The Effects of Light Intensity and External Potassium Level on Root/Shoot Ratio and Rates of Potassium Uptake in Perennial Ryegrass (Lolium perenne L.)

Loliun perenne L. (cv.S. 23) was grown on vermiculite in winterin a heated greenhouse for 8 weeks under factorial combinationsof two potassium regimes (nominally 6 parts/10⁶ and 156 parts/10⁶in Hewitt's solution) and three densities of artificially supplementedvisible radiation flux (36.1, 7.3, and 2.2 W m^–2). Growthand potassium uptake were studied through the calculation ofvarious growth functions from fitted curves. There was little effect of potassium treatment but the experimentalmaterial responded markedly to light. Leaf-area ratio in thethree treatments showed extreme plasticity in increasing from2–3 x 10^–2 through 6 x 10^–2 to 8–9 x10^–2 m² g^–1 as light intensity decreased. Correspondingdecreases in unit leaf rate, however, caused over-all reductionsin relative growth rate. Specific absorption rates for potassium (A_K, dry-weight basis)were strongly reduced at the lower light intensities but alsodisplayed complex ontogenetic drifts. Values of the allometricconstant, k (the ratio of root and shoot relative growth rates),decreased from c. 0.7 at 36.1 W m^–2 through c. 0.3 at7.3 W m^–2 to a value not significantly different fromzero (P < 0.05) at 2.2 W m^–2. In material grown under the two higher light intensities a constantinverse relationship was found between the mass ratio of rootand shoot and the corresponding activity ratio. The resultsconform to this model: Mass ratio = –0.001+45.0 (1/activityratio) where activity ratio is expressed as specific absorptionrate for potassium (in µg g root^–1 h^–1)/unitshoot rate (rate of increase of whole-plant dry weight per unitshoot dry weight, in mg g shoot^–1 h^–1). The implicationsof this relationship are discussed.     

Properties of Phosphoenolpyruvate Carboxylase and Carbohydrate Accumulation in the C3-CAM Intermediate Sedum telephium L. Grown Under Different Light and Watering Regimes

A comparison of the activity and properties of the enzyme phosphoenolpyruvatecarboxylase (PEPC) was made for plants of Sedum telephium L.grown under low (70 µmol m^–2 s^–1) or high(500µmol m^–2 s^–1) PPFD and subjected to varyingdegrees of water stress. Under well-watered conditions onlyplants grown under high PPFD accumulated titratable acidityovernight and the extractable activity of PEPC was almost 2-foldhigher in these plants than in plants grown under low PPFD.Increasing drought stress resulted in a substantial increasein the activity of PEPC extracted both during the light anddark periods and a decrease in the sensitivity to inhibitionby malic acid. The magnitude of these changes was determinedby the severity and duration of drought and by light intensity.A comparison of the kinetic properties of PEPC from severelydroughted plants revealed that plants droughted under high PPFDhad a lower K_m for PEP than plants under low PPFD. Additionof 2·0 mol m^–3 malate resulted in an increase inthe K_m for PEP, with plants draughted under low PPFD havinga significantly higher K_m in the presence of malic acid comparedto those under high _PPFD. Response to the activator glc-6-P,which lowered the K_m for PEP, also varied between plants grownunder the two light regimes. Under well-watered conditions PEPCextracted from plants under high PPFD was more sensitive toactivation by glc-6-P than those under low PPFD. After the severedrought treatment, however, the K_m for PEP in the presence ofglc-6-P was similar for enzyme extracted from plants grown underboth light regimes. Soluble sugars and starch were depletedovernight and were both possible sources of substrate for PEPC.With increasing drought, however, the depletion of starch relativeto soluble sugars increased under both light regimes. The propertiesof PEPC and the characteristics of carbohydrate accumulation/depletionare discussed in relation to the regulation of CAM in S. telephiumgrown under different light and watering regimes. Key words: PEP carboxylase, CAM, carbohydrates, Sedum telephium     

Cloning of the Gene Encoding a Protochlorophyllide Reductase: the Physiological Significance of the Co-Existence of Light-Dependent and -Independent Protochlorophyllide Reduction Systems in the Cyanobacterium Plectonema boryanum

Cyanobacteria have two protochlorophyllide (Pchlide) reductasescatalyzing the conversion of Pchlide to chloro-phyllide, a keystep in the biosynthetic pathway of chlorophylls (Chls); a light-dependent(LPOR) and a light-independent (DPOR) reductase. We found anopen reading frame (ORF322) in a 2,131-bp EcoRI fragment fromthe genomic DNA of the cyanobacterium Plectonema boryanum. Becausethe deduced amino acid sequence showed a high similarity tothose of various plant LPORs and the LPOR activity was detectedin the soluble fraction of Esche-richia coli cells over-expressingthe ORF322 protein, ORF322 was defined as the por gene encodingLPOR in P. boryanum. A por-disrupted mutant, YFP12, was isolatedby targeted mutagenesiss to investigate the physiological importanceof LPOR. YFP12 grew as well as wild type under low light conditions(10-25 µE m^–2 S^–1). However, its growth wassignificantly retarded as a result of a significant decreasein its Chl content under higher light conditions (85-130 µEm^–2 s^–1). Furthermore, YFP12 stopped growing andsuffered from photobleaching under the highest light intensity(170 µE m^–2 s^–1). In contrast, a chlL-dis-rupted(DPOR-less) mutant YFC2 grew as well as wild type irrespectiveof light intensity. From these phenotypic characteristics, weconcluded that, although both LPOR and DPOR contribute to Chlsynthesis in the cells growing in the light, the extent of thecontribution by LPOR increases with increasing light intensity;without it, the cells are unable to grow under light intensitiesof more than 130 µ Em^–2s-^–. (Received September 26, 1997; Accepted November 21, 1997)     

Acclimation of Tomato Leaves to Changes in Light Intensity; Effects on the Function of the Thylakoid Membrane

When young tomato plants grown in high light (400 µmolquanta m^–2s^–1 PAR) were transferred to low light(100 µmol quanta m^–2s^–1 PAR), non-cyclic electrontransport capacity was decreased and the rate of dark re-oxidationof Q^–, the first quinone electron acceptor of photosystemII, was decreased within 1–2 d. In contrast, the amountof coupling factor CF₁, assayed by its ATPase activity, decreasedmore gradually over several days. The total chlorophyll contentper unit leaf area remained relatively constant, although thechlorophyll a/chlorophyll b ratio declined. When young tomato plants grown in low light were transferredto high light, the ATPase activity of isolated thylakoids increasedmarkedly within 1 d of transfer. This increase occurred morerapidly than changes in chlorophyll content per leaf area. Inaddition, in vivo chlorophyll fluorescence induction curvesindicate that forward electron transfer from Q^– occurredmore readily. The functional implications of these changes arediscussed. Key words: Tomato, leaves, light intensity, thylakoid membrane     

Action Potentials Evoked by Light in Traps of Dionaea muscipula Ellis

At low light intensities (less than 50 µmol m^–2s^–1) illumination evokes transient depolarization of membranepotential in mesophyll cells of the leaf-trap of Dionaea muscipulaEllis. Darkening causes hyperpolarization approximately symmetricto the response to illumination. The amplitude as well as therate of potential changes depend on light intensity. After exceedinga definite threshold (usually between 50 and 80 µmol m^–2s^–1)the depolarization plays the role of a generator potential andan all-or-none action potential (AP) is released. Switchinglight off in a depolarization phase of an AP does not changeits shape and the amplitude. When the light intensity is increasedto 80–150 µmol m^–2 s^–1 a single lightstimulus triggers two successive APs. The time interval betweenthe two APs decreases with increasing stimulus strength andreaches the minimum between 300 and 400 µmol m^–2s^–1. At higher light intensities the interval increasesagain, and finally only a single AP is triggered. It was shownthat the effect was evoked by light but not by temperature changeaccompanying illumination. An inhibitor of the photosyn-theticelectron transport chain, DCMU, blocked the generator potentialsmediating between light absorption and APs. Residual responsesto light stimuli in plants treated with DCMU had reverse polarityand strongly reduced the amplitudes. (Received September 16, 1997; Accepted January 16, 1998)     

UV-induced mortality of zoea I larvae of brown shrimp Crangon crangon (Linnaeus, 1758)

Zoea I larvae of the brown shrimp Crangon crangon (Decapoda)were exposed to varying levels of UV radiation in a sunshinesimulator. ‘Short-term exposures’ (0–8 h)were used to determine the highest UV dose with no significanteffect (NOEC; defined by limit of detection) and the lethaldose of 10 and 50% mortality (LD₁₀ and LD₅₀). Crangon crangonshowed a relatively high sensitivity to UVB radiation (NOEC= 10 kJ m^–2, LD₁₀ = 15 kJ m^–2, LD₅₀ = 24 kJ m^–2)compared to other crust-acean species. LD values (1997–1998)showed no adaptation to seasonal light regimes. ‘Long-termexposures’ (0–10 days) were carried out to assessthe range where the ‘law of reciprocity’ is valid.The larvae were exposed to UV levels of 0.2, 0.4 and 0.7 J m^–2for appropriate time intervals, always cumulating in a sublethaldose of 5 kJ m^–2 day^–1. Results reflect a possiblethreshold (0.2–0.4 J m^–2 UVB) in the effect of thedifferent UVB doses used; thus, a proportional relationshipof intensity and exposure time can only be shown at UVB levelsabove this threshold intensity.     

Growth and production of heterotrophic nanoflagellates in a meso-eutrophic lake

The growth of heterotrophic nanoflagellates (HNF) in mesotrophicLake Constance was measured in situ during a 13 month period.Experiments were conducted with 10 µm pre-filtered lakewater incubated in diffusion chambers at 3 m water depth atthe sampling location for 24 h. Growth rates were calculatedfrom changes in cell numbers occurring during the period ofincubation. Growth rates of all dominant taxa showed pronouncedseasonal variation (–0.13 to 1.76 day^–1 and weregenerally highest in summer at high water temperatures. In situgrowth rates were well below maximum growth rates known forthe respective and similar species from laboratory experiments.While water temperature was a key parameter positively relatedto the growth of all HNF species, the effect of various potentialfood items was taxon specific and less clear. Bacterial abundancewas equally important as temperature for growth in the smallbactenvorous Spumella sp., but was insignificant for growthrates of the larger omnivorous Kathablepharis sp. In Spuniellasp., 84% of the observed seasonal variation of its growth ratecould be explained by temperature and bacterial food supply.Based on these results, a multiple linear regression equationwith temperature and bacterial concentration as dependent variableswas calculated for the growth rate of Spumella. Taxon-specificproduction rates were derived from growth rates and averagebiomass of these two species, and compared to total HNF productionestimated from previously measured community growth rates andbiomass in Lake Constance. Production peaks of Spumella sp.and Kathablepharis sp. alternated seasonally. Total HINF productionranged from –0.01 to 10 mg C m^–3 day^–1. Theaverage seasonal production varied between 1.4 and 33 mg C m^–3day^–1 over 6 consecutive years. These small protozoa thuscontribute a substantial amount to total zooplankton productionin Lake Constance.     

A comparison of net and gross rates of oxygen production as a function of light intensity in some natural plankton populations and in a Synechococcus culture

In vitrorates of gross and net oxygen production were measuredas a function of light intensity in some plankton communitiescollected from Bedford Basin, Nova Scotia, and in a monoclonalculture of Synechococcus. The rate of gross oxygen productionwas measured by a technique in which the stable oxygen isotope,¹⁸O, serves as a photosynthetic tracer Net oxygen productionwas measured by automated Winkler technique. The rate of communityrespiration in the light was then determined by the differencebetween gross and net rates of oxygen production. In the naturalpopulations examined, neither gross nor net oxygen productionrates were significantly inhibited at the highest light intensitymeasured (500–800 µE m^–2 s^–1) In a samplein which the dark respiration rate was small relative to themaximal rate of production [P_max;sensu Platt et al (1980) JMar. Res., 38, 687–701] the rates of ‘light’respiration were 3 times greater. In two other communities,with high rates of dark respiration relative to P_maxthe ratesof ‘light’ respiration were closer to rates of darkrespiration. In the Synechococcus clone, both gross and netoxygen production rates were inhibited at high light intensities.Rates of ‘light’ respiration were found to varyas a function of light intensity. The greatest rates of respirationwere measured in samples incubated at light intensities thatwere just saturating (100 µE m^–2 s^–1). Therates of ¹⁴C production were also measured as a function oflight intensity The photosynthetic quotients, based on ¹⁴C productionrates and gross oxygen production rates, average 1 9     

Photoacclimation in the marine alga Nannochloropsis sp. (Eustigmatophyte): a kinetic study

Exponentially growing cultures of Nannochloropsis sp. were transferredfrom high light (650 µ.mol quanta m^–2 s^–1)to low light (30 (µrnol quanta m^–2 s^–1). Thekinetics of changes in the various parameters of the photoacclimationprocess were followed until steady state was reached. In thisorganism, the observed 4.25 increase in cellular chlorophylla in the low-light-acclimated cells was linearly correlatedwith an increase in the number of photosynthetic units (PSU),while the PSU size remained constant. The new steady state wasreached after a transition period of 87 h and following an initialovershoot in the chlorophyll a concentration. During the processof photoacclimation, harvested and utilized light was increaseddue to a combination of increased cellular chlorophyll and anincrease of the quantum yield. These improvements in efficiencywere coupled with the reduction of respiration. The overalleffect of photoacclimation, therefore, amounted to reducingthe impact of low light on the growth rate of the algae. Ourstudy demonstrates the importance of the photoacclimation processin the context of the planktonic way of life. An index of the'effectiveness of photoacclimation' is proposed.     

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     

Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta I. Photocontrol of Carotenoid Production

Rhodotorula minuta cells, which have only traces of carotenoidswhen grown in the dark, started carotenoid production with theonset of illumination and the amount increased almost linearlyuntil 70 hr then remained constant thereafter when incubationwas continued under illumination, with the number of cells continuingto increase. The rate of carotenoid production [Vc (µgg^–1 hr^–1)] depended on the intensity of light [I(ergcm^–2 sec^–1)], with the relationship of Vc=0.74 logI–1.46. The final carotenoid content [C(µg g^–1)]of cells incubated under continuous light was also controlledby the light intensity [I], with the relationship of C=52 logI–81. Control of carotenoid production by light occursas a two-phase process consisting of a temperatureindependentphotochemical reaction and light-independent biochemical reactions. (Received September 12, 1981; Accepted February 20, 1982)     

Planktonic primary production in the German Wadden Sea

By combining weekly data of irradiance, attenuation and chlorophylla concentrations with photosynthesis (P) versus light intensity(E) curve characteristics, the annual cycle of planktonic primaryproduction in the estuarine part of the Northfrisian WaddenSea was computed for a 2 year period. Daily water column particulategross production ranged from 5 to 2200 mg C m^–2 day^–1and showed a seasonal pattern similar to chlorophyll a. Budgetcalculation yielded annual gross particulate primary productionsof 124 and 176 g C m^–2 year^–1 in 1995 and 1996,respectively. Annual amounts of phytoplankton respiration, calculatedaccording to a two-compartment model of Langdon [in Li,W.K.W.and Maestrini,S.Y. (eds), Measurement of Primary Productionfrom the Molecular to the Global Scale. International Councilfor the Exploration of the Sea, Copenhagen, 1993, pp. 20–36],and dissolved production in 1996, were both in the range of24–39 g C m^–2 year^–1. Annual total net productionwas thus very similar to particulate gross production (127 and177 g C m^–2 year^–1 in 1995 and 1996, respectively).Phytoplankton growth was low or even negative in winter. Inspring and summer, production/biomass (Pr/B) ratios varied from0.2 up to 1.7. Phytoplankton growth during the growth seasonalways surpassed average flushing time in the area, thus underliningthe potential of local phytoplankton bloom development in thispart of the Wadden Sea. The chlorophyll-specific maximum photosyntheticrate (P^B_max) ranged from 0.8 to 9.9 mg C mg^–1 Chl h^–1and was strongly correlated with water temperature (r² = 0.67).By contrast, there was no clear seasonal cycle in ^B, which rangedfrom 0.007 to 0.039 mg C mg^–1 Chl h^–1 (µmolphotons m^–2 s^–1)^–1. Its variability was muchless than P^B_max and independent of temperature. The magnitudeand part of the variability of P^B_max and ^B are presumably causedby changes in species composition, as evidenced from the rangeof these parameters found among 10 predominant diatom speciesisolated from the Wadden Sea. The ratio of average light conditionsin the water column (E_av) to the light saturation parameterE_k indicates that primary production in the Wadden Sea regionunder study is predominantly controlled by light limitationand that nutrient limitation was likely to occur for a few hoursper day only during 5 (dissolved inorganic nitrogen) to 10 (PO₄,Si) weeks in the 2 year period investigated.     

Effects of Light/Dark on Anion Fluxes in Isolated Guard Cells of Commelina communis L.

The effects of light/dark on anion fluxes in isolated guardcells of Commelina communis L. have been studied, using ⁸²Brand ³⁶Cl. Transfer of open guard cells from light to dark hasno effect on the ⁸²Br influx, but produces a marked transientstimulation of ⁸²Br or ³⁶Cl efflux, similar to the effect ofsuch transfer on the ⁸⁶Rb fluxes, and to the effects on both⁸⁶Rb and ⁸²Br fluxes of adding ABA. On return of guard cellsto light, after the transient, there is a further reductionin Cl/Br efflux. It is argued that control of a specific processof ion extrusion is important in regulating the ability of guardcells to stay open. In three out of four batches of steady-statetissue labelled with ⁸²Br, the plasmalemma fluxes were highenough, relative to the tonoplast fluxes, for the efflux kineticsto be separable into two exponential components, allowing estimationof bromide contents in cytoplasm and vacuole (Q_c and Q_v), andfluxes at plasmalemma and tonoplast. With opening in light,Q_c increased by 3.9 ± 0.4 pmol mm^–2 µm^–1and Qy by 5.2 ± 0.6 pmol mm^–2 µm^–1(change in content per mm² of epidermis perµm change inaperture). Using rough estimates for the volumes of cytoplasmand vacuole these figures suggest that at 6.1 µm in thedark the concentrations were about 63 mol m^–3 in the cytoplasmand 35 mol m^–3 in the vacuole, rising to about 185 molm^–3 in the cytoplasm and 125 mol m^–3 in the vacuole,at 16.7 µm aperture in light. Neither increase can providean adequate increase in salt concentration to account for theosmotic change required, and some solute other than potassiumsalt must also be involved. In one experiment with 82Br andin the only experiment with 36Cl the plasmalemma flux was lower,and not high enough relative to the tonoplast flux to allowseparation of two phases in the efflux curves, and calculationof cytoplasmic and vacuolar contents and fluxes. The effectsof transfer from light to dark were, nevertheless, similar inboth types of tissue. Key words: Commelina communis L., Light/dark effects, Anion fluxes, Guard cells     

Age, Fluence Rate, and Anthocyanin Production in Zea mays Seedlings

Increase in fluence rates of white light over the range of 5to 80 µmol m^–2 s^–1 brought about a correspondingincrease in amounts of anthocyanin production in shoots of Zeamays L. seedlings. Roots also exhibited a similar relationshipbetween increased fluence rate and increased anthocyanin productionover the range of 5 to 40 µmol m^–2 s^–1 whereasfluence rates above 40 µmol m^–2 s^–1 broughtabout decreases in anthocyanin production. Rates of productionand amounts of accumulation of anthocyanin in both shoots androots were found to vary with the age of the seedlings at thetime of exposure to light. Age, fluence rates, anthocyanin, seedlings, Zea mays     

Summer coastal zooplankton biomass and copepod community structure near the Italian Terra Nova Base (Terra Nova Bay, Ross Sea, Antarctica)

The structure of the zooplankton biotic community and of copepodpopulation in the coastal area of Terra Nova Bay (Ross Sea,Antarctica) was investigated during the 10th Italian AntarcticExpedition (1994/1995). Zooplankton biotic community consistedmainly of pteropods (Limacina helicina and Clione antarctica),Cyclopoid (Oithona similis), Poecilostomatoid (Oncaea curvata)and Calanoid (Ctenocalanus vanus, Paraeuchaeta antarctica, Metridiagerlachei and Stephos longipes) copepods, ostracods, larvalpolychaetes and larval euphausiids. Zooplankton abundance rangedfrom 48.1 ind m^–3 to 5968.9 ind m^–3, and copepodabundance ranged from 45.2 ind m^–3 to 3965.3 ind m^–3.The highest peak of zooplankton abundance was observed between25 m and the surface and was mainly due to the contributionof O. similis, O. curvata and C. vanus. Zooplankton biomassranged from 5.28 mg m^–3 to 13.04 mg m^–3 dry weight;the maximum value was observed between 25 m and the surface.Total lipid content varied from 216.44 to 460.73 mg g^–1dry weight.     

Effects of photon flux density on carbon partitioning and rhizosphere carbon flow of Lolium perenne

The distribution and partitioning of dry matter and photoassimilateof Lolium perenne was investigated under two light regimes providingphotosynthetically active radiation of 350 µmol m^–2s^–1 (low light treatment) or 1000 µmol m^–2s^–1 (high light treatment). Plants were grown at specificgrowth conditions in either soil or sand microcosm units tofollow the subsequent release of carbon into the rhizosphereand its consequent incorporation into the microbial biomass(soil system) or recovery as exudates (sand system). The distributionof recent assimilate between the plant and root released carbonpools was determined using ¹⁴CO₂ pulse-chase methodology atboth light treatments and for both sand- and soil-grown seedlings.A significant (P     

Calcium Activation of Potassium Channels in the Plasmalemma of Eremosphaera viridis

The role of cytoplasmic calcium activity in activation of K⁺-channelsin the unicellular green alga Eremosphaera viridis has beenstudied. As reported previously, after a ‘light off’signal a voltage independent opening of K⁺-channels in the plasmalemmais observed. This effect is indicated by a transient polarization(TP) with a simultaneous increase of the membrane conductance.TPs can also be triggered by different treatments, which allowinvestigations within a ‘short-circuited’ signalchain. (i) After incubation with EGTA a single extended TP canbe released by a sudden increase of the external calcium concentration.The Ca²⁺-channel inhibitors nifedipine (10 ^–2 mol m^–3)and verapamil (5 ? 10^–2 mol m^–3) suppress the releaseof this TP. (ii) In the presence of external calcium the additionof the ionophore A23187 [GenBank] (10–3 mol m^–3) causes anextremely prolonged TP. (iii) Low external concentrations ofbarium (10^–2 mol m^–3) induce repetitive TPs in thepresence of external calcium. In this case the Ca²⁺-channelinhibitors are less effective. (iv) Strontium (0.1–1.0mol m^–3) is able to trigger repetitive TPs even withoutexternal calcium. Whereas barium may stimulate a calcium influx,strontium can serve as a substitute for calcium to induce anopening of K⁺-channels. These results indicate strongly a Ca²⁺-dependentand voltage-independent activation of K⁺-channels in the plasmalemmaof Eremosphaera. The participation of cytoplasmic calcium inthe signal transduction chain after a ‘light off’signal is discussed. Key words: Ca²⁺-dependent K⁺-channels, Ca²⁺-channel effectors, A23187, transient membrane potential, Eremosphaera     

Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.)

Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m^–1 (34.2 mol m^–3 NaCl)and nodulation was completely inhibited at 7 dS m^–1 (61.6mol m^–3 NaCl); the plants died at 8 dS m^–1 (71.8mol m^–3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191^spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 1–4 dS m^–1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N₂ fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N₂ fixation, Rhizobium, salinity     

Discontinuite hydrobiologique dans le detroit du Pas-de-Calais

Hydrobiological studies in the Straits of Dover show a differencebetween the characteristics of the French coastal water andthe open sea water. A cruise between Boulogne-sur-mer and Dover(October 15, 1985) confirms the existence of a frontal area(4 miles off the French coast). This area is characterized byan increase of the salinity (1%) and decrease of the suspendedmatter content (from 27 to 20 mg l^–1), of primary production(from 15 to 3 mg C m^–3h^–1) and of chlorophyll aconcentration (from 4.5 to 1.5 mg m^–3). The presence ofdifferent zooplanktonic species in the two water masses alsocharacterizes this discontinuity. Oncaea sp., Corycaeus anglicus,Centropages typicus and Calanus helgolandicus are indicatorspecies of open sea water, while Cyciopina littoralis and ‘Saphirella’are only present in coastal water.     

A Comparative Study of Germination Responses to High Irradiance Light

Seeds of 19 native British herbaceous species (14 grasses andfive forbs) were exposed to white light at three photon fluencerates: high (19–2 mol m^–2 d^–1), medium (9·6mol m^–1 d^–1) and low (2·3 mol m^–2 d^–2) These photon doses have been found by previous workers to inhibitgermination in several species. High and low photon doses wereapplied only as continuous light, but the medium dose was appliedas both continuous light and as a 12 h light/12 h dark photoperiod.All four treatments, plus a dark control, were carried out at15 °C; the high and low doses were also applied with a dailyalternation of 10/20 °C. The majority of species (15) fell into one of two groups. Inseven species germination was relatively high and consistentacross all treatments, including darkness; in the other eightspp germination was inhibited only in darkness. Mostly thesedata confirmed published results for the same species In contrast in Agrostis capillaris and A. stolonifera germinationwas high only at alternating temperatures, irrespective of photondose, but was also slightly promoted by a constant temperaturecombined with light/dark alternations. Only in Bromus sterilisand B. ereclus was germination inhibited by light, in B. erectusat all photon doses and in B. sterilis only at the highest photondose These results suggest that inhibition of germination by highirradiance light is not widespread among native British species Aira caryophyllea, Arrenatherum elatius, Festuca ovina, F. rubra, Hordeum murinum, Milhim effusum, Silene dioica, Achillea millefolium, Brachypodium syhaticum, Digitalis purpurea, Holcus lanatus, Leucanlhemum vulgare, Phleum pratense, Poa trivialis, Taraxacum officinale, Agrostis capillaris, A. stolonifera, Bromus erectus, B. sterilis, seed, dormancy, germination, light, High irradiance reaction, alternating temperatures, photoperiod