Eliminating hydrolytic activity without affecting the transglycosylation of a GH1 β-glucosidase

Unveiling the determinants for transferase and hydrolase activity in glycoside hydrolases would allow using their vast diversity for creating novel transglycosylases, thereby unlocking an extensive toolbox for carbohydrate chemists. Three different amino acid substitutions at position 220 of a GH1 β-glucosidase from Thermotoga neapolitana caused an increase of the ratio of transglycosylation to hydrolysis (r _s/r _h) from 0.33 to 1.45–2.71. Further increase in r _s/r _h was achieved by modulation of pH of the reaction medium. The wild-type enzyme had a pH optimum for both hydrolysis and transglycosylation around 6 and reduced activity at higher pH. Interestingly, the mutants had constant transglycosylation activity over a broad pH range (5–10), while the hydrolytic activity was largely eliminated at pH 10. The results demonstrate that a combination of protein engineering and medium engineering can be used to eliminate the hydrolytic activity without affecting the transglycosylation activity of a glycoside hydrolase. The underlying factors for this success are pursued, and perturbations of the catalytic acid/base in combination with flexibility are shown to be important factors.

     

Interannual variation in soil CO2 efflux and the response of root respiration to climate and canopy gas exchange in mature ponderosa pine

We examined a 6‐year record of automated chamber‐based soil CO₂ efflux (F_s) and the underlying processes in relation to climate and canopy gas exchange at an AmeriFlux site in a seasonally drought‐stressed pine forest. Interannual variability of F_s was large (CV=17%) with a range of 427 g C m^?2 yr^?1 around a mean annual F_s of 811 g C m^?2 yr^?1. On average, 76% of the variation of daily mean F_s could be quantified using an empirical model with year‐specific basal respiration rate that was a linear function of tree basal area increment (BAI) and modulated by a common response to soil temperature and moisture. Interannual variability in F_s could be attributed almost equally to interannual variability in BAI (a proxy for above‐ground productivity) and interannual variability in soil climate. Seasonal total F_s was twice as sensitive to soil moisture variability during the summer months compared with temperature variability during the same period and almost insensitive to the natural range of interannual variability in spring temperatures. A strong seasonality in both root respiration (R_r) and heterotrophic respiration (R_h) was observed with the fraction attributed to R_r steadily increasing from 18% in mid‐March to 50% in early June through early July before dropping rapidly to 10% of F_s by mid‐August. The seasonal pattern in R_r (10‐day averages) was strongly linearly correlated with tree transpiration (r²=0.90, P<0.01) as measured using sap flux techniques and gross ecosystem productivity (GEP, r²=0.83, P<0.01) measured by the eddy‐covariance approach. R_r increased by 0.43 g C m^?2 day^?1 for every 1 g C m^?2 day^?1 increase in GEP. The strong linear correlation of R_r to seasonal changes in GEP and transpiration combined with longer‐term interannual variability in the base rate of F_s, as a linear function of BAI (r²=0.64, P=0.06), provides compelling justification for including canopy processes in future models of F_s.     

Extracellular,low-affinity β-N-acetylglucosaminidases linked to the dynamics of diatoms and crustaceans in freshwater systems of different trophic degree

Extracellular hydrolysis of 4-methylumbelliferyl β-N-acetylglucosaminide was measured in the oligomesotrophic Piburger See and the eutrophic Římov reservoir during spring and summer phytoplankton blooms, respectively. Total enzymatic activity (TEA) ranged between 0.2 and 19.1 nmol 1⁻¹ h⁻¹ in the reservoir and between 0.8 and 12.4 nmol 1⁻¹ h⁻¹ in the lake. High-affinity (K_m < 1 μmol 1⁻¹) and lowaffinity (K_m > 100 μmol 1⁻¹) enzymes were kinetically identifiable in most samples from both localities. The low-affinity enzyme activity (LEA) usually accounted for >60% (mean: 80%) of TEA. LEA and diatom biomass significantly correlated over time in the reservoir epilimnion (r_s = 0.578) and in the lake metalimnion (r_s = 0.862). As diatoms possess chitin and take up its monomer, N-acetylglucosamine, two explanations of the observed relationships are suggested: extracellular β-N-acetylglucosaminidase activity partly originates either from ectoenzymes of chitinolytic bacteria attached to diatom cells or from ectoenzymes of diatoms, enabling them to take up N-acetylglucosamine from ambient amino sugars instead of synthesizing it de novo. A significant positive correlation of LEA with crustacean abundance was found in the lake epilimnion (r_s = 0.850), apparently reflecting the growing spring populations of frequently moulting juvenile crustaceans. A possible contribution of chitinolytic bacteria, accompanying the crustacean populations, to LEA is discussed.     

Deduction of pulmonary microvascular hematocrit from indicator dilution curves

We have developed a new model describing the relationship between plasma and red cell tracers flowing through the lung. The model is the result of an analysis of the transport of radiolabeled plasma albumin between two flowing phases and shows that differences between red cell and plasma tracer curves are related to microvascular hematocrit. The model was tested in an isolated, blood-perfused dog lung preparation in which we injected⁵¹Cr-labeled red cells and¹²⁵I-labeled plasma albumin into the pulmonary artery. From the tracer concentration-time curves at the venous outflow, we calculatedh _r, the ratio of microvascular hematocrit to large-vessel hematocrit. In 18 baseline experiments,h _r=0.92±0.01 (mn±sem) at a blood flow rate of 10.7±0.3 ml s⁻¹. We determined the effects of (a) glass bead embolization, (b) alloxan, and (c) lobe ligation onh _r. Embolization attenuated the separation between plasma and red cells (increasedh _r), probably as a consequence of passive vasodilation. Alloxan enhanced separation of plasma and red cells (decreasedh _r), possibly as a result of arteriolar vasoconstriction. Ligation of a fraction of the perfused tissue at constant flow did not cause significant change inh _r in the remaining perfused tissue. The model assumes that large-vessel transit times are uniform and that all dispersion occurs in the microvasculature. A theoretical analysis apportioning dispersion between large and small vessels disclosed that the error associated with these assumptions is likely to be less than 15% of the measuredh _r. We conclude from this study that the microvascular hematocrit model describes experimental plasma and red cell curves. The results imply thath _r can be readily deduced from tagged red cells and plasma and can be accounted for in calculating permeability-surface area in diffusing tracer experiments.     

Production of acetone and butanol by Clostridium acetobutylicum in continuous culture with cell recycle

Summary To increase the solvent productivity of the acetone-butanol fermentation, a continuous culture of Clostridium acetobytylicum with cell recycling was used. At a dry cell mass concentration of 8 g l^-1 and a dilution rate of D=0.64 h^-1, a solvent productivity of 5.4 g l^-1 h^-1 was attained. To prevent degeneration of the culture, which occurs with high concentrations of solvents (acetone, butanol and ethanol), different reactor cascades were used. A two-stage cascade with cell recycling and turbidostatic cell concentration control turned out to be the best solution, the first stage of which was kept at relatively low cell and product concentrations. A solvent productivity of 3 and 2.3 g l^-1 h^-1, respectively, was achieved at solvent concentrations of 12 and 15 g l^-1.Symbols D Dilution rate (h^-1) - r _p solvent productivity (g l^-1 h^-1) - s residual glucose concentration (g l^-1) - V _R reactor volume (l) - V _O overall volume (l) - x (dry) cell mass concentration (g l^-1) - Y _P/S solvent yield (g g^-1)     

Age trends in genetic parameters for growth and wood density in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis>

Genetic parameters for stem diameter and wood density were compared at selection (4–5 years) and harvest (16–17 years) age in an open-pollinated progeny trial of Eucalyptus globulus in Tasmania (Australia). The study examined 514 families collected from 17 subraces of E. globulus. Wood density was assessed on a subsample of trees indirectly using pilodyn penetration at both ages and directly by core basic density at harvest age. Significant additive genetic variance and narrow-sense heritabilities ( h_\textop² h_{\text{op}}^2 ) were detected for all traits. Univariate and multivariate estimates of heritabilities were similar for each trait except harvest-age diameter. Comparable univariate estimates of selection- and harvest-age heritabilities for diameter masked changes in genetic architecture that occurred with stand development, whereby the loss of additive genetic variance through size-dependent mortality was countered by the accentuation of additive genetic differences among survivors with age. Regardless, the additive genetic (r _a) and subrace (r _s) correlations across ages were generally high for diameter (0.95 and 0.61, respectively) and pilodyn penetration (0.77 and 0.96), as were the correlations of harvest-age core basic density with selection- and harvest-age pilodyn (r _a −0.83, −0.88; r _s −0.96, −0.83). While r _s between diameter and pilodyn were close to zero at both ages, there was a significant change in r _a from adverse at selection age (0.25) to close to zero (−0.07) at harvest age. We argue that this change in the genetic correlation reflects a decoupling of the genetic association of growth and wood density with age. This result highlights the need to validate the use of selection-age genetic parameters for predicting harvest-age breeding values.     

Leaf growth, stomatal diffusion resistances and photosynthesis during droughting of Lolium perenne populations selected for contrasting stomatal length and frequency

Lolium perenne selection lines with high calculated stomatal resistances to diffusion (r_s) as a result of either few or short stomata, maintained leaf extension rates and photosynthetic rates longer than selection lines with low resistances when deprived of water. There were no significant differences between high and low r_s plants in light saturated CO₂ uptake of turgid attached leaves. When grown in soil drying to 21% moisture, plants with low calculated r_s exhibited lower minimum leaf resistances (r_l) than those with high, measured with a diffusion porometer, on all except the last day. The daily maximum r_l (1.5 h after the start of the light period) became greater among low than high r_s plants as the difference in rate of leaf extension between the two groups of plants increased with drying soil. Rate of leaf extension was negatively correlated with daily maximum r_l and started to decline when relative leaf water content (RLWC), at 5 h after the start of the light period, fell below about 88%. Transpiration rate of plants grown in different soil moisture regimes was correlated (r=+ 0.83, P < 0.01) with mean maximum adaxial leaf conductance (reciprocal of resistance). There was a highly significant correlation (r=+ 0.62, P < 0.01) between calculated adaxial r_s and mean minimum measured r_l among plants growing at high or intermediate soil moisture, but not at low. Therefore, some random variation in minimum r_l, even with adequate moisture, seemed to be unaccounted for by variation in stomatal numbers or size. Selection for increased numbers of adaxial stomata also resulted in more on the abaxial surface, but mean adaxial/abaxial ratio in the ‘frequent’ stomata plants was still only about 9:1.     

Hierarchical Classification I: Single-Linkage Method

This is the first part of a survey of hierarchical clustering algorithms using joining methods: the Single-Linkage algorithm. Complete-Linkage and general algorithms defined by d(A_i, B) = = α,d(A_i, A_r)±α_sd(A_i, A_s)±βd(A_r, A_s) will be discussed in two subsequent papers.     

Seasonal changes in the contribution of root respiration to total soil respiration in a cool-temperate deciduous forest

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (R _trench) and in a control plot (R _control) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (R _D) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO₂ m^–2 h^–1) to August (840–1150 mg CO₂ m^–2 h^–1) and then decreased during autumn (200–650 mg CO₂ m^–2 h^–1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (R _r) and heterotrophic respiration rate (R _h) were estimated from R _control, R _trench, and R _D. We estimated that the contribution of R _r to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between R _h and soil temperature, whereas R _r had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, R _r and R _h.     

HISTORICAL DEMOGRAPHY AND PRESENT DAY POPULATION STRUCTURE OF THE GREENFINCH,CARDUEUS CHLORIS—AN ANALYSIS OF mtDNA CONTROL-REGION SEQUENCES

Genetic variability within and among 10 geographically distinct populations of Greenfinches (Carduelis chloris) was assayed by directly sequencing a 637 BP part of the mtDNA control region from 194 individuals. Thirteen variable positions defined 18 haplotypes with a maximum sequence divergence of 0.8%. Haplotype (h = 0.28–0.77) and nucleotide (π = 0.058–0.17%) diversities within populations were low, and decreased with increasing latitude (h:r_s = –0.81; π: r_s = –0.89). The distribution of pairwise nucleotide differences fit better with expectations of a “sudden expansion” than of an “equilibrium” model, and the estimates of long term effective population sizes were considerably lower than current census estimates, especially in northern European samples. Selection is an unlikely cause of observed patterns because the distribution of variability conformed to expectations of neutral infinite alleles model and haplotype diversity across populations was positively correlated with heterozygosity (H_E) in nuclear genes (r_s = 0.74, P < 0.05). Hence, a recent bottleneck, followed by serial bottlenecking during the process of post-Pleistocene recolonization of northern Europe, together with recent population expansion provide a plausible explanation for the low genetic diversity in the north. Genetic distances among populations showed a clear pattern of isolation-by-distance, and 14% of the haplotypic variation was among populations, the rest being distributed among individuals within populations. In accordance with allozyme and morphological data, a hierarchical analysis of nucleotide diversity recognized southern European populations as distinct from northern European ones. However, the magnitude of divergence in mtDNA, allozymes and morphology were highly dissimilar (morphology > mtDNA > allozymes).     

Enantioselective autocatalysis. III. Configurational and conformational studies on a 1,4-benzodiazepinooxazole derivative

We report here on configurational and conformational studies undertaken on the bromofluoro-1,4-benzodiazepinooxazole derivative I, which has previously been found capable of undergoing total spontaneous resolution under racemizing conditions. Due to its bridgehead N-atom I may exist in any of four diastereomeric forms,C _r N _r (orC _s N _s ) andC _r N _s (orC _s N _r ). Molecular mechanics calculations revealed that in their lowest energy conformations theC _r N _r (orC _s N _s ) diastereomers were favored over theC _r N _s (orC _s N _r ) diastereomers by some 3.42 kcal/mol, while semi-empirical quantum mechanical calculations indicated heats of formation also favoring theC _r N (orC _s N _s ) diastereomers by 3.83 kcal/mol. The¹H NMR spectra of the three crystalline modifications (, and) of I were examined in acetone, and found to be identical. These data, combined with the results of the above calculations, suggest that I exists in methanol or methanol-acetone solutions as theC _r N (orC _s N _s ) enantiomer prior to its racemization.     

Skin resistance to water loss in agamid lizards

Many desert lizards show reduced rates of cutaneous water loss (CWL) compared to their counterparts from more humid environments. It is not clear yet whether reduced CWL is connected to the taxonomic position of the lizard studied, or is affected more by environmental or experimental conditions. To investigate this, we measured the skin resistance to water transfer, R _s, in five closely related lizard taxa of the genus Agama. These diurnal lizards are distributed in Israel from mesic-Mediterranean to extreme desert biotopes. The highest R _s (738 s cm^-1) and the lowest CWL (0.160 mg cm^-2 h^-1) were found in Agama sinaita, which lives in the most arid habitat. The lowest R _s (234 s cm^-1) and the highest CWL (0.548 mg cm^-2 h^-1) were found in A. stellio ssp., which occupies mesic habitats. In addition, only the desert species were able to change their R _s in accordance with the changing experimental conditions. These R _s changes, which probably reflect vasomotor responses, were more pronounced in A. sinaita and presumably enable the desert species to control their CWL in a hot and dry environment.     

Most stomatal closure in woody species under moderate drought can be explained by stomatal responses to leaf turgor

Reduced stomatal conductance (g_s) during soil drought in angiosperms may result from effects of leaf turgor on stomata and/or factors that do not directly depend on leaf turgor, including root‐derived abscisic acid (ABA) signals. To quantify the roles of leaf turgor‐mediated and leaf turgor‐independent mechanisms in g_s decline during drought, we measured drought responses of g_s and water relations in three woody species (almond, grapevine and olive) under a range of conditions designed to generate independent variation in leaf and root turgor, including diurnal variation in evaporative demand and changes in plant hydraulic conductance and leaf osmotic pressure. We then applied these data to a process‐based g_s model and used a novel method to partition observed declines in g_s during drought into contributions from each parameter in the model. Soil drought reduced g_s by 63–84% across species, and the model reproduced these changes well (r² = 0.91, P < 0.0001, n = 44) despite having only a single fitted parameter. Our analysis concluded that responses mediated by leaf turgor could explain over 87% of the observed decline in g_s across species, adding to a growing body of evidence that challenges the root ABA‐centric model of stomatal responses to drought.     

Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmon

Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O₂ h^?1 at 30 cm s^?1 (c. 0·5 BL s^?1) to 3347 mg O₂ h^?1 at 170 cm s^?1 (c. 2·3 BL s^?1). Corrected for fish mass, these values ranged from 122 to 670 mg O₂ kg^?1 h^?1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s^?1, and a third‐order polynomial regression model fitted the data best. The upper critical swim speed (U_crit) of fish tested at two laboratories averaged 155 cm s^?1 (2·1 BL s^?1), but U_crit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s^?1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s^?1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s^?1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the U_crit for the fish used in the EMG trials (mean U_crit 168·2 cm s^?1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ≥80% of the U_crit.     

Solar heat gain in a desert rodent: unexpected increases with wind speed and implications for estimating the heat balance of free-living animals

We quantified metabolic power consumption as a function of wind speed in the presence and absence of simulated solar radiation in rock squirrels, Spermophilus variegatus, a diurnal rodent inhabiting arid regions of Mexico and the western United States. In the absence of solar radiation, metabolic rate increased 2.2-fold as wind speed increased from 0.25 to 4.0 m·s^-1. Whole-body thermal resistance declined 56% as wind speed increased over this range, indicating that body insulation in this species is much more sensitive to wind disruption than in other mammals. In the presence of 950 W·m^-2 simulated solar radiation, metabolic rate increased 2.3-fold as wind speed was elevated from 0.25 to 4.0 m·s^-1. Solar heat gain, calculated as the reduction in metabolic heat production associated with the addition of solar radiation, increased with wind speed from 1.26 mW·g^-1 at 0.25 m·s^-1 to 2.92 mW·g^-1 at 4.0 m·s^-1. This increase is opposite to theoretical expectations. Both the unexpected increase in solar heat gain at elevated wind speeds and the large-scale reduction of coat insulation suggests that assumptions often used in heat-transfer analyses of animals can produce important errors.Abbreviations absorptivity of coat to solar radiation - kinematic viscosity of air (mm²·s^-1) - reflectivity of coat to solar radiation - a r _B expected at zero wind speed (s·m^-1) - A _P projected surface area of animal on plane perpendicular to solar beam (cm²) - A _SKIN skin surface area (cm²) - b Coefficient describing change in r _B with change in square-root of wind speed (s^1.5·m^1.5) - d hair diameter (m) - d characteristic dimension of animal (m) - D _H thermal diffusivity of air (m²·s^-1) - E evaporative heat loss (W·m^-2) - I probability per unit coat depth that photon will strike hair - k constant equalling 1200 J·m^-3·°C^-1 - l _C coat depth m) - l _H hair length (m) - M metabolic rate (W·m^-2) - n density of hairs of skin (m^-2) - Q _A solar heat gain to animal (W·m^-2) - Q _I solar irradiance intercepted by animal (W·m^-2) - RQ respiratory quotient - r _A thermal resistance of boundary layer (s·m^-1) - r _B whole-body thermal resistance (s·m^-1) - r _E thermal resistance between animal surface and environment s·m^-1) - r _R radiative resistance (s·m^-1) - r _S sum of r _B and r _E at 0.25 m·s^-1 (s·m^-1) - r _T tissue thermal resistance s·m^-1) - T _AIR air temperature (°C) - T _B body temperature (°C) - T _E operative temperature of environment (°C) - T _ES standard operative temperature of environment (°C) - u wind speed (m·s^-1)     

Mixed substrate growth of methylotrophic yeasts in chemostat culture: Influence of the dilution rate on the utilisation of a mixture of glucose and methanol

The growth of Hansenula polymorpha and Kloeckera sp. 2201 with a mixture of glucose and methanol (38.8%/61.2%, w/w) and the regulation of the methanol dissimilating enzymes alcohol oxidase, catalase, formaldehyde dehydrogenase and formate dehydrogenase were studied in chemostat culture, as a function of the dilution rate. Both organisms utilized and assimilated glucose and methanol simultaneously up to dilution rates of 0.30 h^-1 (H. polymorpha) and 0.26h^-1, respectively (Kloeckera sp. 2201) which significantly exceeded _max found for the two yeasts with methanol as the only source of carbon. At higher dilution rates methanol utilisation ceased and only glucose was assimilated. Over the whole range of mixed-substrate growth both carbon sources were assimilated with the same efficiency as during growth with glucose or methanol alone.In cultures of H. polymorpha, however, the growth yield for glucose was lowered by the unmetabolized methanol at high dilution rates. During growth on both carbon sources the repression of the synthesis of all catabolic methanol enzymes which is normally caused by glucose was overcome by the inductive effect of the simultaneously fed methanol. In both organisms the synthesis of alcohol oxidase was found to be regulated differently as compared to catalase, formaldehyde and formate dehydrogenase. Whereas increasing repression of the synthesis of alcohol oxidase was found with increasing dilution rates as indicated by gradually decreasing specific activities of this enzyme in cell-free extracts, the specific activities of this enzyme in cell-free extracts, the specific activities of catalase and the dehydrogenases increased with increasing growth rates until repression started. The results indicate similar patterns of the regulation of the synthesis of methanol dissimilating enzymes in different methylotrophic yeasts.Abbreviations and Terms C₁ Methanol - C₆ glucose; D dilution rate (h^-1) - D _c critical dilution rate (h^-1) - q _s specific, rate of substrate consumption (g substrate [g cell dry weight]^-1 h^-1) - q _CO2 and q _O2 are the specific rates of carbon dioxide release and oxygen consumption (mmol [g cell dry weight]^-1 h^-1) - RQ respiration quotient (q _CO2 q _O2 ¹ ) - s ₀(C₁) and s ₀(C₆) are the concentrations of methanol and glucose in the inflowing medium (g l^-1) - s residual substrate concentration in the culture liquid (g l^-1) - Sp. A. enzyme specific activity - x cell dry weight concentration (gl^-1) - Y _X/C6 growth yield on glucose (g cell dry weight [g substrate]^-1     

Equilibrium conditions in polysomic inheritance for a panmictic population

A general model of a large 2m-ploid breeding population, withr loci ands _h alleles at the _h ^th locus is considered. It is assumed that the population is bisexual, non-overlapping and breeds by random mating. The genotypic structure of the population is presented as a bilinear form in the gametic output vectors where the genotype distribution is in the matrix form. Using the concept of the segregation distribution, the genotype proportions in the (n+1)^st generation are given. An equilibrium condition for random chromosome segregation is obtained in terms of gene frequencies.     

Effect of undecanoic acid on germination of microconidia of wild and undecanoic acid resistant mutant of trichophyton rubrum

Effects of undecanoic acid (UDA) on germination of microconidia and elongation of germ tubes in UDA sensitive (uda _s) wild type Trichophyton rubrum and UDA resistant (uda _r) mutant derived from it, were studied. UDA inhibited conidial germination of uda _s and uda _r strains at 30 g/ml and 120 g/ml respectively which were minimum inhibitory concentrations of UDA for these two strains. When spores from both uda _s and uda _r were germinated in presence of subinhibitory concentration of UDA, germ tube growth was short. The elongation of germ tubes of spores pregerminated in absence of UDA was also inhibited by dose of UDA not sufficient to inhibit germination.     

Leaf and environmental parameters influencing transpiration: Theory and field measurements

Summary The influence of variations in the boundary air layer thickness on transpirtion due to changes in leaf dimension or wind speed was evaluated at a given stomatal resistance (r _s) for various combinations of air temperature (T _a) and total absorbed solar energy expressed as a fraction of full sunlight (S _ffs). Predicted transpiration was found to either increase or decrease for increases in leaf size depending on specific combinations of T _a, S _ffs, and r _s. Major reductions in simulated transpiration with increasing leaf size occurred for shaded, highly reflective, or specially oriented leaves (S _ffs=0.1) at relatively high T _a when r _s was below a critical value of near 500 s m^-1. Increases in S _ffs and decreases in T _a lowered this critical resistance to below 50 s m^-1 for S _ffs=0.7 and T _a=20°C. In contrast, when r _s was above this critical value, an increase in leaf dimension (or less wind) resulted in increases in transpiration, especially at high T _a and S _ffs. For several combinations of T _a, S _ffs, and r _s, transpiration was minimal for a specific leaf size. These theoretical results were compared to field measurements on common desert, alpine, and subalpine plants to evaluate the possible interactions of leaf and environmental parameters that may serve to reduce transpiration in xeric habitats.     

Continuous cultivation of the yeast Candida utilis at different dilution rates on pineapple cannery effluent

Candida utilis was grown on a pineapple cannery effluent in a chemostat at dilution rates ranging between 0.05 and 0.65 h^–1 to establish optimal conditions for biomass production and chemical oxygen demand (COD) reduction. Sucrose, fructose and glucose were the main sugars in the effluent. Maximum value for cell yield coefficient and productivity were (0.686, g_x/g_s) and (2.96, g_x/l/h) at a dilution rate of 0.425 and 0.475 h^–1, respectively, while maximum COD reduction (98%) was attained at a dilution rate of 0.1 h^–1. The maintenance coefficient attained a value of (0.093, g_s/g_x/h). An increase in dilution rate produced a higher protein content of the biomass.