Molecular mechanism of seed dormancy release induced by fluridone compared with cod stratification in Notopterygium incisum.

BACKGROUND: Notopterygium incisum is an important Chinese medicinal plant. Its mature seeds have underdeveloped embryos and are physiological dormant. We found the seeds with full developed embryos can germinate after treated by fluridone (FL), an inhibitor of abscisic acid (ABA). In order to understand the molecular mechanisms underlying seed dormancy release by FL, we compared the transcriptomic changes in dormancy release induced by two different methods, FL and cold stratification (CS) in N. incisum. We further analyzed the gene expression patterns involved in seed germination and dormancy using quantitative reverse-transcription PCR. RESULTS: RNA-sequence analysis revealed more dramatic changes in the transcriptomes of FL than those in CS, particularly for genes involved in the biosynthesis and regulation of gibberellins (GAs) and ABA. The down-regulation of ABA biosynthesis genes and the dramatic up-regulation of NiCYP707As, an ABA catabolic gene, contributed to the reduced ABA levels in FL. The increased GA3 levels in CS-treated seeds were due to the up-regulation of NiGA3OX. Both NiABI5 (a positive ABA regulator) and NiGAI (a negative regulator of GA) were down-regulated in FL and CS. The upregulation of strigolactones (SLs; the metabolites with the same precursor as ABA) biosynthesis and regulatory genes in both FL- and CS-treated seeds indicates that SLs contribute positively to seed dormancy release in N. incisum. CONCLUSIONS: Our results indicated that FL- and CS-seed dormancy release possibly depends on two totally different mechanisms: alleviation of the effects of ABA and potentiation of the effects of GA, respectively. However, NiABI5 and NiGAI probably function as common factors integrating the effects of ABA and GA on seed dormancy release.

Females engage in stronger relationships: positive and negative effects of shrubs are more intense for Poa ligularis females than for males.

Background and Aims: Dioecious plants are of particular concern in view of global environmental changes because reproductive females are more sensitive to abiotic stresses, thus compromising population viability. Positive interactions with other plants may counteract the direct effects of any abiotic environmental stress, allowing them to thrive and maintain a viable population in suboptimal habitats, although this process has not been tested for dioecious species. Furthermore, almost no data are available on the outcome of such species interactions and their link with local spatial patterns and sex ratios. Methods: We set up a field experiment with Poa ligularis, a dioecious native grass from the arid grasslands of South America. We studied the interaction of male and female plants with cushion shrubs of contrasting ecological strategies. We experimentally limited direct shrub-grass competition for soil moisture and transplanted plants to evaluate the amelioration of abiotic stress by shrub canopies (i.e. sun and wind) on grasses. We also studied the distribution of naturally established female and male plants to infer process-pattern relationships. Key Results: Positive canopy effects as well as negative below-ground effects were more intense for females than for males. Deep-rooted Mulinum spinosum shrubs strongly facilitated survival, growth and reproduction of P. ligularis females. Naturally established female plants tended to distribute more closely to Mulinum than co-occurring males. Female growth suffered intensive negative root competition from the shallow-rooted Senecio filaginoides shrub. Conclusions: Interactions with other plants may reduce or enhance the effect of abiotic stresses on the seemingly maladapted sex to arid environments. We found that these biased interactions are evident in the current organization of sexes in the field, confirming our experimental findings. Therefore, indirect effects of climate change on population sex ratios may be expected if benefactor species abundances are differentially affected.

Contrasting phenotypic plasticity in the photoprotective strategies of the invasive species Carpobrotus edulis and the coexisting native species Crithmum maritimum.

Photoprotective strategies vary greatly within the plant kingdom and reflect a plant's physiological status and capacity to cope with environment variations. The plasticity and intensity of these responses may determine plant success. Invasive species are reported to show increased vigor to displace native species. Describing the mechanisms that confer such vigor is essential to understanding the success of invasive species. We performed an experiment whereby two species were monitored: Carpobrotus edulis, an aggressive invasive species in the Mediterranean basin, and Crithmum maritimum, a coexisting native species in the Cap de Creus Natural Park (NE Spain). We analyzed their photoprotective responses to seasonal environmental dynamics by comparing the capacity of the invader to respond to the local environmental stresses throughout the year. Our study analyses ecophysiological markers and photoprotective strategies to gain an insight into the success of invaders. We found that both species showed completely different but effective photoprotective strategies: in summer, C. edulis took special advantage of the xanthophyll cycle, whereas the success of C. maritimum in summer stemmed from morphological changes and alterations on ß-carotene content. Winter also presented differences between the species, as the native showed reduced Fv /Fm ratios. Our experimental design allowed us to introduce a new approach to compare phenotypic plasticity: the integrated phenotypic plasticity index (PPint ), defined as the maximum Euclidian distance between phenotypes, using a combination of different variables to describe them. This index revealed significantly greater phenotypic plasticity in the invasive species compared to the native species.

Easy Come, Easy Go: Capillary Forces Enable Rapid Refilling of Embolized Primary Xylem Vessels.

Protoxylem plays an important role in the hydraulic function of vascular systems of both herbaceous and woody plants, but relatively little is known about the processes underlying the maintenance of protoxylem function in long-lived tissues. In this study, embolism repair was investigated in relation to xylem structure in two cushion plant species, Azorella macquariensis and Colobanthus muscoides, in which vascular water transport depends on protoxylem. Their protoxylem vessels consisted of a primary wall with helical thickenings that effectively formed a pit channel, with the primary wall being the pit channel membrane. Stem protoxylem was organized such that the pit channel membranes connected vessels with paratracheal parenchyma or other protoxylem vessels and were not exposed directly to air spaces. Embolism was experimentally induced in excised vascular tissue and detached shoots by exposing them briefly to air. When water was resupplied, embolized vessels refilled within tens of seconds (excised tissue) to a few minutes (detached shoots) with water sourced from either adjacent parenchyma or water-filled vessels. Refilling occurred in two phases: (1) water refilled xylem pit channels, simplifying bubble shape to a rod with two menisci; and (2) the bubble contracted as the resorption front advanced, dissolving air along the way. Physical properties of the protoxylem vessels (namely pit channel membrane porosity, hydrophilic walls, vessel dimensions, and helical thickenings) promoted rapid refilling of embolized conduits independent of root pressure. These results have implications for the maintenance of vascular function in both herbaceous and woody species, because protoxylem plays a major role in the hydraulic systems of leaves, elongating stems, and roots.

Response of Ajowan to water stress induced by polyethylene glycol (PEG) 6000 during seed germination and seedling growth.

Seed germination and subsequent metabolic changes in Ajowan (Trachyspermum ammi L.) (NRCSS AA-2) seedlings was studied under water limiting conditions, imposed by increasing concentrations of polyethylene glycol (PEG 6000). Five water stress conditions (0, -0.05, -0.1, -0.15 and -0.2 MPa) were created in the laboratory in a completely randomized design. The results revealed that water stress (-0.2 MPa) significantly reduced seed germination components like final germination percent (80%) radical (64%) and plumule (63%) length, fresh (63%) and dry (74%) weight of seedlings and vigor index (SVI) by 92% over control. Decrease in osmotic potential resulted in decreased protein content (56%) with concomitant increase in total sugars (55%) at -0.2 MPa as compared to control. Significant increase in free proline and glycine betaine content by 1.5 to 2 folds was observed at the highest water stress condition. The seedlings exhibited increased activity of superoxide dismutase and peroxidase under stressed condition. In the present study, it was found that Ajowan was a moderately drought tolerant species at laboratory level.

Cytological evaluation of Apiaceae Lindl. from Western Himalayas.

The present paper deals with cytological studies on 31 populations covering 17 species belonging to 10 genera of Apiaceae from Western Himalayas. The chromosome numbers in the two species as Chaerophyllum capnoides (n = 11) and Heracleum brunonis (n = 11), along with additional cytotypes for Pimpinella acuminata (n = 9) and Sium latijugum (n = 12) have been reported for the first time on world-wide basis. The genus Pleurospermum, although cytologically worked out earlier from outside India, its species densiflorum (n = 11) makes first representation of the genus from India. Besides, the chromosome number in Chaerophyllum aromaticum (n = 11) have been worked out for the first time from India. The course of meiosis varies from normal to abnormal in different populations of Chaerophyllum villosum, Pimpinella achilleifolia and Sium latijugum while abnormal meiotic course has been observed in all the studied populations of Chaerophyllum acuminatum, C. aromaticum, C. capnoides, Pimpinella acuminata, P. diversifolia, Pleurospermum densiflorum and Vicatia coniifolia. Such taxa are marked with meiotic abnormalities in the form of cytomixis, chromatin stickiness, formation of laggards and bridges resulting into abnormal microsporogenesis. The occurrence of structural heterozygosity has been recorded in the Chaerophyllum acuminatum and C. aromaticum. The effect of these abnormalities is clearly seen on the pollen size and fertility.

Relative embryo length as an adaptation to habitat and life cycle in Apiaceae.

• The factors driving the evolution of the relative embryo length in Apiaceae were examined. We tested the hypothesis that seeds with large relative embryo length, because of more rapid germination, are beneficial in dry and open habitats and for short-lived species. We also analyzed to what extent delayed germination as a result of embryo growth can be considered a dormancy mechanism. • Hypotheses were tested by correlating the relative embryo length with other plant traits, habitat and climatic variables. The adaptive nature of the relative embryo length was determined by comparing the performance of a pure drift, Brownian motion (BM) model of trait evolution with that of a selection-inertia, Ornstein-Uhlenbeck (OU) model. • A positive correlation of the relative embryo length with germination speed and negative correlations with the amount of habitat shade, longevity and precipitation were found. An OU model, in which the evolution of longer embryos corresponded to a transition to habitats of high light, or to a short life cycle, outperformed significantly a BM model. • The results indicated that the relative embryo length may have evolved as an adaptation to habitat and life cycle, whereas dormancy was mainly related to temperature at the sampling sites.

Plant dispersal in the sub-Antarctic inferred from anisotropic genetic structure.

Climatic conditions and landscape features often strongly affect species' local distribution patterns, dispersal, reproduction and survival and may therefore have considerable impacts on species' fine-scale spatial genetic structure (SGS). In this study, we demonstrate the efficacy of combining fine-scale SGS analyses with isotropic and anisotropic spatial autocorrelation techniques to infer the impact of wind patterns on plant dispersal processes. We genotyped 1304 Azorella selago (Apiaceae) specimens, a wind-pollinated and wind-dispersed plant, from four populations distributed across sub-Antarctic Marion Island. SGS was variable with Sp values ranging from 0.001 to 0.014, suggesting notable variability in dispersal distance and wind velocities between sites. Nonetheless, the data supported previous hypotheses of a strong NW-SE gradient in wind strength across the island. Anisotropic autocorrelation analyses further suggested that dispersal is strongly directional, but varying between sites depending on the local prevailing winds. Despite the high frequency of gale-force winds on Marion Island, gene dispersal distance estimates (σ) were surprisingly low (<10 m), most probably because of a low pollen dispersal efficiency. An SGS approach in association with isotropic and anisotropic analyses provides a powerful means to assess the relative influence of abiotic factors on dispersal and allow inferences that would not be possible without this combined approach.

[Study on plant regeneration from somatic embryos of vulnerable medicinal plant Glehnia littoralis].

OBJECTIVE: To study the cause of the seeds dormancy of Glehnia littoralis in vitro and to establish plant regeneration methods via somatic embryos. METHOD: The effects of endosperm and exogenous hormone on the seed dormancy breaking of G. littoralis and the effect of hormone concentration on embryonic callus induction and plant regeneration via somatic embryos were observed, RESULTS: The germination rate of the seeds with 1/3 endosperm was the highest which achieved 31%. TDZ, 6-BA and GA3 treatment could not break seed dormancy but easily lead to abnormal seedlings. Embryogenic callus induction rates was up to 57% on MS supplemented with 1.0 mg x L(-1) 2,4-D. After 20 days culture, embryogenic calli were transferred to MS medium and cotyledonary embryos were formed in 40 days. The regenerated plants were obtained in 20 days. CONCLUSION: An effective system of plant regeneration of G. littoralis was established in this study.

Cryptic spatial aggregation of the cushion plant Azorella selago (Apiaceae) revealed by a multilocus molecular approach suggests frequent intraspecific facilitation under sub-Antarctic conditions.

PREMISE OF THE STUDY: In abiotically severe habitats, intraspecific aggregations can increase species' fitness by ameliorating stressful environmental factors. However, the difficulty of identifying individual plants in some growth forms makes the measurements of intraspecific aggregation, and therefore the assessment of intraspecific facilitation, problematic. In this study, we examined the genotype composition within cushions of Azorella selago, a sub-Antarctic cushion plant, to investigate the potential extent of intraspecific facilitation. METHODS: The study was performed on Marion Island, South Africa. Two to eight samples were collected from 42 A. selago cushions, comprising eight different growth forms. Samples were genotyped using seven microsatellite markers. KEY RESULTS: We showed that all cushion shapes, with the exception of small cushions, may be comprised of more than one genetically distinct individual. CONCLUSIONS: Under harsh sub-Antarctic conditions, intraspecific aggregation between A. selago individuals appears common and may be driven by the positive impacts of environmental amelioration.

Isoarnottinin 4'-glucoside, a glycosylated coumarin from Prangos uloptera, with biological activity.

Coumarins are a well-known group of natural products distributed in the plant kingdom especially in the family Apiaceae with various biological activities. Isoarnottinin 4'-glucoside is a simple glycosylated coumarin found previously in a few genera of Apiaceae, and its biological activities have not been previously described in details. In the present paper, the compound was isolated from Prangos uloptera (Apiaceae) leaves using HPLC techniques. Antimicrobial, phytotoxic and cytotoxic activities of the compound were evaluated by disk diffusion, lettuce assay and MTT method. Our results indicated that the compound has high antibacterial effect against Erwinia carotovora, a common plant pathogen with MIC value of 100 microg/mL. The compound also exhibited significant phytotoxic activity against lettuce and modest cytotoxic activity against HeLa cell line with IC50 of 0 .84 mg/mL. It could be concluded that isoamottinin 4'-glucoside may play phytoalexin or allelopathic role for plant and may be a candidate for an antibacterial agent or a bioherbicide.

Seed longevity and germination characteristics of six fen plant species.

Fens are among the most threatened habitats in Europe as their area has decreased considerably in the last centuries. For successful management and restoration conservationists need detailed knowledge about seed bank formation and seed longevity of plants, as these features are closely related to successional and vegetation dynamical processes. I analysed seed longevity and the germination characteristics of six fen plant species by seed burial experiments. Based on seed weight, seed bank was expected for long-term persistent for the light-seeded Schoenus nigricans, Carex appropinquata, C. pseudocyperus, C. davalliana and Peucedanum palustre and also that for the medium-seeded Cicuta virosa. It was proved that, the latter two species have short-term persistent seed banks, while Carex pseudocyperus has a transient seed bank, therefore these species may only have a limited role in restoration from seed banks. It was found that Schoenus nigricans, Carex appropinquata and C. davalliana have persistent seed banks, because some of their four-year-old seeds have emerged. Fresh seeds had low germination rate in all studied species and majority of seeds emerged after winter, except for Carex pseudocyperus. After the germination peak in spring, the majority of the ungerminated seeds of Schoenus nigricans, Peucedanum palustre, Carex appropinquata, C. davalliana and Cicuta virosa entered a secondary dormancy phase that was broken in autumn. I found the seasonal emergence of the latter three species highly similar.

Environmental regulation of dormancy loss in seeds of Lomatium dissectum (Apiaceae).

BACKGROUND AND AIMS: Lomatium dissectum (Apiaceae) is a perennial, herbaceous plant of wide distribution in Western North America. At the time of dispersal, L. dissectum seeds are dormant and have under-developed embryos. The aims of this work were to determine the requirements for dormancy break and germination, to characterize the type of seed dormancy, and to determine the effect of dehydration after embryo growth on seed viability and secondary dormancy. METHODS: The temperature requirements for embryo growth and germination were investigated under growth chamber and field conditions. The effect of GA(3) on embryo growth was also analysed to determine the specific type of seed dormancy. The effect of dehydration on seed viability and induction of secondary dormancy were tested in seeds where embryos had elongated about 4-fold their initial length. Most experiments examining the nature of seed dormancy were conducted with seeds collected at one site in two different years. To characterize the degree of variation in dormancy-breaking requirements among seed populations, the stratification requirements of seeds collected at eight different sites were compared. KEY RESULTS: Embryo growth prior to and during germination occurred at temperatures between 3 and 6 degrees C and was negligible at stratification temperatures of 0.5 and 9.1 degrees C. Seeds buried in the field and exposed to natural winter conditions showed similar trends. Interruption of the cold stratification period by 8 weeks of dehydration decreased seed viability by about 30 % and induced secondary dormancy in the remaining viable seeds. Comparison of the cold stratification requirements of different seed populations indicates that seeds collected from moist habitats have longer cold stratification requirements that those from semiarid environments. CONCLUSIONS: Seeds of L. dissectum have deep complex morphophysiological dormancy. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter.

Energy balance and temperature relations of Azorella compacta, a high-elevation cushion plant of the central Andes.

The environmental relationships and ecophysiology of Azorella compacta, a giant cushion plant, were investigated in Parque Nacional Lauca, Chile (18 degrees 10'-18 degrees 25' S and 69 degrees 16' W, 4400 m asl). The diurnal temperature range can reach 42 degrees C on some days of the year. The surface temperature of A. compacta was 13 degrees C below that of the air temperature of -7 degrees C at dawn, but from midmorning to late afternoon, the plant surface temperature remained within a few degrees of the air temperature. Soil surface temperatures did not differ between north- and south-facing slopes, but a model showed an increase in radiation reception by north-facing slopes throughout most of the year. Gas exchange measurements of A. compacta measured at the onset of the wet season ranged from -0.6662 to 11.4 micromol.m(-2).s(-1), and maximum stomatal conductance (Gs) was 410 mmol.m(-2).s(-1). The estimated light compensation point was 89 micromol.m(-2).s(-1) and estimated light saturation occurred at about 1280 mumol.m(-2).s(-1). Diurnal water potential measurements for A. compacta ranged from -1.67 to -2.65 MPa. This is one of the first ecophysiological studies of a tropical alpine cushion plant.

Cryopreservation of in vitro shoot apices of Glehnia littoralis - a medical plant.

Cryopreservation was examined as a practical method for preserving the genetic resources of Glehnia littoralis Fr. Schm. a nearly exterminated medical plant. In vitro shoot apices were successfully cryopreserved using vitrification and encapsulation-dehydration. In vitrification, regrowth of apices loaded for 60 min with PVS2 (66.7 +/- 6.7 percent) was preferable to loading with PVS3 (50.0 +/- 5.8 percent). With encapsulation-dehydration, the best regrowth (43.3 +/- 3.3 percent) was achieved when the moisture content in the beads was reduced to 19 percent by drying with silica gel for 6 h. Increased regrowth of shoot tips cryopreserved by encapsulation-dehydration resulted from the addition of 0.1 mM acetylsalicylic acid to the loading solution (86.7 +/- 3.3 percent).

Interactive effects of salinity, nitrate, light, and seed weight on the germination of the halophyte Crithmum maritimum.

Interaction of salinity, nitrate, light, and seed weight on the germination of Crithmum maritimum was investigated. Seeds of three size categories were germinated at 0-200 mM NaCl with either 0, 5 or 20 mM KNO 3 . Experiments were done under darkness, white light, or red light. Regardless of seed weight, germination was maximal in distilled water. Under salinity, the smallest seeds showed the highest germination percentage. Salt impact was amplified by darkness, but was mitigated by nitrate supply, red light and their combination. At the same PPFD, germination of T2 seeds was higher, when exposed to red light than under white light, suggesting that germination was more influenced by the light type than by the PPFD. As a whole, not only salinity, nutrient availability, seed weight, and light, but also their interaction may control the germination of this halophyte.

Seed ecology of the geophyte Conopodium majus (Apiaceae), indicator species of ancient woodland understories and oligotrophic meadows.

Conopodium majus is a geophyte with pseudomonocotyly, distributed in Atlantic Europe. It is an indicator of two declining European habitats: ancient woodland understories and oligotrophic hay meadows. Attempts to reintroduce it by seed have been hindered by scarce seedling emergence and limited knowledge of its seed biology. Micro-CT scanning was used to assess pseudomonocotyly. Embryo growth and germination were studied in the laboratory and the field, using dissection and image analysis. The effects of temperature, light, nitrate and GA3 on germination were tested. Seed desiccation tolerance was investigated by storage at different RHs and by drying seeds at different stages of embryo growth. Seeds possess morphological but not physiological dormancy. Embryo growth and germination were promoted by temperatures between 0 and 5 °C, arrested above 10 °C, and indifferent to alternating temperatures, light, nitrate and GA3 . Pseudomonocotyly appears to result from cotyledon fusion. While seeds tolerated drying to 15% RH and storage for 1 year at 20 °C, viability was lost when storage was at 60% RH. Seeds imbibed at 5 °C for 84 days had significant internal embryo growth but were still able to tolerate drying to 15% RH. Reproduction by seed in C. majus follows a strategy shared by geophytes adapted to deciduous temperate forests. The evolution of fused cotyledons may enable the radicle and the hypocotyl to reach deeper into the soil where a tuber can develop. The embryo is capable of growth within the seed at low temperatures so that germination is timed for early spring.

[Study on rapid propagation of Changium smyrnioides].

OBJECTIVE: For the protection of Changium smyrnioides Wolff germ-plasm resources. METHODS: Rapid propagation was conducted by tissue culture. RESULTS: The best explants were leaves. The optimum culture medium for the induction of callus was MS + 2,4-D 1.0 mg/L + Kt 1.0 mg/L; that of bud was MS + 6-BA 3.0 mg/L + NAA 0.2 mg/L; and that of root was MS + IBA 0.4 mg/L or MS + NAA 0.4 mg/L. CONCLUSION: Rapid propagation of Changium smyrnioides is established with tissue culture, which provides an effective way for the sustainable utilization.

Differential effect of drought regimes on the seedling performance of six floodplain grassland species.

The performance of seedlings is crucial for the survival and persistence of plant populations. Although drought frequently occurs in floodplains and can cause seedling mortality, studies on the effects of drought on seedlings of floodplain grasslands are scarce. We tested the hypotheses that drought reduces aboveground biomass, total biomass, plant height, number of leaves, leaf area and specific leaf area (SLA), and increases root biomass and root-mass fraction (RMF) and that seedlings from species of wet floodplain grasslands are more affected by drought than species of dry grasslands. In a greenhouse study, we exposed seedlings of three confamilial pairs of species (Pimpinella saxifraga, Selinum carvifolia, Veronica teucrium, Veronica maritima, Sanguisorba minor, Sanguisorba officinalis) to increasing drought treatments. Within each plant family, one species is characteristic of wet and one of dry floodplain grasslands, confamilial in order to avoid phylogenetic bias of the results. In accordance with our hypotheses, drought conditions reduced aboveground biomass, total biomass, plant height, number of leaves and leaf area. Contrary to our hypotheses, drought conditions increased SLA and decreased root biomass and RMF of seedlings. Beyond the effects of the families, the results were species-specific (V. maritima being the most sensitive species) and habitat-specific. Species indicative of wet floodplain grasslands appear to be more sensitive to drought than species indicative of dry grasslands. Because of species- and habitat-specific responses to reduced water availability, future drought periods due to climate change may severely affect some species from dry and wet habitats, while others may be unaffected.

[Study on seed quality test and quality standard of Changium smyrnioides].

OBJECTIVE: To study seed quality test methods, and provide basis for establishing seed quality standard of Changium smyrnioides. METHOD: According to the seed testing regulations, the seed quality of C. smyrnioides from different producing area and in different growing years was measured. RESULT AND CONCLUSION: The range of seed purity, weight per 1000 seeds, seed moisture content, seed viability were determined and the primary seed quality classification standard was established.