Showing papers on "Germination published in 1989"

In Vitro Enhancement of Spore Germination and Early Hyphal Growth of a Vesicular-Arbuscular Mycorrhizal Fungus by Host Root Exudates and Plant Flavonoids

Abstract: Comparison of the influence of root exudates of a host plant, or non host plant and of three flavonoids on early events in the pre-infection phases of spore germination and hyphal growth of Gigaspora margarita in vitro

Seed banks, fire season, safe sites and seedling recruitment in five co-occurring Banksia species

Abstract: Quantity of seed stored in the canopy of 5 co-occurring Banksia species varied by nearly 2 orders of magnitude. The 3 species which resprout vegetatively after fire, produced less seeds and retained smaller seed banks than 2 non-sprouting species. Contiguous patches of scrub-heath were burned in spring and autumn. The spring fire was cooler, and both sets of seed released subsequently did not germinate until the following (common) winter. Rate of seed release was higher after the autumn fire. The non-sprouting species released more seeds after each fire and yielded more seedlings per parent than the resprouting species. Percentage (field) germination of the non-sprouters was not consistently different from that of the resprouters. Seeds exposed on the soil surface during summer soon lost viability compared with buried seeds. The large number of seedlings established up to 8 months after the spring fire resulted from many seeds escaping exposure by dispersal into litter-covered "safe' sites. Although litter microsites covered only 30% of the ground surface after the spring burn, they accounted for 80% of seedlings both before and after the summer drought. Litter microsites covered only 14% of the autumn-burned site but accounted for 60% of seedlings before summer and 40% after summer, suggesting density-dependent thinning of seedlings. The autumn-burned site supported more than twice the density of seedlings than the spring-burned site by the end of the 1st winter. Summer mortality of seedlings was 32% in the spring-burned site and 65% in the autumn-burned site, equalizing the seedling:parent ratio at both sites. Net recruitment of 1-yr-old seedlings varied from 0 for 2 resprouters to >100 per parent for a non-sprouter.

Recent advances in the development and germination of seeds

Abstract: Seed Research-Past,Present and Future.- Use of Transgenic Plants for Studies of Seed-Specific Gene Expression.- Impact of Simulated Drought Stress on Protein Body Cycle in Radicles of Developing and Germinating Cotton Seeds.- Synthetic Seed for Clonal Production of Crop Plants.- Synthesis of Acid-Soluble,ABA-Inducible Proteins in Wheat Embryos from Dormant Grain.- Hormones, Genetic Mutants and Seed Development.- Membrane Behavior in Drought and Its Physiological Significance.- The Basis of Recalcitrant Seed Behaviour: Cell Biology of the Homoiohydrous Seed Condition.- Phytin Synthesis and Deposition.- Calcium-Regulated Metabolism in Seed Germination.- Transport and Targeting of Proteins to Protein Storage Vacuoles (Protein Bodies) in Developing Seeds.- Biochemical Adaptations to Anoxia in Rice and Echinochloa Seeds.- Some Aspects of Metabolic Regulation of Seed Germination and Dormancy.- Phytochrome and Sensitization in Germination Control.- The Role of Light and Nitrate in Seed Germination.- Water-Impermeable Seed Coverings as Barriers to Germination.- Control of Germination and Early Development in Parasitic Angiosperms.- Factors Eliciting the Germination of Photoblastic Kalanchoe Seeds.- Factors Influencing the Efficacy of Dormancy-Breaking Chemicals.- Physiological Mechanisms Involved in Seed Priming.- Germination Research Towards the Nineties: A Summary and Prognosis.

Responses of the non7hyphen;mycotrophic plant Salsola kali to invasion by vesicular–arbuscular mycorrhizal fungi

Abstract: SUMMARY Vesicular–arbuscular mycorrhizal fungi reduced the growth and survival of the non-mycotrophic weed, Salsola kali (Chenopodiaceae) in field and greenhouse experiments. To determine the mechanisms by which mycorrhizal fungi can affect a non-mycotrophic plant, we mapped the root responses of S. kali and the mycotrophic grass Agropyron dasystachyum to invasion by a mixture of Glomus spp. and by Gigaspora margarita. The fungi invaded the roots of both species within 10 days following seed germination. In A. dasystachyum normal mycorrhizal development occurred and no root browning or autofluorescence was observed, indicating a compatible reaction. In S. kali, the fungi initially invaded the roots and formed arbuscules and peletons. The roots reacted to invasion by autofluorescing bright yellow, suggesting lignification. With 1 or 2 days following root penetration by the fungus, the invaded root segment turned brown and, with the exception of some vesicles, the fungus disappeared from the root. The fungus sometimes then reinvaded new root segments farther down the root. These observations suggest that there is an incompatible reaction beween this non-mycotrophic annual and VA mycorrhizal fungi whereby the plant actively rejects infection. This response could form the basis for initiating studies on the genetics of mutualistic versus parasitic symbioses.

Interspecific pollen transfer as a mechanism of competition: Consequences of foreign pollen contamination for seed set in the alpine wildflower, Polemonium viscosum

Abstract: Earlier studies showed that under natural conditions foreign pollen receipt is correlated with loss of seed set in populations of P. viscosum. Here, we report on experimental pollinations using foreign pollen from two co-flowering species that share pollinators with P. viscosum. Experiments were designed to ascertain whether improper pollen transfer causes reduced seed set under controlled conditions and, if so, to determine the stage at which interference occurs. In flowers pre-treated by pollination with either Mertensia or Castilleja pollen, adherence of subsequently deposited conspecific pollen grains was unaffected. However, conspecific grains had significantly lower germination and ovule fertilization success in flowers receiving foreign pollen than in controls. These results suggest that pollinator infidelity in high alpine plant communities can reduce female reproductive success of P. viscosum by inhibiting the performance of conspecific pollen grains. Negative effects of Mertensia and Castilleja pollen were comparable despite large interspecific differences in pollen grain morphology. Accordingly, susceptibility to foreign pollen interference appears to be an intrinsic property of P. viscosum that is not dependent on the unique structural properties of pollen produced by competitive species.

Seed and Seedling Ecology of a Monocarpic Tropical Tree, Tachigalia Versicolor

Abstract: Tachigalia versicolor is a monocarpic canopy tree species on Barro Colorado Island, Panama, This 2—yr demographic and physiological study examined whether seed and seedling survival of this monocarpic species is high compared to nonmonocarpic species previously studied, as life history theory predicts. For the weighted average of two trees, the percentage of offspring estimated to survive from dispersed seed to germination, 1 yr, and 2 yr was 30, 7.2, and 4.3%, respectively. The large seeds (500—600 mg) suffered greater mortality in absolute numbers than did the seedlings. Major mortality agents of seeds were bruchid beetles (Amblycerus tachygaliae) and terrestrial vertebrates, while vertebrate herbivores and damping—off fungi killed seedlings. Seedlings survival and growth were enhanced under canopies of dying T. versicolor adults, relative to under canopies of living conspecific and nonconspecific adults. The majority of 2—yr—old seedlings occurred within 0.40 m from the parent trees, reflecting the original peak of the distribution of wind—dispersed seeds. Few seedlings persisted beyond 40 m. Seedling survival in the first 2 mo was higher in shaded understory than in light—gaps, due to higher vertebrate herbivory in sun than shade. Seedling growth and survival beyond 2 mo was higher in light—gaps than in shaded understory. T. versicolor seedlings exhibited a wide range in maximum net photosynthetic rate when grown in contrasting light conditions, and were able to acclimate to a sudden increase in light level by means of morphological and physiological adjustments of newly developed leaves. These results indicate that T. versicolor can utilize a wide range of light environments in the forest during seedling establishment. Relative to nomonocarpic wind—dispersed tree species previously studied in the same community. T. versicolor ranks near the top in its seed mass, dispersal capability, photosynthetic flexibility to contrasting light conditions, and probability of seedling survival in the shaded understory through 1 yr. These characteristics enable T. versicolor to establish large numbers of seedlings. The mean total number of offspring of two trees estimated to survive through 2 yr was 4395 out of 103 055 dispersed seeds and 30 529 germinated seeds. In comparison to nonmonocarpic species, juvenile survival of T. versicolor is high as expected for this monocarpic tree species.

Differential desiccation sensitivity of corn and Pennisetum pollen linked to their sucrose contents

Abstract: . Two pollen species from the Gramineae family were investigated as to their differential sensitivity to desiccation. Germination in vivo ceased to occur after previous drying to 7–8% moisture content in Zea mays and 3% in Pennisetum typhoides. The reduced vitality coincided with extensive membrane damage, as evidenced by the considerable leakage of fluorescein and K+ from the prehumidified grains into liquid media. Further experiments were undertaken to investigate the basis for this interspecific difference: (1) phospholipid analyses revealed little difference in composition and content both before and after drying; (2) free fatty acid contents increased in both species upon drying but levels were generally low; and (3) sucrose was the sole soluble carbohydrate found in both species. Fresh maize pollen contained 5% sucrose, as compared to 14% in Pennisetum pollen. During slow drying (8h) this level went up to 12% and 17%, respectively. Drying corn pollen in the cold (2°C), or at high rate, limited sucrose levels and affected the resistance to drying. The authors conclude that survival of dehydration is correlated with the presence of sucrose. Finally, they tested the ability of sucrose to preserve dry liposomes prepared from phospholipids purified from the two species. When liposomes were dried in the presence of sucrose, fusion and leakage could largely be prevented at mass ratio's of sugar to lipid of > 4. Trehalose was also effective but myo-inositol was not. No species differences were observed. The authors suggest that the presence of sucrose is a key factor in preserving membranes in dry pollen.

Seed Coatings and Treatments and Their Effects on Plant Establishment

Abstract: Publisher Summary This chapter elaborates seed coatings and treatments, and their effects on plant establishment. Seed coating is a mechanism of applying needed materials in such a way that they affect the seed or soil at the seed–soil interface. Seed coating provides an opportunity to package effective quantities of materials such that they can influence the microenvironment of each seed. The treatment of seeds with fungicides and/or insecticides is a relatively common practice compared to other coatings. The most commonly applied seed coatings are those in which a trace quantity of fungicide and/or insecticide is applied to seeds in such a way that this small quantity is evenly distributed among the seeds. The process of seed coating usually involves the use of adhesives to bind materials to the surface of seeds. It is found that the degree of attraction or repulsion of moisture by the seed coating can have large effects on the germination of coated seeds. The mechanical planting of seeds is facilitated by having seeds that are of uniform size and shape, have sufficient size and weight to be easily separated mechanically, and flow readily without clumping together. The incorporation of nutrients in seed coatings provides a unique opportunity to supply each sown seedling with an accurately controlled quantity of nutrient that may be preferentially available to the sown species and less available to any neighboring weed species.

The Effects of Priming and Ageing on Seed Vigour in Tomato

Abstract: A comparison was made of the effects of seed priming or ageing treatments on the performance of tomato (Lycopersiconesculentum Mill. cv. UC204C) seeds according to a number of indices of seed vigour. A single lot of tomato seeds was primed in120 mol rrT 3 K 2 HPO 4 + 150 mol m~ 3 KNO 3 for 5 d at 20 °C, or aged at 13% moisture content (dry weight basis) and 50 °C for6 d. Germination percentage (>98%) was unaffected by priming and reduced to 85% by ageing. X-ray photographs andlongitudinal sections revealed the formation of free space surrounding the embryo in dry primed seeds, which was not evident incontrol or aged seeds. Priming increased the rate of germination at all temperatures above the base temperature (T b ), while ageingdecreased it. T b was unaffected by priming and only slightly increased by ageing. The variation in individual times to germinationwas approximately doubled in both primed and aged seed compared to the control, based upon the slopes of probit germinationpercentage versus log thermal time curves. Root growth after germination tests and seedling growth in both greenhouse and fieldtests were not influenced by either priming or ageing. The conductivity test was found to be unreliable as a vigour test for tomatoseeds. The results identify several indices which can be used to quantify seed vigour in tomato. They also illustrate that seedpriming can enhance seed performance according to some criteria, while having no effect or decreasing quality according to othercriteria. Seed vigour can apparently be separated into various components which can be independently influenced by seedenhancement treatments.Key words: Tomato, seed germination rate, seed priming, seed vigour.

Inhibition of in Vitro Pollen Tube Growth by Isolated S-Glycoproteins of Nicotiana alata.

Abstract: Pollen from three S-genotypes of Nicotiana alata was grown in vitro in the presence of S-glycoproteins isolated from styles of the same three genotypes. Pollen germination was not affected by the presence of the S-glycoproteins, but pollen tube growth of all genotypes was inhibited. S2 pollen was preferentially inhibited by the S2-glycoprotein and S3 pollen by the S3-glycoprotein. The S6-glycoprotein preferentially inhibited growth of both S2 and S6 pollen over S3 pollen. Heat treatment dramatically increased the inhibitory activity of the S-glycoproteins as inhibitors both of pollen germination and tube growth; after heat treatment, S-allele specificity of pollen tube inhibition was not detected.

Variation in germination response to temperature in rubber rabbitbrush (chrysothamnus nauseosus: asteraceae) and its ecological implications

Abstract: Seed collections from 72 rubber rabbitbrush populations occupying a range of habitats in western North America were incubated at 3 C in the laboratory. Collections from warm desert habitats required less than 2 weeks to achieve 90% relative germination under these conditions, while collections from montane habitats showed delayed germination requiring up to 20 weeks. When 13 representative collections were incubated at constant temperatures from 5 to 30 C, all germinated completely at 30 C within 4 weeks. Collections from warm desert habitats germinated rapidly over the whole range of temperatures. Montane collections sometimes exhibited dormancy at intermediate temperatures (15 and 25 C) even though they were ultimately able to germinate at lower temperatures. Results suggest that dormancy is conditional and temperature-dependent in this species. Chilling the seeds extends the temperature range for germination downward to include the chill temperature itself. Germination response to temperature and its variation as a function of habitat are of apparent adaptive significance, serving to time germination so that the probability of seedling survival is maximized in each habitat. Within populations, response to temperature varied as a function of year of harvest and of within-year harvest date, indicating that germination patterns are probably not under rigid genetic control but represent an integration of genetic and environmental factors.

Drought stress effects during seed fill on soybean seed germination and vigor

Abstract: Seed germination and vigor decreased as SDD increased. The effect of drought on germination and vigor was substantially less than that on yield and was inconsistent across years. Drought reduced standard germination percentage and seedling axis dry weight 5 and 12%, respectively and increased single-seed conductivity 19%. Seed quality loss was correlated with reduced single-seed mass. Severe drought that occurred throughout seed fill reduced yield and seed number at a faster rate than seed mass, germination, or vigor, and maintained the development of at least some viable and vigorous seeds

Germination-associated events and the desiccation sensitivity of recalcitrant seeds — a study on three unrelated species

Abstract: The storage behaviour of recalcitrant seeds was assessed using three diverse species: a gymnosperm, Araucaria angustifolia (Bert.) O. Kuntze; a herbaceous monocotyledon, Scadoxus membranaceus (Bak.) Friis Nordal; and a woody dicotyledon, Landolphia kirkii Dyer. Seeds were stored under conditions of high relative humidities that maintained seed moisture content and under low relative humidities that caused drying. At regular intervals moisture content was determined, germinability assessed and the ultrastructure of radicle meristem cells examined. Under storage at high relative humidity, seed moisture content was maintained at the original level and subcellular germination events were initiated in the short-term. Such seeds showed enhanced rates of germination when removed from storage and planted. Long-term storage under these conditions resulted in the initiation of subcellular damage which intensified with time and ultimately resulted in the loss of viability. The rate at which germination events proceeded varied among the three species, and could be directly correlated with the period of viability retention under humid storage conditions. Storage under desiccating conditions resulted in subcellular damage and rapid loss of viability. The rate at which the seeds dried varied among the three species. The proportion of water loss tolerated by the different species before loss of viability, correlated with the rate of drying. The storage behaviour of the seeds of these three species is discussed in terms of a previously described model.

Effects of dehydration and exogenous growth regulators on dormancy, quiescence and germination of grape somatic embryos

Abstract: Dormant grape somatic embryos from five genetically distinct culture lines were subjected either to dehydration or exogenous growth regulators (benzyladenine, gibberellin or abscisic acid). Of growth regulator treatments tested, benzyladenine resulted in the highest germination rate but postgermination growth was abnormal. Abscisic acid treatment resulted in the least germination. Dehydration for 21 d under 75–95% relative humidity was effective only for the culture line that produced well developed embryos. However, for this line, more embryos produced shoots after dehydration (34%) when compared to growth regulator treatments and the postgermination growth resembled that of a seedling. Moisture content of dehydrated somatic embryos was similar to that of seed at equivalent relative humidities. Because dehydrated embryos germinate after addition of water, they are considered to be quiescent or nondormant. Plant recovery rates of 34% after 21 d of dehydrated storage at 70% relative humidity suggests that dehydration of somatic embryos may eventually provide for the conservation of clonally propagated crops in seed gene banks.

Pollen tube attrition in Erythronium grandiflorum

Abstract: Seed set after selfing in E. grandiflorum is often reduced relative to seed set after crossing; however, the compatibility patterns seen are not due to genes of major effect (i.e., S alleles). There is quantitative variation in the proportion of pollen tubes reaching the base of the style after both self- and cross-pollinations. Pollen tubes require between 24 and 72 hr to reach the ovary, but pollen tube growth ceases after 72 hr. When styles were removed from the ovaries 5 days after pollination, between 10 and 80% of the pollen tubes in the stigma had not reached the base of the style. The number of pollen tubes at the base of the style is a much better predictor of seed set than is the number of pollen tubes in the stigma. Pollen tube attrition is not affected by the age of the recipient flower or by the number of pollen donors contributing to the stigmatic pollen pool. The number of pollen tubes reaching the base of the style is dependent upon the source of the pollen and appears to be a decelerating function of the number of pollen tubes present in the stigma. SEED PRODUCTION in angiosperms depends upon a sequence of steps, including pollen transfer to the stigma, pollen germination and pollen tube growth, ovule fertilization and seed development, and finally seed maturation and dispersal. Attrition during each step determines the upper limit on the number of participants (i.e., gametes or zygotes) in subsequent processes, and variation in the number of gametes or embryos successfully passing a particular stage contributes to variation in the reproductive success of the sporophytes in

Characteristics and stability of a new cytoplasmic-nuclear male-sterile source in pearl millet

Abstract: In 3 yr, male-sterile plants with A 1 cytoplasm averaged 0.91 fertile revertant events per 1000 inflorescences, while no fertile revertants were observed for plants with A m cytoplasm. The number of fertile revertants for A 1 cytoplasm increased with age of seed fro 1 to 3 yr. Seeds stored at 24 o C produced plants with significantly more fertile revertants than seeds stored at 5 or −5 o C. Differences in seed germination and vigor of seedlings with A 1 and A m cytoplasms were nonsignificant or of little practical significance. The new cytoplasm, desiganted A 4 , is different from A 1 , A 2 and A 3 cytoplasms based on fertility of hybrids, morphological characters, and stability

Dispersal and Germination of Big Sagebrush (Artemisia tridentata) Seeds

Abstract: The purpose of this study was to investigate seed dispersal and germination of seeds in the soil as factors in establishment of big sagebrush seedlings. Seed dispersal began at seed maturity in December. Under the shrub canopy the dispersal of seeds was greater to the east. Between shrubs the dispersal of seeds tended to be uniform. For 6 months of each year there were no detectable germinable seeds in the litter and surface soil at the sites sampled. Germinable seeds in the soil increased rapidly during seed dispersal but were not detected by June of the next season. Enrichment of bioassay samples with GA3 or KNO3 did not enhance emergence of big sagebrush seedlings. Big sagebrush seedlings were found at very low densities in areas previously burned in wildfires. This suggests the presence of viable big sage- brush seeds in the soil at a very low density. Nomenclature: Big sagebrush, Artemisia tridentata Nutt. #3 ARTTR; potas- sium nitrate, KNO3; gibberlin, GA3. Additional index words. Range ecology, Bromus tectorum L., BROTE, ARTTR.

The Role of Maturation Drying in the Transition from Seed Development to Germination VII. EFFECTS OF PARTIAL AND COMPLETE DESICCATION ON ABSCISIC ACID LEVELS AND SENSITIVITY IN RICINUS COMMUNIS L. SEEDS

Abstract: During mid-development (25-40 d after pollination: DAP) of the castor bean seed the amount of abscisic acid (ABA) increases in both the endosperm and the embryo, declining substantially thereafter until there is little present in the mature dry (60 DAP) seed. Premature desiccation of the seed at 35 DAP also leads to a major decline in ABA within the embryo and endosperm. Partial water loss from the seed at 35 DAP which, like natural and premature desiccation, leads to subsequent germination upon return of the seed to full hydration, causes a much smaller decline in ABA levels. In contrast, ABA declines substantially in the non-dried (hydrated) control at 35 DAP, but the seeds do not germinate. Hence, a clear negative correlation between ABA content and germinability is not observed. Both drying, whether natural or imposed prematurely, and partial drying decrease the sensitivity of the isolated embryo to exogenous ABA by about 10-fold. The protein synthetic response of the castor bean embryo exposed to 01 mol m"3 ABA following premature desiccation exhibits some similarity to the response of the non-dried developing embryo—in both cases the synthesis of some developmental proteins is enhanced by ABA, and germination is suppressed. Germination of mature seeds is also suppressed by 01 mol m~3 ABA, but the same developmental proteins are not synthesized. In the cotyledons of prematurely-desiccated seed, some proteins are hydrolysed upon imbibition in 01 mol m 3 ABA, a phenomenon that occurs also in the cotyledons of similarly treated mature embryos, but not in developing non-dried embryos. Hence the embryo exhibits an 'intermediate' response upon rehydration in 01 mol m~3 ABA following premature desiccation; viz. some of the responses are developmental and some germinative. Following natural or imposed drying, the isolated embryo becomes relatively insensitive to 0 01 mol rrT 3 ABA: germination is elicited and post-germinative reserve breakdown occurs in the radicle and cotyledons. The reduced sensitivity of the embryo to ABA as a consequence of desiccation may be an important factor in eliciting the switch to germination and growth within the whole seed.

Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean

Abstract: Controlled environment experiments were performed to determine the effects of temperature and water potential on germination, radicle elongation and emergence of mungbean (Vigna radiata (L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (15-45 °C) and water potentials (0 to -2-2 MPa) on germination and radicle elongation rates were studied using an osmoticum technique, in which seeds were held against a semi-permeable membrane sac containing a polyethylene glycol solution. Linear relationships were established between median germination time (Gtso) and water potential at different temperatures, and between reciprocal Gtso (germination rate) and temperature at different water potentials. Germination occurred at potentials as low as — 2-2 MPa at favourable temperatures (30-40 °C), but was fastest at 40 °C when water was not limiting, with an estimated base temperature (Tb) of about 10 °C. Subsequent radicle elongation, however, was restricted to a slightly narrower temperature range and was fastest at 35 °C. The concept of thermal time was used to develop an equation to model the combined effects of water potential and temperature on germination. Predictions made using this model were compared with the actual germination obtained in a related series of experiments in columns of soil. Some differences observed suggested the additional importance of the seed/soil/water contact zone in influencing seed germination in soil. Seedling emergence appeared to reflect further the radicle elongation results by occurring within a narrower range of temperatures and water potentials than germination. Emergence had an estimated Tb of 12-6 °C and was fastest at 35 °C. A soil matric potential of not less than about — 0-5 MPa at sowing was required to obtain 50% or more seedling emergence.

Maturation, germination, and conversion of norway spruce (Picea abies L.) somatic embryos to plants

Abstract: Quantitative data are presented on the efficiency of three stages of plant regeneration from somatic embryos of Norway spruce (Picea abies L.): 1) Maturation, the development of immature embryos to the cotyledonary stage; 2) Germination, primary root growth; and 3) Conversion, plantlet survival and continued growth in nonaxenic conditions. Maturation frequency was calculated relative to the number of immature somatic embryos induced to develop on the basal medium of von Arnold and Eriksson (1981). The average number of immature somatic embryos was 700 per gram of embryogenic callus, on medium supplemented with ABA and IBA (1 μM each). Maturation was the least efficient stage of regeneration; an average of 3% of the embryos induced to develop reached the cotyledonary stage. Mean germination frequencies were improved on treatments which avoided immersion of the radicle in medium solidified with agar. Whereas, 27% of the somatic embryos germinated when radicles were immersed in agar medium, 45% germinated when placed on the surface of the medium, and 56% germinated when cotyledons were immersed in agar medium and the culture vessel inverted. Twenty-nine percent of the somatic embryos germinatedin vitro were converted to plants. Under greenhouse conditions these plants set dormant buds, subsequently survived overwintering (to −5°C), and renewed vegetative growth synchronously with seedlings grown under the same conditions. Our results verified long-term (2 year) growth and development potential of conifer somatic embryo plants.

Evidence that the adverse effect of urea fertilizer on seed germination in soil is due to ammonia formed through hydrolysis of urea by soil urease.

Abstract: Studies using seeds of wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.), and corn (Zea mays L.) indicated that the adverse effect of urea fertilizer on seed germination in soil is due to ammonia formed through hydrolysis of urea by soil urease and is not due to urea itself, to urea fertilizer impurities such as biuret, or to nitrite formed by nitrification of urea nitrogen. Support for this conclusion was obtained from (i) comparison of the effects on seed germination in soil of purified urea, urea fertilizers, urea fertilizer impurities, and compounds formed by enzymatic and microbial transformations of urea in soil; (ii) studies showing that ammonia volatilized from soils treated with urea completely inhibited germination of seeds close to, but not in contact with, these soils; and (iii) experiments showing that the adverse effect of urea fertilizer on seed germination in soil was completely eliminated when the soil was autoclaved to destroy urease or was treated with phenylphosphorodiamidate to inhibit soil urease activity before treatment with urea fertilizer.

Selective interaction between free-living rhizosphere bacteria and vesiculararbuscular mycorrhizal fungi

Abstract: Plant growth and nutrient uptake of tomato ( Lycopersicum esculentum ) were studied in a sand-vermiculite medium inoculated with two rhizosphcre bacteria (A or P) and three vesicular-arbuscular mycorrhizal (VAM) fungi ( G. mosseae, G. fasciculatum or G. sp; E 3 type). A selective interaction between free-living rhizosphere microorganisms and VAM fungi was tested. The effect of Glomus species on plant growth and nutrient content was related to the bacterial associated groups. Generally, bacterial inoculation increased the growth of mycorrhizal plants. Inoculation with A did not affect responses to G. mosseae treatment. Mycorrhizal plants with G. fasciculatum showed increased growth with A or P inoculation. This effect was significantly greater with dual A plus P inoculation. In the case of G . sp. (E 3 type) P treatment did not increase plant growth. Germination, hyphal growth and vegetative spores production of G. mosseae spores, cultivated in vitro under axenic conditions, were increased in the presence of P or A bacterial inoculum. P was more effective than A. The effects of A and P were not correlated with the degree of mycorrhizal colonization quantified at the end of the experiment.

The effects of salinity and temperature on the germination of the inland halophyte Hordeum jubatum

Abstract: The roles of temperature and salinity in controlling the germination of Hordeum jubatum were investigated. Germination is inhibited by simulation of warm summerlike thermoperiods. Seeds of H. jubatum will germinate at the time of dispersal if exposed to a favorable temperature regime. Seeds germinate readily at salinities higher than those favorable to growth and reproduction. Thus, germination is not the life-cycle stage that limits the distribution of H. jubatum along a soil salinity gradient. This pattern differs from that of other species at the study site and from many other halophytes. The germination response to salinity and temperature is enhanced after a cold treatment. Storage conditions significantly alter the germination of H. jubatum seeds when exposed to a gradient of constant temperatures. Discrepancies between the results of previous germination studies with H. jubatum could be due to the differences in seed handling procedures.