The Sensitivity of Net Photosynthesis in Several Plant Species to Short-term Fumigation with Sulphur Dioxide

The effects of exposure of up to 2 h with sulphur dioxide ona range of plant species was observed by measuring changes inthe rate of net photosynthesis under closely controlled environmentalconditions. Ryegrass, Lolium perenne ‘S23’ was thespecies most sensitive to SO₂; significant inhibition was detectedat 200 nl l^–1. Fumigations at 300 nl l^–1 also inhibitedphotosynthesis in field bean (Vicia faba cv. ‘Three FoldWhite’ and ‘Blaze’) and in barley (Hordeumvulgare cv. ‘Sonja’). No effect was detected inwheat (Triticum aestivum cv. ‘Virtue’) at concentrationsup to 600 nl l^–1 SO₂, or in oil-seed rape (Brassica napuscv. ‘Rafal’) except at 800 nl l^–1 SO₂). Recoverycommenced immediately after the fumigation was terminated andwas complete within 2 h when inhibition had not exceeded 20%during the SO₂ treatment. Key words: Sulphur dioxide, short-term fumigation, photosynthesis     

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.     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

Reanalysis of Vernalization Data of Wheat and Carrot

Vernalization is an important determinant of the growth, development,and yield of biennial and perennial crops. Accurate simulationof its response to temperature is thus an important componentof successful crop systems modelling. Vernalization has a lowoptimum temperature compared to other temperature responsesof plants, and thus may be difficult to treat using expressionsthat are appropriate for other plant processes. This paper examinesthe application of a simple equation that has been used forother processes. It reads as v=V_max(T_max-T_{Tmax- Topt} ) (T_Topt)^{T_optTmax-T_opt}, where v is thedaily rate of vernalization progress at temperature T, T_optandT_maxare the optimum and maximum temperatures for vernalization,respectively, andV_max is the maximum daily rate of vernalization(the inverse of the minimum number of days required to completevernalization), which occurs at T_opt. The model was appliedto published vernalization data for wheat and carrot. The fitsto data were good (adjusted R²for wheat of 0.94, for carrot0.98), with estimatedT_opt and T_maxbeing 5.7±0.5 and 21.3±1.4°C, respectively, for wheat ‘Norin 27’ and 6.6±0.2and 14.1±0.3 °C for carrot ‘ Chantenay RedCored’. The estimated parameters, in particular the highT_maxfor wheat, were close to those reported using differentanalytical approaches. It was suggested that the function wouldbe useful for summarizing vernalization data, and that its usewould avoid the abrupt changes that are inevitable when differentlinear relationships are used for part of the overall response.It was also suggested the high T_maxshould be taken into accountwhen interpreting data obtained with wheat grown under warmconditions. Copyright 1999 Annals of Botany Company Plant, vernalization, temperature response, modelling, wheat (Triticum aestivum L.), carrot (Daucus carota L.).     

ERRATA

Effects of coupled solute and water flow in plant roots withspecial reference to Brouwer's experiment. Edwin L. Fiscus. p. 71 Abstract: Line 3 delete ‘interval’ insert‘internal’. p. 73 Materials and Methods: line 6: delete ‘diversion’ insert ‘division’ line 9 equation should read J_v=L_p P–RT(C⁰–C¹). 74 Last line of figure legend: 10^–1 should read 10^–11. 75 Line 11: delete ‘seems’ insert ‘seem’. le 1 column heading—10⁶ should read 10¹¹. 77 delete ‘...membrane in series of...’ insert ‘membranein series or...’ Delete final paragraph.     

Ontogeny of growth, respiration and feeding rate of the freshwater calanoid copepod Eudiaptomus graciloides

The calanoid copepod, Eudiaplomus graciloides, was reared fromegg to adult on uni-algal diets (0.1. 0.5 and 2.5 mg dry wt1^–1) using the green alga, Chlamydomonas reinhardtii,as food, or on a mixed diet consisting of Lake Esrom water filteredthrough a plankton net with pore size 45 µm and supplementedwith C. reinhardtii (2.5 mg dry wt 1^–1). On the mixeddiet at 21.0°C growth in body dry wt (W, µg dry wt)was exponential, and the growth constants were 0.21 day^–1in the early to mid juvenile stage (N1 - C4) and 0.11 day^–1in the late juvenile to early adult stage (C4-A). At 14.5°Cthe corresponding growth rate constants were 0.10 and 0.08 day^–1.Similar growth rates were found at uni-algal concentrationsof 0.5 and 2.5 mg dry wt I^–1, and it was argued that thethreshold concentration for growth in Eudiaptomus was closeto 0.1 mg dry wt I^–1. The clearance (C, ml h^–1)of copepodites was measured on the uni-algal diets. The constantsof the regression (C = aW^b) were: a = 0.125, b = 0.858 (2000C. reinhardtii ml^–1), a = 0.068, b = 0.849 (10 000), a= 0.028, b = 0.875 (50 000). Ingestion rates were calculatedfrom the clearances and the average algal concentrations. Atthe three food levels the average daily rations were 30, 67and 125% of body dry wt. The respiration rate (R, nl O₂ h^–1)was measured in individuals reared on the mixed diet. The constantsof the regression (R = aW^b) were: a = 4.82, b = 1.07 (nauplii,14.5°C), a = 4.17, b = 0.904 (copepodites and adults, 14.5°C),a = 6.87, b = 0.757 (copepodites and adults, 21.0°C). Nosignificant difference in the respiration rate of copepoditesreared on uni-algal diets and the mixed diet could be demonstrated.Energy budgets were calculated. The assimilation efficiencyand the gross growth efficiency of copepodites decreased markedlywith increasing food concentration, the net growth efficiencyvaried from an average of 0.44 at the lowest algal concentrationto 0.60 on the mixed diet. The results are discussed in relationto previous findings with both freshwater and marine copepods.     

Relative Sensitivity and Tolerance of some Gladiolus Cultivars to Sulphur Dioxide

Five Gladiolus cultivars, namely ‘Aldebaran’, ‘BrightEye’, ‘Illusion’, ‘Manisha’ and‘Manmohan’, were exposed to 1 and 2 µg l^–1sulphur dioxide to test their relative-sensitivity toleranceto the pollutant Plants were fumigated experimentally for 2h daily Foliar injury symptoms were observed first in ‘Manisha’followed by ‘Aldebaran’ and ‘Illusion’at the higher dose Photosynthetic pigments and leaf extractpH were significantly decreased, particularly in ‘Manisha’and ‘Illusion’ Overall disturbances in the plantmetabolism due to SO₂ treatment led to retarded growth of plants,as evident from decreased shoot length and phytomass valuesThe order of sensitivity of the five Gladiolus cultivars toSO₂ was as follows, with the greatest first Manisha, Illusion,Aldebaran, Bright Eye, Manmohan Cultivars, Gladiolus, sensitivity, sulphur dioxide, tolerance     

Effect of Inorganic Phosphate on the Biosynthesis of Purine and Pyrimidine Nucleotides in Suspension-Cultured Cells of Catharanthus roseus

The levels of purine and pyrimidine nucleotides in suspensioncultures of Catharanthus roseus were determined 24 h after stationary-phasecells were transferred to fresh complete (‘+Pi’)or phosphate-deficient (‘–Pi’) Murashige-Skoogmedium. The levels of ATP, GTP, UTP and CTP were from approx.3 to 5-fold greater in the cells grown in ‘+Pi’medium than in the cells grown in ‘–Pi’ medium.The levels of almost all other nucleotides were slightly higherin the cells in ‘+Pi’ medium. The rates of de novoand salvage biosynthesis of purine and pyrimidine nucleotideswere estimated from the rates of incorporation of radioactivityfrom [¹⁴C]formate, [2–¹⁴C]glycine, NaH¹⁴CO₃, [6–¹⁴C]orotate,[8–¹⁴C]adenine, [8–¹⁴C]adenosine, [2–¹⁴C]uraciland [2–¹⁴C]uridine. The results indicated that the activityof both the de novo and the salvage pathway was higher in thecells in ‘+Pi’ medium than in the cells in ‘–Pi’medium. The rate of degradation estimated from the rate of releaseof ¹⁴CO₂ from labelled purines and pyrimidines indicated thatdegradation of uridine was significantly reduced in the cellsin ‘+Pi’ medium, but no significant difference wasfound in the degradation of adenine, adenosine and uracil. Thepossible role of Pi in the control of the biosynthesis of nucleotidesand in the degradation of uridine is discussed. Catharanthus roseus, Madagascar periwinkle, suspension culture, inorganic phosphate, nucleotides, purines, pyrimidines, biosynthesis, degradation     

The optical properties of a turbid reservoir and its phytoplankton in relation to photosynthesis and growth (Mount Bold Reservoir, South Australia)

In situ light measurements were used to obtain information oninherent and apparent optical properties. The average verticalattenuation coefficient K_d(ave) varied from 1.1 to 4.6 In unitsm^–1 During three periods the variation in K_d(ave) correlatedwith changes in chlorophyll a concentration and specific attenuationcoefficients K_s, of 0.013, 0.014 and 0.022 m² mg Chl a^–1were calculated. Chlorophyll-specific diffuse absorption coefficients(A,) for these periods were 0.012. 0.013 and 0.017 m² mg Chla^–1 and only varied significantly from estimates of K_sin the period when scattering was intense. Absorption coefficientsa(z^mid) and scattering coefficients b(z^mid) calculated for themid-point of the euphotic zone ranged between 0.45 and 2.9 mand 3.5–52.0 m respectively. Chlorophyll-specific absorptioncoefficients K_a, of 0.005, 0.006 and 0.007 m² mg Chl a^–1and scattering coefficients K_b of 0.05. 0.09 and 0.191 m² mgChl a^–1 were measured during the three periods. The highK_b value occurred when gas-vacuolate cyanobactena were dominant.Algal photosynthesis and light absorption were related throughthe maximum quantum yield _m which varied between 0.019 and 0.11mol C Einstein^–1 while average quantum yields _a, variedbetween 0.006 and 0.024 with a mean of 0.013 mol C Einstein^–1A comparison of changes in the mean irradiance of the mixedzone and chlorophyll concentration indicated that growth waslight limited below 0.04–0.05 Einsteins absorbed mg Chla^–1 day^–1.     

Developmental control of xylem hydraulic resistances and vulnerability to embolism in Fraxinus excelsior L.: impacts on water relations

The freezing tolerance of many plants, such as pea (Pisum sativum),is increased by exposure to low temperature or abscisic acidtreatment, although the physiological basis of this phenomenonis poorly understood. The freezing tolerance of pea shoot tips,root tips, and epicotyl tissue was tested after cold acclimationat 2C, dehydration/rehydration, applications of 10^–4M abscisic acid (ABA), and deacclimation at 25C. Tests wereconducted using the cultivar ‘Alaska’, an ABA-deficientmutant ‘wil’, and its ‘wildtype’. Freezinginjury was determined graphically as the temperature that caused50% injury (T₅₀) from electrical conductivity. Endogenous ABAwas measured using an indirect enzyme-linked immunosorbant assay,and novel proteins were detected using 2-dimensional polyacrylamidegel electrophoresis. The maximum decrease in T₅₀ for root tissuewas 1C for all genotypes, regardless of treatment. For ‘Alaska’shoot tips and epicotyl tissue, exogenous ABA increased thefreezing tolerance by –1.5 to –4.0C, while coldtreatment increased the freezing tolerance by –7.5 to–14.8C. Cold treatment increased the freezing toleranceof shoot tips by –9 and –15C for ‘wil’and ‘wild-type’, respectively. Cold acclimationincreased endogenous ABA concentrations in ‘Alaska’shoot tips and epicotyls 3- to 4-fold. Immunogold labeling increasednoticeably in the nucleus and cytoplasm of the epicotyl after7 d at 2C and was greatest after 30 d at the time of maximumfreezing tolerance and soluble ABA concentration. Cold treatmentinduced the production of seven, three, and two proteins inshoot, epicotyl, and root tissue of ‘Alaska’, respectively.In ‘Alaska’ shoot tissue, five out of seven novelproteins accumulated in response to both ABA and cold treatment.However, only a 24 kDa protein was produced in ‘wil’and ‘wild-type’ shoot and epicotyl tissues aftercold treatment. Abscisic acid and cold treatment additivelyincreased the freezing tolerance of pea epicotyl and shoot tissuesthrough apparently independent mechanisms that both resultedin the production of a 24 kDa protein. Key words: Pisum sativum, cold acclimation, immuno-localization     

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     

Occurrence of mycosporine-like amino acids in the red-tide dinoflagellate Alexandrium excavatum: UV-photoprotective compounds?

Water extracts of the red-tide dinoflagellate Alexandrium excavatumgrown at ‘high’ light intensity (200 µE m^–2s^–1) show a broad absorbance maximum in the UV regionof the spectrum (310–360 nm). Using TLC and reverse-phaseHPLC a series of mycosporine-like amino acids have been characterized:mycosporine-glycine (_max = 310 nm), palythine (_max = 320 nm),asterina-330 (_max = 330 nm), shinorine (_max = 334 nm), porphyra-334(_max= 334 nm), palythenic acid (_max = 337 nm) and the isomericmixture of usujirene and palythene (_max = 359 nm). From theobserved spectral changes during transference from ‘low’(20 µE m^–2 s^–1) to ‘high’ (200µE m^–2 s^–1) light intensities and vice versa,the series of compounds are supposed to be biogenically relatedto one another. The presence of these compounds in A.excavatumis discussed in relation to their possible role in the photoprotectionto deleterious UV radiation.     

Freezing tolerance, protein composition, and abscisic acid localization and content of pea epicotyl, shoot, and root tissue 3

The freezing tolerance of many plants, such as pea (Pisum sativum),is increased by exposure to low temperature or abscisic acidtreatment, although the physiological basis of this phenomenonis poorly understood. The freezing tolerance of pea shoot tips,root tips, and epicotyl tissue was tested after cold acclimationat 2C, dehydration/rehydration, applications of 10^–4M abscisic acid (ABA), and deacclimation at 25C. Tests wereconducted using the cultivar ‘Alaska’, an ABA-deficientmutant ‘wil’, and its ‘wildtype’. Freezinginjury was determined graphically as the temperature that caused50% injury (T₅₀) from electrical conductivity. Endogenous ABAwas measured using an indirect enzyme-linked immunosorbant assay,and novel proteins were detected using 2-dimensional polyacrylamidegel electrophoresis. The maximum decrease in T₅₀ for root tissuewas 1C for all genotypes, regardless of treatment. For ‘Alaska’shoot tips and epicotyl tissue, exogenous ABA increased thefreezing tolerance by –1.5 to –4.0C, while coldtreatment increased the freezing tolerance by –7.5 to–14.8C. Cold treatment increased the freezing toleranceof shoot tips by –9 and –15C for ‘wil’and ‘wild-type’, respectively. Cold acclimationincreased endogenous ABA concentrations in ‘Alaska’shoot tips and epicotyls 3- to 4-fold. Immunogold labeling increasednoticeably in the nucleus and cytoplasm of the epicotyl after7 d at 2C and was greatest after 30 d at the time of maximumfreezing tolerance and soluble ABA concentration. Cold treatmentinduced the production of seven, three, and two proteins inshoot, epicotyl, and root tissue of ‘Alaska’, respectively.In ‘Alaska’ shoot tissue, five out of seven novelproteins accumulated in response to both ABA and cold treatment.However, only a 24 kDa protein was produced in ‘wil’and ‘wild-type’ shoot and epicotyl tissues aftercold treatment. Abscisic acid and cold treatment additivelyincreased the freezing tolerance of pea epicotyl and shoot tissuesthrough apparently independent mechanisms that both resultedin the production of a 24 kDa protein. Key words: Pisum sativum, cold acclimation, immuno-localization     

Some Experimental and Theoretical Observations Concerning Mass Flow in the Vascular Bundles of Heracleum

The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, L_EE = 5 ? 10–⁴ mho cm^–1,L_pE = 9 ? 10^–6 cm³ s^–1 cm^–2 volt^–1 cm,and L_PP = 0.16 cm³ s^–1 cm^–2 (J cm^–3)^–1cm. In uncut phloem strands L_EE is about 1 ? 10^–3 mhocm^–1. In xylem in 2 x 10^–3 N KCI, L_pp = 50 to 225,L_PE = 2 ? 10^–4, and L^EE = 4 ? 10^–3. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga ‘long distance’ current pathway can be the majormotive ‘force’ for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm^–1endogenous in the phloem.     

A Cytochrome P450 Mediated Naringenin 3'-Hydroxylase from Sweet Orange Cell Cultures

A microsomal flavonoid 3'-hydroxylase (F3'H) catalyzing themetabolism of naringenin to eriodictyol in Citrus sinensis (L.)Osbeck cv. ‘Hamlin’ cell suspension cultures wasshown to be a cytochrome P450 enzyme. This reaction requiredO₂ and NADPH and was inhibited by CO, with partial reversalof CO-inhibition by light at 450 nm. Cytochrome P450 contentranged from 10–20 pmol (mg microsomal protein)^–1.The F3'H reaction was shown to be linear in regard to proteinconcentration between 2.5 and 25 µg of microsomal protein.The optimum pH for the reaction was 7.4–7.6 and the temperatureoptimum was between 30 and 37°C. The apparent K_m and V_maxfor naringenin were 24 µM±3.2 and 81.4±7.9pmol eriodictyol min^–1 (mg protein)^–1, respectively.The microsomal F3'H was also capable of forming dihydroquercetinfrom dihydrokaempferol (40 pmol min^–1 (mg protein)^–1)and of quercetin from kaempferol (3.25 pmol min^–1 (mgprotein^–1). Cytochrome c and ketoconazole were the bestinhibitors of WH activity followed by piperonyl butoxide anda-naphthoflavone. Light was shown to be an inducer of the F3'Halmost doubling the specific activity and increasing the microsomalcytochrome P450 content by 30% over that of dark grown cells.F3'H activity was also confirmed in microsomal preparationsof young (new flush) leaves from ‘Hamlin’ treesand flavedo of ‘Hamlin’ oranges, ‘Marsh’grapefruit, and ‘Lisbon’ lemon. No activity wasobserved in older, hardened leaves and albedo of all the fruittested. Initiation of embryogenesis in the ‘Hamlin’cell suspension cultures by switching from a sucrose mediumto a glycerol-based medium resulted in the down-regulation ofF3'H. ¹Mention of a trademark, warranty, proprietary product, or vendordoes not constitute a guarantee by the U.S. Department of Agricultureand does not imply its approval to the exclusion of other productsor vendors that may also be suitable.     

Strategies d'adaptation photosynthetique chez des diatomees des I'Ocean Antarctique: variations du nombre et de la talile des unites photosynthetiques

Les diatomes Nitzschia turgiduloides et Chaetoceros deflandrei,rcoltes en fvrier–Mars 1980 dans le secteur indiende l'Ocan Antarctique, ont t maintenues en culture au laboratoire,sous des intensits himineuss variant de 140 2 µE m^–2s^–2. The production versus intensite lumineuse, tabliespar cellule et par unit de chlorophylle a, suggrent, selonla mthode de Richardson et al. (1983), une adaptation des espcesantarctiques la lumire par variation de la taille (estimepar la valeur I_k) et du nombre (volution de la pente initiale) des units photosynthtiques. Au plan ecologique, les valeursdes paramtres photosynthetiques en lumire Bmitante et en lumiresaturante sont faibles, caractristiques des algues ‘d'ombre’:concentration en chlorophylle a et productivit par celluleplus fortes quand les espces sont acclimates a des faiblesintensites lumineuses. Ce travail met ainsi en vidence I'importancedu facteur lumineux par rapport la basse temprature sur laproduction primaire de l'Ocan Antarctique.     

The Apparent Induction of Nitrate Uptake by Chara corallina Cells following Pretreatment with or without Nitrate and Chlorate

Nitrate provision has been found to regulate the capacity forChara corallina cells to take up nitrate. When nitrate was suppliedto N sufficient cells maximum nitrate uptake was reached after8 h. Prolonged treatment of the cells in the absence of N alsoresulted in the apparent ability of these cells to take up nitrate.Chlorate was found to substitute partially for nitrate in the‘induction’ step. The effects on nitrate reductionwere separated from those on nitrate uptake by experiments usingtungstate. Tungstate pretreatment had no effect on NO^–₃uptake ‘induced’ by N starvation, but inhibitedNO^–₃ uptake associated with NO^–₃ pretreatment. Chloridepretreatment similarly had no effect on NO^–₃ uptake ‘induced’by N deprivation, but inhibited NO^–₃ uptake followingNO^–₃ pretreatment. The data suggest that there are atleast two mechanisms responsible for the ‘induction’of nitrate uptake by Chara cells, one associated with NO^–₃reduction and ‘induced’ by CIO^–₃ or NO^–₃and one associated with N deprivation. Key words: Nitrate, Chlorate, Chara corallina, Induction     

Defoliation in White Clover: Nodule Metabolism, Nodule Growth and Maintenance, and Nitrogenase Functioning During Growth and Regrowth

In two experiments, the functioning and metabolism of nodulesof white clover, following a defoliation which removed abouthalf the shoot tissue, were compared with those of undefoliatedplants. In one experiment, the specific respiration rates of nodulesfrom undefoliated plants varied between 1160 and 1830 µmolCO₂ g^–1h^–1, of which nodule ‘growth and maintenance’accounted for 22 ± 2 per cent, or 27 ± 3.6 percent, according to method of calculation. Defoliation reducedspecific nodule respiration and nodule ‘growth and maintenance’respiration by 60–70 per cent, and rate of N₂ fixationby a similar proportion. The original rate of nodule metabolismwas re-established after about 5 d of regrowth; during regrowthnodule respiration was quantitatively related to rate of N₂,fixation: 9.1 µmol CO₂ µmol^–1N₂. With the possible exception of nodules examined 24 h after defoliation,the efficiency of energy utilization in nitrogenase functioningin both experiments was the same in defoliated and undefoliatedplants: 2.0±0.1 µmol CO₂ µmol^–1 C₂H₄;similarly, there was no change in the efficiency of nitrogenasefunctioning as rate of N₂ fixation increased with plant growthfrom 1 to 22 µmol N₂ per plant h^–1. Exposure of nodulated white clover root systems to a 10 percent acetylene gas mixture resulted in a sharp peak in rateof ethylene production after 1.5–2.5 min; subsequently,rate of ethylene production declined rapidly before stabilisingafter 0.5–1 h at a rate about 50 per cent of that initiallyobserved. Regression of ‘peak’ rate of ethyleneproduction on rate of N₂ fixation indicated a value of 2.9 µmolC₂H₄ µmol^–1 N₂, for rates of N₂ fixation between1 and 22 µmol N₂ per plant h^–1. The relationshipsbetween nitrogenase respiration, acetylene reduction rates andN₂ fixation rates are discussed. Trifolium repens, white clover, defoliation, nodule respiration, N₂, fixation, nitrogenase     

Are Mistletoes Shade Plants? CO2Assimilation and Chlorophyll Fluorescence of Temperate Mistletoes and their Hosts

Mistletoes usually have slower rates of photosynthesis thantheir hosts. This study examines CO₂assimilation, chlorophyllfluorescence and the chlorophyll content of temperate host–parasitepairs (nine hosts parasitized by Ileostylus micranthus and Carpodetusserratus parasitized by Tupeia antarctica). The hosts of I.micranthus had higher mean annual CO₂assimilation (3.59 ±0.41 µmol m^-2 s^-1) than I. micranthus(2.42 ± 0.20µmol m^-2 s^-1), and C. serratus(2.41 ± 0.43 µmolm^-2 s^-1) showed higher CO₂assimilation than T. antarctica(0.67± 0.64 µmol m^-2 s^-1). Hosts saturated at significantlyhigher electron transport rates (ETR) and light levels thanmistletoes. The positive relationship between CO₂assimilationand electron transport suggests that the lower CO₂assimilationrates in mistletoes are a consequence of lower electron transportrates. When photosynthetic rates, ETR and chlorophyll a /b ratioswere adjusted for photosynthetically active radiation, hostsdid not have significantly higher CO₂assimilation (3.21 ±0.37 µmol m^-2 s^-1) than mistletoes (2.54 ± 0.41µmol m^-2 s^-1), but still had significantly higher ETRand chlorophyll a / b ratios. The electron transport rates,saturating light and chlorophyll a / b ratios of sun leavesfrom mistletoes were similar to host shade leaves. These responsesindicate that in comparison with their hosts, mistletoe leaveshave the photosynthetic characteristics of the leaves of shadeplants. Copyright 2000 Annals of Botany Company CO₂assimilation, photosynthetic active radiation (PAR), chlorophyll fluorescence, electron transport rate (ETR), photochemical quenching (q_p), non-photochemical quenching (q_n), sun and shade leaves, chlorophyll content, Ileostylus micranthus, Tupeia antarctica, New Zealand     

Photosynthetic parameters, pigment composition and respiration rates of the marine diatom Skeletonema costatum grown in continuous light and a 12:12 h light-dark cycle

Nutrient-sufficient cultures of a Trondheimsfjord (Norway) cloneof the marine centric diatom Skeleionema costatum (Grev.) Clevewere grown at 75 µmol m^–2 s^–1 and 15C at24 and 12 h daylength to study diurnal variations and the effectof daylength on pigment and chemical composition, photosyntheticparameters, dark respiration rates and scaled fluorescence excitationspectra (F), the latter used as estimates for the absorptionof energy available to Photosystem II. Specific growth rateswere 1.06 and 0.56 day^– in 24 and 12 h daylength, respectively,while dark respiration rates were generally 85% of the net growthrate. The Chla-normalized photosynthetic coefficients P^B_m anda^B were {small tilde}20–25% higher in continuous lightthan at 12 h daylength, while the Chla:C ratio was {small tilde}15%lower (0.051 versus 0.061 w:w). Thus, the carbon-normalizedcoefficients P^c_m and a^c were <11% lower at 24 h than at 12h daylength. The maximum quantum yield _max, the Chla:C ratioand F differed negligibly, as did the light saturation indexl_k, the N:C ratio and the ratios Chlc:Chla and Fucoxanthin:Chla. P^B_m and l_k did not exhibit diurnal variations at 24 hdaylength, and varied within 23% of the daily mean at 12 h daylength.Predictions of the daily gross photosynthetic rate based ondata for a given time of the day should thus not be >10%in error relative to an integrated value based on several datasets collected through 24 h. _max was 0.084–0.117 mol O₂(mol photons)^– for gross oxygen evolution. However, ifused in mathematical models for predicting the gross and netgrowth rates (i.e. the gross and net carbon turnover rates),‘practical’ values of 0.076 and 0.040 g-at C (molphotons)^–, respectively, should be employed. Correspondingly,values for a^B and P^B_m should be adjusted pro rata. ¹Present address: College of Marine Studies, Sjmannsveien 27,N-6008 lesund, Norway