Effects of Root Temperature and Form of Nitrogen Nutrition on Nitrate Reductase Activity in Oilseed Rape (Brassica napus L.)

The effect of root temperature and form of inorganic nitrogensupply on in vitro nitrate reductase activity (NRA) was studiedin oilseed rape (Brassica napus L. cv. bien venu). Plants weregrown initially in flowing nutrient solution containing 10 µMNH₄NO₃ and then supplied with either nitrate or ammonium for15 d at root temperatures of 3, 7, 11 or 17 °C. Shoot temperatureregime was similar for all plants; 20/15 °C, day/night.Root NRA was highest when roots were grown at 3 and 7 °C.In laminae and petioles NRA was highest when roots were 11 or17 °C. The plants supplied with ammonium had much lowerlevels of NRA in roots after 5 d than the plants supplied onlywith nitrate. NRA in the laminae of plants supplied with ammoniumwas low relative to that in plants supplied with nitrate onlywhen root temperature was 11 or 17 °C. Values of the apparent activation energy (E_a) of NR, calculatedfrom the Arrhenius equation, in laminae and petioles were differentfrom roots suggesting difference in enzyme conformation. Evidencethat the temperature at which roots were growing affected E_awas equivocal. Oilseed rape, Brassica napus L., activation energy, ammonium, Arrhenius equation, nitrate, root temperature, nitrate reductase     

Use of the Plastochron Index to Evaluate Effects of Light, Temperature and Nitrogen on Growth of Soya Bean (Glycine max L. Merr.)

The plastochron index (PI) has been compared with leaf growthand biomass accumulation in young soya bean plants of severalcultivars that were grown in controlled environments with differentirradiance levels and durations, temperatures, and nitrogen(N) regimes. Increasing the photoperiod from 10 to 16 h day^–1 increasedthe plastochron rate (PR) and the proportion of axillary growth.Doubling the photosynthetic photon flux density (PPFD) to 1000µmol m^–2S^–1, increased PR and the proportionof roots to total plant weight, but decreased the proportionof stems plus petioles to total. In a series of experiments,the plants were grown in an 8 h photoperiod at constant temperaturesof 17, 20, 26 or 32 °C. As temperature increased, PR increased,but the duration of leaf expansion decreased. Leaves were largestat 20 and progressively smaller at 26, 32 and 17 °C. Biomasswas greatest for a given PI at 20 °C and decreased in theorder of 26, 32, and 17 °C. The proportion of axillary growthalso was greatest at 20 °C. When plants were grown in a15 h photoperiod at temperatures from 17.1 to 26.6 °C, leafsize continued to increase up to the highest temperature. At17 °C, the PR in the 15 h photoperiod (PPFD 390 µmol;m^–2S^–1) was about threefold greater than in 8 h(500 µmol m^–2 S^–1); biomass accumulation perday was about fivefold greater. Increasing N from 3 to 36 mMincreased PR about 10 per cent, altered biomass partitioningamong plant parts, and increased the biomass of the plants.The NO₂ form of N markedly stimulated axillary growth as comparedwith the NH₄⁺ form. Environment or cultivar had little influenceon the duration of leaf expansion in terms of PI. Cultivarsdid not differ consistently in biomass production and allocationin the different environments. Glycine max (L.) Merrill, soybean, soya bean, plastochron index, leaf development, growth analysis, partitioning, light, nitrogen, temperature     

Sink-Regulation of Photosynthesis in Relation to Temperature in Sunflower and Rape

Stimulation of the rate of photosynthesis at 2·0 kPaO₂ in comparison with 21 kPa O₂ and carbohydrate accumulationover 4h were measured during exposure of sunflower (Helianthusannuus L.) and rape (Brassica napus L.), grown at 30 °Cand 13 °C, to temperatures between 7 °C and 35 °C.The effect of reducing source: sink ratio by shading on theresponse of photosynthetic rate to temperature was also determined.Stimulation of photosynthesis by 2·0 kPa O₂ in comparisonwith 21 kPa O₂ decreased over 4 h at cool temperatures in sunflowerplants grown at 30 °C but not in rape grown at 30 °C.Stimulation did not decrease over 4 h in plants grown at 13CC. Sucrose was the main carbohydrate accumulated over 4 h;its accumulation increased with decreasing temperature. Starchaccumulation either decreased or remained the same with decreasingtemperature. In plants grown at 30 °C more carbohydrateaccumulated between 8 °C and 21 °C in sunflower thanin rape, but more carbohydrate accumulated at 30 °C in rapethan in sunflower. In plants grown at 13 °C much less carbohydrateaccumulated between 13 °C and 23 °C than in plants grownat 30 °C. Photosynthetic rate in plants grown at 30 °Cexposed to between 20 °C and 35 °C over 32 h (14 h light-10h dark-8 h light), declined over 32 h at 20 °C and 25 °Cin sunflower and at 20 °C in rape. This fall over 32 h,especially at 20 °C in sunflower, was significantly reducedby shading the rest of the plant. Shading had little effecton photosynthetic rate above 25 °C. The work confirms thatlow temperature imposes a sink-limitation on photosynthesiswhich occurs at higher temperatures in sunflower than in rape.This limitation may be relieved by decreasing the source:sinkratio. Key words: Sunflower, rape, photosynthesis, carbohydrates, sink demand, temperature     

The Freezing Response of an Arctic Cushion Plant, Saxifraga caespitosa L.: Acclimation, Freezing Tolerance and Ice Nucleation

Cold hardiness in actively growing plants of Saxifraga caespitosaL., an arctic and subarctic cushion plant, was examined. Plantscollected from subarctic and arctic sites were cultivated ina phytotron at temperatures of 3, 9, 12 and 21 °C undera 24-h photoperiod, and examined for freezing tolerance usingcontrolled freezing at a cooling rate of 3–4 °C eitherin air or in moist sand. Post-freezing injury was assessed byvisual inspection and with chlorophyll fluorescence, which appearedto be well suited for the evaluation of injury in Saxifragaleaves. Freezing of excised leaves in moist sand distinguishedwell among the various treatments, but the differences werepartly masked by significant supercooling when the tissue wasfrozen in air. Excised leaves, meristems, stem tissue and flowerssupercooled to –9 to –15 °C, but in rosettesand in intact plants ice nucleation was initiated at –4to –7 °C. The arctic plants tended to be more coldhardy than the subarctic plants, but in plants from both locationscold hardiness increased significantly with decreasing growthtemperature. Plants grown at 12 °C or less developed resistanceto freezing, and excised leaves of arctic Saxifraga grown at3 °C survived temperatures down to about –20 °C.Exposure to –3 °C temperature for up to 5 d did notsignificantly enhance the hardiness obtained at 3 °C. Whenwhole plants of arctic Saxifraga were frozen, with roots protectedfrom freezing, they survived –15 °C and –25°C when cultivated at 12 and 3 °C, respectively, althougha high percentage of the leaves were killed. The basal levelof freezing tolerance maintained in these plants throughoutperiods of active growth may have adaptive significance in subarcticand arctic environments. Saxifraga caespitosa L., arctic, chlorophyll fluorescence, cold acclimation, cushion plant, freezing stress, freezing tolerance, ice nucleation, supercooling     

Effect of Temperature and Nitrogen Supply on the Growth of Perennial Ryegrass and White Clover. 2. A Comparison of Monocultures and Mixed Swards

White clover (Trifolium repens L.) and Perennial ryegrass (Loliumperenne L.) plants were grown, in Perlite, in simulated swardsas either monocultures or mixtures of equal plant numbers. Theywere supplied with a nutrient solution either high (220 µgg^–1) or low (40 µg g^–1) in ¹⁵N-labelled nitrateand grown to ceiling yield at either high (20°C day/15°Cnight) or low (10°C day/8°C night) temperature. Temperature had little effect on the maximum rates of grosscanopy photosynthesis which were similar in High-N grass andHigh-N and Low-N clover monocultures. However these maxima werereached more slowly in clover than grass, and more slowly atlow rather than high temperature. Nitrogen supply increasedphotosynthesis in grass but not in clover. Clover had higherN contents than grass in all four treatments, although in anygiven treatment its N content was lower, and contribution ofN₂-fixation relative to nitrate uptake higher, in mixture thanin monoculture. Conversely, grass had higher N contents in mixturethan monoculture, because more nitrate was available per plantand not because of transfer of biologically fixed N from clover. Under Low-N, clover outyielded grass in mixture, particularlyat high temperature. The grass plants in the Low-N mixtureshad higher N contents and higher SLA, LAR and shoot: root ratiosthan those in monoculture. It is proposed that competition forlight is the cause of the low relative yield and negative aggressivityof grass in these swards. Under High-N, grass outyielded cloverin monoculture and mixture, at both temperatures but particularlyat low temperature when grass had a high aggressivity. Nitrogenand yield component analyses shed no light on clover's apparentlylow competitive ability and evidence is drawn from the previouspaper to demonstrate that grass grew faster than clover onlyas spaced individuals during non-com petitive growth. The relativemerits of measures of competitive ability based on final harvestdata and physiological data taken over a growth period are discussed. Trifolium repens L., white clover, Lolium perenne, perennial ryegrass, competition, temperature, nitrogen     

Components of Growth and Dark Respiration of Kikuyu (Pennisetum clandestinum Chiov.) at Various Temperatures

Growth and dark respiration were measured in dense, miniatureswards of kikuyu grass grown at constant temperatures of 15,20, 25 and 30 °C. Total respiration over the first 12 hof darkness was very high and CO² efflux per unit surface areavaried from 2.4 to 3.9 g CO₂ m^–2 h^–1 at 15 and 30°C respectively. Such rates were consistent with the correspondinglyhigh net growth rates of 24 and 63 g d. wt m^–2 d^–1and the heavy yields of herbage. When plants were kept in thedark, CO₂ efflux subsequently declined rapidly to a lower, constantrate which was taken to be the maintenance respiration rate.The half-life of the declining phase of respiration averaged10.9 and 6.0 h at 15 and 30 °C respectively, and was curvilinearlyrelated to the specific maintenance respiration rate (m). Therapid decline in respiration was consistent with the low concentrationsof total soluble carbohydrate and starch in the herbage. Valuesof m for lamina and top growth increased with temperature witha Q₁₀ of 2.6 and 1.42 respectively, but m of stems alone wasnot affected by temperature. Using results from this study forkikuyu and from McCree (1974) for sorghum and white clover,it was noted that all three species have similar m when grownat temperatures which are near their respective optimums forgrowth. Kikuyu, Pennisetum clandestinum, growth, respiration, temperature     

Acclimation of Lolium temulentum to enhanced carbon dioxide concentration

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

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.     

The Effects of Nitrogen Supply on the Absorption and Distribution of Copper in Red Clover (Trifolium pratense L.) Grown in Flowing Solution Culture with a Low, Maintained Concentration of Copper

The absorption and distribution of Cu in red clover (Trifoliumpratense L.) were measured in plants grown in flowing solutionculture with Cu maintained throughout at 0.5 µg 1^–1and N supplied either as nitrate or through symbiotic fixation.Although there was a decrease in Cu absorption, both with time,and with a depleted nitrate supply, it increased to its formerrate when nitrate was adjusted to 10 mg N 1^–1 after aperiod of depletion. Differences in absorption between plantsdependent upon fixation and those supplied with nitrate wererelated to the slower initial growth of the plants fixing N.Considerable proportions (> 30 per cent) of the absorbedCu were retained by the roots. At the final harvest, and withthe exception of plants grown with nitrate adjusted to 0.1 mgN 1^–1 after a period of depletion, the proportion of theCu retained was related to the concentration of N in the roots.The different N treatments produced differences in Cu concentrationin the shoots, and the effects were greater in the youngestfully expanded leaves than in older leaves. Trifolium pratense L., red clover, absorption, copper, flowing solution culture, nitrogen     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Long Term Effects of High CO2 Concentration on Photosynthesis of Water Hyacinth (Eichhornia crassipes (Mart.) Solms)

The photosynthetic response to CO₂ concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO₂ or at10000 µmol(CO₂) mol^–1 and in winter at 6000 µmol(CO₂)mol^–1 Plants grown and measured at ambient CO₂ had highphotosynthetic rate (35 µmo1(CO₂) m^–2 s^–1),high saturating photon flux density (1500–2000) µmolm^–2 s^–1 and low sensitivity to temperature in therange 20–40 °C. Maximum photosynthetic rate (63 µmol(CO₂)m^–2 s^–1) was reached at an internal CO₂ concentrationof 800 µmol mol^–1. Plants grown at high CO₂ in summerhad photosynthetic capacities at ambient CO₂ which were 15%less than for plants grown at ambient CO₂, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO₂and high light intensity had typical response curves to internalCO₂ concentration with saturation at high CO₂, but for plantsgrown under high CO₂ and low light and plants grown under lowCO₂ and high light intensity photosynthetic rates decreasedsharply at internal CO₂ concentrations above 1000 µmol^–1. Key words: Photosynthesis, CO₂, enrichment, Eichhornia crassipes     

Light, temperature and nitrogen as interacting factors affecting diel vertical migrations of dinoflagellates in culture

Diel vertical migrations of the marine dinoflagellates Gonyaulaxpolyedra Stein and Ceratium furca (Ehr.) Clap, et Lachm. werefollowed in a laboratory tube (2.02 m x 0.25 m) under a 12:12hlight:dark cycle. The effects of temperature stratification,two levels of surface irradiance and nitrogen depletion on patternsof vertical migrations were examined. At temperatures between22–26°C with small temperature gradients, both speciesmigrated at a rate of 0.7 –1.0 m h^–1. Steeper thermoclines(ca. 0.8°C 0.1 m^–1) with temperatures below ca. 20°Ccaused a marked decrease in swimming speed which resulted inaccumulations of cells in these thermocline regions. Under conditionsof nutrient sufficiency both algae migrated into the surfacelayers at irradiance values of over 1000 µE m^–2s^–1. Increasing nitrogen depletion caused the downwardmigration of both algae to commence progressively earlier inthe day and before the end of the light period. The earlierdownward migrations enabled a more complete descent throughthe thermocline. Nitrogen depleted cells of Gonyaulax continuedto undertake vertical migrations but avoided high irradiancesthus forming subsurface maxima at irradiance levels close to150 µE m^–2 s^–1. Ceratium cells which exhaustedboth inorganic nitrogen and phosphorus ceased to migrate accompaniedby a large change in cellular fluorescence.     

Effect of High Temperature on Photosynthesis in Potatoes

The effect of high temperatures on the rate of photosynthesiswas studied in several potato varieties. Temperatures of upto 38 °C did not cause a reduction in the photosynthesisof plants that had been grown at these temperatures for longperiods prior to measurement. Higher temperatures of 40–42°C, or the transfer of plants from daytime temperature regimesof 22 °C to 32 °C, caused a reduction in net photosynthesis.This reduction was found to be essentially mesophyllic in origin.High temperature was found to be associated with a decreasein stomatal resistance, an increase in transpiration, and alarger difference between air and leaf temperatures. Dark respirationrates and compensation points for CO₂ concentration were alsogreater at the high temperatures. It was concluded that thepotato crop can be adopted to grow and have an adequate rateof photosynthesis even at relatively high temperatures. Source-sinkrelationships, which were modified by the later formation oftubers at higher temperatures, did not affect photosynthesisin this study. Varietal differences in resistance to heat stresswere observed, with the clone Cl-884 showing a more efficientcapacity for photosynthesis at temperatures up to 40 °Cthan many commonly grown varieties. High temperature, photosynthesis, potato, Solanum tuberosum L     

Soyabean Stem In Vivo Nitrate Reductase Activity

Stem from three- and four-week-old Soyabean [Glycine max (L.)Merr. cv. Tracy] plants reduced from 0.3 to 0.7 µmol nitrateh^–l g^–l f. wt. Leaf activity was 4.7–7.6 µmolnitrate h^–l g^–l f. wt. Outer stem was two to fourtimes more active at reducing nitrate than was inner stem. Plantnitrate nutrition had a strong effect upon the ratio of activitypresent in stem and leaf. More nitrate increased the proportionpresent in leaves. Glycine max L., soyabean, nitrate assimilation, nitrogen metabolism, Rhizobium japonicum     

Functional Manganese Requirement and its use as a Critical Value for Diagnosis of Manganese Deficiency in Subterranean Clover (Trifolium subterraneum L. cv. Seaton Park)

The effects of manganese supply on plant growth and on photosynthesisand manganese concentrations in young leaves were examined inSeaton Park subterranean clover in three glasshouse water cultureexperiments. Plants werc grown initially with a copious supply of manganese,and transferred to solutions either with or without manganese.Sequential harvests were taken to determine the effects of developingmanganese deficiency on dry matter (DM) yield of whole plantsand selected characteristics [manganese, chlorophyll and photosyntheticoxygen evolution (POE)] of youngest open leaf blades (YOL).In addition, the deffect of leaf age and iron supply on POEwerc examined. Manganese concentrations and POE in YOL declined markedly andrapidly in plants transferred to solutions without manganese,while chlorophyll concentrations of YOL and plant DM yield respondedmore weakly and more slowly. As a result, a level of manganesedeficiency which depressed POE in young leaves by more than50 per cent had no effed on DM production. In youngleaves (YOL, YOL + 1, YOL–1), POE declined whentheir manganese concentrations were < 20 µg g^–1DM. Iron supply did not affect this rdationship. When learnwith < 20 µg Mn g^–1 DM were detached and incubatedfor 24 h in solutions containing high concentrations of manganese,their POE increased to normal rates; leaves with higher manganeseconcentrations did not respond. It is suggested that the valueof 20 µg Mn g^–1 DM is the functional manganese requirementfor POE in young subterranean clover leaves It is also suggestedthat this value may be used as a critical value for indicatingmanganese deficiency in subterranean clover. Functional nutrient requirements determined in this way by correlationof nutrient concentrations in young leaves with their biochemicalor physiological activities appear to offer more accurate andconsistent standards for use an critical values for diagnosisof plant nutrient status than do the critical values determinedin the usual way by correlation with plant dry weight. Trifolium subterraneum L. subterranean clover, manganese, functional requirements, deficiency diagnosis, nutrient requirements, critical values, photosynthetic oxygen evolution     

Effects of Irradiance and Temperature on Flowering of Chrysanthemum morifolium Ramat. in Continuous Light

The short-day plant Chrysanthemum morifolium cv. Polaris initiatedflower buds in all irradiances of continuous light from 7.5to 120 W m^–2. As the irradiance increased, the transitionto reproductive development began earlier and the number ofleaves initiated before the flower bud was reduced. The autumn-floweringcultivars Polaris and Bright Golden Anne, and the summer-floweringGolden Stardust were also grown in continuous light at differenttemperatures; all initiated flower buds at temperatures from10 to 28 °C but only the buds of Golden Stardust developedto anthesis and then only at 10 and 16°C. Flower initiationbegan earliest at 16–22 °C, and the number of leavesformed before the flower bud was increased at 28°C. GoldenStardust was exceptional in that the number of leaves formedwas also increased at 10 °C. Axillary meristems adjacentto the terminal meristem initiated flower buds rapidly at 10°C but not at 28 °C in all three cultivars. These resultsare discussed in relation to the autonomous induction of flowerinitiation and the effects of the natural environment on floweringof chrysanthemum. Chrysanthemum morifolium Ramat, flowering, irradiance, temperature     

Triadimenol Increases Nitrate Levels and Nitrate Reductase Activity in Canola Leaves

Nitrate reductase activity in the first true leaves of canola(Brassica napus L.) seedlings grown in one-quarter strengthHoagland's solution from seeds pretreated with triadimenol (0.3or 30 g (a.i.) kg^–1 of seed) was higher than controlsduring the growth period of 15 to 25 d after planting. Triadimenolalso increased chlorophyll levels, the increase being more pronouncedat its lower concentration. The treatment also increased theweight and nitrate content of the leaves. When seedlings weregrown in nutrient solution containing 1 to 20 mM nitrate, theincrease in nitrate reductase activity by triadimenol was higherat lower rather than at higher nitrate concentrations. The nitratelevels and Kjeldahl nitrogen in the triadimenol-treated leaveswas higher than the controls at concentrations of added nitrateabove 2 mM. Addition of nitrate to plants grown in ammonium,increased nitrate reductase activity more in plants grown fromtriadimenol-treated seeds than controls. However, addition of10µM triadimenol for 24 h to ammonium-grown plants hadlittle effect on enzyme activity, both in the absence as wellas the presence of nitrate. This study demonstrates that triadimenolincreases nitrate reductase activity and nitrate accumulationin the leaves and at least part of the increased enzyme activityis independent of nitrate accumulation. Key words: Triazoles, nitrate content, nitrate reductase activity     

Pigment Production by Cultured Florets of Chrysanthemum morifolium

Individual florets (4–5 mm long) of a purple cultivar(Fandango) of the horticultural chrysanthemum (Chrysanthemummorifolium Ramat) were taken from flower buds just prior toopening and cultured in a sterile liquid medium (containinginorganic salts and sucrose) at 15 °C under a 12-h day.For the first 14 days increase in wet weight was exponential.Anthocyanin appeared on the third day and was then synthesizedrapidly. Chlorophyll and carotenoid were present initially:carotenoid levels rose quickly while chlorophyll remained almostconstant. Highest pigment content and most growth were foundwhen the florets were grown on 3 per cent sucrose. However,the highest anthocyanin concentration was found with 4 per centsucrose, the highest carotenoid concentration with 0.6 per centsucrose. No anthocyanin was produced when the florets were grownat 6 or 30 °C; maximum yield was at 15 °C. Most carotenoidwas formed at 30 °C and most chlorophyll was found at 20–5°C. All florets from 1 to 7 mm long could be cultured. Theseresults are discussed in relation to flower colour and pigmentformation in vivo.     

The Growth and Development of the Wheat Apex: The Effects of Photoperiod on Spikelet Production and Sucrose Concentration in the Apex

Spring wheat (Triticum aestivum cv. Warimba) plants were grownin a controlled environment (20°C) in two photoperiods (8or 16 h). In the first instance, plants were maintained in eachof the photoperiods from germination onwards at the same irradiance(375 µE m^–2 s^–1). In the second case, allplants were grown in a long photoperiod until 4 days after double-ridgeinitiation when half the plants were transferred to a shortphotoperiod with double the irradiance (16 h photoperiod at225 or 8 h at 475 µE ^–2 s^–1). The rates of growth and development of the apices were promotedby the longer photoperiod in both experiments. Shoot dry weightgain was proportional to the total light energy received perday whereas the dry weight of the shoot apex increased withincreasing photoperiod even when the total daily irradiancewas constant. The principal soluble carbohydrate present in the shoot apexwas sucrose, although low concentrations of glucose and fructosewere found in the apices of long photoperiod plants late indevelopment. Sucrose concentration was invariably greater inthe slow-growing apices of short photoperiod plants, but roseto approach this level in the long photoperiod plants when theterminal spikelet had been initiated. Triticum aestivum, wheat, apex, spikelet initiation, photoperiod, flower initiation     

Transient nitrate uptake and assimilation in Skeletonema costatum cultures subject to nitrate starvation under low irradiance

Batch cultures of the nitrate-grown marine diatom, Skeletonemacostatum, were grown in various levels of nitrate supply, fromfull sufficiency of nitrate to 96 h of nitrate starvation Allthe cultures were maintained at low light intensity (50 µEm^–2 s^–1) to simulate the light regime of naturalphytoplankton populations in turbid waters or at the edge ofthe photic zone. The response of S costatum cells to perturbationswith 10 µM nitrate after variable starvation periods wasstudied At the deficiency-starvation borderline, the specieswas able to both increase its uptake rate and store intracellularnitrate pools. Surge, or initially high, uptake is characteristicof this situation. After long starvation periods the cells neededto acclimate to a nitrate environment before being able to utilizeit The time required for this was proportional to the previousstarvation period. Time courses of nitrate uptake and reductionwere strongly non-linear. Nitrate excretion was high (up to3 µM) under intermediate (24 and 36 h) starvation periods.Differences in the rates and times of uptake, reduction andassimilation produced strong uncoupling of the three processesThe results suggest that there is an adaptation to nitrate utilizationunder low light, nitrate shortage and discontinuous, suddennitrate inputs.