Inorganic phosphate speeds loaded shortening in rat skinned cardiac myocytes

Force generation in striated muscle is coupled with inorganic phosphate (P_i) release from myosin, because force falls with increasing P_i concentration ([P_i]). However, it is unclear which steps in the cross-bridge cycle limit loaded shortening and power output. We examined the role of P_i in determining force, unloaded and loaded shortening, power output, and rate of force development in rat skinned cardiac myocytes to discern which step in the cross-bridge cycle limits loaded shortening. Myocytes (n = 6) were attached between a force transducer and position motor, and contractile properties were measured over a range of loads during maximal Ca²⁺ activation. Addition of 5 mM P_i had no effect on maximal unloaded shortening velocity (V_o) (control 1.83 ± 0.75, 5 mM added P_i 1.75 ± 0.58 muscle lengths/s; n = 6). Conversely, addition of 2.5, 5, and 10 mM P_i progressively decreased force but resulted in faster loaded shortening and greater power output (when normalized for the decrease in force) at all loads greater than 10% isometric force. Peak normalized power output increased 16% with 2.5 mM added P_i and further increased to a plateau of 35% with 5 and 10 mM added P_i. Interestingly, the rate constant of force redevelopment (k_tr) progressively increased from 0 to 10 mM added P_i, with k_tr 360% greater at 10 mM than at 0 mM added P_i. Overall, these results suggest that the P_i release step in the cross-bridge cycle is rate limiting for determining shortening velocity and power output at intermediate and high relative loads in cardiac myocytes. muscle mechanics; force-velocity relationship; cross-bridge cycle     

G protein activation inhibits gating charge movement in rat sympathetic neurons

G protein-coupled receptors (GPCRs) control neuronal functions via ion channel modulation. For voltage-gated ion channels, gating charge movement precedes and underlies channel opening. Therefore, we sought to investigate the effects of G protein activation on gating charge movement. Nonlinear capacitive currents were recorded using the whole cell patch-clamp technique in cultured rat sympathetic neurons. Our results show that gating charge movement depends on voltage with average Boltzmann parameters: maximum charge per unit of linear capacitance (Q_max) = 6.1 ± 0.6 nC/µF, midpoint (V_h) = –29.2 ± 0.5 mV, and measure of steepness (k) = 8.4 ± 0.4 mV. Intracellular dialysis with GTPS produces a nonreversible 34% decrease in Q_max, a 10 mV shift in V_h, and a 63% increase in k with respect to the control. Norepinephrine induces a 7 mV shift in V_h and 40% increase in k. Overexpression of G protein ₁₄ subunits produces a 13% decrease in Q_max, a 9 mV shift in V_h, and a 28% increase in k. We correlate charge movement modulation with the modulated behavior of voltage-gated channels. Concurrently, G protein activation by transmitters and GTPS also inhibit both Na⁺ and N-type Ca²⁺ channels. These results reveal an inhibition of gating charge movement by G protein activation that parallels the inhibition of both Na⁺ and N-type Ca²⁺ currents. We propose that gating charge movement decrement may precede or accompany some forms of GPCR-mediated channel current inhibition or downregulation. This may be a common step in the GPCR-mediated inhibition of distinct populations of voltage-gated ion channels. ion channel modulation; G protein-coupled receptors; charge movement     

An empirical model of primary productivity (14C) using mesocosm data along a nutrient gradient

The two parameters of the hyperbolic tangent equation, P_m and, were estimated from in situ vertical profiles of primary productionusing mesocosm data along a nutrient gradient. The parameters,derived from 4-h (around noon) ¹⁴C incubations, were used togetherwith the photosynthesis-light curve and hourly solar radiationdata to calculate daily primary production rates (P_d). Approximately40% of the daily production occurred in the 4 h around noon.Considering parameter uncertainty, there was no indication ofan increase in variation in production with increased nutrientloading, nor did biomass-specific P-I parameters increase. Annualproduction ranged from 82 to 901 g C m^–2 year^–1and was highest in the highest nutrient treatment tank. Dailyproductivity ranged from 0.02 to 9.1 g C m^–2 day^–1and was significantly correlated, in all treatments, with acomposite parameter BI₀/k (where B is phytoplankton biomass;I₀ is daily radiation and k is the extinction coefficient).Linear regressions of P_d against BI₀/k indicated that much ofthe variability (86%) in productivity was explained by lightavailability and phytoplankton biomass. Two approaches for predictingproductivity were compared: (i) predicting production directlyfrom environmental variables (i.e. BI₀/k) and (ii) predictingthe parameters of the P-I curve from environmental variablesand using these to calculate daily production.     

Elastic moduli of excised constricted rat lungs

When airways constrict, the surrounding parenchyma undergoesstretch and distortion. Because of the mechanical interdependence between airways and parenchyma, the material properties of the parenchyma are important factors that modulate the degree ofbronchoconstriction. The purpose of this study was to investigate theeffect of changes in transpulmonary pressure (Ptp) and inducedconstriction on parenchymal bulk (k)and shear (µ) moduli. In excised rat lungs, pressure was measured atthe airway opening, and pressure-volume curves were obtained byimposing step decreases in volume with a calibrated syringe from totallung inflation. Calculation was made ofk during small-volume oscillations (1 Hz). Absolute lung volume at 0 cmH₂O Ptp was obtained bysaline displacement. To calculate µ, a lung-indentation test wasperformed. The lung surface was deformed with a cylindrical punch(diameter = 0.45 cm) in 0.25-mm increments, and the force required toeffect this displacement was measured by a weight balance. Measurementsof k and µ were obtained at 4 and 10 cmH₂O Ptp, and again at 4 cmH₂O Ptp, after delivery ofmethacholine aerosol (100 mg/ml) into the trachea. Values ofk and µ in rat lungs were similar tothose reported in other species. In addition, k and µ were dependent on Ptp. Afterinduced constriction, k and µ increased significantly. That k and µ can increase after induced constriction has important implicationsvis a vis the factors modulating airway narrowing.

     

Molecular determinants for the distinct pH sensitivity of Kir1.1 and Kir4.1 channels

Kir1.1 (ROMK1) is inhibited by hypercapnia andintracellular acidosis with midpoint pH for channel inhibition(pK_a) of ~6.7. Another close relative,Kir4.1 (BIR10), is also pH sensitive with much lower pH sensitivity(pK_a ~6.0), although it shares a high sequencehomology with Kir1.1. To find the molecular determinants for thedistinct pH sensitivity, we studied the structure-functional relationship using site-directed mutagenesis. AnNH₂-terminal residue (Lys-53) was found to be responsiblefor the low pH sensitivity in Kir4.1. Mutation of this lysine to valine(K53V), a residue seen at the same position in Kir1.1, markedlyincreased channel sensitivity to CO₂/pH. Reverse mutationon Kir1.1 (V66K) decreased the CO₂/pH sensitivities.Interestingly, mutation of these residues to glutamate greatly enhancedthe pH sensitivity in both channels. Other contributors to the distinctpH sensitivity were histidine residues in the COOH terminus, whosenumbers are fewer in Kir4.1 than Kir1.1. Mutation of two of thesehistidine residues in Kir1.1 (H342Q/H354N) reduced CO₂/pHsensitivities, whereas the creation of two histidines (S328H/G340H) inKir4.1 increased the CO₂/pH sensitivities. Combinedmutations of the lysine and histidine residues in Kir4.1(K53V/S328H/G340H) gave rise to a channel that had CO₂/pHsensitivities almost identical to those of the wild-type Kir1.1. Thusthe residues demonstrated in our current studies are likely themolecular basis for the distinct pH sensitivity between Kir1.1 andKir4.1.

     

Isotonic contractile and fatigue properties of developing rat diaphragm muscle

Postnatal transitions in myosin heavy chain (MHC) isoformexpression were found to be associated with changes in both isometric and isotonic contractile properties of rat diaphragm muscle(Dia_m). Expression of MHC_neo predominated inneonatal Dia_m fibers but was usually coexpressed withMHC_slow or MHC_2A isoforms. Expression ofMHC_neo disappeared by day 28. Expression ofMHC_2X and MHC_2B emerged at day 14 andincreased thereafter. Associated with these MHC transitions in theDia_m, maximum isometric tetanic force (P_o), maximum shortening velocity, and maximum power output progressively increased during early postnatal development. Maximum power output ofthe Dia_m occurred at ~40% P_o at days0 and 7 and at ~30% P_o in older animals.Susceptibility to isometric and isotonic fatigue, defined as a declinein force and power output during repetitive activation, respectively,increased with maturation. Isotonic endurance time, defined as the timefor maximum power output to decline to zero, progressively decreasedwith maturation. In contrast, isometric endurance time, defined as thetime for force to decline to 30-40% P_o, remained>300 s until after day 28. We speculate that with thepostnatal transition to MHC_2X and MHC_2Bexpression energy requirements for contraction increase, especiallyduring isotonic shortening, leading to a greater imbalance betweenenergy supply and demand.

     

Interaction of leg stiffness and surface stiffness during human hopping

Ferris, Daniel P., and Claire T. Farley. Interaction ofleg stiffness and surface stiffness during human hopping.J. Appl.Physiol. 82(1): 15-22, 1997.When mammals run,the overall musculoskeletal system behaves as a single linear "legspring." We used force platform and kinematic measurements todetermine whether leg spring stiffness(k_leg) isadjusted to accommodate changes in surface stiffness(k_surf) whenhumans hop in place, a good experimental model for examiningadjustments tok_leg in bouncinggaits. We found thatk_leg was greatlyincreased to accommodate surfaces of lower stiffnesses. The seriescombination ofk_leg andk_surf[total stiffness(k_tot)]was independent ofk_surf at a givenhopping frequency. For example, when humans hopped at a frequency of 2 Hz, they tripled theirk_leg on the leaststiff surface(k_surf = 26.1 kN/m; k_leg = 53.3 kN/m) compared with the most stiff surface(k_surf = 35,000 kN/m; k_leg = 17.8 kN/m). Values fork_tot were notsignificantly different on the least stiff surface (16.7 kN/m) and themost stiff surface (17.8 kN/m). Because of thek_leg adjustment,many aspects of the hopping mechanics (e.g., ground-contact time andcenter of mass vertical displacement) remained remarkably similardespite a >1,000-fold change ink_surf. This studyprovides insight into howk_leg adjustmentscan allow similar locomotion mechanics on the variety of terrainsencountered by runners in the natural world.

     

Pliometric contraction-induced injury of mouse skeletal muscle: effect of initial length

Hunter, Kam D., and John A. Faulkner. Pliometriccontraction-induced injury of mouse skeletal muscle: effect of initial length. J. Appl. Physiol. 82(1):278-283, 1997.For single pliometric (lengthening) contractionsinitiated from optimal fiber length (L_f), the mostimportant factor determining the subsequent force deficit is the workinput during the stretch. We tested the hypothesis that regardless ofthe initial length, the force deficit is primarily a function of thework input. Extensor digitorum longus muscles of mice were maximallyactivated in situ and lengthened at 2 L_f /s from oneof three initial fiber lengths (90, 100, or 120% of L_f) to one ofthree final fiber lengths (150, 160, or 170% of L_f). Maximalisometric force production was assessed before and after the pliometriccontraction. No single mechanical factor, including thework input(r² = 0.34), was sufficient to explain the differences in force deficits observed among groups. Therefore, the force deficit appears to arisefrom a complex interaction of mechanicalevents. With the data grouped by initial fiber length,the correlation between the average work and the average force deficitwas high(r² = 0.97-0.99). Consequently, differences in force deficits among groups were best explained on the basis of the initial fiber length andthe work input during the stretch.

     

Mechanical strain memory in airway smooth muscle

We investigated the effect of a singlerapid stretch on poststretch force and myosin phosphorylation in bovinetracheal smooth muscle. When unstimulated muscle strips were stretchedfrom suboptimal length to optimal length (L_o),poststretch steady-state force was not significantly different fromthat of unstretched control at L_o. However, whencarbachol-activated muscle strips were stretched from suboptimal lengthto L_o, poststretch force and myosin phosphorylation were lower than control and significantly correlated with initial length. When poststretch muscle strips were allowed to relax for 1 hand then activated by K⁺ depolarization, the developedforce remained significantly correlated with initial length. When thesame strain was applied in 23 increments to minimize peak stress,poststretch force and myosin phosphorylation increased significantly,approaching the levels expected at L_o. Furthermore,poststretch force development increased after each cycle of contractionand relaxation, approaching the control level after four cycles. Theseresults suggest that activated airway smooth muscle cells can retainrelatively precise memory of past strain when they are stretchedrapidly with high stress.

     

A model for phosphocreatine resynthesis

Nevill, Alan M., David A. Jones, David McIntyre, Gregory C. Bogdanis, and Mary E. Nevill. A model forphosphocreatine resynthesis. J. Appl.Physiol. 82(1): 329-335, 1997.A model for phosphocreatine (PCr) resynthesis is proposed based on a simple electric circuit, where the PCr store in muscle is likened to thestored charge on the capacitor. The solution to the second-order differential equation that describes the potential around the circuitsuggests the model for PCr resynthesis is given byPCr(t) = R  [d₁ ^· exp(k₁ ^· t) ± d₂ ^· exp(k₂ ^· t)],where R is PCr concentration at rest,d₁,d₂, k₁, andk₂ are constants, andt is time. By using nonlinear leastsquares regression, this double-exponential model was shown to fit thePCr recovery data taken from two studies involving maximal exerciseaccurately. In study 1, when themuscle was electrically stimulated while occluded, PCr concentrations rose during the recovery phase to a level above that observed at rest.In study 2, after intensive dynamicexercise, PCr recovered monotonically to resting concentrations. Thesecond exponential term in the double-exponential model was found tomake a significant additional contribution to the quality of fit inboth study 1 (P < 0.05) andstudy 2 (P < 0.01).

     

Short-term 17{beta}-estradiol decreases glucose Ra but not whole body metabolism during endurance exercise

The female sexhormone 17-estradiol (E₂) has been shown to increaselipid and decrease carbohydrate utilization in animals. Weadministrated oral E₂ and placebo (randomized, doubleblind, crossover) to eight human male subjects for 8 days (~3 mg/day) and measured respiratory variables, plasma substrates, hormones (E₂, testosterone, leptin, cortisol, insulin, andcatecholamines), and substrate utilization during 90 min of enduranceexercise. [6,6-²H]glucose and[1,1,2,3,3-²H]glycerol tracers were used to calculatesubstrate flux. E₂ administration increased serumE₂ (0.22 to 2.44 nmol/l, P < 0.05) anddecreased serum testosterone (19.4 to 11.5 nmol/l, P < 0.05) concentrations, yet there were no treatment effects on any of theother hormones. Glucose rates of appearance (R_a) anddisappearance (R_d) were lower, and glycerolR_a-to-R_d ratio was not affected byE₂ administration. O₂ uptake, CO₂production, and respiratory exchange ratio were not affected byE₂; however, there was a decrease in heart rate (P < 0.05). Plasma lactate and glycerol wereunaffected by E₂; however, glucose was significantly higher(P < 0.05) during exercise after E₂administration. We concluded that short-term oral E₂ administration decreased glucose R_a and R_d,maintained plasma glucose homeostasis, but had no effect on substrateoxidation during exercise in men.

     

Growth Analysis of Solution Culture-grown Winter Rye, Wheat and Triticale at Different Relative Rates of Nitrogen Supply

At low nitrogen (N) supply, it is well known that rye has ahigher biomass production than wheat. This study investigateswhether these species differences can be explained by differencesin dry matter and nitrogen partitioning, specific leaf area,specific root length and net assimilation rate, which determineboth N acquisition and carbon assimilation during vegetativegrowth. Winter rye (Secale cereale L.), wheat (Triticum aestivumL.) and triticale (X Triticosecale) were grown in solution cultureat relative addition rates (R_N) of nitrate-N supply rangingfrom 0.03–0.18 d^-1and at non-limiting N supply under controlledconditions. The relative growth rate (R_W) was closely equalto R_Nin the range 0.03–0.15 d^-1. The maximalR_W at non-limitingnitrate nutrition was approx. 0.18 d^-1. The biomass allocationto the roots showed a considerable plasticity but did not differbetween species. There were no interspecific differences ineither net assimilation rate or specific leaf area. Higher accumulationof N in the plant, despite the same relative growth rate atnon-limiting N supplies, suggests that rye has a greater abilityto accumulate reserves of nitrogen. Rye had a higher specificroot length over a wide range of sub-optimal N rates than wheat,especially at extreme N deficiency (R_N=0.03–0.06 d^-1).Triticale had a similar specific root length as that of wheatbut had the ability to accumulate N to the same amount as ryeunder conditions of free N access. It is concluded that thebetter adaptation of rye to low N availability compared to wheatis related to higher specific root length in rye. Additionally,the greater ability to accumulate nitrogen under conditionsof free N access for rye and triticale compared to wheat maybe useful for subsequent N utilization during plant growth.In general, species differences are explained by growth componentsresponsible for nitrogen acquisition rather than carbon assimilation.Copyright 1999 Annals of Botany Company Growth analysis, nitrogen, nitrogen productivity, partitioning, specific root length, Secale cereale L.,Triticum aestivum L., X Triticosecale, winter rye, winter wheat, winter triticale.     

Contraction-induced injury to single muscle fibers: velocity of stretch does not influence the force deficit

We tested the null hypothesis that theseverity of injury to single muscle fibers following a singlepliometric (lengthening) contraction is not dependent on the velocityof stretch. Each single permeabilized fiber obtained from extensordigitorum longus muscles of rats was maximally activated and thenexposed to a single stretch of either 5, 10, or 20% strain [%of fiber length (L_f)] ata velocity of 0.5, 1.0, or 2.0 L_f /s. Theforce deficit, the difference between maximum tetanic isometric force(P_o) before and after the stretch expressed as apercentage of the control value forP_o before the stretch, provided anestimate of the magnitude of muscle injury. Despite a fourfold rangefrom the lowest to the highest velocities, force deficits were notdifferent among stretches of the same strain. At stretches of 20%strain, even an eightfold range of velocities produced no difference inthe force deficit, although 40% of the fibers were torn apart at a velocity of 4 L_f /s. We conclude that, withinthe range of velocities tolerated by single permeabilized fibers, theseverity of contraction-induced injury is not related to the velocityof stretch.

     

E-C coupling failure in mouse EDL muscle after in vivo eccentric contractions

The objectives of this research were to determine thecontribution of excitation-contraction (E-C) coupling failure to the decrement in maximal isometric tetanic force(P_o) in mouse extensor digitorumlongus (EDL) muscles after eccentric contractions and to elucidatepossible mechanisms. The left anterior crural muscles of femaleICR mice (n = 164) wereinjured in vivo with 150 eccentric contractions.P_o, caffeine-,4-chloro-m-cresol-, andK⁺-induced contracture forces,sarcoplasmic reticulum (SR) Ca²⁺release and uptake rates, and intracellularCa²⁺ concentration([Ca²⁺]_i)were then measured in vitro in injured and contralateral control EDLmuscles at various times after injury up to 14 days. On the basis ofthe disproportional reduction inP_o (~51%) compared with caffeine-induced force (~11-21%), we estimate that E-C coupling failure can explain 57-75% of theP_o decrement from 0 to 5 days postinjury. Comparable reductions inP_o andK⁺-induced force (51%), and minorreductions (0-6%) in the maximal SRCa²⁺ release rate, suggest thatthe E-C coupling defect site is located at the t tubule-SR interfaceimmediately after injury. Confocal laser scanning microscopy indicatedthat resting[Ca²⁺]_iwas elevated and peak tetanic[Ca²⁺]_iwas reduced, whereas peak4-chloro-m-cresol-induced[Ca²⁺]_iwas unchanged immediately after injury. By 3 days postinjury, 4-chloro-m-cresol-induced[Ca²⁺]_ibecame depressed, probably because of decreased SRCa²⁺ release and uptake rates(17-31%). These data indicate that the decrease inP_o during the first several daysafter injury primarily stems from a failure in the E-C couplingprocess.

     

Dynamic properties of lung parenchyma: mechanical contributions of fiber network and interstitial cells

Yuan, Huichin, Edward P. Ingenito, and Béla Suki.Dynamic properties of lung parenchyma: mechanical contributions offiber network and interstitial cells. J. Appl.Physiol. 83(5): 1420-1431, 1997.We investigatedthe contributions of the connective tissue fiber network andinterstitial cells to parenchymal mechanics in a surfactant-freesystem. In eight strips of uniform dimension from guinea pig lung, weassessed the storage (G) and loss (G") moduli by usingpseudorandom length oscillations containing a specially designed set ofseven frequencies from 0.07 to 2.4 Hz at baseline, during methacholine(MCh) challenge, and after death of the interstitial cells.Measurements were made at mean forces of 0.5 and 1 g and strainamplitudes of 5, 10, and 15% and were repeated 12 h later in the same,but nonviable samples. The results were interpreted using a linearviscoelastic model incorporating both tissue damping (G) and stiffness(H). The G and G" increased linearly with the logarithmof frequency, and both G and H showed negative strain amplitude andpositive mean force dependence. After MCh challenge, the G andG" spectra were elevated uniformly, and G and H increased by<15%. Tissue stiffness, strain amplitude, and mean force dependencewere virtually identical in the viable and nonviable samples. The G andhence energy dissipation were ~10% smaller in the nonviable samplesdue to absence of actin-myosin cross-bridge cycling. We conclude thatthe connective tissue network may also dominate parenchymal mechanicsin the intact lung, which can be influenced by the tone or contractionof interstitial cells.

     

Internode Length in Pisum. A New Allele at the le Locus

In Pisum sativum L. a third, more severe, allele at the internodelength locus le is identified and named le^d. Plants homozygousfor le^d possess shorter internodes and appear relatively lessresponsive to GA₂₀ than comparable le (dwarf) plants. Gene le^dmay act by reducing the 3ß-hydroxylation of GA₂₀ tothe highly active GA₁ more effectively than does gene le. Theresults indicate that le is a leaky mutant and therefore thatendogenous GA₁ influences internode elongation in dwarf (le)plants. Pisum sativum, peas, internode length, genetics, gibberellin, dwarf elongation     

Comparison of carbon-specific growth rates and rates of cellular increase of phytoplankton in large limnetic enclosures

Potential carbon-specific growth rates of phytoplankton wereestimated from a series of measurements of photosynthetic radio-carbonuptake over 4- and 24-h exposure periods in the light fieldsof three large limnetic enclosures (‘Lund Tubes’),each providing different limnological and trophic conditions.Photosynthetic behaviour and short-term, chlorophyll-specificcarbon-fixation rates conformed to well-established criteriabut, over 24 h, the net retention represented 23–82% ofthe carbon fixed during the daylight hours. Potential mean growthrates (k'_p, of the photo-autotrophic community were calculatedas the net exponential rates of daily carbon-accumulation relativeto derived, instantaneous estimates of the cell carbon-content.Apparent actual community growth rates (k'_D were calculatedas the sum of the exponential rates of change of each of themajor species present, corrected for probable rates of in situgrazing and sinking, and expressed relative to the fractionof total biomass for which they accounted. The correspondingvalues were only occasionally similar, k'_p generally exceedingK'_D by a factor of between 1 and 30 or 1 and 14, depending uponthe carbon:chlorophyll ratio used. The ratio, K'_p/K'_D was foundto vary inversely both to k'_D and to k_n, the net rate of changein phytoplankton biomass, suggesting that measured carbon fixationrates merely represent a capacity for cellular increase which,owing to other likely limitations upon growth, is seldom realized.Apparent rates of loss of whole cells do not account for theloss of carbon; that the ‘unaccounted’ loss rates(K'_p–K'_D varied in direct proportion to K'_p (i.e., losseswere least when chlorophyll-specific photosynthetic productivitywas itself limited) is best explained by physiological voidingof excess carbon (for instance, by respiration, photorespiration,excretion) prior to the formation of new cells.     

Modelling and Measuring Transpiration from Scots Pine with Increased Temperature and Carbon Dioxide Enrichment

Starting in 1996, individual trees of Scots pine (Pinus sylvestrisL.) aged 30 years, were grown in closed-top chambers and exposedto either normal ambient conditions (CON), elevated CO₂(approx.700 µmol mol^-1; Elev. C), elevated temperature (approx.2 °C and approx. 6 °C above the outside ambient temperatureduring the ‘growing season’ and ‘off season’,respectively; Elev. T) or a combination of elevated CO₂and warmertemperature (Elev. CT). Sap flow was monitored simultaneouslyby the constant-power heat balance method in a total of 16 trees,four for each treatment, over a 32 d period in summer 1998 (afterthe completion of needle expansion and branch elongation). Toquantify the contributions of crown and physical environmentalvariables to total crown transpiration, a ‘sun/shade model’was developed and used to partition the changes in transpirationto different sources. The results of the sap flow measurementsindicate that (1) total daily sap flow (E_tree.d) varied from0.15–3.41 kg per tree; (2) the treatment effect on E_tree.ddependedgreatly on the weather conditions; (3) the cumulative E_tree.dforthe 32 d dropped significantly by 22% relative to CON (P =0.038)under Elev. C and increased significantly by 21% (P =0.043)and 16% (P =0.048) under Elev. T and Elev. CT, respectively.In general, the modelled transpiration gave good agreement withthe sap flow results. The model computations showed that, ona typical sunny day in summer, the effect of treatment on crownstomatal conductance was responsible for approx. 80% of thechange inE_tree.d , while the increase in needle area and theeffect on total radiation absorption contributed only a smallpercentage. Furthermore, sunlit needles were responsible forover 60% of change in transpiration. The effect of the treatmentson E_tree.dwas larger at high temperature and vapour pressuredeficit but was not sensitive to incident daily radiation. Copyright2000 Annals of Botany Company Transpiration model, sap flow, CO₂and temperature elevation, environment-controlled chamber, Pinus sylvestris L.     

Common canonical variates

Canonical correlation analysis measures the linear relationshipbetween two random vectors X₁ and X₂ as the maximum correlationbetween linear combinations of X₁ and linear combinations ofX₂. Several generalisations of canonical correlation analysisto k2 random vectors X₁ ..., X_k have been proposed in the literature(Kettenring, 1971, 1985), based on the principle of maximisingsome generalised measure of correlation. In this paper we proposean alternative generalisation, called common canonical variates,based on the assumption that the canonical variates have thesame coefficients in all k sets of variables. This generalisationis applicable in situations where all X_i have the same dimension.We present normal theory maximum likelihood estimation of commoncanonical variates, and illustrate their use on a morphometricdata set.