Sodium-calcium interactions in two wheat species differing in salinity tolerance

White spruce [ Picea glauca (Moench) Voss.] seedlings were used to study the changes in cell wall composition and elasticity in mature needles before and after the resumption of growth following winter dormancy. Dormant seedlings showed high cell wall elasticity that decreased after the resumption of shoot growth. Cell wall hemicellulose content increased 3 days after planting and decreased after the buds flushed. Non-cellulosic glucose and arabinose were the sugars showing the most pronounced changes related to shoot growth. Arabinose was the most abundant sugar residue in the pectin and hemicellulose fractions and it decreased until day 10 after planting. At the same time, the levels of glucose in pectin and hemicellulose increased. The results provide evidence for cell wall carbohydrate turnover in dormant and active seedlings before and after bud flushing.     

Response of red-osier dogwood (Cornus stolonifera) seedlings to sodium sulphate salinity: effects of supplemental calcium

A greenhouse study was designed to test the effects of sodium sulphate (Na₂SO₄) on red-osier dogwood (Cornus stolonifera Michx) seedlings in the presence and absence of additional calcium (Ca²⁺). Changes in growth parameters, ion and carbohydrate accumulation and cell wall composition were examined. Calcium alleviated the effect of Na₂SO₄ on shoot height; however, it did not affect the reduction in shoot and root dry weights. An increased level of sodium (Na⁺) in roots of plant exposed to Na₂SO₄ was recorded in the presence of supplemental Ca²⁺ whereas there was no change in potassium (K⁺) and Ca²⁺ levels. In shoots of seedlings treated with Na₂SO₄, the addition of Ca²⁺ did not affect Na⁺, K⁺ and Ca²⁺ levels. The amount of soluble carbohydrates was increased in leaves of seedlings treated with Na₂SO₄ both in the absence and presence of supplemental Ca²⁺. The decrease in cell wall material in response to salt stress was alleviated by Ca²⁺ in stem tissues although Ca²⁺ did not alter the changes in hemicellulose and cellulose. Sugar composition of pectins and hemicellulose were modified in stems and leaves by Na₂SO₄ and/or Ca²⁺. The results of this study showed that calcium was able to alleviate the effects of salt stress on shoot height and cell wall content of red-osier dogwood stems. Furthermore, changes occurred in cell wall composition of red osier seedlings treated with Na₂SO₄.     

Cell wall changes in white spruce (Picea glauca) needles subjected to repeated drought stress

White spruce [ Picea glauca (Moench) Voss] seedlings were preconditioned by subjecting them to 3 cycles of a mild drought stress. After 1 week of stress relief their water status, soluble carbohydrate content and cell wall composition in newly formed needles were examined and compared with those in control seedlings. Both preconditioned and control seedlings were subsequently subjected to a severe drought stress and again analyzed. Preconditioning treatment both before and during subsequent stress exposure lowered osmotic potentials at full hydration, and after the loss of turgor, decreased lignin content and increased hemicellulose content of the cell walls. Severe drought had similar but more drastic effects on seedling water relations, sugar accumulation and cell wall hemicellulose content; it also decreased cell wall pectin levels. The decrease in pectin levels was accompanied by a loss of galactose and glucose from pectic substances. Little change in cellulose content was observed as a result of preconditioning and severe drought.     

Effects of NaCl and Na2SO4 on red-osier dogwood (Cornus stolonifera Michx) seedlings

Sodium chloride and sodium sulfate are commonly present in extraction tailings waters produced as a result of surface mining and affect plants on reclaimed areas. Red-osier dogwood (Cornus stolonifera Michx) seedlings were demonstrated to be relatively resistant to these high salinity oil sands tailings waters. The objectives of this study were to compare the effects of Na₂SO₄ and NaCl, on growth, tissue ion content, water relations and gas exchange in red-osier dogwood (Cornus stolonifera Michx) seedlings. In the present study, red-osier dogwood seedlings were grown in aerated half-strength modified Hoagland's mineral solution containing 0, 25, 50 or 100 mM of NaCl or Na₂SO₄. After four weeks of treatment, plant dry weights decreased and the amount of Na⁺ in plant tissues increased with increasing salt concentration. Na⁺ tissue content was higher in plants treated with NaCl than Na₂SO₄ and it was greater in roots than shoots. However, Cl^– concentration in the NaCl treated plants was higher in shoots than in roots. The decrease in stomatal conductance and photosynthetic rates observed in presence of salts is likely to contribute to the growth reduction. Our results suggest that red-osier dogwood is able to control the transport of Na⁺ from roots to shoots when external concentrations are 50 mM or less.     

Improving NaCl resistance of red-osier dogwood: role of CaCl2 and CaSO4

The influence of Ca²⁺ salts on the resistance of red-osier dogwood (Cornus sericea) seedlings to salinity was investigated. Red-osier dogwood seedlings were exposed to 5 and 10 mM of CaCl₂ or CaSO₄ in the presence or absence of 50 mM NaCl for 40 days in a controlled environment. Seedlings exposed to CaCl₂ and CaSO₄ recovered from NaCl-induced transpiration reduction after 20 days at a concentration of 10 mM and after 30 days at a concentration of 5 mM; while in absence of additional Ca²⁺, the seedlings recovered only after 40 days. Addition of 10 mM Ca²⁺ to NaCl treatment also limited the accumulation of proline in leaf tissues and caused an increase in leaf and lateral shoot K⁺ content. These results suggest that 10 mM Ca²⁺ could alleviate, at least in part, the osmotic effect of NaCl on red-osier dogwood via control of stomatal closure. On the other hand, ion analysis showed that Ca²⁺ addition was able to reduce the NaCl-induced Na⁺ concentration only in stem tissues suggesting that Ca²⁺ had only a limited effect on the ionic stress. The present study also showed an unexpected NaCl-induced increase in Ca²⁺ content of leaves, lateral shoots and stems that was not observed in our previous hydroponics experiments and seems to be more characteristic of plants growing on sandy soils.     

Salinity Stress Inhibits Bean Leaf Expansion by Reducing Turgor, Not Wall Extensibility

Treatment of bean (Phaseolus vulgaris L.) seedlings with low levels of salinity (50 or 100 millimolar NaCl) decreased the rate of light-induced leaf cell expansion in the primary leaves over a 3 day period. This decrease could be due to a reduction in one or both of the primary cellular growth parameters: wall extensibility and cell turgor. Wall extensibility was assessed by the Instron technique. Salinity did not decrease extensibility and caused small increases relative to the controls after 72 hours. On the other hand, 50 millimolar NaCl caused a significant reduction in leaf bulk turgor at 24 hours; adaptive decreases in leaf osmotic potential (osmotic adjustment) were more than compensated by parallel decreases in the xylem tension potential and the leaf apoplastic solute potential, resulting in a decreased leaf water potential. It is concluded that in bean seedlings, mild salinity initially affects leaf growth rate by a decrease in turgor rather than by a reduction in wall extensibility. Moreover, longterm salinization (10 days) resulted in an apparent mechanical adjustment, i.e. an increase in wall extensibility, which may help counteract reductions in turgor and maintain leaf growth rates.     

Changes of Cell Wall Composition and Polymer Size in Primary Roots of Cotton Seedlings Under High Salinity

The aim of this study was to investigate changes in cell wallchemical composition and polymer size in the root tip of intactcotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) grownin saline environments, in order to relate the interaction betweenhigh salinity and root growth to possible changes in cell wallmetabolism. Cotton seedlings were grown in modified Hoagland nutrient solutionwith various combinations of NaCl and CaCl₂. Cell walls werefractionated into four fractions (pectin, hemicellulose 1 and2, cellulose), and analysed for their total sugar content, neutralsugar composition and size of polysaccharides. At 1 mol m^–3Ca, 150 mol m^–3 NaCl resulted in a significant increasein the cell wall uronic acid content, but a reduction in cellulosecontent on a per unit dry weight basis. Supplemental Ca overcamethe inhibitory effect of high Na on cellulose content. The neutralsugar composition of the cell wall fractions showed no majorchanges caused by varied Na/Ca ratios. Determinations of polysaccharidepolymer size showed that high Na at 1 mol m^–3 Ca led toan increase in the amount of polysaccharides of intermediatemolecular size and a decrease in that of small size in the hemicellulose1 fraction, indicating a possible inhibition of polysaccharidedegradation by high Na. This change was not observed in the10 mol m^–3 Ca treatments. The results reveal a relationshipbetween the effects of high salinity on root growth and cellwall metabolism, particularly in regard to cellulose biosynthesis Key words: Gossypium hirsutum, salinity, root, cell wall     

Rehydration-induced changes in pressure-volume relationships of Artemisia tridentata Nutt. ssp. tridentata

Abstract. Pressure-volume measurements were made on Artemisia tridentata Nutt. ssp. tridentata samples rehydrated for 0, 1.5, 3, 6 or 24 h. Increasing rehydration time caused a significant increase in osmotic potential at turgor loss, cell elasiticity, and the relative water content at turgor loss, and a significant decrease in pressure potential at saturation. Osmotic potential at saturation was changed significantly by rehydration, but no consistent trend was observed. The symplastic water fraction did not differ significantly among treatments. The increase in the osmotic potential at turgor loss did not correspond with decreasing cell elasticity or synthesis of solutes. Instead, the leaf solute content remained constant suggesting a redistribution of solutes between the symplast and apoplast. Using non-rehydrated samples for pressure-volume analysis introduced errors in estimates of the symplastic water fraction, osmotic potential at full turgor, and the relative water content at turgor loss. These errors are due to uncertainties in the determination of saturated weights.     

Seasonal variation in the tissue water relations of Picea glauca

Seasonal variation in water relations of 3-yearold white spruce (Picea glauca (Moench) Voss) shoots, monitored with pressure-volume curves over 28 months, was closely related to shoot phenology and was sensitive to environmental fluctuations during both summer growth and winter dormancy. Turgor maintenance capacity was lowest during rapid shoot elongation from late May to early July; this was indicated by the lowest total turgor pressures, the highest (least negative) osmotic potentials at full turgor and the turgor loss point, the smallest differences between osmotic potentials at full turgor and the turgor loss point, the highest relative water contents at turgor loss and a linear decline in cell elasticity with decreasing turgor pressure. This suggests that the high susceptibility of white spruce seedlings to growth check after transplanting is largely attributable to the poor turgor maintenance capacity of this species in early summer.     

Critical Water Potential for Stomatal Closure in Sitka Spruce

Steady state rates of net photosynthesis and stomatal conductance at high water potentials were measured under controlled conditions in a leaf chamber on Sitka spruce [Picea sitchensis (Bong.) Carr.] shoots detached from the forest canopy or on seedlings. The water supply to the seedlings was terminated by excision and the shoot water potential (or critical water potential) and osmotic potential at the onset of stomatal closure measured. The turgor potential was calculated. The initial osmotic potential before insertion of the shoot into the chamber was also measured. Shoot water potential and osmotic potential at stomatal closure, and initial osmotic potential were significantly higher (less negative) in foliage from the lowest level in the canopy compared with foliage in the upper canopy, and higher in shoots of seedlings transferred to low light than in those at high light. Critical water potential also varied with season, being higher in July than in October and November. In all except one instance, turgor potential at the onset of stomatal closure was negative, possibly because of dilution of the cell sap by the extracellular water during the estimate of osmotic potential. Over all the experiments variation in critical water potential was correlated with variation in critical osmotic potential and, to a lesser extent, the initial osmotic potential. However, turgor potential at the critical potential varied from +0.6 to -4.6 bar. This suggests that difference in turgor between the guard cells and subsidiary cells, which controls stomatal aperture, is only loosely coupled with the bulk leaf turgor and hence that bulk leaf turgor is not a good index of the turbor relations of the guard cells.     

Salinity tolerance of Cornus sericea seedlings from three provenances

Red-osier dogwood (Cornus sericea L.) seedlings from three seed sources of different climatic conditions were treated hydroponically with 0?C100?mM NaCl to compare their salinity tolerance. The control seedlings from the coldest location, Alberta (AB) had the lowest biomass and transpiration rate, as well as the highest photosynthetic water use efficiency. When exposed to 100?mM NaCl for 1?week, the seedlings from AB maintained a higher photosynthetic rate and stomatal conductance than the seedlings from the low precipitation location, British Columbia (BC), and the high precipitation location, New Brunswick (NB). After 2?weeks of treatment at this highest salt concentration, leaf injury occurred in the plants from all the locations suggesting that in spite of early differences, the seedlings from all locations may not be able to survive the salinity stress over time. In contrast, when plants were exposed to 50?mM NaCl, the seedlings from AB had low level of leaf injury, followed by the plants from BC compared with the NB seedlings. Furthermore, at this moderate salt concentration, the seedlings from NB (with the highest biomass for the control) had the lowest root relative growth rate and the highest leaf area; while the seedlings from AB and BC had the highest photosynthetic water use efficiency. The seedlings from AB were able to retain more K in the roots than the seedlings from NB, suggesting a higher level of salinity tolerance. Lower chloride content was observed in the leaves of the AB seedlings than in the BC seedlings. The results of this study show that when exposed to 50?mM NaCl, the seedlings from the cold (AB) and dry (BC) locations had higher salt tolerance than the seedlings from the milder climate (NB). These results suggest that cross tolerance may occur in red-osier dogwood; however, it varies depending on the level of salinity stress.     

Endophytic and epiphytic phyllosphere fungi of red-osier dogwood (<Emphasis Type="Italic">Cornus stolonifera</Emphasis>) in British Columbia

Endophytic and epiphytic phyllosphere fungi associated with red-osier dogwood (Cornus stolonifera), a deciduous shrub, were examined in coastal British Columbia, Canada. Current-year shoots were divided into four types based on the absence or presence of inflorescence and secondary elongated shoots at the apex of primary shoots. Leaves on these shoots were then classified into six categories so as to examine the effect of flowering, secondary shoot elongation, and shoot order within current-year shoots on the occurrence of phyllosphere fungi. Species composition of fungi was markedly different between the interior and surface of leaves, whereas it was relatively similar among the six leaf categories in the interior or on the surface. Frequencies of the eight major species were not different between leaves on flowering and nonflowering shoots. The frequency of Colletotrichum gloeosporioides in the leaf interior was greater on leaves on the primary shoots that elongated the secondary shoots than on those that did not, and was greater on leaves on the primary shoots than on those on the secondary shoots. On the other hand, secondary shoot elongation and shoot order had no effect on the frequencies of C. gloeosporioides and the other seven epiphytes on leaf surfaces.     

Probing the mechanical contributions of the pectin matrix: Insights for cell growth

The plant cell wall has a somewhat paradoxical mechanical role in the plant: it must be strong enough to resist the high turgor of the cell contents, but at the right moment it must yield to that pressure to allow cell growth. The control of the cell wall's mechanical properties underlies its ability to regulate growth correctly. Recently, we have reported on changes in cell wall elasticity associated with organ formation at the shoot apical meristem in Arabidopsis thaliana. These changes in cell wall elasticity were strongly correlated with changes in pectin matrix chemistry, and we have previously shown that changes in pectin chemistry can dramatically effect organ formation. These findings point to a important role of the cell wall pectin matrix in cell growth control of higher plants. In this addendum we will discuss the biological significance of these new observations, and will place the scientific advances made possible through Atomic Force Microscopy-based nano-indentations in a relatable context with past experiments on cell wall mechanics.     

Effects of hypergravity on growth and cell wall properties of cress hypocotyls

Elongation growth of etiolated hypocotyls of cress (Lepidium sativum L.) was suppressed when they were exposed to basipetal hypergravity at 35 x g and above. Acceleration at 135 x g caused a decrease in the mechanical extensibility and an increase in the minimum stress-relaxation time of the cell wall. Such changes in the mechanical properties of the cell wall were prominent in the lower regions of hypocotyls. The amounts of cell wall polysaccharides per unit length of hypocotyls increased under the hypergravity condition and, in particular, the increase in the amount of cellulose in the lower regions was conspicuous. Hypergravity did not influence the neutral sugar composition of either the pectin or the hemicellulose fraction. The amount of lignin was also increased by hypergravity treatment, although the level was low. The data suggest that hypergravity modifies the metabolism of cell wall components and thus makes the cell wall thick and rigid, thereby inhibiting elongation growth of cress hypocotyls. These changes may contribute to the plants' ability to sustain their structures against hypergravity.     

The relative contribution of elastic and osmotic adjustments to turgor maintenance of woody species.

To determine how tissue water relations vary and contribute to turgor maintenance in species from contrasting ecological zones, seedlings of jack pine ( Pinus banksiana Lamb.), black spruce ( Picea mariana [Mill] B.S.P.) and flooded gum ( Eucalyptus grandis W. Hill ex Maiden) were subjected to an 8 day drought stress by water withholding with and without prior mild water stress conditioning. Jack pine, a deep-rooted species from dry, sandy boreal sites, lost turgor at the lowest relative water content (75–65%) and water potential, and had lowest maximum bulk elastic modulus (E_max of 5.2–5.8 MPa). Although this suggests a high inherent dehydration tolerance, jack pine did not further adjust its elasticity when repeatedly stressed. Black spruce, a shallow-rooted species from predominantly moist sites in the boreal region, lost turgor at intermediate relative water content (86–76%) and water potential, but could adjust its elasticity to maintain turgor in repeatedly stressed tissues. Flooded gum, a deep-rooted species from moist, warm temperate-subtropical regions, had a low inherent drought tolerance since it lost turgor at higher relative water content (88–84%) and water potential, but was capable of some adjustment when the stress was repeated. Elastic adjustment (<3.7 MPa) was more important for turgor maintenance than osmotic adjustment (<0.13 MPa), which was statistically nonsignificant. Maximum bulk modulus of elasticity, but not osmotic potentials at full turgor, was significantly correlated with the relative water content and water potential at zero turgor in droughted seedlings. These results highlight the importance of tissue shrinkage for dehydration tolerance. Both the inherent capacity for turgor maintenance of a species under drought and its ability to adjust to repeated drought should be considered in genetic selections for drought tolerance.     

Symplast Volume, Turgor, Stomatal Conductance and Growth in Relation to Osmotic and Elastic Adjustment in Droughted Sugarcane1

Leaf water relations, stomatal conductance (g) and shoot growthrate (SGR) were monitored during a soil drying cycle in threesugarcane cultivars growing in pots in a greenhouse. The pressure-volumetechnique was used to evaluate diurnal and droughtinduced variationin leaf water relations characteristics. Leaf solute contentand bulk elasticity varied diurnally in both irrigated and droughtedplants and were highest at midday. Solute accumulation and increasedelasticity were also observed as leaf water deficits developedmore slowly during soil drying. This osmotic and elastic adjustmentmaintained symplast volume essentially constant both diurnallyand during soil drying, whereas turgor was only partially maintained.The extent of osmotic adjustment associated with drought wasnot reflected in the leaf osmotic potential at full turgor becausethe concurrent increase in tissue elasticity resulted in a largersymplast volume at full turgor. Cultivar responses over therange of leaf water deficits imposed did not provide conclusiveevidence for genotypic variation in osmotic and elastic adjustment.It appeared that behavioural differences in rates of water usemay have determined the magnitude of osmotic and elastic adjustmentin response to drought. In the early stages of soil drying,reductions in SGR and g were not accompanied by significantreductions in bulk leaf water status. This suggested that otherfactors, presumably signals originating from the roots, mayhave regulated SGR and g.     

Leaf morphology and water status changes in Triticum durum under water stress

Water relations, leaf morphology and the chemical composition of cell walls in irrigated and unirrigated plants of three durum wheat eultivars were measured at two growth stages (booting and flowering). Plant response to water stress differed at the two stages: cell wall elasticity increased at booting and osmotic potential values decreased at flowering; this may be due to the changes in stress history, leaf development and plant growth stage between the two harvests. Leaf tissue characteristics were modified by water stress only at flowering: accumulation of fibrous constituents and hemicellulose in the cell walls, reduction of acid detergent fiber (ADF) per unit of leaf area, increase in specific leaf weight (SLW), decrease in turgid weight/dry weight ratio (TW/DW) and alteration in mesophyll cell morphology (cell area / ceil perimeter ratio) were observed.
Generally, cv. Valforte (the less drought-resistant cultivar) had the greatest mesophyll cell area and perimeter and it had greater values of neutral detergent fiber (NDF) at the booting stage than cv. Appulo. Reactivity to water stress differed in the eultivars: Valforte showed the greatest increase in hemicellulose content and decrease in cell dimensions under drought at flowering.
No significant relationships between osmotic potential and mesophyll cell characters were observed; there were no correlations among cell wall elasticity, cell morphology and the chemical components of leaf tissue. The total fiber content and the hemicellulose per unit of leaf area were correlated with the TW/DW ratio at flowering. This parameter decreased more in plants subjected to water stress owing to accumulation of hemicellulose. Correlations between leaf structural constituents and $$ suggest that the absorptive capacity of the cell wall may significally affect the osmotic volume of the cell.     

Turnover of cell-wall polysaccharides during somatic embryogenesis and development of celery (Apium graveolens L.)

Non-embryogenic cells (NEC) and embryogenc cells (EC) were separated from cell clusters derived from the hypocotyl segments of celery seedlings, which had been suspension-cultured in MS medium supplemented with 10⁵ M 2,4-D. The EC formed globular embryos in medium without 2,4-D. The globular embryo developed through heart-shaped, torpedo to cotyledonary embryos within 10 days. The EC and developing embryos were fractionated into symplastic [MeOH, hot water (HW), starch (S)] and apoplastic [pectin, hemicellulose, TFA (trifluoroacetic acid)-soluble and cellulose] fractions. The EC contained lower levels of sugar in the MeOH fraction and higher levels of starch than NEC. In the apoplastic fractions, there were no differences of total sugar amounts between NEC and EC. Cellulose contents were about 10% of the wall polysaccharides. During somatic embryogenesis, total sugar contents of the MeOH and HW fractions increased till the heart-shaped embryo stage, and then decreased during the torpedo and cotyledonary embryo stages. The sugar contents of the starch, pectin, TFA-soluble, and cellulose fractions did not change during the stages mentioned above. However, the hemicellulose substances remarkably increased during embryogenesis, and then decreased as the development proceeded. The neutral sugar components of the hemicellulosic fractions were analyzed. Arabinose increased markedly in EC to the globular embryo stage, but decreased as the development proceeded. Galactose increased only at the torpedo and cotyledonary embryo stages. Xylose was present at lower levels in all stages of embryogenesis than in the differentiated hypocotyl cell walls. These results suggest that there was a high turnover of arabinogalactan polysaccharides during embryogenesis, and that xylan accumulated in the cell walls of differentiated cells     

Genotypic variation in tissue water relations of leaves and roots of black walnut (Juglans nigra) seedlings

Genetic variation in the drought response of leaf and root tissue water relations of seedlings of eight sources of black walnut ( Juglans nigra L.) was investigated using the pressure-volume technique. Tissue water relations were characterized at three stages of a drying cycle during which well-watered plants were allowed to desiccate and then were reirrigated.
Sources varied both in the capacity for and degree of leaf and root osmotic adjustment, and in the mechanism by which it was achieved. A decrease in osmotic potential at the turgor loss point (ψ_πp) of 0.4 MPa was attributable to increased leaf tissue elasticity in seedlings of four sources, while seedlings of an Ontario source exhibited a 0.7–0.8 MPa decline in ψ_πp as a result of both increased solute content and increased leaf tissue elasticity. Seedlings of a New York source showed no detectable osmotic adjustment.
In roots, decreased ψ_πp (osmotic potential at full hydration) and ψ_πp were observed under drought. Sources that exhibited significant leaf osmotic adjustment also generally showed a similar response in roots. Tissue elasticity and ψ_πp of roots were higher than those of shoots, whereas ψ_πp of the two organs was similar for most sources. Because of greater elasticity, roots exhibited a more gradual decline in turgor and total water potential than did leaves as tissue relative water content decreased.     

Induction of Frost Hardiness in Stem Cortical Tissues of Cornus stolonifera Michx. by Water Stress: II. Biochemical Changes

A decrease of protein, RNAs, and starch, and an increase of sugar were observed in 3-day water-stressed red osier dogwood plants (Cornus stolonifera Michx.) when the frost hardiness increased from −3 to −6 C. As the frost hardiness increased to −11 C after 7 days of treatment, the starch continuously decreased, however, the proteins and RNAs increased with a continuous increase of sugar. Further water stress treatment had little effect on the changes of these chemicals. Control plants in short days showed similar gradual biochemical changes in patterns. From the results of frost hardiness increases, the pattern of biochemical changes, and the mechanism of the increased freezing resistance, it appears that the water stress and short days accomplished essentially the same physiological end(s) in inducing frost hardiness in red-osier dogwood.