Showing papers on "Seedling published in 2018"

Effects of hydrogel amendment on water storage of sandy loam and loam soils and seedling growth of barley, wheat and chickpea

Abstract: The hydrogel amendments may improve seedling growth and establishment by increasing water retention capacity of soils and regulating the plants available water supplies, particularly under arid environments. The effects of dif ferent levels of a locally prepared hydrogel were studied on the moisture properties of sandy loam and loam soils (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA, Luvic Yermosol, FAO) and on growth response of three plant species, viz. barley (Hordeum vulgare L.), wheat (Triticum aestivum L.) and chickpea (Cicer arietinum L.). Water absorption by gel was rapid and highest in distilled water and was inhibited by an increase in water salinity. The addition of 0.1, 0.2 and 0.3% hydrogel increased the moisture retention (θr) at field capacity linearly ( r = 0.988) and thus the amount of plant available water significantly in both sandy loam and loam soils compared to the untreated soils. Seed germination of wheat and barley was not affected but seedling growth of both species was improved by the gel amendment. In loam soil, seed germination of chickpea was higher with 0.2% gel and seedling growth increased with increase in gel level compared with control conditions. The hydrogel amendment caused a delay by 4–5 days in wilting of seedlings grown in both soils compared with control conditions. The hydrogel amendment was effective in improving soil moisture availability and thus increased plant establishment. However, the varied responses of plant species in sandy loam and loam soils warrant further studies on the behaviour of different soil types with gel amend ments.

Phosphorus Nutrition: Plant Growth in Response to Deficiency and Excess

Abstract: Phosphorus (P) is an essential element determining plants’ growth and productivity. Due to soil fixation of P, its availability in soil is rarely sufficient for optimum growth and development of plants. The uptake of P from soil followed by its long-distance transport and compartmentation in plants is outlined in this chapter. In addition, we briefly discuss the importance of P as a structural component of nucleic acids, sugars and lipids. Furthermore, the role of P in plant’s developmental processes at both cellular and whole plant level, viz. seed germination, seedling establishment, root, shoot, flower and seed development, photosynthesis, respiration and nitrogen fixation, has been discussed. Under P-deficient condition, plants undergo various morphological, physiological and biochemical adaptations, while P toxicity is rarely reported. We also summarize the antagonistic and synergistic interaction of P with other macro- and micronutrients.

Molecular Mechanisms Underlying Abscisic Acid/Gibberellin Balance in the Control of Seed Dormancy and Germination in Cereals.

Abstract: Seed dormancy is an adaptive trait that does not allow the germination of an intact viable seed under favorable environmental conditions. Non-dormant seeds or seeds with low level of dormancy can germinate readily under optimal environmental conditions, and such a trait leads to preharvest sprouting, germination of seeds on the mother plant prior to harvest, which significantly reduces the yield and quality of cereal crops. High level of dormancy, on the other hand, may lead to non-uniform germination and seedling establishment. Therefore, intermediate dormancy is considered to be a desirable trait as it prevents the problems of sprouting and allows uniformity of postharvest germination of seeds. Induction, maintenance, and release of seed dormancy are complex physiological processes that are influenced by a wide range of endogenous and environmental factors. Plant hormones, mainly abscisic acid (ABA) and gibberellin (GA), are the major endogenous factors that act antagonistically in the control of seed dormancy and germination; ABA positively regulates the induction and maintenance of dormancy, while GA enhances germination. Significant progress has been made in recent years in the elucidation of molecular mechanisms regulating ABA/GA balance and thereby dormancy and germination in cereal seeds, and this review summarizes the current state of knowledge on the topic.

Why seedlings grow: influence of plant attributes

Abstract: Successful forest restoration requires planting quality seedlings with optimal growth potential. Thus, nurseries need to produce seedlings with plant attributes that favor the best chance of successful establishment once they are field planted. From the mid-twentieth century on, research foresters have critically examined plant attributes that confer improved seedling growth under various restoration site conditions. This review examines the value of commonly measured seedling quality attributes (i.e., height, diameter, root mass, shoot-to-root ratio, drought resistance, freezing tolerance, nutrient status, root growth potential, and root electrolyte leakage) that have been recognized as important in explaining why seedlings with improved attributes have better growth after planting. Seedlings with plant attributes that fall within the appropriate range of values can increase the speed with which they overcome planting stress, initiate growth, and become “coupled” to the forest restoration site, thereby ensuring successful seedling establishment. Although planting high quality seedlings does not guarantee successful seedling establishment, it increases chances for successful establishment and growth.

Bacterial endophytes from rice cut grass (Leersia oryzoides L.) increase growth, promote root gravitropic response, stimulate root hair formation, and protect rice seedlings from disease

Abstract: Leersia oryzoides, a wild relative of rice (Oryza sativa), may carry potential seed-borne bacterial endophytes which could be used to enhance growth of rice. We hypothesized that seed-associated bacteria from L. oryzoides would be compatible with rice and promote seedling growth, development, and survival. We isolated bacteria from seed of L. oryzoides and checked compatibility with rice as well as Bermuda grass seeds for seedling growth promotion. Internal colonisation of bacteria into root cells was observed by ROS staining and microscopic observation. Growth promoting bacteria were evaluated for IAA production, phosphate solubilization and antifungal activities. Overall, ten bacteria were found to be growth promoting in rice seedlings with effects including restoration of root gravitropic response, increased root and shoot growth, and stimulation of root hair formation. All bacteria were identified by 16S rDNA sequencing. Six bacteria were found to become intracellular in root parenchyma and root hairs in rice and in Bermuda grass seedlings. Six bacteria were able to produce IAA in LB broth with highest (47.06 ± 1.99 μg ml−1) by LTE3 (Pantoea hericii). Nine isolates solubilized phosphate and inhibited at least one soil borne fungal pathogen. Seed bacteria of L. oryzoides are compatible with rice. Many of these bacteria become intracellular, induce root gravitropic response, increase root and shoot growth, and stimulate root hair formation in both rice and Bermuda grass seedlings. Presence of bacteria protects seedlings from soil pathogens during seedling establishment. This research suggests that bioprospecting microbes on near relatives of rice and other crop plants may be a viable strategy to obtain microbes to improve cultivation of crops.

The γ-Aminobutyric Acid (GABA) Alleviates Salt Stress Damage during Seeds Germination of White Clover Associated with Na+/K+ Transportation, Dehydrins Accumulation, and Stress-Related Genes Expression in White Clover

Abstract: The objective of this study was to determine the effect of soaking with γ-aminobutyric acid (GABA) on white clover (Trifolium repens cv. Haifa) seed germination under salt stress induced by 100 mM NaCl. Seeds soaking with GABA (1 μM) significantly alleviated salt-induced decreases in endogenous GABA content, germination percentage, germination vigor, germination index, shoot and root length, fresh and dry weight, and root activity of seedling during seven days of germination. Exogenous application of GABA accelerated starch catabolism via the activation of amylase and also significantly reduced water-soluble carbohydrate, free amino acid, and free proline content in seedlings under salt stress. In addition, improved antioxidant enzyme activities (SOD, GPOX, CAT, APX, DHAR, GR and MDHR) and gene transcript levels (Cu/ZnSOD, FeSOD, MnSOD, CAT, GPOX, APX, MDHR, GPX and GST) was induced by seeds soaking with GABA, followed by decreases in O2∙−, H2O2, and MDA accumulation during germination under salt stress. Seeds soaking with GABA could also significantly improve Na+/K+ content and transcript levels of genes encoding Na+/K+ transportation (HKT1, HKT8, HAL2, H+-ATPase and SOS1) in seedlings of white clover. Moreover, exogenous GABA significantly induced the accumulation of dehydrins and expression of genes encoding dehydrins (SK2, Y2K, Y2SK, and dehydrin b) in seedlings under salt stress. These results indicate that GABA mitigates the salt damage during seeds germination through enhancing starch catabolism and the utilization of sugar and amino acids for the maintenance of growth, improving the antioxidant defense for the alleviation of oxidative damage, increasing Na+/K+ transportation for the osmotic adjustment, and promoting dehydrins accumulation for antioxidant and osmotic adjustment under salt stress.

Genome-Wide Association Mapping of Seedling Heat Tolerance in Winter Wheat.

Abstract: Heat stress during the seedling stage of early-planted winter wheat (Triticum aestivum L.) is one of the most abiotic stresses of the crop restricting forage and grain production in the Southern Plains of the United States. To map quantitative trait loci (QTLs) and identify single-nucleotide polymorphism (SNP) markers associated with seedling heat tolerance, a genome-wide association mapping study (GWAS) was conducted using 200 diverse representative lines of the hard red winter wheat association mapping panel, which was established by the Triticeae Coordinated Agricultural Project (TCAP) and genotyped with the wheat iSelect 90K SNP array. The plants were initially planted under optimal temperature conditions in two growth chambers. At the three-leaf stage, one chamber was set to 40/35°C day/night as heat stress treatment, while the other chamber was kept at optimal temperature (25/20°C day/night) as control for 14 days. Data were collected on leaf chlorophyll content, shoot length, number of leaves per seedling, and seedling recovery after removal of heat stress treatment. Phenotypic variability for seedling heat tolerance among wheat lines was observed in this study. Using the mixed linear model (MLM), we detected multiple significant QTLs for seedling heat tolerance on different chromosomes. Some of the QTLs were detected on chromosomes that were previously reported to harbor QTLs for heat tolerance during the flowering stage of wheat. These results suggest that some heat tolerance QTLs are effective from the seedling to reproductive stages in wheat. However, new QTLs that have never been reported at the reproductive stage were found responding to seedling heat stress in the present study. Candidate gene analysis revealed high sequence similarities of some significant loci with candidate genes involved in plant stress responses including heat, drought, and salt stress. This study provides valuable information about the genetic basis of seedling heat tolerance in wheat. To the best of our knowledge, this is the first GWAS to map QTLs associated with seedling heat tolerance targeting early planting of dual-purpose winter wheat. The SNP markers identified in this study will be used for marker-assisted selection (MAS) of seedling heat tolerance during dual-purpose wheat breeding.

Indigenous endophytic seed bacteria promote seedling development and defend against fungal disease in browntop millet (Urochloa ramosa L.)

Abstract: Aims This study was conducted to investigate indigenous seed endophyte effects on browntop millet seedling development. We report that seed-inhabiting bacterial endophytes are responsible for promoting seedling development, including stimulation of root hair formation, increasing root and shoot length growth and increasing photosynthetic pigment content of seedlings. Bacterial endophytes also improved resistance of seedlings to disease. Methods and results A total of four endophytic bacteria were isolated from surface-sterilized seeds and identified by 16S rDNA sequencing as Curtobacterium sp. (M1), Microbacterium sp. (M2), Methylobacterium sp. (M3) and Bacillus amyloliquefaciens (M4). Removal of bacteria with streptomycin treatment from the seeds compromised seedling growth and development. When endophytes were reinoculated onto seeds, seedlings recovered normal development. Strains M3 and M4 were found to be most potent in promoting growth of seedlings. Bacteria were found to produce auxin, solubilize phosphate and inhibit fungal pathogens. Significant protection of seedlings from Fusarium infection was found using strain M4 in microcosm assays. The antifungal lipopeptide genes for surfactin and iturin were detected in M4; culture extracts of M4 showed a positive drop collapse result for surfactins. Conclusions This study demonstrates that browntop millet seeds vector indigenous endophytes that are responsible for modulation of seedling development and protection of seedlings from fungal disease. Significance and impact of the study This study is significant and original in that it is the first report of seed-inhabiting endophytes of browntop millet that influence seedling development and function in defence against soilborne pathogens. This study suggests that conservation and management of seed-vectored endophytes may be important in development of more sustainable agricultural practices.

Drought stress has transgenerational effects on seeds and seedlings in winter oilseed rape ( Brassica napus L.)

Abstract: Drought stress has a negative effect on both seed yield and seed quality in Brassica napus (oilseed rape, canola). Here we show that while drought impairs the maternal plant performance, it also increases the vigour of progeny of stressed maternal plants. We investigated the transgenerational influence of abiotic stress by detailed analysis of yield, seed quality, and seedling performance on a growth-related and metabolic level. Seeds of eight diverse winter oilseed rape genotypes were generated under well-watered and drought stress conditions under controlled-environment conditions in large plant containers. We found a decrease in seed quality in seeds derived from mother plants that were exposed to drought stress. At the same time, the seeds that developed under stress conditions showed higher seedling vigour compared to non-stressed controls.This effect on seed quality and seedling vigour was found to be independent of maternal plant yield performance. Drought stress has a positive transgenerational effect on seedling vigour. Three potential causes for stress-induced improvement of seedling vigour are discussed: (1) Heterotic effects caused by a tendency towards a higher outcrossing rate in response to stress; (2) an altered reservoir of seed storage metabolites to which the seedling resorts during early growth, and (3) inter-generational stress memory, formed by stress-induced changes in the epigenome of the seedling.

Root:shoot ratio in developing seedlings: How seedlings change their allocation in response to seed mass and ambient nutrient supply.

Abstract: Root:shoot (R:S) biomass partitioning is one of the keys to the plants' ability to compensate for limiting resources in the environment and thus to survive and succeed in competition. In adult plants, it can vary in response to many factors, such as nutrient availability in the soil or reserves in the roots from the previous season. The question remains whether, at the interspecific level, reserves in seeds can affect seedlings' R:S ratio in a similar way. Proper allocation to resource-acquiring organs is enormously important for seedlings and is likely to determine their survival and further success. Therefore, we investigated the effect of seed mass on seedling R:S biomass partitioning and its interaction with nutrient supply in the substrate. We measured seedling biomass partitioning under two different nutrient treatments after 2, 4, 6, and 12 weeks for seventeen species differing in seed mass and covering. We used phylogenetically informed analysis to determine the independent influence of seed mass on seedling biomass partitioning. We found consistently lower R:S ratios in seedlings with higher seed mass. Expectedly, R:S was also lower with higher substrate nutrient supply, but substrate nutrient supply had a bigger effect on R:S ratio for species with higher seed mass. These findings point to the importance of seed reserves for the usage of soil resources. Generally, R:S ratio decreased over time and, similarly to the effect of substrate nutrients, R:S ratio decreased faster for large-seeded species. We show that the seed mass determines the allocation patterns into new resource-acquiring organs during seedling development. Large-seeded species are more flexible in soil nutrient use. It is likely that faster development of shoots provides large-seeded species with the key advantage in asymmetric above-ground competition, and that this could constitute one of the selective factors for optimum seed mass.

Seed treatment with nano-iron (III) oxide enhances germination, seeding growth and salinity tolerance of sorghum

Abstract: In recent decades, nanoparticles have been intensively applied in agriculture. Two experiments were carried out to demonstrate the potential of nano‐iron oxide (n‐Fe₂O₃) as seed treatment (soaking and priming) at different concentrations (0, 10, 50, 100 and 500 mg/L) for enhancing sorghum (Sorghum bicolor (L.) Moench) germination and seedling growth under non‐stressed conditions (Experiment I), and to investigate the impacts of n‐Fe₂O₃ seed priming treatments (0, 10, 50, 100 and 500 mg/L) on growth, chlorophyll content, chlorophyll a fluorescence, gas exchange, water relations and lipid peroxidation under salt stress (150 mmol NaCl solution) (Experiment II). Results indicated that seed soaking with n‐Fe₂O₃ at 10 mg/L was the best treatment in improving speed and per cent of germination, while seed priming with n‐Fe₂O₃ at 50 and 100 mg/L was the most effective treatment in improving seedling (12 days old) growth. Salt stress decreased chlorophyll content, photosynthetic rate, stomatal conductance, transpiration rate, relative water content, osmotic potential and growth, along with increased lipid peroxidation. Among chlorophyll a fluorescence parameters, the photosynthetic performance index of PSII (PIABS) was the most salt‐responsive. Seed priming with n‐Fe₂O₃ at 500 mg/L increased sorghum growth (45 days old), through increased photosystem II efficiency, chlorophyll index, photosynthetic rate and relative water content with decreased lipid peroxidation. Overall, this study indicated that use of n‐Fe₂O₃ as a pre‐sowing seed treatment can enhance germination and seedling growth of sorghum and protect from negative impacts of salinity stress.

Silicon Improves Chilling Tolerance During Early Growth of Maize by Effects on Micronutrient Homeostasis and Hormonal Balances.

Abstract: Low soil temperature in spring is a major constraint for the cultivation of tropical and subtropical crops in temperate climates, associated with inhibition of root growth and activity, affecting early growth and frequently plant performance and final yield. This study was initiated to investigate the physiological base of cold-protective effects induced by supplementation with silicon (Si), widely recommended as a stress-protective mineral nutrient. Maize was used as a cold-sensitive model plant, exposed to chilling stress and low root-zone temperature (RZT) during early growth in a lab to field approach. In a pot experiment, 2-weeks exposure of maize seedlings to low RZT of 12-14°C, induced leaf chlorosis and necrosis, inhibition of shoot and root growth and micronutrient limitation (particularly Zn and Mn). These phenotypes were mitigated by seed treatments with the respective micronutrients, but surprisingly, also by Si application. Both, silicon and micronutrient treatments were associated with increased activity of superoxide dismutase in shoot and roots (as a key enzyme for detoxification of reactive oxygen species, depending on Zn and Mn as cofactors), increased tissue concentrations of phenolics, proline, and antioxidants, but reduced levels of H2O2. These findings suggest that mitigation of oxidative stress is a major effect of Zn, Mn, and Si applied as cold stress protectants. In a soil-free culture system without external nutrient supply, Si significantly reduced large leaching losses of Zn and Mn from germinating seeds exposed to low-temperature stress. Silicon also increased the translocation of micronutrient seed reserves to the growing seedling, especially the Zn shoot translocation. In later stages of seedling development (10 days after sowing), cold stress reduced the root and shoot contents of important hormonal growth regulators (indole acetic acid, gibberellic acid, zeatin). Silicon restored the hormonal balances to a level comparable with non-stressed plants and stimulated the production of hormones involved in stress adaptation (abscisic, salicylic, and jasmonic acids). Beneficial effects of Si seed treatments on seedling establishment and the nutritional status of Zn and Mn were also measured for a field-grown silage maize, exposed to chilling stress by early sowing. This translated into increased final biomass yield.

Disease protection and allelopathic interactions of seed-transmitted endophytic pseudomonads of invasive reed grass ( Phragmites australis )

Abstract: Non-native Phragmites australis (haplotype M) is an invasive grass that decreases biodiversity and produces dense stands. We hypothesized that seeds of Phragmites carry microbes that improve seedling growth, defend against pathogens and maximize capacity of seedlings to compete with other plants. We isolated bacteria from seeds of Phragmites, then evaluated representatives for their capacities to become intracellular in root cells, and their effects on: 1.) germination rates and seedling growth, 2.) susceptibility to damping-off disease, and 3.) mortality and growth of competitor plant seedlings (dandelion (Taraxacum officionale F. H. Wigg) and curly dock (Rumex crispus L.)). Ten strains (of 23 total) were identified and characterized; seven were identified as Pseudomonas spp. Strains Sandy LB4 (Pseudomonas fluorescens) and West 9 (Pseudomonas sp.) entered root meristems and became intracellular. These bacteria improved seed germination in Phragmites and increased seedling root branching in Poa annua. They increased plant growth and protected plants from damping off disease. Sandy LB4 increased mortality and reduced growth rates in seedlings of dandelion and curly dock. Phragmites plants associate with endophytes to increase growth and disease resistance, and release bacteria into the soil to create an environment that is favorable to their seedlings and less favorable to competitor plants.

Signaling Molecule Hydrogen Sulfide Improves Seed Germination and Seedling Growth of Maize (Zea mays L.) Under High Temperature by Inducing Antioxidant System and Osmolyte Biosynthesis.

Abstract: Hydrogen sulfide (H2S) is a novel type signaling molecule in plants Seed germination is a key stage of life cycle of plants, which is vulnerable to environmental stress including high temperature However, under high temperature stress, whether pre-soaking of maize seeds with NaHS (a H2S donor) could improve seed germination and seedling growth and the possible mechanisms are not completely clear In this study, maize seeds pre-soaked with NaHS enhanced germination percentage, sprout length, root length, and fresh weight compared with the control without NaHS treatment, illustrating that H2S could improve maize seed germination and seedling growth under high temperature In addition, in comparison to the control, NaHS pre-soaking stimulated antioxidant enzymes [ascorbate peroxidase (APX), glutathione reductase (GR), guaiacol peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT)] activities and the contents of water soluble non-enzymatic antioxidants [ascorbic acid (AsA) and glutathione (GSH)], as well as the ratio of reduced antioxidant to oxidized antioxidant Moreover, pre-soaking with NaHS activated Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase [OAT; both are rate-limiting enzymes in proline (Pro) synthesis], betaine aldehyde dehydrogenase [BADH; a key enzyme in glycine betaine (GB)], and trehalose (Tre)-6-phosphate phosphatase (a key step in Tre synthesis), which in turn accumulated Pro, GB, and Tre in germinating seeds compared with the control Also, an improved germination by NaHS under high temperature was reinforced by the above osmotic adjustment substances (osmolytes) alone, while deteriorated by the inhibitors of osmolyte biosynthesis [gabaculine (GAB), disulfiram (DSF), and sodium citrate (SC)] These results imply that H2S could improve maize seed germination and seedling growth under high temperature by inducing antioxidant system and osmolyte biosynthesis

Zinc Oxide Nanoparticles Boosts Phenolic Compounds and Antioxidant Activity of Capsicum annuum L. during Germination

Abstract: The effects of zinc oxide nanoparticles on seed germination and seedling growth of Capsicum annuum L. were determined in this research. Total phenols content, total flavonoids, and condensed tannins, as well as 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant capacity was determined. Results indicated that treatment with zinc oxide nanoparticles (ZnO-NPs) improved seed germination rate during the first seven days. The seed vigor germination increased 123.50%, 129.40% and 94.17% by treatment with ZnO-NPs suspensions at 100, 200 and 500 ppm, respectively. The morphological parameters tested revealed that ZnO-NPs treatments did not significantly affect plumule development, but they had a significant impact (p ≤ 0.01) on radicle length. Suspensions at 100, 200 and 500 ppm of ZnO-NPs inhibited seedling radicle growth and promoted accumulation of phenolic compounds, with a phytotoxic effect in this organ. Results suggested that zinc oxide nanoparticles influence seed vigor and seedling development and promoted the accumulation of desirable phenolic compounds in the radicle.

Genetic basis of drought tolerance during seed germination in barley

Abstract: Drought is one of the harshest abiotic stresses hindering seed germination, plant growth, and crop productivity. A high rate and uniformity of germination under stressful conditions are vital for crop establishment and growth; thus, for productivity. A better understanding of the genetic architecture of seed germination under drought stress is a prerequisite for further increasing yield potential. Barley is considered one of the most abiotic stresses-tolerant cereals. Elucidating the drought tolerance of barley during seed germination would indeed pave the way towards improving the performance of all cereals. However, we still know relatively little about the genetic control of drought tolerance during the seed germination phase. In our study, 218 worldwide spring barley accessions were subjected to PEG-induced drought during seed germination. Induced drought stress "20% PEG" significantly reduced the seed germination parameters and seedling related traits. A genome-wide association scan (GWAS) was used to identify genomic regions associated with our trait of interest. In total, 338 single nucleotide polymorphisms (SNPs) were found to be associated with several traits distributed across seven barley chromosomes, of which 26 genomic regions were associated with candidate genes. The current study found some of the quantitative trait loci (QTL) that have previously been reported to be linked to seed germination-related traits under drought conditions, as well as some new associations. Noteworthy, the identified QTL colocalized with a number of genes (within interval ±0.5 Mbp) that are exclusively distributed on chromosomes 1H, 2H, and 5H. The annotation of these genes in barley shows their roles in drought tolerance through encoding different transcription factors. The function of the identified genes during seed germination was also confirmed by the annotation of their counterparts in Arabidopsis. The current analyses show the power of the GWAS both for identifying putative candidate genes and for improving plant adaptive traits in barley.

The sucrose non-fermenting-1-related protein kinases SAPK1 and SAPK2 function collaboratively as positive regulators of salt stress tolerance in rice

Abstract: The sucrose non-fermenting-1-related protein kinase 2 family (SnRK2s) unifies different abiotic stress signals in plants. To date, the functions of two rice SnRK2s, osmotic stress/ABA-activated protein kinase 1 (SAPK1) and SAPK2, have been unknown. We investigated their roles in response to salt stress by generating loss-of-function lines using the CRISPR/Cas9 system and by overexpressing these proteins in transgenic rice plants. Expression profiling revealed that SAPK1 and SAPK2 expression were strongly induced by drought, NaCl, and PEG treatment, but not by ABA. SAPK2 expression was highest in the leaves, followed by the roots, whereas SAPK1 was highest expressed in roots followed by leaves. Both proteins were localized to the nucleus and the cytoplasm. Under salt stress, sapk1, sapk2 and, in particular, sapk1/2 mutants, exhibited reduced germination rates, more severe growth inhibition, more distinct chlorosis, reduced chlorophyll contents, and reduced survival rates in comparison with the wild-type plants. In contrast, SAPK1- and SAPK2-overexpression lines had increased germination rates and reduced sensitivities to salt; including mild reductions in growth inhibition, reduced chlorosis, increased chlorophyll contents and improved survival rates in comparison with the wild-type plants. These results suggest that SAPK1 and SAPK2 may function collaboratively as positive regulators of salt stress tolerance at the germination and seedling stages. We also found that SAPK1 and SAPK2 affected the osmotic potential following salt stress by promoting the generation of osmotically active metabolites such as proline. SAPK1 and SAPK2 also improved reactive oxygen species (ROS) detoxification following salt stress by promoting the generation of ROS scavengers such as ascorbic acid, and by increasing the expression levels of proteins such as superoxide dismutase (SOD) and catalase (CAT). SAPK1 and SAPK2 may function collaboratively in reducing Na+ toxicity by affecting the Na+ distribution between roots and shoots, Na+ exclusion from the cytoplasm, and Na+ sequestration into the vacuoles. These effects may be facilitated through the expression of Na+-and K+-homeostasis-related genes. SAPK1 and SAPK2 may function collaboratively as positive regulators of salt stress tolerance at the germination and seedling stages in rice. SAPK1 and SAPK2 may be useful to improve salt tolerance in crop plants.

Karrikin-KAI2 signalling provides Arabidopsis seeds with tolerance to abiotic stress and inhibits germination under conditions unfavourable to seedling establishment.

Abstract: The control of seed germination in response to environmental conditions is important for plant success. We investigated the role of the karrikin receptor KARRIKIN INSENSITIVE2 (KAI2) in the response of Arabidopsis seeds to osmotic stress, salinity and high temperature. Germination of the kai2 mutant was examined in response to NaCl, mannitol and elevated temperature. The effect of karrikin on germination of wild-type seeds, hypocotyl elongation and the expression of karrikin-responsive genes was also examined in response to such stresses. The kai2 seeds germinated less readily than wild-type seeds and germination was more sensitive to inhibition by abiotic stress. Karrikin-induced KAI2 signalling stimulated germination of wild-type seeds under favourable conditions, but, surprisingly, inhibited germination in the presence of osmolytes or at elevated temperature. By contrast, GA stimulated germination of wild-type seeds and mutants under all conditions. Karrikin induced expression of DLK2 and KUF1 genes and inhibited hypocotyl elongation independently of osmotic stress. Under mild osmotic stress, karrikin enhanced expression of DREB2A, WRKY33 and ERF5 genes, but not ABA signalling genes. Thus, the karrikin-KAI2 signalling system can protect against abiotic stress, first by providing stress tolerance, and second by inhibiting germination under conditions unfavourable to seedling establishment.

Fungal endophytes from seeds of invasive, non-native Phragmites australis and their potential role in germination and seedling growth

Abstract: We characterized fungal endophytes of seeds of invasive, non-native Phragmites from three sites in the Great Lakes region to determine if fungal symbiosis could contribute to invasiveness through their effects on seed germination and seedling growth. Field-collected seeds were surface sterilized and plated on agar to culture endophytes for ITS sequencing. Prevalence of specific endophytes from germinated and non-germinated seeds, and from seedlings, was compared. One-third of 740 seeds yielded endophyte isolates. Fifteen taxa were identified with Alternaria sp. representing 54% of all isolates followed by Phoma sp. (21%) and Penicillium corylophilum (12%). Overall germination of seeds producing an isolate (36%) was significantly higher than seeds not producing an isolate (20%). Penicillium in particular was strongly associated with increased germination of seeds from one site. Sixty-three isolates and 11 taxa were also obtained from 30 seedlings where Phoma, Penicillium and Alternaria respectively were most prevalent. There was a significant effect of isolating an endophyte from the seed on seedling growth. These results suggest that many endophyte taxa are transmitted in seeds and can increase seed germination and seedling growth of invasive Phragmites. The role of fungal endophytes in host establishment, growth and invasiveness in nature requires further research.

Effects of cadmium on growth and antioxidant responses in Glycyrrhiza uralensis seedlings

Abstract: In the present study, Glycyrrhiza uralensis (Leguminosae) seeds were germinated and grown with different con centrations (0, 0.05, 0.1, 0.2 and 0.4 mmol/l) of cadmium acetate, in order to investigate the effects of cadmium on the growth, uptake, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities in Glycyrrhiza uralensis seedlings. Uptake of Cd in different tis sues of seedlings increased with increasing Cd concentrations in the tested medium, with most accumulation in the radicles. Results suggested that increased cadmium concentrations lead to decreased shoot elongation and seedling biomass. SOD activity in the cotyledons, hypocotyls and radicles increased gradually up to 0.2, 0.1 and 0.4 mmol/l, respectively. POD activity in the cotyledons, hypocotyls and radicles concentrations increased continuously with rising cadmium concentrations up to 0.2, 0.1 and 0.1 mmol/l, respectively. CAT activity in the cotyledons, hypocotyls and radicles increased gradually with increasing cadmium concentrations up to 0.2, 0.2 and 0.1 mmol/l, respectively. PPO activity showed significant increases in the cotyledons, hypocotyls and radicles at 0.4, 0.1 and 0.2 mmol/l cadmium, respectively. A significant change of PAL activity in the cotyledons, hypocotyls and radicles was observed with increasing cadmium concentrations up to 0.2, 0.4 and 0.2 mmol/l, respectively. Results of POD isoenzymes suggested that the staining intensities of isoform patterns were consistent with the changes of the activities assayed in solutions. These results suggested that Glycyrrhiza uralensis seedlings may have a better protection against oxidative stress by increasing antioxidant enzymes and PAL activity exposed to cadmium toxicity.

Assessment of drought tolerance in mung bean cultivars/lines as depicted by the activities of germination enzymes, seedling’s antioxidative potential and nutrient acquisition

Abstract: Drought stress hampers firm crop stand establishment and yield in arid and semiarid regions The present study was conducted to examine the drought tolerance of various mung bean cultivars/lines based on the seed germination characteristics in relation with the seedling’s antioxidative potential and nutrient uptake Activities of germination enzymes, seed germination attributes, seedling biomass production and nutrient uptake of studied cultivars/lines were adversely affected due to PEG-induced drought but the total soluble proteins (TSP) and malondialdehyde (MDA) contents were increased The activities of catalse (CAT) and ascorbate peroxidase (APX) increased in all cultivars/lines being the maximum in cv/line NM-2006 and 8005 The activities of superoxide dismutase (SOD) and peroxidase (POD) were increased in cv/line NM-2006 and 8005 under drought condition The ascorbic acid (AsA) and total phenolic content (TPC) decreased and total flavonoid content (TFC) increased in all cultivars/lines due

New Insights into Different Reproductive Effort and Sexual Recruitment Contribution between Two Geographic Zostera marina L. Populations in Temperate China.

Abstract: Seagrasses are important components of global coastal ecosystems, and the eelgrass Zostera marina L. is widely distributed along the Atlantic and Pacific coasts in the temperate northern hemisphere, but limited datum related to the contribution of sexual reproduction to population recruitment have been reported. This study aimed to understand eelgrass sexual reproduction and population recruitment in Swan Lake (SLL), and Huiquan Bay (HQB) was included for comparison. Random sampling, permanent quadrats or cores and laboratory seed germination-based experimental methods were employed. The flowering, seed production, seed banks, seed germination, seedling survival and seedling growth of eelgrass were investigated from July 2014 to December 2015 to evaluate the contribution of sexual reproduction to population recruitment. Results indicated a dominant role of asexual reproduction in HQB, while sexual reproduction played a relatively important role in SLL. The highest flowering shoot density at center cite in SLL was 2.5 times greater than that of HQB, and SLL produced 1.8 times more seeds than HQB. The maximum sediment seed bank in SLL was 2.7 times greater than that in HQB. However, seeds in HQB were significantly larger and heavier than those in SLL (size: P = 0.004; weight: P < 0.001). Seeds in SLL were acclimated to spring germination (middle March–end May), while in HQB, they were acclimated to autumn germination (early October–late November). The recruitment from seedlings accounted for 41.36%-50.52% of the Z. marina population recruitment in SLL, while that accounted for as low as 2.53% in HQB. Our laboratory seed germination experiment showed that the seed germination percent in HQB was significantly greater than in SLL at optimal germination temperatures (10 and 15°C; P < 0.001). A laboratory seed germination test at suitable temperature may be a potential approach to identify the ecological differences among different geographic populations. It is suggested that the Z. marina population recruitment may have different strategies and acclimated to specific local conditions, such as in SLL and HQB, and the temperature regime may control morphological and phonological variations.

Exogenous Hydrogen Sulfide Ameliorates Seed Germination and Seedling Growth of Cauliflower Under Lead Stress and Its Antioxidant Role

Abstract: Lead (Pb) is a widespread ecosystem pollutant and affects food security and public health. Hydrogen sulfide (H2S) plays prominent roles in mediating a variety of responses to stresses. The effects of sodium hydrosulfide (NaHS), a fast releaser of H2S, on cauliflower (Brassica oleracea L. var botrytis L. cv. Xiahua 60 d) seed germination and seedling growth under lead acetate stress were investigated in the present study. Pb (0.25 and 0.5 mM) stresses markedly inhibited seed germination and seedling growth, whereas the inhibition was effectively mitigated by NaHS application. Germination percentage, root length, shoot length, and fresh weight of single seedling significantly increased. In addition, NaHS elevated endogenous H2S contents and reduced malonyldialdehyde, superoxide anion ( $${\text{O}}_{\text{2}}{\cdot}^ -$$ ), and hydrogen peroxide (H2O2) production, thereby preventing oxidative damage from Pb or Pb and antioxidant enzyme inhibitor (diethyldithiocarbamate or 3-amino-1,2,4-triazole) dual stresses. The protective roles of NaHS were equivalent to the ROS scavengers, 4,5-dihydroxy-1,3-benzene disulfonic acid? and N,N′-Dimethylthiourea. Moreover, NaHS elevated non-protein thiols and total glutathione levels to chelate Pb or scavenge ROS directly. Our results demonstrated the strong protective and antioxidant roles of H2S.