Regeneration of plantlets from cell suspension culture derived callus of white poplar (Populus alba L.)

Friable calli derived from the stem tissues of Populus alba were used to establish cell suspension cultures which were characterized for in vitro growth and regeneration capacity. Suspended cells and callus recovered from these cells were maximal on a fresh weight basis using MS liquid medium containing 0.44 M BAP and 4.52 M 2,4-D. Shoot regeneration from the recovered callus was observed within 30 to 40 days of culture. The number of shoots was increased by subculturing the shoot-forming callus 2 to 3 times on MS medium supplemented with 19.7 M 2iP and 0.05 M IBA. Regenerated shoots were easily rooted on half-strength MS medium lacking growth regulators, and the plantlets were transferred to pots containing vermiculite for greenhouse growth.Abbreviations BAP 6-benzylaminopurine - 2iP 2-isopentenyladenine - NAA 1-naphthaleneacetic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid - 2,4-D 2,4-dichlorophenoxyacetic acid - PCV packed cell volume - MS medium Murashige and Skoog medium (1962)     

Fine-root growth, fine root mortality, and leaf morphological change of Populus alba in response to fluctuating water tables

Water table fluctuation in arid land regions may alter tree fine-root growth and mortality, thereby affecting leaf growth. To reveal the effects of water table fluctuation on fine-root growth and mortality and their relation to leaf growth, we exposed P. alba L. cuttings to various fluctuating water table depths. 1-year-old rooted cuttings were grown individually in pots containing sandy soil in a greenhouse in three water table depth treatments for 45 days: constant depth at 45 cm from the soil surface, fluctuating depths between 45 and 30 cm, and fluctuating depths between 45 and 15 cm. Fine-root biomass and mortality, biomass partitioning among plant parts, and whole-tree growth responses were determined in cuttings harvested every 15 days. Fluctuation of water tables increased the mortality of fine roots at the layers near the soil surface. Fine-root mortality increased during the shallower water table depth period. At the whole-root system level, although fine-root mortality increased when the water table was shallower, fine-root biomass was similar among the treatments, suggesting that P. alba cuttings would sustains its standing fine-root biomass under fluctuating water table depth conditions. Our structural equation modeling showed the fine-root proportion affects leaf morphological changes, suggesting that there would be a parallel relationship of morphological changes between roots and leaves with fluctuating water tables.     

Responses of two poplar species (Populus alba and Populus x canadensis) to high copper concentrations

With the aim to examine their potentials as renewable resources to decontaminate polluted soils, growth, photosynthesis and nitrogen balance were analyzed in two poplar species (Populus x canadensis, Adda clone and Populus alba, Villafranca clone) to investigate the tolerance to high copper (Cu) concentrations. The two clones showed different responses to Cu in terms of tolerance and metal allocation: P. x canadensis accumulated Cu in roots, displaying features sought in plants suitable for phytostabilization, while P. alba accumulated the metal in leaves, like an indicator species.     

Hormonal Responses to Water Deficit in Cambial Tissues of Populus alba L.

Changes in the concentrations of bioactive gibberellins and abscisic acid in the cambial region of white poplar (Populus alba L.) were investigated in 1-year-old plants, to highlight how these phytohormone signals are modulated in response to water deficit. Plants were cultivated in pots outdoor and, at the time of maximum cambial growth (T ₀), irrigation was withdrawn for 8 days, inducing a mild water deficit, thus mimicking a condition that is recurrent in Mediterranean climates when white poplar attains its maximum growth rate. The water deficit was suspended by resuming irrigation (T _max) throughout a recovery period of 2 weeks (T _rec). Cambial tissues were sampled at T ₀, T _max, and T _rec. Significant changes of leaf and stem relative water content, leaf water potential, stomatal conductance, transpiration, carbon assimilation, stem shrinkage, and leaf number were induced by soil water shortage, which also negatively affected cambium development. Nevertheless, these responses were almost fully reversed following the resumption of irrigation. Water deficit induced the accumulation of large amounts of abscisic acid in cambial tissues, but the hormone was brought back to pre-stress levels after the recovery period. With regard to bioactive gibberellins, GA₁ was several folds more abundant than GA₄ and reached the greatest level in the plants recovering from the water status imbalance. The possible functions of gibberellins and abscisic acid in the response of cambial tissues to water deficit are discussed in view of the known physiological roles and molecular mechanisms of action of these hormonal signals.     

Induction of haploids in Populus maximowiczii via embryogenic callus

Anthers of Populus maximowiczii with microspores at the mononucleate stage were cultured at 20°C in the dark on agar-solidified Murashige and Skoog medium after 4 days of cold treatment (4°C). After 4 to 8 weeks anthers on medium supplemented with 0.5, 1.0 or 2.0 mg l^-1 2,4-D in combination with 0.1 mg l^-1 kinetin developed calli that were characterized by smooth surface and gel-like consistency. These calli were comprised of expanding microspores surrounded by a mucilaginous matrix. After transfer of anthers with embryogenic calli to MS medium with low hormone levels (NAA at 0, 0.1 and 0.1 mg l^-1 and BA at 0, 0.1 and 1.0 mg l^-1) microspores started to divide and initiated independent meristematic nests, which developed into embryoidal structures, resembling globular to bi-polar heart-shaped embryoids. The embryoids germinated precociously without developing cotyledons. After transfer to medium with a range of levels of BA (1.0, 2.5 and 5.0 mg l^-1), adventitious shoots developed mainly from the roots. Shoots were rooted in half strength MS medium supplemented with 0.025 mg l^-1 NAA. Via this pathway anther response in the best treatment combination was 10%.Abbreviations BA benzyladenine - MS Murashige & Skoog - NAA naphthaleneacetic acid - 2,4-D-2,4 dichlorophenoxyacetic acid     

Extensive Clonal Assemblies in Populus alba and Populus x canescens from the Iberian Peninsula

Riparian vegetation in temperate zones holds great environmental importance and thus its conservation should be a priority. Among riverine tree species, genus Populus stands out, being also a model organism in research. In this work, we present a genetic analysis of the hybrid Populus x canescens and its parent species Populus alba and Populus tremula, with special emphasis in P. alba with which backcrosses frequently occur. This study focuses on the river Douro basin (Spain) where the presence of hybrids has been previously reported. Nuclear microsatellite markers and Bayesian statistical analysis have been used for the detection of hybrids and purebred stands. This methodology has also made possible the study of clonality in the taxonomic continuum P. alba–P. x canescens. Our results highlight the existence of a small number of genotypes accounting for most of the individual trees and stands. Possible causes leading to this situation are discussed. Also, the presence of individuals genetically close to ornamental cultivars is reported for the first time. Finally, concern about the present situation of P. alba genetic resources is brought up.     

西藏地区银白杨的组织培养和快速繁殖

1　植物名称　银白杨 (Ｐｏｐｕｌｕｓａｌｂａ)。2　材料类别　优良单株休眠枝水插萌动芽。3　培养条件　芽萌动培养基 :( 1 )ＭＳ ＫＴ 1 .0ｍｇ·Ｌ- 1 (单位下同 ) ＩＢＡ 0 .2 ;( 2 )ＭＳ ＫＴ 0 .5 ＩＢＡ 0 .1。诱导丛生芽培养基 :( 3)ＭＳ 6 ＢＡ0 .3 ＮＡＡ 0 .     

Assessment of salt tolerance in Populus alba clones using chlorophyll fluorescence

Cuttings of five Populus alba clones (S18 F1-26, Al29 F8-35, J3 F1-4, GU1 F16-36, PO9 F21-88), Populus euphratica, and Populus×euramericana (I-214) were submitted during 45 d to regular watering with NaCl solutions of electrical conductivity of 7 and 14 dS m⁻¹. Chlorophyll a fluorescence in response to the salinity stress was assessed, using F₀ and F_v/F_m. Differences in reaction to the salt were found in P. alba clones, F₀ and F_v/F_m being the fluorescence parameters used to check out this stress. Minimal constant fluorescence of dark-adapted plants (F₀) showed a better correlation with the disease index exhibited by plants and also with salinity dose than the parameter F_v/F_m. Some of the P. alba clones showed the same behaviour, assessed through fluorescence parameters, as P. euphratica, which was previously defined as salt tolerant, while the rest exhibited the same characteristics as I-214, which was very sensitive.     

Metabolism of cell wall polysaccharides in cell suspension cultures of Populus alba in relation to cell growth

Changes in the composition of cell walls and extracellular polysaccharides (ECP) were studied during the growth of suspension-cultured Populus alba cells. Three growth phases, namely the cell division phase, cell elongation phase and stationary phase, were distinguished. The active deposition of polysaccharides in cell wall fractions (50 m M Na₂CO₃-, 1 M KOH-, 4 M KOH-soluble and 4 M KOH-insoluble) was observed during the elongation phase. A 50 m M Na₂CO₃-soluble pectic fraction mainly composed of 1,4-linked galactan and arabinan except acidic sugars. The 1,4-linked galactan decreased markedly during elongation. In 1 and 4 M KOH-soluble hemicellulosic fractions, non-cellulosic 1,4-glucan and xyloglucan were observed as major components, respectively. These polysaccharides also decreased during elongation. A large amount of polysaccharides was secreted into the medium as ECP. Neutral sugars were detected predominantly by sugar composition analysis. Acidic sugars, such as galacturonic acid, were less than 12% of total. In this study, active metabolism of pectic polysaccharides in addition to hemicellulosic polysaccharides, especially neutral side chains of pectin, during cell growth, was clarified.     

Plant growth, biomass partitioning and soil carbon formation in response to altered lignin biosynthesis in Populus tremuloides

We conducted a glasshouse mesocosm study that combined (13)C isotope techniques with wild-type and transgenic aspen (Populus tremuloides) in order to examine how altered lignin biosynthesis affects plant production and soil carbon formation. Our transgenic aspen lines expressed low stem lignin concentration but normal cellulose concentration, low lignin stem concentration with high cellulose concentration or an increased stem syringyl to guaiacyl lignin ratio. Large differences in stem lignin concentration observed across lines were not observed in leaves or fine roots. Nonetheless, low lignin lines accumulated 15-17% less root C and 33-43% less new soil C than the control line. Compared with the control line, transformed aspen expressing high syringyl lignin accumulated 30% less total plant C - a result of greatly reduced total leaf area - and 70% less new soil C. These findings suggest that altered stem lignin biosynthesis in Populus may have little effect on the chemistry of fine roots or leaves, but can still have large effects on plant growth, biomass partitioning and soil C formation.     

Plant regeneration capacity of callus derived from leaf,stem, and root segments of Populus alba L. x P. grandidentata Michx.

Summary Expiants for establishing callus cultures originated from in vitro cultured hybrid poplar (Populus alba L. X P. grandidentata Michx.). Plant regeneration was achieved from established callus cultures derived from stem internodes (SI), leaf discs (LD), and root segments (RS). Shoot regeneration from callus occurred within 4 weeks of culture on most of the media tested. Frequency of shoot formation was greatly increased by subculturing the selected organogenic calli on regeneration media. The highest rate of multiple shoot formation (an average number of 7/SI, 11/LD, and 8/RS) was obtained by using 0.05 M IBA in combination with 22.5 M 2iP, 22.5 M zeatin, and 12.5 M 2iP, respectively. Regenerated shoots were easily rooted in polyterra peat plugs in transparent plastic boxes. The rooted plantlets were subsequently transferred to pots containing an artificial potting mix.Abbreviations BA 6-benzylaminopurine - 2iP N⁶-isopentenyladenine - Z zeatin - 2,4-D 2,4-dichlorophenoxyacetic acid - IBA indole-3-butyric acid - WPM Woody Plant Medium - PGR Plant Growth Regulator Journal Paper No. J-14119 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, Project No. 2210     

A fission yeast B-type cyclin functioning early in the cell cycle.

We have cloned a fission yeast gene, cig1+, encoding a 48 kd product that is most similar to cyclin B proteins. The cig1+ protein has a "cyclin box" approximately 40% identical to B-type cyclins of other species, but lacks the "destruction box" required for proteolysis of mitotic cyclins. Deletion of cig1+ had no observable effect on cell viability or progression through G2 or M phase, but instead caused a marked lag in the progression from G1 to S phase. G1 constituted approximately 70% of the cell cycle in cig1 deletion strains, as compared with less than 10% in cig1+ strains. Constitutive cig1+ overexpression was lethal, causing cessation of growth and arrest in G1. Expression of cig1+ failed to rescue an S. cerevisiae strain lacking CLN Start cyclins. Thus, cig1+ identifies a new class of B-type cyclin acting in G1 or S phase that appears to be functionally distinct from all previously described cyclin proteins.     

Cell differentiation in protoplast cultures from embryogenic callus ofAbies alba L.

Protoplasts were isolated from embryogenic callus ofAbies alba L. which originated from immature seeds. The protoplasts were immobilized in alginate beads in order to follow the development of single protoplasts.Surrounding culture medium was modified from Kao and Michayluk (1975). After cell wall regeneration subsequent cell divisions lead to the formation of colonies showing an early differentiation of small meristematic cells and large vacuolated suspensor-type cells.Abbreviations 6-BA N⁶-benzyladenine - IAA 3-indoleacetic acid (potassium salt) - KM Kao and Michayluk (1975) - MES 2-(N-morpholino)ethanesulfonic acid - NAA 1-naphthalene acetic acid (sodium salt) - PVP Polyvinylpyrrolidone - SH Schenk and Hildebrandt (1972) - Tween 80 Polyoxyethylene- sorbitan - monooleate - WPM (woody plant medium), Lloyd and McCown (1981)     

Effects of boron deficiency in cell suspension cultures of Populus alba L.

Cell suspension cultures of Populus alba L. (original cells) require at least 10 M boron for appropriate growth. Using original cells we established a cell line, T-5B, which can grow in a medium containing low levels of boron (5 M). The level of boron localized in the cell walls of T-5B cells was one-half that found in the cell walls of original cells maintained in medium containing 100 M boron, and the level of the rhamnogalacturonan II dimer, cross-linked by a borate ester, also decreased in the former. The sugar composition of whole cell walls of the T-5B cell line was similar that of the original cells, however pectic polysaccharides composed of arabinose or galacturonic acid were easily extracted from T-5B cell walls with 50 mM trans-1,2-cyclohexanediamine-N,N,N,N-tetraacetic acid. Our results suggest that boron deficiency causes a weakening of the interaction among pectic polysaccharides due to a decrease in boron-rhamnogalacturonanII cross-linkage.     

Maintenance of MLOs (Mycoplasma-like Organisms) on Populus alba Micropropagation

Populus alba plantlet micropropagation has been used for maintaining MLOs more than three years in samples collected from infected trees in Paris. Symptoms were observed on plantlets obtained from subcultures of the apical, middle and basal parts of the stems, and from the roots. Fluorescent microscopy failed to detect MLOs in the apical part of the plantlets and showed that they increased near the roots. Electron microscopy confirmed their presence. Some root sieve tubes were completely packed with MLOs. The sensitivity of the two methods used, subculturing and microscopy, for detection of MLOs is discussed. The symptoms remained for one year in plants regenerated from diseased plantlets and grown in the greenhouse. Then they started to disappear.