Fine Root Productivity and Turnover in Two Evergreen Central Himalayan Forests

Fine root production and mortality in central Himalayan evergreenforests consisting of Quercus leucotrichophora (banj oak) andPinus roxburghii (chir pine) were measured. Fine root productionand mortality decreased with increasing soil depth. Annual fineroot production was higher in the broadleafed forest than inthe coniferous forest, across months and seasons (1.3 and 1.5-timesmore living and dead root biomass, respectively in banj oakthan in chir pine). Live fine root production was 2508 kg ha^-1year^-1inchir pine forest and 3631 kg ha^-1year^-1in banj oak forest. Deadfine roots accumulated at a rate of 1197 and 1525 kg ha^-1year^-1inchir pine and in banj oak forest, respectively. In both forests,the greatest fine root production was recorded in the rainyseason followed by summer and winter seasons. Both soil androot nitrogen concentration decreased with increasing soil depth.Nitrogen uptake was higher in banj oak forest (12.1 kg ha^-1year^-1)than chir pine forest (7.2 kg ha^-1year^-1).Copyright 1999 Annalsof Botany Company Fine root production, fine roots, necromass, banj oak, chir pine, Quercus leucotrichophora , Pinus roxburghii .     

Effects of Photoperiod and Maturity Genes on Plant Growth, Partitioning, Radiation Use Efficiency, and Yield in Soyabean [Glycine max(L.) Merrill] 'Clark'

Plants of four isolines of soyabean [Glycine max(L.) Merrill]‘Clark’, viz‘L71-920’ (maturity genecomplemente₁e₂e₃ ), ‘L80-5914’ (E₁e₂e₃), ‘Clark’(e₁E₂E₃), and ‘L65-3366’ (E₁E₂E₃), were grown inshort (12.25 h d ^{- 1}natural light) and long days (12.25 h d^{- 1}natural light supplemented with 2.75 h d ^{- 1}low-irradianceartificial light) from first flowering to maturity in a polythenetunnel maintained at 30/24°C (day/night). Whereas therewere few differences among the isolines grown in short days,in long days the dominant alleles increased crop duration, biomassand seed yield substantially. Increases in biological and economicyield were not solely a consequence of longer crop duration:the dominant alleles also increased crop growth rate and radiationuse efficiency in long days (from 1.3 g MJ ^{- 1}total radiationine₁e₂e₃ to 2.8 g MJ ^{- 1}inE₁E₂E₃ ). Greater radiation use efficiencyresulted from a relatively longer leaf area duration, betterdistribution and orientation of a larger mass of leaves withinthe canopy, and smaller partitioning of assimilates to reproductivestructures. The work reveals the substantial effects of thethree lociE₁ / e₁, E₂/ e₂and E₃/e₃ on the response of plantgrowth, as well as development, to environment. Their relevanceto crop adaptation is discussed. Copyright 2000 Annals of BotanyCompany Glycine max(L.) Merrill, soyabean, maturity genes, flowering, phenology, growth, yield     

Cyclic AMP in Rhizobia and Symbiotic Nodules

Cyclic adenosine 3',5'-monophosphate (cAMP) content of variouscultured rhizobia strains and tissues of legumes and non-leguminousplants was measured by enzyme immunoassays. Most rhizobia, culturedfor 44 to 165 h, contained cAMP ranging from 0.6 to 5 pmol mg^-1proteinexcept forAzorhizobium caulinodansORS571. The culture mediaalso contained varying amounts of cAMP depending on the strainof rhizobia.Azorhizobiumcells and their media contained no detectablecAMP. Nodules from most legumes and non-legumes had cAMP contentsranging from 2–70 pmol g^-1f.wt. However, nodules fromSesbaniarostrata,Crotalaria spectabilisandParasponia andersoniishowedundetectable cAMP levels, and those fromGlycine maxandVignaangularisoccasionally showed levels below the detection limit.The leaves of non-legumes mostly had cAMP levels below detectionlimit (approx. 1.0 pmol g^-1 f.wt), while the leaves ofa few legumes occasionally had detectable cAMP. The possiblerole of cAMP as a symbiotic signal is discussed. cAMP; legumes; modules; rhizobia; symbiosis     

Modulation of K+ currents in monocytes by VCAM-1 and E-selectin on activated human endothelium

Resting membrane potential (RMP) and whole cell currents wererecorded in human THP-1 monocytes adherent to polystyrene, unstimulated human umbilical vein endothelial cells (HUVECs),lipopolysaccharide (LPS)-treated HUVECs, immobilizedE-selectin, or vascular cell adhesion molecule 1 (VCAM-1)using the patch-clamp technique. RMP after 5 h on polystyrene was24.3 ± 1.7 mV (n = 42) with delayed rectifier K⁺(I_dr) andCl currents(I_Cl) presentin >75% of the cells. Inwardly rectifying K⁺ currents(I_ir) werepresent in only 14% of THP-1 cells. Adherence to unstimulated HUVECsor E-selectin for 5 h had no effect on I_ir orI_Cl but decreasedI_dr. Five hoursafter adherence to LPS-treated HUVECs, outward currents were unchanged,but I_ir waspresent in 81% of THP-1 cells. A twofold increase inI_ir and ahyperpolarization (41.3 ± 3.7 mV,n = 16) were abolished by pretreatmentof THP-1 cells with cycloheximide, a protein synthesis inhibitor, orherbimycin A, a tyrosine kinase inhibitor, or by pretreatment of theLPS-treated HUVECs with anti-VCAM-1. Only a brief (15-min) interactionbetween THP-1 cells and LPS-treated HUVECs was required toinduce I_ir expression 5 h later. THP-1 cells adherent to VCAM-1 exhibited similarconductances to cells adherent to LPS-treated HUVECs. Thus engagementof specific integrins results in selective modulation of differentK⁺ conductances.

     

Light Dependency of Carboxylation Efficiency and Ribulose-1, 5-Bisphosphate Carboxylase Activation in Trifolium subterraneum L. Leaves

The effect of photosynthetic photon flux density (PPFD) on carboxylationefficiency, estimated as the initial slope (IS) of net CO₂ assimilationrate versus intercellular CO₂ partial pressure response curve,as well as on ribulose-1, 5-bisphosphate carboxylase (Rubisco)activation was measured in Trifolium subterraneum L. leavesunder field conditions. The relationship between IS and PPFDfits a logarithmic curve. Rubisco activation accounts for theIS increase only up to a PPFD of 550 µmol photons m^-2s^-1. Further IS increase, between 550 and 1000 µmol photonsm^-2 s^-1, could be related to a higher ribulose fcwphosphate(RuBP) availability. The slow, but sustained IS increase above1000 µmol photons m^-2 s^-1 could be explained by the mesophyllCO₂ diffusion barriers associated with the high chlorophylland protein content in field developed leaves. Key words: Photosynthesis, initial slope, ribulose-1, 5-bissphosphate carboxylase activation, light response, Trifolium subterraneum L     

Quantal Response of Seed Germination in Seven Genera of Cruciferae to White Light of Varying Photon Flux Density and Photoperiod

The response of the germination of seeds of Barbarea vema (Mill.)Aschers, Brassica chinensis L., Brassica juncea (L.) Czern.& Coss., Brassica oleracea L. var. gongylodes L., Camelinasaliva (L.) Crantz, Eruca saliva Mill., Lepidium sativum L.,Nasturtium officinale R. Br., and Rorippa palustris (L.) Besserto white fluorescent light of different photon flux densitiesapplied for different daily durations in a diurnal alternatingtemperature regime of 20 °C/30 °C (16 h/8 h) was quantifiedby linear relations between probit percentage germination andthe logarithm of photon dose, the product of photon flux densityand duration. The low energy reaction, in which increasing dosepromotes germination, was detected in all the seed populationsbut in Barbarea vema and Brassica Juncea the lowest photon doseapplied (10^–5–2 and 10^{–5 7} mol m^–2 d^–1,respectively) was sufficient to saturate the response. Comparisons,where possible, between photoperiods demonstrated reciprocity,i.e. germination was proportional to photon dose irrespectiveof photoperiod, for the low energy reaction in Brassica oleracea(1 min d^–1 to 1 h d^–1), Camelina saliva (1 min d^–1to 8 h d^–1), Eruca saliva (1 min d^–1 to 24 h d^–1),Lepidium sativum (I min d^–1 to 8 h d^–1) and Rorippapalustris (1 min d^–1 to 8 h d^–1), but not in Brassicachinensis and Nasturtium officinale. The high irradiance reaction,in which increasing dose inhibits germination, was detectedin Barbarea vema, Brassica chinensis, Brassica juncea, Brassicaoleracea, and Camelina saliva. The minimum dose at which inhibitionwas detected was lO^–0–3 mol m^–2 d^–1.These results are discussed in the context of devising optimallight regimes for laboratory tests intended to maximize germination The response of germination to photon dose was also quantifiedwith 3 x 10^–4 M GA₂, co-applied (Brassica chinensis, Camelinasaliva, and Lepidium sativum) and with 2 x 10^–2 M potassiumnitrate co-applied (Brassica chinensis). In the latter casepotassium nitrate had no effect in the dark and inhibited germinationin the light, but GA₂, promoted germination substantially inall three species. Variation amongst seeds in the minimum photondose required to stimulate germination was not affected by co-applicationof GA₂, in Brassica chinensis and Camelina saliva, whereas seedsof Lepidium salivum showed a narrower distribution of sensitivitiesto the low energy reaction in the presence of GA₂ Barbarea vema (Mill.) Aschers, Brassica chinensis L., Brassica juncea (L.) Czern. & Coss., Brassica oleracea L. var. gongylodes L., Camelina saliva (L.) Crantz, Eruca saliva Mill., Lepidium satiaum L., Nasturtium officinale R. Br., Rorippa palustris (L.) Besser, Cruciferae, light, gibberellic acid, seed germination, seed dormancy     

The Effects of Temperature and Light Intensity on Embryo Numbers in Wheat Doubled Haploid Production through WheatxMaize Crosses

Triticum aestivumxZea mayscrosses are now widely used in theproduction of wheat doubled haploids to produce homozygous lines.Seasonal effects are known to influence the number of haploidembryos produced through wheatxmaize crosses, but the effectsof temperature and light have not been quantified. This studyinvestigated the effect of temperature and light intensity onhaploid embryo production. New Zealand wheat cultivars weregrown in a glasshouse until booting when they were transferredto growth cabinets at three temperatures (day/night; 17/12,22/17 or 27/22 °C at an irradiance of 250 µmol m^-2s^-1PAR).In another experiment, wheat lines were transferred to a growthcabinet at one of three light intensities (300, 500 or 1000µmol m^-2s^-1PAR at 22/17 °C day/night, with a photoperiodof 16 h). The temperature and light intensity at which pollinationswere made and subsequent fertilisation and embryo developmentoccurred, significantly (P<0.01) influenced the frequencyof haploid embryo production. The optimal temperature for embryorecovery was 22/17 °C. The greatest number of embryos wasproduced at a light intensity of 1000 µmol m^-2s^-1. Thesefindings will result in improvements in the overall efficiencyof the wheatxmaize system for wheat doubled haploid production.Copyright1998 Annals of Botany Company Intergeneric crossing, temperature, light intensity,Triticum aestivum,wheat,Zea mays,maize.     

Inward and Outward Movement of Ammonium in Root Systems: Transient Responses during Recovery from Nitrogen Deprivation in Presence of Ammonium

Morgan, M. A. and Jackson, W. A. 1988. Inward and outward movementof ammonium in root systems: transient responses during recoveryfrom nitrogen deprivation in presence of ammonium.— J.exp. Bot. 39: 179-191. Net ammonium uptake by 20-d-old wheat (Triticum aestivum cv.Kleiber) and oat (Avena sativa cv. Tarok) seedlings was increased5- to 10-fold when the seedlings were deprived of nitrate duringthe 14-20 d period. The effect of nitrogen deprivation was toincrease net ¹⁵N-ammonium influx and decrease net ¹⁴N-ammoniumefflux during a 1 h assay period. The sizeable rate of net ¹⁵N-ammoniuminflux resulting from nitrogen deprivation was stimulated furtherby prior exposure of the seedlings to ¹⁴N-ammonium for 5 h.Additional exposure to ¹⁴N-ammonium caused the stimulated rateof ¹⁵N-ammonium influx to decline. During the 1 h assays in¹⁵N-ammonium, net ¹⁴N-ammonium efflux increased after 2 h exposureto ¹⁴N-ammonium, peaked at 5–10 h, and then declined.The consequence of the differential response of the influx andefflux processes in wheat was a marked decrease in net ammoniumuptake in the initial 2–5 h, followed by a recovery which,in turn, was followed by a slow decline. In oat, there was norecovery in net ammonium uptake after 2–5 h. Interference in ammonium assimilation by presence of methioninesulphoximine after 5 h did not inhibit expression of the ammonium-stimulatednet ¹⁵N-ammonium influx at 10 h but did substantially increasenet ¹⁴N-ammonium efflux. In nitrogen depleted seedlings, andin those exposed to ¹⁴N-ammonium for 2 h, subsequent net ¹⁴N-ammoniumefflux during 1 h in ¹⁵N-ammonium exceeded the quantity of ¹⁴N-ammoniuminitially in the roots. The increase in ¹⁵N-ammonium influx upon nitrogen deprivation,its further stimulation with 5-10 h exposure to ammonium andits subsequent decline, are discussed as possibly resultingfrom (a) the operation of two ammonium influx systems (b) theinterplay of tissue ammonium and a product of its assimilationrespectively acting as positive and negative effectors of asingle influx system and (c) variations in energy supply fromthe shoots. Key words: Net ammonium uptake, stimulated ammonium influx, ammonium efflux, tissue ammonium     

Stomatal Functioning of In Vitro and Greenhouse Apple Leaves in Darkness, Mannitol, ABA, and CO2

Leaves from in vitro and greenhouse cultured plants of Malusdomestica (Borkh.) cv. Mark were subjected to 4 h of darkness;4 h of 1 M mannitol induced water stress; 1 h of 10^–4M to 10^–7 M cis-trans abscisic acid (ABA) treatment; 1h of 0.12% atmospheric CO₂. Stomatal closure was determinedby microscopic examination of leaf imprints. In all treatments,less than 5% of the stomata from leaves of in vitro culturedplants were closed. The diameter of open stomata on leaves fromin vitro culture remained at 8 µm. In contrast, an averageof 96% of the stomata on leaves of greenhouse grown plants wereclosed after 4 h in darkness; 56% after 4 h of mannitol inducedwater stress; 90% after 1 h of 10^–4 M ABA treatment; 61%after 1 h in an atmosphere of 0.12% CO₂. Stomata of in vitroapple leaves did not seem to have a closure mechanism, but acquiredone during acclimatization to the greenhouse environment. Thelack of stomatal closure in in vitro plants was the main causeof rapid water loss during transfer to low relative humidity.     

Circadian Rhythms of Potassium and Sodium Contents in the Growing Front of Neurospora crassa

The temporal changes of potassium (K⁺) and sodium (Na⁺) contentsin the growing front of Neurospora crassa (al-2, bd strain)grown on solid medium showed circadian rhythms which persistedfor at least 45 h in the dark. The K⁺ content reached a maximumat about 10 and 30 h after the transfer from light to darkness,while the Na⁺ content was at a minimum at these times. Boththe rhythms were set off by the light to dark transition andwere not observed in constant light. The phase of the circadianrhythm of conidiation of this strain was delayed by 5 h by exposureto 50 min of white light (photon fluence rate 20.7 W/m²) 7 hafter the light to dark transition. The same exposure significantlychanged the ratio of K⁺ to Na⁺ content in the growing frontmeasured 8 h after the exposure. ³ Present address: Pesticides Research Laboratory, TakarazukaResearch Center, Sumitomo Chemical Co., Ltd., 2-1, 4-chome,Takatsukasa Takarazuka, Hyogo 665, Japan. (Received June 26, 1984; Accepted January 11, 1985)     

Photosynthesis of Stands of Tomato, Cucumber and Sweet Pepper Measured in Greenhouses under Various CO2-concentrations

The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO₂-concentrations between 200 and 1200 µmolmol^-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO₂ balance, usingnitrous oxide (N₂O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO₂ concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyP_max 5-9 g m^-2 h^-1 CO₂ uptake; ratio P_max/LAI 1·5-3 gm^-2 h^-1; light compensation point 32-86 µmol s^-1 m^-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol^-1 and CO₂ compensation point 18-54 µmolmol^-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO₂, CO₂ balance, CO₂ use efficiency, cucumber, _{Cucumis sativus} L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas     

Auxin Stimulates Cl-Uptake by Oat Coleoptiles

The effects of auxin on net ion fluxes near parenchyma of oatcoleoptiles were studied using the non-invasive MIFE systemto measure specific ion fluxes using ion selective microelectrodes.Application of 10 µM1-naphthaleneacetic acid (NAA) for3 h caused doubling of coleoptile segment growth, without changingthe pH of the unbuffered bathing solution from pH 5.4 duringthat time. Short term experiments revealed that auxin led toan immediate three-fold increase of chloride influx to 1200nmol m^-2s^-1, maintained for at least 1 h. In the first minutesafter auxin application, proton fluxes were small (-25 nmolm^-2s^-1, an efflux) and tended to decrease, whereas potassiumand calcium fluxes changed little, fluctuating from -100 to0 nmol m^-2s^-1and from -15 to 0 nmol m^-2s^-1, respectively. Itis suggested that one target of auxin action in plant cellsis the plasma membrane chloride transport system mediating increasedchloride uptake.Copyright 1998 Annals of Botany Company Auxin, chloride transport, ion flux,Avena sativaL., oat.     

Temperature Response of Early Foliar Expansion of Potato and Wheat

We studied the course of early leaf area expansion and specificleaf area (S_LA) in potato (Solanum tuberosum L.) and wheat (Triticumaestivum L.) genotypes and tested whether air temperature explainsdifferences in these courses within different environments.Such knowledge can be used to improve crop growth modelling.The relative rate of leaf area expansion (R_L) of potato andwheat decreased with thermal time, but was nearly linear upto a leaf area index (L) of 1.0. TheR_L (L < 1; mean: 17.9x 10^-3°C^-1 d^-1) of potato showed an interaction betweengenotype and environment, and varied with year. TheR_L (L <1; mean: 7.1 x 10^-3°C^-1 d^-1) of winter wheat was lower thanthat of spring wheat (mean: 10.9 x 10^-3°C^-1 d^-1), and bothvaried with year. S_LAof potato increased nearly linearly withthermal time from 5 to 15 m² kg^-1at 50% emergence, to 20 to25 m² kg^-1at 155°Cd, and then decreased slightly. The S_LAofboth winter and spring wheat began at 16 to 23 m² kg^-1and inmost cases increased slightly with thermal time. In potato,regression parameters of S_LAwith thermal time were affectedby environment (management conditions and year) and genotype;in wheat they were affected by environment (year and site).Treatment effects on R_Lof potato were not correlated with thoseon S_LA , and were only partly correlated for wheat. Thereforewe conclude that the early foliar expansion of potato is associatedwith a strong increase in S_LA , and not so for wheat. For bothcrops the course of early leaf area expansion and ofS_LA withair temperature is not robust over environments and genotypes.The consequences of these results for modelling are discussed.Copyright 2000 Annals of Botany Company Triticum aestivum, spring wheat, winter wheat, Solanum tuberosum, leaf area expansion, specific leaf area, early growth, genotype, environment, modelling     

Differing temporal roles of Ca2+ and cAMP in nicotine-elicited elevation of tyrosine hydroxylase mRNA

The involvement of cAMP- andCa²⁺-mediated pathways in theactivation of tyrosine hydroxylase (TH) gene expression by nicotine wasexamined in PC-12 cells. ExtracellularCa²⁺ and elevations inintracellular Ca²⁺ concentration([Ca²⁺]_i)were required for nicotine to increase TH mRNA. The nicotine-elicited rapid rise in[Ca²⁺]_iwas inhibited by blockers of either L-type or N-type, and to a lesserextent P/Q-, but not T-type, voltage-gatedCa²⁺ channels. With continualnicotine treatment,[Ca²⁺]_ireturned to basal levels within 3-4 min. After a lag of~5-10 min, there was a smaller elevation in[Ca²⁺]_ithat persisted for 6 h and displayed different responsiveness toCa²⁺ channel blockers. This secondphase of elevated[Ca²⁺]_iwas blocked by an inhibitor of store-operatedCa²⁺ channels, consistent with theobserved generation of inositol trisphosphate.1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM), when added before or 2 h after nicotine,prevented elevation of TH mRNA. Nicotine treatment significantly raised cAMP levels. Addition of the adenylyl cyclase inhibitor2',5'-dideoxyadenosine (DDA) prevented thenicotine-elicited phosphorylation of cAMP response element bindingprotein. DDA also blocked the elevation of TH mRNA only when addedafter the initial transient rise in [Ca²⁺]_iand not after 1 h. This study reveals that several temporal phases areinvolved in the induction of TH gene expression by nicotine, each ofthem with differing requirements forCa²⁺ and cAMP.

     

The Interactive Effects of Atmospheric Carbon Dioxide and Light on Stem Elongation in Seedlings of Four Species

Four species,Sinapis albaL.,Medicago sativaL.,Gypsophila paniculataL.andPicea abies(L.) Karsten, were grown in three light regimes:darkness, low light (25 µmol m^-2s^-1for 10 min d^-1) andhigh light (120 µmol m^-2s^-1for 12 h  d^-1) and fourlevels of carbon dioxide: 0, 350, 700 and 1400±50 µll^-1. Germination was not affected by any of the treatments.The effects of carbon dioxide on stem elongation were identicalin low and high light: stem length increased at a decreasingrate with level of carbon dioxide in all species. Level of carbondioxide also affected stem elongation in complete darkness,but the pattern was more complex and varied among species. Totalweight did not vary with level of carbon dioxide to any significantextent in either darkness or low light, but increased with levelof carbon dioxide at high light in all four species. Due tothe absence of any effect of carbon dioxide on growth in darknessand low light, we suggest the effects of carbon dioxide on stemelongation are independent of effects on growth and may be dueto a direct interaction with developmental processes. In contrast,level of carbon dioxide had little effect on allocation patternsin the dark and low light experiments, but had marked effectsin high light. Therefore, the effect of carbon dioxide on allocationwas probably due to the effects of carbon dioxide on growthrather than to any direct interaction between carbon dioxideand development. An understanding of the mechanisms by whichcarbon dioxide affects development may help us understand theoften variable effects of carbon dioxide upon plants.Copyright1998 Annals of Botany Company Sinapis albaL.;Medicago sativaL.;Gypsophila paniculataL. andPicea abies(L.) Karsten; elevated carbon dioxide; stem elongation; germination; allocation; phytochrome.     

The effects of food deprivation, prey density and volume on clearance rates and ingestion rates of Diacyclops thomasi

The ingestion rates of the copepod, Diacyclops thomasi, on thesoft-bodied rotifer, Synchaeta pectinata, increased 10-fold(0.07–0.77 Synchaeta h^–1) over the range 50–250prey l^–1. The saturating functional response curve appearedsigmoid but was statistically indistinguishable from a parabola.The response curve was more linear and 10 times lower over thesame range of density when Diacyclops was offered Kerarellacochleans, a species having a stiffened lorica. Diacyclops maximizedits ingestion rate on Synchaeta as a function of the availablegut space. Predation effort, measured as clearance rates, waslinked tentatively to changes in swimming speed of Diacyclopsand was a function of hunger level. Diacyclops, which were starvedfor varying periods of time, increased their ingestion rateson Synchaeta up to a maximum (-3.0 h^–1) after 7–10h of food deprivation. The gut passage time of Diacyclops wasestimated to be 7–8 h. Therefore, ingestion rates (andclearance rates) appeared to be strongly correlated to the volumeof food in the gut.     

Environmental Control of Flowering in Barley (Hordeum vulgare L.). II. Rate of Developement as a Function of Temperature and Photoperiod and its Modification by Low-temperature Vernalization

Plants of six contrasting genotypes of barley were raised fromvernalized (imbibed at 1 °C for 30 d) or non-vernalizedseeds and grown in 12 different controlled environments comprisingfactorial combinations of three photoperiods (10, 13 and 16h d^–1), two day temperatures (18 and 28 °C) and twonight temperatures (5 and 13 °C). Except at longer daysfor Athenais or Arabi Abiad, the 28 °C day temperature wasgenerally supra-optimal and delayed awn emergence. At lowertemperatures and in photoperiods shorter than the critical value,P_C, which delay awn emergence, the time from sowing to awn emergencefor five of the genotypes conformed to the equation 1/f=a +bT{macron}+cPwhere f is the time to awn emergence (d), T{macron} is meandiurnal temperature (°C), P is photoperiod (h d^–1)and a, b and c are genotype-specific constants. In Arabi Abiad,however, significant responses to temperature were not detected.The low temperature pre-treatment of the seeds reduced the subsequenttime to awn emergence in Athenais and the autumn-sown genotypesAger, Arabi Abiad and Gerbel B, especially in longer days, buteither had no effect or tended to delay awn emergence in thespring-sown types Emir and Mona. In the spring-sown types P_Cwas outside the range investigated (i.e. > 16 h d^–1),but in Ager it was approx. 13 h d^–1 and in Gerbel B justover 13 h d^–1. For plants of Arabi Abiad grown from vernalizedseeds P_c was almost 15 h, but     

Irradiance and daylength effects on growth and chemical composition of Gyrodinium aureolum Hulburt in culture

For Gyrodinium aureolum significant irradiance and daylengtheffects were found on the division rate and on the growth-relevantChla-normalized photosynthetic rate (^gP^B). Optimum conditionsof irradiance and daylength were found at 230 µmol m^–2s^–1 and 14 h for the division rate, and at >260 µmolm^–2 s^–1 and <6 h for ^gP^B.^gP^B showed no photoinhibition,while the division rate decreased markedly at irradiances abovesaturation. This difference and the difference in optimum irradiancebetween the division rate and ^gP^B are explained by a decreasein cellular Chla/carbon ratio with increasing irradiance. Thecellular content of carbon and nitrogen decreased significantlywith increasing irradiance. Total phosphorus was independentof irradiance and daylength. Below the saturation irradiancefor ^gP^B the daily Chla-normalized carbon yield may be describedas an exponential function of the daily irradiance (irradiancex daylength).     

Post-transcriptional Control of Nitrate Reductase Formation in Green Algae

Cycloheximide (2·0 µg ml^–1) inhibits theincorporation of [¹⁴C]phenylalanine and [¹⁴C]adenine into insolublecompounds in Ankistrodesmus braunii. 6-Methylpurine (1·0mM) inhibits only the incorporation of [14C]adenine and it isconcluded that it inhibits RNA synthesis. When ammonium-growncells of Ankistrodesmus or Chlorella are nitrogen-starved orwhen ammonium-grown cells of Dunalitlla are resuspended in nitratemedium, the appearance of nitrate reductase in these organismsis not inhibited by 6-methylpurine. The appearance of nitratereductase activity in Ankistrodesmus or Chlorella is inhibitedby 6-methylpurine when ammonium-grown organisms are preincubatedwith this substance for 1-2 h before nitrogen starvation. Itis concluded that cells growing with ammonium and lacking nitratereductase activity nevertheless contain preformed mRNA for nitratereductase synthesis.     

Effects of Temperature and Photoperiod on Phenological Development in Three Genotypes of Bambara Groundnut (Vigna subterranea)

Factorial combinations of four photoperiods (10, 11·33,12·66 and 16 h d^-1) and three mean diurnal temperatures(20·2, 24·1 and 28·1°C) were imposedon nodulated plants of three Nigerian bambara groundnut genotypes[Vigna subterranea (L.) Verdc., syn. Voandzeia subterranea (L.)Thouars] grown in glasshouses in The Netherlands. The photothermalresponse of the onset of flowering and the onset of poddingwere determined. The time from sowing to first flower (f) wasdetermined by noting the day on which the first open flowerappeared. The time from sowing to the onset of podding (p) wasestimated from linear regressions of pod dry weight againsttime from sowing. Developmental rates were derived from thereciprocals of f and p. In two genotypes, 'Ankpa 2' and 'Yola',flowering occurred irrespective of photoperiod and 1/f was controlledby temperature only, occurring sooner at 28·1 than at20·2°C. The third genotype, 'Ankpa 4', was sensitiveto temperature and photoperiod and f was increased by coolertemperatures and photoperiods > 12·66 h d^-1 at 20·2°Cand > 11·33 h d^-1 at 24·1 and 28·1°C.In contrast, p was affected by temperature and photoperiod inall three genotypes. In bambara groundnut photoperiod-sensitivitytherefore increases between the onset of flowering and the onsetof podding. The most photoperiod-sensitive genotype with respectto p was 'Ankpa 4', followed by 'Yola' and 'Ankpa 2'. Therewas also variation in temperature-sensitivity between the genotypesinvestigated. Evaluation of bambara groundnut genotypes foradaptation to different photothermal environments will thereforerequire screening for flowering and podding responses.Copyright1994, 1999 Academic Press Vigna subterranea (L.) Verdc., Voandzeia subterranea (L.) Thouars, bambara groundnut, phenology, photoperiod, daylength, temperature, flowering, podding