Indirect Compartmental Analysis of Copper in Live Ryegrass Roots; Comparison with Model Systems

The technique of indirect compartmental analysis of ⁶⁴Cu elutionmeasurements was applied to cellulose discs, a ryegrass (Loliumperenne L. cv. Premo) root cell wall isolate and live and deadroots of whole ryegrass seedlings. Curves of logarithm countsremaining in the material versus time resolved into four phasesin each case. The half-time of exchange of the slowest compartmentranged from 3.6 to 66.1 h for cellulose discs and live ryegrassroots, respectively. Plots of logarithm efflux versus time againresolved into four phases for cellulose discs, isolated rootcell wall, and dead ryegrass roots; the efflux of these materialsobeyed first order kinetics. In live ryegrass roots the plotof logarithm efflux versus time could not be resolved beyondthe initial curve; efflux from live ryegrass roots did not obeyfirst order kinetics. A full compartmental analysis of copperin live ryegrass roots could not be performed. It is suggestedthat, in live ryegrass roots, cell wall adsorption sites areresponsible for a wide continuous range of half-time of exchangevalues which overlie the elution curves of the vacuolar andcytoplasmic compartments. The technique of indirect compartmentalanalysis artificially splits the total elution curve into fourdiscrete compartments, the slowest of which has contributionsfrom both the vacuole and cell wall. Key words: Copper efflux, cell wall, ryegrass     

Modifying Effects of Non-toxic Levels of Aluminium on the Uptake and Transport of Phosphate in Ryegrass

Apparent uptake and transport of H₂³²PO₄^– from nutrientsolutions containing 100 mmol m^–3 phosphate were characterizedasfunctions of time, concentration and pH in ryegrass seedlings.On a log/log plot, concentration versus uptake to the root resolvedintotwo linear phases, suggesting a change in uptake mechanism orefflux at the break. These results were compared with thosefor ³²P uptake and transport in solutions containing Al rangingfrom 0–185 mmol m^–3. Al addition depressed pH, butbecauseuptake of P was unaffected by pH below 5–0, noadjustments were attempted. Uptake time-courses revealed clearlythe usualinitial adsorption shoulder in the uptake curve, increasingwith Al concentration up to 37 mmol m^–3. Beyond about2 h, P uptaketo the root became linear, at rates increasingwith external Al concentration up to 37 mmol m^–3. Concentrationsof Al muchabove 100 mmol m^–3 were toxic. Al treatmentsdid not affect P transport to the shoot and absorbed Al wasconfined to the root.The quantities of P and Al taken up intothe root indicated storage in cortex cell vacuoles, lockingup significant amounts of P.Experiments with tillering plantsshowed similar characteristics to those with seedlings. Sequesteringof P with Al within the rootcortex cells was evident, particularlyin plants which had been grown in nutrient containing Al fromsoon after germination. Aland P solution chemistry is discussedin the context of this work and the consequences of effectson P uptake for the economy ofphosphate poor upland soils wereconsidered. Key words: Phosphate, aluminium, adsorption, uptake, Lolium perenne L     

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     

Distribution of polycyclic aromatic hydrocarbons in subcellular root tissues of ryegrass (Lolium multiflorum Lam.)

Background

Because of the increasing quantity and high toxicity to humans of polycyclic aromatic hydrocarbons (PAHs) in the environment, several bioremediation mechanisms and protocols have been investigated to restore PAH-contaminated sites. The transport of organic contaminants among plant cells via tissues and their partition in roots, stalks, and leaves resulting from transpiration and lipid content have been extensively investigated. However, information about PAH distributions in intracellular tissues is lacking, thus limiting the further development of a mechanism-based phytoremediation strategy to improve treatment efficiency.

Results

Pyrene exhibited higher uptake and was more recalcitrant to metabolism in ryegrass roots than was phenanthrene. The kinetic processes of uptake from ryegrass culture medium revealed that these two PAHs were first adsorbed onto root cell walls, and they then penetrated cell membranes and were distributed in intracellular organelle fractions. At the beginning of uptake (< 50 h), adsorption to cell walls dominated the subcellular partitioning of the PAHs. After 96 h of uptake, the subcellular partition of PAHs approached a stable state in the plant water system, with the proportion of PAH distributed in subcellular fractions being controlled by the lipid contents of each component. Phenanthrene and pyrene primarily accumulated in plant root cell walls and organelles, with about 45% of PAHs in each of these two fractions, and the remainder was retained in the dissolved fraction of the cells. Because of its higher lipophilicity, pyrene displayed greater accumulation factors in subcellular walls and organelle fractions than did phenanthrene.

Conclusions

Transpiration and the lipid content of root cell fractions are the main drivers of the subcellular partition of PAHs in roots. Initially, PAHs adsorb to plant cell walls, and they then gradually diffuse into subcellular fractions of tissues. The lipid content of intracellular components determines the accumulation of lipophilic compounds, and the diffusion rate is related to the concentration gradient established between cell walls and cell organelles. Our results offer insights into the transport mechanisms of PAHs in ryegrass roots and their diffusion in root cells.     

Inhibition of the biosynthesis of plant cell wall materials, especially cellulose biosynthesis, by coumarin

Coumarin in a concentration range from of 10–100 ppm inhibitedthe growth of rice, mung bean, lettuce and clover seedlings.These growth inhibitions were accompanied by remarkable tissueswelling in the stem-base and root tip zones. Microscopic observationof the swollen tissue showed that there was no increase in cellnumber, but swelling of individual cells was observed. In aconcentration range of 25–100 ppm, coumarin increasedthe fresh weight of plumular hook sections of mung bean, butdecreased the dry weight. This phenomenon indicates that abnormalwater-imbibition by cells occurs as an effect of coumarin. Inaddition, 25 ppm of coumarin noticeably induced wilting in thenewly developing leaves of rice plants. With plumular hook sectionsof mung bean, 100 ppm of coumarin did not affect the incorporationof ¹⁴C-glucose into the cytoplasm, but did inhibit its incorporationinto the cell wall by about 30%. Of the inhibition ratios for¹⁴C-glucose incorporation into the cell wall fraction, thatinto cellulose was conspicuous at about 70%, while ratios intoother cell wall fractions were less than 10%. It has also beendemonstrated that the inhibition of ¹⁴C-glucose incorporationinto cellulose by coumarin is due to the inhibition of its biosynthesisand not to a stimulation of its breakdown. The relation of theinhibition of cellulose biosynthesis by coumarin to the inductionof cell swelling is discussed, illustrating coumarin's effecton isolated root cells of soybean. ¹Present address: International Rice Research Institute, P.O. Box 1300, M. C. C, Makati, Philippines. ²Present address: Nippon Roche Research Center, Kamakura, Japan. (Received July 12, 1972; )     

Bioregulator enhancement of sink activity in sugar beet

The sink mobilizing abillity is partially determined by sugar uptake rates of storage cells. Two synthetic growth regulators (Pix and BAS 106W) were tested for their effect on sucrose uptake in root tissue discs or glucose uptake in cell cultures of sugar beet. In tissue discs, uptake at the plasmalemma was determined by incubating the discs for 1 h in the presence of 5 mM sucrose and at the tonoplast for 4 h in the presence of 40 mM sucrose. Cell cultures were incubated for 1 h in the presence of 1 mM glucose. Pix (10 mg l^–1) caused a 20% stimulation of active sucrose uptake at the plasmalemma. Active sucrose uptake at the tonoplast was increased 67% by 100 mg l^–1 Pix. No effect of BAS 106W was observed on sucrose uptake in tissue discs. In cell cultures, a 65% enhancement of active glucose uptake was observed with both Pix and BAs 106W. When the bioregulators were applied to the root medium of seedlings, Pix but not BAS 106W resulted in increased root/shoot ratio, translocation of ¹⁴C-assimilates, and allocation of more biomass to the root sink. The data suggested that sugar transport and translocation may be used as biochemical criteria for rapid screening of effective yield enhancing bioregulators.     

Mating type specific induction of cell wall lytic factor by agglutination of gametes in Chlamydomonas reinhardtii

When mt⁺ and mt^– gametes of Chlamydomonas reinhardtiiwere mixed, shedding of cell walls took place in both matingtypes during massive agglutination and/or pairing. This wascaused by a cell wall lytic factor that had been induced byflagellar agglutination and excreted into the medium by cellsconcurrently with their cell wall release. When glutaraldehyde-fixed gametes and isolated flagella of onemating type caused isoagglutination of live gametes of the othermating type, the live mt⁺ gametes induced the lytic factor andshed their walls, whereas none of the live mt^– did this.The cell walls of mt^– gametes were lost only when thelytic factor, which had been excreted by mt⁺ gametes into themedium, acted from the outside. These data imply that mt⁺ gametesare responsible for the induction of the lytic factor by agglutination,which acts on cell walls of both mating types either endogenouslyor exogenously. (Received February 28, 1978; )     

Biosorption of cadmium,copper and lead by isolated mother cell walls and whole cells of Chlorella fusca

Using a new method for the isolation of released mother cell walls of Chlorella fusca, the biosorption of cadmium, copper and lead by purified cell wall isolates and whole cell suspensions was comparatively characterized. In all cases whole cells accumulated more metal ions than isolated cell walls. Both the Langmuir and Freundlich isotherm models were suitable for describing the short-term adsorption of cadmium, copper and lead by cell walls and the cadmium and copper adsorption by whole cells. However, neither model could sufficiently explain the lead accumulation by whole cells. The feasibility of a practical use of whole cells or isolated cell walls as biosorbents is discussed.     

The Effect of Low Osmotic Potential on Phosphate Uptake and Metabolism by Beetroot Discs

The uptake of phosphate by aged beetroot discs was examinedunder a range of water deficits which were induced osmoticallywith mannitol or polyethylene glycol At low water potentialsthe absorption of labelled phosphate was enhanced when the ambientconcentration of phosphate was high (10^–3 M) and the timefor absorption was short (30 mm): this occurred even when themetabolism was inhibited (by the water deficit), as indicatedby lowered oxygen consumption and incorporation of ³³P intohexose-phosphate, phosphoglycenc acid, a liquid fraction, anda precipitate consisting mainly of cell walls. The Q₁₀ of theuptake process approached unity at these low water potentials.Accompanying the enhanced uptake there was an increase in leakageof previously absorbed phosphate. It is postulated that thestimulation in uptake of phosphate in low osmotic potentialswas due to an increase in permeability Over long periods (6 h) uptake was inhibited by treatment atlow osmotic potentials. This is interpreted in terms of inhibitionof a metabolic component of phosphate uptake.     

Crystalline Cellulose in Hydrated Primary Cell Walls of Three Monocotyledons and One Dicotyledon

The molecular ordering of cellulose, including its crystallinity,in the unlignified primary cell walls of three monocotyledons(Italian ryegrass, pineapple, and onion) and one dicotyledon(cabbage) was characterized by solid-state ¹³C NMR spectroscopy.These species were chosen because their primary cell walls havedifferent non-cellulosic polysaccharides and this may affectthe molecular ordering of cellulose. Values of the proton rotating-framerelaxation [T_1p(H)] and spin-spin relaxation [T₂(H)] time constantsshowed that the cellulose in the cell walls of all four specieswas in a crystalline rather than an amorphous state. Furthermore,a resolution enhancement procedure showed that the triclinic(I) and the monoclinic (I_rß) crystal forms of cellulosewere present in similar proportions in these cell walls. However,the calculated cross-sectional dimensions of the cellulose crystallitesvaried among the cell walls (in the range 2–3 nm): thelargest were in the Italian ryegrass, the smallest were in theonion and cabbage, and those of intermediate size were in thepineapple. The crystallite dimensions may thus be affected bythe non-cellulosic polysaccha-ride compositions of the cellwalls. ⁴Present address: Food Science Postgraduate Programme, Departmentof Chemistry, The University of Auckland, Private Bag 92019,Auckland, New Zealand.     

Ion Absorption and Allocation of Carbon Resources in Excised Pea Roots Grown in Liquid Medium in Absence or Presence of NaCl

Freshly excised pea roots (Pisum sativum cv. Alaska) when transferredto growth medium (130 mOsm) or growth medium containing salt( 370 mOsm) suffer an initial osmotic shock and lose water.Contol roots tended to accumulate potassium, particularly inthe apical zone, while those exposed to NaCl accumulated mainlysodium, potassium accumulation being depressed. Exposure tosalinity for 6 d caused increases in root protein, cellulose,uronic acid and lignin content per cell. In roots supplied with¹⁴C-glucose for 24 h immediately after excision there was littledifference in uptake of glucose and in its use in respirationbetween control and salt treated roots. However, there werenoticeable differences in incorporation of labelled carbon intoseveral cell fractions, and particularly into the cellulosefraction in the upper parts of the root. When roots were grownfor six days in culture before being supplied with [¹⁴C]glucose,uptake per root was greater in the 120 mM NaCl treatment, andthe fraction diverted to respiration was decreased by salinity.On a per cell basis incorporation into soluble starch, uronicacid and cellulose fractions was increased in the salt treatedroots. The data obtained are in accord with the previous findingsand are suggestive of increased synthesis of cell wall materials.No conclusion could be drawn as to whether the changes describedare of adaptive value. Pisum sativum L. cv. Alaska, root culture, salinity, osmoregulation, cell wall     

The Uptake and Distribution of Copper in Some Forage Grasses as Affected by Nitrate-nitrogen Supply in Flowing Solution Culture

The effect of changes in nitrate-nitrogen supply on the absorptionand distribution of copper was examined in grasses grown inflowing solution culture with a maintained concentration ofcopper. Absorption by roots (µg Cu g^–1 dry root)decreased markedly when nitrogen had been depleted or was maintainedat 0.1 mg l^–1 N, but there was an immediate increase whennitrogen was maintained at 1.0 or 10.0 mg l^–1. There werealso large increases in the concentration of copper in the shootsof plants grown with 1.0 and 10.0 mg 1^–1 N. The rootsof plants grown with 0.1 or 1.0 mg 1^–1 N retained similarproportions of uptake, but a lower proportion was retained whenthe plants were grown with 10.0 mg 1^–1. Although a lowerproportion of the copper was associated with cell walls in theplants grown at 10.0 mg 1^–1 N this was the result of alower content of cell walls rather than an effect on copperitself. In a longer-term experiment in conventional solutionculture with a range of nitrogen concentration, the concentrationof copper in shoots was largely determined by shoot growth. Dactylis glomerata, Festuca arundinacea, Lolium perenne, cell walls, copper absorption, copper distribution, flowing solution culture, nitrate-nitrogen     

硝普钠缓解镧引起的黑麦草幼苗生长抑制和根系氧化损伤

采用水培方法,研究了外源一氧化氮（NO）供体硝普钠（SNP）对300 μmol·L^-1 LaCl₃胁迫下黑麦草幼苗生长和根系活性氧代谢的影响。结果表明：在LaCl₃胁迫下,喷施50 μmol·L^-1 SNP能够抑制镧（La）从黑麦草根系向地上部的转运,缓解La对幼苗生长的抑制作用;提高幼苗根系超氧化物歧化酶和抗坏血酸过氧化物酶活性,降低过氧化物酶活性及谷胱甘肽、脯氨酸、H₂O₂、丙二醛含量、超氧阴离子产生速率和质膜相对透性,对过氧化氢酶活性和抗坏血酸含量无显著影响。表明NO可通过活性氧代谢的调节,缓解高浓度La胁迫对黑麦草幼苗生长的抑制作用。     

Altered Synthesis and Composition of Cell Wall of Grape (Vitis vinifera L.) Leaves during Expansion and Growth-Inhibiting Water Deficits

The rate and composition of cell wall polysaccharide synthesisduring development and growth-inhibiting water deficits wereinvestigated in leaves of grape (Vitis vinifera L.). The rateof leaf expansion was monitored as plant water status was manipulatedby modulating the supply of irrigation water to potted plantsover several days. The corresponding wall synthesis was determinedby incubating leaf tissue with [¹⁴C]glucose and quantifyingincorporation into wall components. Samples were obtained fromrapidly expanding and mature leaves before, during, and following(recovery from) moderate water deficits. Uptake was approximately2-fold greater for mature leaf tissue than for rapidly expandingtissue at both high and low water status. In contrast, incorporationinto cell wall polysaccharides was 18 to 41% (under low andhigh water status) of uptake in expanding leaves but less than4% in mature tissue. Incorporation of precursor into wall polysaccharideswas insensitive to plant water status in mature leaves, butwas inhibited to less than 50% of well-watered controls in expandingleaves at low water potential. Incorporation of label into cellulose,uronic acid, and neutral sugar fractions was differentiallyaffected by water deficits, with cellulose synthesis apparentlyexhibiting the greatest sensitivity to low water status. Afterrewatering, growth, as well as uptake and incorporation of labelrecovered, although the latter did not attain prestress rates.The results indicate a high sensitivity of wall polysaccharide(particularly cellulose) synthesis to growth-inhibiting waterdeficits. ¹ Supported by United States Department of Agriculture, CompetitiveResearch grant GAM 8502539. (Received November 15, 1989; Accepted January 17, 1990)     

The Effect of pH on the Binding of Calcium to Pea Epicotyl Cell Walls and its Implications for the Control of Cell Extension

Cell walls were prepared from the epicotyls of dark-grown pea(Pisum sativum L.) seedlings. The walls were found to bind externally-added⁴⁵Ca²⁺, with a binding constant of 4 ? 10^–4 mol dm^–3and a maximum capacity of 1.5 ? 10^–8 g-ions of Ca²⁺ perg fresh weight of epicotyl. The binding capacity decreased asthe pH of the medium was decreased below 6.0, suggesting thatthe calcium was bound by an anionic group with an apparent pKof 4.7. More than half the calcium binding was due to polygalacturonicacid in the wall, since up to 60% of the calcium binding capacitywas removed by pre-incubation of the cell walls with polygalacturonase(E.C.3.2.1.15). Only small decreases in calcium binding wereseen following pre-incubation with protease, nucleases, phospholipaseand hemicellulase. These results indicate that calcium willbe displaced from the cell wall at hydrogen ion concentrationswhich are known to occur in the wall during wall extension.They are consistent with a mechanism by which calcium inhibitswall extension by forming ionic bridges between polygalacturonicacid molecules, and also with the hypothesis that calcium andhydrogen ions exert opposing influences on cell wall extensionby competing for the same binding sites on the polygalacturonicacid. Key words: Pea epicotyl, Cell wall, Calcium, pH     

Evidence for in vitro binding of pectin side chains to cellulose

Pectins of varying structures were tested for their ability to interact with cellulose in comparison to the well-known adsorption of xyloglucan. Our results reveal that sugar beet (Beta vulgaris) and potato (Solanum tuberosum) pectins, which are rich in neutral sugar side chains, can bind in vitro to cellulose. The extent of binding varies with respect to the nature and structure of the side chains. Additionally, branched arabinans (Br-Arabinans) or debranched arabinans (Deb-Arabinans; isolated from sugar beet) and galactans (isolated from potato) were shown bind to cellulose microfibrils. The adsorption of Br-Arabinan and galactan was lower than that of Deb-Arabinan. The maximum adsorption affinity of Deb-Arabinan to cellulose was comparable to that of xyloglucan. The study of sugar beet and potato alkali-treated cell walls supports the hypothesis of pectin-cellulose interaction. Natural composites enriched in arabinans or galactans and cellulose were recovered. The binding of pectins to cellulose microfibrils may be of considerable significance in the modeling of primary cell walls of plants as well as in the process of cell wall assembly.     

Triaziflam and Diaminotriazine derivatives affect enantioselectively multiple herbicide target sites

Enantiomers of triaziflam and structurally related diaminotriazines were synthesized and their herbicidal mode of action was investigated. The compounds caused light and dark-dependent effects in multiple test systems including heterotrophic cleaver and photoautotrophic algal cell suspensions, the Hill reaction of isolated thylakoids and germinating cress seeds. Dose-response experiments revealed that the (S)-enantiomers of the compounds preferentially inhibited photosystem II electron transport (PET) and algae growth with efficacies similar to that of the herbicide atrazine. In contrast, the (R)-enantiomers of the diaminotriazines were up to 100 times more potent inhibitors of growth in cleaver cell suspensions and cress seedlings in the dark than the (S)-enantiomers. The most active compound, the (R)-enantiomer of triaziflam, inhibited shoot and root elongation of cress and maize seedlings at concentrations below 1 microM. The meristematic root tips swelled into a club shape which is typical for the action of mitotic disrupter herbicides and cellulose biosynthesis inhibitors. Microscopic examination using histochemical techniques revealed that triaziflam (R)-enantiomer blocks cell division in maize root tips 4 h after treatment. The chromosomes proceeded to a condensed state of prometaphase but were unable to progress further in the mitotic cycle. Disruption of mitosis was accompanied by a loss of spindle and phragmoplast micotubule arrays. Concomitantly, cortical microtubules decreased which could lead to isodiametric cell growth and consequently to root swelling. In addition, a decline in cellulose deposition in cell walls was found 24 h after treatment. Compared to the (R)-form, triaziflam (S)-enantiomer was clearly less active. The results suggest that triaziflam and related diaminotriazines affect enantioselectively multiple sites of action which include PET inhibitory activity, mitotic disruption by inhibiting microtubule formation and inhibition of cellulose synthesis.     

The Growth and Development of Simulated Swards of Perennial Ryegrass: I. Leaf Growth and Dry Weight Change as Related to the Ceiling Yield of a Seedling Sward

The leaf growth, tiller production, light interception, anddry weight increase of a simulated sward of S24 perennial ryegrass(Lolium perenne) were followed during the development of thesward from a collection of two-leaved seedlings to a closedcanopy with an LAI of 23, of which 15 consisted of green leaflaminae. The dry weight of live shoots increased exponentiallyat first, but then entered a long linear phase of increase.This was equivalent to a crop growth rate of 200 Kg ha^–1day^–1 and a conversion efficiency of radiant energy (400–700nm) of 7.2 per cent. Towards the end of the growth period therate of increase of live shoots declined rapidly to zero anda ceiling yield was reached equivalent to 10 metric tons ha^–1.Leaf growth continued at a high rate, but was equalled by therate of leaf death, so that the weight of live leaf tissue remainedconstant. By this time the swards had achieved a stable tillerpopulation (about 1 cm^–1), each tiller bore a constantnumber of live leaves (about three), and the length of eachnewly expanded leaf equalled the length of the old leaf it replaced(about 70 cm). The swards were grown in Perlite so that in theabsence of soil fauna dead leaves accumulated at the base ofthe sward where, after 12 weeks, they accounted for 19 per centof the total weight of dry matter produced.     

Polygalacturonase Activity in Ripening Tomato Fruit Determined using Pericarp Discs

Discs prepared from the outer pericarp of tomato (Lycopersiconesculentum Mill. cv. Sunny) and placed in buffer exhibit anenzymic release of pectin fragments. Over a 2.5 h period at34 °C, discs from mature-green, 4 d and 10 d postbreakerfruit released approximately 90, 440 and 675 µg galacturonicacid equivalents (g^–1 disc fr. wt.), respectively. Bio-GelP-2 chromatography of the products revealed the presence ofpolymeric, oligomeric and monomeric uronic acids. The similarityof these products to those released from isolated, enzymatically-activecell walls and from enzymatically-inactive walls treated withpurified PG 2 provides evidence for the participation of polygalacturonase(PG, E. C. 3.2.1.15 [EC] ) in the release of pectin from disc tissue. The magnitude of pectin release from external pericarp discswas found to parallel ripening and increase progressively indiscs from the blossom, equatorial and shoulder regions, respectively.The use of discs and other systems to estimate in vivo PG activitywill be discussed. Key words: Cell wall, polyuronides     

Effects of Calcium Ion Concentration on Cel Wall Synthesis

Cuttings of 6-week-old Norway spruce (Picea abies (L.) Karst.)seedlings were placed in liquid media containing various concentrationsof Ca²⁺. Cytoplasmic concentrations of Ca²⁺ were manipulatedusing the ionophore A 23 187. The effects of Ca²⁺ concentrationson the deposition of total cell wall material as well as onthe deposition of cellulose, lignin, and non-cellulosic polysaccharidesin the hypocotyls were investigated. At low concentrations ofCa²⁺ wall deposition was reduced, mainly as a result of theinhibition of lignin and non-cellulosic polysaccharide deposition.High concentrations of Ca²⁺ stimulated non-cellulosic polysaccharideand lignin deposition, whereas cellulose deposition was almosttotally inhibited. Key words: Conifers, calcium, cell wall, lignin, cellulose