Showing papers on "Seedling published in 2017"

Influence of nitrogen and phosphorous on the growth and root morphology of Acer mono.

Abstract: Nitrogen and phosphorous are critical determinants of plant growth and productivity, and both plant growth and root morphology are important parameters for evaluating the effects of supplied nutrients. Previous work has shown that the growth of Acer mono seedlings is retarded under nursery conditions; we applied different levels of N (0, 5, 10, and 15 g plant-1) and P (0, 4, 6 and 8 g plant-1) fertilizer to investigate the effects of fertilization on the growth and root morphology of four-year-old seedlings in the field. Our results indicated that both N and P application significantly affected plant height, root collar diameter, chlorophyll content, and root morphology. Among the nutrient levels, 10 g N and 8 g P were found to yield maximum growth, and the maximum values of plant height, root collar diameter, chlorophyll content, and root morphology were obtained when 10 g N and 8 g P were used together. Therefore, the present study demonstrates that optimum levels of N and P can be used to improve seedling health and growth during the nursery period.

Enhanced seed germination and plant growth by atmospheric pressure cold air plasma: combined effect of seed and water treatment

Abstract: The combined effect of non-thermal plasma treatment of water and seeds on the rate of germination and plants growth of radish (Raphanus sativus), tomato (Solanum lycopersicum), and sweet pepper (Capsicum annum) have been investigated using dielectric barrier discharges in air under atmospheric pressure and room temperature. A cylindrical double dielectric barrier discharge reactor is used for water activation and a plate-to-plate double DBD reactor is employed for seed treatment. The activation of water, for 15 and 30 min, lead to acidic solutions (pH ≈ 3) with moderate concentrations of nitrate (NO3−) and hydrogen peroxide (H2O2). Plasma activated water (PAW) has shown a significant impact on germination as well as plant growth for the three types of seeds used. Interestingly, the positive effect, in seed germination and seedling growth, has been observed when the PAW and plasma-treated seeds (10 and 20 min) were combined. In one hand, when the seeds were (tomato and pepper) exposed to 10 min plasma and watered with PAW-15 for first 9 days followed by tap water for 51 days, the stem length is increased about 60% as compared to control sample. On the second hand, for longer exposures of seeds and water to plasma discharges, a negative effect is observed. For instance, plasma-treated seeds watered with PAW-30, the plant growth and vitality were decreased as compared to control sample. These results revealed that the developed cold plasma reactors could be used to significantly improve the seed germination as well as plant growth, nevertheless, the plasma treatment time has to be optimized for each seeds.

Extensive transcriptomic and epigenomic remodelling occurs during Arabidopsis thaliana germination.

Abstract: Seed germination involves progression from complete metabolic dormancy to a highly active, growing seedling. Many factors regulate germination and these interact extensively, forming a complex network of inputs that control the seed-to-seedling transition. Our understanding of the direct regulation of gene expression and the dynamic changes in the epigenome and small RNAs during germination is limited. The interactions between genome, transcriptome and epigenome must be revealed in order to identify the regulatory mechanisms that control seed germination. We present an integrated analysis of high-resolution RNA sequencing, small RNA sequencing and MethylC sequencing over ten developmental time points in Arabidopsis thaliana seeds, finding extensive transcriptomic and epigenomic transformations associated with seed germination. We identify previously unannotated loci from which messenger RNAs are expressed transiently during germination and find widespread alternative splicing and divergent isoform abundance of genes involved in RNA processing and splicing. We generate the first dynamic transcription factor network model of germination, identifying known and novel regulatory factors. Expression of both microRNA and short interfering RNA loci changes significantly during germination, particularly between the seed and the post-germinative seedling. These are associated with changes in gene expression and large-scale demethylation observed towards the end of germination, as the epigenome transitions from an embryo-like to a vegetative seedling state. This study reveals the complex dynamics and interactions of the transcriptome and epigenome during seed germination, including the extensive remodelling of the seed DNA methylome from an embryo-like to vegetative-like state during the seed-to-seedling transition. Data are available for exploration in a user-friendly browser at https://jbrowse.latrobe.edu.au/germination_epigenome .

Enhancement of Germination and Seedling Growth of Wheat Seed Using Dielectric Barrier Discharge Plasma with Various Gas Sources

Abstract: The influences of non-thermal discharge plasma treatment on wheat seed germination and seedling growth were investigated using a dielectric barrier discharge (DBD) plasma system at atmospheric pressure and room temperature. DBD plasma with various gas sources (oxygen, air, argon, and nitrogen) was employed in this study. Germination characteristics, seedling growth parameters, surface changes of the seed coat, permeability, and soluble protein of the seedlings were measured after the DBD plasma treatments. The experimental results showed that moderate-intensity DBD plasma had active impacts on wheat seed germination and seedling growth. Germination potential significantly increased by 24.0, 28.0, and 35.5% after 4 min of the air plasma, nitrogen plasma, and argon plasma treatments, respectively, compared with the control; and the shoot and root length also increased; however, no enhancement was observed after the oxygen plasma treatment. Scanning electron microscope analysis showed that etching effects on the seed coat occurred after the air plasma, nitrogen plasma, and argon plasma treatments, which affected the hygroscopicity and permeability of the wheat seed. In addition, moderate-intensity DBD plasma could also activate several physiological reactions in wheat seed, resulting in the increase of soluble protein production in wheat seedlings.

Seed-vectored endophytic bacteria modulate development of rice seedlings

Abstract: Aim The aim of the present study was to evaluate the effects of the removal of indigenous bacteria from rice seeds on seedling growth and development. Here we report the presence of three indigenous endophytic bacteria in rice seeds that play important roles in modulating seedling development (shoot and root lengths, and formation of root hairs and secondary roots) and defence against pathogens. Methods and Results Seed-associated bacteria were removed using surface sterilization with NaOCl (bleach) followed by antibiotic treatment. When bacteria were absent, growth of seedlings in terms of root hair development and overall seedling size was less than that of seedlings that contained bacteria. Reactive oxygen staining of seedlings showed that endophytic bacteria became intracellular in root parenchyma cells and root hairs. Roots containing endophytic bacteria were seen to stain densely for reactive oxygen, while roots free of bacteria stained lightly for reactive oxygen. Bacteria were isolated and identified as Enterobacter asburiae (VWB1), Pantoea dispersa (VWB2) and Pseudomonas putida (VWB3) by 16S rDNA sequencing. Bacteria were found to produce indole acetic acid (auxins), inhibited the pathogen Fusarium oxysporum and solubilized phosphate. Reinoculation of bacteria onto seedlings derived from surface-disinfected rice and Bermuda grass seeds significantly restored seedling growth and development. Conclusion Rice seeds harbour indigenous bacterial endophytes that greatly influence seedling growth and development, including root and shoot lengths, root hair formation and disease susceptibility of rice seedlings. Significance and Impact of the Study This study shows that seeds of rice naturally harbour bacterial endophytes that play key roles in modulation of seedling development.

Alleviation of adverse effects of drought stress on wheat seed germination using atmospheric dielectric barrier discharge plasma treatment.

Abstract: Atmospheric dielectric barrier discharge (DBD) was attempted to improve the resistance of wheat seed to drought stress. Effects of DBD plasma on wheat seed germination, seedling growth, osmotic-adjustment products, lipid peroxidation, reactive oxygen species (ROS), antioxidant enzyme activity, abscisic acid, and drought resistant related genes expression under drought stress were investigated. The changes of the wheat seed coat before and after the DBD plasma treatment were explored. Experimental results showed that the DBD plasma treatment could alleviate the adverse effects of drought stress on wheat seed germination and seedling growth; the germination potential and germination rate increased by 27.2% and 27.6%, and the root length and shoot length of the wheat seedlings also increased. Proline and soluble sugar levels under drought stress were improved after the DBD plasma treatment, whereas the malondialdehyde content decreased. ROS contents under drought stress were reduced after the DBD plasma treatment, whereas the activities of superoxide dismutase, catalase, and peroxidase were promoted. DBD plasma treatment promoted abscisic acid generation in wheat seedlings, and it also regulated functional gene LEA1 and stimulated regulation genes SnRK2 and P5CS to resist drought stress. Etching effect and surface modification occurred on the seed coat after the DBD plasma treatment.

The Synergistic Priming Effect of Exogenous Salicylic Acid and H2O2 on Chilling Tolerance Enhancement during Maize (Zea mays L.) Seed Germination

Abstract: Chilling stress is an important constraint for maize seedling establishment in the field. To examine the role of salicylic acid (SA) and hydrogen peroxide (H2O2) in response to chilling stress, we investigated the effects of seed priming with SA, H2O2 and SA+H2O2 combination on maize resistance under chilling stress (13°C). Priming with SA, H2O2 and especially SA+H2O2 shortened seed germination time and enhanced seed vigor and seedling growth as compared with hydropriming and non-priming treatments under low temperature. Meanwhile, SA+H2O2 priming notably increased the endogenous H2O2 and SA content, antioxidant enzymes activities and their corresponding genes ZmPAL, ZmSOD4, ZmAPX2, ZmCAT2 and ZmGR expression levels. The α-amylase activity was enhanced to mobilize starch to supply metabolites such as soluble sugar and energy for seed germination under chilling stress. In addition, the SA+H2O2 combination positively up-regulated expressions of gibberellic acid (GA) biosynthesis genes ZmGA20ox1 and ZmGA3ox2, and down-regulated GA catabolism gene ZmGA2ox1 expression; while it promoted GA signaling transduction genes expressions of ZmGID1 and ZmGID2 and decreased the level of seed germination inhibitor gene ZmRGL2. The abscisic acid (ABA) catabolism gene ZmCYP707A2 and the expressions of ZmCPK11 and ZmSnRK2.1 encoding response receptors in ABA signaling pathway were all up-regulated. These results strongly suggested that priming with SA and H2O2 synergistically promoted hormones metabolism and signal transduction, and enhanced energy supply and antioxidant enzymes activities under chilling stress, which were closely relevant with chilling injury alleviation and chilling-tolerance improvement in maize seed.

Effects of Low pH on Photosynthesis, Related Physiological Parameters, and Nutrient Profiles of Citrus

Abstract: Seedlings of 'Xuegan' (Citrus sinensis) and 'Sour pummelo' (Citrus grandis) were irrigated daily with nutrient solution at a pH of 2.5, 3, 4, 5 or 6 for nine months. Thereafter, seedling growth, root, stem and leaf concentrations of nutrient elements, leaf gas exchange, pigment concentration, ribulose-1,5-bisphosphate carbohylase/oxygenase activity and chlorophyll a fluorescence, and root and leaf relative water content, total soluble protein level, H2O2 production and electrolyte leakage were investigated in order to (a) determine how low pH affects photosynthesis, related physiological parameters and mineral nutrient profiles; and (b) to understand the mechanisms by which low pH causes a decrease in leaf CO2 assimilation. pH 2.5 greatly inhibited seedling growth and many physiological parameters were altered only at pH 2.5; pH 3 slightly inhibited seedling growth; pH 4 had almost no influence on seedling growth; and seedling growth and many physiological parameters reached a maximum at pH 5. No seedlings were killed at each given pH. These results demonstrated that citrus were insensitive to low pH. H+-toxicity might directly damage citrus roots, hence affecting the uptake of mineral nutrients and water. H+-toxicity, decreased uptake of nutrients (i.e., nitrogen, phosphorus, potassium, calcium and magnesium) and water were probably responsible for the low pH-induced inhibition of growth. Leaf CO2 assimilation was inhibited only at pH 2.5. The combinations of impaired photosynthetic electron transport chain, increased production of reactive oxygen species, and decreased uptake of nutrients and water might account for the pH 2.5-induced decrease in CO2 assimilation. Mottled bleached leaves only occurred in pH 2.5-treated C. grandis seedlings. Furthermore, the pH 2.5-induced alterations of leaf CO2 assimilation, water use efficiency, chlorophylls, polyphasic chlorophyll a fluorescence (OJIP) transients and many fluorescence parameters, root and leaf total soluble proteins, H2O2 production and electrolyte leakage were slightly greater in C. grandis seedlings than in C. sinensis ones. Obviously, C. sinensis was slightly more tolerant to low pH than C. grandis. In conclusion, our findings provided some novel clues on the causes of low pH-induced inhibition of seedling growth and leaf CO2 assimilation.

Soilborne fungi have host affinity and host-specific effects on seed germination and survival in a lowland tropical forest

Abstract: The Janzen–Connell (JC) hypothesis provides a conceptual framework for explaining the maintenance of tree diversity in tropical forests. Its central tenet—that recruits experience high mortality near conspecifics and at high densities—assumes a degree of host specialization in interactions between plants and natural enemies. Studies confirming JC effects have focused primarily on spatial distributions of seedlings and saplings, leaving major knowledge gaps regarding the fate of seeds in soil and the specificity of the soilborne fungi that are their most important antagonists. Here we use a common garden experiment in a lowland tropical forest in Panama to show that communities of seed-infecting fungi are structured predominantly by plant species, with only minor influences of factors such as local soil type, forest characteristics, or time in soil (1–12 months). Inoculation experiments confirmed that fungi affected seed viability and germination in a host-specific manner and that effects on seed viability preceded seedling emergence. Seeds are critical components of reproduction for tropical trees, and the factors influencing their persistence, survival, and germination shape the populations of seedlings and saplings on which current perspectives regarding forest dynamics are based. Together these findings bring seed dynamics to light in the context of the JC hypothesis, implicating them directly in the processes that have emerged as critical for diversity maintenance in species-rich tropical forests.

ABI4 represses the expression of type-A ARRs to inhibit seed germination in Arabidopsis

Abstract: The plant hormone abscisic acid (ABA) plays a crucial role in regulating seed germination and post-germination growth. ABSCISIC ACID INSENSITIVE4 (ABI4), an APETALA2 (AP2)-type transcription factor, is required for the ABA-mediated inhibition of seed germination. Cytokinins promote seed germination and seedling growth by antagonizing ABA signaling. However, the interaction between ABA and cytokinin signaling during seed germination remains unclear. Here, we report that ABA signaling downregulates Arabidopsis response regulators (ARRs), a class of cytokinin-inducible genes, during seed germination and cotyledon greening. We found that the application of exogenous ABA repressed the expression of type-A ARRs in Arabidopsis seeds and seedlings. Among the type-A ARR family members, the expression of ARR6, ARR7 and ARR15 was upregulated in ABA-deficient mutants, indicating that the transcriptional inhibition of type-A ARRs requires the ABA signaling pathway. Single and multiple mutations of these ARRs resulted in increased ABA sensitivity during germination and cotyledon greening; overexpression of ARR7 or ARR15 led to an ABA-insensitive phenotype. These observations suggest that type-A ARRs inhibit the ABA response during seed germination and cotyledon greening. Further analysis showed that ABI4 negatively regulated the transcription of ARR6, ARR7 and ARR15 by directly binding to their promoters. Genetic analysis showed that loss-of-function mutations of ARR7 and ARR15 partially rescued the ABA insensitivity of abi4-1. Thus, this study revealed that ABI4 plays a key role in ABA and cytokinin signaling by inhibiting the transcription of type-A ARRs to inhibit seed germination and cotyledon greening.

Abiotic niche partitioning and negative density dependence drive tree seedling survival in a tropical forest.

Abstract: In tropical tree communities, processes occurring during early life stages play a critical role in shaping forest composition and diversity through differences in species9 performance. Predicting the future of tropical forests depends on a solid understanding of the drivers of seedling survival. At the same time, factors determining spatial and temporal patterns of seedling survival can play a large role in permitting species coexistence in diverse communities. Using long-term data on the survival of more than 45 000 seedlings of 238 species in a Neotropical forest, we assessed the relative importance of key abiotic and biotic neighbourhood variables thought to influence individual seedling survival and tested whether species vary significantly in their responses to these variables, consistent with niche differences. At the community level, seedling survival was significantly correlated with plant size, topographic habitat, neighbourhood densities of conspecific seedlings, conspecific and heterospecific trees and annual variation in water availability, in descending order of effect size. Additionally, we found significant variation among species in their sensitivity to light and water availability, as well as in their survival within different topographic habitats, indicating the potential for niche differentiation among species that could allow for species coexistence.

Previous crop and rotation history effects on maize seedling health and associated rhizosphere microbiome

Abstract: To evaluate crop rotation effects on maize seedling performance and its associated microbiome, maize plants were grown in the greenhouse in soils preceded by either maize, pea, soybean or sunflower. Soils originated from a replicated field experiment evaluating different four-year rotation combinations. In the greenhouse, a stressor was introduced by soil infestation with western corn rootworm (WCR) or Fusarium graminearum. Under non-infested conditions, maize seedlings grown in soils preceded by sunflower or pea had greater vigor. Stress with WCR or F. graminearum resulted in significant root damage. WCR root damage was equivalent for seedlings regardless of soil provenance; whereas F. graminearum root damage was significantly lower in maize grown in soils preceded by sunflower. Infestation with WCR affected specific microbial taxa (Acinetobacter, Smaragdicoccus, Aeromicrobium, Actinomucor). Similarly, F. graminearum affected fungal endophytes including Trichoderma and Endogone. In contrast to the biological stressors, rotation sequence had a greater effect on rhizosphere microbiome composition, with larger effects observed for fungi compared to bacteria. In particular, relative abundance of Glomeromycota was significantly higher in soils preceded by sunflower or maize. Defining the microbial players involved in crop rotational effects in maize will promote selection and adoption of favorable crop rotation sequences.

Physiological Response to Heat Stress During Seedling and Anthesis Stage in Tomato Genotypes Differing in Heat Tolerance

Abstract: Tomato cultivars differ in their sensitivity to heat stress, and the sensitivity depends on the developmental stage of the plants. It is less known how heat stress affects tomato at the anthesis stage in terms of leaf physiology and fruit set and whether the ability of tomato to tolerate heat at different developmental stages is linked. To investigate photosynthetic gas exchange characteristics, carbohydrate content and fruit set during heat stress, a thermo-tolerant cultivar (‘LA1994’) and a thermo-sensitive cultivar (‘Aromata’) were studied at the seedling and anthesis stage. The photosynthetic parameters, maximum quantum efficiency of photosystem II (Fv/Fm), chlorophyll content, carbohydrate content and fruit set were determined in plants grown at 26/18 °C (control) and 36/28 °C (heat stress). The physiological responses including net photosynthetic rate (PN), chlorophyll content and Fv/Fm decreased in ‘Aromata’ at both developmental stages during heat stress, whereas they were unaltered in ‘LA1994’ during heat stress as compared to the respective control. This was accompanied by lower contents of glucose and fructose in mature leaves of ‘Aromata’ at the seedling stage under heat stress. In contrast, the glucose content increased while the fructose content was unaltered in mature leaves of ‘LA1994’ at the seedling stage under heat stress. High temperature induced a similar change in carbohydrate content in the young leaves of both cultivars at anthesis. The fructose and sucrose content were unaffected in the mature leaves of ‘Aromata’ but significantly increased in ‘LA1994’ under heat stress at anthesis. The heat stress treatment decreased pollen viability and inhibited fruit set due to flower wilting and abnormal abscission in ‘Aromata’, whereas fruit set was not inhibited in ‘LA1994’. A decrease in chlorophyll content, photosynthesis and carbohydrate content in the mature leaves of tomato could be related to fruit set failure at high temperature. The results show that physiological responses to heat stress at the seedling stage correspond with the responses at the anthesis stage, demonstrating that screening for heat stress sensitivity can be carried out in young plants.

Interplay between Light and Plant Hormones in the Control of Arabidopsis Seedling Chlorophyll Biosynthesis.

Abstract: Chlorophyll biosynthesis is one of the most important cellular processes and is essential for plant photosynthesis. After germination under the soil, dark-grown seedlings are etiolated and accumulate the chlorophyll precursor protochlorophyllide (Pchlide) in cotyledons. Upon exposure to light, Pchlide is rapidly converted to chlorophyll to initiate photoautotrophic growth. In this light-regulated de-etiolation process, multiple endogenous phytohormones are also involved. Although the co-regulation of seedling greening by light and hormones has long been observed, recent studies greatly advanced our understanding of their interplay by identifying the key components connecting these pathways. The integrators, such as PHYTOCHROMEINTERACTING FACTORs (PIFs), ELONGATED HYPOCOTYL 5 (HY5), ETHYLENE INSENSTIVE 3 (EIN3) and DELLA proteins, are key transcription regulators in light or hormone signaling pathways. This review focuses on these integrators and illustrates the regulatory networks of light and hormone interactions in chlorophyll biosynthesis.

Pre-treatment of seeds with static magnetic field improves germination and early growth characteristics under salt stress in maize and soybean

Abstract: Maize and Soybean seeds were pre-treated with static magnetic field (SMF) of 200 mT for 1 h to evaluate the effect of magnetopriming on germination and early growth characteristics of seeds under saline conditions. The adverse effect of NaCl induced salt stress was found on percentage germination and germination related parameters. Enhanced percentage germination and early seedling growth parameters (root and shoot length, and vigour indices) under different salinity levels (0–100 mM NaCl) indicated that magnetopriming was more effective in alleviating salinity stress at early seedling stage of both maize and soybean as compared to untreated seeds. α- amylase and protease activities were also higher in SMF treated seeds under both non-saline and saline conditions. This could have resulted in faster hydration of enzymes in SMF treated seeds leading to higher rate of germination. Increased levels of superoxide radical and hydrogen peroxide was found in germinating magnetoprimed seeds of maize and soybean, under both the growing conditions. Enhancement in seed germination and seedling vigour under both the growing conditions by SMF treatment may be due to the combined effect of enhanced α- amylase and protease activities and enhanced levels of free radicals in the seeds.

Air Atmospheric Dielectric Barrier Discharge Plasma Induced Germination and Growth Enhancement of Wheat Seed

Abstract: Air atmospheric dielectric barrier discharge plasma (DBD) was attempted to pretreat wheat seed to improve its germination and growth in this study. The effects of the DBD plasma treatment on the wheat seed germination, seedling growth, osmotic-adjustment products, lipid peroxidation level, and antioxidant enzymes activity were investigated. The experimental results showed that the DBD plasma treatment with an appropriate time scale could promote the wheat seed germination and seedling growth. The germination potential, germination rate, germination index, and vigor index increased by 26.7, 9.1, 16.9, and 46.9% after 7 min’s DBD plasma treatment, respectively; the root length, shoot length, fresh weight, and dry weight of the seedlings also increased after the DBD plasma treatment. The osmotic-adjustment products, proline and soluble sugar contents, in the wheat seedlings were significantly enhanced after the DBD plasma treatment with an appropriate time scale, while the malondialdehyde content decreased. Moreover, the activities of superoxide dismutase and peroxidase also increased after the DBD plasma treatment. The DBD plasma treatment led to etching effect on the wheat seed coat, resulting in the improvement of its water absorption capacity.

Application of bacteria from non-cultivated plants to promote growth, alter root architecture and alleviate salt stress of cotton.

Abstract: Aims Cotton seeds are frequently treated with acid to remove fibres and reduce seed-transmitted diseases. This process also eliminates beneficial bacteria on the seed surface. The goal of this research was to seek and apply beneficial bacteria to acid delinted cotton seeds to evaluate their growth-promoting and salt stress alleviating effects in seedlings. Methods and Results Bacteria were isolated from non-cultivated plants in the Malvaceae. Seeds were collected from Portia tree (Thespesia populnea) and wild cotton (Gossypium hirsutum) from coastal and arid areas of Puerto Rico. Bacillus amyloliquefaciens, Curtobacterium oceanosedimentum and Pseudomonas oryzihabitans were inoculated onto acid delinted cotton seeds. Bacteria increased cotton seed germination and length of emerging seedling radicles. Cotton seeds were inoculated with B. amyloliquefaciens to evaluate growth and root architecture of non-stressed and salt stressed seedlings. Inoculating cotton seeds with B. amyloliquefaciens led to a greater percentage of seedlings with expanded cotyledons after 8 days, enhanced primary and lateral root growth, and altered root architecture. Similar results were obtained when okra seeds were inoculated with B. amyloliquefaciens. Conclusion The data supported the hypothesis that non-cultivated plants in the Malvaceae growing in stressful environments possess bacteria that promote growth, alter root architecture and alleviate salt stress of cotton and okra seedlings. Significance and Impact of the Study This study demonstrated the effects of applying beneficial bacteria on acid delinted cotton seeds. Inoculating seeds with salt stress alleviating bacteria could improve the growth of crop seedlings that are vulnerable to soil salinization.

Regulatory-associated protein of TOR (RAPTOR) alters the hormonal and metabolic composition of Arabidopsis seeds, controlling seed morphology, viability and germination potential.

Abstract: Summary Target of rapamycin (TOR) is a positive regulator of growth and development in all eukaryotes, which positively regulates anabolic processes like protein synthesis, while repressing catabolic processes, including autophagy. To better understand TOR function we decided to analyze its role in seed development and germination. We therefore performed a detailed phenotypic analysis using mutants of the REGULATORY-ASSOCIATED PROTEIN OF TOR (RAPTOR1B), a conserved TOR-interactor, acting as a scaffold protein, which recruits substrates for the TOR kinase. Our results show that raptor1b plants produced seeds, which were delayed in germination and less resistant to stresses, leading to decreased vitaliy. These physiological phenotypes were accompanied by morphological changes including decreased seed coat pigmentation and reduced production of seed coat mucilage. A detailed molecular analysis revealed that many of these morphological changes were associated with significant changes of the metabolic content of raptor1b seeds, including elevated levels of free amino acids, as well as reduced levels of protective secondary metabolites and storage proteins. Most of these observed changes, were accompanied by significantly altered phytohormone levels in the raptor1b seeds with increases in abscisic acid, auxin and jasmonic acid, which are known to inhibit germination. Delayed germination and seedling growth, observed in the raptor1b seeds, could be partially restored by the exogenous supply of gibberellic acid, indicating that TOR is in the center of a regulatory hub controlling seed metabolism, maturation and germination. This article is protected by copyright. All rights reserved.

Melatonin application confers enhanced salt tolerance by regulating Na+ and Cl− accumulation in rice

Abstract: The mitigating effects of melatonin (MT) treatment on salt-stressed seed germination capacity and of MT pretreatment (including the whole period of seed germination and seedling cultivation) on the salt tolerance of two rice (Oryza sativa L. ssp. japonica) cultivars, Liaojing 4 (LJ4, salt tolerant) and Nipponbare (Nipp, salt sensitive), and the related physiological and molecular events were investigated in this study. The results showed that when additional MT solutions (10–500 μM) were added, the NaCl-decreased seed germination potential (GP), germination index (GI) and vigor index (VI) of LJ4 and Nipp were clearly restored. When MT pretreatment occurred during the period of seed germination and seedling cultivation prior to NaCl stress, relative electrolytic leakage in roots and leaves clearly decreased and thus restored the root vigor and growth of both plants. This could be fulfilled by multiple physiological mechanisms. For example, improving seed germination ability (GP, GI and VI), strengthening root vigor, reducing Na+ and Cl− contents in roots and leaves (especially for Cl− in roots and Na+ in leaves), and enhancing the activities of antioxidant enzymes (such as catalase and superoxide dismutase) in roots and leaves resulted in a decrease in H2O2 level. Moreover, the reduced contents of Na+ and Cl− in the roots and leaves of both salt-stressed rice plants under MT pretreatment displayed clear relations with the enhanced transcription of OsSOS1 in roots and of OsCLC1 and OsCLC2 in roots and leaves. These results could indicate that soaking with MT during seed germination and/or root application of MT at the seedling stage are very simple operations that require small doses and can effectively solve the problems of low germination rate and poor seedling establishment in saline soils. Therefore, these results provide a theoretical basis and technical support for the chemical regulation of salt tolerance and cultivation practices of rice and other crops in saline areas.

Importance of animal and plant traits for fruit removal and seedling recruitment in a tropical forest

Abstract: The traits of animals and plants influence their interaction networks, but the significance of species' traits for the resulting ecosystem functions is poorly understood. A crucial ecosystem function in the tropics is seed dispersal by animals. While the importance of species' traits for structuring plant–frugivore networks is supported by a number of studies, no study has so far identified the functional traits determining the subsequent processes of fruit removal and seedling recruitment. Here, we conducted a comprehensive field study on fruit removal by frugivorous birds and seedling recruitment along an elevational gradient in the Colombian Andes. We measured morphological traits of birds (body mass, bill width, Kipp's index) and plants (plant height, crop mass, fruit width and seed mass) which we expected to be related to fruit removal and seedling recruitment. We tested 1) which bird and plant traits influence fruit removal, and 2) whether network metrics at plant species level, functional identities of frugivores (community-based mean trait values) and/or plant traits were the main determinants of seedling recruitment. We found that large-bodied bird species contributed more to fruit removal than small-bodied bird species and that small-sized fruits were more frequently removed than large-sized fruits. Small plant species and plants with heavy seeds recruited more seedlings than did large plants and plants with light seeds. Network metrics and functional identities of seed dispersers were unrelated to seedling recruitment. Our findings have two important implications. First, large birds are functionally more important than small birds in tropical seed-removal networks. Second, the detected tradeoff between fruit size and seed mass in subsequent recruitment processes suggests that the adaptability of forest plant communities to a loss of large frugivores is limited by life-history constraints. Hence, the protection of large-bodied frugivores is of primary importance for the maintenance of diverse tropical plant communities.

Increasing the germination envelope under water stress improves seedling emergence in two dominant grass species across different pulse rainfall events

Abstract: Summary 1.Demographic recruitment processes, such as seed germination and seedling emergence, are critical transitional phases to the re-establishment of degraded plant populations, but often fail due to rainfall not supporting plant requirements. Using species from the widespread arid Australian perennial grass genus Triodia, we investigated the interactions of seeds in different dormancy states and their functional germination envelope in response to water stress after simulated pulse rainfall events. 2.Seed dormancy was alleviated in Triodia species to varying degrees by wet/ dry cycling or by removing floret structures from seeds. The seeds were then exposed to different rainfall frequency and quantity events mimicking the 25th, median, 75th and 95th percentile rainfall events found in natural habitats for the study species in the north-west Australian arid zone. 3.Under 95th percentile rainfall conditions recruitment was highest, but still limited to 35% germination and 10% emergence of cleaned seeds (i.e. the least dormant state evaluated). This was related to the functional germination envelope as indicated by more negative base water potential thresholds (Ψb50) for cleaned seeds (≥ -0.33 MPa) compared to intact florets (≥ -0.26 MPa). As a result the maximum cumulative time where soil water potentials were optimal for germination (Ψsoil ≥ Ψb50) were 1.6–2.6 times longer for cleaned seeds in large frequent rainfall events when compared to intact florets. Furthermore, seed dormancy, that usually prolongs seed survival, was linked to a short-term reduction in seed viability, which may further reduce recruitment rates. 4.Synthesis and applications. Our findings indicate that large frequent rainfall events raised soil water potentials above critical thresholds for germination and are important for successful plant establishment. If recruitment bottlenecks are a result of seed dormancy and variable rainfall for arid grass species, then this study shows benefits for alleviating seed dormancy prior to seeding in restoration sites, as this increases the environmental envelope for germination. This article is protected by copyright. All rights reserved.

Seed Germination and Early Growth Responses to Seed Pre-treatment by Non-thermal Plasma in Hemp Cultivars (Cannabis sativa L.)

Abstract: The two key questions addressed in this paper were whether different cultivars of hemp (Cannabis sativa L.) have the same reactions to non-thermal plasma seed pre-treatments and whether different plasma sources have different effects on the seeds. Seed germination and early growth of hemp in design of hierarchical analysis of variance was conducted. Differences in response among seeds of three hemp cultivars (‘Finola’, ‘Bialobrzeskie’, ‘Carmagnola’) to the non-thermal plasma pre-treatment generated by two apparatuses (gliding arc and downstream microwave devices) in four time expositions (0, 180, 300, 600 s) were found. The high importance was found in type of apparatus and time exposition. A positive/neutral effect was observed in all measured characteristics after gliding arc plasma pre-treatment. Gliding arc pre-treatment increased the length of seedlings, seedling accretion and weight of seedling in both cv. ‘Finola’ and cv. ‘Bialobrzeskie’ hemp. On the other hand, the downstream microwave apparatus had an inhibiting effect on all tested hemp cultivars. It was the first time when significant differences in response to non-thermal pre-treatment were found in taxonomically close plants. The results obtained in this study describes different effect of various plasma treatment on germination and early growth of hemp seeds. The direct pre-treatment of non-thermal plasma discharge in condition of atmospheric pressure was better. Results of our experiment show that the use of non-thermal plasma pre-treatment may increase survival of some hemp cultivars during seedlings establishment in a drier period and may be used in new agro-technical measures in unconventional agriculture.

Mycorrhizal specificity does not limit the distribution of an endangered orchid species

Abstract: What factors determine the distribution of a species is a central question in ecology and conservation biology. In general, the distribution of plant species is assumed to be controlled by dispersal or environmentally controlled recruitment. For plant species which are critically dependent on mycorrhizal symbionts for germination and seedling establishment, specificity in mycorrhizal associations and availability of suitable mycorrhizal fungi can be expected to have a major impact on successful colonization and establishment and thus ultimately on a species distribution. We combined seed germination experiments with soil analyses and fungal assessments using 454 amplicon pyrosequencing to test the relative importance of dispersal limitation, mycorrhizal availability and local growth conditions on the distribution of the orchid species Liparis loeselii, which, despite being widely distributed, is rare and endangered in Europe. We compared local soil conditions, seed germination and mycorrhizal availability in the soil between locations in northern Belgium and France where L. loeselii occurs naturally and locations where conditions appear suitable, but where adults of the species are absent. Our results indicated that mycorrhizal communities associating with L. loeselii varied among sites and plant life cycle stages, but the observed variations did not affect seed germination, which occurred regardless of current L. loeselii presence and was significantly affected by soil moisture content. These results indicate that L. loeselii is a mycorrhizal generalist capable of opportunistically associating with a variety of fungal partners to induce seed germination. They also indicate that availability of fungal associates is not necessarily the determining factor driving the distribution of mycorrhizal plant species.

Effect of seaweed liquid extracts from Ulva lactuca on seedling growth of mung bean (Vigna radiata)

Abstract: Seaweed extracts contain a variety of compounds, such as macro- and micronutrients and plant growth regulators, which can be used by plants. Such extracts can have both negative and positive effects (depending on the concentration) when directly applied to seeds and plants. The aim of this study was to assess the effects of acid seaweed liquid extracts on growth and biochemical parameters of mung bean (Vigna radiata) under laboratory and greenhouse conditions, using direct applications to seeds and seedlings. Extracts of Ulva lactuca were obtained by hydrolysis with H2SO4 at 2, 4, 6, 8 and 10% concentrations. The effects of seaweed extracts with different concentrations, 0.2, 0.4, 0.6, 0.8 and 1.0% were tested on germination parameters (percentage index, mean time, seedling vigour index) and growth parameters (plumule and radicle length, shoot and root length as well as fresh and dry weight) in addition to biochemical parameters (protein content, total chlorophyll, total and reduced sugar) in mung bean. The results suggest that addition of acid extracts at low concentrations (0.2%) can significantly enhance seed germination rates. Higher germination rates were associated with lower mean germination time, high germination index and, consequently, greater seedling vigour and greater plumule, radicle, shoot and root length. In addition, production (fresh and dry weight) of mung bean was significantly higher compared to the control treatments. Biochemical analysis of the seedlings treated with acid seaweed liquid extracts at 0.2% showed higher protein contents. Total chlorophyll concentration of seedlings in all treatments was significantly higher than in the controls plants, whereas the accumulation of total and reducing sugars was highest in treated plants with almost all treatments at higher concentrations.

Regulation of ZnO nanoparticles-induced physiological and molecular changes by seed priming with humic acid in Oryza sativa seedlings

Abstract: The present investigation explored the capability of priming treatment with 250 mg L−1 of humic acid (HA) to improve nano-ZnO tolerance of two rice cultivars seedlings (Zhu Liang You 06 and Qian You No. 1). The results showed that seed germination, seedling growth, total soluble protein, sugar and starch contents significantly improved by seed priming with HA especially under high nano-ZnO stress (500 and 750 mg L−1) as compared to unprimed seeds. In contrast, electrolyte leakage significantly increased after exposure to 500 and 750 mg L−1 nano-ZnO, but decreased obviously after HA priming in both cultivars. Abscisic acid (ABA) content in the seeds germinated under nano-ZnO stress was higher than those grown under non-stress condition; while gibberellins (GA) content decreased under nano-ZnO stress. HA priming down-regulated the relative expression levels of OsABA8ox2 and OsNCED1, which were key genes in ABA biosynthesis and catabolism of rice seeds. In contrast, up-regulation in OsGA20ox2 and OsGA3ox1 were induced by HA priming. The histochemical analysis reported that higher concentration of hydrogen peroxide (H2O2) and superoxide radical (O2·−) were observed in stressed roots with nano-ZnO as compared with non-stress condition, indicating reduction of root cell viability and severe oxidative burst. However, HA priming reduced obviously H2O2, O2·−, antioxidant enzymes activities (SOD, POD, CAT) and malondialdehyde (MDA) content of rice seedlings under stress. Significant increases in dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDAR) activities were observed in nano-ZnO stressed seedlings, but they were diminished evidently by HA priming. In addition, the improvement of HA on cell ultra structure of root tip and leaf mesophyll was detected under nano-ZnO stress especially 750 mg L−1 concentration. Therefore, it was suggested that HA priming could definitely improve the rice seed germination and seedling growth under nano-ZnO stress to some extent.

Terpenoid trans-caryophyllene inhibits weed germination and induces plant water status alteration and oxidative damage in adult Arabidopsis.

Abstract: trans-Caryophyllene (TC) is a sesquiterpene commonly found as volatile component in many different aromatic plants. Although the phytotoxic effects of trans-caryophyllene on seedling growth are relatively explored, not many information is available regarding the phytotoxicity of this sesquiterpenes on weed germination and on adult plants. The phytotoxic potential of TC was assayed in vitro on weed germination and seedling growth to validate its phytotoxic potential on weed species. Moreover, it was assayed on the metabolism of Arabidopsis thaliana adult plants, through two different application ways, spraying and watering, in order to establish the primary affected organ and to deal with the unknown mobility of the compound. The results clearly indicated that TC inhibited both seed germination and root growth, as demonstrated by comparison of the ED50 values. Moreover, although trans-caryophyllene-sprayed adult Arabidopsis plants did not show any effect, trans-caryophyllene-watered plants became strongly affected. The results suggested that root uptake was a key step for the effectiveness of this natural compound and its phytotoxicity on adult plants was mainly due to the alteration of plant water status accompanied by oxidative damage.