrium officinale. The two species provide different means to separate the light-effects. In S. officinale, stimulation of germination by R depends on the stimultaneous presence of nitrate (light-effect I). The effect of both factors is completely blocked by tetcyclacis, an inhibitor of gibberellin (GA)-biosynthesis. Addition of a mixture of gibberellins A(4) and A(7) (GA(4+7)) antagonizes the inhibition. In the absence of nitrate, R shifts germination to lower GA-requirement (light-effect II). In A. thaliana a similar second light-effect is seen on the GA-requirement of GA-deficient ga-1 mutant seeds. R stimulates germination of wild type seeds in water (light-effect I). For both species, light-effect I shows a fluence threshold value of approximately 10(-5) moles per square meter, which is independent of the nitrate concentration. Increasing nitrate concentrations narrow the fluence-range required for maximal germination whereby the product of nitrate concentration and fluence value determines the germination level, indicating a multiplicative interaction between R and nitrate. Fluence-response curves for light-effect II are similar for both species. Germination occurs in the range of 10(-6) to 10(-2) moles per square meter fluence. The maximal level of germination is determined by the level of dark-germination and light-effect II. Increasing GA(4+7) concentrations induce a shift to lower fluence values. It is shown that in the second effect the co-action of R and exogenous GA(4+7) is clearly additive. It is concluded that light-effect I induces a chain of events leading to GA biosynthesis. Light-effect II seems to enhance the sensitivity of the seeds to GAs.

Journal Article↗
PubMed1999

Latrunculin B has different effects on pollen germination and tube growth.

The actin cytoskeleton is absolutely required for pollen germination and tube growth, but little is known about the regulation of actin polymer concentrations or dynamics in pollen. Here, we report that latrunculin B (LATB), a potent inhibitor of actin polymerization, had effects on pollen that were distinct from those of cytochalasin D. The equilibrium dissociation constant measured for LATB binding to maize pollen actin was determined to be 74 nM. This high affinity for pollen actin suggested that treatment of pollen with LATB would have marked effects on actin function. Indeed, LATB inhibited maize pollen germination half-maximally at 50 nM, yet it blocked pollen tube growth at one-tenth of that concentration. Low concentrations of LATB also caused partial disruption of the actin cytoskeleton in germinated maize pollen, as visualized by light microscopy and fluorescent-phalloidin staining. The amounts of filamentous actin (F-actin) in pollen were quantified by measuring phalloidin binding sites, a sensitive assay that had not been used previously for plant cells. The amount of F-actin in maize pollen increased slightly upon germination, whereas the total actin protein level did not change. LATB treatment caused a dose-dependent depolymerization of F-actin in populations of maize pollen grains and tubes. Moreover, the same concentrations of LATB caused similar depolymerization in pollen grains before germination and in pollen tubes. These data indicate that the increased sensitivity of pollen tube growth to LATB was not due to general destabilization of the actin cytoskeleton or to decreases in F-actin amounts after germination. We postulate that germination is less sensitive to LATB than tube extension because the presence of a small population of LATB-sensitive actin filaments is critical for maintenance of tip growth but not for germination of pollen, or because germination is less sensitive to partial depolymerization of the actin cytoskeleton.

Actins↗
PubMed2005

Effect of mechanical abrasion on the viability, disruption and germination of spores of Bacillus subtilis.

AIMS: To elucidate the factors influencing the sensitivity of Bacillus subtilis spores in killing and disrupting by mechanical abrasion, and the mechanism of stimulation of spore germination by abrasion. METHODS AND RESULTS: Spores of B. subtilis strains were abraded by shaking with glass beads in liquid or the dry state, and spore killing, disruption and germination were determined. Dormant spores were more resistant to killing and disruption by abrasion than were growing cells or germinated spores. However, dormant spores of the wild-type strain with or without most coat proteins removed, spores of strains with mutations causing spore coat defects, spores lacking their large depot of dipicolinic acid (DPA) and spores with defects in the germination process exhibited essentially identical rates of killing and disruption by abrasion. When spores lacking all nutrient germinant receptors were enumerated by plating directly on nutrient medium, abrasion increased the plating efficiency of these spores before killing them. Spores lacking all nutrient receptors and either of the two redundant cortex-lytic enzymes behaved similarly in this regard, but the plating efficiency of spores lacking both cortex-lytic enzymes was not stimulated by abrasion. CONCLUSIONS: Dormant spores are more resistant to killing and disruption by abrasion than are growing cells or germinated spores, and neither the complete coats nor DPA are important in spore resistance to such treatments. Germination is not essential for spore killing by abrasion, although abrasion can trigger spore germination by activation of either of the spore's cortex-lytic enzymes. SIGNIFICANCE AND IMPACT OF THE STUDY: This work provides new insight into the mechanisms of the killing, disruption and germination of spores by abrasion and makes the surprising finding that at least much of the spore coat is not important in spore resistance to abrasion.

Bacillus subtilis↗
PubMed2006

Different signalling pathways involving a Galpha protein, cAMP and a MAP kinase control germination of Botrytis cinerea conidia.

Conidial germination of the grey mould fungus Botrytis cinerea was found to be induced by different chemical and physical signals, namely the amount and quality of nutrients as well as the hydrophobicity and rigidity of the surface. A B. cinerea Deltabcg3 mutant disrupted in the Galpha3 subunit of the heterotrimeric G protein was specifically defective in germination induced by carbon sources. A similar germination defect of an adenylate cyclase mutant, and the complementing effect of cAMP addition to conidia of these mutants confirmed the involvement of cAMP. In contrast, a Deltabmp1 MAP kinase mutant was delayed in carbon source-induced germination, but completely unable to germinate on hydrophobic surfaces. Based on these data, it is proposed that the germination response of B. cinerea conidia is controlled by three signalling pathways: Germination induction by rich media is weakly dependent on BMP1; induction by carbon sources requires BCG3, cAMP and BMP1; and induction by contact to hydrophobic surfaces is absolutely dependent on BMP1. Other defects of the Deltabcg3 mutant, such as low conidiation, excessive formation of sclerotia and delayed host infection, were also restored by cAMP. Microscopical studies of germling growth and differentiation on host cuticles revealed that the delayed infection of the Deltabcg3 mutant was due to a surface sensing defect leading to a reduced penetration. Thus, in addition to their role in germination, Galpha3, cAMP as well as BMP1 are required also for proper host surface recognition and penetration ability of germinated conidia.

Botrytis↗
PubMed1996

Effects of nifedipine, metronidazole, and nitric oxide donors on spore germination and cell culture infection of the microsporidia Encephalitozoon hellem and Encephalitozoon intestinalis.

Two species of microsporidia, Encephalitozoon hellem and Encephalitozoon intestinalis, were isolated from AIDS patients and cultured in green monkey kidney cells. A spore germination assay and a cultured-cell infection assay were used to test the efficacy of candidate antiparasitic agents. The calcium channel blocker nifedipine, metronidazole, and two nitric oxide (NO) donors, S-nitroso-N-acetylpenicillamine and sodium nitroprusside, were tested in the two assays. Nifedipine (10(-8) M) significantly inhibited E. hellem spore germination in three of four germination media. Metronidazole (10(-5) M) inhibited germination weakly and significantly inhibited E. intestinalis germination in a single germination medium. The inhibitory effect of nifedipine and metronidazole used together was greater than the sum of the effects of the drugs used alone in all E. hellem germination assays. The NO donors also inhibited spore germination. The inhibitory effect of nifedipine and metronidazole could be reversed by washing the spores, while that of the NO donors was not reversible. In early cultured-cell infections, both nifedipine (10(-8) M) and metronidazole (10(-5) M) significantly reduced the number of cells being infected. As the infection spread, these agents were less effective. Some inhibition of the spread of the infection was also demonstrated with the NO donors at a concentration (10(-5) M) not obviously toxic to the cultured cells. These data suggest that combination drug therapy targeting spore germination and intracellular parasite development is promising.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Effects of Cellulolytic Ruminal Bacteria and of Cell Extracts on Germination of Euonymus americanus L. Seeds.

In past attempts, the experimental germination of the seeds of Euonymus americanus L. in vitro has had little success. However, treatment of seeds with ruminal fluid containing viable microflora has been successful in stimulating germination. In the presence of the cellulolytic ruminal bacterium, Clostridium cellobioparum ATCC 15832, seeds of E. americanus were stimulated to germinate. Subsequent studies were designed to determine whether the bacterium synthesized a cellulolytic enzyme responsible for initiating germination. The cell-free endocellulase from C. cellobioparum induced germination of the seeds. To support the hypothesis that the endocellulase from C. cellobioparum was responsible for triggering germination, a 1,4-beta-d-glucan glucanohydrolase (EC 3.2.1.4) from Penicillum funiculosum was used to treat the seeds. In addition, no germination was obtained from seeds treated with a commercial exocellulase enzyme. Also, Ruminococcus flavefaciens FD-1 was found to initiate germination of E. americanus seeds. Thus, cellulase activity is indicated in the degradation of the testa of the seed, allowing imbibition and germination.

Journal Article↗
PubMed2004

Transcriptional transitions during Dictyostelium spore germination.

Many protozoa form spores in response to adversity; therefore, spore germination is a key process in their life cycle. Dictyostelium discoideum sporulates in response to starvation following a developmental program. Germination is characterized by two visible changes, spore swelling and the emergence of amoeba from the spore capsule. Several studies have indicated that an additional process termed spore activation is also required, but the physiological changes that characterize the three phases are largely uncharacterized. We used microarrays to monitor global transcriptional transitions as a surrogate measure of the physiological changes that occur during germination. Using two independent methods to induce germination, we identified changes in mRNA levels that characterized the germination process rather than changes that resulted from the induction method. We found that germination is characterized by three transitions. The first transition occurs during activation, while the spores appear dormant, the largest transition occurs when swelling begins, and the third transition occurs when emergence begins. These findings indicate that activation and swelling are not passive occurrences, such as dilution of inhibitors or spore rehydration, but are active processes that are accompanied by dramatic events in mRNA degradation and de novo transcription. These findings confirm and extend earlier reports that genes such as celA are regulated during spore germination. We also found by mutation analysis that the unconventional myosin gene myoI, which is induced during early germination, plays roles in the maintenance of dormancy and in spore swelling. This finding suggests that some of the observed transcriptional changes are required for spore germination.

Animals↗
PubMed1970

Conditions Affecting Germination of Clostridium botulinum 62A Spores in a Chemically Defined Medium.

Spores of Clostridium botulinum type 62A were germinated in a chemically defined medium (8 mm l-cysteine, 11.9 mm sodium bicarbonate, 4.4 mm sodium thioglycolate; buffered with 100 mm TES, pH 7.0). The rate and extent of germination were increased when an aqueous spore suspension was heated sublethally (80 C, 60 min) before addition to the germination medium. Neither sublethal nor lethal doses of gamma radiation had any marked effect on subsequent germination. Maximum germination (>90% in 2 hr) in the defined medium occurred in the pH range of 6.5 to 7.5, at 30 to 37 C, with an l-cysteine level of 8 mm. Increasing l-cysteine to 32 mm increased the rate (over that with 8 mm l-cysteine) but not the extent of germination. The rate and extent of germination increased with NaHCO(3) addition to 8.3 mm, but increasing levels to 11.9 mm had no further effect. For maximum germination, 2.2 mm sodium thioglycolate was required and higher levels (to 8.8 mm) had no further enhancing or inhibitory effect. Under optimal conditions for germination, 97% of the spores had become heat sensitive; 98% had become sensitive to radiation; 88 and 91% had become phase dark and stainable, respectively, and the spore suspension had lost 46% of its initial optical density by 2 hr. Loss of heat resistance preceded loss of radiation resistance, acquisition of stainability, and phase darkening by about 12 min.

Journal Article↗
PubMed1973

Ribonucleic acid and protein synthesis during germination of Myxococcus xanthus myxospores.

Ribonucleic acid (RNA) and protein synthesis during myxospore germination were examined. When RNA synthesis was inhibited more than 90% by either actinomycin D (Act D) or rifampin, germination was prevented. The data were consistent with the interpretation that rifampin did not interfere with protein synthesis in any way other than by inhibition of messenger RNA formation. Act D concentrations as high as 20 mug/ml did not totally inhibit RNA synthesis. In the presence of 8 mug of Act D/ml, germinating myxospores synthesized transfer RNA, 16S RNA, and 23S RNA. Evidence was presented which indicated that messenger RNA was also synthesized early in the germination period both in the presence and absence of 8 mug of Act D/ml. One explanation for the escape synthesis of RNA in germinating myxospores is that Act D exerts a differential effect on the transcription of larger versus smaller cistrons, the latter having a lower probability of binding Act D. We have found that in the presence of 8 mug of Act D/ml, escape RNA synthesis in myxospores was 25% for 23S RNA, 55% for 16S RNA, and more than 90% for 4S RNA. We have shown that germination of myxospores requires both RNA and protein synthesis during the first 25 to 35 min in germination medium. This finding does not support the earlier suggestion by Ramsey and Dworkin that a stable germination messenger RNA is required for germination of the myxospores of Myxococcus xanthus.

Bacteria↗
PubMed1976

Nutritionally defined conditions for germination of Streptomyces viridochromogenes spores.

Spores of Streptomyces viridochromogenes were removed from the surface of solid media with glass beads and suspended in a buffer-detergent solution. Addition of yeast extract and glucose resulted in rapid loss of refractility of the spores. Appearance of germ tubes followed. Germination was accompanied by a decrease in the optical density (OD) of the suspension. The OD decrease was used as an assay for germination. A defined germination medium (DGM) comprised of L-alanine, L-glutamic acid, adenosine, para-aminobenzoic acid, and calcium and magnesium ions provided a germination rate nearly equal to that of complex media. The germination rate was essentially the same if D-alanine and D-glutamate replaced the L-isomers. The optimum pH and temperature for germination were 7.0 and 35 C. Germination was absolutely dependent on the presence of CO2. Spores harvested after growth for longer periods than the usual time (10 days) became less germinable in DGM. The same was observed for spores grown at 37 C as compared with 30 C. Spores incubated in DGM for various time periods before being transferred to a buffer solution did not continue to germinate. Spores harvested after growth of eight species of Streptomyces did not show a decrease in OD when incubated in yeast extract medium. Another strain of S. viridochromogenes did exhibit an OD decrease in the medium. Comparative properties of spores of streptomycetes, fungi, and bacilli are discussed.

Adenosine↗