Role In Germination Research Articles

The effect of sunlight on allergen release from spores of the fungus Alternaria

Airborne fungal spores are known carriers of allergen. Correlations between spore counts and allergen concentrations are poor. It is known that germination increases allergen release, implicating spore viability as a determinant of allergen release. During aerial dispersal, spores can be exposed to prolonged periods of ultraviolet (UV) light which can reduce viability of spores. We examined the relation between spore viability and allergen release in two experiments: firstly spores from culture were treated with a UV wavelength of 254 nm (not present in sunlight reaching the earth's surface) or autoclaved, and secondly, spores were exposed to simulated sunlight over three days. In both studies viability was measured (by germination on agar and by metabolic activity with nitro-blue tetrazolium vital stain) and allergen release by the Halogen immunoassay. The UV light reduced the proportion of spores able to germinate but did not affect metabolic activity or allergen release. Autoclaving reduced the proportion of spores releasing allergen by half (p<0.0001). Three days' exposure to simulated sunlight correlated negatively with spore germination and metabolic activity (p<0.0001), but did not affect allergen release (p=0.799). In conclusion, simulated sunlight reduced the metabolic activity and germinability of spores however the proportion releasing allergen remained unaffected. These findings suggest that spore counts may reflect allergen concentrations in the air if spores are dead or dormant. The contribution of viable spores to concentrations of airborne allergen, as well as the role of germination in allergen delivery to the respiratory tract, remains to be resolved.

Arabidopsis actin gene ACT7 plays an essential role in germination and root growth.

Arabidopsis contains eight actin genes. Of these ACT7 is the most strongly expressed in young plant tissues and shows the greatest response to physiological cues. Adult plants homozygous for the act7 mutant alleles show no obvious above-ground phenotypes, which suggests a high degree of functional redundancy among plant actins. However, act7-1 mutant plants are at a strong selective disadvantage when grown in competition with wild-type plants and therefore must have undetected physical defects. The act7-1 and act7-4 alleles contain T-DNA insertions just after the stop codon and within the first intron, respectively. Homozygous mutant seedlings of both alleles showed less than 7% of normal ACT7 protein levels. Mutants displayed delayed and less efficient germination, increased root twisting and waving, and retarded root growth. The act7-4 mutant showed the most dramatic reduction in root growth. The act7-4 root apical cells were not in straight files and contained oblique junctions between cells suggesting a possible role for ACT7 in determining cell polarity. Wild-type root growth was fully restored to the act7-1 mutant by the addition of an exogenous copy of the ACT7 gene. T-DNA insertions just downstream of the major polyadenylation sites (act7-2, act7-3) appeared fully wild type. The act7 mutant phenotypes demonstrate a significant requirement for functional ACT7 protein during root development and explain the strong negative selection component seen for the act7-1 mutant.

Scarification and Moisture Effects on Triploid Watermelon Seed Germination

Triploid watermelon [Citrullus lanatus (Thunb.) Matsum &amp; Nakai] consumption is increasing in the United States However, some of the original problems, poor and inconsistent germination, still exist. Seeds of several triploid and diploid watermelon cultivars were subjected to a variety of treatments to improve germination. Control and scarified seeds, by nicking, were incubated at 25 or 30 °C in either 5 or 10 mL H2O or hydrogen peroxide (H2O2). Triploid seed germination was strongly inhibited in all cultivars when seeds were at 10 mL of H2O or H2O2; both nicking and H2O2 increased germination but not equal to rate of the control in 5 mL H2O or H2O2. Germination of diploid cultivars was unaffected by any treatment. Seed morphological measurments indicated that triploid seed has a smaller embryo with a large and highly variable (cv = 105%) air space surrounding the embryonic axis as compared with the diploid seed. These data suggests that triploid watermelon seed germination is not inhibited by the seed coat thickness alone. Seed moisture plays a significant role in germination, emergence, and stand uniformity.

204 Scarification and Moisture Effects on Triploid Watermelon Seed Germination

Triploid watermelon [Citrullus lanatus (Thunb.) Matsum &amp; Nakai] consumption is increasing in the U.S. However, some of the original problems, poor and inconsistent germination, still exist. Seeds of several triploid and diploid watermelon cultivars were subjected to a variety of treatments to improve germination. Control and scarified seeds, by nicking, were incubated at 25 or 30 °C in either 5 or 10 mL H2O or hydrogen peroxide (H2O2). Triploid seed germination was strongly inhibited in all cultivars when seeds were at 10 mL of the H2O or H2O2; both nicking and H2O2 increased germination, but not equal to rate of the control in 5 mL H2O or H2O2. Germination of diploid cultivars was unaffected by any treatment. Seed morphological measurments indicated that triploid seed has a smaller embryo with a large and highly variable (CV = 105%) air space surrounding the embryonic axis as compared with the diploid seed. These data suggests that triploid watermelon seed germination is not inhibited by the seedcoat thickness alone. Seed moisture plays a significant role in germination, emergence, and stand uniformity.

Microsporidian Intrasporal Sugars and Their Role in Germination

The hypothesis that spores of terrestrial and aquatic microsporidia differ in their utilization of sugars was tested by evaluating the sugars in germinated and ungerminated spores of several species in each category. The aquatic species tested wereVavraia culicis, Edhazardia aedis,andNosema algeraeand the terrestrial species wereVairimorpha necatrix, Nosema disstriae, Nosema apis, Vairimorpha lymantriae,andNosemaspp. fromSpodoptera exiguaandPlutella xylostella.The percentage germination varied between species, ranging between 40 and 92%. Total sugars (anthrone reactive) and reducing sugars (Nelson's test) remained unchanged through germination in the three terrestrial species tested; however, reducing sugars increased significantly in the aquatic species. High-performance liquid chromatography and gas chromatography revealed a preponderance of trehalose in all species and large quantities of sorbitol in all species exceptN. algeraeandE. aedis.Other sugars were present in some species in much lower concentrations. After germination no changes in sugar content were observed in terrestrial species; however, all aquatic species lost trehalose with a concomitant increase in fructose and/or glucose concentrations. Increased osmotic potential from breakdown of trehalose has been postulated to induce germination of the aquatic species, but another explanation must be found for the terrestrial species.

Interaction between algae and seed germination in tropical dune slack species: a facilitation process

The importance of algae dune slack stabilisation has been extensively analysed, but little has been done regarding their potentially favourable role in germination and establishment of phanerogams. Dune slack is a seasonal freshwater habitat that depends on water table level fluctuation. Our hypothesis is that in these highly unpredictable systems, algae maintain a certain degree of humidity in the soil and, thus, permit phanerogam germination and establishment. The objective of this study was to compare the germination of four species characteristic of tropical dune systems: Cyperus articulatus L., Fimbristylis cymosa R. Br., Fuirena simplex Vahl and Rhynchospora colorata (L.) Pfeiffer, in different substrates and degrees of humidity. For germination trials, seeds of the four species were placed each on three substrates: in sand (control), filamentous algae on sand and cotton on sand. Two irrigation protocols were followed: continual watering (wet treatment) and weekly watering (dry treatment). Each week during a 21-week period, the number of germinated seeds from each species was recorded. The highest percentage of germination for the four species was observed during wet treatment. C. articulatus had the highest germination rate of the four species in algae (70%), and cotton (51%) on sand. Highest germination for F. simplex, F. cymosa and R. colorata took place in algae, although the percentages were very low. Differences in germination between the three substrates for these species were statistically significant ( P<0.05). During dry treatment, C. articulatus was the only species that exhibited a significant germination, principally in algae and cotton. The results suggest that algae maintain substrate humidity and favour germination of the four species. This could be important in sand dune slacks where marked fluctuations in temperature and humidity occur.

Cultural Methods for Establishing Wyoming Big Sagebrush on Mined Lands

Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle Y however, soil management and competition treatment effects were still apparent in the second year. Mulch type had limited effects on sagebrush seedling density by the third year of the study. This research indicates that big sagebrush seed viability in the soil is longer than previously thought and that seed dormancy, safe site development, and climactic conditions play important roles in germination, establishment, and seedling survival of this species.

Mechanism of smoke‐induced seed germination in a post‐fire chaparral annual

1 Smoke‐stimulated germination in the post‐fire flora of California chaparral does not appear to be triggered by nitrate. Application of freshly prepared unbuffered KNO3 solutions (pH c. 6.2) failed to enhance germination of five populations of Emmenanthe penduliflora or one Phacelia grandiflora population, regardless of light or stratification conditions. 2 KNO3 buffered at acidic pH (or unbuffered solutions equilibrated with atmospheric CO2) did induce germination, but KNO3 solutions at pH 7 failed to induce germination. Induction of germination is therefore not due to the nitrate ion per se, but rather to high [H+], although buffered controls gave weak germination at low pH, suggesting a role for H+ plus nitrate. However, other anions such as sulphate were equally as effective as nitrate at breaking dormancy. 3 The germination response to KNO3 was affected by the type of filter paper used and this may be linked to differences in pH. 4 NO2, at concentrations present in biomass smoke, was highly effective at inducing germination, and other oxidizing agents also induced germination. 5 Several growth regulators, including nitrite and gibberellin, were stimulatory only at acidic pH, but KCN was stimulatory across a broad pH range. 6 Germination decreased at smoke exposures longer than a few minutes. Also, smoked water samples effective at breaking dormancy were acidic and were less effective when buffered to pH &gt;7. 7 Physical scarification of the seed coat induced germination but the effect was not due to penetration of a water barrier, or to enhanced oxygen uptake or to wound responses such as CO2 or ethylene production. 8 Different effects of the gibberellin inhibitor CCC (chlorocholine chloride) suggested that the mechanisms of scarification‐induced and smoke‐induced germination may differ. 9 We conclude that either oxidizing gases in smoke and/or acids generated on burnt sites play a role in germination of post‐fire annuals in chaparral.

Light environment, phytochrome and germination of Datura stramonium L. seeds

The role in germination of the maternal pre-existing far-red absorbing form of phytochrome (Pfr) was studied in seeds harvested at different developmental stages. Datura stramonium seeds acquired marked dormancy in the later ripening stages, independently of phytochrome phototransformation. However, the balance between stimulators, such as Pfr, and inhibitors (probably abscissic acid and/or phenolic substances) in the stage prior to complete dehydration appeared to play a crucial role in the degree of progeny dormancy. Enrichment of the far-red (FR) wavelength (simulated canopy light) induced light-dependent dormancy if stage IV progeny were incubated in darkness in suboptimal conditions. In contrast, natural storage of seeds in soil led to a uniform degree of dormancy. An increase in photosensitivity owing to storage in soil appeared to be linked to simultaneous loss of inhibitors. It should be noted, however, that this extreme sensitivity to very low Pfr levels (724 nm monochromatic light pulse) was acquired only by seeds stored deep in the soil (typical very low fluence response). It is postulated that these reactions are induced by an elevated quantity of phytochrome typical of etiolated tissue, in conditions of near-absence of inhibitors.

A pollen-specific cDNA of Phalaris coerulescens shows homology to Zm13

Genes expressed by the male gametophyte have been divided into two classes, the early genes, which are expressed shortly after meiosis, and the late genes, which accumulate after microspore mitosis and are thought to play a role in germination, pollen-stigma interactions and early pollen tube growth (Mascarenhas 1989). Among the best-studied examples of late genes are Zm13 of maize (Hamilton et al. 1989: Hanson et al. 1989) and its homologs PS1 from rice (Zou et al. 1994) and LAT52 of tomato (Twell et al. 1989). Here we report the cDNA sequence of a Zm13 homologue from Phalaris coerulescens, a mediterranean grass which is used as a model system for the study of self-incompatibility in the Poaceae (Li et al. 1994). A cDNA library was constructed from pollen of Phalaris coerulescens in bacteriophage vector Lambda gt10. In order to isolate pollen-specific clones, this library was differentially screened with cDNA probes from leaves, roots, seeds, 7-day-old seedlings and young anthers around meiosis. AWPC-C7c was selected on the basis that it did not show hybridization with cDNA from any of the non-pollen tissues. A developmental RNA blot confirmed that AWPC-C7c expression is restricted to Nucleotide sequence data will appear in the EMBL, GenBank and DDBJ databases under the accession number U85499.

Plant population dynamics in subterranean clover and murex medic swards. 3. Effect of pod burial, summer grazing and autumn cultivation on emergence

Murex medic (Medicago murex Willd.) seedling recruitment is more sensitive to soil water at the time of emergence than subterranean clover (Trifolium subterraneum L.). Murex medic pods normally lay on the soil surface. Shallow burial of pods may be beneficial when soil moisture is marginal for germination and emergence. In addition, the tightly coiled structure of murex medic pods may also act as a barrier to water uptake by the seed. Two methods of burying murex medic pods were investigated in the field: (i) trampling by sheep hooves through summer grazing; and (ii) through light cultivation in autumn. A glasshouse experiment was also conducted to examine the interaction between the length of time that the soil stays moist and pod burial for CD26 and CD53 murex medic and Dalkeith, Junee, Seaton Park and Woogenellup subterranean clover. In the glasshouse, pod burial was important for the attainment of maximum emergence in all genotypes when soil water was limiting. However, pod structure did not appear to have a limiting role in germination and emergence in murex medic. When tested in the field, pod burial by sheep trampling through summer grazing improved emergence in CD26, possibly because the smaller more open pod was more easily trampled than that of CD53. Summer grazing in CD53 and Dalkeith and autumn cultivation in all genotypes did not improve emergence; possible reasons for this are discussed so to is the role of murex medic in ley farming systems in eastern Australia.

Soil Light Penetration and Dormancy of Jimsonweed (Datura stramonium) Seeds

Trials were carried out to determine the degree of light transmittance through soil and its role in photo-induced germination of buried weed seeds. Transmittance was found to be strongly dependent on soil type and decreased with decreasing particle size and with an increase in darker components. In each soil examined, light penetration fell below 0.01% at a depth of no more than 4 mm. It was also noted that with increasing soil depth, light permeability was proportional to wavelength, leading to progressive decline in the red-far red ratio. Low light penetration played a crucial role in germination of jimsonweed seeds, which had became light-sensitive after prolonged burial. Although this effect is a function of soil type, it may represent an important ecological factor influencing seed emergence in the first few mm of upper soil layers.

Evaluation of Cultural Methods for Establishing Wyoming Big Sagebursh on Mined Lands

Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis) is one of the most widely distributed and adapted shrub species in Wyoming and the region. However, its reestablishment on mined lands has proven difficult because of low seedling vigor, its inability to compete with herbaceous species, poor seed quality, and altered edaphic conditions. Field research evaluating the effect of topsoil management, mulching practice, and plant competition have shown that all of these factors significantly influence early initial sagebrush establishment. Greater sagebrush establishment occurred on fresh topsoil compared to 5 year old stockpiled topsoil. Stubble and surface applied mulch and elimination of herbaceous species competition also significantly increased big sagebrush establishment in the first growing season. However, a cool, wet second year growing season (April-September) resulted in large increases in sagebrush seedling density across all treatments. These large increases resulted in some changes in response to imposed treatments; however, greater sagebrush seedling densities were still evident on fresh compared to stockpiled topsoil and competition still significantly reduced seedling density on the fresh topsoil treatment. Mulch type showed limited effects on sagebrush seedling density in the later phases of the study. This research indicated that big sagebrush seed viability may be longer than previouslymore » thought and that seed dormancy, safe site development, and climatic conditions play an important role in germination and establishment of this species.« less

Mediterranean pasture dynamics: the role of germination.

. Meteorological patterns have a decisive influence on the inter‐annual dynamics of therophyte pastures under Mediterranean climatic conditions. The germination behaviour of annual pasture species was studied by subjecting two collections of seeds taken from plants and soil‐seed banks to two phytotron‐simulated weather patterns: early and late autumn rains. Species from these pastures were arranged along a gradient of sensitivity to temperature on the arrival of the first persistent rain. This sensitivity was manifested in both the total germination success of the species and the germination time profile. The different germination patterns of the species can provide competitive advantages depending on the autumn weather conditions.

Nitrate and nitrate reductase in Erythrina caffra seeds: Enhancement of induction by anoxia and possible role in germination

The nitrate level in seed embryonic axes of Erythrina caffra Thunb. which is capable of anaerobic germination, was about 2.5 times higher than in seed axes of Pisum sativum L. a species incapable of anaerobic germination. Nitrate levels in E. caffra seeds decreased during germination and this was not due to leaching. Both NADH- and NADPH-dependent nitrate reductase (NAR) activities increased during germination. The increase was prevented by cycloheximide. The activity of NADH-NAR (EC 1.6.6.1) was higher than that of NADPH-NAR (EC 1.6.6.3). Both NAR activities were higher in anoxia than in air during germination. The NAR activities in Pisum seeds were very much lower than in Erythrina seeds. Anoxia (N2 or argon) enhanced the induction of NAR by KNO3 in germinated E. caffra axes. The NADH- and NADPH-NAR activities were induced to equally high levels by KNO3 under anoxia. The enhancement was depressed by cycloheximide. It is concluded that nitrate and NAR activity may play a role in the anaerobic germination of E. caffra seeds.

Comparative Requirement for Endogenous Ethylene during Seed Germination

Requirement for endogenous ethylene during seed germination of the following ten species was determined: Lycopersicon esculentum Mill. (tomato), Allium cepa L. (onion), Arena fatua L., dormant pure line AN-51 (wild oats), Cucumis sativus L. (cucumber), Sinapis arvenis L. (wild mustard), Tagetes erecta L. (marigold), Raphanus sativus L. (radish), Triticum aestivum L. (wheat), Catharanthus roseus L. (periwinkle), and Phaseolus aureus L. (mung bean). Experiments were done under controlled conditions suited for the germination of each species. Criteria used to determine the need for endogenous ethylene were: (i) temporal relationship between ethylene production and seed germination; (ii) parallel inhibition of ethylene synthesis and seed germination by L-alpha-(2-aminoethoxyvinyl)-glycine or CoCl2; (iii) inhibition of seed germination by 2.5-norbornadiene, a competitive inhibitor of ethylene action; and (iv) prevention by exogenous ethylene of the effects of each inhibitor on germination. All the species produced ethylene in amounts that increased concomitantly with germination. According to all the criteria used, ethylene synthesis and action were found to be necessary for the germination of T. erecta. Norbornadiene inhibited the germination of R. sativus, T. aestivum and C. roseus, and exogenous ethylene overcame this inhibition. However, inhibitors of ethylene synthesis generally did not affect the germination of these species. One exception was the inhibition of R. sativus germination by CoCl2, but this was not overcome by exogenous ethylene, indicating that CoCl2, did not act specifically by blocking ethylene synthesis. In all other species, ethylene produced by seeds appears to play no role in germination. The results show that there is no general requirement for endogenous ethylene during germination, even though all species studied so far produce ethylene. This requirement is also not linked specifically to dormancy breakage.

Identification of germination gene of [formula omitted

Glucose, KNO 3, proline and leucine initiate the spore germination of B. megaterium ATCC 12872, but not of B. megaterium ATCC 19213. In order to isolate the gene concerning germination of B. megaterium ATCC 12872, we constructed its gene library in plasmid vector, and introduced into B. megaterium ATCC 19213. We obtained a transformant whose spores differed from those of the wild type strain with respect to germinability. Spores of this transformant could be germinated by glucose, proline or leucine. The recombinant plasmid prepared from this transformant was found to carry 2 kilobase pairs fragment of B. megaterium ATCC 12872 DNA. This fragment may contain the gene encoding the protein which plays an important role in germination.

Calcium and Early Development in Fucoid Algae.

Understanding the mechanism by which a fertilized egg establishes an embryonic axis is of fundamental importance to the study of developmental biology. Much of what we have learned about axis formation in plants derives from investigations of fucoid algae. In this report I review the data concerning the role of Ca2+ in the early development of Fucus and Pelvetia. The evidence shows that Ca2+ plays an important role in germination and rhizoid growth, but its function in polarization remains uncertain.

QUANTITATIVE ULTRASTRUCTURE AND PROTEIN COMPOSITION OF DATE PALM (PHOENIX DACTYLIFERA) SEEDS: A COMPARATIVE STUDY OF ENDOSPERM VS. EMBRYO

Comparative studies on the ultrastructure and protein composition of the embryo and endosperm of date palm (Phoenix dactylifera L.) were conducted. Cells of the embryo cotyledon and endosperm function in reserve storage and contained cell walls, nuclei, and cytoplasm rich in lipid and protein bodies. Morphometric analysis from light and electron micrographs showed that the cell walls of the endosperm occupied 65% of the total cell volume, but only 6% in the embryo. The protein bodies of the endosperm accounted for 11%, whereas those of the embryo occupied more than half of the total cell volume. The volume of organelles and organelle‐free cytoplasm in the endosperm was negligible, suggesting that most of the extractable endosperm proteins are localized in the protein bodies. Extractable proteins in the embryo may come from cytoplasm, protein bodies, and other organelles. The endosperm contains relatively lower amounts of proteins than does the embryo. Proteins extracted from both tissues were compared using SDS‐polyacrylamide gel electrophoresis, tube gel isoelectric focusing, and two‐dimensional electrophoresis. Proteins of both the tissues were heterogeneous in molecular mass and charge. The majority of the proteins were similar in molecular mass and charge in the two tissues, suggesting that most of the storage proteins are probably the same. However, there were also several embryo‐ and endosperm‐specific proteins apparent in both the first‐ and second‐dimension gels. The endosperm‐specific proteins may play an important role in germination and seedling development.

The role of germination in sorghum reconstitution

Commercial reconstitution of sorghum for cattle feed was simulated in the laboratory, with partial germination of the grain prior to anaerobic storage as an added variable. After steeping to 30–35% moisture, samples of red hybrid sorghum grain were allowed to germinate for up to 2 days prior to anaerobic storage periods of 0–21 days. Changes in nitrogen and carbohydrate solubility, reducing sugars, enzyme activity, dry matter loss and particle size index were determined. Chemical and physical modification of the grain appeared to be minimal during anaerobic storage when it was not preceded by germination. Significantly higher nitrogen and carbohydrate solubility were achieved in 6 days (1 day germination + 5 days storage) than in 21 days of strictly anaerobic storage. The rapid incorporation of soluble nitrogen and carbohydrate into bacterial cell mass and exo-polysaccharide slime appeared to limit the increases in dry-matter loss resulting from germination. Protease activity resulted from both germination and bacterial growth, while amylase activity could be attributed only to germinating seeds. Reductions in particle size index could be attributed to steeping, germination and storage effects, the largest component appearing to result from steeping. It was concluded that the onset of germination can greatly accelerate the beneficial bacterial fermentation occurring during sorghum reconstitution, probably by increasing bacterial growth rates and surface area accessible to bacterial action.