A sensitivity analysis of the 'Transmittance-Reflectance' method for measuring light absorption by aquatic particles

A thorough sensitivity analysis of the ‘Transmittance–Reflectance’(T-R) method for measuringin vivo light absorption by aquaticparticles retained on glass-fiber filters has been carried out.Particular attention has been devoted to the error contributionby the variability of the optical properties of the GF/F filtersused. The overall error of the measurement of the filter-retainedparticle optical density, OD_s, has been evaluated as ~0.002(1), with 0.0015 error contribution by the filter variability.The corresponding error of the optical density of the particlesuspension, OD_sus, has been obtained by differentiation of theequation expressing the experimental correlation (OD_susversusOD_s); the error increases with the optical density value, from= 0.0015 (for OD_sus = 0.05) to = 0.027 at the upper limit ofthe optical density range tested (OD_sus = 0.59). The validityrange of the experimental (OD_sus versus OD_s) correlation hasbeen shown to extend to OD_s = 0.75. The importance of the accuratecorrection for light backscattering performed by the T-R methodhas been investigated by comparison with results given by thestandard ‘Transmittance’ (T) method; it has beenshown that the coarse correction for light scattering includedin the T method may cause serious errors in the measured opticaldensity spectra of mineral detritus. This evidence confirmsthe need to resort to the T-R method for the measurement ofparticle samples of detritus-rich coastal waters. The papersummarizes the latest developments of the T-R method and includesan Appendix with asynopsis of the routine now used by the authors.     

Proposal for the simultaneous measurement of light absorption and backscattering by aquatic particulates

The paper presents a new experimental method that measures lightabsorption and backscattering by aquatic particles, combiningthe innovative features of the ‘modified filter–transfer–freeze’(FTF) and ‘transmittance–reflectance’ (T-R)techniques, namely no path-length amplification and accuratecorrectionfor scattering loss, respectively. This method (in short: theFTF/T-R method) measures both the transmittance and the reflectanceof particles deposited on a glass slide, using a double-beamspectrophotometer equipped with an integrating-sphere attachment.The data are interpreted by an algorithm that yields both theabsorption and the backscattering coefficients of the particlesample. The paper includes a summary of results of validationtests, that have been performed using samples ranging from purephytoplankton (low light scattering) to pure detrital particles(high light scattering), as well as a detailed analysis of theexperimental error. The FTF/T-R measurement is somewhat morelaborious than the standard transmittance measurement of particlesretained on glass fibre filters. However, it has the importantasset of permitting the simultaneous determination of lightabsorption and backscattering and it yields more accurate absorptiondata in situations where the magnitude of path amplificationby glass fibre filters is uncertain and light scattering bythe particles is high.     

Measurement of light absorption by aquatic particles retained on filters: determination of the optical pathlength amplification by the 'transmittance-reflectance' method

The optical pathlength amplification (ß factor), inducedby multiple scattering in glass-fibre filters used for lightabsorption measurements of aquatic particles, has been measuredby the transmittance-reflectance (T-R) method for algal specieswith cell diameter in the range from 1 to 5 µm. Theßfactors obtained showed a much lower dispersion than that observedin similar measurements carried out by the standard transmittancemethod, suggesting that this could be due, at least in part,to the incomplete account of the scattering losses taken bythe latter method. An experimental test has verified that theß factor expression derived from measurements carriedout by the T-R method on an algal culture is also applicableto detrital particles.     

f-Ratio and its relationship to ambient nitrate concentration in coastal waters

The relationship between thef-ratio [NO₃^– uptake/(NO₃^–+ NH₄⁺) uptake] and ambient nitrate concentration was evaluatedfor eight data sets from coastal waters. The f-ratio increasedasymptotically with increase in nitrate concentration in mostdata sets. However, the rate at which f-ratio increased at lownitrate concentration (slope = m) and the maximum attained f-ratio(f_max) varied among regions; the initial slope varied most withvalues ranging in excess of an order of magnitude. The datawere analyzed in relation to environmental factors and methodologicalconsiderations known to influence the f-ratio. Ambient ammoniumconcentration was important in accounting for regional differencesin the f versus NO₃^– relationship. A further analysisof the data, relating f-ratio to the ratio of NO₃^–/(NO₃^–+ NH₄⁺) concentrations yielded a much more regionally consistentand approximately linear relationship; slopes varied by lessthan a factor of two in the extreme cases. Inclusion of knownalternative (aside from NH₄⁺) sources of reduced-N (e.g. urea)and correction for methodological/computational errors (isotopedilution) systematically reduce f-ratio estimates. Other factors,e.g. reduced-N uptake by microheterotrophs, may systematicallyincrease the f-ratio.     

Diurnal regulation of NO-3 uptake in soybean plants IV. Dependence on current photosynthesis and sugar availability to the roots

The short-term dependence of NO^–₃ uptake upon photosynthesisand sugar supply to the roots of soybean plants was investigatedin a series of experiments where CO₂ availability, light intensityor conduction of phloem sap to the roots were severely limited.Removal of CO₂ from the atmosphere or girdling of the stem equallyprevented the stimulation of NO^–₃ uptake when plants weretransferred from darkness to the light. The effect of thesetwo treatments can be reversed by CO₂ re-supply or by additionof 10 mM glucose in the nutrient solution, respectively. Glucosewas also more effective in stimulating NO^–₃ uptake byintact plants in darkness than in light. Collectively, theseobservations are interpreted as evidence that the diurnal changesin NO^–₃ uptake are due to decreased phloem transport ofphotosynthates in darkness. Accordingly, the magnitude of thesechanges was much dependent on starch accumulation in the leavesat the end of the photo-period. Shading the plants lowered thisaccumulation, and resulted in an amplification of the diurnalchanges in NO^–₃ uptake. These results are discussed inconnection with the hypothesis that the carbon-dependent plasticityof the night/day ratio of NO^–₃ uptake is an importantfeature of the co-ordination of the acquisition of N and C bythe plant. Key words: Glycine max, light/dark cycle, NO^–₃ uptake, C and N acquisition     

Acclimation of Lolium temulentum to enhanced carbon dioxide concentration

Acclimation of single plants of Lolium temulentum to changing[CO₂] was studied on plants grown in controlled environmentsat 20°C with an 8 h photoperiod. In the first experimentplants were grown at 135 µ;mol m^–2 s^–1 photosyntheticphoton flux density (PPFD) at 415µl l^–1 or 550µll^–1 [CO₂] with some plants transferred from the lowerto the higher [CO₂] at emergence of leaf 4. In the second experimentplants were grown at 135 and 500 µmol m^–2 s^–1PPFD at 345 and 575 µl l^–1 [CO₂]. High [CO₂] during growth had little effect on stomatal density,total soluble proteins, chlorophyll a content, amount of Rubiscoor cytochrome f. However, increasing [CO₂] during measurementincreased photosynthetic rates, particularly in high light.Plants grown in the higher [CO₂] had greater leaf extension,leaf and plant growth rates in low but not in high light. Theresults are discussed in relation to the limitation of growthby sink capacity and the modifications in the plant which allowthe storage of extra assimilates at high [CO₂]. Key words: Lolium, carbon dioxide, photosynthesis, growth, stomatal density     

Effect of Supra-High Irradiation on the Photosynthetic System of the Cyanophyte Synechocystis PCC 6714

Stability of thylakoid components under supra-high irradiancewas studied with the cyanophyte Synechocystis PCC 6714. Theactivity of overall photosynthesis was quickly inactivated (T_1/2=20min) under supra-high irradiance (300 W m^–2, white light).In parallel with the inactivation of photosynthesis, QA in PSII was also inactivated. Both inactivations were acceleratedby chloramphenicol (CAP) addition. The reactivation of PS IIrequired weak irradiation and was suppressed by CAP. However,PS I measured as P700 was very stable. The level of PS I measuredas P700 was not significantly reduced by the irradiation for12 h even in the presence of CAP while the level of Cyt b₅₅₉,component of PS II, was decreased markedly. The function ofPS I before and after supra-high irradiation with CAP was examinedby comparing sizes of P700 oxidation induced by a short flash,by a continuous light, and by determination of O₂-and ferredoxin-reduction.No difference was observed in PS I actions before and afterthe irradiation treatment. These results indicate that the PSI complex is very tolerant of supra-high irradiation. However,the cells grown under supra-high irradiance contained much fewerPS I and PS II complexes than Cyt b₆–f complexes. Theformer levels were reduced to a half to one fourth of thosebefore growth while the level of Cyt b₆–f complex wasnot reduced so much. A possible mechanism for changes in thylakoidcomposition under supra-high irradiation was discussed. (Received February 16, 1991; Accepted June 12, 1991)     

Light Distribution in Discontinuous Canopies: Calculation of Leaf Areas and Canopy Volumes Above Defined 'Irradiance Contours' for use in Productivity Modelling

Plant canopies can be considered as assemblages of leaves, stemsand fruits growing in zones of differing irradiance demarcatedby contours of mean irradiance as measured on a horizontal surface. The following general equations have been derived to calculatethe leaf area (L_I) and the canopy volume (CV_I) in zones externalto any chosen contour of mean irradiance: (1) L_I = ((1nl)/(–K)(I–T_f) or leaf area index (LAI) if this is less (2) CV_I = L_I/(leaf area density m² m^–2), where I is the specified value of irradiance (horizontal surface)expressed as a decimal fraction of that above the canopy, Kis the appropriate extinction coefficient and T_f is the proportionof the total of available radiation which, if the canopy isdiscontinuous, would reach the ground by passing through gapsbetween the discrete canopy units. Where the canopy is continuousT_f is zero so expression (1) simplifies to L₁ = 1n I/–K(or LAI if this is less). For a range of model hedgerow orchards of varying dimensions,spacings and LAIs, it has been shown that the use of these equationsgives very similar results to those obtained by detailed calculationof light penetration. They therefore seem to be of potentialuse in calculating both potential dry-matter production by discontinuouscanopies of any type and, in the case of orchard fruit crops,the potential effect of changes in tree size, leaf area density,spacing etc. on the canopy volume in which irradiation is adequatefor fruit bud initiation and fruit colour development. light distribution, discontinuous canopy, irradiance contours, leaf area index, orchards     

Light-induced changes in chlorophyll a fluorescence and cytochrome f in intact spinach chloroplasts: The site of light-dependent regulation of electron transport

Dark-adapted intact spinach chloroplasts exhibited two peaks,P and M₁, at the early phase of fluorescence induction and atransient reduction of cytochrome f shortly after its initialphotooxidation and in parallel to the appearance of P. Analysisof the peak P and the transient reduction of cytochrome f indicatedthat electron transport in intact spinach chloroplasts was regulatedby light: electron transport was inactivated at the reducingside of photosystem I in the dark-adapted chloroplasts but rapidlyreactivated by illumination. The fluorescence peak M₁ was correlatedto the proton gradient formed across the thylakoid membrane. Effects on P and transient reduction of cytochromef of NO₂^–,3-phosphoglycerate (PGA) and oxalacetate (OAA), which can penetrateinto intact chloroplasts and accept electrons at different sitesafter photosystem I, were studied to determine the site of thelight regulation. NC₂^–, which receives electrons fromreduced ferredoxin, markedly diminished both P and the transientreduction of cytochrome.f, whereas PGA and OAA, the reductionsof which are NADP-dependent, failed to affect the two transients.The ineffectiveness of PGA and OAA could not be attributed tothe dark inactivation of glyceraldehyde-3-phosphate and malicdehydrogenases, because dark-adapted chloroplasts still retainedsufficiently high levels of the enzyme activities. The resultsindicate that electron transport in intact spinach chloroplastsis regulated by light after ferredoxin but before NADP, i.e.,at the reducing terminal of the electron transport chain. (Received May 29, 1980; )     

Measuring the Canopy Net Photosynthesis of Glasshouse Crops

A null balance method is described for measuring net photosynthesisof mature canopies of cucumber and other protected crops overperiods of 10 min in a single-span glasshouse (c. 9m x 18m inarea). Accuracy of control of the CO₂ concentration in the greenhouseatmosphere is within ±10 vpm of the normal ambient level(c. 350 vpm). The amounts of CO₂ used in canopy net photosynthesisare measured with linear mass flowmeters accurate to within±0.80g. The total errors incurred in measuring canopynet photosynthesis at an ambient CO₂ level are estimated tobe of the order of ± 1·2% in bright light (350W m^–2, PAR)and ±3·6% in dull light (100W m^–2, PAR). Measurements of the rates of net photosynthesis of a maturecanopy of a cucumber crop were made at near-ambient CO₂ concentrationsover a range (0–350 W m^–2) of natural light fluxdensities. A model of light absorption and photosynthesis applicableto row crops was used to obtain a net photosynthesis versuslight response curve for the cucumber crop. At a light fluxdensity of 350 W m^–2 the fitted value of canopy net photosynthesiswas 2.65 mg CO₂ m^–2s^–1 (equivalent to over 95 kgCO₂ ha^–1h^–1). The results are discussed in relationto the need for CO₂ supplements to avoid depletion in both ventilatedand unventilated glasshouses during late spring and summer. Key words: Glasshouse crops, cucumber, measurement, canopy photosynthesis, light, CO₂     

Phytoplanktonic carbon isotope fractionation: equations accounting for CO2-concentrating mechanisms

A model of carbon isotope discrimination by phytoplankton wasdeveloped which took into account the occurrence of a carbon-concentratingmechanism (CCM). A simple equation was obtained for the modelinvolving CO₂ active transport. In the case of HCO₃^– activetransport, another equation was developed based on a seriesof approximations. The former equation was used to analyse reportedand newly obtained data from culture experiments and field observationsin both freshwater and marine environments. In most cases, alinear relationship between a combined parameter, (1–f)Ci,which was made up of the relative contribution of active CO₂uptake to total carbon uptake (f) and the intracellular CO₂concentration (Ci), and CO₂ concentration in bulk solution (Ce)was obtained as (1–f)Ci = ace–b, with a high correlationcmfficient (r²>0.9). The slope a is suggested as a measureof the ratio of diffusive to total (diffusive+active) CO₂ transport,while bla represents CO₂ demand.     

Dark uptake of inorganic14C in oligotrophic oceanic waters

Dark uptake of inorganic ¹⁴C by offshore plankton was measuredat two depths at 36 stations in the Atlantic Ocean from 52°Sto 26°N, mainly along 30°W. The samples were incubatedfor 2 h with and without inhibition of biological activity withHgCl₂. In addition, six time course experiments were performed.The mean dark uptake rate varied from 0.68 to 4.82 (µmolC m^–3 h^–1 over the transect and showed a significantpositive relationship with chlorophyll a. The dark uptake wasusually >5% of the maximum photosynthetic capacity (P^m),and higher values relative to P^m were associated with low valuesof P_m and not with high absolute dark values. A linear relationshipbetween dark uptake and P_m was found with a background value(y-axis intercept) of 0.51 (µmol C m^–3 h^–1and a slope of 0.77% of P^m. A major fraction of the dark signal,66–80% of the total signal, persisted in bottles treatedwith HgCl2, indicating that most of the dark signal was independentof biological activity. Time course experiments showed a lineardark uptake with time for the first hours, whereafter the uptakeceased. At stations with low concentrations of inorganic nitrogen[>1 (µmol (NH₄⁺+NO₃^–)], a second stage was observedafter 3–8 h, probably due to an increase in bacterialactivity. The results suggest three mechanisms for the darkvalue in short-term incubations in oligotrophic waters. A backgroundvalue independent of biomass and incubation time which was thedominant part of the dark signal in samples with very low phytoplanktonbiomass (>0.3 p-g Chi a 1"). Another important part was residualsof ¹⁴C associated with plankton, probably adsorbed to compoundsinside the cells. This fraction was dominant in short-term incubationsat chlorophyll concentrations >0.3 p.g Chi a H. Active uptakeby living cells (total minus ‘HgCl2 uptake‘) wasonly a minor part of the dark signal in short-term incubations,but dominated at longer incubation time (>3–9 h), probablydriven by an increase in bacterial activity. A significant enhancementof the non-photosynthetic uptake of ¹⁴C was observed in light,probably associated with a carbon-concentrating mechanism inphytoplankton or light stimulation of ß-carboxylationactivity. The results strongly suggest that dark values shouldbe subtracted from the light uptake. This correction is particularlyimportant when photosynthetic rates are low, e.g. at low lightor in short-term incubations where a time-zero background becomesa significant part of the total uptake in light. Present address: National Environmental Research Institute,Department of Marine Ecology and Microbiology, Frederiksborgvej399, PO Box 358, DK-4000 Roskilde, Denmark     

Physiological evaluation of temperature effect on the growth processes of the mysid, Neomysis intermedia Czerniawsky

Ingestion, respiration, and molting loss rates were measuredover the 3 – 29°C range in Neomysis intermedia. Weightspecific rates of these physiological processes ranged from2 to 140% body C day^–1 for ingestion, from 2 to 15% bodyC day^–1 for respiration, and from 0.1 to 5% body C day^–1for molting loss. All weight-specific rates showed a logarithmicdecrease with a logarithmic increase in body weight, and a logarithmicincrease with a linear increase in temperature below 20 or 25°C.The effect of temperature, however, was different between thephysiological rates, with a large temperature dependency foringestion (Q₁₀ = 2.6 –3.9) and molting loss (Q¹⁰ = 2.9– 3.6) and a moderate temperature dependency for respiration(Q₁₀ = 1.9 – 2.1). Calculated assimilation efficiencychanged with body size, but was constant over the temperaturerange examined. Allocation of assimilated materials varied witha change in temperature, reflecting the different temperaturedependence between physiological processes. It was deduced thatthe strong temperature dependency of the growth rate in N. intermediaobserved in the previous studies resulted from the large temperatureeffect on ingestion and assimilation rates, superimposed bythe different allocation of assimilated materials. ¹Present address: Department of Botany, University of Tokyo,Hongo, Tokyo 113, Japan     

Sample preconditioning for measurement of fluorescence induction of chlorophyll a in marine phytoplankton

Conditions for measuring fluorescence induction curves (time-scalems) of in vivo chlorophyll ^a were studied using cultures ofDunaliella tertiolecta Butcher (Chlorophyceae) and of Thalassiosirapseudonana Hustedt (3H) (Bacillariophyceae), and samples ofnatural phytoplankton populations from the Grand Banks. Thearea above the fluorescence induction curve (A_DCMU) and themaximum fluorescence intensity (F_max) measured in the presenceof 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) were computedby microcomputer. Cells must be ‘conditioned’ or‘adapted’ prior to obtaining a fluorescence inductioncurve; dark-adaptation resulted in a lower A_DCMU and F_max thandid adaptation in far-red (720 nm) light, and was the conditioningmethod chosen. A_DCMU and F_max increased linearly with increasingirradiance up to 32.8 W m^–2 the highest actinic irradianceavailable. Information on the light history of D. tertiolectawas obtained by following the time-course of change in A_DCMUand in F_max for cells exposed for 10 min to far-red or to bluelight. The rise-time of the fluorescence induction curve andvalues of F_max were greater for samples of D. tertiolecta concentratedonto glass-fiber filters than for liquid samples, however, valuesof A_DCMU for filtered and liquid samples were not significantlydifferent. Samples of Grand Banks phytoplankton collected ontoglass-fiber filters and frozen for 28 d exhibited a significantdecrease in F_max and in A_DCMU relative to the same freshly-filteredsamples. Filtration and freezing of samples is not recommended. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP). Second International Workshop heldat the National Oceanographic Institute. Haifa. Israel in April–May1984.     

Growth of Plants in Different Oxygen Concentrations

Dwarf french beans (Phaseolus vulgaris var. Canadian Wonder)were grown in chambers at 25?C with the roots aerated at 20per cent oxygen and tops variously maintained at: T₁ O₂ 0.21;CO₂ 270?10^–6: T₂; O₂ 0.05, CO₂, CO₂ 270?10^–6: T₃;O₂ 0.21; CO₂ 550?10^–6. Experiment 1 (T₁ and T₂) lasted2 weeks: Experiment 2 (T₁ T₂ and T₃) only one week. Hourly estimatesof CO₂ uptake were made by gas analysis and weekly estimatesof fresh weight, dry matter in tops and roots, and leaf area,by sampling. Light intensity was 80 W m^–2 of photosyntheticallyactive radiation. An attempt was made to explain the results in terms of a simplelight absorption model such that where dV/dt is the rate of CO₂ uptake per plant, ßis the photosynthetic efficiency, I₀ is the incident light intensity,f is the fraction of incident light absorbed by unit leaf layerand L is the leaf area index. The analysis showed that ß(T₂)was at least double ß(T₁), whilst f(T₂) was smallerthan f(T₁) at a given leaf area. The results also required thatthroughout the period of the experiment, fL(T₁)=fL(T₂) at anygiven time, i.e. the treatment with the larger leaf area (T₂)has the smaller value of f, and therefore intercepts less lightper unit leaf area. This could be advantageous for plant growth,but requires further experiments. The photosynthetic rates per unit leaf are about 40 per centgreater in T₂ than T₁. Over the relatively short period of the experiment the resultsare adequately described by U=btⁿ, where U is the accumulatedcarbon dioxide uptake, b is related to the photosynthetic efficiency(different for the differing treatments), and n is a constant(similar for all treatments). This relationship with time isbelieved to be a relationship with accumulated radiation, forthe light was constant throughout the experiments. Comparisons of carbon fixed (measured gas uptake) and dry matteraccumulation (sampling) show great scatter with an average valueof 0.43. The first week's results were generally smaller thanthis value and the second week's greater. Energy fixation as a fraction of photosynthetically active radiationon the ground area covered by the plants ranged from 3.5 to10 per cent. The results from treatment T₃ were similar to T₂ suggestingthat increasing CO₂ concentration decreases the growth inhibitionat 21 per cent O₂.     

LIGHT-INDUCED OXYGEN EVOLUTION CAUSED BY HYDROGEN PEROXIDE IN CATALASE-INHIBITED CHLORELLA CELLS

1. Chlorella cells and spinach chioroplasts, whose catalase activityhad been more than 90% inhibited by 10^–5 M azide, werefound to decompose H₂O₂ photochemically to liberate oxygen,indicating that H₂O₂ was used as an oxidant of the HILL reaction.
2. That, however, the observed phenomena cannot be fully accountedfor in terms of the HILL reaction with H₂O₂ was revealed bythe observation that an extract of Chiorella cells, which hadbeen completely freed from chlorophyll, also showed a light-acceleratedO2 evolution from H₂O₂ in the presence of 10^–5 M azide.This extract contained a large quantity of catalase, which seemedto have been, in some way, involved in the reaction in question.
3. The catalatic H₂O₂ decomposition caused by crystalline catalaseof mammalian liver (in the presence of 10^–5 M azide) wasnot accelerated by the effect of light.

¹ Present address: Department of Biology, Faculty of Science,Niigata University, Niigata. (Received June 4, 1961; )     

Characteristics of the Cl- Action Site in the O2 Evolving Reaction in PS II Particles: Electrostatic Interaction with Ions

The role of Cl^– in the reactivation of O₂ evolution inphotosystem II (PS II) particles derived from spinach chloroplastswas studied in the presence of various salts. Multivalent ion(especially anion) salts were found to strongly suppress thereactivation of O₂ evolution by Cl^– in the Cl^–-depletedPS II particles in a competitive manner. The effectiveness ofanions in the suppression of Cl^–-supported O₂ evolutionwas in the order of trivalent>divalent>monovalent ones.Multivalent anions similarly suppressed O₂ evolution in theuntreated PS II particles under low and moderate Cl^– concentrations.pH dependence of the Cl^–-affinity (K_m) value for Cl^–)was also studied. Within the pH range 5.5 to 8 the K_m valuebecame higher as the pH of the medium increased. These resultssuggest that the membrane surface in the vicinity of the Cl^–action site is net positively charged and attracts Cl^–electrostatically, and that the site is almost freely accessibleto various anions. The origin and role of the local net positivedomain and the role of peripheral proteins are discussed. (Received May 27, 1985; Accepted October 8, 1985)     

IAA-oxidase in Impatiens balsamina Affected by GA3 and Tannic Acid

The activity of IAA-oxidase increased in the leaves of Impatiensbalsamina plants receiving inductive photoperiodic cycles andin plants receiving treatments with gibberellic acid (GA₃) and/ortannic acid (TA), even under non-inductive photoperiods; theactivity also increased in the stem receiving inductive photoperiodiccycles (8 h). Treatment with GA₃ and TA mimics the effect ofSD cycles in the development of some isoenzymes of IAA-oxidase.Thus a new isoenzyme at R_f 0.48 developed in the leaves andone at R_f 0.82 developed in both the stem and the leaves ofall plants receiving inductive treatments – photoperiodicor chemical – but not in water-treated controls undernon-inductive photoperiods. Another isoenzyme at R_f 0.68 developedonly in the stems. Flowering, gibberellic acid, IAA oxidase, Impatiens, phenols, photoperiod     

Leaf Development in Lolium temulentum: Photosynthesis and Photosynthetic Proteins in Leaves Senescing under Different Irradiances

Changes in carbon fixation rate and the levels of photosyntheticproteins were measured in fourth leaves of Lolium temulentumgrown until full expansion at 360 µmol quanta m^–2s^–1 and subsequently at the same irradiance or shadedto 90 µmol m^–2 s^–1. Ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco), light-harvesting chlorophylla/b protein of photosystem II (LHCII), 65 kDa protein of photosystemI (PSI), cytochrome f (Cytf) and coupling factor 1 (CF₁) declinedsteadily in amount throughout senescence in unshaded leaves.In shaded leaves, however, the decrease in LHCII and the 65kDa protein was delayed until later in senescence whereas theamount of Cyt f protein decreased rapidly following transferto shade and was lower than that of unshaded leaves at the earlyand middle stages of senescence. Decreases in the Rubisco andCF₁ of shaded leaves occurred at slightly reduced rates comparedwith unshaded leaves. These results indicate that chloroplastproteins in fully-expanded leaves are controlled individually,in a direction appropriate to acclimate photosynthesis to agiven irradiance during senescence. (Received August 20, 1992; Accepted January 5, 1993)     

Measurement of the Carbon Dioxide Compensation Point and the Rate of Loss of 14CO2 in the Light and Dark in Some Bryophytes

The CO₂ compensation point at 25 °C and 250 µEinsteinsm^–2 s^–1 wasmeasured for 27 bryo-phyte species, andwas found to be in the range of 45–160 µl CO₂ I^–1air. Under the same conditions Zea mays gave a value of 11 µlI^–1 and Horde um vulgare 76 µI^–1. The rate of loss of photosyntheticallyfixed ¹⁴CO₂ in the light and dark in six bryophytes (three mosses,two leafy liverworts, one thalloid liverwort) was determinedin CO₂-free air and 100% O₂. The rate of ¹⁴CO₂ evolution inthe light was less than that in the dark in CL₂-free air, butin 100% O₂ the rate in the light increased, so that in all butthe leafy liverworts it was greater than that in the dark. Raisingthe temperature tended to increase the rate of 14CO₂ evolutioninto CO₂-free air both in the light and dark, so that the light/dark(L/D) ratio did not greatly vary. The lower rate of loss of¹⁴CO₂ in the light compared tothe dark could be due to partialinhibition of ‘dark respiration’ reactions in thelight, a low rate of glycolate synthesis and oxidation, or partialreassimilation of the ¹⁴CO₂ produced, or a combination of someor all of these factors.