Red wheats (Triticum aestivum L.) are generally more dormant and sprout resistant than white wheats. Whether this is caused by pleiotropic effectsof the red grain colour genes (R) on dormancy and coat colour, or to tight linkage between R and dormancy genes has not been fully resolved. To directly determine the effect of the R1 allele on dormancy, mutations were induced with sodium azide in a pure line selection of the red genotype (R1R1r2r2r3r3) Chinese Spring wheat. Two white mutants (CSW01, CSW02) were recovered from M3 caryopses derived from approximately 20,000 M2 plants. Both mutants were shown to be allelic to a domesticwhite genotype (r1r1r2r2r3r3). Except for seed coat colour, CSW01 and CSW02 are morphologically indistinguishable from the wild type and are presumed to be near isogenic lines of Chinese Spring. Freshly harvested grainsproduced under four different environments were evaluated for post-harvest dormancy. In all environments, intact caryopses of all three isolines exhibited high temperature dormancy typical of cereal species, although the red wild type consistently exhibited greater dormancy than the white mutant isolines. Dormancy was dissipated by afterripening in dry storage at 37°C in a similar manner for the red and white isolines. Excised embryos of the three isolines exhibited similar levels of dormancy and sensitivities to exogenous abscisic acid. These results indicate a functional R1 allele is not absolutely required for dormancy in wheat, but does enhance its expression in caryopses with dormant (sensitive) embryos

An image analysis system is described to study the process of imbibition in white cabbage (Brassica oleracea L.) seeds. The system consists of two components: 1) an environmental system where seeds germinate; 2) a computer imaging system, composed of a Charged Coupled Device (CCD)-imaging sensor, an image frame grabber, a computer and a video monitor. The measurement software can determine area, perimeter, width, length and eccentricity as descriptors of changes in seed size during swelling. The captured images of imbibing seeds allowed estimation of timing of ‘visible germination’ occurrence without any subjective evaluation. Using the area parameter, the imbibition process can be described graphically by a series of curves similar to the triphasic pattern of water uptake, with extension and rate depending on the degree of seed viability and germination medium conditions. Imbibitional osmotic stress, provided by -1.5 MPa mannitol, induced a large delay in germination and, upon stress removal, a more uniform radicle emergence. The versatility and the sensitivity of the method, together with the feasibility to investigate germination rate in individual seeds within a population, suggest that image analysis techniques have high potential in seed biology studies.

This paper examines the composition and density of soil seed banks under a mature seasonal rain forest (>150 years old), three secondary forests (4 yr Trema orientalis forest, 9 yr Macaranga denticulata forest and 25 yr Mallotus paniculatus forest) and in a slash-and-burn field of Xishuangbanna, southwest China. Seeds in the secondary forests germinated most rapidly in the first week, while the seeds of the seasonal rain forest and the slash-and-burn field soils germinated slowly over the first 6 weeks and peaked in the seventh and eighth weeks. Seed densities were 4585–65,665 seeds m−2 for forest sites and 1130 seeds m−2 for the slash-and-burn field in the top 10 cm of the soils. The seed density decreased with soil depth in the forest sites and tended to decline during succession. Herbs accounted for the largest proportion of seeds at all five sites. The importance of woody species, however, increased as forests became older. Slash and burn eliminated a large number of seeds in the upper soil and, consequently, reversed the vertical distribution of seeds in the soil and had a negative impact on family, genus and species richness of the soil seed bank as well.

Dormancy-breaking requirements and types of dormancy were determined for seeds of Lonicera fragrantissima Lindl. & Paxt., L. japonica Thunb., L. maackii (Rupr.) Maxim. and L. morrowii A. Gray. Seeds of all four species have underdeveloped spatulate embryos that are about 20–40%fully developed (elongated) when dispersed. Embryos in freshly matured, intact seeds grew better at 25/15°C than at 5°C. Gibberellic acid (GA3) (tested only in the light) was more effective in breaking dormancy in L. maackii and L. morrowii than in L. fragrantissima and L. japonica. Warm- followed by cold stratification was required to break dormancy in seeds of L. fragrantissima, whereas seeds of L. japonica required cold stratification only. Thus, seeds of L. fragrantissima have deep simple morphophysiological dormancy (MPD) and those of L. japonica nondeep simple MPD. About 50%of the seeds of L. maackii required warm- or cold stratification only to come out of dormancy and 50% of those of L. morrowii required warm stratification only, whereas the other 50% did not require stratification to germinate. Thus, about half of the seeds of the two species has nondeep simple MPD, and the other half has morphological dormancy (MD). In these laboratory tests, seeds of L. japonica, L. maackii, and L. morrowii generally germinated to significantly higher percentages in light than in darkness; seeds of L. fragrantissima were not tested in darkness. Peaks of germination for seeds of L. fragrantissima, L. japonica, L. maackii and L. morrowii sown on a soil surface and covered with Quercus leaves under near-natural temperature conditions shortly after seed maturity and dispersal in late June 1997, late November 1997, early November 1996 and late June 1998, respectively, occurred in early March 1998, late February 1998, late March 1997 and early October 1998, respectively. The germination phenologies of seeds of the same species and seed lots buried in soil were similar to those of seeds under leaf litter. High percentages of seeds of all four species germinated both under litter (78–96%) and beneath the soil surface (78–97%). These germination patterns correspond closely with the requirements for embryo growth and dormancy break in the four Lonicera species.

Abstract In isolated embryos from dormant barley grains, synergistic effects of fusicoccin (FC) and gibberellic acid (GA3) were observed on the induction of α-amylase mRNA expression. However, no α-amylase mRNA expression could be induced by both agents in embryos from non-dormant grains. Both light- and electron-microscopy studies demonstrated that there were large numbers of starch granules present in mature embryos (mainly in scutellum) from dormant barley grains but none or almost none in embryos from non-dormant grains. Furthermore, the content of reducing sugars in embryos from dormant grains was about half of that from non-dormant grains. In contrast to GA3, FC was able to induce a strong acidification of extracellular pH (pHe). Clamping the pHe to prevent FC-induced acidification, by using 50 mM MES buffer (pH 5.6), caused an inhibition of GA3- or FC-induced α-amylase mRNA expression but did not affect the germination of embryos from dormant grains. In addition, in MES buffer, addition of FC or a combination of FC and GA3increased the germination rate of embryos isolated from dormant grains, though large numbers of starch granules were still present in these embryos. Based on these observations, the presence of starch granules and a low reducing sugar level in embryos from dormant grains is not a factor for control of grain dormancy and germination.

Secondary seed dormancy in cucumber (Cucumis sativus L.) cv. Poinsett 76 could be broken with ethanol. Breakage of dormancy was accompanied by significant changes in the composition of membrane proteins in various seed parts. Compared to the intracellular membranes, a change in the protein composition of plasma membranes from the embryonic axis and cotyledons was evident early in the time-course of ethanol-induced germination of dormant seeds. While few alterations in the membrane protein composition in response to ethanol treatment occurred both in dormant and nondormant seeds, a number of changes occurred exclusively in ethanol-treated dormant seeds. Notably, a 14 kD protein in the plasma membrane from the embryonic axis and a 35 kD protein in the microsomal membranes from the perisperm-endosperm envelope disappeared in the ethanol-treated dormant seeds, but not in the ethanol-treated nondormant seeds. Also marked decrease in the content of a 23 kD protein in the plasma membrane from the cotyledons was observed in ethanol-treated dormant seeds only. It is suggested that the particular changes in cellular membrane proteins, which occurred in ethanol-treated dormant seeds much before the first visible indication of germination, might be related to dormancy breaking rather than to the germination process.

While investigating germinability in the new-crop meadowfoam (Limnanthes alba Benth.), it was desired to gain maximum information despite minimal seed material and prior knowledge. Extended use of the Richards function in a factorial germination experiment proved very powerful. The functions yielded estimates of four correlated coefficients, requiring multivariate analysis of variance (MANOVA) to provide valid F-tests among germination profiles. These germination functions provided more rigorous discrimination among treatments than the univariate final germination level. The functions for the imbibants KNO3 and GA4+7, in darkness at 10/5°C, were best, being characterized by high mean absolute germination rate, relatively short duration, and high final germination (upper asymptote). The results provided insights into possible dormancy mechanisms.

In Britain, Lobelia urens (L.) (the heath lobelia) occurs in rough grassland, is rare and only found in southern England, where it is at the northern limit of its range. Emergence and survival of L. urens was investigated at six locations in two geographically distinct sites experiencing spring, autumn or no grazing in two consecutive years. Four factors were evaluated qualitatively, as a means of characterizing microhabitats for germination and survival: all permutations of higher plant cover, bryophytes, plant litter and surface depressions. The potential effect of adjacent plants on recruitment was also assessed using the nearest neighbour distance (NND). Grazing created depressions, removed plant litter and increased the proportion of sites with higher plant cover. It also resulted in a more open sward with higher NNDs. None of these changes stimulated recruitment. Instead, small increases in the frequency of some rare or very rare microhabitat types were vital in making grazed rough grassland more suitable for emergence. Reduced litter loads and a greater quantity of moss were two key responses. Overall, survival of L. urens was less than 1% and was particularly favoured by moss and an increase in NNDs. Shading from higher plants, with or without plant litter, decreased emergence, but the precise role of litter was complex and most probably related to its quantity. In an experimental seed bed, only empty depressions favoured emergence. The microhabitat relationships of L. urens were unusually consistent among locations and consecutive years. L. urens requires high soil surface temperatures but also adequate water for large scale recruitment, and such conditions are encouraged by grazing. The particular problems of experimental design and statistical analysis of data from recruitment experiments are also discussed.

Seeds of four African tree species from the Sahelian zone (Boscia senegalensis) and the Sudanian zone (Butyrospermum parkii, Cordyla pinnata and Saba senegalensis) lose viability after moisture contents drop below 22 and 30%, depending on the species. Seed longevity in wet and airtight storage does not exceed a few months. Temperatures close to zero elicit symptoms of chilling injury leading to rapid seed death. The optimum storage temperature is 15°C. These results allow the four species to be classified as recalcitrant seed species. Boscia senegalensis is therefore an exception in arid zones where most species have orthodox seeds.

Some physiological characteristics of ACC-Nmalonyltransferase (ACC-N-MTase) have been studied in the seeds of chick-pea (Cicer arietinum L.). This enzymatic activity was detectable during all periods of zygotic embryogenesis; however, the highest values were found in the dry seed. In dry seeds, the enzymatic activity was greater in the embryonic axis than in the cotyledons. During the onset of germination, activity increased more strongly in the cotyledons than in the embryonic axis, reaching its highest values in the storage organs coinciding with radicle emergence (18 to 24 h). Removal of the cotyledons strongly diminished enzymatic activity in the embryonic axis. Low concentrations of ethrel (50 µM) stimulated the axis ACC-N-MTase. The highest specific activity was found in the apical meristem of the embryonic axis, declining over the length of the organ. The role of ACC-N-MTase activity in the germinative process is discussed, together with the regulatory effect of ethylene on this ACCconjugating enzyme.

Germination of native tree and shrub species from seed can be unpredictable. Germination of Rosa corymbifera ‘Laxa’ was 2% under normal commercial conditions. This was obtained in the presence of the natural microflora found on the seeds. The microflora originated on the hips and the seeds become inoculated during extraction. Exclusion of microbes from such pretreatments resulted in no germination. Inoculation of surface sterilized seeds with members of the natural microflora resulted in 3% germination. The addition of GarottaTM, a commercial compost activator, to the commercial pretreatment increased germination to 95%. This high germination percentage was sustained over a 5 year period using seeds from the same stock bushes. Addition of the compost activator resulted in a 20-fold increase of microbial activity in the pretreatment mixture, indicating that enhanced microbial growth resulted in higher and more predictable germination percentages.

Experiments on the facultative winter annuals Carduus acanthoides and Anagallis arvensis were performed: (i) to determine thermal conditions that induce or release dormancy, (ii) to investigate to what extent changes in dormancy level resulting from those thermal conditions explain the seasonal pattern of emergence of these species, and (iii) to estimate required thermal time and base temperature for the germination of non-dormant seeds. Carduus acanthoides required high temperatures followed by decreasing temperatures for dormancy release; however, low winter temperatures did not induce secondary dormancy as expected for a winter annual. To the contrary, low temperatures stimulated dormancy release in the long term. In A. arvensis, dormancy relief was enhanced by dry storage at 25°C, and the response to low temperature was different depending on moisture conditions. Prolonged exposure to moist-chilling increased the dormancy level of the population, while dry storage at 4°C relieved dormancy. For both species, changes in the thermal range permissive for germination as a result of dormancy modifications explained to a large extent the timing of the emergence periods observed in the field. In neither species did base temperature for germination change with the dormancy level of the population. Thermal time required forgermination of C. acanthoides varied with dormancy, while for A. arvensis seeds it was constant.

Germination responses of nonstratified (conditionally dormant) and of cold-stratified (nondormant) seeds of three Solidago species were tested in darkness at 30/15°C following various lengths of exposure [0 (control), 5 and 30 min, 1, 6 and 14 h] to green (mostly 500–600 nm) or white (400–700 nm) light. Prior to exposures, nonstratified seeds were imbibed in darkness at laboratory conditions for 24 h, and cold-stratified seeds were kept in darkness at 5°C on a moist substrate for 8 wk. Nonstratified seeds of S. altissima, S. nemoralisand S. shortii germinated to 0–46%, 0–25% and 36–99%, respectively, in darkness following 5 min to 14 h of green or white light, whereas cold-stratified seeds germinated to 53–98%, 31–85% and 82–100%, respectively. Thus, sensitivity of seeds to both green and white light increased as they passed from conditional dormancy to nondormancy. Moreover, sensitivity to green and white light was similar to the hierarchy of seed size. Green safe lights must be used with caution in interpreting the results of studies on light/dark responses of seeds.

Molecular mobility is hypothesised to be a key factor influencing storage stability of seeds because it may control the rate of deteriorative reactions responsible for reduced shelf life. The relationship between the longevity of lettuce seeds and the molecular mobility was investigated in the cytoplasm of lettuce radicles. Longevity of lettuce seeds was predicted using the viability equation of Ellis and Roberts, and the molecular mobility was determined by saturation transfer electron paramagnetic resonance spectroscopy measurements of rotational motion of a polar spin probe inserted into the cytoplasm. Increasing the temperature resulted in faster rotational motion and shorter longevity. There was a linear relationship between the logarithms of rotational motion and estimated seed longevity for temperatures above 5°C. Below 5°C, there was a deviation from linearity. Based on the hypothesis that the molecular mobility in the cytoplasm determines the rate of detrimental reactions, seed longevity at sub-zero temperatures was predicted by extrapolation of the rotational motion using the linear relationship. Predictions of longevity at sub-zero temperatures based on rotational motion indicated longer survival times than those based on the viability equation. A kinetic approach to ageing using molecular mobility measurements is expected to improve our understanding of seed storage stability and might eventually lead to realistic predictions of longevity at low temperatures.

On headlands in Newfoundland, four of the seven sympatric Vaccinium species co-occur frequently at the quadrat level in tundra communities. We hypothesized that differentiation at the regeneration niche level was a prerequisite for the coexistence of these sympatric congeners. After a description and quantification of parameters affecting whole berry and seed dispersal and those affecting seed germination, differentiation at these two levels of the regeneration niches of the seven Vaccinia was investigated using numerical clustering techniques. Differentiation patterns were similar in both the germination and the dispersal dendrograms; three species were most dissimilar (viz. V. angustifolium, V. boreale and V. uliginosum), and the remaining four were separated into single species groups at the 62% and 75% similarity levels by the germination and dispersal dendrograms, respectively. Overall, patterns reflect divergence in dispersal mechanisms and germination abilities among the seven species, in support of the thesis that sympatric congeners have varied regeneration strategies. Differences in the germination success observed after testing natural dispersal units (e.g. seed from scat and seed within whole berries) points to the need to conduct germination trials in ecologically relevant ways. This approach reveals how divergent regeneration strategies are possible in species having similar, palatable baccate fruits (e.g. V. angustifolium and V. uliginosum) and highlights our lack of insight into regeneration strategies of the groups. The cranberry seeds, despite germination success gauged by results from standard germination protocols, exhibit no germination in trials conducted with the natural dispersal unit, the whole berry.

Germination in light and darkness was compared after cold stratification of seeds of 54 species known or suspected to accumulate persistent seed banks. Germination became less dependent on light with increasing seed mass. This pattern was clear in a direct correlation of individual species data (P <0.0001) as well as when considering phylogenetically independent contrasts (P <0.001). The latter analysis suggests that light response and seed mass coevolved.