Seed yield as a function of cytokinin-regulated gene expression in wild Kentucky bluegrass (Poa pratensis).

BACKGROUND: Kentucky bluegrass (Poa pratensis L.) panicle development is a coordinated process of cell proliferation and differentiation with distinctive phases and architectural changes that are pivotal to determine seed yield. Cytokinin (CK) is a key factor in determining seed yield that might underpin the second "Green Revolution". However, whether there is a difference between endogenous CK content and seed yields of Kentucky bluegrass, and how CK-related genes are expressed to affect enzyme regulation and downstream seed yield in Kentucky bluegrass remains enigmatic. RESULTS: In order to establish a potential link between CK regulation and seed yield, we dissected and characterized the Kentucky bluegrass young panicle, and determined the changes in nutrients, 6 types of endogenous CKs, and 16 genes involved in biosynthesis, activation, inactivation, re-activation and degradation of CKs during young panicle differentiation of Kentucky bluegrass. We found that high seed yield material had more meristems compared to low seed yield material. Additionally, it was found that seed-setting rate (SSR) and lipase activity at the stage of spikelet and floret primordium differentiation (S3), as well as 1000-grain weight (TGW) and zeatin-riboside (ZR) content at the stages of first bract primordium differentiation (S1) and branch primordium differentiation (S2) showed a significantly positive correlation in the two materials. And zeatin, ZR, dihydrozeatin riboside, isopentenyl adenosine and isopentenyl adenosine riboside contents were higher in seed high yield material than those in seed low yield material at S3 stage. Furthermore, the expressions of PpITP3, PpITP5, PpITP8 and PpLOG1 were positively correlated with seed yield, while the expressions of PpCKX2, PpCKX5 and PpCKX7 were negatively correlated with seed yield in Kentucky bluegrass. CONCLUSIONS: Overall, our study established a relationship between CK and seed yield in Kentucky bluegrass. Perhaps we can increase SSR and TGW by increasing lipase activity and ZR content. Of course, using modern gene editing techniques to manipulate CK related genes such as PpITP3/5/8, PpLOG1 and PpCKX2/5/7, will be a more direct and effective method in Kentucky bluegrass, which requires further trial validation.

Morphology, photosynthetic and molecular mechanisms associated with powdery mildew resistance in Kentucky bluegrass.

Kentucky bluegrass (Poa pratensis L.), one of the most widely used cool-season turfgrasses around the world, is sensitive to powdery mildew (PM; Blumeria graminis). The PM strain identification and regulation mechanisms of Kentucky bluegrass in response to pathogens still remain unclear. Through morphological and molecular analyses, we identified that the pathogen in Kentucky bluegrass was B. graminis f. sp. poae. The infection of B. graminis led to a reduction of the sclerenchyma area, expansion of vesicular cells and movement of chloroplasts. The infected leaves had significantly lower values in net photosynthesis, stomatal conductance and transpiration rate, maximal quantum yield of PSII photochemistry, photochemical quenching and non-regulated energy dissipation compared to mock-inoculated leaves. Expressions of light-harvesting antenna protein genes LHCA and LHCB and photosynthetic electron transport genes petE and petH decreased significantly in infected leaves. Furthermore, upregulations of genes involved in plant-pathogen interaction, such as HSP90, RBOH, and RPM and downregulations of EDS, RPS and WRKY were observed in infected leaves. The findings may help design a feasible approach to effectively control the PM disease in Kentucky bluegrass and other related perennial grass species.

Root cell wall polysaccharides and endodermal barriers restrict long-distance Cd translocation in the roots of Kentucky bluegrass.

Soil Cd pollution is a significant environmental issue faced by contemporary society. Kentucky bluegrass is considered a potential phytoremediation species, as some varieties have excellent cadmium (Cd) tolerance. However, the mechanisms of Cd accumulation and transportation in Kentucky bluegrass are still not fully understood. The Cd-tolerant Kentucky bluegrass cultivar 'Midnight' (M) exhibits lower Cd translocation efficiency and a higher leaf Cd concentration compared to the Cd-sensitive cultivar 'Rugby II' (R). We hypothesized that Cd translocation from roots to shoots in cultivar M is hindered by the endodermal barriers and cell wall polysaccharides; hence, we conducted Cd distribution, cytological observation, cell wall component, and transcriptomic analyses under Cd stress conditions using the M and R cultivars. Cd stress resulted in the thickening of the endodermis and increased synthesis of cell wall polysaccharides in both the M and R cultivars. Endodermis development restricted the radical transport of Cd from the root cortex to the stele, while the accumulation of cell wall polysaccharides promoted the binding of Cd to the cell wall. These changes further inhibited the long-distance translocation of Cd from the roots to the aerial parts. Furthermore, the M cultivar exhibited limited long-distance Cd translocation efficiency compared to the R cultivar, which was attributed to the enhanced development of endodermal barriers and increased Cd binding by cell wall polysaccharides. This study provides valuable insights for screening high Cd transport efficiency in Kentucky bluegrass based on anatomical structure and genetic modification.

Chemical Composition and Phytotoxic Activity of Mentha vagans Boriss. Essential Oil.

This study explored the composition of essential oil (EO) and the first phytotoxic screening of EO obtained from the stems and leaves of Mentha vagans Boriss (MVEO) via hydro-distillation technique. The EO ingredients were detected through Gas Chromatography-Mass Spectrometry (GC-MS). GC-MS analysis revealed that MVEO contained 49 constituents, constituting 93.95 % of the total oil. Among MVEO constituents, dihydrocarvone was observed as the dominant constituent (24.14 %), followed by D-carvone (16.28 %) and piperitone (18.14 %). The phytotoxic effects of MVEO and its dominant compounds were examined against Amaranthus retroflexus, Lolium perenne, and Poa annua. Significant inhibition was observed by MVEO in comparison with the major constituents and their mixture, suppressing the seedling growth of tested species at the lowest dosage (0.01 mg/mL); in general, seedling growth of all tested species was markedly inhibited when applied concentration of the EO and its constituents reached 0.05 mg/mL. Our results also indicated that constituents other than the dominant compounds of MVEO possessed considerable phytotoxic effects because the EO's activity was stronger than its major constituents and their mixture. Thus, additional studies are required to investigate MVEO and its constituents and commercialize them as environment-friendly bio-herbicides.

Native and Alien Antarctic Grasses as a Habitat for Fungi.

Biological invasions are now seen as one of the main threats to the Antarctic ecosystem. An example of such an invasion is the recent colonization of the H. Arctowski Polish Antarctic Station area by the non-native grass Poa annua. This site was previously occupied only by native plants like the Antarctic hair grass Deschampsia antarctica. To adapt successfully to new conditions, plants interact with soil microorganisms, including fungi. The aim of this study was to determine how the newly introduced grass P. annua established an interaction with fungi compared to resident grass D. antarctica. We found that fungal diversity in D. antarctica roots was significantly higher compared with P. annua roots. D. antarctica managed a biodiverse microbiome because of its ability to recruit fungal biocontrol agents from the soil, thus maintaining a beneficial nature of the endophyte community. P. annua relied on a set of specific fungal taxa, which likely modulated its cold response, increasing its competitiveness in Antarctic conditions. Cultivated endophytic fungi displayed strong chitinolysis, pointing towards their role as phytopathogenic fungi, nematode, and insect antagonists. This is the first study to compare the root mycobiomes of both grass species by direct culture-independent techniques as well as culture-based methods.

From invasive species stand to species-rich grassland: Long-term changes in plant species composition during Solidago invaded site restoration.

Biological invasions degrade ecosystems, negatively affecting human well-being and biodiversity. Restoration of invaded agricultural ecosystems is among specific goals of European Union Biodiversity Strategy. Successful restoration of invaded lands is a long-term process that requires monitoring to assess the effects of interventions. Here, we present the results of a long-term experiment (8 years) on restoration of semi-natural grassland on abandoned arable field overgrown by invasive Solidago species (S. gigantea and S. canadensis). We examined effect of different invaders removal methods (rototilling, turf stripping, herbicide application) and seed application practices (commercial seed mixture, fresh hay) on changes in species composition and taxonomic diversity of restored vegetation. Our results showed a positive effect of grassland restoration on taxonomic diversity and species composition, manifested by a decrease in Solidago cover and an increase in cover and richness of target graminoids and forbs characteristic of grassland. The seed source had a longer lasting and still observable effect on the vegetation composition than the Solidago removal treatments, which ceased to differ significantly in their influence after the first few years. Applying fresh hay as a seed source increased the cover of grassland species such as Arrhenatherum elatius and Poa pratensis. For commercial seed mixture, we observed the high cover of Lolium perenne and Schedonorus pratensis (introduced with seed mixture) at the beginning and the slow decrease along the experiment course. The most striking effect was the fresh hay with herbicide application, which resulted in the lowest Solidago cover and the highest cover of target graminoids. Nonetheless, with years the non-chemical methods, including no treatment, gives comparable to herbicide effectiveness of restoration. Overall, during the experiment, alpha diversity increased, while beta and gamma diversity reached a species maximum in the third year, and then decreased. In conclusion, this study gives guidance to successful restoration of species-rich grasslands on sites invaded by Solidago. It should be emphasised that short-term effect differ considerably from long-term outputs, especially highlighting the importance of seed source, as well as effectiveness of environmentally friendly methods such as regular mowing to control the invader.

Homoeologous evolution of the allotetraploid genome of Poa annua L.

BACKGROUND: Poa annua (annual bluegrass) is an allotetraploid turfgrass, an agronomically significant weed, and one of the most widely dispersed plant species on earth. Here, we report the chromosome-scale genome assemblies of P. annua's diploid progenitors, P. infirma and P. supina, and use multi-omic analyses spanning all three species to better understand P. annua's evolutionary novelty. RESULTS: We find that the diploids diverged from their common ancestor 5.5 - 6.3 million years ago and hybridized to form P. annua ≤ 50,000 years ago. The diploid genomes are similar in chromosome structure and most notably distinguished by the divergent evolutionary histories of their transposable elements, leading to a 1.7 × difference in genome size. In allotetraploid P. annua, we find biased movement of retrotransposons from the larger (A) subgenome to the smaller (B) subgenome. We show that P. annua's B subgenome is preferentially accumulating genes and that its genes are more highly expressed. Whole-genome resequencing of several additional P. annua accessions revealed large-scale chromosomal rearrangements characterized by extensive TE-downsizing and evidence to support the Genome Balance Hypothesis. CONCLUSIONS: The divergent evolutions of the diploid progenitors played a central role in conferring onto P. annua its remarkable phenotypic plasticity. We find that plant genes (guided by selection and drift) and transposable elements (mostly guided by host immunity) each respond to polyploidy in unique ways and that P. annua uses whole-genome duplication to purge highly parasitized heterochromatic sequences. The findings and genomic resources presented here will enable the development of homoeolog-specific markers for accelerated weed science and turfgrass breeding.

Carbon and nitrogen metabolism affects kentucky bluegrass rhizome expansion.

BACKGROUND: Rhizome is vital for carbon and nitrogen metabolism of the whole plant. However, the effect of carbon and nitrogen in the rhizome on rhizome expansion remains unclear. RESULTS: Three wild Kentucky bluegrass (Poa pratensis L.) germplasms with different rhizome expansion capacity (strong expansion capacity, 'YZ'; medium expansion capacity, 'WY'; and weak expansion capacity, 'AD') were planted in the field and the rhizomes number, tiller number, rhizome dry weight, physiological indicators and enzyme activity associated carbon and nitrogen metabolisms were measured. Liquid chromatography coupled to mass spectrometry (LC-MS) was utilized to analyze the metabolomic of the rhizomes. The results showed that the rhizome and tiller numbers of the YZ were 3.26 and 2.69-fold of that of the AD, respectively. The aboveground dry weight of the YZ was the greatest among all three germplasms. Contents of soluble sugar, starch, sucrose, NO3--N, and free amino acid were significantly higher in rhizomes of the YZ than those of the WY and AD (P < 0.05). The activities of glutamine synthetase (GS), glutamate dehydrogenase (GDH) and sucrose phosphate synthase (SPS) of the YZ were the highest among all three germplasm, with values of 17.73 A·g- 1 h- 1, 5.96 µmol·g- 1 min- 1, and 11.35 mg·g- 1 h- 1, respectively. Metabolomics analyses revealed that a total of 28 differentially expressed metabolites (DEMs) were up-regulated, and 25 DEMs were down-regulated in both comparison groups (AD vs. YZ group and WY vs. YZ group). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis demonstrated that metabolites related to histidine metabolism, tyrosine metabolism, tryptophan metabolism, and phenylalanine metabolism were associated with rhizomes carbon and nitrogen metabolism. CONCLUSIONS: Overall, the results suggest that soluble sugar, starch, sucrose, NO3--N, and free amino acid in rhizome are important to and promote rhizome expansion in Kentucky bluegrass, while tryptamine, 3-methylhistidine, 3-indoleacetonitrile, indole, and histamine may be key metabolites in promoting carbon and nitrogen metabolism of rhizome.

24-epibrassinolide improves cadmium tolerance and lateral root growth associated with regulating endogenous auxin and ethylene in Kentucky bluegrass.

The application of phytohormones is a viable technique to increase the efficiency of phytoremediation in heavy metal-contaminated soils. The objective of this study was to determine how the application of 24-epibrassinolide (EBR), a brassinosteroid analog, could regulate root growth and tolerance to cadmium (Cd) stress in Kentucky bluegrass. As a result, the number of lateral root primordia and total root length in the Cd-treated seedlings decreased by 33.1 % and 56.5 %, respectively. After the application of EBR, Cd accumulation in roots and leaves, and the negative effect of Cd on root growth were reduced under Cd stress. Additionally, the expression of the brassinosteroid signaling gene PpBRI1 was significantly upregulated by exogenous EBR. Moreover, exogenous EBR upregulated the expression of genes encoding antioxidant enzymes and improved the activity of antioxidant enzymes, thereby reduced oxidative stress in roots. Finally, targeted hormonomics analysis highlighted the utility of the application of EBR to alleviate the effect of Cd on the reduction in auxin (IAA) content and the increase in ethylene (ACC) content. These were known to be associated with the upregulation in the expression of auxin biosynthesis gene PpYUCCA1 and downregulation in the expression of ethylene biosynthesis gene PpACO1 in the roots treated with Cd stress. Overall, the application of EBR alleviated Cd-induced oxidative stress in addition to improving root elongation and lateral root growth crosstalk with auxin and ethylene in Kentucky bluegrass subjected to Cd stress. This study further highlights the potential role of brassinosteroids in improving the efficiency of phytoremediation for Cd-contaminated soils.

Iron Sulfate and Phosphorous Acid Affect Turfgrass Surface pH and Microdochium Patch Severity on Annual Bluegrass.

Microdochium patch is a turfgrass disease caused by the fungal pathogen Microdochium nivale. Iron sulfate heptahydrate (FeSO4•7H2O) and phosphorous acid (H3PO3) applications have previously been shown to suppress Microdochium patch on annual bluegrass putting greens when applied alone, although either disease suppression was inadequate or turfgrass quality was reduced from the applications. A field experiment was conducted in Corvallis, Oregon, U.S.A., to evaluate the combined effects of FeSO4•7H2O and H3PO3 on Microdochium patch suppression and annual bluegrass quality. The results of this work suggest that the addition of 3.7 kg H3PO3 ha-1 with 24 or 49 kg FeSO4•7H2O ha-1 applied every 2 weeks improved the suppression of Microdochium patch without substantially compromising turf quality, which occurred when 98 kg FeSO4•7H2O ha-1 was applied with or without H3PO3. Spray suspensions reduced the pH of the water carrier, therefore two additional growth chamber experiments were conducted to better understand the effects of these treatments on leaf surface pH and Microdochium patch suppression. On the application date in the first growth chamber experiment, at least a 19% leaf surface pH reduction was observed compared with the well water control when FeSO4•7H2O was applied alone. When 3.7 kg H3PO3 ha-1 was combined with FeSO4•7H2O, regardless of the rate, the leaf surface pH was reduced by at least 34%. The second growth chamber experiment determined that sulfuric acid (H2SO4) at a 0.5% spray solution rate was always in the group that produced the lowest annual bluegrass leaf surface pH, but did not suppress Microdochium patch. Together, these results suggest that while treatments decrease leaf surface pH, this decrease in pH is not responsible for the suppression of Microdochium patch.

Genome Resources for Four Clarireedia Species Causing Dollar Spot on Diverse Turfgrasses.

Dollar spot (DS) is a destructive fungal disease impacting almost all warm- and cool-season turfgrasses worldwide. Multiple fungal species in the genus Clarireedia are causal agents of DS. Here, we present whole-genome assemblies of nine fungal isolates in the genus Clarireedia, including four species (C. paspali, C. hainanense, C. jacksonii, and C. monteithiana) causing DS on seashore paspalum (Paspalum vaginatum Sw.), creeping bentgrass (Agrostis stolonifera L.), and Kentucky bluegrass (Poa pratensis L.) in China. This work provides valuable baseline genomic data to support further research and management of DS pathogens on turfgrasses.

Pseudomonas cultivated from Andropogon gerardii rhizosphere show functional potential for promoting plant host growth and drought resilience.

BACKGROUND: Climate change will result in more frequent droughts that can impact soil-inhabiting microbiomes (rhizobiomes) in the agriculturally vital North American perennial grasslands. Rhizobiomes have contributed to enhancing drought resilience and stress resistance properties in plant hosts. In the predicted events of more future droughts, how the changing rhizobiome under environmental stress can impact the plant host resilience needs to be deciphered. There is also an urgent need to identify and recover candidate microorganisms along with their functions, involved in enhancing plant resilience, enabling the successful development of synthetic communities. RESULTS: In this study, we used the combination of cultivation and high-resolution genomic sequencing of bacterial communities recovered from the rhizosphere of a tallgrass prairie foundation grass, Andropogon gerardii. We cultivated the plant host-associated microbes under artificial drought-induced conditions and identified the microbe(s) that might play a significant role in the rhizobiome of Andropogon gerardii under drought conditions. Phylogenetic analysis of the non-redundant metagenome-assembled genomes (MAGs) identified a bacterial genome of interest - MAG-Pseudomonas. Further metabolic pathway and pangenome analyses recovered genes and pathways related to stress responses including ACC deaminase; nitrogen transformation including assimilatory nitrate reductase in MAG-Pseudomonas, which might be associated with enhanced drought tolerance and growth for Andropogon gerardii. CONCLUSIONS: Our data indicated that the metagenome-assembled MAG-Pseudomonas has the functional potential to contribute to the plant host's growth during stressful conditions. Our study also suggested the nitrogen transformation potential of MAG-Pseudomonas that could impact Andropogon gerardii growth in a positive way. The cultivation of MAG-Pseudomonas sets the foundation to construct a successful synthetic community for Andropogon gerardii. To conclude, stress resilience mediated through genes ACC deaminase, nitrogen transformation potential through assimilatory nitrate reductase in MAG-Pseudomonas could place this microorganism as an important candidate of the rhizobiome aiding the plant host resilience under environmental stress. This study, therefore, provided insights into the MAG-Pseudomonas and its potential to optimize plant productivity under ever-changing climatic patterns, especially in frequent drought conditions.

Two-Sex Demography, Sexual Niche Differentiation, and the Geographic Range Limits of Texas Bluegrass (Poa arachnifera).

AbstractUnderstanding the mechanisms that generate biogeographic range limits is a long-standing goal of ecology. It is widely hypothesized that distributional limits reflect the environmental niche, but this hypothesis is complicated by the potential for intraspecific niche heterogeneity. In dioecious species, sexual niche differentiation may cause divergence between the sexes in their limits of environmental suitability. We studied range boundary formation in Texas bluegrass (Poa arachnifera), a perennial dioecious plant, testing the alternative hypotheses that range limits reflect the niche limits of females only versus the combined contributions of females and males, including their interdependence via mating. Common garden experiments across a longitudinal aridity gradient revealed female-biased flowering approaching eastern range limits, suggesting that mate limitation may constrain the species' distribution. However, a demographic model showed that declines in λ approaching range limits were driven almost entirely by female vital rates. The dominant role of females was attributable to seed viability being robust to sex ratio variation and to low sensitivity of λ to reproductive transitions. We suggest that female-dominant range limits may be common to long-lived species with polygamous mating systems and that female responses to environmental drivers may often be sufficient for predicting range shifts in response to environmental change.

Comparative transcriptome analysis of resistant and susceptible Kentucky bluegrass varieties in response to powdery mildew infection.

BACKGROUND: Poa pratensis is one of the most common cold-season turfgrasses used for urban turf building, and it is also widely used in ecological environment management worldwide. Powdery mildew is a common disease of P. pratensis. To scientifically and ecologically control lawn powdery mildew, the molecular mechanism underlying the response of P. pratensis to powdery mildew infection must better understood. RESULTS: To explore molecular mechanism underlying the response of P. pratensis to powdery mildew infection, this study compared physiological changes and transcriptomic level differences between the highly resistant variety 'BlackJack' and the extremely susceptible variety 'EverGlade' under powdery mildew infection conditions. We analyzed DEGs using reference canonical pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and the results showed that "starch and sucrose metabolism", "photosynthesis" and "fatty acid metabolism"pathways were only enriched in 'BlackJack', and the expression of DEGs such as HXK, INV, GS, SS, AGpase and ß-amylase in "starch and sucrose metabolism" pathway of 'BlackJack' were closely related to powdery mildew resistance. Meanwhile, compared with 'EverGlade', powdery mildew infection promoted synthesis of sucrose, expression of photosynthesis parameters and photosynthesis-related enzymes in leaves of 'BlackJack' and decreased accumulation of monosaccharides such as glucose and fructose. CONCLUSIONS: This study identified the key metabolic pathways of a P. pratensis variety with high resistance to powdery mildew infection and explored the differences in physiological characteristics and key genes related to sugar metabolism pathways under powdery mildew stress. These findings provide important insights for studying underlying molecular response mechanism.

Effect of soil contamination with polycyclic aromatic hydrocarbons from drilling waste on germination and growth of lawn grasses.

In many studies, grasses were used to increase the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil because they are the most common plant species on the ground level and are quite resistant to contamination with these compounds. One of the main failures in PAH remediation in soil using plant species was the negative impact on germination and seedling growth. The objective of this study was to evaluate grass seed germination and seedling growth affected by drill cuttings to determine the resistance of selected grass species to the impact of PAH and their suitability for an effective phytoremediation of soils contaminated with waste that contain compounds from this group. In the study four grass species: tall fescue (Festuca arundinacea), red fescue (Festuca rubra), perennial ryegrass (Lolium perenne) and common meadow-grass (Poa pratensis). The germination energy of all species decreased as the amount of drill cuttings increased. Among the species studied, the highest germination energy and capacity were found in Lolium perenne (54.1 and 73.2 respectively), and the lowest - in Poa pratensis (16.7 and 23.3 respectively). With an increasing amount of drill cuttings, the root and seedling height were decreased. Festuca arundinacea seedlings were distinctly the highest and had the longest roots (96.7 and 52.7, respectively), while Poa pratensis seedlings showed the significantly slowest seedling and root elongation rate (30.4 and 12.4, respectively). However, the strongest decrease in seedling height and root length compared to the control was observed in Festuca rubra. Based on IC50, the greatest tolerance to the addition of drilling waste to the substrate was found for Festuca arundinacea and Festuca rubra. The conducted investigation indicates that Festuca arundinacea and Lolium perenne are grass species that are least sensitive to drilling waste in the substrate because no significant differences were found in root length and seedling height between the control soil and the soil where a PAH dose of 5% and 10% was applied.

First Asp-2078-Gly Mutation Conferring Resistance to Different ACCase Inhibitors in a Polypogon fugax Population from China.

Asia minor bluegrass (Polypogon fugax) is a common and problematic weed throughout China. P. fugax that is often controlled by acetyl-CoA carboxylase (ACCase) inhibitors in canola fields. Herein, we confirmed a P. fugax population (R) showing resistance to all ACCase inhibitors tested with resistance indexes ranging from 5.4-18.4. We further investigated the resistance mechanisms of this R population. Molecular analyses revealed that an amino acid mutation (Asp-2078-Gly) was present in the R population by comparing ACCase gene sequences of the sensitive population (S). In addition, differences in susceptibility between the R and S population were unlikely to be related to herbicide metabolism. Furthermore, a new derived cleaved amplified polymorphic sequence (dCAPS) method was developed for detecting the Asp-2078-Gly mutation in P. fugax efficiently. We found that 93.75% of plants in the R population carried the Asp-2078-Gly mutation, and all the herbicide-resistant phenotype of this R population is inseparable from this mutation. This is the first report of cross resistance to ACCase inhibitors conferred by the Asp-2078-Gly target-site mutation in P. fugax. The research suggested the urgent need to improve the diversity of weed management practices to prevent the widespread evolution of herbicide resistance in P. fugax in China.

Salinity Tolerance of Halophytic Grass Puccinellia nuttalliana Is Associated with Enhancement of Aquaporin-Mediated Water Transport by Sodium.

In salt-sensitive plants, root hydraulic conductivity is severely inhibited by NaCl, rapidly leading to the loss of water balance. However, halophytic plants appear to effectively control plant water flow under salinity conditions. In this study, we tested the hypothesis that Na+ is the principal salt factor responsible for the enhancement of aquaporin-mediated water transport in the roots of halophytic grasses, and this enhancement plays a significant role in the maintenance of water balance, gas exchange, and the growth of halophytic plants exposed to salinity. We examined the effects of treatments with 150 mM of NaCl, KCl, and Na2SO4 to separate the factors that affect water relations and, consequently, physiological and growth responses in three related grass species varying in salt tolerance. The grasses included relatively salt-sensitive Poa pratensis, moderately salt-tolerant Poa juncifolia, and the salt-loving halophytic grass Puccinellia nuttalliana. Our study demonstrated that sustained growth, chlorophyll concentrations, gas exchange, and water transport in Puccinellia nuttalliana were associated with the presence of Na in the applied salt treatments. Contrary to the other examined grasses, the root cell hydraulic conductivity in Puccinellia nuttalliana was enhanced by the 150 mM NaCl and 150 mM Na2SO4 treatments. This enhancement was abolished by the 50 µM HgCl2 treatment, demonstrating that Na was the factor responsible for the increase in mercury-sensitive, aquaporin-mediated water transport. The observed increases in root Ca and K concentrations likely played a role in the transcriptional and (or) posttranslational regulation of aquaporins that enhanced root water transport capacity in Puccinellia nuttalliana. The study demonstrates that Na plays a key role in the aquaporin-mediated root water transport of the halophytic grass Puccinellia nuttalliana, contributing to its salinity tolerance.

Choline-Mediated Lipid Reprogramming as a Dominant Salt Tolerance Mechanism in Grass Species Lacking Glycine Betaine.

Choline, as a precursor of glycine betaine (GB) and phospholipids, is known to play roles in plant tolerance to salt stress, but the downstream metabolic pathways regulated by choline conferring salt tolerance are still unclear for non-GB-accumulating species. The objectives were to examine how choline affects salt tolerance in a non-GB-accumulating grass species and to determine major metabolic pathways of choline regulating salt tolerance involving GB or lipid metabolism. Kentucky bluegrass (Poa pratensis) plants were subjected to salt stress (100 mM NaCl) with or without foliar application of choline chloride (1 mM) in a growth chamber. Choline or GB alone and the combined application increased leaf photochemical efficiency, relative water content and osmotic adjustment and reduced leaf electrolyte leakage. Choline application had no effects on the endogenous GB content and GB synthesis genes did not show responses to choline under nonstress and salt stress conditions. GB was not detected in Kentucky bluegrass leaves. Lipidomic analysis revealed an increase in the content of monogalactosyl diacylglycerol, phosphatidylcholine and phosphatidylethanolamine and a decrease in the phosphatidic acid content by choline application in plants exposed to salt stress. Choline-mediated lipid reprogramming could function as a dominant salt tolerance mechanism in non-GB-accumulating grass species.

Chemical Composition and Phytotoxic Activity of Artemisia selengensis Turcz. Volatiles.

The chemical profile and allelopathic action of the volatiles produced by Artemisia selengensis were studied. Artemisia selengensis was found to release volatile chemicals to the environment to influence other plants' growth, which suppressed the root length of Amaranthus retroflexus and Poa annua by 50.46 % and 87.83 % under 80 g/1.5 L treatment, respectively. GC/MS analysis led to the identification of 41 compounds (by hydrodistillation, HD) and 48 compounds (by headspace solid-phase microextraction, HS-SPME), with eucalyptol (15.45 % by HD and 28.09 % by HS-SPME) being detected as the most abundant constituent. The essential oil (EO) of A. selengensis completely inhibited the seed germination of A. retroflexus and P. annua at 1 mg/mL and 0.5 mg/mL, respectively. However, eucalyptol displayed much weaker activity compared with the EO, indicating that other less abundant constituents might contribute significantly to the EO's activity. Our study is the first report on the phytotoxicity of A. selengensis EO, suggesting that A. selengensis might release allelopathic volatile agents into the environment that negatively affect other plants' development so as to facilitate its own dominance; the potential value of utilizing A. selengensis EO as an environmentally friendly herbicide is also discussed.

Effects of Arbuscular Mycorrhiza on Primary Metabolites in Phloem Exudates of Plantago major and Poa annua and on a Generalist Aphid.

Arbuscular mycorrhiza (AM), i.e., the interaction of plants with arbuscular mycorrhizal fungi (AMF), often influences plant growth, physiology, and metabolism. Effects of AM on the metabolic composition of plant phloem sap may affect aphids. We investigated the impacts of AM on primary metabolites in phloem exudates of the plant species Plantago major and Poa annua and on the aphid Myzus persicae. Plants were grown without or with a generalist AMF species, leaf phloem exudates were collected, and primary metabolites were measured. Additionally, the performance of M. persicae on control and mycorrhizal plants of both species was assessed. While the plant species differed largely in the relative proportions of primary metabolites in their phloem exudates, metabolic effects of AM were less pronounced. Slightly higher proportions of sucrose and shifts in proportions of some amino acids in mycorrhizal plants indicated changes in phloem upload and resource allocation patterns within the plants. Aphids showed a higher performance on P. annua than on P. major. AM negatively affected the survival of aphids on P. major, whereas positive effects of AM were found on P. annua in a subsequent generation. Next to other factors, the metabolic composition of the phloem exudates may partly explain these findings.