Populus Alba Research Articles

Sand-fixing measures improve soil particle distribution and promote soil nutrient accumulation for desert – Yellow River coastal ecotone, China

In the fragile desert ecosystems of the world, sand-fixing measures play an irreplaceable part in ecological restoration. However, it is unclear how the long-term establishment of sand-fixing measures affects soil particle distribution and soil nutrients for the desert – Yellow River coastal ecotone. Therefore, we selected sand-fixing measures that have been established for fifteen years: Pinus sylvestris (PS), Populus alba (PA), Elaeagnus angustifolia (EA), Hedysarum scoparium (HS), Salix psammophila (SC), Salix psammophila checkerboard barriers (SCSB), and mobile sandy land (LS). We analyzed soil physical properties, chemical properties, soil fractal dimension (D), and multi-fractal parameters in the top soil layer (0–20 cm). The results showed that the establishment of sand-fixing measures significantly increased the clay and silt, and decreased the sand (p < 0.05). Sand-fixing measures promote the heterogeneity of soil particle distribution and increase its dispersion. The soil nutrition content was significantly increased under different sand-fixing measures (p < 0.05), and soil organic carbon (SOC) and alkaline nitrogen (AN) changed significantly. The D value is between 2.18 and 2.39. The D value and multifractal parameters were driven by soil physicochemical properties and aboveground biomass (AGB). The regression model demonstrates a significant correlation between the D values and multi-fractal parameters (R2 = 0.58–0.77, p < 0.001). Therefore, we suggest that multifractal parameters can replace the D values as indicators of soil environmental changes in desertification. This study complements the information on the restoration of soils in the desert-Yellow River coastal ecotone by sand-fixing measures. In addition, we suggest that desert ecological management should be tailored to regional environmental differences to establish an integrated model of restoration of sand-fixing measures in the future. The results of this study scientifically provide a theoretical basis for the future reconstruction of ecologically fragile areas.

A Comparison of Water Uptake by Transpiration from Different Soil Depths among Three Land Cover Types in the Arid Northwest of China

In recent decades, the frequency, intensity, and extent of extreme drought events have posed serious threats to ecosystems in vulnerable regions. With low annual precipitation, the arid area in northwest China is a typical ecologically fragile area, and extreme drought events will aggravate desertification in this area. In order to control desertification, various experimental plantations have been established in Northwest China. However, there is no consensus on which plantations are more suitable to become widespread. To explore this, we conducted a comparative study on different plantations from the perspective of long-term deep (100 cm depth) soil moisture balance. In our study, six typical ecosystems were selected for comparison of the variation of soil moisture and control factors. The results showed three main findings. First, the soil moisture of all six ecosystems showed a similar hierarchy of increasing moisture with the increasing depth of the soil layer. However, the deep layer soil moisture (mean = 0.33 ± 0.22 cm3·cm−3) of the artificial poplar (Populus alba) forest exhibited a downward trend over time after the fifth year, but did not at the shallow layer for this ecosystem. Second, the trends of the maximum canopy coverage between the different ecosystems from 2010 to 2019 showed significant differences from one another, with the maximum value of the leaf area index for the poplar forest being the highest (Maximum = 7.13). Third, a negative correlation (R2 = 0.52) was found between deep soil moisture and transpiration for the poplar forest, and a positive correlation (R2 ≥ 0.23) between these two metrics was found for the other five ecosystems. The results revealed that transpiration processes had a different consumption of deep soil moisture due to the differences in the root and canopy density of several plantations. Among these ecosystems, the transpiration of the artificial poplar forest is noticeably large, resulting in a unilateral decline in soil moisture.

Allele-Specific Transcriptional Regulation of Shoot Regeneration in Hybrid Poplar

Plant tissue regeneration is a key process for genetic transformation and genome editing. The exploration of regulatory mechanisms in plant regeneration would improve regeneration efficiency. In comparison to some model plants, the genomic heterozygosity is much higher in forest trees, increasing the complexity of transcriptional regulation. Here, we report the allele-specific transcriptional analysis in hybrid poplar 84K (Populus alba × P. tremula var. glandulosa cv. 84K) during the shoot regeneration process. Firstly, 180 regeneration-related genes (REGs) and 2446 REG-homologous genes (REGHs) were identified in hybrid poplar. The expression patterns of REGs exhibited that about half of them were positively correlated between poplar and Arabidopsis at the locus level. The expression levels of REGHs vary among the gene family at different stages during callus and shoot induction. Among the gene clusters with similar expression patterns, the distribution of gene families in poplar and Arabidopsis also exhibits large variations. At the allele level, most of the allele pairs of REGs were positively correlated in expression. The expression patterns of genes in auxin synthesis, transport, and signaling pathways agree with the general patterns. Due to the presence/absence of variations between two subgenomes, two YUC alleles and two IAA alleles are present only in one subgenome, and the expression patterns of the two alleles are greatly different. Our analysis indicates the conservativeness and diversity of transcriptional regulation during shoot regeneration in poplar and Arabidopsis. The complexity in allele expression contributed by heterozygosity suggests the importance of genotyping in the screening of explants for plant regeneration.

The glutamate receptor gene GLR3.3: A bridge of calcium-mediated root development in poplar

Poplar is one of the fastest-growing temperate trees in the world and is widely used in ornamental horticulture for shade. The root is essential for tree growth and development and its utilization potential is huge. Calcium (Ca), as a signaling molecule, is involved in the regulation of plant root development. However, the detailed underlying regulatory mechanism is elusive. In this study, we analyzed the morphological and transcriptomic variations of 84K poplar (Populus alba × P. glandulosa) in response to different calcium concentrations and found that low Ca2+ (1 mmol · L−1) promoted lateral root development, while deficiency (0.1 mmol · L−1 Ca2+) inhibited lateral root development. Co-expression analysis showed that Ca2+ channel glutamate receptors (GLRs) were present in various modules with significance for root development. Two GLR paralogous genes, PagGLR3.3a and PagGLR3.3b, were mainly expressed in roots and up-regulated under Ca2+ deficiency. The CRISPR/Cas9-mediated signal gene (crispr-PagGLR3.3a, PagGLR3.3b) and double gene (crispr-PagGLR3.3ab) mutants presented more and longer lateral roots. Anatomical analysis showed that crispr-PagGLR3.3ab plants had more xylem cells and promoted the development of secondary vascular tissues. Further transcriptomic analysis suggested that knockout of PagGLR3.3a and PagGLR3.3b led to the up-regulation of several genes related to protein phosphorylation, auxin efflux, lignin and hemicellulose biosynthesis as well as transcriptional regulation, which might contribute to lateral root growth. This study not only provides novel insight into how the Ca2+ channels mediated root growth and development in trees, but also provides a directive breeding of new poplar species for biofuel and bioenergy production.

Potential of a new phytoseiid species Neoseiulus setarius (Acari: Phytoseiidae) as a biocontrol agent: Biological and demographic parameters on prey and non-prey foods

Neoseiulus setarius Ma, Meng & Fan is a newly described phytoseiid species found in Inner Mongolia of China. To evaluate the potential of N. setarius as a biocontrol agent, we studied life table parameters of N. setarius reared on four food resources, including western flower thrips Frankliniella occidentalis Pergande, eriophyoid mite Aceria pallida Keifer, cattail pollen Typha latifolia L. and poplar pollen Populus alba L. Neoseiulus setarius fed on two prey species developed faster and produced more eggs than those fed with two kinds of pollen. Neoseiulus setarius had the shortest juvenile development time on A. pallida (5.38 days), and the highest daily fecundity on F. occidentalis (2.43 eggs/female/day). The juvenile development time of N. setarius was similar on cattail pollen and poplar pollen, but the fecundity of N. setarius was significantly higher on cattail pollen. There were significant differences in the demographic parameters of N. setarius reared on the four different diets. The highest intrinsic rate of increase (rm) was on F. occidentalis (0.178 day−1), followed by A. pallida (0.159 day−1), cattail pollen (0.127 day−1) and poplar pollen (0.092 day−1). Neoseiulus setarius showed higher fitness in development and reproduction on prey (F. occidentalis and A. pallida) and cattail pollen. These results suggest that N. setarius could be a promising biocontrol agent for the management of thrips and gall mites.

Drought and Salinity Tolerance of the PtWRKY33 Gene in Populus

In this study, the PtWRKY33 gene sequence was cloned by PCR from cDNA, and systematic evolutionary analysis was performed. qRT–PCR was performed to measure the expression of the PtWRKY33 gene in the roots, stems and leaves of Populus tremuloides under drought and saline stresses, and overexpression vectors were constructed and genetically transformed into tobacco. The results showed that the WRKY transcription factors of Populus trichocarpa, Populus euphratica and Populus alba were in the same branch and were closely related to each other. Treating poplar seedlings with 20% PEG6000 solution to simulate drought stress showed that expression of the PtWRKY33 gene was induced and increased 1.89 times, 3.45 times and 11.6 times in leaves, stems and roots. The relative expression of the PtWRKY33 gene was slower to respond to 150 mM NaCl treatment but was nonetheless induced. At 48 h, the increase was 1–3 times in leaves, stems and roots, respectively. NaHCO3 (60 mM) was used to treat poplar seedlings with alkaline salt stress; the results indicated that the PtWRKY33 gene was sensitive to NaHCO3 stress treatment, and that its relative expression was significantly increased and increased 10.51 times (24 h), 6.56 times (6 h) and 5.16 times (24 h) in leaves, stems and roots, respectively. In this study, we found that NaCl and NaHCO3 stress treatments were able to induce an increase in the expression of the NtSOD1 and NtAPX2 genes using qRT–PCR, and the significant increase in expression under the treatments compared with WT may be caused by overexpression of the PtWRKY33 gene. Overexpression of the PtWRKY33 gene in tobacco enhanced the antioxidant stress capacity and improved the salinity tolerance of transgenic tobacco. These results indicate that the PtWRKY33 gene is a key gene for improved salinity-tolerant growth, which is important for future molecular breeding of tree resistance.

Suitability Assessment of Six Tree Species through Combined Analysis of PM2.5 Capture Ability and Air Pollution Tolerance Index for Urban Green Belt

Increasing concentrations of atmospheric particulate matter (PM) can cause a serious threat to urban air quality and human health. To reduce PM pollution in urban environments, pragmatic screening and planting of tolerant tree species can be effective and sustainable ways. However, our understanding of the effects of the capture ability of PM2.5 on plant tolerance, and efforts to devise explicit assessment tools for suitability analysis for urban green belt plantations, are still inadequate. In this study, six common green tree species (Pinus tabuliformis, Abies holophylla, Juniperus chinensis, Salix babylonica, Robinia pseudoacacia, and Populus alba) from three pollution sites in Shenyang City, China, were collected in order to assess their PM2.5 capture ability, biochemical characteristics, leaf microstructures, and air pollution tolerance index (APTI). The results revealed that different sites and tested plant species can significantly affect the amount of PM2.5 retained by leaf surfaces. The PM2.5 retention amount of Abies holophylla was the highest at the SFH site and 1.41–8.89 times that of other tested species (p &lt; 0.05). Morphological plant attributes, such as leaf surface roughness (r = 0.52 **) and contact angle (r = −0.57 **), were strongly related to the PM2.5 retention amount. The PM2.5 retention amount per unit leaf area had the strongest and most significant negative influence on total chlorophyll content (r = −0.743 **), indicating that the accumulation of leaf PM2.5 reduced the photosynthetic efficiency of the plants. Among the tested plants, Robinia pseudoacacia had the highest APTI value and was identified as the most resilient plant at all three sites, whereas Juniperus chinensis had the lowest APTI at all study sites. However, the integration of PM2.5 capture ability with APTI showed Pinus tabuliformis to be the best species for the construction of urban green belts in Shenyang City.

Stem and leaf photosynthesis of seven desert woody species and its influencing factors

Stem photosynthesis widely presents in desert plants, which increases carbon uptake capacity. In this study, we measured the photosynthetic characteristics of leaves and stems in seven desert woody plants (Populus euphratica, Populus alba var. pyramidalis, Populus pruinose, Haloxylon ammodendron, Calligonum rubicundum, Calligonum caput-medusae, Ammopiptanthus mongolicus) in the same habitat, using a portable Li-6400XT photosynthesis system combined with P-Chamber. We analyzed stem photosynthetic rate and its relationship with leaf photosynthetic rate. We measured the stem functional traits, including water content, stem dry matter content, chlorophyll content, water potential, non-structure carbohydrate (NSC), etc., to find out the main affecting factors of stem photosynthesis. The results showed that stem photosynthetic rate of seven species ranged from 0.72 to 1.71 μmol·m-2·s-1, with the largest of P. pruinose and the smallest of H. ammodendron. Stem photosynthetic rate could offset CO2 of stem respiration by 57%-83%. Leaf photosynthetic rate of the seven sepceis ranged from 12.80 to 22.54 μmol·m-2·s-1, with H. ammodendron and A. mongolicus being lower than those of the other five species. There was a significant positive correlation between leaf photosynthetic rate and stem photosynthetic rate. Stem water use efficiency was 2.2-7.7 times of the leaf. Chlorophyll content, NSC, stem respiration rate, and leaf photosynthetic rate were the main factors affecting stem photosynthesis.

Different Responses of Soil Moisture to Different Artificial Forest Species on the Loess Plateau

The Chinese Loess Plateau has undertaken a large-scale “Grain for Green” project since 1999. Understanding how reforestation affects soil moisture is crucial for ecological construction and the region’s revegetation. In this study, soil sensors were installed to monitor the soil moisture content (SMC) and soil desiccation intensity in a 0–200 cm soil profile online during the growing season, with farmland as a control and Robinia (R.) pseudoacacia L., Pinus (P.) tabulaeformis Carr., Populus (P.) alba L., and Ulmus (U.) pumila L. were selected. The results showed that the SMC increased with soil depth, and the soil moisture storage (SMS) in the 0–200 cm soil profile was ranked as R. pseudoacacia L. (424.3 mm) &lt; farmland (479.8 mm) &lt; U. pumila L. (569.8 mm) &lt; P. alba L. (583.9 mm) &lt; P. tabulaeformis Carr. (589.8 mm). Secondly, the percentages of inefficient water and gravimetric water in soil moisture were ranked as R. pseudoacacia L. (63%) &gt; farmland (49%) &gt; U. pumila L. (43%) &gt; P. alba L. (17%) &gt; P. tabulaeformis Carr. (11%). The soil desiccation intensity of artificial forests was heavy in June, light in April and July, and no desiccation in the other months. Moderate desiccation was discovered in the 0–40 cm soil layer and mild desiccation occurred in the 40–60 cm soil layer. Additionally, the representative soil layer for SMS in farmland for P. tabulaeformis Carr., U. pumila L., and R. pseudoacacia L. was the 90 cm soil layer, and the SMS representative soil layer for P. alba L. was the 70 cm soil layer. In brief, an SMS deficit occurred after the conversion of the farmland to R. pseudoacacia L., but there was an SMS surplus after the conversion of the farmland to P. alba L., U. pumila L., and P. tabulaeformis Carr. This suggests that the artificial forest species could be optimized by introducing P. tabulaeformis Carr. instead of R. pseudoacacia L., and the degradation of R. pseudoacacia L. could be suppressed by the application of a nitrogen fertilizer. Our research demonstrated that soil moisture depletion patterns were closely related to artificial forest species, and attention should be paid to the vegetation restoration and maintenance of afforestation achievements in water-constrained arid regions in the future.

Transcriptomic Analysis Revealed That Low-Density Aphid Infestation Temporarily Changes Photosynthesis and Disease Resistance but Persistently Promotes Insect Resistance in Poplar Leaves

Insect infestations cause substantial changes in the leaves they attack, but the effects of insect infestation on photosynthesis and gene expression in the whole infestation period are rarely reported. In this study, the effects of poplar aphid (Chaitophorus populialbae Boyer de Fonscoloube) on photosynthetic rate and gene expression of Populus alba var. pyramidalis were studied, from 2 to 36 days after low-density aphid inoculation (DAI). The results revealed a dynamic change of photosynthesis in poplar after aphid infestation: compensatory increased at 8 DAI, was inhibited at 17 DAI, but repaired after 21 DAI. Aphid infestation promoted the expression of the majority of differentially expressed genes (DEGs) at 4, 6, 8, and 21 DAI. The DEGs were enriched into a plant–pathogen interaction, plant hormone signal transduction, and MAPK signaling pathway, suggesting a significant but transient resistance to disease or other stresses. Photosynthesis-related DEGs were downregulated at 8 DAI, which might result in photosynthetic inhibition at 17 DAI. The expression of flavonoid biosynthesis-related DEGs dynamic changed from all downregulated at 2 DAI to almost all upregulated at 21 DAI, suggesting a persistent resistance to insect infestation. This study reveals dynamic changes in photosynthesis, resistance to pathogens, and insects in poplar leaves after aphid infestation.

Transcriptomic and Physiological Analysis Reveals Genes Associated with Drought Stress Responses in Populus alba × Populus glandulosa.

Drought stress affects plant productivity by altering plant responses at the morphological, physiological, and molecular levels. In this study, we identified physiological and genetic responses in Populus alba × Populus glandulosa hybrid clones 72-30 and 72-31 after 12 days of exposure to drought treatment. After 12 days of drought treatment, glucose, fructose, and sucrose levels were significantly increased in clone 72-30 under drought stress. The Fv/Fo and Fv/Fm values in both clones also decreased under drought stress. The changes in proline, malondialdehyde, and H2O2 levels were significant and more pronounced in clone 72-30 than in clone 72-31. The activities of antioxidant-related enzymes, such as catalase and ascorbate peroxidase, were significantly higher in the 72-31 clone. To identify drought-related genes, we conducted a transcriptomic analysis in P. alba × P. glandulosa leaves exposed to drought stress. We found 883 up-regulated and 305 down-regulated genes in the 72-30 clone and 279 and 303 in the 72-31 clone, respectively. These differentially expressed genes were mainly in synthetic pathways related to proline, abscisic acid, and antioxidants. Overall, clone 72-31 showed better drought tolerance than clone 72-30 under drought stress, and genetic changes also showed different patterns.

First Report and Genetic Analysis of the Invasive Species A. fruticosa L. in Greece: A Combined Genetic and Regeneration Study

A first assessment of genetic diversity and expansion of the invasive species Amorpha fruticosa L. was estimated in the 91E0* (Annex I Dir. 92/43/EEC) priority habitat of Nestos. A. fruticosa is a perennial deciduous shrub belonging to the family Fabaceae and is native to the south-western part of North America, which recently was introduced to Europe as an ornamental plant. Its expansion through the cross-border river of Nestos has significant negative effects on the 91E0* habitat (a habitat with Alnus glutinosa, Populus alba, and Ulmus minor). Herein, we studied the genetic diversity with amplified fragment length polymorphisms fragments of eastern and western populations in order to see if there is one genetic pool for the species. Furthermore, we estimated the regeneration index (IR) in order to see the potential expansion of this invasive species. Results showed that eastern and western populations have almost equal heterozygosity (He) and with a slightly higher value for the western population, which was in agreement with the results of the IR. This is an innovative study that discusses the implications of A. fruticosa of 91E0* habitat in Nestos and proposes management measures to eliminate its expansion and improve the resilience of the habitat.

PabCIPK24 plays an important role in the response of hybrid poplar to salt stress

The CBL-Interacting Protein Kinases (CIPK) is an important protein in stress responses. However, the research of CIPK function is limited in poplar. The research objective is to improve the salt tolerance of poplar using CIPK. In the present study, a CIPK24 gene from Populus alba × P. Berolinensis (PabCIPK24) was cloned, which possesses a kinase domain and a regulatory domain and shows the closest homology to CIPK24 of Populus alba (PaCIPK24). Seven PabCIPK24 overexpression transgenic lines were obtained through Agrobacterium-mediated transformation. Under salt stress treatment, transgenic lines accumulated less sodium ions and more potassium ion accumulation than wild type (WT) and had lower degree of cell damage. The transgenic line shows significant differences compared to the WT in terms of root length (The transgenic line is 0.83 cm taller than the WT.), dry weight (The transgenic lines weighs 0.07 g more than the WT), and seedling height (The transgenic line is 1.52 cm taller than the WT) during the tissue culture seedling stage. Additionally, transgenic lines have strong reactive oxygen species (ROS) scavenging ability and increases the gene expression of salt tolerant related genes. The study indicates that PabCIPK24 positively regulates salt stress, and obtained salt tolerant transgenic poplar.

Molecular cloning and functional analysis of flavanone 3-hydroxylase (f3h）gene in Passiflora edulis Sims

Flavanone 3-hydroxylase (F3H) plays a crucial role in the biosynthesis of flavonoids. In the present study, one F3H gene (P_edulia040010337.g) from Passiflora edulis Sims, which has a coding sequence (CDS) of 1161 bp, encoding a protein consisting of 386 amino acid residues was cloned. The PeF3H protein contains a non-heme dioxygenase (DIOX-N superfamily) domain and a typical F3H protein functional domain (2OG-FeII-Oxy dioxygenase). Phylogenetic analysis revealed that the PeF3H protein shared high similarity with F3H proteins in Turnera subulata, Populus alba, and Populus tomentosa, with 88% identities of amino acid sequences. The PeF3H protein lacks a transmembrane structure, indicating it is likely to be expressed in the mitochondria. Additionally, 3D structure, protein and protein interaction, and KEGG pathway of PeF3H were anticipated based on homologous proteins. qRT-PCR analysis showed that PeF3H was highly expressed in leaves, followed by stems and roots. These studies have provided insights into the molecular mechanisms underlying flavonoid biosynthesis and predicted potential targets for genetic engineering to improve the nutritional and medicinal properties of passion fruit. Bangladesh J. Bot. 52(2): 613-623, 2023 (June) Special

Molecular cloning and functional analysis of flavanone 3-hydroxylase (f3h）gene in Passiflora edulis Sims

Flavanone 3-hydroxylase (F3H) plays a crucial role in the biosynthesis of flavonoids. In the present study, one F3H gene (P_edulia040010337.g) from Passiflora edulis Sims, which has a coding sequence (CDS) of 1161 bp, encoding a protein consisting of 386 amino acid residues was cloned. The PeF3H protein contains a non-heme dioxygenase (DIOX-N superfamily) domain and a typical F3H protein functional domain (2OG-FeII-Oxy dioxygenase). Phylogenetic analysis revealed that the PeF3H protein shared high similarity with F3H proteins in Turnera subulata, Populus alba, and Populus tomentosa, with 88% identities of amino acid sequences. The PeF3H protein lacks a transmembrane structure, indicating it is likely to be expressed in the mitochondria. Additionally, 3D structure, protein and protein interaction, and KEGG pathway of PeF3H were anticipated based on homologous proteins. qRT-PCR analysis showed that PeF3H was highly expressed in leaves, followed by stems and roots. These studies have provided insights into the molecular mechanisms underlying flavonoid biosynthesis and predicted potential targets for genetic engineering to improve the nutritional and medicinal properties of passion fruit. Bangladesh J. Bot. 52(2): 613-623, 2023 (June) Special

Study on the Interactions of Cyclins with CDKs Involved in Auxin Signal during Leaf Development by WGCNA in Populus alba.

Cell division plays an indispensable role in leaf morphogenesis, which is regulated via the complexes formed by cyclin and cyclin-dependent kinase (CDK). In this study, gene family analysis, exogenous auxin stimulation, RNA-seq and WGCNA analysis were all used to investigate the molecular mechanisms by which cell-cycle-related factors participated in the auxin signaling pathway on leaf morphogenesis. Sixty-three cyclin members and seventeen CDK members in Populus alba were identified and systematically analyzed. During the evolution, WGD was the main reason that resulted in the expansion of cyclin and CDK genes. Firstly, after a short time treating with auxin to matured leaves of seedlings, genes related to cell division including GRF and ARGOS were both upregulated to restart the transition of cells from G1-to-S phase. Secondly, with three days of continuous auxin stimulation to leaves at different developmental stages, leaves area variation, transcriptomes and hormones were analyzed. By PCA, PCoA and WGCNA analyses, the turquoise module was both positively related to leaf development and auxin. Based on the co-expression analysis and Y2H experiment, PoalbCYCD1;4, PoalbCYCD3;3 and PoalbCYCD3;5 were supposed to interact with PoalbCDKA;1, which could be the trigger to promote the G1-to-S phase transition. The ARF transcription factor might play the key role of connecting the auxin signaling pathway and cell division in leaf morphogenesis by affecting CYC-CDK complexes.

Study of antioxidant enzymes’ activity in reaction wood of poplar tree (Populus alba L.)

Summary Studying biochemical variation in reaction wood is needed to understand the nature of reaction wood formation and the physiology of trees. The activity of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX)) was studied in normal wood (NW) and reaction wood (RW) (opposite wood (OW) and tension wood (TW)) in the bole of poplar trees (Populus alba L.). Four-year-old trees were induced to produce reaction wood by forced bending. The activity of antioxidant enzymes was studied with repeated sampling during a growing season. The results showed that total protein content and antioxidant enzymes are sensitive to mechanically induced stress. TW and OW showed higher activity of enzymes than NW as well as higher amounts of total protein. OW showed a higher concentration of CAT and SOD than TW. APX was more active than GPX in both TW and OW. In addition to mechanical stress, the effect of other climate factors was observed in the reactive oxygen species accumulation.

Kraft lignins from different poplar genotypes obtained by selective acid precipitation and their use for the production of electrospun nanostructures

Kraft lignins from different poplar genotypes (Populus alba L. “PO-10-10-20” and Populus x canadensis “Ballotino”) were isolated by selective acid precipitation (pH 5 and 2.5), chemically and structurally characterized and used together with cellulose acetate (CA) for the manufacture of nanostructures by electrospinning. Generally, lignins showed a predominance of β-β´ resinols substructures (4.7–5.3 linkages per 100 aromatic units) followed by β-O-4´ (1.6–3.3 linkages per 100 aromatic units) and β-5´ phenylcoumarans (0.5–2.4 linkages per 100 aromatic units) and a high abundance of S lignin units (S/G 3.0–4.3). Moreover, lignins showed low molecular weight values (between 5.14 and 5.59 KDa) and high phenolic content (529.1 –644.5 mg GAE/g lignin). Regarding the electrospun nanostructures obtained from Kraft lignins/CA solutions, all of them presented uniform cross-linked nanofibers with a few beaded fibers according to the suitable range values of surface tension (29.18–29.71 mN/cm), electrical conductivity (131.2–158.9 μS/cm) and dynamic viscosity (0.28–0.32 Pa.s) that biopolymer solutions showed. Nevertheless, electrospun Kraft lignins/CA nanostructures with larger mean diameters were generated from lignins at pH 5, which displayed higher phenolic and β-O-4´ contents compared to lignins at pH 2.5. On the other hand, the type of poplar lignin genotype did not exert a significant influence on the mean fiber diameter.

Carbohydrate dynamics in Populus trees under drought: An expression atlas of genes related to sensing, translocation, and metabolism across organs.

In trees, nonstructural carbohydrates (NSCs) serve as long-term carbon storage and long-distance carbon transport from source to sink. NSC management in response to drought stress is key to our understanding of drought acclimation. However, the molecular mechanisms underlying these processes remain unclear. By combining a transcriptomic approach with NSC quantification in the leaves, stems, and roots of Populus alba under drought stress, we analyzed genes from 29 gene families related to NSC signaling, translocation, and metabolism. We found starch depletion across organs and accumulation of soluble sugars (SS) in the leaves. Activation of the trehalose-6-phosphate/SNF1-related protein kinase (SnRK1) signaling pathway across organs via the suppression of class I TREHALOSE-PHOSPHATE SYNTHASE (TPS) and the expression of class II TPS genes suggested an active response to drought. The expression of SnRK1α and β subunits, and SUCROSE SYNTHASE6 supported SS accumulation in leaves. The upregulation of active transporters and the downregulation of most passive transporters implied a shift toward active sugar transport and enhanced regulation over partitioning. SS accumulation in vacuoles supports osmoregulation in leaves. The increased expression of sucrose synthesis genes and reduced expression of sucrose degradation genes in the roots did not coincide with sucrose levels, implying local sucrose production for energy. Moreover, the downregulation of invertases in the roots suggests limited sucrose allocation from the aboveground organs. This study provides an expression atlas of NSC-related genes that respond to drought in poplar trees, and can be tested in tree improvement programs for adaptation to drought conditions.

Manipulating microRNA miR408 enhances both biomass yield and saccharification efficiency in poplar

The conversion of lignocellulosic feedstocks to fermentable sugar for biofuel production is inefficient, and most strategies to enhance efficiency directly target lignin biosynthesis, with associated negative growth impacts. Here we demonstrate, for both laboratory- and field-grown plants, that expression of Pag-miR408 in poplar (Populus alba × P. glandulosa) significantly enhances saccharification, with no requirement for acid-pretreatment, while promoting plant growth. The overexpression plants show increased accessibility of cell walls to cellulase and scaffoldin cellulose-binding modules. Conversely, Pag-miR408 loss-of-function poplar shows decreased cell wall accessibility. Overexpression of Pag-miR408 targets three Pag-LACCASES, delays lignification, and modestly reduces lignin content, S/G ratio and degree of lignin polymerization. Meanwhile, the LACCASE loss of function mutants exhibit significantly increased growth and cell wall accessibility in xylem. Our study shows how Pag-miR408 regulates lignification and secondary growth, and suggest an effective approach towards enhancing biomass yield and saccharification efficiency in a major bioenergy crop.