Showing papers on "Germination published in 1973"

Accelerated Germination by Osmotic Seed Treatment

Abstract: CROP seeds sown in cold soil are notoriously slow to emerge and it would obviously be desirable to shorten the time from sowing to seedling emergence and the time between the emergence of the first and the last seedling. This has occasionally been achieved by the pre-sowing seed treatment sometimes referred to as ‘hardening’1–3 or ‘advancing’4 involving repeated cycles of imbibition of a carefully controlled quantity of water, followed by drying back the seeds before the radicles emerge but results have not been consistent. There have been some successful attempts to replace this method by imbibition of seeds in salt solutions5–7; tomato seeds thus treated for 6 d exhibit a much higher level of RNA production during germination than untreated seeds8.

Comparative effects of propylene oxide, sodium azide, and autoclaving on selected soil properties

Abstract: Samples of soil (25 g) were treated with 1 or 2 ml of propylene oxide, 400 or 800 parts/106 of sodium azide, or autoclaved for 1.5 or 3.0 h. Soil sterilization was achieved by the propylene oxide and autoclaving treatments. Sodium azide inhibited the bacteria and actinomycetes and drastically reduced the fungal population. The autoclaving treatment decreased the soil pH 0.2 unit, while propylene oxide and sodium azide treatments increased it 0.5–1.1 units. Extractable manganous—Mn was increased 2- to 3-fold by all treatments except for a 90- to 120-fold increase in an autoclaved soil; extractable Ca was not affected; and the extractable K changes were slight. Total extractable N was increased 10–20 parts/106, and available P was generally increased by the treatments. Propylene oxide induced the least chemical alterations upon sterilization and is considered an appropriate sterilant to study chemical transformations in soils; but, germination and growth of wheat and alfalfa were retarded in propylene oxide treated soil.

Germination of Bacillus megaterium Spores After Various Extraction Procedures

Abstract: The initiation of germination of Bacillus megaterium QM B1551 spores, grown in supplemented nutrient broth, has been studied. The initiation properties depend on buffer concentrations and the particular batch of spores. Initiation in l-alanine, KBr, calcium dipicolinate, or in buffer alone increases as a function of the spore age; whereas initiation in glucose, l-leucine, or l-proline remains relatively constant. Extraction of spores with alkali, sodium dodecyl sulfate-dithiothreitol, or lithium diiodosalicylate removes variable amounts of dipicolinic acid, hexosamine, and protein. These extracted spores are still capable of initiation and, in some cases, initiation is stimulated. However, extraction of spores with 8 M urea-10% mercaptoethanol inhibits subsequent initiation.

Simulation of Drought and Its Effect on Germination of Five Pasture Species1

Abstract: While studying the effect of drought on seed germination, water potentials are usually simulated by addition of various osmotic substrates to water Studies showing the comparative effects of these simulated water potentials and of true drought are rather scarce A study was undertaken whereby drought was simulated by sodium chloride (NaCl)), mannitol, and polyethylene glycol (PEG, 20,000 mol wt), and its effect on the germination characteristics of Trifolium repens L, Lolium perenne L, Danthonia caespitosa Gaudich, Atriplex vesicaria Hew ex Benth and A nummularia Lindl was determined These osmotic drought effects were compared with those of true drought The rate and total germination of all the species declined with decreasing levels of water potential The extent of such reduction varied considerably among species and with the type of osmotic medium On iso-potential basis, the order of osmotic medium with respect to the severity of their effect on germination reduction in all the species was PEG > NaCl> mannitol It was suspected that both NaCl and mannitol entered the seeds, and also that the toxic effects of NaCl were either equally or dominantly offset by the solute entry effects Under artificial conditions when soil/seed contact and water flow properties of soil media were nonlimiting and there was no undesirable microbial activity, the equivalence of osmotic-PEG and matric potential held for all the species under study Osmotic solutions created by PEG did serve as a convenient and satisfactory media for studying the effect of true drought on seed germination However, caution must be exercised in extending these results to predict germination behavior in soil/water media where the so-called “nonlimiting” conditions may not always be met The order of species with respect to drought tolerance at germination was: L perenne > A nummularia = D caespitosa > A vesicaria > T repens This tolerance may be a reliable indication for species as regards their ease of germination under comparatively adverse soil/ water conditions However, it is suggested that it is not necessarily an acceptable index of drought tolerance in mature plants

Aspects of the Biology of Trientalis Borealis Raf

Abstract: Three species and one subspecies of Trientalis are recognized in North America, but only Trientalis borealis Raf., the northern starflower, occurs in eastern North America. The life cycle consists of three distinct phases each year: shoot development, rhizome growth, and tuber formation. Asexual reproduction by tubers is more important than reproduction by seed. Of the annual dry matter produced, 64.8% is apportioned to asexual reproduction and less than 2% to sexual tissue. Rhizome growth and tuber formation are regulated by photo—period; short days favor tuberization and long days favor rhizome growth. Tuber formation under field conditions began in July, when the photoperiod was about 15 hr. Cool nights and warm days were more favorable for the accumulation of dry matter than warm nights and days. The number of degree—hours accumulated during shoot development of northern and southern populations was similar at sites 200 miles apart on a north—south gradient, but shoot development occurred during a shorter period of time at the northern site. Seedlings of T. borealis have not been found in the field, but relatively high germination rates were achieved under laboratory conditions, Cold treatment increased the percentage germination of trientalis borealis seeds. Ninety days of stratification delayed the period of peak germination and increased the length of time before germination began after the seeds were exposed to room temperatures. The duration of germination and peak period of germination after stratification were about the same for controls and seeds exposed to 30— or 60—day periods of stratification.

Seed and Embryo Germination in Syringa vulgaris and S. reflexa as Affected by Temperature during Seed Development

Abstract: Effects of controlled temperature conditions during seed development on seed and embryo germination of Syringa vulgaris were studied using vegetatively propagated mother plants. Seeds from mother plants grown at 18–24°C were partially dormant at low (15°C) but not at high (21°C) germination temperature, while seeds from outdoors or from plants grown at 12°C were not dormant at all. Seed dormancy at low temperatures was induced as well when branches from outdoor plants were kept at 18–24°C for the last two-three weeks before harvesting. The dormancy induced by 24°C during seed development was not broken by keeping branches at 12°C for the last two-three weeks. In most cases the induced seed dormancy was broken completely by gibberellic acid. Embryo germination at 24 or 15°C was not affected by mother plant temperature. Part of the embryos from plants grown at 24°C were, however, dormant at 9°C. The ability of embryos to germinate in osmoticum was only slightly affected by mother plant temperature. The mechanical resistance of the endosperm was significantly higher in the seeds from plants grown at 24°C than in seeds from 12°C. Both the embryos and the seeds of S. reflexa were dormant at the time of termination of embryo elongation. Experiments with three seed-propagated mother plants indicated that the water potential of embryos may be reduced by high mother plant temperature.

The ninety‐year period for dr. beal's seed viability experiment

Abstract: In 1879 Dr. W. J. Beal selected seeds of 23 different species of locally common plants, mixed 50 seeds of each species with moist sand in unstoppered one-pint bottles, and buried the bottles in a sandy knoll to be unearthed and the viability of the seeds tested periodically. The year 1970 marked the ninetieth year the seed had been buried, and the thirteenth bottle was recovered to test for seed viability. Of the three species which had germinated in the 1960 test (curly dock, Rumex crispus; evening primrose, Oenothera biennis; and moth mullein, Verbascum blattaria), only V. blattaria had viable seed with 20% germination. No other species germinated. All ten seedlings of V. blattaria were grown to maturity, and seeds were then harvested to study the possible deviations from normality and the requirements for seed germination. All seedlings emerging from the first progeny seed appeared normal. The most prominent requirement for germination was light, and this is a possible explanation of why the seeds had remained viable but dormant for so long a period. One-third of the freshly harvested seed germinated in darkness and, furthermore, redrying of dark-moistened seed in the absence of light induced additional germination. Germination of dark-moistened seed was not completely restored when the still moist seeds were subsequently exposed to light. However, when dark-moistened seeds were dried and then remoistened in the light, germination was about 95 %. About 5 % of the seed did not germinate under the conditions used. We find that 5 % of the population of V. blattaria seeds are dormant for unknown reasons, that 30 % will germinate if supplied only with moisture, and that 65 % are inhibited and require light and moisture simultaneously for germination. Supplying this 65 % of the population with moisture in darkness results in the development of a second type of inhibition which is no longer light reversible. It appears that the simultaneous requirement for light and moisture is an important factor in permitting V. blattaria seeds to remain dormant during prolonged burial. THE SPRING OF 1970 marked the 90-year period for the seed viability experiment initiated by Dr. W. J. Beal, then professor of botany and forestry at the Michigan Agricultural College in East Lansing. The experiment is best described by Dr. Beal (1905): "In the autumn of 1879 I began the following experiments, with the view of learning something more in regard to the length of time the seeds of some of our most common plants would remain dormant in the soil and yet germinate when exposed to favorable conditions. I selected fifty freshly grown seeds from each of twenty-three different kinds of plants. Twenty such lots were prepared with the view of testing them at different times in the future. Each lot or set of seeds was well mixed in moderately moist sand, just as it 1 Received for publication 12 May 1972. This work was supported, in part, by The National Science Foundation (GB-18353X). Journal Article No. 5920 from the Michigan Agricultural Experiment Station. We wish to thank Professor J. A. D. Zeevaart and Mr. Donald E. Davis for their help and consultation and for the use of greenhouse facilities supported by the Atomic Energy Commission, Contract AT-(11-1)-1338. was taken from three feet below the surface, where the land had never been plowed. The seeds of each set were well mixed with the sand and placed in a pint bottle, the bottle being filled and left uncorked, and placed with the mouth slanting downward so that water could not accumulate about the seeds. These bottles were buried on a sandy knoll in a row running east and west." During the first 35 years of the experiment, germination tests were performed every fifth year, and every tenth year thereafter (Beal, 1884, 1885, 1889, 1894, 1904, 1905, 1911; Darlington, 1922, 1931, 1941, 1951; Darlington and Steinbauer, 1961). The thirteenth bottle was recovered for testing on April 18, 1970, leaving seven more bottles for future tests. GERMINATION TESTS WITH THE BEAL SEEDSGermination tests were performed in a greenhouse during the summer months of 1970. A soil mixture, consisting of approximately equal parts of well-sifted loam, sand, and muck soil, was steamsterilized for 12 hr under 10-12 lb pressure. Three clean plastic trays, with perforated bottoms

Establishment of Early Successional Plant Populations on Forest and Prairie Soil

Abstract: Seed germination and plant community development on adjacent forest and prairie soils (Typic Hapludalf and Typic Halplaquoll) were studied to elucidate the causes of variation in plant community composition during the first growing season after crop harvest. The number of plant individuals in July on the forest soil was three times larger than on the prairie soil. Abutilon theophrasti, Chenopodium album, Polygonum pensylvanicum, and Setaria faberii occurred in large numbers on the forest soil but were considerably less important on the prairie soil. Ipomoea hederacea predominated on the prairie soil. The seed load after abandonment on the forest soil was larger than on the prairie soil both before and after overwintering. Total numbers of plants that reached maturity were significantly higher (at the 5% level) on the forest soil than on the prairie soil. Population levels were generally constant throughout the growing season. Diversity peaked in June and was higher on the prairie soil than on the forest soil throughout the growing season. Germination of Ambrosia artemisiifolia, Lactuca scariola, and Polygonum was enhanced by moist soil conditions, whereas germination of Amaranthus hybridus was higher under dry soil conditions. Lactuca and Polygonum were the most sensitive to water stress and Abutilon and Setaria the most tolerant. It appears that the kinds and numbers of plants that become established in an abandoned field are a function of the number of germinable seeds present in the soil and the seed—soil water relationships. Of the soil parameters that may control seed germination, there is strong evidence to suggest that soil moisture the extreme upper portion of the profile is the major factor.

Promotion of seed germination by cyanide.

Abstract: Potassium cyanide at 3 mum to 10 mm promotes germination of Amaranthus albus, Lactuca sativa, and Lepidium virginicum seeds. l-Cysteine hydrogen sulfide lyase, which catalyzes the reaction of HCN with l-cysteine to form beta-l cyanoalanine, is active in the seeds. beta-l-Cyanoalanine is the most effective of the 23 alpha-amino acids tested for promoting germination of A. albus seeds. Aspartate, which is produced by enzymatic hydrolysis of asparagine formed by hydrolysis from beta-cyanoalanine, is the second most effective of the 23 amino acids. Uptake of aspartate-4-(14)C is much lower than of cyanide.Radioactive tracer in K(14)CN shows uptake of about 1.5 mumoles of HCN per gram of A. albus and L. sativa seeds after 20 hours of imbibition. Extracts of the seeds gave high (14)C activity in beta-cyanoalanine, asparagine, and aspartate. The acid-hydrolyzed protein extract gave high activity only in aspartate. Tests were negative for free cyanide in the seed. Respiration of the seed is inhibited more than 75% by KCN and by KN(3) at 10 mm. Azide at greater than 1.0 mm inhibits the promotion of germination by cyanides. Neither 0.1 mm KCN nor KN(3) inhibit O(2) consumption, whereas lower concentrations promote germination. It is concluded that the high rate of utilization of cyanide in the reaction to form beta-l-cyanoalanine and the subsequent incorporation into protein limit any inhibition of oxygen consumption. The promotion of seed germination is substrate-limited by asparagine-aspartate, which is required for protein synthesis.

Intrapopulational variation in the germination of seeds in Hyptis suaveolens

Abstract: Seeds collected from the same population of Hyptis sauveolens Poit. show a great variability in size, which is correlated with differences in the germination response. For experimental purposes these seeds were grouped in three weight categories and subjected to continuous light or darkness at five temperatures (20 degrees to 40 degrees C). Substantial differences, both in total germination percentages and in rate of germination, were observed between the groups tested. The period necessary for light saturation depends on the conditions of previous incubation in darkness and on the weight class tested. Both in initial photosynthetic area and in dry weight, seedlings derived from the smallest seeds differ significantly from seedlings derived from the other groups. The possible ecological significance of the heterogeneity in the germination reponse and in the early performance of the plantlets, may have important ecological significance. See full-text article at JSTOR

Effect of Soil Application of Dairy Manure on Germination and Emergence of Some Selected Crops

Abstract: Germination and emergence of sudangrass (Sorghum sudanense Stapf ‘Piper’), barley (Hordeum vulgare L. ‘Numar’), radish (Raphanus sativus L. ‘Cherry Belle’), and spinach (Spinacea oleracea L. ‘Bloomsdale’) in a glasshouse were investigated using a Chino loam soil where various amounts (0, 5, 10, 15, and 20% dry manure by weight) of dairy manure were added. The degree of germination injury depended on the crop species and rate of application or the salt and N inputs. The crop sensitivity to salt or NH3 were as follows: barley < sudangrass and spinach < radish. Barley and sudangrass were more tolerant to salt or NH3 than spinach and radish. Barley germination data from treatments which had NaCl added to the soil extracts to obtain the same osmotic potential as those treated with urine, urea, or manure suggest that the germination injury was not salt specific and that other compounds such as NH3 were also contributing factors. Germination injury can be minimized by planting several days after soil application of large amounts of dairy or feedlot manure to allow volatilization of a significant quantity of NH3 or after adequate preirrigation, or both.

Seed Dormancy in Acer CHANGES IN ENDOGENOUS CYTOKININS, GIBBERELLINS AND GERMINATION INHIBITORS DURING THE BREAKING OF DORMANCY IN ACER SACCHARUM MARSH

Abstract: The present studies on changes in the levels of cytokinins, gibberellins, and germination inhibitors during stratification of Acer saccharum seeds suggest that the breaking of dormancy is a phasic process Stratification at 5 °C led to a marked increase in the butanol-soluble cytokinins after 20 d Further chilling resulted in a loss of cytokinin The majority of the detectable cytokinin activity co-chromatographed with zeatin Similarly, at day 40, acidic gibberellin-like substances increased and declined with further chilling A loss of acidic germination inhibitors was also detected during stratification The acidic fraction was shown to contain abscisic acid (ABA) by its behaviour on GLC and isomerization with ultra-violet light Determinations of endogenous levels of ABA by combined GLC and isotope dilution methods indicated a loss of 97-9 per cent ABA during stratification The data suggest that the breaking of seed dormancy at low temperature involves the initiation of an ordered sequence of events that include the changes in growth hormones necessary to determine the course of development for the removal of dormancy

Changes in the Activity of Some Hydrolases, Peroxidase, and Catalase in the Rice Seed during Germination

Abstract: A study was made of the changes in activity of enzymes involved in the breakdown of stored phytin, lipid, and hemicellulose in the aleurone layer of rice seed (Oryza sativa L., variety IR8) during the 1st week of germination in the light. Enzyme assays were made on crude extracts from degermed seed, and activities were expressed on a per seed basis. Phytase activity increased within the 1st day of germination. The increase in activity of most other enzymes—phosphomonoesterase, phosphodiesterase, esterase, lipase, peroxidase, catalase, β-glucosidase, and α- and β-galactosidase—closely followed the increase in protein content. Their peak activities occurred by the 5th to the 7th day. Some enzymes, such as β-1, 3-glucanase and α-amylase, continued to increase in activity after the 7th day. Phytase, β-1, 3-glucanase, and α-amylase followed a similar sequence of production in embryoless seed halves incubated in 0.12 μM gibberellin A3, but the production of lipase was delayed.

Photocontrol of the germination of onoclea spores: I. Action spectrum.

Abstract: Light stimulates the germination of spores of the fern Onoclea sensibilis L. At high dosages, broad band red, far red, and blue light promote maximal germination. Maximal sensitivity to these spectral regions is attained from 6 to 48 hours of dark presoaking, and all induced rapid germination after a lag of 30 to 36 hours. Maximal germination is attained approximately 70 hours after irradiation. Dose response curves suggest log linearity. The action spectrum to cause 50% germination shows that spores are most sensitive to irradiation in the red region (620-680 nm) with an incident energy less than 1000 ergs cm−2; sensitivity decreases towards both shorter and longer wavelengths. Although the action spectrum is suggestive of phytochrome involvement, photoreversibility of germination between red and far red light has not been demonstrated with Onoclea spores. An absorption spectrum of the intact spores reveals the presence of chlorophylls and carotenoids. Since the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea does not inhibit germination, it is concluded that photosynthesis does not play a role in the germination process.

Growth requirements and development of Cypripedium reginae in axenic culture

Abstract: In preliminary studies of terrestrial orchids of the Thunder Bay region Cypripedium reginae showed greatest promise as a species for the investigation of the effects of temperature, light, and nutrients. The orchid was grown from seed in sterile cultures on agar slopes of media consisting of various combinations of minerals, sugars, casein hydrolysate, yeast extract, potato extract, the vitamins thiamine, pantothenic acid, and pyridoxine, and the aminopurines kinetin, kinetin riboside, 6(γ,γ-dimethylallylamino)purine, and zeatin.Better germination and growth occurred at 25 °C vs. 15 °C. Germination was better in the dark than in the light. The young protocorms are adversely affected by light until a crucial stage of development is reached. Premature exposure to light, even at the low intensity of 70 lm/ft2, caused mortality.There was no germination on sterile-distilled-water agar or on mineral media alone. Mineral–sugar media produced fairly healthy plantlets; better results were obtained with sucrose, de...

Reaction of Germinating Maize Pollen to Helminthosporium maydis Pathotoxins 1

Abstract: Pollen from fertile plants of corn (L.), with normal and restored male-sterile cytoplasm (), from various sources was assayed for germination on media containing pathotoxins extracted from infected leaves. The “pathotoxin” from race O inhibited neither germination nor growth of pollen from any of the or normal cytoplasm sources tested, as compared with controls. The pathotoxin from race T, however, inhibited germination and growth of pollen from and plants. Growth of pollen from , and normal cytoplasm sources was not inhibited by race T pathotoxin. The advantages of a pollen bioassay are discussed, as are possible special applications of this procedure.

The nutritional evaluation of kidney beans (Phaseolus vulgaris). The effect on nutritional value of seed germination and changes in trypsin inhibitor content

Abstract: The total N content of kidney beans (Phaseolus vulgaris) was found to increase on germination. The overall amino acid composition however changed very little. Rats fed on a diet containing raw beans lost more weight than the protein-free controls (negative n.p.u. value). Germination was found to bring about a gradual improvement in nutritive value probably through the elimination of some of the toxic constituents of the seed. The near doubling of the amount of trypsin inhibitors by the 8th day of germination taken together with the substantial improvement in the nutritive value of the bean appeared to rule out trypsin inhibitors as the main toxic components of raw beans.

Cascade activation of genome transcription in wheat.

Abstract: TRANSCRIPTIONAL events are arrested in developing plant seeds when maturation is completed. The RNA synthesis may be resumed when suitable changes in the environment make it possible for the seed to germinate. It is not known, however, how early and in what order the synthesis of cellular RNA species is activated in response to the stimulus to germinate. Our previous observations1,2 indicate that RNA synthesis is triggered almost immediately before the activation of protein synthesis in vivo but other reports3–5 suggest that RNA synthesis remains repressed for many hours after germination starts. Further attempts to establish the time course of RNA synthesis in germinating wheat embryos were therefore undertaken.

Inoculation of seeds and soil with basidiospores of mycorrhizal fungi

Abstract: It was demonstrated that basidiospores of the fungus Rhizopoyon luteolus , mycorrhizal for Pinus radiata , could be used successfully as seed inoculum after freeze-drying and storage for 3 months at 22°C, provided the inoculum level was increased 100-fold. Spore inoculum applied to seed could be held dry for at least 2 days before planting provided inoculum was increased 10-fold. On sowing freshly inoculated seed to sterile soil, 3 × 10 3 basidiospores/seed were adequate for infection but maximum mycorrhizal infection occurred with 3 × 10 4 spores/seed. A dose-response curve was obtained for mycorrhizal infection when basidiospores were applied to soil. As few as 100 spores/290 cm 3 pot were sufficient for mycorrhizal infection although infection increased with greater spore dose to a maximum of 10 5 spores/pot. Plant growth response was related to intensity of infection. It is suggested that the percentage germination of basidiospores in the rhizosphere may be considerably greater than those reported in studies with synthetic medium. A rhizosphere effect on germination of basidiospores was demonstrated and a method developed to facilitate studies of spore germination in the rhizosphere.

Effects of Kinetin, Gibberellins and (±) Abscisic acid on the Germination of Lettuce (Lactuca sativa)

Abstract: Germination responses of achenes of lettuce (Lactuca sativa L, cv. Arctic King) to treatment with kinetin, gibbe-rellins and abscisic acid were examined over a range of temperatures: in both light and dark. Kinetin (0.1–10 mg/l) strongly promoted germination at temperatures above 27±C in continuous light or after short periods of illumination during the early stages of imbibition. It also relieved the inhibitory affects of abscisic acid in these conditions. In total darkness however kinetin treatment resulted in only a minor promotive effect. Treatment with gibberellic acid (A3) or a mixture of gibberellins A4 and A7 were much less effective in promoting germination at higher temperatures of lettuce achenes exposed to light but were strongly promotive in the dark.

The effects of imbibition drying treatments on wheat seeds

Abstract: SUMMARY Wheat seeds were imbibed and re-dried under conditions that did not give rise to radicle protrusion through the seed coat. When seeds pre-treated in this way were planted in moist vermiculite, coleoptile emergence was faster than from untreated seeds. This advancing effect on coleoptile emergence (‘seed invigoration’) was most marked when the seedlings were grown at low temperature or under osmotic stress (i.e. under unfavourable conditions). The seed-borne pathogen Septoria nodorum was not affected by an imbibing-drying treatment. Conditions of imbibition and drying giving optimal invigoration are described and data on the metabolism of untreated and invigorated seeds are presented. Oxygen uptake and [14C]-leucine incorporation into protein were more enhanced in aleurone layers than in embryos isolated from invigorated seeds. Both untreated and invigorated seeds showed very low α-amylase levels when dry, although a-amylase activity developed more rapidly in invigorated seeds during germination. Gibberellic acid alone was not able to replace an imbibing-drying treatment.

Patterns in the evolution of amentiferous fruits

Abstract: The diversity of fruit types within the Amentiferae appears to be the result of different seed dispersal and seedling establishment strategies that have evolved independently in the amentiferous families within the confines imposed by the wind-pollination syndrome. Dispersal of unadorned fruits and seeds by wind (e.g.,Betula, Rhoiptelea, Casuarina) has preceded the development of more efficient air-borne devices (e.g.,Ostrya, Carpinus, Engelhardia). Animal dispersal is the most advanced strategy, relying rarely on drupes, as in the shrubby Myricaceae, or on nuts, as inCorylus, Quercus, Carya, Juglans, Alfaroa, etc. The pattern of seedling establishment shows a structural-functional relationship to the seeddispersal strategy. Epigeal germination predominates in plants of open habitats. Those species with small fruits rely on wind dispersal, and their seeds have a relatively short germination time, whereas species with medium-sized fruits are often animal-dispersed with seeds that may have protracted germination times. In either case the reserve food supply for the young seedling is limited, and light is needed to spark photosynthesis. Hypogeal germination has evolved independently in several amentiferous families (e.g., Betulaceae, Fagaceae, Juglandaceae). This pattern is associated with closed habitats and plants with large seeds that have the capability of establishing vigorous seedlings in microhabitats of reduced light intensity where photosynthesis is impaired. The subterranean protection afforded the cotyledons and axillary meristems is a correlative feature that may have considerable importance in seedling survival where desiccation and predation are intense.

The chemical environment of leaf surfaces with special reference to spore germination of pathogenic fungi

Abstract: The release of diffusible substances from plant leaves, fungal spores or from pollen into water droplets on the surface of leaves is discussed in relation to (1) direct and indirect effects on spores of pathogens and (2) the effect on the growth of saprophytic micro-organisms. Evidence suggests that competition for nutrients in droplets on leaves may limit germination of spores of some pathogens. Modification of the chemical environment of leaf surfaces by saprophytic micro-organisms is discussed in relation to lytic enzyme and antibiotic production, cuticle degradation, production of growth substances and fixation of nitrogen. Examples are given of the effect on pathogenic fungi of diffusible toxins from leaves and inhibitors associated with surface wax. Treatments of leaves that remove or reduce surface wax can result in a stimulation of spore germination of some pathogenic fungi. The possible occurrence of phytoalexins on leaf surfaces prior to entry of pathogens into leaves is discussed in relation to differences in host-pathogen interaction.

The Effect of Stratification on the Endogenous Cytokinin Levels of Seed of Protect compacta and Leucadendron daphnoides

Abstract: The soybean callus assay was used to study the effect of stratification on the cytokinin levels of the embryo dormant seed of Protea compacta R.Br. and the seed of Leucadendron dapbnoides Meisn., where dormancy is coat imposed. Chilling the seed for 30 days increased germination significantly, and resulted in a simultaneous increase in the butanol soluble cytokinins of both species. It would appear as if these compounds are either synthesized or released from a bound form in embryo dormant seed. In contrast, an interconversion from water soluble to butanol soluble cytokinins appears to account for the increase where dormancy is coat imposed. The results also indicate that for germination to take place a threshold concentration of cytokinin may be required. It is suggested that the increase in butanol soluble cytokinins may lead to the breaking of dormancy, probably by increasing radicle elongation and/or cotyledon expansion.

Changes in Endogenous Cytokinins of Lettuce Seed during Germination

Abstract: Using the soybean callus bioassay it has been shown that dormant lettuce seeds (Lactuca sativa L. cv. Grand Rapids) contain large amounts of water soluble cytokinins and small amounts of butanol soluble ones. When the seeds are irradiated with red light, or imbibed with 5 mg/1 gibberellic acid in the dark, the total cytokinin content of the seeds decreases, the level of water soluble cytokinins decreases, and the level of the butanol soluble cytokinins increases. Far-red light does not reverse this effect completely although cytokinin activity in the butanol extracts decreases following such irradiation. It is proposed that the interconversion of cytokinins initiated by red light, or gibberellic acid in the dark, is one of the primary events leading to radicle elongation in light-sensitive lettuce seed.