Plasma membrane and cell wall properties of an aspen hybrid (Populus tremula × tremuloides) parenchyma cells under the influence of salt stress

The effect of salinity on cell turgor, plasma membrane permeability and cell wall elasticity has been measured in petioles of an aspen hybrid using the cell pressure probe. Control plants were grown in soil without the addition of NaCl and treated plants were grown in soil with 50 mM of NaCl for 1, 2, 3 and 4 weeks. In parenchyma cells from Populus tremula × tremuloides petioles with an increased level of NaCl in the soil: (a) turgor pressure was reduced after 1 week of treatment but afterward it was similar to untreated plants, (b) the value of elastic modulus of the cell walls increased, and (c) hydraulic conductivity of the plasma membrane of treated plants decreased in comparison to untreated ones. No histological differences and distribution of JIM5 antibody between the petioles of plants grown under salinity and the untreated were found. In cell walls of parenchyma and collenchyma from plants grown under salinity, the presence of pectic epitopes recognized by JIM7 antibodies was increased in comparison to the control plants. The obtained results indicate that under salt stress the permeability of water through plasma membrane is disturbed, cell walls became more rigid but the turgor pressure did not change.     

Daylength and spatial expression of a gibberellin 20-oxidase isolated from hybrid aspen (Populus tremula L. × P. tremuloides Michx.)

Physiologically active gibberellins (GAs) are key regulators of shoot growth in trees. To investigate this mechanism of GA-controlled growth in hybrid aspen, we cloned cDNAs encoding gibberellin 20-oxidase (GA 20-oxidase), a key, highly regulated enzyme in the biosynthesis of GAs. Clones were isolated from leaf and cambium cDNA libraries using probes generated by polymerase chain reaction, based on conserved domains of GA 20-oxidases. Upon expression in Escherichia coli, the GST-fusion protein was shown to oxidise GA12 as well as oxidising the 13-hydroxylated substrate GA53, successively to GA9 and GA20, respectively. The gene PttGA20ox1 was expressed in meristematic cells and growing tissues such as expanding internodes, leaves and roots. The expression was negatively regulated by both GA4 and overexpression of phytochrome A. RNA analysis also showed that the expression was down-regulated in late-expanding leaf tissue in response to short days (SDs). Actively growing tissues such as early elongating internodes, petioles and leaf blades had the highest levels of C19-GAs. Upon transfer to SDs an accumulation of GA19 was observed in early elongating internodes and leaf blades. The levels of C19-GAs were also to some extent changed upon transfer to SDs. The levels of GA20 were down-regulated in internodes, and those of GA1 were significantly reduced in early expanding leaf blades. In roots the metabolites GA19 and GA8 decreased upon shifts to SDs, while GA20 accumulated slightly. The down-regulation of GA 20-oxidase activity in response to SDs was further indicated by studies of [14C]GA12 metabolism in shoots, demonstrating that the substrate for GA 20-oxidase, [14C]GA53, accumulates in SDs.     

Successful hybridisation of normally incompatible hybrid aspen (Populus tremula?��?P. tremuloides) and eastern cottonwood (P. deltoides)

Hybrid aspen (Populus tremula × P. tremuloides) belong to the section Populus. Eastern cottonwood (P. deltoides) is a member of the section Aigeiros within the genus Populus. These poplar sections are generally considered to be incompatible. Here, we describe successful hybridisation between these parents, producing an offspring family with 27 individuals. The hybrid character of individuals was proven by genotypes at 16 nuclear microsatellite loci. One individual was suspected to have more than the diploid chromosome number of 2n = 38 due to the observation of more than two alleles at several loci. This individual is a triploid, ascertained by flow cytometry. Two distinct growth classes of tall and dwarf plants were observed in the progeny, reflecting different degrees of postzygotic incompatibility. Two loci linked to the tested microsatellites have an effect on height growth. Some fast-growing individuals were micropropagated to test them for biomass performance together with other clones in field trials.     

The partitioning of carbohydrates and the biomass of leaves in Populus tremula L . canopy

 This study was aimed at making a quantitative evaluation of the biomass, carbohydrates and mineral nutrients partitioning in the canopy of aspen (Populus tremula L.) growing in a forest stand. Tree canopy biomass was divided into ten equal horizontal layers and the material for the study was sampled from all canopy layers. The results indicated that the specific leaf mass and the dry matter content increased but the area of leaves decreased toward the top of the canopy. The content of the non-structural carbohydrates depended largely on the position of the leaves in the canopy and the N, P and K contents in the leaves, reaching a maximum in the upper canopy layers better exposed to light. Regression analysis showed a linear relationship between the leaf mass per area and the percentage of dry matter on the one hand and the content of carbohydrates, N, P and K in the canopy on the other. Received: 11 March 1997 / Accepted: 16 June 1997     

Oxidation and reduction of sulfite contribute to susceptibility and detoxification of SO2 in Populus × canescens leaves

Key Message

The critical level for SO ₂ susceptibility of Populus × canescens is approximately 1.2 μL L ^?1 SO ₂ . Both sulfite oxidation and sulfite reduction and assimilation contribute to SO ₂ detoxification.

Abstract

In the present study, uptake, susceptibility and metabolism of SO₂ were analyzed in the deciduous tree species poplar (Populus × canescens). A particular focus was on the significance of sulfite oxidase (SO) for sulfite detoxification, as SO has been characterized as a safety valve for SO₂ detoxification in herbaceous plants. For this purpose, poplar plants were exposed to different levels of SO₂ (0.65, 0.8, 1.0, 1.2 μL L^?1) and were characterized by visible injuries and at the physiological level. Gas exchange parameters (stomatal conductance for water vapor, CO₂ assimilation, SO₂ uptake) of the shoots were compared with metabolite levels (sulfate, thiols) and enzyme activities [SO, adenosine 5′-phosphosulfate reductase (APR)] in expanding leaves (80–90 % expanded). The critical dosage of SO₂ that confers injury to the leaves was 1.2 μL L^?1 SO₂. The observed increase in sulfur containing compounds (sulfate and thiols) in the expanding leaves strongly correlated with total SO₂ uptake of the plant shoot, whereas SO₂ uptake rate was strongly correlated with stomatal conductance for water vapor. Furthermore, exposure to high concentration of SO₂ revealed channeling of sulfite through assimilatory sulfate reduction that contributes in addition to SO-mediated sulfite oxidation to sulfite detoxification in expanding leaves of this woody plant species.     

Cellulose and lignin biosynthesis is altered by ozone in wood of hybrid poplar (Populus tremula × alba)

Wood formation in trees is a dynamic process that is strongly affected by environmental factors. However, the impact of ozone on wood is poorly documented. The objective of this study was to assess the effects of ozone on wood formation by focusing on the two major wood components, cellulose and lignin, and analysing any anatomical modifications. Young hybrid poplars (Populus tremula × alba) were cultivated under different ozone concentrations (50, 100, 200, and 300 l l(-1)). As upright poplars usually develop tension wood in a non-set pattern, the trees were bent in order to induce tension wood formation on the upper side of the stem and normal or opposite wood on the lower side. Biosynthesis of cellulose and lignin (enzymes and RNA levels), together with cambial growth, decreased in response to ozone exposure. The cellulose to lignin ratio was reduced, suggesting that cellulose biosynthesis was more affected than that of lignin. Tension wood was generally more altered than opposite wood, especially at the anatomical level. Tension wood may be more susceptible to reduced carbon allocation to the stems under ozone exposure. These results suggested a coordinated regulation of cellulose and lignin deposition to sustain mechanical strength under ozone. The modifications of the cellulose to lignin ratio and wood anatomy could allow the tree to maintain radial growth while minimizing carbon cost.     

1H, 13C, and 15N resonance assignments of reduced GrxS14 from Populus tremula × tremuloides

GrxS14 is a monothiol Glutaredoxin (Grx) from Populus tremula × tremuloides, which has a CGFS active site. GrxS14 is located in the chloroplasts and has been found to occur ether as an apo form or as a holo form with a [2Fe-2S] cluster. The holo form contains two monomers of apo GrxS14 bridged by the iron sulphur center, in the presence of two external glutathione molecules (Bandyopadhyay et al. 2008). The NMR assignments of the GrxS14 are essential for its solution structure determination.     

In vitro induction of secondary xylem-like tracheary elements in calli of hybrid poplar (Populus sieboldii × P. grandidentata)

The formation of tracheary elements was induced in calli derived from petioles of hybrid poplar (Populus sieboldii × P. grandidentata) after 10 days of culture on medium that lacked auxin but contained 1 μM brassinolide. Some differentiated cells formed broad regions of cell walls and bordered pits, which are typical features of tracheary elements of secondary xylem. Other differentiated cells resembled tracheary elements of primary xylem, with spiral or reticulate thickening of cell walls. The tracheary elements that developed in calli were formed within cell clusters. This induction system provides a new model for studies of the mechanism of differentiation of secondary xylem cells in vitro.     

Cell suspension cultures of Populus tremula × P. tremuloides exhibit a high level of cellulose synthase gene expression that coincides with increased in vitro cellulose synthase activity

Summary. Compared to wood, cell suspension cultures provide convenient model systems to study many different cellular processes in plants. Here we have established cell suspension cultures of Populus tremula L. × P. tremuloides Michx. and characterized them by determining the enzymatic activities and/or mRNA expression levels of selected cell wall-specific proteins at the different stages of growth. While enzymes and proteins typically associated with primary cell wall synthesis and expansion were detected in the exponential growth phase of the cultures, the late stationary phase showed high expression of the secondary-cell-wall-associated cellulose synthase genes. Interestingly, detergent extracts of membranes from aging cell suspension cultures exhibited high levels of in vitro cellulose synthesis. The estimated ratio of cellulose to callose was as high as 50 : 50, as opposed to the ratio of 30 : 70 so far achieved with membrane preparations extracted from other systems. The increased cellulose synthase activity was also evidenced by higher levels of Calcofluor white binding in the cell material from the stationary-phase cultures. The ease of handling cell suspension cultures and the improved capacity for in vitro cellulose synthesis suggest that these cultures offer a new basis for studying the mechanism of cellulose biosynthesis. Correspondence and reprints: School of Biotechnology, Royal Institute of Technology, AlbaNova University Centre, 106 91 Stockholm, Sweden. Present address: Department of Biotechnology, Beijing Forestry University, Beijing, People’s Republic of China     

Warm temperature accelerates short photoperiod-induced growth cessation and dormancy induction in hybrid poplar (Populus × spp.)

There is increasing evidence that temperature, in addition to photoperiod, may be an important factor regulating bud dormancy. The impact of temperature during growth cessation, dormancy development, and subsequent cold acclimation was examined in four hybrid poplar clones with contrasting acclimation patterns: ‘Okanese’—EARLY, ‘Walker’—INT1, ‘Katepwa’—INT2, and ‘Prairie Sky’—LATE. Four day–night temperature treatments (13.5/8.5, 18.5/13.5, 23.5/8.5, and 18.5/3.5°C) were applied during a 60-day induction period to reflect current and predicted future annual variation in autumn temperature for Saskatoon, SK. Warm night temperature (18.5/13.5°C) strongly accelerated growth cessation, dormancy development, and cold acclimation in all four clones. Day temperature had the opposite effect of night temperature. Day and night temperatures appeared to act antagonistically against each other during growth cessation and subsequent dormancy development and cold acclimation. Growth cessation, dormancy development, and cold acclimation in EARLY and LATE were less affected by induction temperature than INT1 and INT2 suggesting that genotypic variations exist in response to temperature. Separating specific phenological stages and the impact by temperature on each clone revealed the complexity of fall phenological changes and their interaction with temperature. Most importantly, future changes in temperature may affect time to growth cessation, subsequently altering the depth of dormancy and cold hardiness in hybrid poplar.     

Ozone-induced microscopical changes and quantitative carbohydrate contents of hybrid poplar (Populus × euramericana)

Summary Cuttings of hybrid poplar (Populus × euramericana var. Dorskamp) were exposed to ozone (80 g/m³ from 2100 hours to 0700 hours, 180 g/m³ from 0700 hours to 2100 hours) for 3 months. Ozone reduced the starch content in leaves and stem bark, whereas starch granules accumulated in bundle sheath cells along small leaf veins. At the same time, sucrose and inositol content increased in the leaves. Mesophyll cells in the vicinity of the stomata were injured first, and droplet-like material appeared on their walls. In the sieve plates of fumigated trees, the pores showed a higher degree of narrowing than those of the control treatment. Cell collapse in the leaves was accompanied by water loss and an increase in air space. In the stems, the ozone treatment led to a reduced radial width, particularly in the xylem tissue. These results are discussed in relation to reduced or inhibited phloem loading and ozone-induced drought stress. The plants injured by ozone showed quite distinct patterns of metabolite responses as well as enzyme activities (PEP- and RubP-carboxylase) in the leaves from the top to the bottom. There were also remarkable differences in the reaction of sucrose and inositol between leaves and stem bark. Future research should therefore increasingly follow a whole-plant approach for a better understanding of complex plant reactions.     

Expression of multiple resistance genes enhances tolerance to environmental stressors in transgenic poplar (Populus × euramericana 'Guariento')

Commercial and non-commercial plants face a variety of environmental stressors that often cannot be controlled. In this study, transgenic hybrid poplar (Populus × euramericana 'Guariento') harboring five effector genes (vgb, SacB, JERF36, BtCry3A and OC-I) were subjected to drought, salinity, waterlogging and insect stressors in greenhouse or laboratory conditions. Field trials were also conducted to investigate long-term effects of transgenic trees on insects and salt tolerance in the transformants. In greenhouse studies, two transgenic lines D5-20 and D5-21 showed improved growth, as evidenced by greater height and basal diameter increments and total biomass relative to the control plants after drought or salt stress treatments. The improved tolerance to drought and salt was primarily attributed to greater instantaneous water use efficiency (WUEi) in the transgenic trees. The chlorophyll concentrations tended to be higher in the transgenic lines under drought or saline conditions. Transformed trees in drought conditions accumulated more fructan and proline and had increased Fv/Fm ratios (maximum quantum yield of photosystem II) under waterlogging stress. Insect-feeding assays in the laboratory revealed a higher total mortality rate and lower exuviation index of leaf beetle [Plagiodera versicolora (Laicharting)] larvae fed with D5-21 leaves, suggesting enhanced insect resistance in the transgenic poplar. In field trials, the dominance of targeted insects on 2-year-old D5-21 transgenic trees was substantially lower than that of the controls, indicating enhanced resistance to Coleoptera. The average height and DBH (diameter at breast height) of 2.5-year-old transgenic trees growing in naturally saline soil were 3.80% and 4.12% greater than those of the control trees, but these increases were not significant. These results suggested that multiple stress-resistance properties in important crop tree species could be simultaneously improved, although additional research is needed to fully understand the relationships between the altered phenotypes and the function of each transgene in multigene transformants.     

Expression of Cellulose Synthase Genes During the Gravistimulation of Flax (Linum usitatissimum) and Poplar (Populus alba × tremula) Plants

Russian Journal of Bioorganic Chemistry - Plant cellulose is synthesized on the plasma membrane by the cellulose synthase complex and a number of coenzymes. Different cellulose synthases are...