In vitro comparison of ceftazidime,aztreonam, cefpirome,gentamicin, imipenem,enoxacin, and ticarcillin plus clavulanic acid against 108 strains ofPseudomonas maltophilia

Pseudomonas maltophilia is an uncommon cause of hospital-acquired infection and is resistant to most of the antimicrobial agents used in the treatment of gram-negative infections. Susceptibility of 108 isolates ofP. maltophilia to ceftazidime, aztreonam, defpirome, gentamicin, imipenem, enoxacin, and ticarcillin plus clavulanic acid was determined by an agar dilution method. The isolates were in general resistant to the antibiotics. Imipenem and cefpirome were not active at clinically achievable levels. Of the isolates, 20% were susceptible to 16 g/ml ceftazidime, 53% were susceptible to 4 g/ml enoxacin, 10% were susceptible to 4 g/ml gentamicin, and 25% were susceptible to 64 g/ml ticarcillin plus 2 g/ml clavulanic acid.     

Electrogenic properties of the sodium-alanine cotransporter in pancreatic acinar cells: II. Comparison with transport models

Summary In this paper, the results of the preceding electrophysiological study of sodium-alanine cotransport in pancreatic acinar cells are compared with kinetic models. Two different types of transport mechanisms are considered. In the simultaneous mechanism the cotransporterC forms a ternary complexNCS with Na⁺ and the substrateS; coupled transport of Na⁺ andS involves a conformational transition between statesNCS andNCS with inward- and outward-facing binding sites. In the consecutive (or ping-pong) mechanism, formation of a ternary complex is not required; coupled transport occurs by an alternating sequence of association-dissociation steps and conformational transitions. It is shown that the experimentally observed alanine- and sodium-concentration dependence of transport rates is consistent with the predictions of the simultaneous model, but incompatible with the consecutive mechanism. Assuming that the association-dissociation reactions are not rate-limiting, a number of kinetic parameters of the simultaneous model can be estimated from the experimental results. The equilibrium dissociation constants of Na⁺ and alanine at the extracellular side are determined to beK _N <-64mm andK _S <-18mm. Furthermore, the ratioK _N /K _N ^S of the dissociation constants of Na⁺ from the binary (NC) and the ternary complex (NCS) at the extracellular side is estimated to be <-6. This indicates that the binding sequence of Na⁺ andS to the transporter is not ordered. The current-voltage behavior of the transporter is analyzed in terms of charge translocations associated with the single-reaction steps. The observed voltage-dependence of the half-saturation concentration of sodium is consistent with the assumption that a Na⁺ ion that migrates from the extracellular medium to the binding site has to traverse part of the transmembrane voltage.     

Susceptibility of clinical isolates of yeasts to anti-fungal agents

The antimicrobial activity of amphotericin B, 5-fluorocytosine, nystatin, clotrimazole and miconazole were compared in vitro against 244 strains of yeasts that had been isolated from clinical specimens. The yeasts used in this study included 20 species of Candida, Cryptococcus, Saccharomyces Geotrichum, Rhodotorula, Torulopsis and Trichosporon. The majority of the strains (78%) had an MIC of 0.5 g/ml for amphotericin B, 81% an MIC of 1 g/ml for 5-fluorocytosine, 99% 8 g/ml for nystatin, 91%, 8.0 g/ml for clotrimazole and 98% had an MIC of 4.0 for miconazole. Of the anti-fungal agents tested, 5-fluorocytosine and nystatin were found to have the greatest antifungal activity.     

UDP-GlcNAc: Galβ3GalNAc-Mucin: (GlcNAc → GalNAc) β6-N-Acetylglucosaminyltransferase and UDP-GlcNAc: Galβ3(GlcNAcβ6) GalNAc-Mucin (GlcNAc → Gal)β3-N-Acetylglucosaminyltransferase from Swine Trachea Epithelium

Summary Two specific -N-acetylglucosaminyltransferases involved in the branching and elongation of mucin oligosaccharide chains, namely, a 1,6 N-acetylglucosaminylsaminyltransferase that transfers N-acetylglucosamine from UDP-N-acetylglucosamine to Gal3GalNAc-Mucin to yield Gal3(GlcNAc6)GalNAc-Mucin and a 3-N-acetylglucosaminyl transferase that transfers N-acetylglucosamine from UDP-N-acetylglucosamine to Gal3(GlcNAC6)GalNAc-mucin to yield GlcNAc3Gal3 (GlcNAc6)GalNAc-Mucin were purified from the microsomal fraction of swine trachea epithelium. The 1,6-N-acetylglucosaminyltransferase was purified about 21,800-fold by procedures which included affinity chromatography on DEAE columns containing bound asialo Cowper's gland mucin glycoprotein with Gal1,3GalNAc side chains. The apparent molecular weight estimated by gel filtration was found to be about 60 Kd. The purified enzyme showed a high specificity for Gal1,3GalNAc chains and the most active substrates were mucin glycoproteins containing these chains. The apparent Km of the 6-glucosaminyltrans-ferase for Cowper's gland mucin glycoprotein containing Gal1,3GalNAc chains was 0.53 µM; for UDP-N-acetylglucosamine, 12 µM; and for Gal 1,3GalNAc NO₂ø, 4 mM. The activity of the 6-glucosaminyltransferase was dependent on the extent of glycosylation of the Gal3GalNAc chains in Cowper's gland mucin glycoprotein.The best substrate for the partially purified 3-Glucosaminyltransferase was Cowper's gland mucin glycoprotein containing Gal1,3(GlcNAc6)GalNAc side chains. This enzyme showed little or no activity with intact sialylated Cowper's gland mucin glycoprotein or derivatives of this glycoprotein containing GalNAc or Gal1,3GalNAc side chains.The radioactive oligosaccharides formed by these enzymes in large scale reaction mixtures were released from the mucin glycoproteins by treatment with alkaline borohydride, isolated by gel filtration on Bio-Gel P-6 and characterized by methylation analysis and sequential digestion with exoglycosidases. The oligosaccharide products formed by the 6- and 3-glucosaminyltransferases were shown to be Gal3(GlcNAC6) GalNAc and GlcNAc3 Gal3(GlcNAC6)GalNAc respectively.Taken collectively, these results demonstrate that swine trachea epithelium contains two specific N-acetylglucosaminyltransferases which catalyze the initial branching and elongation reactions involved in the synthesis of O-linked oligosaccharide chains in respiratory mucin glycoproteins. The first enzyme a 6-glucosaminyltransferase converts Gal3GalNAc chains in mucin glycoproteins to Gal3(GlcNAc6)GalNAc chains. This product is the substrate for a second 3-glucosaminyltransferase which converts the Gal3(GlcNAc6)GalNAc chains to GlcNAc3Gal(GlcNAc6)GalNAc chains in the glycoprotein. The 3-glucosaminyltransferase did not utilize Gal3GalNAc chains as a substrate and this results in an ordered sequence of addition of N-acetylglucosamine residues to growing oligosaccharide chains in tracheal mucin glycoproteins.Abbreviations NeuNAc N-acetylneuraminic acid - GalNAcol N-acetylgalactosaminitol - CGMG Cowper's gland mucin glycoprotein - GalNAc-CGMG Cowper's gland mucin glycoprotein containing GalNAc side chains O-glycosidically linked to serine or threonine - Gal3GalNAc-CGMC Cowper's gland mucin glycoprotein containing Gal3GalNAc side chains - MES 2-(N-morpholino) Ethane Sulfonic acid - PBS Phosphate Buffered Saline     

Hydrogen isotope discrimination in higher plants: Correlations with photosynthetic pathway and environment

Summary The ratio of deuterium to hydrogen (expressed as D) in hydrogen released as water during the combustion of dried plant material was examined. The D value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C₃ plants show mean D values of-132 for shoots and -117 for roots; C₄ plants show mean D values of -91 for shoots and-77 for roots and CAM plants a D value of-75 for roots and shoots. The difference between the D value of shoot material from C₃ and C₄ plants was confirmed in species growing under a range of glasshouse conditions. This difference in D value between C₃ and C₄ species does not appear to be due to differences in the D value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C₃ and C₄ plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in D values are discussed. In CAM plants grown in the laboratory or collected from the field D values range from-75 to +50 and are correlated with ¹³C values. When deprived of water, the D value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different D value of available water in areas of increasing aridity. Whatever the origin of the variable D value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.     

A structural model for elongation factor 1 (EF-1) and phosphorylation by protein kinase CKII

EF-1a binds aminoacyl-tRNA to the ribosome with the hydrolysis of GTP; the complex facilitates the exchange of GDP for GTP to initiate another round of elongation. To examine the subunit structure of EF-1 and phosphorylation by protein kinase CKII, recombinant , , and subunits from rabbit were expressed in E. coli and the subunits were reconstituted into partial and complete complexes and analyzed by gel filtration. To determine the availability of the and subunits for phosphorylation by CKII, the subunits and the reconstituted complexes were examined as substrates for CKII. Formation of the nucleotide exchange complex increased the rate of phosphorylation of the subunit and reduced the Km, while addition of to or the complex inhibited phosphorylation by CKII. However, a had little effect on phosphorylation of . Thus, the and subunits in EF-1 were differentially phosphorylated by CKII, in that phosphorylation of was altered by association with other subunits, while the site on was always available for phosphorylation by CKII. From the availability of the subunits for phosphorylation by CKII and the composition of the reconstituted partial and complete complexes, a model for the subunit structure of EF-1 consisting of (22)2 is proposed and discussed.     

Contribution of flow cytometry to estimate picoplankton biomass in estuarine systems

Picoplankton (plankton 3 m) biomass was determined by flow cytometry in three European estuarine systems (Krka Estuary in Croatia, Rhône Delta in France, and Lena Delta and Laptev Sea in Russia). The size of natural phytoplankton groups was obtained by a calibration curve, with different picoplankton's strains (from 1.6 to 3.4 m), measured by a Coulter counter (size) and a flow cytometer (light-scattering). Two natural groups of picoplankton were identified by flow cytometry in the three systems: Synechococcus sp and picoeukaryotes. Picoplankton cells abundance ranged between: 2800 and 42000, 5000 and 37000, 1000 and 50000 cells ml^–1 in the Krka estuary, in the Rhône delta and in the Lena-Laptev system, respectively. In the Krka estuary, picoplankton biomass ranges between 11 and 68 gC l^–1. It can make up as much as 88% of the total photosynthetic plankton population and 50% of total organic particulate carbon. Picoplankton biomass was greater in the summer than in the autumn. At the halocline layer this biomass can attempt ca. 390 gC l^–1during the summer cruise. In the Rhône delta, a lower picoplankton biomass (6–39 gC l^–1) was observed at the end of the winter. These biomass represented between 0.4 and 22% of the particulate organic carbon, which could reach 71% of the total photosynthetic plankton biomass at the marine station. In the Lena-Laptev system, picoplankton biomass varied between 6 and 56 gC l^–1 in surface waters. Picoplankton biomass decreased with depth, but picoeukaryotes were still observed in deep samples (20, 30 m) in the Laptev Sea, showing a considerable autotrophic activity in spite of low temperatures (0–1 °C). Although the widely dispersed estuary geographic distribution and their different estuarine characteristics, the data point out that these small organisms can also play an important role in the transfer of organic carbon from rivers to oceans and that flow cytometry can be able to detect these small cells in turbid systems.     

Chromosomal locations of the gene coding for the CD3 (T3) γ subunit of the human and mouse CD3/T-cell antigen receptor complexes

The gene coding for the M _r 26000 chain of the human CD3 (T3) antigen/T-cell antigen receptor complex was mapped to chromosome band 11q23 by using a cDNA clone (pJ6T3 -2), by in situ hybridization to metaphase chromosomes and by Southern blot analysis of a panel of human-rodent somatic cell hybrids. The mouse homolog, here termed Cdg-3, was mapped to chromosome 9 using the mouse cDNA clone pB10.AT3 -1 and a panel of mouse-hamster somatic cell hybrids. Similar locations for the CD3 genes have been described previously. Thus, the corporate results indicate that the CD3 and genes have remained together since they duplicated about 200 million years ago.     

Role of mitogen-activated protein kinase pathway in reactive oxygen species-mediated endothelin-1-induced β-myosin heavy chain gene expression and cardiomyocyte hypertrophy

Endothelin-1 (ET-1) has been found to increase cardiac -myosin heavy chain (-MyHC) gene expression and induce hypertrophy in cardiomyocytes. ET-1 has been demonstrated to increase intracellular reactive oxygen species (ROS) in cardiomyocytes. The exact molecular mechanism by which ROS regulate ET-1-induced -MyHC gene expression and hypertrophy in cardiomyocytes, however, has not yet been fully described. We aim to elucidate the molecular regulatory mechanism of ROS on ET-1-induced -MyHC gene expression and hypertrophic signaling in neonatal rat cardiomyocytes. Following stimulation with ET-1, cultured neonatal rat cardiomyocytes were examined for ³H-leucine incorporation and -MyHC promoter activities. The effects of antioxidant pretreatment on ET-1-induced cardiac hypertrophy and mitogen-activated protein kinase (MAPKs) phosphorylation were studied to elucidate the redox-sensitive pathway in cardiomyocyte hypertrophy and -MyHC gene expression. ET-1 increased ³H-leucine incorporation and -MyHC promoter activities, which were blocked by the specific ET_A receptor antagonist BQ-485. Antioxidants significantly reduced ET-1-induced ³H-leucine incorporation, -MyHC gene promoter activities and MAPK (extracellular signal-regulated kinase, p38, and c-Jun NH₂ -terminal kinase) phosphorylation. Both PD98059 and SB203580 inhibited ET-1-increased ³H-leucine incorporation and -MyHC promoter activities. Co-transfection of the dominant negative mutant of Ras, Raf, and MEK1 decreased the ET-1-induced -MyHC promoter activities, suggesting that the Ras-Raf-MAPK pathway is required for ET-1 action. Truncation analysis of the -MyHC gene promoter showed that the activator protein-2 (AP-2)/specificity protein-1 (SP-1) binding site(s) were(was) important cis-element(s) in ET-1-induced -MyHC gene expression. Moreover, ET-1-induced AP-2 and SP-1 binding activities were also inhibited by antioxidant. These data demonstrate the involvement of ROS in ET-1-induced hypertrophic responses and -MyHC expression. ROS mediate ET-1-induced activation of MAPK pathways, which culminates in hypertrophic responses and -MyHC expression. Tzu-Hurng Cheng, Neng-Lang Shih: These authors have equally contributed to this work     

Immobilized Lotus tetragonolobus agglutinin binds oligosaccharides containing the Lex determinant

A defined set of oligosaccharides and glycopeptides containing -linked fucose were used to examine the specificity of the immobilized fucose-binding lectin Lotus tetragonolobus agglutinin (LTA1), also known as lotus lectin. Glycans containing the Lewis x determinant (Lex) Gal1-4[Fuc1-3]GlcNAc1-3-R were significantly retarded in elution from high density LTA-Emphaze columns. The lectin also bound the fucosylated lacdiNAc trisaccharide GalNAc1-4[Fuc1-3]GlcNAc. The lectin did not bind glycans containing either sialylLex or VIM-2 determinants, nor did it bind the isomeric Lea, Gal1-3[Fuc1-4]GlcNAc-R. Although 2-fucosyllactose Fuc1-2Gal1-4Glc) was retarded in elution from the columns, larger glycans containing the H-antigen Fuc1-2Gal1-3(4)GlcNAc-R interacted poorly with immobilized LTA. Our results demonstrate that immobilized LTA is effective in isolating glycans containing the Lex antigen and is useful in analyzing specific fucosylation of glycoconjugates. Abbreviations: LTA, Lotus tetragonolobus agglutinin; UEA-1, Ulex europaeus agglutinin-I; LNT, AAL, Aleuria aurantia agglutinin; Gal1-3GlcNAc1-3Gal1-3Glc; LNnT, Gal1-4GlcNAc1-3Gal1-3Glc; Lex, Lewis x antigen; Lea, Lewis a antigen; GDPFuc, guanosine 5-diphosphate--L-fucose     

Multivariate morphometric study of theCardamine pratensis group (Cruciferae) in the Carpathian and Pannonian area

A multivariate morphometric study of theCardamine pratensis group is presented, based on 84 population samples collected from the Carpathian and Pannonian area in the Czech Republic, Slovakia, Poland, Ukraine, Hungary, and Romania. Among the multivariate methods, principal component analysis, cluster analysis, and classificatory and canonical discriminant analysis were used. The analysis of chromosome numbers from all populations studied showed wide variation. The morphometric study showed that not all groups of populations characterised by their chromosome numbers and geographical criteria are morphologically, and thus taxonomically, distinguishable. Besides the morphologically well characterised speciesCardamine dentata andC. rivularis, the following species were recognised in the area studied:C. matthioli, C. majovskii andC. pratensis. Within the last species, besides the typical populations, two diploid types are provisionally recognised: type ucranica and type rivularis auct..     

The frequency of the γ chain variant AγT in different populations,and its use in evaluating γ gene expression in association with thalassemia

Summary The occurrence of the ^AT chain (i.e. ^A75 Ile Thr) in different populations was evaluated through a study of 4250 cord blood samples and blood samples from more than 350 SS¹ patients. High frequencies were observed in Italy, Yugoslavia, Turkey, Holland, but also in Japan, Vietnam, and India. The chain is (nearly) absent in the Black population of Ghana and Kenya, and low frequencies were observed in China and Australian aborigines. Only a few adult SS patients (18 out of 357) were ^AT heterozygotes. The chromosomes with the ^AT globin gene were mapped through an evaluation of the presence of 10 different restriction sites. The ^AT chromosomes from different populations were closely related and had the same subhaplotypes of [--++-+] (Hinc II 5 to ; Xmn I 5 to ^G; Hind III in ^G and ^A; Hinc II in and 3 to ), quite different from the subhaplotypes seen for ^AT negative chromosomes.² This suggests a common ancestor which may have originated in Southern Europe. An evaluation of the chain production by both chromosomes in SS patients and -thalassemia heterozygotes was possible for subjects with an ^AT heterozygosity. It was concluded that in -thalassemia trait, the chain synthesis is directed for about two-thirds by the thalassemic chromosome and for about onethird by the normal chromosome; the contribution by the normal chromosome decreases with a decrease in total chain production.This is contribution #0890 of the Department of Cell and Molecular Biology, Medical College of Georgia, Augusta, GA 30912, USA     

Stimulation of non-specific resistance to tumors in the mouse using a poly(maleic-acid-styrene)-conjugated neocarzinostatin

Summary The development of non-specific resistance to tumors following stimulation with poly(maleic-acid-styrene)-conjugated neocarzinostatin (SMANCS), a polymer-conjugated derivative of neocarzinostatin, was investigated in mice. The growth of syngeneic solid tumors (Meth-A fibrosarcoma and RL 1 leukemia) inoculated into BALB/c mice was suppressed after one treatment with SMANCS at doses ranging from 0.14 mg/kg to 3.4 mg/kg i.v. 24 h before tumor implantation. Since previously observations concerning SMANCS have shown that it disappeared within 1.5 h after i.v. administration in mice and that it was inactivated quickly in plasma, SMANCS evidently inhibited tumor growth by mediating non-specific resistance. In addition, the non-specific resistance to tumors stimulated by SMANCS could be passively transferred to untreated mice by serum which was shown to contain interferon (IFN) from 12 h to 20 h after SMANCS administration. However, the resistance was not produced by serum prepared from mice at 8 h or 32 h after administration presumably because of the observation that the interferon activity was only demonstrated from 12 h to 28 h after SMANCS stimulation. When the serum specimens were treated with anti-IFN- antiserum, the antitumor activity of the sera was abrogated. However, no significant change was detected in the antitumor activity of the specimens following treatment with anti-IFN-/ antiserum. Treatment of mice with SMANCS and anti-IFN- antiserum together resulted in the elimination of the non-specific resistance to tumors. The IFN induced in the sera of mice by SMANCS was shown to be 57% IFN- and 41% IFN-/. Half of the interferon produced in SMANCS-stimulated mice could be eliminated by treatment with anti-IFN-, and treatment of SMANCS-stimulated mice with both anti-IFN- and anti-IFN-/ antisera resulted in a total absence of detectable interferon. These findings suggest that while the administration of SMANCS induces both IFN- and IFN-/ production, in this case, it is only the former which mediates the non-specific resistance to tumors.     

Cryptic growth in Klebsiella pneumoniae

Summary The ability of Klebsiella pneumoniae to grow on its own soluble lysis products is shown in a series of batch growth experiments. Maximum specific growth rate coefficients ranging from 0.69 to 1.46 h^-1 were obtained with experimental cryptic yield coefficients ranging between 0.42 to 0.52 (mg-cell-C/mg-substrate-C). These kinetic data are used to calibrate a model which demonstrates that depression of theoretical maximum yield coefficients relative to experimentally obtained values can be explained by cryptic growth phenomena without the need to resort to the use of physiologically undefined, mathematical constants. Growth of K. pneumoniae on sonicated cells derived from steady-state chemostat cultures was followed in batch culture and observed to occur with no lag phase. Batch growth curves did not indicate either diauxic or polyauxic growth, suggesting simultaneous utilization of the complex organic substrate mixture. These data suggest that cryptic growth is probably a real event occurring in growing chemostat cultures under ideal growth conditions and most probably also under starvation conditions.     

Regional Differentiation in the Dynamics of the Pollen Seasons of Alnus, Corylus and Fraxinus in Poland (Preliminary Results)

In 1995–1996 a study of pollen concentrations of Corylus, Alnus and Fraxinus was performed at seven sites in regions of different climatic and natural conditions. The aim of the study was to determine whether regional differences in the course and duration of pollen seasons occur in Poland. The study was performed using a volumetric method. Several phases during the pollen season were defined for each taxon (1, 2.5, 5, 25, 50, 75, 95, 97.5, 99% of annual total) and duration of the pollen seasons was calculated using 98 and 90% methods. Dynamics and duration of the pollen seasons and a start of particular phases of the season were compared among sites. On the basis of the preliminary analysis it could be supposed that regional differences were most evident in the case of Corylus. The pollen season of this taxon started the earliest in Pozna where thermal conditions were most favourable and the latest in Gdask, a place at the furthest to the north ( ², 0.05). In montane regions (Zakopane, Rabka) last phases of the season were significant extended ( ², 0.05). Probably it results from secondary pollen deposition and a long-distance transport by montane wind. In case of Fraxinus the significant regional differences in the start of the pollen season were not found. The study supported that weather conditions have the substantial influence on the start of consecutive phases of the pollen season.     

On the sufficiency of the velocity field for perception of heading

All models of self-motion from optical flow assume the instantaneous velocity field as input. We tested this assumption for human observers using random-dot displays that simulated translational and circular paths of movement by manipulating the lifetime and displacement of individual dots. For translational movement, observers were equally accurate in judging direction of heading from a velocity field with a two-frame dot life and a direction field in which the magnitudes of displacement were randomized while the radial pattern of directions was preserved, but at chance with a speed field in which the directions were randomized, preserving only magnitude. Accuracy declined with increasing noise in vector directions, but remained below 2.6° with a 90° noise envelope. Thus, the visual system uses the radial morphology of vector directions to determine translational heading and can tolerate large amounts of noise in this pattern. For circular movement, observers were equally accurate with a 2-frame velocity field, 3-frame acceleration displays, and 2-frame and 3-frame direction fields, consistent with the use of the pattern of vector directions to locate the center of rotation. The results indicate that successive independent velocity fields are sufficient for perception of translational and circular heading.     

The microbial production of 3aα-H-4α- (3′-propionic acid)-5α-hydroxy-7aβ-methylhexahydro-indan-1-one-δ-lactone from cholesterol

Summary A mutant strain of Rhodococcus australis CSIR-236.457 which accumulates 3a-H-4-(3-propionic acid)-5-hydroxy-7a-methylhexahydro-indan-1-one--lactone from cholesterol, stigmasterol and -sitosterol was studied. The product is produced in a 60% molar yield in a dilute black strap molasses medium containing 6–12g/l cholesterol after a 72 hour fermentation period.     

Effects of light quantity and quality during development on the morphology and stomatal physiology of Commelina communis

Summary The effects on plant growth and stomatal physiology of alterations in light quantity and quality during development were investigated in the C₃ monocot, Commelina communis. Reduction in light intensity resulted in decreased branching and stem elongation, with effects more severe under neutral shade (R:FR1.0) than under leaf shade (R:FR0.4) conditions. Shade treatments had no effect on the leaf area or stomatal density of newly expanded leaves. Gas exchange measurements on leaves that had expanded under the different treatments indicated that a reduction in light intensity decreased the magnitude and slowed the kinetics of stomatal responses to pulses of blue light, particularly in plants from the neutral shade treatment. These results indicate that the specific stomatal response to blue light is plastic, and is modulated by the light environment prevailing during leaf development.     

A vapor pressure deficit effect on crop canopy photosynthesis

Canopy CO₂-exchange rates (CER), air temperatures, and dew points were measured throughout ten days during the 1987 growing season for cotton (Gossypium hirsutum L.), grain sorghum [Sorghum bicolor (L) Moench], and five soybean [Glycine max (L) Merr.] cultivars, and throughout seven days in 1988, on maize (Zea maize L.). The objective was to determine if the decline in CER per unit light during the afternoon is associated with a vapor pressure deficit (VPD) increase. Some of the soybean and maize plots were kept as dry as possible. A VPD term significantly contributed (P0.05) to a canopy CER regression model in 54 of 80 data sets in 1987. Grain sorghum was less sensitive than the well-watered soybean genotypes to an increasing VPD (P0.05) on three of the ten measurement days and less sensitive than cotton (P0.05) on only one day. Cotton demonstrated less VPD sensitivity than soybean (P0.05) on one day. The moisture stressed soybean plots showed a greater CER sensitivity to VPD (P0.05) than the well-watered soybean plots. In 1988, the frequently irrigated maize plots were less sensitive to VPD (P0.05) than the rain-fed plots early in the season, before the rain-fed plots were excessively damaged by moisture stress. These results indicate that the afternoon declines in canopy CER found in a number of different species are associated with increases in the VPD; recent work of others suggests that this may be due to partial stomatal closure.Abbreviations CER carbon dioxide exchange rate - VPD vapor pressure deficit - PPFD photosynthetic photon flux density - DAP days after planning