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1.
COMPARATIVE LIFE-CYCLE, BIOMASS AND SECONDARY PRODUCTION OF THREE SYMPATRIC FRESHWATER GASTROPOD SPECIES 总被引:1,自引:0,他引:1
The life cycles, biomass and secondary production of three sympatricfreshwater basommatophoran snails, Lymnaea palustris (MÜller),Physa fontinalis Linnaeus and Anisus rotundatus (Poiret) werestudied during two years in a freshwater ditch. L. palustrisexhibited an iteroparous life-cycle whereas the two other speciespresented a semelparous life-cycle, adults died just after oviposition.L. palustris secondary production (dry weight) value was higher(P = 11 298.4 mg 0.1 m1 yr1) than those of P.fontinalis (P = 846.3 mg 0.1 m2 yr1) and A. rotundatus(P = 1192 mg 0.1 m2 yr1). (Received 16 March 1992; accepted 30 June 1992) 相似文献
2.
The Cyt f and P700 contents in leaves of three Sorghum, varietieswere measured, in relation to their carbon assimilation, underdifferent light intensities during growth. At the maximum irradiationused (1,800 µE m2 s1) the ratio of P700to Cyt f was close to unity, whereas under low irradiation (450µE m2 s1) the ratio of P700 to Cyt f rangedfrom two to three. A strikingly positive correlation existedbetween the P700 contents of the leaves and their rates of carbondioxide fixation, dry matter production and Cyt f contents,only when the plants were grown under high light intensities.The P700 content of the leaves in plants grown under low irradiationwas unrelated to the contents of Cyt f. Thus, at a high lightintensity there is a close relationship between the Cyt f andP700 levels, but at low intensities the amounts of electroncarriers and the reaction centre are independent. (Received March 7, 1983; Accepted August 24, 1983) 相似文献
3.
DAVIES E. C.; CHOW W. S.; LE FAY J. M.; JORDAN B. R. 《Journal of experimental botany》1986,37(2):211-220
When young tomato plants grown in high light (400 µmolquanta m2s1 PAR) were transferred to low light(100 µmol quanta m2s1 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 12 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 相似文献
4.
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 m2 S1). However, its growth wassignificantly retarded as a result of a significant decreasein its Chl content under higher light conditions (85-130 µEm2 s1). Furthermore, YFP12 stopped growing andsuffered from photobleaching under the highest light intensity(170 µE m2 s1). 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 Em2s-. (Received September 26, 1997; Accepted November 21, 1997) 相似文献
5.
The population abundances and rates of biomass production ofheterotrophic nanoplankton (HNAN) in Georgia coastal waterswere evaluated by epifluorescence microscopy. HNAN populations(mostly non-pigmented microflagellates <10 µm in diameter)ranged from 0.3 x 103 cells ml1 in shelf waters 15 kmoffshore to 6.3 x 103 cells ml1 in waters 0.25 km fromthe coast. There was a strong correlation (r = 0.83) betweenHNAN and free bacterioplankton population abundances, but noapparent relation (r = 0.38) between HNAN and phototrophic nanopLankton(PNAN) abundances. HNAN biomass production in estuarine andnearshore shelf waters, as estimated from increases in HNANpopulations during laboratory incubations of natural water samples,ranged from 0.10 to 0.79 mg C m3 h3, with populationgeneration times of 9.7 to 26.5 h. There was a significant linearrelation (r = 0.95) between HNAN biomass and HNAN productivity.We calculated that HNAN may graze at least 30% to 50% of dailybacterioplankton production in Georgia coastal waters. 相似文献
6.
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 m2 s1) or high(500µmol m2 s1) 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 Km for PEP than plants under low PPFD. Additionof 2·0 mol m3 malate resulted in an increase inthe Km for PEP, with plants draughted under low PPFD havinga significantly higher Km in the presence of malic acid comparedto those under high PPFD. Response to the activator glc-6-P,which lowered the Km 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 Km 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 相似文献
7.
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 m2). 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 from23 x 102 through 6 x 102 to 89 x102 m2 g1 as light intensity decreased. Correspondingdecreases in unit leaf rate, however, caused over-all reductionsin relative growth rate. Specific absorption rates for potassium (AK, 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 m2 through c. 0.3 at7.3 W m2 to a value not significantly different fromzero (P < 0.05) at 2.2 W m2. 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 root1 h1)/unitshoot rate (rate of increase of whole-plant dry weight per unitshoot dry weight, in mg g shoot1 h1). The implicationsof this relationship are discussed. 相似文献
8.
Retusa obtusa held individually in the laboratory carried largeoocytes in the gonad but did not spawn in December-late January.In late Jan-early Feb, however, the first few individuals producedbatches of 817 eggs and, by early February, most individualswere producing means of 24 eggs d1 and maximain late Feb of <7.9 d1. Spawning declined to low levelsin few individuals in late March. By early April, spawning hadvirtually ceased prior to the drastic loss of adults in thepopulation by May. Larger R. obtusa generally produced more eggs than smaller onesand the few specimens shorter than 3.8 mm produced markedlyfewer than those of 3.85.0 mm shell length. Twenty of the 34 R. obtusa held in the main breeding period(4 sets started 29 Jan-3 Mar) spawned in 3 or more successiveweeks whereas only 6 of them failed to spawn in 2 consecutiveweeks, so indicating that several successive batches of eggsare commonly produced. Yet in virtually all individuals (exceptat the start of breeding) more eggs were produced in the firstweek of captivity than subsequently. These first-week valuesimply total production by individuals in the spawning seasonof some 112-305 eggs comprising about 2.8-7.6 mg dry weightor, by the Forth estuary population, of 26880-73200 eggs m2comprising 0.67-1.83 g dry weight m2. (Received 19 August 1988; accepted 30 September 1988) 相似文献
9.
Measuring the Canopy Net Photosynthesis of Glasshouse Crops 总被引:3,自引:0,他引:3
HAND D. W.; CLARK G.; HANNAH M.A; THORNLEY J. H. M.; WILSON J. WARREN 《Journal of experimental botany》1992,43(3):375-381
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 m2, PAR)and ±3·6% in dull light (100W m2, PAR). Measurements of the rates of net photosynthesis of a maturecanopy of a cucumber crop were made at near-ambient CO2 concentrationsover a range (0350 W m2) 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 m2 the fitted value of canopy net photosynthesiswas 2.65 mg CO2 m2s1 (equivalent to over 95 kgCO2 ha1h1). 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 相似文献
10.
Effects of photon flux density on carbon partitioning and rhizosphere carbon flow of Lolium perenne 总被引:1,自引:0,他引:1
Hodge Angela; Paterson Eric; Thornton Barry; Millard Peter; Killham Ken 《Journal of experimental botany》1997,48(10):1797-1805
The distribution and partitioning of dry matter and photoassimilateof Lolium perenne was investigated under two light regimes providingphotosynthetically active radiation of 350 µmol m2s1 (low light treatment) or 1000 µmol m2s1 (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 相似文献
11.
Holbrook Gabriel P.; Campbell William J.; Rowland-Bamford Amanda; Bowes George 《Journal of experimental botany》1994,45(8):1119-1126
A comparative study was made of the inhibition of ribulose-1,5-bisphosphatecarboxylase-oxygenase (Rubisco) amongst six cultivars of Glycinemax L. Merr., associated with synthesis of 2-carboxyarabinitol1-phosphate (CA1P) during darkness. Significantly lower meanvalues of dark inhibition of Rubisco were observed in soybeancv. Davis than in cvs Bragg, Cobb, Hardee, Gordon, and Kirby.The CA1P synthesis/degradation cycle during dark/light transitionsremained operational in cv. Bragg plants grown at low irradiance(40 µmol photons m2 s1). However, CA1P synthesisand degradation rates were slower in the dark (t0.5 = 240 versus25 min), and light (t0.5 = 20 versus 3.8 min) respectively,as compared to plants grown at higher irradiance (550 µmolphotons m2 s1). In addition, the activation stateof Rubisco in low-light-grown plants showed only a small declineafter a transition to darkness. We conclude that (a) cultivar-dependentvariation occurs amongst soybeans with respect to CAlP regulationof Rubisco, and (b) soybeans acclimated to low irradiance maydepend more on CA1P synthesis/degradation to regulate Rubisco,and less on changes in the enzyme activation state. Key words: Activation state, Glycine max, photosynthesis, Rubisco, 2-carboxyarabinitol 1-phosphate 相似文献
12.
Increase in fluence rates of white light over the range of 5to 80 µmol m2 s1 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 m2 s1 whereasfluence rates above 40 µmol m2 s1 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 相似文献
13.
At low light intensities (less than 50 µmol m2s1) 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 m2s1)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 80150 µmol m2 s1 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 m2s1. 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) 相似文献
14.
The population dynamics of the scyphomedusa Aurelia aurita inSouthampton Water is characterized. Strobilation, indicatedby the presence of 1 mm ephyrae, occurred from the end of Januaryto the middle of March. Maximum abundances of up to 8.71 m3occurred soon after ephyrae release, after which numbers declinedsteadily until the end of June, when the population was absentfrom Southampton Water. The residence time of 34 monthsis somewhat less than that reported in many other areas, includingKiel Bight and Gullmarfjord. The carbon biomass of A.auritaaccounted for 9297% of the predominant gelatinous biomass(A.aurita, Pleurobrachia pileus and Phialidium hemisphericum)in the upper estuary, and this reached a maximum of 30.2 mgC m3 in May 1990 and 27.6 mg C m3 in June 1991.Coincident with increased water temperature and mesozooplanktonabundance during May, growth rates increased from 0.020.30mm day1 to a peak of 4.8 mm day1, with a maximumbell diameter of 120140 mm reached in late May/earlyJune. Size to maturity was variable, although the smallest medusaobserved to be ripe, i.e. containing dividingeggs and planula larvae in the brood sacs on the oral arms,were 6471 mm. Aurelia aurita is believed to be endemicto Southampton Water, but because of the double high water inthe area, short flushing rates of between 4.5 and 20 days maybe responsible for such short residence times of Aurelia medusae.The effects of strong NE winds were considered as factors governingthe distribution of medusae in years of atypical temporal abundance. 相似文献
15.
Fujiki Tetsuichi; Suzue Takahiko; Kimoto Hideshi; Saino Toshiro 《Journal of plankton research》2007,29(2):199-208
A comparison of photosynthesis-irradiance response curves (PEresponse curves) obtained through fast repetition rate (FRR)fluorometry and radiocarbon (14C) tracer method was made inthe chlorophyte, Dunaliella tertiolecta, grown under differentirradiance conditions. In FRR-based PE response curveexperiments, actinic light provided by white light-emittingdiodes (LEDs) was increased gradually from 0 to 1500 µmolquanta m2 s1 and the rate of photosyntheticelectron transport was determined at each light level. Short-termexperiments (20 min) of 14C-based PE response curvewere carried out with an improved photosynthetron, which containswhite LEDs as the light source. Irrespective of growth irradiance,the ratios of FRR to 14C-based initial slopes were almost uniform.The ratios of FRR- to 14C-based maximum rates were 2536%higher than those of FRR- to 14C-based initial slopes. The relationshipbetween electron transport and carbon assimilation was non-linearwith increasing discrepancy towards high actinic light. Thisnon-linear relationship between FRR- and 14C-based estimatesis primarily due to the effect of physiological processes stimulatedat high levels of light, such as cyclic electron flow and theMehler reaction. The results of this study indicate that theFRR fluorometry can be used as a good indicator of photosyntheticrates from low to middle light levels, but becomes increasinglyquestionable as the maximum photosynthetic rate is approached.The degree to which this relationship is further affected bynutrient-status warrants investigation. 相似文献
16.
Photoadaptation in Antarctic phytopfankton: variations in growth rate, chemical composition and P versus I curves 总被引:1,自引:0,他引:1
The response of phytoplankton to variations in the light regimewas studied during the VULCAN and ACDA cruises in the Antarctic.Unenriched batch cultures of 1219 days' duration reachedchl concentrations of 1050 µg1 and exhibitedexponential growth rates, with the maximal rate being 0.41 doubl,day1. Ice edge algae exhibited maximum growth rates atphoton flux densities (PFD) of 30100 µE m2S1and the growth rate was reduced by about 30% at 5001000µE m2S1 The chl/C ratio ranged between 0.004and 0.018, with the lowest ratios at PFDs above 500 µEm2S1 chl/C ratios were also below maximum at PFDsbelow 4050 µE m2S1 The C:N:P ratioswere close to the Redfield ratios; the Si/C ratio averaged 0.16(atoms), and the ATP/C ratio averaged from 0.0024 to 0.0050in different culture senes. When thawed after having been frozenfor 10 days, shade-adapted cultures were in a much better conditionthan sun-adapted ones. P versus I data showed that the maximumassimilation number varied from 0.75 to 4.4 µg C (µgchl)1h1. It varied inversely with the chl/C ratio;therefore the maximum carbon turnover rate varied little betweensamples (0.024/0.035 h1). Low biomass communities exhibitedrelatively high values for (the initial slope of P versus Icurves), low values for 1sat (160330 µE m2S1),and they were susceptible to photoinhibition. In contrast, communitiesdominated by Odontella weissflogii exhibited low values for, a high value for Isat (560 µE m2S1 andthey tolerated high PFDs. The photo-adaptational status of thephytoplankton in natural water samples is discussed relativeto the profile of water column stability and mixing processes. 相似文献
17.
Bioluminescence of sound-scattering layers in the Gulf of Maine 总被引:2,自引:0,他引:2
Submersible-based investigations of bioluminescence were conductedin sound-scattering layers (SSLs) in the Gulf of Maine, usingintensified video and dual-beam acoustic methods. Stimulatedbioluminescence in the SSLs was high (341 µW sr1m3 while spontaneous bioluminescence was not detected.The average intensity of individual bioluminescent sources inthe SSLs was 30200 times greater than the intensity oflight emitters outside the SSLs. The two brightest sources ofbioluminescence were identified as the euphausiid, Meganyctiphanesnorvegica and the cydippid ctenophore, Euplokamis sp. Meganyctiphanesnorvegica formed a SSL within 50 m of the bottom during theday and migrated to the uppermost 30 m of the water column atnight, forming a near-surface SSL. Euplokamis sp., which producedexceptionally intense and long-lasting bioluminescent secretions,occurred within the near-bottom SSL in concentrations up to7 m3. Our findings indicate that traditional methodsof identifying the primary light emitters in a region, basedon light measurements from net- or pump-captured organisms,may have underestimated the significant in situ bioluminescencepotential of euphausiids and gelatinous zooplankton.
3 Present address: NOAA/NURP/R-OR2, Silver Spring, MD 20910,USA 相似文献
18.
The influence of irradiance on growth, photosynthesis and respiration of Gyrodinium cf. aureolum 总被引:1,自引:0,他引:1
The bloom-forming marine dinoflagellate Gyrodinium cf. aureolumwas grown in batch cultures over a range of irradiances (35380µmolm2 s1 and growth, photosynthesis and respirationrates determined. Saturation of growth occurred at irradiancesof 100µmol m2 s1 Below this light level,decreases in growth rates and cell size, and a relative increasein carbon specific respiration rates, were observed. On theother hand, photosynthesis-irradiance relationships determinedfrom dissolved oxygen incubations showed that on a cellularand carbon basis, cultures grown at low irradiances had higherrates of light-limited and light-saturated photosynthesis, mainlyas a result of large increases in cell chlorophyll content.This adaptation strategy enables low-light-grown organisms toexploit available high irradiance through a relatively highphotosynthetic capacity. In cells grown at higher light levels(>100µmol m2 s1), excess photosynthatemay be diverted to storage rather than used for growth. 相似文献
19.
Seeds of 19 native British herbaceous species (14 grasses andfive forbs) were exposed to white light at three photon fluencerates: high (192 mol m2 d1), medium (9·6mol m1 d1) and low (2·3 mol m2 d2) 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 相似文献
20.
The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m2 s1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m2 s1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m2s1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m2 s1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the end-of-dayphytochrome effect. Key words: Blue light, extension growth, phytochrome 相似文献