Showing papers on "Seedling published in 2007"
TL;DR: Upregulation of the anti-oxidant system appears to play a role in salt tolerance of rice, with tolerant genotypes also maintaining relatively higher photosynthetic function; during both the vegetative and reproductive stages.
627 citations
TL;DR: It was found that, in keeping with previous studies, most species are seed limited, however, the effects of seed addition are typically small, and most added seeds fail to recruit to the seedling stage, so establishment limitation is stronger than seed limitation.
Abstract: We examine the relative importance of processes that underlie plant population abundance and distribution. Two opposing views dominate the field. One posits that the ability to establish at a site is determined by the availability of suitable microsites (establishment limitation), while the second asserts that recruitment is limited by the availability of seeds (seed limitation). An underlying problem is that establishment and seed limitation are typically viewed as mutually exclusive. We conducted a meta-analysis of seed addition experiments to assess the relative strength of establishment and seed limitation to seedling recruitment. We asked (1) To what degree are populations seed and establishment limited? (2) Under what conditions (e.g., habitats and life-history traits) are species more or less limited by each? (3) How can seed addition studies be better designed to enhance our understanding of plant recruitment? We found that, in keeping with previous studies, most species are seed limited. However, the effects of seed addition are typically small, and most added seeds fail to recruit to the seedling stage. As a result, establishment limitation is stronger than seed limitation. Seed limitation was greater for large-seeded species, species in disturbed microsites, and species with relatively short-lived seed banks. Most seed addition experiments cannot assess the relationship between number of seeds added and number of subsequent recruits. This shortcoming can be overcome by increasing the number and range of seed addition treatments.
474 citations
TL;DR: The existence of soil moisture thresholds that control establishment provides insights into plant population dynamics in dry environments.
Abstract: Summary
1Seedling survival is one of the most critical stages in a plant's life history, and is often reduced by drought and soil desiccation. It has been hypothesized that root systems accessing moist soil layers are critical for establishment, but very little is known about seedling root growth and traits in the field.
2We related seedling mortality to the presence of deep roots in a field experiment in which we monitored soil moisture, root growth and seedling survival in five Mediterranean woody species from the beginning of the growing season until the end of the drought season.
3We found strong positive relationships between survival and maximum rooting depth, as well as between survival and soil moisture. Species with roots in moist soil layers withstood prolonged drought better, whereas species with shallow roots died more frequently. In contrast, biomass allocation to roots was not related to establishment success.
4Access to moist soil horizons accounted for species-specific survival rates, whereas large root : shoot (R:S) ratios did not. The existence of soil moisture thresholds that control establishment provides insights into plant population dynamics in dry environments.
416 citations
TL;DR: It is concluded that carbohydrate storage in stems and roots enhances long-term survival in shade by enabling seedlings to cope with periods of biotic and abiotic stress.
Abstract: Summary
1
To survive in forest understoreys, seedlings must depend on carbohydrate reserves when they experience negative carbon balance imposed by occasional light reduction and tissue loss to herbivores and diseases. We present the first experimental evidence in support of this hypothesis, using seven woody neotropical species.
2
We transplanted seedlings that had recently expanded their first photosynthetic cotyledon or leaf to the forest understorey (1% of full sun) and quantified initial biomass and total non-structural carbohydrate (TNC) in stems, roots and storage cotyledons. We then randomly assigned seedlings to control and two stress treatments: light reduction (0.08% of full sun for 8 weeks) and complete defoliation.
3
First-year survival of control seedlings, a comparative measure of shade tolerance, differed widely among species. The two stress treatments reduced survival and relative growth rates (RGR) of all species. Shade-tolerant species were little impacted by the stress treatments, whereas the two least shade-tolerant species experienced 100% mortality.
4
In all treatments, 8-week and first-year survival was positively correlated with initial TNC pool size in stems and roots. By contrast, survival was generally not correlated with initial TNC concentration in any organ, TNC pools in cotyledons, seed mass or seedling biomass.
5
TNC in stems and roots, but not in cotyledons, decreased in response to light reduction and defoliation over 8 weeks. Leaf area recovery of defoliated seedlings was positively correlated with initial TNC pools in stems and roots.
6
First-year survival in each treatment was negatively correlated with 0–8 week RGR of control seedlings, suggesting higher stress tolerance of species with inherently slow growth rates in shade. RGR of control seedlings from 0 to 8 weeks was negatively correlated with initial TNC pools, but not concentrations, in stems and roots. After 8 weeks, RGR was positive for all species, without clear relationships with survival or TNC.
7
We conclude that carbohydrate storage in stems and roots enhances long-term survival in shade by enabling seedlings to cope with periods of biotic and abiotic stress. Carbohydrate storage is a key functional trait that can explain species differences in growth and survival that lead to species coexistence through niche assembly processes and life-history trade-offs.
312 citations
TL;DR: It was found that germination was delayed at lower salinity levels and inhibited at higher salinity regimes, and the activity of proline oxidase (PROX) decreased and the γ-glutamyl kinase (γ-GK) activity increased.
288 citations
TL;DR: The results showed a reduction of these parameters for most of magnetic treatments, therefore their rate of germination was increased, and the greatest increases were obtained for plants continuously exposed to 125 or 250 mT.
255 citations
TL;DR: Overall, vermicompost could be an environmentally friendly substitute for peat in potting media with similar or beneficial effects on seedling performance and fruit quality, however, at least for tomatoes, variety-specific responses should be considered when giving recommendations on the optimum proportion of verMicompost amendment to horticultural potting substrate.
249 citations
TL;DR: It is hypothesized that hunting large seed predators favors large seeds by reducing predation and increasing survival and that the harvest of large birds and mammals that disperse many seeds favors other species whose seeds are dispersed by bats, small birds, and mechanical means.
Abstract: We evaluated predictions that hunters favor lianas, large seeds, and seeds dispersed by bats, small birds, and mechanical means for seedling banks in central Panama. We censused 3201 trees in 20 1-ha plots and 38,250 seedlings in the central 64 m 2 of each plot. We found significant differences in the species composition of the seedling bank between nine protected sites in the Barro Colorado Nature Monument and 11 hunted sites in the contiguous Parque Nacional SoberanLianas, species with large seeds, and species with seeds dispersed by bats, small birds, and mechanical means were all overrepresented at hunted sites. The latter two findings could also be evaluated relative to the species composition of reproductively mature adults for canopy trees. The tree species present in the seedling bank had significantly heavier seeds than the tree species present as adults at hunted sites but not at protected sites. The representation of seed dispersal modes among the species present in the seedling bank did not reflect pre-existing differences in the local species composition of adults. We hypothesize that hunting large seed predators favors large seeds by reducing predation and increasing survival. We also hypothesize that the harvest of large birds and mammals that disperse many seeds favors other species whose seeds are dispersed by bats, small birds, and mechanical means. This process also favors lianas because the seeds of disproportionate numbers of liana species are dispersed by wind. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.
220 citations
TL;DR: It is suggested that microclimatic modifications associated with cushion plants could be important for the establishment and survival of other plant species, both native and non-native, in the high alpine communities of central Chile.
Abstract: Cushion plants are one of the most common growth forms in alpine habitats. Their low stature, dense canopy, and compact form allow them to decouple their microclimate from the surrounding environment, mitigating the effect of low temperatures and drought, enhancing the survival of other species. In this study, we evaluated the modifications on soil temperature and moisture over an entire growing season by two cushion species (Laretia acaulis and Azorella monantha) in alpine communities located at two different elevations in the central Chilean Andes. Additionally, w ep erformed seedling survival experiments with two native herbaceous species (Hordeum comosum and Erigeron andicola) and the non-native forb Cerastium arvense to assess if seedling survival is higher within cushions than outside them. Our results indicated that cushions ameliorated extreme low and high substrate temperatures, improved soil moisture, and enhanced seedling survival of the three herbaceous plant species evaluated. Our results suggest that microclimatic modifications associated with cushion plant sc ould be important for the establishment and survival of other plant species, both native and non-native, in the high alpine communities of central Chile.
194 citations
TL;DR: In this paper, the plastidial DNA content of tissue ranging in age from 2-day old cotyledons to 37-day-old senescent rosette leaves was examined.
Abstract: Summary
Little is known about DNA and RNA metabolism during leaf development and aging in the model organism Arabidopsis. Therefore we examined the nuclear and plastidial DNA content of tissue ranging in age from 2-day-old cotyledons to 37-day-old senescent rosette leaves. Flow-cytometric analysis showed an increase in nuclear DNA ploidy levels of up to 128 genome copies per nucleus in older leaves. The copy numbers of nuclear 18S-rRNA genes were determined to be 700 ± 60 per haploid genome. Adjusted to the average level of nuclear DNA polyploidism per cell, plastome copy numbers varied from about 1000 to 1700 per cell without significant variation during development from young to old rosette leaves. The transcription activity of all studied plastid genes was significantly reduced in older rosette leaves in comparison to that in young leaves. In contrast, levels of plastidial transcript accumulation showed different patterns. In the case of psbA, transcripts accumulated to even higher levels in older leaves, indicating that differential regulation of plastidial gene expression occurs during leaf development. Examination of promoter activity from clpP and rrn16 genes by primer extension analyses revealed that two RNA polymerases (NEP and PEP) transcribe these genes in cotyledons as well as in young and senescent leaves. However, PEP may have a more prominent role in older rosette leaves than in young cotyledons. We conclude that in cotyledons or leaves of different ages plastidial gene expression is regulated at the transcriptional and post-transcriptional levels, but not by plastome copy number.
179 citations
TL;DR: New evidence is provided indicating that GRP2 plays important roles in seed germination, seedling growth and freezing tolerance of Arabidopsis under stress conditions, and thatGRP2 exerts its function by modulating the expression and activity of various classes of genes.
Abstract: Summary
Although glycine-rich RNA-binding protein 2 (GRP2) has been implicated in plant responses to environmental stresses, the function and importance of GRP2 in stress responses are largely unknown. Here, we examined the functional roles of GRP2 in Arabidopsis thaliana under high-salinity, cold or osmotic stress. GRP2 affects seed germination of Arabidopsis plants under salt stress, but does not influence seed germination and seedling growth of Arabidopsis plants under osmotic stress. GRP2 accelerates seed germination and seedling growth in Arabidopsis plants under cold stress, and contributes to enhancement of cold and freezing tolerance in Arabidopsis plants. No differences in germination between the wild-type and transgenic plants were observed following addition of abscisic acid (ABA) or glucose, implying that GRP2 affects germination through an ABA-independent pathway. GRP2 complements the cold sensitivity of an Escherichia coli BX04 mutant and exhibits transcription anti-termination activity, suggesting that it has an RNA chaperone activity during the cold adaptation process. Mitochondrial respiration and catalase and peroxidase activities were affected by expression of mitochondrial-localized GRP2 in Arabidopsis plants under cold stress. Proteome analysis revealed that expression of several mitochondrial-encoded genes was modulated by GRP2 under cold stress. These results provide new evidence indicating that GRP2 plays important roles in seed germination, seedling growth and freezing tolerance of Arabidopsis under stress conditions, and that GRP2 exerts its function by modulating the expression and activity of various classes of genes.
TL;DR: The results suggest that HSI2 and HSL1 repress the sugar-inducible expression of the seed maturation program in seedlings and play an essential role in regulating the transition from seedmaturation to seedling growth.
Abstract: During development of plant seeds, embryos import nutrients and store massive amounts of reserves. Seed reserves are rapidly degraded and mobilized to support seedling development after germination. HIGH-LEVEL EXPRESSION OF SUGAR-INDUCIBLE GENE 2 (HSI2) of Arabidopsis thaliana is a B3 DNA-binding domain protein that represses the transcription of sugar-inducible reporter gene. Although disruption of HSI2 or HSI2-Like 1 (HSL1) did not affect growth, seeds with disruption of both HSI2 and HSL1 (KK mutant) developed abortive seedlings that stopped growing 7–9 days after imbibition. KK seedlings developed swollen hypocotyls that accumulated seed storage proteins and oil on medium containing sucrose or other metabolizable sugars, and calluses developed from KK seedlings also accumulated seed storage reserves. The expression of seed maturation genes, which include LEAFY COTYLEDON-type master regulators, in KK seedlings depended on the concentration of sucrose, suggesting that sugar controls the expression of seed maturation genes. Our results suggest that HSI2 and HSL1 repress the sugar-inducible expression of the seed maturation program in seedlings and play an essential role in regulating the transition from seed maturation to seedling growth.
TL;DR: The results showed that germination percentage, germination index, and vigour index of lucerne seeds primed with brassinolide were significantly higher than those of the non-primed seeds under salinity stress in each variety, suggesting that primingLucerne seed with brass inolide at a suitable concentration can improve germination and seedling growth under high-saline soils.
Abstract: Salt stress is an important constraint to lucerne (Medicago sativa L.) production in many parts of the world. Seeds of 3 lucerne varieties, cvv. Victoria, Golden Empress, and Victor, were used to investigate the effects of seed priming with 5 µm/L brassinolide on germination and seedling growth under a high level of salt stress (13.6 dS/m NaCl solution). The results showed that germination percentage, germination index, and vigour index of lucerne seeds primed with brassinolide were significantly higher than those of the non-primed seeds under salinity stress in each variety. Seed priming with brassinolide significantly increased the shoot fresh weight, shoot dry weight, and root dry weight in 2 varieties, and significantly increased the root length and root vigour in each variety. It also significantly increased the activities of antioxidant enzymes, peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), in Victoria and Victor seedlings. During seedling growth, the primed seeds significantly reduced the malondialdehyde (MDA) accumulation. This suggests that priming lucerne seed with brassinolide at a suitable concentration can improve germination and seedling growth under high-saline soils.
TL;DR: Sixteen wheat genotypes including local varieties were tested in completely randomized design with three repeats, showing highly significant differences for all traits in response to the moisture stress.
Abstract: Sixteen wheat genotypes including local varieties were tested in completely randomized design with three repeats. Data were recorded at four different moisture levels by using polyethylene glycol (PEG) 6000 on germination percentage, germination rate index, shoot length, root length, fresh weight of shoot, dry weight of shoot, fresh weight of root, dry weight of root, shoot/root ratio and analysed for significance. The genotypes differ significantly in response to the moisture stress. There were highly significant differences for all traits. PK-18199 gave the maximum germination percentage, germination rate index, shoot length root length, coleoptile length, fresh shoot weight, dry shoot weight, fresh root weight, dry root weight and root/shoot ratio under all four moisture stresses. PK-18175 showed maximum resistance against moisture stress while WAFAQ 2001 showed minimum resistance. AS-2002 and KC033 also gave the better performance under all four moisture levels for most of the traits at seedling stage. 99FJ03 gave maximum root/shoot length ratio while PK 18199 gave minimum value of root/shoot length ratio showing resistance against water stress.
TL;DR: Priming improved the initial seedling vigor and resulted in improved growth, yield and quality of transplanted fine rice while traditional soaking behaved similar to that of untreated control, and significant positive correlation was found between mean emergence time of nursery seedlings and Kernel yield, nursery seedling dry weight and kernel yield, fertile tillers and kernelield, and leaf area duration and kernel yields.
Abstract: Transplanting is the major method of rice cultivation in the world, in which seedlings are raised in nursery and then transplanted into well puddle and prepared fields. The traditional nursery sowing method is tedious and produces week seedlings that reduce the final yield due to high mortality. The potential of seed priming to improve the nursery seedlings and thus the transplanted rice was evaluated in the present study. The experiment was conducted in the rice growing area (31.45° N, 73.26° E, and 193 m) of Pakistan, during 2004–2005. Seed priming tools employed during the investigation included traditional soaking, hydropriming for 48 h, osmohardening with KCl or CaCl2 (Ψs −1.25 MPa) for 24 h (one cycle), 10 ppm ascorbate for 48 h or seed hardening for 24 h. Priming improved the initial seedling vigor and resulted in improved growth, yield and quality of transplanted fine rice while traditional soaking behaved similar to that of untreated control. Osmohardening with CaCl2 resulted in the best performance, followed by hardening, ascorbate priming and osmohardening with KCl. Osmohardening with CaCl2 produced 3.75 t ha−1 (control: 2.87 t ha−1) kernel yield, 11.40 t ha−1 (control: 10.03 t ha−1) straw yield and 24.57% (control: 22.27%) harvest index. The improved yield was attributed due to increase in the number of fertile tillers. Significant positive correlation was found between mean emergence time of nursery seedlings and kernel yield, nursery seedling dry weight and kernel yield, fertile tillers and kernel yield, and leaf area duration and kernel yield.
TL;DR: It is demonstrated that seed germination of warm-season grasses is significantly responsive to oxidative conditions and highlights the complex interplay between seed redox status, ABA, ROS and NO in this system.
Abstract: Hydrogen peroxide (H2O2) as a source of reactive oxygen species (ROS) signiWcantly stimulated ger- mination of switchgrass (Panicum virgatum L.) seeds with an optimal concentration of 20 mM at both 25 and 35°C. For non-dormant switchgrass seeds exhibiting diVerent levels of germination, treatment with H 2 O 2 resulted in rapid germination (<3 days) of all germinable seeds as compared to seeds placed on water. Exposure to 20 mM H 2 O 2 elicited simultaneous growth of the root and shoot system, resulting in more uniform seedling development. Seeds of big bluestem (Andropogon gerardii Vitman) and indiangrass (Sorghastrum nutans (L.) Nash) also responded positively to H2O2 treatment, indicating the universality of the eVect of H 2 O 2 on seed germination in warm-season prairie grasses. For switchgrass seeds, abscisic acid (ABA) and the NADPH-oxidase inhibitor, diphenyleneiodonium (DPI) at 20 M retarded germination (radicle emergence), stunted root growth and partially inhibited NADPH-oxidase activ- ity in seeds. H2O2 reversed the inhibitory eVects of DPI and ABA on germination and coleoptile elongation, but did not overcome DPI inhibition of root elongation. Treatment with H 2 O 2 appeared to enhance endogenous production of nitric oxide, and a scavenger of nitric oxide abolished the perox- ide-responsive stimulation of switchgrass seed germination. The activities and levels of several proteins changed earlier in seeds imbibed on H 2 O 2 as compared to seeds maintained on water or on ABA. These data demonstrate that seed ger- mination of warm-season grasses is signiWcantly responsive to oxidative conditions and highlights the complex inter- play between seed redox status, ABA, ROS and NO in this system.
TL;DR: Investigation of Pythium spp.
Abstract: Cool, moist conditions in combination with minimum tillage, earlier planting, and recent shifts in commercial fungicide seed-treatment active ingredients have led to an increase in corn (Zea mays) and soybean (Glycine max) seedling establishment problems. This situation resulted in an investigation of Pythium spp. associated with seed and seedling diseases. Samples of diseased corn and soybean seedlings were collected from 42 production fields in Ohio. All isolates of Pythium recovered were identified to species using morphological and molecular techniques and evaluated in an in vitro pathogenicity assay on both corn and soybean seed, and a subset of the isolates was tested for sensitivity to fungicides currently used as seed treatments. Eleven species and two distinct morphological groups of Pythium were identified, of which six species were moderately to highly pathogenic on corn seed and nine species were highly pathogenic on soybean seed. There was significant variation (P < 0.05) in sensitivity to mefenoxam, azoxystrobin, trifloxystrobin, and captan both across and within species. Multiple species of Pythium had the capacity to reduce germination of both corn and soybean seed. Results indicated that mefenoxam, azoxystrobin, trifloxystrobin, or captan, when used individually, may not inhibit all pathogenic species of Pythium found in Ohio soils.
TL;DR: Spatial patterns of seedling recruitment were investigated in two populations of the terrestrial orchid Orchis purpurea using both univariate and bivariate point pattern analysis, parentage analysis and seed germination experiments, providing a clear and coherent picture of recruitment patterns in a tuberous, perennial orchid.
Abstract: Seed dispersal and the subsequent recruitment of new individuals into a population are important processes affecting the population dynamics, genetic diversity and spatial genetic structure of plant populations. Spatial patterns of seedling recruitment were investigated in two populations of the terrestrial orchid Orchis purpurea using both univariate and bivariate point pattern analysis, parentage analysis and seed germination experiments. Both adults and recruits showed a clustered spatial distribution with cluster radii of c. 4-5 m. The parentage analysis resulted in offspring-dispersal distances that were slightly larger than distances obtained from the point pattern analyses. The suitability of microsites for germination differed among sites, with strong constraints in one site and almost no constraints in the other. These results provide a clear and coherent picture of recruitment patterns in a tuberous, perennial orchid. Seed dispersal is limited to a few metres from the mother plant, whereas the availability of suitable germination conditions may vary strongly from one site to the next. Because of a time lag of 3-4 yr between seed dispersal and actual recruitment, and irregular flowering and fruiting patterns of adult plants, interpretation of recruitment patterns using point patterns analyses ideally should take into account the demographic properties of orchid populations.
TL;DR: It is proposed that a key benefit from restricting germination to high R : FR is a reduction in the time-frame over which the initially small seedlings remain small and hence highly vulnerable to mortality: high R-FR is likely to indicate high-light levels which would facilitate rapid seedling growth.
Abstract: Summary
1The effect of the ratio of red : far red light (R : FR) on seed germination of herbaceous species from northern temperate deciduous forest has received little attention Here for 27 such species, we investigated the relationship between seed mass and the suitability of micro-sites for germination Germination in light and in darkness was compared after cold stratification, and for the light-requiring species, the germination response to R : FR was determined In addition, seed bank persistence was monitored over 4 years
2With increasing seed mass, germination became less dependent on light and seed bank persistence decreased Furthermore, for the light-dependent species, there was a significant negative relationship between the R : FR that resulted in 50% germination and seed mass
3These data suggest that small-seeded species only germinate in micro-sites with a high R : FR, which signals the absence of over-topping vegetation or leaf litter Such micro-sites are comparatively rare, which may necessitate persistence in the soil seed bank
4For small-seeded species, we propose that a key benefit from restricting germination to high R : FR is a reduction in the time-frame over which the initially small seedlings remain small and hence highly vulnerable to mortality: high R : FR is likely to indicate high-light levels which would facilitate rapid seedling growth
TL;DR: It is concluded that negative density dependence could promote species coexistence in this rain forest community but that the scale dependence of interactions differs between rare and common species.
Abstract: Factors affecting survival and recruitment of 3531 individually mapped seedlings of Myristicaceae were examined over three years in a highly diverse neotropical rain forest, at spatial scales of 1-9 m and 25 ha. We found convincing evidence of a community compensatory trend (CCT) in seedling survival (i.e., more abundant species had higher seedling mortality at the 25-ha scale), which suggests that density-dependent mortality may contribute to the spatial dynamics of seedling recruitment. Unlike previous studies, we demonstrate that the CCT was not caused by differences in microhabitat preferences or life history strategy among the study species. In local neighborhood analyses, the spatial autocorrelation of seedling survival was important at small spatial scales (1-5 m) but decayed rapidly with increasing distance. Relative seedling height had the greatest effect on seedling survival. Conspecific seedling density had a more negative effect on survival than heterospecific seedling density and was stronger and extended farther in rare species than in common species. Taken together, the CCT and neighborhood analyses suggest that seedling mortality is coupled more strongly to the landscape-scale abundance of conspecific large trees in common species and the local density of conspecific seedlings in rare species. We conclude that negative density dependence could promote species coexistence in this rain forest community but that the scale dependence of interactions differs between rare and common species.
TL;DR: Water channels play an important role in seed germination, acting, at least partly, in response to the NO signaling pathway, according to the expression patterns of the PIPs.
Abstract: Previous studies have demonstrated the possible role of several aquaporins in seed germination. But systematic investigation of the role of aquaporin family members in this process is lacking. Here, the developmental regulation of plasma membrane intrinsic protein (PIP) expression throughout germination and post-germination processes in rice embryos was analyzed. The expression patterns of the PIPs suggest these aquaporins play different roles in seed germination and seedling growth. Partial silencing of the water channel genes, OsPIP1;1 and OsPIP1;3, reduced seed germination while over-expression of OsPIP1;3 promoted seed germination under water-stress conditions. Moreover, spatial expression analysis indicates that OsPIP1;3 is expressed predominantly in embryo during seed germination. Our data also revealed that the nitric oxide (NO) donors, sodium nitroprusside (SNP) and S-nitrosoglutathione (GSNO), promoted seed germination; furthermore, the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, inhibited germination and reduced the stimulative effects of SNP and GSNO on rice germination. Exogenous NO stimulated the transcription of OsPIP1;1, OsPIP1;2, OsPIP1;3 and OsPIP2;8 in germinating seeds. These results suggest that water channels play an important role in seed germination, acting, at least partly, in response to the NO signaling pathway.
TL;DR: In all species, the correlation between seed mass and seedling mass increased with a decrease in light, suggesting that seedlings growing in low light depend more upon their seed reserves.
Abstract: Three hypotheses have been proposed to explain the functional relationship between seed mass and seedling performance: the reserve effect (larger seeds retain a larger proportion of reserves after germinating), the metabolic effect (seedlings from larger seeds have slower relative growth rates), and the seedling-size effect (larger seeds produce larger seedlings). We tested these hypotheses by growing four Mediterranean Quercus species under different light conditions (3, 27, and 100% of available radiation). We found evidence for two of the three hypotheses, but none of the four species complied with all three hypotheses at the same time. The reserve effect was not found in any species, the metabolic effect was found in three species (Q. ilex, Q. pyrenaica, and Q. suber), and the seedling-size effect in all species. Light availability significantly affected the relationships between seed size and seedling traits. For Q. ilex and Q. canariensis, a seedling-size effect was found under all three light conditions, but only under the lowest light (3%) for Q. suber and Q. pyrenaica. In all species, the correlation between seed mass and seedling mass increased with a decrease in light, suggesting that seedlings growing in low light depend more upon their seed reserves. A causal model integrates the three hypotheses, suggesting that larger seeds generally produced larger seedlings.
TL;DR: In this paper, the authors show that loss-of-function mutations in GCL1 did not confer ABA insensitivity in three independent gCR2 alleles and generated gcr2 gcl1 double mutants and found that the double mutants still had near wild-type responses to ABA.
Abstract: *† Summary Abscisic acid (ABA) is perceived by several different types of receptors in plant cells. At the cell surface, the ABA signal is proposed to be perceived by GCR2, which mediates ABA responses in seed germination, early seedling development and stomatal movement. GCR2 was also proposed to be a seven-transmembrane (7TM) G-protein-coupled receptor (GPCR). Here we characterize GCR2 and one of its two homologs, GCR2-LIKE 1 (GCL1), in ABA-mediated seed germination and early seedling development in Arabidopsis. We show that lossof-function mutations in GCL1 did not confer ABA insensitivity. Similarly, we did not observe ABA insensitivity in three independent gcr2 alleles. Furthermore, we generated gcr2 gcl1 double mutants and found that the double mutants still had near wild-type responses to ABA. Consistent with this, we found that the transcription of ABA marker genes was induced by ABA to levels that were comparable in wild type and gcr2 and gcl1 single and double mutants. On the other hand, the loss-of-function alleles of the sole Arabidopsis heterotrimeric G protein a subunit, GPA1, were hypersensitive to ABA in the ABA-inhibition of seed germination and early seedling development, disfavoring a genetic coupling of GCR2 by GPA1. Using multiple robust transmembrane prediction systems, GCR2 was predicted not to be a 7TM protein, a structural hallmark of GPCRs. Taken together, our results do not support the notion that GCR2 is an ABA-signaling GPCR in seed germination and early seedling development.
TL;DR: It is found that while smoke stimulated germination in a number of species it also had negative impacts on other species, and butenolide was effective on the widest range of species in terms of enhancing germination percentage, rate and seedling mass.
Abstract: We tested the applicability of the recently identified major germination cue from smoke (a butenolide 3-methyl-2Hfuro[2,3-c]pyran-2-one) on 18 weed species from non-fire prone environments. For the study species we compared the relative effectiveness of alternating temperatures, KNO3, GA3, smoke water and the butenolide on germination percentage, germination rate and seedling mass. We found that while smoke stimulated germination in a number of species it also had negative impacts on other species. In addition, the butenolide was effective on the widest range of species in terms of enhancing germination percentage, rate and seedling mass. However, none of the treatments, including butenolide were effective on all species. Our data demonstrate that butenolide may have wide applicability as a germination and seedling growth stimulant irrespective of whether the species come from fire-prone habitats.
TL;DR: The fact that seeds reach micro-sites suitable for establishment (ant nests) supports the directed dispersal hypothesis as a possible force favouring myrmecochory in this ecosystem.
TL;DR: The seed and early seedling growth stages of the life cycle of H. strobilaceum are very salt tolerant, and their physiological responses differ somewhat between the Mediterranean 'salt steppe' of Spain and the inland cold salt desert of north-west China.
TL;DR: The MDA content was linearly and positively correlated with seed germination frequency, biomass increment, root length and shoot height elongation, suggesting that MDA may be useful as a biological indicator of Cd and As toxicity in wheat.
TL;DR: Evidence that phytochrome-mediated germination pathways simultaneously respond to light and temperature cues in ways that affect germination is provided using Arabidopsis thaliana to reveal a potentially novel role for phy tochrome pathways in regulating the seasonal timing of germination.
Abstract: Germination timing is a fundamental life-history trait, as seedling establishment predicates realized fitness in the wild. Light and temperature are two important cues by which seeds sense the proper season of germination. Using Arabidopsis thaliana, we provide evidence that phytochrome-mediated germination pathways simultaneously respond to light and temperature cues in ways that affect germination. Phytochrome mutant seeds were sown on agar plates and allowed to germinate in lit, growth chambers across a range of temperatures (7 degrees C to 28 degrees C). phyA had an important role in promoting germination at warmer temperatures, phyE was important to germination at colder temperatures and phyB was important to germination across a range of temperatures. Different phytochromes were required for germination at different temperatures, indicating a restriction or even a potential specialization of individual phytochrome activity as a function of temperature. This temperature-dependent activity of particular phytochromes reveals a potentially novel role for phytochrome pathways in regulating the seasonal timing of germination.