Drought Tolerance in Two Mosses: Correlated with Enzymatic Defence Against Lipid Peroxidation

Drought-induced changes in the activities of superoxide dismutase(SOD) and catalase, level of lipid peroxidation, and membranepermeability (solute leakage) have been studied in two mosses,the drought-tolerant Tortula ruralis and the drought-sensitiveCratoneuron filicinum. In T. ruralis the activities of SOD andcatalase increase during slow drying. The level of lipid peroxidationconsequently declines. On subsequent rehydration the enzymeactivities decline and the level of lipid peroxidation risesgradually to normal levels. The leakage of preloaded ⁸⁶Rb onrehydration of slowly dried T. ruralis is similar to that inturgid moss, i.e. leakage of about 20% of tissue ⁸⁶Rb. WhenT. ruralis is subjected to rapid drying there is no change inthe enzyme activities or in lipid peroxidation. However, whenthis moss is rehydrated there is a large immediate increasein lipid peroxidation. Half of the tissue ⁸⁶Rb is leaked intothe bathing medium during the first hour of rehydration. Butwithin the next hour, when SOD and catalase activities haveincreased to high levels, lipid peroxidation quickly declinesto a level lower than that in the turgid control moss, and the⁸⁶Rb leaked earlier is partly reabsorbed indicating that membranerepair is well underway. On prolonged rehydration the enzymeactivities decline and the level of lipid peroxidation risesgradually to reach normal levels found in control turgid moss.In the case of drought-sensitive C. filicinum the activitiesof SOD and catalase decline during drying as well as duringsubsequent rehydration. There is a rapid increase in lipid peroxidationduring rehydration and most of the preloaded ⁸⁶Rb leaks intothe bathing medium irreversibly. The changes in lipid peroxidationduring drying and subsequent rehydration of both the mossesappear to coincide in time with the reported changes in O₂ uptake,indicating that the drought-induced membrane damage may be dueto free radical-induced lipid peroxidation which is known torequire active O₂ uptake. Furthermore, there appears to be agood correlation between an ability of the tissue to controllipid peroxidation and its ability to retain solutes. It issuggested that ability of plant tissues to mobilize enzymaticdefence against uncontrolled lipid peroxidation may be an importantfacet of their drought tolerance.     

Mitochondrial Interaction with Helminthosporium maydis Race T Toxin: Blocking by Dicyclohexylcarbodiimide

Treatment of mitochondria isolated from Texas male sterile cytoplasmcorn (T mitochondria) with high concentrations of dicyclohexylcarbodiimide(DCCD) (140 nmol DCCD mg^–1 mitochondrial protein) completelyand immediately inhibited T mitochondrial swelling by Helminthosporiummaydis Race T toxin (HmT toxin). In order to obtain a specificinteraction between DCCD and the ATPase complex T mitochondriawere incubated with lower DCCD concentrations (1–5 nmolDCCD mg^–1 mitochondrial protein) for up to 8 h at 4 °C.After 8 h incubation in the presence of 3.75 nmol DCCD mg^–1mitochondrial protein, toxin-induced swelling was decreasedby 69%. Specificity of DCCD action upon the ATPase complex wasconfirmed by (1) SDS gel electrophoresis and fluorographic analysesof proteins from [¹⁴C]-DCCD-treated T mitochondria and immunoprecipitatesand (2) physiological experiments showing that DCCD exertednone of its other documented effects. These data suggest thatHmT toxin interacts with the ATPase complex of T mitochondriaeither at or near the DCCD-binding protein within the membranesector of the complex. Key words: Zea mays L., Helminthosporium maydis, Mitochondria     

The concentration of selected cations in normal and crown-gall tumors obtained from potato discs

Crown-gall tumor tissue obtained from potato discs inoculatedwith virulent strains of Agrobacterium tumefadens containedhigher concentrations of K⁺, Mg²⁺ and Ca²⁺ than the correspondingnormal tissue. These tumors also contained higher concentrationsof these cations than normal tissue inoculated with an avirulentstrain of Agrobacterium tumefadens, or than normal tissue adjacentto the crown-gall tumors on the same potato disc. The concentrationof these cations remained significantly higher than controltissue regardless of the tumor age. 2,4-Dinitrophenol and myo-inositol,while affecting the concentration of Ca²⁺ in these tissues,had no effect on the Mg²⁺ and K⁺ concentrations. These resultssuggest increased concentrations of certain cations may be aspecific property of crown-gall tumors. (Received August 16, 1978; )     

Salt Tolerance in the Triticeae: The Contribution of the D Genome to Cation Selectivity in Hexaploid Wheat

Inorganic cation concentrations were measured in shoots of hexaploidbread wheat (Triticum aestivum L.) and its presumed ancestorsgrown at 100 mol m^–3 external NaCl. Aegilops squarrosaand T. aestivum had high K/Na ratios while T. dicoccoides andAe. speltoides had low K/Na ratios. T. monococcum although havinga high K/Na ratio, had the highest total salt load of the fivespecies tested. The effect of the D genome (from Ae. squarrosa)was further investigated in seedlings of synthetic hexaploidwheats, and was again found to improve cation selectivity. Differentresponses were obtained from root and shoot tissue in this experiment.One synthetic hexaploid and its constituent parents were grownto maturity at 100 mol m^-3 NaCl and the yields recorded. Despitecomplications due to increased tillering in the stressed hexaploid,it was possible to show that the addition of the D genome enhancedyield characteristics in the hexaploid wheat. An experimentwith synthetic hexaploids derived from the tetraploid wheatvariety "Langdon" and several Ae. squarrosa accessions revealeddifferences in vegetative growth rates between the differentsynthetic hexaploids in the presence or absence of 150 or 200mol m^–3 external NaCl. The possibility of transferringsalt tolerance genes from Ae. squarrosa to hexaploid wheat usingsynthetic hexaploids as bridging species is discussed. Key words: Salt stress, wheat, D genome, Aegiops squarrosa, synthetic hexaploids     

热冲击和加氯后亚热带海区浮游植物细胞数量的动态变化

 近年来, 随着电厂在河口和港湾等生态脆弱区和敏感区的急剧增多, 电厂冷却系统热冲击和加氯对浮游生物造成的伤害已成为沿海地区非常严峻的生态安全问题。为探明冷却系统升温和加氯联合作用对亚热带海区浮游植物的影响程度, 针对滨海电厂的实际运作情况, 在室内对采自浙江省乐清湾海域的四季浮游植物进行了不同水平的热冲击和加氯胁迫, 并观察了这些浮游植物细胞数量在15 d内的动态变化。结果表明, 热冲击、加氯和季节均显著影响浮游植物细胞数量的恢复(p＜0.001), 其中, 加氯的影响最大, 季节次之, 热冲击影响最小, 但热冲击增强了氯对浮游植物的毒性。自然水温越高、升温幅度越大, 细胞数量恢复越慢。春、秋、冬季自然水温较低时, 升温4～12 ℃后, 细胞数量仅需1～6 d即可恢复到对照组水平; 夏季自然水温较高, 升温4～8 ℃后, 细胞数量需4～9 d恢复到对照组水平, 但升温12 ℃后, 细胞数量在15 d内未能恢复到对照组水平。加氯浓度越高, 细胞数量恢复越慢。加氯1.0～1.8 mg•L^−1后, 浮游植物生长虽受影响, 但大多能在15 d内恢复; 而加氯5.6 mg•L^−1后, 其生长受到完全抑制, 细胞数量在15 d内未恢复到对照组水平。     

Alterations of O-glycan biosynthesis in human colon cancer tissues

Human colon cancer is associated with antigenic and structuralchanges in mucin-type carbohydrate chains (O-glycans). To elucidatethe control of the biosynthesis of these O-glycans in coloncancer, we have studied glycosyltransferase and sulphotransferaseactivities involved in the assembly of elongated O-glycan structures.We analysed homogenates prepared from cancer tissue, adjacentnormal and distal normal tissue from 20 patients. Several transferaseactivities showed pronounced changes in cancer tissue. The changescorrelate with previous findings of a loss of O-glycans in cancermucins, but did not always correlate with levels of Tn, sialyl-Tn,T and Le^x antigens in homogenates or with the differentiationstatus and Duke's stages of the cancer tissue or the patient'sblood type, sex and age. UDP-GlcNAc: Gal NAc-R ß3-N-acetylglucosaminyltransferase(where GlcNAc is N-acetyl-D-glucosamine and GalNAc is N-acetyl-D-galactosamine)synthesizing O-glycan core 3, GlcNAcß1-3GalNAc-, CMP-sialicacid: GalNAc-peptide     

UMBONIUM VESTIARIUM (L.) (GASTROPODA, TROCHACEA) AS THE FOOD SOURCE FOR NATICID GASTROPODS AND A STARFISH ON A MALAYSIAN SANDY SHORE

Umbonium vestiarium (L.) forms virtually the entire diet of3 (possibly 4) species of naticid snails and the starfish Astropectenvappa Mueller annd Troschel on some north Penang sandy shores.Umbonium comprises about 99% of numbers and tissue of macrofauna.Predation totalled some 1.75 Umbonium (ca. 33 mg dry tissue).m^-2.day^-1 across much of the downshore sand flats rising to 2.3Umbonium (ca. 45 mg). m^-2. day^-1 near MLWS. Natica maculosaLamarck comprised > 80% of the predators and took 77–94%of the Umbonium eaten. Natica antonii Phillippi alone addedto this toll on the upper reaches of the zone while Polinicesspp and Astropecten appear to have taken 12–14% of thetotal toll of Umbonium near MLWS. Total predation is indicatedat 237–327 kJ.m^-2. year^-1 across the shore and this representsalmost the total flow of energy from primary consumers to intertidalbenthic predators on such shores and accounts for some 15.6%(lower shore)—20.5% (upper shore) of total Umbonium production. (Received 10 September 1982;     

Photosynthetic carbon metabolism in wild, primitive and cultivated forms of wheat at three levels of ploidy: Role of the glycolate pathway

¹⁴CO₂ assimilation was studied with diploid, tetraploid, hexaploidspecies of the genera Triticum and their wild relatives Aegilops.Attached mature leaves of 3–4 weekold plants were allowedto undergo photosynthesis under air at ambient temperature.The pattern of distribution of ¹⁴C was notably similar in Triticumand Aegilops species whatever the level of ploidy. Sucrose wasthe sink for photosynthetic carbon. ¹⁴C for sucrose synthesis was supplied either through the glycolatepathway by glycolate, the product of the photorespiration orby the Calvin cycle intermediates exported into the cytoplasm.Depending on the species, the glycolate pathway provided 40to 75%of the sucrose ¹⁴C. The higher labeling of sucrose was associated with the greaterparticipation of the glycolate pathway in the wild diploid (DD)A. squarrosa and in the cultivated hexaploid (AABBDD) T. aestivum.The results suggest that the expression of the male D genomeis dominant over the female AB genome in T. aestivum. In T. aestivum under ambient conditions lowering (low temperature)or hindering (1% O₂ ) photorespiration, sucrose labeling decreased,but serine and glycine labeling was favoured. We propose thatin wheat leaves, the role of photorespiration is to drain artof the carbon exported from the chloroplast as glycolate, towardssucrose synthesis. (Received March 16, 1979; )     

Feeding of planktonic rotifers on ciliates: a method using natural ciliate assemblages labelled with fluorescent microparticles

A method was developed to allow direct measurements of predationexerted by metazooplankton on ciliates. The method relied onthe use of ciliates labelled with fluorescent microparticles(FMP). Optimal labelling conditions were determined with ciliatesfrom cultures (Tetrahymena pyriformis) and with natural ciliateassemblages sampled in a river. Labelled T. pyriformis wereused as tracer food to determine gut passage time (GPT) andingestion rates of the rotifer Brachionus calyciflorus in thelaboratory. Predation of metazooplankton from the lowland riverMeuse (Belgium) was determined by labelling natural assemblagesof ciliates and using them as tracer food for metazooplankterssampled in the river. Optimal labels of ciliates, i.e. sharpdistribution of FMP in cells, were obtained with short incubations(10 min) and low FMP concentrations (1 x 10⁵ mL^–1). GPTvaried between 30 and 45 min for B. calyciflorus and from 25up to >35 min for rotifers from the river. The ingestionrate of B. calyciflorus fed with T. pyriformis was 3.3 ±0.6 ciliate rot^–1 h^–1, i.e. 1.4 ± 0.3 ngCrot^–1 h^–1. Metazooplankton species for which theingestion of ciliates could be measured were the rotifers Keratellacochlearis, Euchlanis dilatata and Synchaeta spp. Ingestionrates measured ranged from 0.4 to 12.5 ngC rot^–1 h^–1.The method proposed proved to be useful in estimating the predationof microplankton on ciliates in semi- in situ conditions; infurther developments, labelled natural assemblages of ciliatescould be used for in situ incubations with the Haney chamber.     

Comparative mapping of HKT genes in wheat, barley, and rice, key determinants of Na+ transport, and salt tolerance

Salt tolerance of plants depends on HKT transporters (High-affinityK⁺ Transporter), which mediate Na⁺-specific transport or Na⁺-K⁺co-transport. Gene sequences closely related to rice HKT geneswere isolated from hexaploid bread wheat (Triticum aestivum)or barley (Hordeum vulgare) for genomic DNA southern hybridizationanalysis. HKT gene sequences were mapped on chromosomal armsof wheat and barley using wheat chromosome substitution linesand barley–wheat chromosome addition lines. In addition,HKT gene members in the wild diploid wheat ancestors, T. monococcum(A^m genome), T. urartu (A^u genome), and Ae. tauschii (D^t genome)were investigated. Variation in copy number for individual HKTgene members was observed between the barley, wheat, and ricegenomes, and between the different wheat genomes. HKT2;1/2-like,HKT2;3/4-like, HKT1;1/2-like, HKT1;3-like, HKT1;4-like, andHKT1;5-like genes were mapped to the wheat–barley chromosomegroups 7, 7, 2, 6, 2, and 4, respectively. Chromosomal regionscontaining HKT genes were syntenic between wheat and rice exceptfor the chromosome regions containing the HKT1;5-like gene.Potential roles of HKT genes in Na⁺ transport in rice, wheat,and barley are discussed. Determination of the chromosome locationsof HKT genes provides a framework for future physiological andgenetic studies investigating the relationships between HKTgenes and salt tolerance in wheat and barley. Key words: Barley, comparative mapping, HKT, rice, salt tolerance, sodium transport, wheat     

Ca(2+) regulates fluid shear-induced cytoskeletal reorganization and gene expression in osteoblasts

Osteoblasts subjected to fluid shearincrease the expression of the early response gene, c-fos, andthe inducible isoform of cyclooxygenase, COX-2, two proteins linked tothe anabolic response of bone to mechanical stimulation, in vivo. Theseincreases in gene expression are dependent on shear-induced actinstress fiber formation. Here, we demonstrate that MC3T3-E1osteoblast-like cells respond to shear with a rapid increase inintracellular Ca²⁺ concentration([Ca²⁺]_i) that wepostulate is important to subsequent cellular responses to shear. Totest this hypothesis, MC3T3-E1 cells were grown on glass slides coatedwith fibronectin and subjected to laminar fluid flow (12 dyn/cm²). Before application of shear, cells were treatedwith two Ca²⁺ channel inhibitors or various blockers ofintracellular Ca²⁺ release for 0.5-1 h. Althoughgadolinium, a mechanosensitive channel blocker, significantly reducedthe [Ca²⁺]_i response, neithergadolinium nor nifedipine, an L-type channel Ca²⁺ channelblocker, were able to block shear-induced stress fiber formation andincrease in c-fos and COX-2 in MC3T3-E1 cells. However, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraaceticacid-AM, an intracellular Ca²⁺ chelator, or thapsigargin,which empties intracellular Ca²⁺ stores, completelyinhibited stress fiber formation and c-fos/COX-2 production in shearedosteoblasts. Neomycin or U-73122 inhibition of phospholipase C, whichmediates D-myo-inositol 1,4,5-trisphosphate (IP₃)-induced intracellular Ca²⁺ release, alsocompletely suppressed actin reorganization and c-fos/COX-2 production.Pretreatment of MC3T3-E1 cells with U-73343, the inactive isoform ofU-73122, did not inhibit these shear-induced responses. These resultssuggest that IP₃-mediated intracellular Ca²⁺release is required for modulating flow-induced responses in MC3T3-E1 cells.

     

Cadaver validation of skeletal muscle measurement by magnetic resonance imaging and computerized tomography

Magnetic resonance imaging (MRI) and computerizedtomography (CT) are promising reference methods for quantifying wholebody and regional skeletal muscle mass. Earlier MRI and CTvalidation studies used data-acquisition techniques and data-analysisprocedures now outdated, evaluated anatomic rather than adiposetissue-free skeletal muscle (ATFSM), studied only the relatively largethigh, or found unduly large estimation errors. The aim ofthe present study was to compare arm and leg ATFSM cross-sectional areaestimates (cm²) by usingstandard MRI and CT acquisition and image-analysis methods withcorresponding cadaver estimates. A second objective was to validate MRIand CT measurements of adipose tissue embedded within muscle(interstitial adipose tissue) and surrounding muscle (subcutaneousadipose tissue). ATFSM area (n = 119)by MRI [38.9 ± 22.3 (SD)cm²], CT (39.7 ± 22.8 cm²), and cadaver (39.5 ± 23.0 cm²) were not different(P > 0.001), and both MRI and CTestimates of ATFSM were highly correlated with corresponding cadavervalues [MRI: r = 0.99, SE of estimate (SEE) 3.9 cm²,P < 0.001; and CT:r = 0.99, SEE = 3.8 cm²,P < 0.001].Similarly good results were observed between MRI- and CT-measured vs.cadaver-measured interstitial and subcutaneous adipose tissue. ForMRI-ATFSM the intraobserver correlation for duplicate measurements invivo was 0.99 [SEE = 8.7 cm²(2.9%), P < 0.001]. Thesefindings strongly support the use of MRI and CT as reference methodsfor appendicular skeletal muscle, interstitial and subcutaneous adiposetissue measurement in vivo.

     

Time to Seed Death as a Function of the Gibbs Free Energy of Water Vapour: Practical and Theoretical Implications

Time (t) to loss of seed viability (e.g. log t or log ) is modelledin the literature as the sum of a moisture term and a quadratictemperature term, f(T,T²). The coefficients inf(T,T²) have beenshown to be ‘identical’ in orthodox seeds. I postulatethat this identity is due to a parameter common to all seedsand, consistent with that hypothesis, report a close correlation(R²=0.9998) between f(T,T²) and the Gibbs free energy of watervapour, G, over the temperature range 0–90 °C. Thehypothesis has the statistical advantage of reducing the numberof independent variables from two to one, without changing thefit. This is demonstrated from analysis of data for lettuceand barley. An explanation for this correlation of time to seeddeath with G is that water vapour is the proximate source ofenergy leading to decomposition of individual molecules, withthe ultimate result of seed death. Copyright 1999 Annals ofBotany Company Seed longevity, temperature effect, Gibbs free energy of water vapour, moisture-temperature interactions, Hordeum vulgare L., barley, Lactuca sativa L., lettuce.     

Inhibition of Sugar and Salt Elimination by Glands with the Amino Acid Analog p-Fluorophenylalanine

The amino acid analog p-fluorophenylalanine (FPA) inhibitedsugar and K⁺ secretion by nectary glands. FPA specifically reducedthe net excretion of Na⁺ and Cl^– by the salt glands ofthe halophyte Limonium vulgare and ³⁶Cl^–excretion by theglands of the pitcher walls of the carnivorous plant Nepenthes.Net uptake and net accumulation of Na⁺ and Cl^– by Limoniumleaf tissue and ³⁶Cl^– accumulation in Nepenthes pitchertissue were much less inhibited than excretion. The resultsare discussed in relation to literature reporting similar specificeffects of FPA on transport of ions from the symplast of barleyroots into the dead xylem elements. Limonium vulgare, Nepenthes hookeriana, salt-glands, excretion, p-fluorophenylalanine     

Characterization, Functional Reconstitution and Activation by Fusicoccin of a Ca2+-ATPase from Corydalis sempervirens Pers. Cell Suspension Cultures

Cell suspension cultures of Corydalis sempervirens have provenideal for the study of fusicoccin action [Schulz et al. (1990)Planta 183: 83] and express the fusicoccin-binding protein aswell as a plasma membrane H⁺-ATPase which is activated by thefungal toxin. Microsomal vesicles prepared from these cellsaccumulate Ca²⁺ in the presence of Mg-ATP. The protonophorecar-bonylcyanide m-chlorophenylhydrazone did not inhibit theMg-ATP dependent Ca²⁺-transport into the vesicles. This processis thus due to the activity of at least one primary active,ATP-driven, Ca²⁺-pump. The enzyme was characterized in detail.It has a pH optimum of 7.2, an apparent K_m of 0.3 mu (ATP),12pm (Ca²⁺), accepts ATP>ITP GTP>CTP UTP, and is strongly(Kⁱ, app 0.75 µmM) inhibited by erythrosine B but lessso (Kⁱ, app 95 µM) by or-thovanadate. These characteristicsare typical for the plasma membrane Ca²⁺-ATPase characterizedfrom differentiated tissues [Graf and Weiler (1990) Physiol.Plant. 75: 634]. Fusicoccin activates the erythrosine-sensitiveCa²⁺-pump by lowering its K_m for ATP, when added to living cellsprior to tissue homogenization. Thus, fusicoccin appears toactivate at least two ion-translocating ATPases in one and thesame tissue, suggesting that the toxin's mechanism of actionis complex and not restricted to activation of the H⁺-ATPase.FC has no effect when administered to microsomes. The microsomalenzyme was solubilized and reconstituted into asolec-tin liposomesin functional form. The reconstituted, erythrosine sensitiveCa²⁺-ATPase was insensitive to fusicoccin. Thus, componentsessential for toxin action are either lost or inactivated duringsubcellular fractionation. It is likely that FC action requiressoluble components. (Received April 22, 1991; Accepted July 24, 1991)     

Response to Waterlogging and Differing Sensitivity to Divalent Iron and Manganese in Clones of Dactylis glomerata L. derived from Well-drained and Poorly-drained Soils

Clonally propagated plants of Dactylis glomerata derived froma well-drained, heavily grazed cliff habitat (clone L) and froman undergrazed poorly-drained soil (clone A) were tested forwaterlogging tolerance in soil-culture. Water-logging did notaffect the two clones differentially, a result, which contrastedstrongly with that of a previous experiment in which simulatedgrazing (clipping to 20 cm) unexpectedly caused clone A to beless tolerant of waterlogging than clone L. Maximum leaf andleaf sheath length was reduced more by water-logging in cloneL than in clone A (P < 0.05). In solution-culture when providedwith factorial combinations of 0.5, 5 and 50 mg dm^–2 ofFe²⁺ and Mn²⁺ the shoot dry weight yield of the dry-soil clonewas reduced more than that of the wet-soil clone by 50 mg Fedm^–3 irrespective of Mn²⁺ concentration (P < 0.01)but the reduction of growth was less at higher Mn²⁺ concentrations.Fifty milligrams of Mn²⁺ dm^–3 reduced the growth of thedry soil clone but increased the growth of the wet soil clonewith Fe²⁺ at 5 mg dm^–2 (P < 0.05). Iron at 0.5 mg dm^–2was suboptimal for shoot growth of both clones at any levelof Mn²⁺ and caused more severe leaf chlorosis in the wet soilclone. Leaf tissue of clone L contained more iron than thatof clone A after waterlogging (P < 0.01) but in solutionculture, though increasing iron from 0.5 to 50 mg dm^–3almost doubled leaf iron content (P < 0.001), the interactionClones x Mn x Fe just failed to reach significance at P <0.05. The manganese content of leaf tissue from the two clonesvaried differently in response to solution manganese (Clonesx Mn P < 0.01), clone A showing a slightly greater increaseof manganese content at high solution concentration. Iron at50 mg dm^–3 suppressed Mn uptake (Mn x Fe, P < 0.001)in both clones. The two clones thus show marked environmentaladaptation to the chemistry of wet and dry soils. Dactylis glomerata, Cocksfoot grass, Orchard grass, waterlogging, iron, manganese, toxicity, deficiency, ecotypes     

Possible role of the cytosol pathway of acetyl-CoA supply in terpene biosynthesis in sweet potato infected with Ceratocystis fimbriata

Pyruvate was converted into acetyl-CoA by the cytosol enzymefraction prepared from sweet potato root tissue infected withCeratocystis fimbriata. The conversion was dependent on thiaminepyrophosphate, NAD⁺, ATP and CoA. Activities of pyruvate decarboxylase,aldehyde dehydrogenase and acetyl CoA synthetase increased indiseased tissue. These results indicate the operation of thecytosol pathway of acetyl-CoA supply for terpene biosynthesisin C. fimbriata-infected tissue which consists of the abovethree enzymes. ¹This paper constitutes Part 135 of the Phytopathological Chemistryof Sweet Potato with Black Rot and Injury. This work was supportedin part by a Grant-in-Aid from the Ministry of Education, Scienceand Culture. ²Present address: Biochemistry Department, University of Queensland,St. Lucia 4067, Queensland, Australia. (Received April 21, 1980; )     

The Interaction of Ultraviolet-B Radiation and Water Deficit in Two Arabidopsis thaliana Genotypes

It has been demonstrated, in both herbaceous and woody species,that tissue hydration resulting from exposure to drought isless pronounced if plants are concurrently exposed to ultraviolet-Bradiation (UV-B). An explanation for the mechanisms underlyingthis phenomenon has been elusive. Arabidopsis thaliana(L.) Heynh.genotypes, defective in specific defences against UV-B exposure,may permit more insightful study of drought-UV-B interactionsthan is possible with genetically uniform plants. Arabidopsishas a rosette stature and has predominantly abaxial stomata.Thus, it is difficult to investigate its stomatal behaviourand gas exchange using conventional techniques and instrumentation.In this study, the relative abundance of¹³C and¹²C in leaf tissue(¹³C) was used as a means of determining water use efficiency(WUE) and the relative balance, at the site of carbon fixation,between CO₂supply and demand. UV-B insensitive (L er) and sensitive(fah1)Arabidopsis genotypes were raised in a growth chamberand exposed to 6 kJ m^-2 d^-1UV-B irradiation and subjected todrought. In both genotypes, leaf desiccation was less pronouncedthan that of control plants that were subjected to drought butnot exposed to UV-B. The relatively low (more negative) leaf¹³C values (indicating low WUE), but high dry matter productionof the UV-B exposed plants suggest that their higher leaf watercontent was not primarily due to stomatal closure. We proposethat the mechanisms underlying the maintenance of higher leafwater content involved UV-B and water stress induced biosynthesisof stress proteins and compatible osmolytes. Copyright 2000Annals of Botany Company Arabidopsis thaliana, ultraviolet-B, water deficit, stable carbon isotopes, ¹³C, stomatal opening, tissue dehydration, dehydrin     

Direct Somatic Embryoid Formation on Immature Embryos of Trifolium repens, T. pratense and Medicago sativa, and Rapid Clonal Propagation of T. repens

By direct somatic embryogenesis in vitro a clone of asepticplantlets can be raised from a single immature embryo of Trifoliumrepens (white clover) within about 6 weeks of pollination. Embryoidsare induced directly from intact zygotic embryonic tissue ona culture medium containing 0·025 or 0·05 mg 1^–1BAP and 1·0 g 1^–1 yeast extract. Similar directsomatic embryogenesis has also been achieved for Trifolium pratense(red clover) and Medicago sativa (lucerne). Applications ofembryo propagation by direct somatic embryogenesis are discussed,particularly in relation to multiple screening of host genotypesfor analysis of host/pathogen and legume/Rhizobium interactions. Trifolium repens L., Trifolium pratense L., Medicago sativa L., clover, lucerne, tissue culture, embryoid, somatic embryogenesis, legumes     

Differential regulation of CD43 glycoforms on CD4+ and CD8+ T lymphocytes in graft-versus-host disease

Two distinct T-cell glycoforms of CD43 result from differentialglycosylation of a single gene product in vivo. The 115 kDaglycoform carries mainly tetrasaccharides and is a pan T-cellmarker, whereas the 130 kDa glycoform carries mainly hexasaccharidesand is associated with T-cell activation. CD43 has been shownto play a role both in enhancing and inhibiting cell adhesion;however, the function of the individual glycoforms is unknown.We have examined the distribution and regulation of the CD43glycoforms in a murine model of acute graft-versus-host disease(GVHD) using monoclonal antibodies (mAbs) S7 and 1B11 specificfor the 115 and 130 kDa CD43 glycoforms, respectively. An increasein T-lymphocyte CD43 130 kDa expression occurred during GVHDfrom day 4 onwards and coincided with splenomegaly and upregulationof the ß1-6GlcNAc transferase (C2GnT), the key enzymeresponsible for the addition of complex O-glycan branching toCD43. When T-lymphocyte subsets were examined for CD43 expression,we found that in GVHD, both CD43 glycoforms were upregulatedon CD4⁺ T cells. However, in CD8⁺ T cells, CD43 115 kDa wasdownregulated while CD43 130 kDa was dramatically upregulated,such that two distinct CD8⁺1B11⁺ T-cell subsets were observed.These data demonstrate differential expression of the CD43 glycoformsin both resting and activated CD4⁺ and CD8⁺ T cells, and suggestthat glycosylation differences between the CD43 glycoforms mayreflect participation in the different functions of these T-cellsubsets in immune disorders in vivo. activation CD43 glycosyltransferases graft-versushost disease T lymphocytes