Showing papers on "Germination published in 1983"

Physiology and Biochemistry of Seeds. in Relation to Germination

Abstract: Physiology and biochemistry of seeds in relation to germination , Physiology and biochemistry of seeds in relation to germination , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Induction of dormancy during seed development by endogenous abscisic acid: studies on abscisic acid deficient genotypes of Arabidopsis thaliana (L.) Heynh.

Abstract: Mutant lines of Arabidopsis thaliana (L.) Heynh., which are characterized by symptoms of withering and the absence of seed dormancy, showed much lower levels of endogenous abscisic acid (ABA) in developing seeds and fruits (siliquae) than the wild type. Reciprocal crosses of wild type and ABA-deficient mutants showed a dual origin of ABA in developing seeds. The genotype of the mother plant regulated a sharp rise in ABA content half-way seed development (maternal ABA). The genotype of the embryo and endosperm was responsible for a second ABA fraction (embryonic ABA), which reached much lower levels, but persisted for some time after the maximum in maternal ABA. The onset of dormancy correlated well with the presence of the embryonic ABA fraction and not with the maternal ABA. Dormancy developed in both the absence and presence of maternal ABA in the seeds. In this respect maternal ABA resembled exogenously applied ABA which did not induce dormancy in ABA-deficient seeds. However, both maternal and applied ABA stimulated the formation of a mucilage layer around the testa, which could be observed during imbibition of the mature seeds. In the mature state, ABA-deficient seeds germinated in the siliquae on the plant, but only when the atmosphere surrounding the plant was kept at high relative humidity. In younger stages germination in siliquae occurred after isolation from the plants and incubation on wet filter paper. Therefore, it seems that limited access to water is the primary trigger for the developmental arrest in these seeds.

A comparative study of germination responses to diurnally-fluctuating temperatures

Abstract: (1) Seeds collected from populations of a range of native herbaceous plants in the Sheffield region were subjected to experimental treatments providing a range of amplitudes of diurnal fluctuations in temperature. All experiments involved a photoperiod of 18 h combined in some species with a comparable series of temperature treatments applied in continuous darkness. (2) In the light a stimulation of germination by fluctuating temperature was observed in forty-six of the 112 species tested. The responses varied from those indicating an absolute requirement in all seeds for large (>5 OC) fluctuations (e.g. Rorippa islandica) to polymorphisms (e.g. Carex otrubae) in which some seeds germinated at constant temperatures whilst the remainder responded to small (<5 OC) fluctuations. (3) The capacity to respond to fluctuating temperatures in the light was prominent in species of wetland where it appears to provide a mechanism whereby spring germination may be initiated by increasing irradiance and falling water table. (4) In certain species (e.g. Ranunculus repens) the effect of continuous darkness was to increase the amplitude of temperature fluctuation necessary for germination. Small-seeded species known to form buried seed reserves (e.g. Juncus effusus) were inhibited by darkness and in the absence of light did not respond to fluctuating temperatures. (5) Sensitivity to temperature fluctuations in darkness was observed in species of grassland, wetland and disturbed habitats, and was conspicuous among species forming persistent seed banks. It seems likely that responses to temperature fluctuations in darkness provide mechanisms of depth-sensing by buried seeds and may initiate establishment from seed within canopy gaps. (6) Many of the species found to respond to temperature fluctuations in darkness are successful weeds of arable land or pasture. A polymorphic response to temperature fluctuations may account partially for the unpredictability of appearance of infestations of these weeds. The ability to invade canopy gaps throughout the year is important to the success of many pasture weeds (e.g. Rumex obtusifolius, Ranunculus repens) and is notably absent from the major sown species, Lolium perenne.

Seed Germination in a Seasonal Tropical Forest in Panama: A Community Study

Abstract: Seed germination in the seasonal tropical forest on Barro Colorado Island, Panama, was studied at the community level to (1) determine the seasonal timing of germination of the community, (2) identify primary selective factors controlling timing of germination, (3) determine the relative importance of dormancy vs. timing of seed dispersal as mechanisms controlling timing of germination, (4) examine inter— and intraspecific components of variance in length of dormancy, and (5) identify major seed germination syndromes. Three community—level measures of seedling emergence indicated that there was a unimodal community peak in germination within the first 2 mo of the 8—mo—long rainy season. Of the °185 dicot, mostly woody, species germinating each year, the median time of emergence of 75% of the species occurred within the 1st 3 mo. There was a unimodal peak in germination in pioneer tree species, lianas, canopy trees, wind— and animal—dispersed species, and seedlings with and without persistent seed reserves. In contrast, there was no distinct peak period of emergence in understory species and shade—tolerant tree species. Initial seedling height of species emerging sequentially throughout the rainy season did not increase. The early emergence of most species, including three—fourths of the 35 species fruiting in the late rainy season, indicated that the early rainy season was the optimal time to emerge. Maximizing the length of the first growing season was not an important factor selecting for early emergence, because later—emerging species did not compensate for the shorter growing season by being larger at germination or by having seed reserves for rapid growth. Seedling—seedling competition is a primary biotic factor selecting for early emergence in pioneer species growing in the intensely competitive light—gap habitat. In shaded understory habitats, where competition among seedlings is much less intense, understory and shade—tolerant tree species emerged throughout the rainy season. Mean length of dormancy (MLD),the time between sowing and germination, of 157 woody dicot species on Barro Colorado Island ranged from 2 to 370 d. In over half the species, MLD exceeded 4 wk; hence, delays in germination are common. The season in which seeds were dispersed and the dispersal mechanism explained small but significant portions of the variance in MLD among species; life form explained none; but differences among three germination syndromes explained two—thirds of this variance. In the delayed—rainy syndrome (18% of all species) seeds were dispersed in the rainy season but were dormant until the beginning of the next rainy season, 4—8 mo later. Dormancy is the primary mechanism controlling time of germination. In the delayed—rainy syndrome and the intermediate—dry syndrome which follows, the length of the dormant period decreased as the interval between seed dispersal and the beginning of the rainy season decreased. In the intermediate—dry syndrome (42% of all species) seeds were dispersed during the during the dry season and remained dormant until the beginning of the rainy season. Seeds are primarily dispersed 1—2 mo before the beginning of the rainy season, which reduces the number of false germination cues encountered and decreases the length of time seeds are exposed to postdispersal predation while dormancy prevents germination during dry season rains. In the rapid—rainy syndrome (40% of all species) seeds were dispersed in the rainy season and germinated during, but not early in, that season. Dormancy has been replaced entirely by timing of dispersal as a mechanism controlling time of germination. Half of these species germinated in <2 wk, the rest in 2—16 wk.

Role of peroxidase in the development of water-impermeable seed coats in Sida spinosa L

Abstract: The seed coats of S. spinosa (prickly sida, Malvaceae) become impermeable to water during seed development on the mother plant. After the seeds have dehydrated during the final maturation stages, piercing of seed coats is necessary to induce imbibition of water and germination. Onset of impermeability occurs during seed coat browning, well in advance of seed dehydration. I. Marbach and A.M. Mayer (1975, Plant Physiol. 56, 93-96) implicated polyphenol oxidase (PO; EC 1.10.3.1) as catechol oxidase in the formation of insoluble polymers during development of coat impermeability in a wild strain of pea (Pisum elatius) seeds. We found, however, that peroxidase (EC 1.11.1.7), not PO, is instrumental in the development of water-impermeable seed coats in prickly sida. We isolated coats and embryos from seeds harvested at several stages of development. Highest peroxidase activity of coat extracts correlated well with the developmental stages of maximum conversion of soluble phenolics to insoluble lignin polymers. Although seed extracts oxidized dihydroxyphenylalanine, this activity was eliminated by catalase, indicating that the oxidation of phenolics in the coat is catalyzed by peroxidase rather than PO. Histochemical localization of peroxidase was strongest in the palisade layer; both the level and time of appearance of activity was proportional to the spectrophotometric assays of seed-coat extracts. The presence of peroxidase and the absence of PO in the seed coat were also confirmed with immunocytochemistry. Our results support the view that peroxidase is involved in the polymerization of soluble phenolics to insoluble lignin polymers during development of prickly sida seed coats, causing the formation of a water-impermeable barrier prior to seed dehydration. As dehydration proceeds, the chalazal area finally becomes impermeable resulting in the hard mature seeds of prickly sida.

Allelopathic effects of juglone on germination and growth of several herbaceous and woody species

Abstract: Laboratory experiments were conducted to determine juglone sensitivity of 16 species (Trifolium incarnatum, Coronilla varia, Vicia villosa, Lespedeza stipulacea, L. cuneata, Acer ginnala, Caragana arbor-escens, Elaegnus angustifolia, E. umbellata, Lonicera maackii, Quercus alba, Fraxinus americana, Liriodendron tulipifera, Alnus glutinosa, Pinus strobus, andP. sylvestris) being considered for mixed plantings withJugions nigra (black walnut). All species were sensitive to juglone, but seed germination and radicle elongation were less affected than shoot elongation and dry weight accumulation. Seed germination and radicle elongation were affected by juglone in 6 and 11 species, respectively, mainly by the higher concentrations (10−3 M and 10−4 M). Shoot elongation and dry weight accumulation of all species were affected by juglone; many species were sensitive to concentrations as low as 10−6 M. Seedlings of all species were severely wilted and eventually killed by 10−3 M juglone, and most were chlorotic and severely retarded by 10−4 M juglone. Seedlings inhibited by 10−6 M and 10−5 M juglone did not showany visible signs of injury. Based on the effects on seedling shoot elongation and dry weight accumulation, the five species found to be most sensitive to juglone were:Lonicera maackii, Lespedeza cuneata, Trifolium incarnatum, Alnus glutinosa, and Elaeagnus umbellata.

Spore dormancy in vesicular-arbuscular mycorrhizal fungi

Abstract: Spores of four species of VA mycorrhizal fungi were unable to germinate when first formed. The change in their capacity to germinate was examined by using populations of newly-formed spores with a narrow age range. Percentage germination and length of hyphae produced by the spores when incubated in soil or on nutrient agar media was measured during storage at constant temperatures between 5 and 37 °C in both wet (−0.15 MPa) and dry (−300 MPa) soil. The results supported the hypothesis that spores of these species were innately dormant when first formed and suggest that changes occurred with close synchrony. The dormancy period in wet soil was approximately 6 weeks for Glomus caledonium and G. monosporum , and 12 weeks for Gigaspora calospora . This period was significantly reduced to 1 week for the Glomus spp. and 6 weeks for Gigaspora calospora in dry soil. For Acaulospora laevis the dormancy period was 6 months under all conditions. Plant roots had no effect on the change to quiescence of spores of any species, however newly-quiescent spores were effective propagules.

Sunflowers (Helianthus annuus) are allelopathic to weeds.

Abstract: Laboratory, greenhouse, and field studies were conducted to determine the allelopathic potential of sunflower (Helianthus annuus L.) cultivars to suppress weed germination and growth. Germination of wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler] seeds at 25 C in undiluted aqueous extracts of sunflower leaf tissue was inhibited 75%, but was stimulated by up to 150% at 10- and 100-fold dilutions. Stem-tissue extracts at all concentrations stimulated wild mustard seed germination. The germination response of other weed species varied with the sunflower cultivar and concentration of tissue extract. In sand culture, leachates of dried sunflower leaf and stem tissue inhibited broadleaf - weed seedling growth, but had little or no effect on the growth of grass weeds. Sunflower root exudates inhibited seedling growth, but were less effective than leaf and stem tissue leachates. Germination of weed seeds was unaffected by root exudates. Over a 5 -yr period, weed density and percent ground cover increased less in field plots of sunflower than in control plots.

Longevity of Weed Seeds after 5.5 Years in the Stoneville 50 - Year Buried - Seed Study'

Abstract: Seeds of 20 weed species buried at depths of 8, 23, and 38 cm in 1972 and 1973 were exhumed at regular intervals and tested for viability and germination. Burial depth had little to no significant influence on longevity. After 5.5 yr 48% of johnsongrass (Sorghum halepense (L.) Pers.), 36% of velvedeaf (Abutilon theophrasti Medic.), 33% of purple moonflower (Ipomoea turbinata Lag.), 30% of spurred anoda (Anoda cristata (L.) Schlecht), 18% of hemp sesbania (Sesbania exaltata (Raf.) Cory), and 13% of pitted morningglory (Ipomoea lacunosa L.) seeds were still viable. No more than 6% of the original population for any other species was viable at 5.5 yr. Hard seeds com - prised a high percentage of the longer - lived seeds. Seeds of longest - lived species were losing viability at an average of 26% of the existing population each year from 3.5 to 5.5 yr. Additional index words. Seed viability, dormancy, germina- tion, seed coats.

Interactions between seed priming treatments and nine seed lots of carrot, celery and onion. I. Laboratory germination

Abstract: SUMMARY Samples of three seed lots of each of three cultivars of carrot, celery and onion were primed in polyethylene glycol solution for 2 weeks at 15 °C. Priming reduced the mean germination times (recorded at 15 °C) of all seed lots (compared to the untreated control) by 3–4 days in carrot, 6–10 days in celery and 3–5 days in onion. The largest reductions in mean germination time occurred in the slowest-germinating seed lots. There were highly significant interactions between priming and cultivars, and between priming and seed lots within cultivars for each species. Drying back the primed seeds at 15 °C increased the mean germination times (compared to primed seed which had not been dried) by 0·6 day in carrot and 1·4 days in celery, and there was no interaction with cultivars or seed lots. The corresponding increase for onion was either 1·0 or 1·8 days, according to the cultivar, but this variation was largely attributable to differences in time taken for the dried seeds to re-imbibe. Seeds dried back at 30 °C germinated 0·2·0·7 day (depending on the species) later than those dried at 15 °C. Percentage germination was not affected by either priming or drying back. Priming reduced the spread of germination times in all cultivars. For primed and dried-back seed, the spread of germination times was larger than that of primed seed in certain cultivars, but was always smaller than that of untreated seeds.

Inhibition of pitted morning glory (Ipomoea lacunosa L.) and certain other weed species by phytotoxic components of wheat (Triticum aestivum L.) straw.

Abstract: This study was conducted to determine if well-known phytotoxic effects of plant residues on crop growth could also be responsible for observed reductions of certain weed species in no-till cropping systems. An aqueous extract of field-grown wheat (Triticum aestivum L.) reduced the germination and root length of pitted morning glory (Ipomoea lacunosa L.) and common ragweed (Ambrosia artemisiifolia L.). Phytotoxicity was increased by about 70% when bioassays with the wheat extract on morning glory and ragweed were conducted in the presence of light. Phytotoxic substances were extracted from wheat with 2 N NaOH. The hydrolyzed extract was fractionated by thin-layer chromatography (TLC). The compound isolated by TLC having the greatest inhibitory effects on morning glory germination was identified using mass spectrometry and determined to be ferulic acid (4-hydroxy-3-methoxycinnamic acid). Ferulic acid at 5 × 103 M inhibited the germination and root length of morning glory 23 and 82%, respectively, and prickly sida (Sida spinosa L.) with carpels 85 and 82%, respectively. Crabgrass (Digitaria sanguinalis L.) germination was inhibited 100%. Ferulic acid had no effect on ragweed or prickly sida without carpels. Morning glory root and shoot biomass were reduced 52 and 26%, respectively, when morning glory was grown in sand and watered with a 5 × 103 M solution of ferulic acid. Ferulic acid in the presence of prickly sida seed carpels was found to undergo decarboxylation, forming a styrene derivative, 2-methoxy-4-ethenylphenol. The more phytotoxic styrene compound was produced by a bacterium isolated from the carpels of prickly sida seed. The study showed that ferulic acid and other compounds may indeed play a role in reducing the growth of certain weeds in no-tillage cropping systems.

Seasonal changes in the germination responses of buried seeds of arabidopsis thaliana and ecological interpretation

Abstract: Buried seeds of Arabidopsis thaliana exposed to natural seasonal temperature changes exhibited an annual dormancy/nondormancy cycle. The majority of freshly matured seeds were dormant. During burial in summer, fresh seeds and those that had been buried for 1 and 2 yr afterripened. During afterripening, seeds first germinated at 15/6 C and then at progressively higher temperatures until they were nondormant by October, when they germinated to high percentages at all thermoperiods except 35/20 C. Light was required for germination of both conditionally dormant and nondormant seeds. During autumn and winter, seeds reentered dormancy, first losing the ability to germinate at high and then at low temperatures. Thus, seeds can germinate in the field only in autumn, and germination is restricted to those seeds on or near the soil surface where both light and moisture can be nonlimiting In spring, seeds are dormant; in summer, temperatures are too high for germination, and in winter, they are too low. Consequentl...

Influence of Cultivation Regime Upon Buried Weed Seeds in Arable Cropping Systems

Abstract: (1) The effects of cultivation on the number of seeds of different species in arable land were investigated at four sites over several years. Soil cores were obtained from uncultivated and ploughed plots, and the seed content determined by germinating the seeds and counting and identifying the emerged seedlings. (2) Distribution of seeds was not uniform in the soil profile, and fluctuated annually on ploughed plots. Seed decline, although not markedly different between treatments, was more rapid in ploughed soil. The rate of seed decline at different depths was similar for both uncultivated and ploughed plots. Successful germination alone could not account for the rate of seed decline reported,4indicating that losses from other causes were substantial. (3) A considerable number of species were recorded in the seed bank (23-30), but only a few (3-4) comprised the majority. A number of species present in the seed bank of uncultivated soil were absent from the seedling flora.

Seed Ecology of Selected Amazon Basin Successional Species

Abstract: Two adjacent forest sites-a mixed forest on well-drained Oxisols and a caatinga forest on waterlogged Spodosols-were similar in the number of viable seeds m-2 in the seed bank: 180 for the mixedforest site, 200 for the caatinga site. Most germinated seeds were of successional pioneer tree species Seeds were entering the mixed-forest seed bank at a rate of ca 50 seeds m-2 yr-1. Agricultural and pasture sites tended to have larger seed banks (580-1,250 viable seeds m-2) composed almost entirely of grasses and forbs. The most common grass, forb, shrub, and pioneer tree species in the forest and disturbed-site seed banks (eight species in all) were tested for their ability to persist for 1 yr in open storage cans on the forest floor and for their response to a variety of germination triggers. Seeds of all species tested were still alive after 1 yr of incubation on the forest floor. In a lighted environment these species showed good germination under both moist and flooded conditions, but neither daily tempera...

Mechanical Resistance of the Seed Coat and Endosperm during Germination of Capsicum annuum at Low Temperature

Abstract: Decoated pepper ( Capsicum annuum L. cv Early Calwonder) seeds germinated earlier at 25°C, but not at 15°C, compared to coated seeds. The seed coat did not appear to impose a mechanical restriction on pepper seed germination. Scarification of the endosperm material directly in front of the radicle reduced the time to germination at both 15°C and 25°C. The amount of mechanical resistance imposed by the endosperm on radicle emergence before germination was measured using the Instron Universal Testing Machine. Endosperm strength decreased as imbibition time increased. The puncture force decreased faster when seeds were imbibed at 25°C than at 15°C. The reduction in puncture force corresponded with the ability of pepper seeds to germinate. Most radicle emergence occurred at 15°C and 25°C after the puncture force was reduced to between 0.3 and 0.4 newtons. Application of gibberellic acid 4+7 (100 microliters per liter) resulted in earlier germination at 15°C and 25°C and decreased endosperm strength sooner than in untreated seeds. Similarly, high O 2 concentrations had similar effects on germination earliness and endosperm strength decline as did gibberellic acid 4+7 , but only at 25°C. At 15°C, high O 2 concentrations slowed germination and endosperm strength decline.

Salt sensitivity of corn at various growth stages

Abstract: This study was conducted to determine the relative salt tolerance of corn (Zea mays L.) at different growth stages from germination to maturity when grown in organic soil. Another objective was to determine how rapidly and to what extent the salinity of the irrigation water can be increased during the growing season without decreasing the yield of corn. Germination tests on 16 cultivars showed that corn is relatively tolerant during germination. All but 2 cultivars germinated satisfactorily at soil water salinities, ECsw up to 10 dS/m (1 dS/m=1 mmho/cm). In separate greenhouse experiments, emergence of nine corn cultivars grown in an organic muck soil was delayed by increasing soil salinity but the final emergence percentage 6 days after planting was unaffected by ECsw up to 9.3 dS/m. Seedling growth was much more sensitive to salinity than seed germination. The threshold ECsw for dry matter yields at 21 days was below 1.0 dS/m for most cultivars. Salinities above this threshold of 1 dS/m decreased seedling growth 4.9% per unit increase in ECsw. The salt tolerance thresholds for ear and grain yields were much higher than for seedling growth, while yield decrements per unit increase in EC, above this threshold were greater. Fresh ear yields of Bonanza, a sweet corn cultivar, decreased 7.7% per unit increase in ECsw above a threshold of 5.8 dS/m. Dry grain yields decreased 10.1% per unit increase above 5.5 dS/m. Increasing the salinity of the irrigation water to 9 dS/m at the tasseling and/or grain filling stages did not significantly decrease yields below those obtained where irrigation water salinities were kept constant.

Studies on copper and cobalt tolerance in three closely related taxa within the genus Silene L. (Caryophyllaceae) from Zaire

Abstract: Experiments were carried out on the tolerance to and uptake of copper and cobalt by three members of a phylogenetic series of taxa within the genusSilene from Zaire which were reputed to represent a progression of increasing adaptation to metalliferous soils. Plants studied were the widespread and presumably non-tolerantSilene burchelli var.angustifolia (B), a more tolerant variant of this taxon (E) designated an ecotype, and the metallophyteS. cobalticola (C). Studies on the effects of both metals, singly and in combination, on seed germination, seedling and plant performance and yield, and metal uptake from soil cultures, confirmed in general the sequence B

Fruit size variation and its effects on germination and seedling growth in Xanthium strumarium

Abstract: Fruits of Xanthium strumarium L. from a population in southwestern Ontario exhibited an eightfold range in size. The effects of fruit size on seed size, germination, and seedling growth were investigated. Correlations between fruit size and seed size were strongly positive. In general, germination percentage and germination rate were both correlated positively with fruit size, although germination rate appeared to level off for the largest fruits. Cotyledon area and primary root length of newly emerged seedlings also were positively correlated with fruit size, although both variables and especially primary root length showed smaller increases over larger fruit sizes. The weights of newly emerged seedlings were highly positively correlated with fruit size. However, this relationship was not maintained for older seedlings. Weights of 15- and 30-day-old seedlings were constant over the majority of fruit sizes. This trend resulted from a negative correlation between seedling growth rate and fruit size which c...

Temperature relations of spore germination and hyphal growth of vesicular-arbuscular mycorrhizal fungi in soil

Abstract: Spores of Glomus caledonium, Gigaspora calospora and Acaulospora laevis from the same source and grown under the same conditions had different temperature limits for germination. Within these limits, temperature affected the duration of the period between imbibition and the onset of germination. Over most of the range, for each fungus, temperature caused no change in either the proportion of the spores which germinated, the time (after onset of germination) taken for the maximum proportion to germinate or the rate and extent of hyphal growth. At temperatures close to the limits, the rate of both spore germination and hyphal extension were decreased. The upper temperature limits for germination were less than those in moist soils in the natural habitat of the fungi, a feature which may have an ecological role.

Effect of Water Stress, Seed Coat Restraint, and Abscisic Acid upon Different Germination Capabilities of Two Tomato Lines at Low Temperature

Abstract: Two tomato (Lycopersicon esculentum Mill.) lines with greatly different capabilities to germinate at 10 degrees C were compared with respect to sensitivity to experimental treatments which affect the water status of the embryo. Germination rates and final percentages could be drastically changed (at 25 degrees C) by (a) removing the mechanical constraint from the radicle tip, (b) imposing water stress by an osmoticum, (c) stress hardening of the seeds through osmotic pretreatment, and (d) inhibiting embryo expansion by abscisic acid (ABA). All treatments showed a similar difference in germination vigor between the two lines indicating that cold sensitivity is in fact a matter of water relations rather than of phase transitions in membrane lipids. Inhibition of germination by ABA was completely abolished by removing the mechanical constraint from the radicle tip. Osmotic stress of -3 bar which quantitatively replaced this constraint in inhibiting germination also restored the sensitivity to ABA. It is concluded that all these treatments act on the balance between the hydraulic extension force of the embryo radicle and the opposing force of the seed layers covering the radicle tip. The difference in cold sensitivity between the two seed lines resides either in the osmotic potential or the pressure potential of the germinating embryo.

The activities of earthworms and the fates of seeds

Abstract: Viable seeds which fall on to the soil surface may germinate, die, be lost or pass into the seed bank (Sagar, 1970). Seeds at the soil surface are more vulnerable to predation by birds, rodents and insects and to germination in unfavourable conditions (Roberts, 1970). Seed burial is a potent factor in prolonging the survival of seeds (Harper, 1957). The studies of Brenchley (1918), Chippendale and Milton (1934) and Rabotnov (1969) have shown that vast numbers of viable seeds lie buried in soil.

Seed Dormancy in Red Rice III. Response to Nitrite, Nitrate, and Ammonium Ions

Abstract: Sodium nitrite at 10 millimolar breaks dormancy of dehulled red rice ( Oryza sativa ). While germination is light independent, low pH conditions (pH 3) are required for maximum response. Water and buffer controls at pH 3 remain dormant. The response to nitrite occurs at 25 and 30°C but is reduced at 20°C, although nondormant seeds germinate readily at this temperature. The contact time for response to nitrite is less than 2 h at the start of imbibition. Seeds imbibed first in water show reduced germination when subsequently transferred to nitrite. Dehulled seeds show little or no response to nitrate and ammonium ions. Intact seeds remain dormant in the presence of nitrite or nitrate unless partially dry-afterripened. The pH dependence of nitrite sensitivity is reduced in intact, afterripening seeds. In highly dormant seeds, vacuum infiltration experiments suggest that the hull restricts uptake of nitrite.

Effects of Germination on Proteins, Raffinose Oligosaccharides, and Antinutritional Factors in the Great Northern Beans (Phaseolus vulgaris L.)

Abstract: During 5 day germination, the major reserve proteins of the Great Northern bean (Phaseolus vulgaris L.) were substantially hydrolyzed. In vitro trypsin digestion of the extracted proteins up to 4 hr at 37°C indicated that the major storage proteins in germinated and the ungerminated seeds, although substantially hydrolyzed, could not be completely degraded. In vitro susceptibility of the extracted proteins was improved on moist heat treatment (97°C, 30 min). A substantial increase in soluble essential amino acids occurred during germination. Highest decrease in stachyose + raffimose (76.40%) was observed at the end of the third day of germination. Trypsin, chymotrypsin, and α-amylase inhibitory activities and phytic acid were reduced respectively by 62.9, 73.4, 67.1, and 57.8% after 5 days of germination.

Light Control of Seed Germination

Abstract: Seed germination in many plant species is influenced by light. Promotive effects of light were first documented in the second half of the 19th century, but later inhibitory effects were also described. Historical reviews are given by Barton and Crocker (1948) and by Evenari (1956,1965). There are also general reviews on light and seed germination by Black (1969), Rollin (1972), Toole (1973), Kendrick (1976) and Vidaver (1977).