Old-Culture Flowering of Lemna paucicostata 6746 in Aged Hutner's Medium

Lemna paucicostata 6746, a short-day plant, flowers in agedHutner's medium even under continuous light, when the endogenousnitrogen level decreases to below 1.6 µmg fr wt. At thesenitrogen levels, daylength-independent flowering of the plantcan be induced even in fresh Hutner's medium. Thus, old-cultureflowering in Hutner's medium is due to nitrogen deficiency inthe plants. ¹Present address: Biological Institute, Faculty of Science,Shizuoka University, Shizuoka 422, Japan. (Received February 12, 1987; Accepted August 28, 1987)     

Effect of Source of Nitrogen on the Growth of Fiskeby Soya Bean: the Carbon Economy of Whole Plants

Fiskeby V soya bean was grown from seed germination to seedmaturation with two contrasting patterns of nitrogen metabolism:either wholly dependent on dinitrogen fixation, or with an abundantsupply of nitrate nitrogen, but lacking root nodules. The carbonand nitrogen economies of the plants were assessed at frequentintervals by measurements of photosynthesis, shoot and rootrespiration, and organic and inorganic nitrogen contents. Plantsfixing atmospheric nitrogen assimilated only 25–30 percent as much nitrogen as equivalent plants given nitrate nitrogen:c. 40 per cent of the nitrogen of ‘nitrate’ plantswas assimilated after dinitrogen fixation had ceased in ‘nodulated’plants. The rates of photosynthesis and respiration of the shootsof soya bean were not markedly affected by source of nitrogen;in contrast, the roots of ‘nodulated’ plants respiredtwice as rapidly during intense dinitrogen fixation as thoseof ‘nitrate’ plants. The magnitude of this respiratoryburden was calculated to increase the daily whole-plant respiratory loss of assimilate by 10–15 per cent over thatof plants receiving abundant nitrate. It is concluded that ‘nodulated’plants grew more slowly than ‘nitrate’ plants inthese experiments for at least two reasons: firstly, the symbioticassociation fixed insufficient nitrogen for optimum growth and,secondly, the assimila tion of the nitrogen which was fixedin the root nodules was more energy-demanding in terms of assimilatethan that of plants which assimilated nitrogen by reducing nitratein their leaves.     

The Volatilization of Ammonia from Perennial Ryegrass During Decomposition, Drying and Induced Senescence

The volatilization of gaseous ammonia was measured from cutherbage (leaf lamina + sheath) of perennial ryegrass (Loliumperenne L.), during a 70 d period of either decomposition ordrying, and also from intact plants of perennial ryegrass subjectedto induced senescence by shading. Volatilization during decompositionamounted to 20–47% of the herbage nitrogen, but volatilizationduring drying, and from intact plants during induced senescence,amounted to less than 1% of the herbage nitrogen. During decomposition, volatilization of ammonia was proportionallygreater from herbage containing 3.52% nitrogen than from herbagecontaining 2.32% nitrogen. Volatilization occurred more rapidlyat 20 °C than at 10 °C but, with both samples of herbageand at both temperatures, at least 4 d elapsed before appreciablevolatilization occurred. Ammonia, atmosphere, decomposition, leaves, Lolium perenne L, nitrogen, perennial ryegrass     

Reproductive Development and Nitrogen Fixation in Soybean (Glycine max [L.] Merril)

Gomes, M. A. F. and Sodek, L. 1987. Reproductive developmentand nitrogen fixation in soybean (Glycine max (L.) Merril).—J.exp. Bot. 38: 1982–1987. Nitrogenase activity (acetylene reduction) was measured duringthe growth cycle of soybean plants induced to flower at twodifferent ages. The decline in nitrogenase activity towardsthe end of the cycle was clearly associated with pod-fillingfor both flowering dates when plants were cultivated under lowerlight and temperature conditions (out of season). Under higherlight and temperature conditions (normal growing season) thedecline was independent of the flowering date. Furthermore,the timing of the decline was not altered when plants were maintainedunder long-day (vegetative) conditions nor when flowers wereremoved. It is suggested that under more favourable growth conditionsthe diversion of assimilates by the fruits is not the primarycause of the decline in nodule activity, but competition bythe fruits may be important when the production of photo-assimilatesis more limited. Key words: Glycine max, nitrogenase, source-sink     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: IV. EFFECT OF PHOSPHATE CONCENTRATION ON THE GROWTH OF TRIFOLIUM REPENS L. SUPPLIED WITH NITRATE, OR DEPENDENT UPON SYMBIOTICALLY FIXED NITROGEN

Breeze, V. G. and Hopper, M. J. 1987. The uptake of phosphateby plants from flowing nutrient solution. IV. Effect of phosphateconcentration on the growth of Trifolium repens L. suppliedwith nitrate, or dependent upon symbiotically fixed nitrogen.—J.exp. Bot. 38: 618–630. Nodulated white clover plants were subjected to a range of phosphateconcentrations in flowing solution culture (0.32 to 8.0 mmolm^–3 P) at 41 d from sowing, either supplied with nitrateor dependent on symbiotically-fixed nitrogen. No effect of phosphateconcentration in solution on dry matter production, relativegrowth rate, root/shoot ratio, or water soluble carbohydrateconcentration of the plant tissue was observed after 24 d fromthe start of the experiment, although the plants supplied withnitrate yielded more than the others. Phosphate uptake throughoutthe experimental period was related to the solution concentration,but the source of nitrogen did not affect the phosphorus concentrationsof the shoots. However, the roots of the plants dependent onsymbiotically-fixed nitrogen had higher concentrations of phosphorusthan those supplied with nitrate, but this did not appear tobe due to an increased phosphorus requirement for nitrogen fixation,because the amount fixed was unaffected by the phosphate concentrationin solution. The cation-anion balance showed that plants dependenton nitrogen fixation had no larger requirement for calcium thanplants supplied with nitrate, but a requirement for hydroxylions equivalent to over 130 kg lime per tonne of dry shoot.It is suggested that the enhanced phosphate uptake by plantsdependent on nitrogen fixation is due to this need for a cation-chargebalancing anion. Key words: Phosphate uptake, nitrogen fixation, Trifolium repens L., repens L., cation-anion balance, flowing solution culture     

The Influence of Nitrogen, Light and Water Stress on CO2 Exchange and Organic Acid Accumulation in the Tropical C3-CAM Tree, Clusia minor

The carbon balance and changes in leaf structure in Clusia minorL., were investigated in controlled conditions with regardto nitrogen supply and responses to low and high photosyntheticallyactive radiation (PAR). Nitrogen deficiency and high PAR ledto the production of smaller leaves with higher specific leafdry weight (SLDW) and higher leaf water content, but with lowerchlorophyll content. Nitrogen and PAR levels at growth alsoaffected CO₂ exchange and leaf area. In – N conditions,total daily net CO₂ uptake and leaf area accumulation were slightlyless for high-PAR-grown plants. In contrast, high-PAR-grownplants supplied with nitrogen showed about a 4-fold higher totaldaily CO₂ uptake and about twice the total leaf area of low-PAR-grownplants. Although total daily net CO₂ uptake of +N plants wasonly slightly higher than –N plants under the low PARlevel, –N plants produced almost three times more leafarea but with lower SLDW. Under well-watered conditions, low-PAR-grownplants showed only CO₂ evolution during the night and malicacid levels decreased. However, there was considerable night-timeaccumulation of titratable protons due to day/night changesin citric acid levels. High-PAR-grown plants showed net CO₂uptake, malate and citrate accumulation during the dark period.However, most of the CO₂ fixed at night probably came from respiratoryCO₂. Positive night-time CO₂ exchange was readily observed forlow-PAR-grown plants when they were transferred to high PARconditions or when they were submitted to water stress. In plantsgrown in high and low PAR, CAM leads to a substantial increasein daily water use efficiency for water-stressed plants, althoughtotal net CO₂ uptake decreased.     

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     

Flowering Induced by Nitrogen Deficiency in Lemna paucicostata 151

Lemna paucicostata 151 is a weakly responsive short-day plantwhen grown in non-aseptic ten-fold diluted E medium supplementedwith 1 µM 6-benzyladenine, but it flowered even underlong-day conditions (continuous light) when grown in this mediumfor more than 14 days. On the 14th day of culture, the levelof endogenous nitrogen in the plants decreased to about 60%of that in the plants inoculated at the start of the culture.The flowering obtained under long-day conditions was suppressedby raising the concentration of nitrogen in the medium, whileit was induced more rapidly by lowering the concentration ofnitrogen in the medium. Benzyladenine did not cause floweringby itself, but it was required for the flowering that was inducedby a reduction in the level of nitrogen in the medium. Thus,the flowering observed under long-day conditions is due to nitrogendeficiency in the plants. Two inhibitors of proteases, bestatin and elastatinal, clearlyinhibited the flowering induced by nitrogen deficiency. It appears,therefore, that the induction or activation of some protease(s)is involved in the flowering that is induced by nitrogen deficiency. (Received March 19, 1991; Accepted August 16, 1991)     

Grain Yield of Pennisetum americanum Adjusts to Nitrogen Supply by Changing Rates of Grain Filling and Root Uptake of Nitrogen

Coaldrake, P. D., Pearson, C. J. and Saffigna, P. G. 1987. Grainyield of Pennisetum americanum adjusts to nitrogen supply bychanging rates of grain filling and root uptake of nitrogen.–J.exp. Bot 38: 558–566. Pearl millet (Pennisetum americanum(L.)Leeke) was grown in containers at three constant rates of nitrogensupply or with the nitrogen supply increased from the lowestto the highest rate during panicle differentiation or at anthesis.We measured the rate and duration of nitrogen and dry weightgain by individual grains and nitrogen (¹⁵N) uptake by rootsand its distribution during grain filling. The total amountsof nitrogen and dry weight in all grain per plant at the lowestnitrogen supply were 8% and 14% respectively of plants growncontinuously at the highest rate of nitrogen. This was becauselow rates of nitrogen supply reduced grain number, mean grainweight and the nitrogen content of each individual grain. Theamino acid composition of the grain protein was affected onlyslightly by nitrogen treatments. Rates of grain growth were sensitive to nitrogen supply whereasthe duration of nitrogen movement to the grain was not. Nitrogenuptake by roots continued throughout grain filling; rates ofuptake per g root in plants given least nitrogen were one-halfthose of plants given the highest amount of nitrogen. A changefrom lowest to highest nitrogen supply at panicle differentiationincreased the uptake of nitrogen by roots and the rates of growthof individual grains, to the rates observed in plants whichhad been supplied continuously with the highest nitrogen. Whenthe change in supply was made at anthesis there was rapid movementof nitrogen into the plant but this was not translated intomore rapid grain growth. Key words: Nitrogen supply, Pennisetum americanum, grain yield, root uptake     

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     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

Flower Induction by Nitrogen Deficiency in Lemna paucicostata 6746

Lemna paucicostata 6746, a short-day plant, produced flowerbuds even under continuous light when cultured in nitrogen-deficientmodified Hoagland medium with 1% sucrose for 3 days or morefollowed by culture on nitrogen-rich medium (either nitrateor ammonium). Flowering was also induced by culture on mediumcontaining 20–100 µM nitrate as the sole nitrogensource for 10 days or more, but not on medium with a low ammoniumconcentration. However, if plants cultured on medium containing5–20 µM ammonium as the sole nitrogen source for10 days were grown in a nitrogen-rich medium for a further 4days, they produced flower buds. Thus, nitrogen deficiency caninduce day length-independent flowering in Lemna paucicoslata6746, but nitrogen is required for the manifestation of flowering. (Received January 31, 1986; Accepted April 24, 1986)     

ABA in Roots and Leaves of Flooded Pea Plants

Zhang, J. and Davies, W. J. 1987. ABA in roots and leaves offlooded pea plants.—J. exp. Bot. 38: 649–659. Roots of potted pea (Pisum sativum L. cv. Feltham First) seedlingswere flooded with tap water. Within a few hours of the startof the flooding treatment the content of free ABA in roots increasedcompared to contents of roots of unflooded control plants butthis increase was not statistically significant until the beginningof the second day after flooding. Approximately 36 h after firstflooding significant increases in the free-ABA content of leaveswere detected. This was 14 h after significant increases inthe amount of ABA in the roots of the same plants. There wasmarked diurnal variation in free-ABA content of leaves and rootsof plants that had been flooded for several days, with maximumcontents recorded 3 h or more after the beginning of the lightperiod. Very rapidly after the lights were switched oft ABAcontents declined. On day 3 of the flooding treatment, therewas more than a 5-fold decrease in the free-ABA content of leaveswithin a few hours of the beginning of the dark period. Radio-immunoassaysuggested that a very large proportion of the total ABA in theplant was in a bound form. This form of ABA increased substantiallyas the flooding period progressed. The importance of variation in ABA content for the control ofwater relations and gas exchange of flooded plants is discussed. Key words: Flooding, Pisum sativum, ABA, water relations     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Translocation of Nitrogenous Compounds in Symbiotic and Nitrate-Fed Amide-Exporting Legumes

Peoples, M. B., Sudin, M. N. and Herridge, D. F. 1987. Translocationof nitrogenous compounds insymbiotic and nitrate-fed amide-exportinglegumes.–J. exp. Bot. 38: 567–579. The transport of nitrogen from the roots and nodules of chickpea(Cicer anetinum L.), lentil (Lens culinaris Medic), faba bean(Vicia faba L.) and pea (Pisum sativum L.) was examined in glasshouse-grownplants supplied either with nitrate-free nutrients or with nutrientssupplemented with 1,2,4 or 8 mol m^-3153N-nitrate. A sixth treatmentcomprised uninoculated plants supplied with 8–0 mol m^-31513N-nitrate. For each species, more than 75% of the nitrogenwas exported from the nodules as the amides, asparagine andglutamine. In fully symbiotic plants, the amides also dominatednitrogen transport to the shoot When N2 fixation activity wasdecreased by the addition of nitrate to the rooting medium,the N-composition of xylem exudate and stem solutes changedconsiderably. The relative concentrations of asparagine tendedto increase in the xylem whilst those of glutamine were reduced;the levels of nitrate increased in both xylem exudate and thesoluble nitrogen pool of the stem with a rise in nitrate supply.The changes in relative nitrate contents reflected generallythe contributions of root and shoot to overall nitrate reductaseactivity at the different levels of nitrate used. The relationshipsbetween the relative contents of xylary or stem nitrate andamino nitrogen and the plants' reliance on N2 fixation (determinedby the ¹⁵N isotope dilution procedure) were examined. Data suggestthat compositional relationships based on nitrate may be reasonableindicators of symbiotic dependence for all species under studyexcept faba bean when greater than 25% of plant nitrogen wasderived from N2 fixation. Key words: Nitrogen, translocation, legumes     

The Uptake and Utilization of Phosphorus and Nitrogen by Diploid, Tetraploid and Hexaploid Wheats (Triticum spp.)

Twenty genotypes of Triticum and Aegilops wheats including diploid,tetraploid and hexaploid types, were grown under contrastingphosphorus (P) regimes (control and low P) at 15 °C by dayand 10 °C at night. Dry-matter production and phosphorusand nitrogen uptake and distribution were measured on matureplants. Phosphorus efficiency (PE) was considered in terms of yieldper unit of P in the main shoot and concentration of phosphorusin grain (per cent P). In the low-P set, PE, which ranged from110 to 715 mg grain mg^–1 P, increased as the yield perculm and dry-matter partitioning (harvest index) increased,with hexaploid > tetraploid > diploid. In both the controland low-P plants percentage P in grain decreased in the orderdiploids > tetraploids > hexaploid wheats. Grain phosphoruswas highly negatively correlated with the log of grain yield(r = –0.74; –0.88) and the log of harvest index(r = –0.80 and –0.88) for control and low-P plants,respectively. This suggests that future gains in plant harvestindex will cause smaller reductions in grain phosphorus concentrations.But, within either a high or low phosphorus supply, wheats witha given grain harvest index have significantly different grainphosphorus concentrations, and conscious selection for thischaracter is feasible. Low-P plants had similar grain nitrogen concentrations but lowernitrogen harvest indexes than control plants. Aegilops spp., Triticum spp., wheat, yield components, harvest index, polyploidy, evolution, phosphorus efficiency     

Comparative Growth and Symbiotic Performance of Seedlings of Acacia spp. in Defined Pot Culture or as Natural Understorey Components of a Eucalypt Forest Ecosystem in S.W. Australia

Hansen, A. P. and Pate, J. S. 1987. Comparative growth and symbioticperformance of seedlings of Acacia spp. in defined pot cultureor as natural understorey components of a eucalypt forest ecosystemin S.W. Australia.—J. exp. Bot. 38: 13–25 Growth, nitrogen accumulation, nodulation and nitrogenase activity(C₂H₂ reduction activity) were monitored in a dense stand ofseedlings of Acacia pulchella R.Br. and A. alata R.Br. duringtwo growing seasons after fire at a jarrah (Eucalyptus marginataDonn ex Sm.) forest site at Illawarra, 35 km south-east of Perth.Nitrogen fixation, estimated by a previously calibrated C₂H₂reduction assay, was essentially restricted to the winter andspring months (July to October) and was estimated to contribute37% and 9% respectively of the total N accumulated by A. pulchelladuring the first and second seasons of growth. Comparable valuesfor A. alata were 29% and 2%. Comparisons with fully symbioticplants raised in a glasshouse in supposedly non-limiting growthconditions in minus nitrogen sand culture indicated that waterstress rather than high temperatures was responsible for lossof nodules, cessation of symbiotic activity and attenuationof growth during summer in the field. By 19 months glasshouseplants had gained 130–230 times the dry weight and accumulated110–160 times the total N of similarly aged, field grownplants. Growth, nodulation and N₂ fixation of symbiotically-dependentsand cultured plants of A. pulchella and A. alata respondedmarkedly to phosphate, and additions of water and nutrientsto 3-year plants of A. pulchella during a winter growing seasonin the field indicated that periods of reduced soil moistureand low availability of nutrients, particularly phosphorus,might limit symbiotic performance under natural conditions. Key words: Seasonal nitrogen fixation, Acacia spp     

Flower-Inducing Activity of Lysine in Lemna paucicostata 151 Cultured on Nitrogen-Deficient Medium

Lemna paucicostata 151, a weakly responsive short-day plant,flowers even under continuous illumination when cultured onnitrogen-free medium for more than 72 hours with subsequentculture on nitrogen-rich medium. During the nitrogen-free culture,the protease activity and protein content of the plant increasedand decreased, respectively. The plant contained a protein(s)that induced flowering of the plant when added to the medium.The level of this protein(s) also decreased during the nitrogen-freeculture. The total amount of free amino acids in plants culturedon nitrogen-free medium for 96 hours decreased to about 15%of that in plants at the start of nitrogen-free culture, butlevels of some amino acids increased. These amino acids wereexamined for their effects on flowering of plants cultured onnitrogen-deficient or nitrogen-free medium. Most of the aminoacids had no effect on flowering. However, profuse floweringwas induced when lysine was added to the medium. Lysine promotedthe flower-inductive process(es) rather than the developmentof flower buds. These results suggest that nitrogen deficiency-induced floweringof the plants is induced by lysine, which is generated froma specific protein(s) by proteolysis. (Received May 11, 1992; Accepted July 30, 1992)     

Morphogenesis of 2,4-D Induced Abnormalities of the lnflorescence of Bread Wheat (Triticum aestivum, L.).

Treatment of Triticum plants with 2,4-D profoundly affects inflorescencemorphogenesis and results in the production of various abnormalities,amongst which are branched heads, whorls of spikelets. superimposedpairs of spikelets (‘banana’ twin spikelets) andpaired spikelets borne at the same level (‘yoked’spikets). Often more than one kind of abnormality is observedin a single head. Except for ‘banana’ twin spikelets,none of the induced abnormalities are duplicated by abnormalitieswhich occur spontaneously in untreated plants. Disturbance dueto treatment is only temporary and later the terminal regionof the apex recommences growth along a normal pattern of morphogenesis.