Regulation of Storage Protein Synthesis by Sulphur and Nitrogen Nutrition in Cultured Immature Caryopses of Barley

Techniques are described for the culture of developing barley(Hordeum vulgare L.) caryopses. Over a 7 d period in culturethe dry weights and the amounts of starch and protein increasedby at least twofold. Growth was sustained for at least 20 d.The effects of glutamine and cysteine on the amount and compositionof the hordein storage proteins were also studied. Glutaminestimulated total hordein accumulation but caused a disproportionateincrease in the amount of the S-poor ‘C’ hordeinswhen supplied at 100 mol m^–3. Addition of cysteine at1·0 mol m^–3 did not increase the amount of Srich‘B’ hordeins. The results suggest that althoughisolated caryopses are able to take up sucrose and glutamineand convert them to starch and protein there is some limitationin their ability to convert externally supplied cysteine intoproteins. Key words: Hordeum vulgare L., Caryopses, Glutamine, Cysteine, Storage proteins     

Nitrogen Assimilation in Barley (Hordeum vulgare L. cv. Mazurka) in Response to Nitrate and Ammonium Nutrition

Barley plants (Hordeum vulgare L. cv. Mazurka) were grown inaerated solution cultures with 2 mM or 8 mM inorganic nitrogensupplied as nitrate alone, ammonium alone or 1:1 nitrate+ammonium.Activities of the principal inorganic nitrogen assimilatoryenzymes and nitrogen transport were measured. Activities ofnitrate and nitrite reductases, glutamine synthetase and glutamatesynthase were greater in leaves than in roots but glutamatedehydrogenase was most active in roots. Only nitrate and nitritereductases changed notably (4–10 times) in response tothe different nitrogen treatments. Nitrate reductase appearedto be rate-limiting for nitrate assimilation to glutamate inroots and also in leaves, where its total in vitro activitywas closely related to nitrate flux in the xylem sap and wasslightly in excess of that needed to reduce the transportednitrate. Xylem nitrate concentration was 13 times greater thanthat in the nutrient solution. Ammonium nitrogen was assimilatedalmost completely in the roots and the small amount releasedinto the xylem sap was similar for the nitrate and the ammoniumtreatments. The presence of ammonium in the nutrient decreasedboth export of nitrate to the xylem and its accumulation inleaves and roots. Nitrate was stored in stem bases and was releasedto the xylem and thence to the leaves during nitrogen starvation.In these experiments, ammonium was assimilated principally inthe roots and nitrate in the leaves. Any advantage of this divisionof function may depend partly on total conversion of inorganicnitrogen to amino acids when nitrate and ammonium are givenin optimal concentrations. Hordeum vulgare L., barley, nitrate, ammonium, nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, glutamate dehydrogenase, nitrogen transport     

Resource Capture by Localized Root Proliferation: Why Do Plants Bother?

Using data from a well-known, published experiment [Drew (1975)TheNew Phytologist75: 479–490], the potential exploitationof locally available nutrients by barley roots is calculated.Local proliferation of lateral roots does not necessarily achievesignificantly greater exploitation of mobile soil resourceslike nitrate, but it does for less mobile ones such as phosphate.Despite this, the magnitude of the proliferative response isas great to locally available nitrate as it is to phosphate.This implies an ‘over-production’ of roots in responseto localized nitrate availability, prompting a re-evaluationof the nature and implications of the response mechanism(s)of roots to soil heterogeneity. Hordeum vulgare; barley; carbon; heterogeneity; lateral root; nitrate; localized nutrient supply; phosphate; proliferation; root     

The Effect of Applications of a Synthetic Cytokinin on Shoot Dominance and Grain Yield in Spring Barley

Spring barley cv Ark Royal was grown in pots in the open, andsoil drenches containing 6-benzyl-aminopurine were repeatedlyapplied during the pre-heading phase starting either ‘early’when the main shoot apex had reached the glume primordium stage,during tillering, or ‘later’ at the anther primordiumstage, at the start of stem elongation Although grain yield was unaffected by the ‘late’cytokinin treatments, it was increased by up to 57 per centby the ‘early’ treatments. The increase was dueto greater grain yields of the smaller shoots of each plantthere was no effect on the yields of the two largest shootsor on the total number of fertile shoots The increased grain yield of these smaller shoots was attributableto increased weights of their individual kernels, especiallyin the basal and distal parts of the ears such that a greateruniformity of kernel size within the ear was achieved Thus the cytokinin treatment increased uniformity both betweenshoots and between spikelets within the ears Hordeum vulgare L, spring barley, cytokinin, 6-benzylaminopunne, shoot dominance, harvest index, grain yield     

Drought Influences the Activity of Enzymes of the Chloroplast Hydrogen Peroxide Scavenging System

Smirnoff, N. and Colomb?, S. V. 1988. Drought influences theactivity of enzymes of the chloroplast hydrogen peroxide scavengingsystem.—J. exp. Bot. 39: 1097–1108. The effect of drought on the activity of ascorbate peroxidase(AP), glutathione reductase (GR) and monodehydroascorbate reductase(MDAR) in leaves of barley (Hordeum vulgare) and tef {Eragrostistef) was studied. These enzymes are components of the chloroplasthydrogen peroxide scavenging system. Severe leaf water deficit(<–30 M Pa) resulted in increased activity (leaf dryweight basis) of GR and MDAR in barley and of AP and MDAR intef. The specific activity of all the scavenging enzymes wasgreater in droughted plants. The activities (dry weight basis)of two ‘control’ enzymes, malate dehydrogenase (barley)and phosphoenolpyruvate carboxylase (tef), not directly involvedin the scavenging system, were not affected by drought. These data suggest that drought may cause an increase in thecapacity of the hydrogen peroxide scavenging system and thatit may, therefore, increase the rate of hydrogen peroxide formationin chloroplasts. Key words: Water stress, hydrogen peroxide, enzyme activity     

The Occurrence of Nitrate Reduction in the Leaves of Woody Plants

Nitrate reductase activities greater than 02 µmol h^–1g^–1 f. wt, measured by an in vivo assay, occurred in 41per cent of a large sample (555 species) of woody plants. Ifseveral taxonomic groups (Gymnosperms, Ericaceae and Proteaceae)with consistently low activities were discounted activitiesgreater than 02 µmol h^–1 g^–1 f. wt occurredin 73 per cent of the species. This compares with 93 per centin herbaceous species, suggesting that leaf nitrate reductionis of common occurrence in woody plants. In a small sample ofspecies leaf nitrate reductase activity correlated with nitrateconcentration in the xylem sap. Low activities occurred consistentlyin the Gymnosperms, Ericaceae and Proteaceae. Feeding cut shootsof representatives of these groups with nitrate caused inductionof leaf nitrate reductase activity in the Gymnosperms and Proteaceae,but only limited induction in the Ericaceae. The Ericaceae,with the exception of two species, had low activities and lownitrate reductase inducibility. Root assimilation may predominatein the Gymnosperms and Proteaceae. It is suggested that nitratereduction generally occurs in the leaves of trees from a varietyof plant communities and that this may be related to the lowerenergy cost of leaf, as opposed to root, nitrate assimilation. Nitrate reductase, trees and shrubs, leaves, nitrate assimilation, nitrate translocation, nitrate reductase induction, energy cost, plant ecology     

Synthesis and degradation of barley nitrate reductase

Nitrate and light are known to modulate barley (Hordeum vulgare L.) nitrate reductase activity. The objective of this investigation was to determine whether barley nitrate reductase is regulated by enzyme synthesis and degradation or by an activation-inactivation mechanism. Barley seedling nitrate reductase protein (cross-reacting material) was determined by rocket immunoelectrophoresis and a qualitative immunochemical technique (western blot) during the induction and decay of nitrate reductase activity. Nitrate reductase cross-reacting material was not detected in root or shoot extracts from seedlings grown without nitrate. Low levels of nitrate reductase activity and cross-reacting material were observed in leaf extracts from plants grown on nitrate in the dark. Upon nitrate induction or transfer of nitrate-grown etiolated plants to the light, increases in nitrate reductase activity were positively correlated with increases in immunological cross-reactivity. Root and shoot nitrate reductase activity and cross-reacting material decreased when nitrate-induced seedlings were transferred to a nitrate-free nutrient solution or from light to darkness. These results indicate that barley nitrate reductase levels are regulated by de novo synthesis and protein degradation.     

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     

Substrate induction of nitrate reductase in barley aleurone layers

Nitrate induces the formation of nitrate reductase activity in barley (Hordeum vulgare L. cv. Himalaya) aleurone layers. Previous work has demonstrated de novo synthesis of α-amylase by gibberellic acid in the same tissue. The increase in nitrate reductase activity is inhibited by cycloheximide and 6-methylpurine, but not by actinomycin D. Nitrate does not induce α-amylase synthesis, and it has no effect on the gibberellic acid-induced synthesis of α-amylase. Also, there is little or no direct effect of gibberellic acid (during the first 6 hr of induction) or of abscisic acid on the nitrate-induced formation of nitrate reductase. Gibberellic acid does interfere with nitrate reductase activity during long-term experiments (greater than 6 hr). However, the time course of this inhibition suggests that the inhibition may be a secondary one. Barley aleurone layers therefore provide a convenient tissue for the study of both substrate- and hormone-induced enzyme formation.     

Effect of Casein on the Extractability and Stability of Nitrate Reductase From Wheat Leaves

The effect of casein on the extraction and stability of nitratereductase (EC 1.6.6.1 [EC] ) from the primary leaf of the wheat (Triticumaestivum L.) cultivar Olympic was examined. The use of 2 percent casein in the extraction medium resulted in a small butsignificant (P > 0·05) increase in nitrate reductaseactivity at the time of assay. This increase in activity wasnot attributable to improved extraction but was a result ofincreased stability of the enzyme between time of extractionand assay. The presence of casein actually resulted in lessactivity being extracted during the grinding procedure. Othercultivars of wheat examined showed a small increase in activityat the time of assay when extracted in the presence of casein.However, the ranking of these cultivars with respect to nitratereductase activity did not alter markedly when casein was used.A number of other species examined showed a wide variation inresponse to casein, while buckwheat (Fagopyrum esculenta) andoats (Avena sativa) had an absolute requirement, maize (Zeamays cv. XL45) was relatively unaffected. Nitrate reductasein crude extracts decayed exponentially with time at both 0°and 10 °C with a half-life of 216 and 109 min respectively.Casein added before or after extraction completely stabilizedthe enzyme over a period of several hours at 0 °C whileat 10 °C the enzyme had a half-life of approximately 16h. The effect of casein at both 0° and 10 °C was independentof the concentration used within the range 0·5 to 4·0per ant. casein, genotype, nitrate reductase, stability, Triticum aestivum L.     

The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

Polyamine Content in Relation to Embryo Growth and Dedifferentiation in Barley (Hordeum vulgare L.)

Putrescine, spermidine, and spermine content were analysed inzygotic embryos of barley (Hordeum vulgare L.). Changes in polyaminecontent were observed during zygotic embryo growth. In two cultivars,‘Bomi’ and ‘Golden Promise’, the totalpolyamine content in the embryos was 2.6–2.9 nmol mg^–1fresh weight 10 d after anthesis, the highest content observed.It dropped to 1.3 nmol mg^–1 fresh weight 14 d after anthesis.This drop was caused by decreases in all three polyamine concentrations.From 14 to 35 d after anthesis the putrescine content continuedto decrease while the spermidine and spermine content increased,thus the total polyamine content remained constant until 35d after anthesis. The mutant ‘Ris? 1508’ showeda constant polyamine content around 1.3 nmol mg^–1 freshweight from 14 to 35 d after anthesis. The polyamine patternwas conserved in all three lines throughout the period of investigationshowing a spermidine content higher than putrescine contentwhich was, in turn, higher or equal to the spermine content.The polyamine content measured as nmol µg^–1 proteindecreased from 14 to 21 d post anthesis in all three lines,because the protein content (µg mg^–1 fresh weight)increased during the period. In dedifferentiating zygotic embryoscultured in vitro the putrescine content (nmol mg^–1 freshweight) rose by a factor of nine and the spermidine contentdoubled within the first week of cultivation, whereas sperminecontent did not change. For embryoderived calli a repeated patternof change in polyamine content was observed throughout the subculturingperiod. Key words: Polyamines, Hordeum vulgare L., embryo development     

Comparative Leaf Epidermal Anatomy of Mutants of Barley (Hordeum vulgare L. 'Himalaya') which Differ in Leaf Length

We wished to determine the nature of differences in epidermalcell numbers and dimensions between leaves of different lengthin mutants of barley (Hordeum vulgare L. ‘Himalaya’).Three comparisons were made: leaf one (L1)vs. leaf four (L4);wild typevs. nine dwarf mutants and wild typevs. a slender mutant.L1 was shorter than L4, and for most lines this was associatedwith a change in epidermal cell number for the blade, and inboth cell number and length for the sheath. Compared to wildtype, the smaller leaves of dwarf plants generally had shorterand fewer cells in both blade and sheath. The blade of slenderplants was the same length (L1) or longer (L4) than wild type,while the sheath was longer than that of wild type for bothL1 and L4. Slender plants had longer but fewer cells than thewild type along the blade of L1, and shorter but more cellsfor the blade of L4. In the sheath, slender plants had longerand more (L1) or fewer (L4) cells than did the wild type. ForL1, variation in blade width amongst the barley lines was associatedwith a change in file width and file number. For L4, blade widthvaried only with file number, except for slender plants wherenarrow blades were associated with reduced file width. Hencethere was no consistent correlation between changes in cellsize or cell (or file) number with changes in leaf length orwidth. Differences depended on the leaf (L1vs. L4), leaf part(bladevs. sheath), and the nature of the mutation (dwarfvs.slender). Barley (Hordeum vulgare L. ‘Himalaya’); leaf epidermis; dwarf mutant; slender mutant     

Ethylene Production by Fe-deficient Roots and its Involvement in the Regulation of Fe-deficiency Stress Responses by Strategy I Plants

Species that showed marked morphological and physiological responsesby their roots to Fe-deficiency (Strategy I plants) were comparedwith others that do not exhibit these responses (Strategy IIplants). Roots from Fe-deficient cucumber (Cucumis sativusL.‘Ashley’), tomato (Lycopersicon esculentumMill.T3238FER) and pea (Pisum sativumL. ‘Sparkle’) plantsproduced more ethylene than those of Fe-sufficient plants. Thehigher production of ethylene in Fe-deficient cucumber and peaplants occurred before Fe-deficient plants showed chlorosissymptoms and was parallel to the occurrence of Fe-deficiencystress responses. The addition of either the ethylene precursorACC, 1-aminocyclopropane-1-carboxylic acid, or the ethylenereleasing substance, Ethephon, to several Fe-sufficient StrategyI plants [cucumber, tomato, pea, sugar beet (Beta vulgarisL.),Arabidopsis(Arabidopsis thaliana(L.) Heynh ‘Columbia’), plantago(Plantago lanceolataL.)] promoted some of their Fe-deficiencystress responses: enhanced root ferric-reducing capacity andswollen root tips. By contrast, Fe-deficient roots from severalStrategy II plants [maize (Zea maysL. ‘Funo’), wheat(Triticum aestivumL. ‘Yécora’), barley (HordeumvulgareL. ‘Barbarrosa’)] did not produce more ethylenethan the Fe-sufficient ones. Furthermore, ACC had no effecton the reducing capacity of these Strategy II plants and, exceptin barley, did not promote swelling of root tips. In conclusion,results suggest that ethylene is involved in the regulationof Fe-deficiency stress responses by Strategy I plants.Copyright1999 Annals of Botany Company. Arabidopsis (Arabidopsis thaliana(L.) Heynch), barley (Hordeum vulgareL.), cucumber (Cucumis sativusL.), ethylene, iron deficiency, maize (Zea maysL.), pea (Pisum sativumL.), plantago (Plantago lanceolataL.), ferric-reducing capacity, sugar beet (Beta vulgarisL.), tomato (Lycopersicon esculentumMill.), wheat (Triticum aestivumL.).     

Effect of High Temperature During Grain-filling on the Structure of Developing and Malted Barley Grains

High temperatures (up to 35 °C) were applied to plants ofmalting barley,Hordeum vulgareL. (‘Schooner’) fora period of 5 d during grain-filling. Heat treatment had a profoundeffect on the structure of the mature barley grain. There wasevidence of degradation of endosperm storage products in heat-treatedgrain. Starch granule development was reduced in sub-aleuronecells following heat treatment and alterations to starch granuledistribution and growth were observed in the endosperms of thesegrains. Endosperm cell wall and crushed cell layer (CCL) developmentwere sensitive to high temperatures, with the reduced thicknessof the CCL and generally patchy Calcofluor fluorescence of endospermcell walls indicative of partial hydrolysis of ß-glucans.Increased growth of the embryo took place in heat-treated grainscompared with control grains. Endosperm texture was generallymore friable in heat-treated grains than in control grains,and these grains overmodified during malting, with considerabledegradation of starch in the form of extensive pitting of A-typestarch granules. Evidence is presented for developmental andgermination events occurring simultaneously within the developinggrain.Copyright 1998 Annals of Botany Company Barley,Hordeum vulgareL., starch granules, crushed cell layer, scutellum, embryo, fluorescence microscopy, scanning electron microscopy, confocal microscopy, malting quality.     

Characterization of the 'In Vivo' Nitrate Reductase Activity in the Roots and Leaves of Eichhornia crassipes

Studies of in vivo nitrate reductase activity (NRA) in Eichhorniacrassipes showed that adding 5% isopropanol gave highest NRAin all parts of the plant, but it was also necessary to flushthe assay media containing leaves with N₁ to obtain the maximalactivity. There were differences in the pH optima for NRA, theroot optimum being 6·5 leaf 7·5–8·0,and the petiole showing a major peak at 6·5 and a minorpeak at 7·.5–8·0. Possible significancesof these differences are discussed. Nitrate reductase activity, Eichhornia crassipes     

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.     

Nitrate Reductase Acivity in Leaves of Barley (Hordeum vulgare) and Durum Wheat (Triticum durum) during Field and Rapidly Applied Water Deficits

Smirnoff, N., Winslow, M. D. and Stewart, G. R. 1985. Nitratereductase activity in leaves of barley (Hordeum vulgare) anddurum wheat (Triticum durum) during field and rapidly appliedwater deficits.-J. exp. Bot 36: 1200-1208. The effect of field and rapidly applied water deficits on nitratereductase activity in the leaves of two barley varieties andone durum wheat variety was investigated. In field experimentsplants were subjected to irrigation at different rates in threeMediterranean environments by means of a line source sprinklerirrigation system. The environments differed in rainfall andnitrogen fertility. Plant water potentials decreased from –1.5MPa to between –2.5 and –3.0 MPa as the irrigationrate decreased. Nitrate reductase activity in the leaves ofthese plants during heading was either unaffected or sometimesincreased where the least water was supplied. Nitrate reductaseactivity was highest in the plants growing with an ample nitrogensupply irrespective of water regime. In contrast, seedlingssubject to rapidly applied water stress over 6 d lost 30-85%of their nitrate reductase activity when leaf water potentialfell from between –0.33 and –0.75 MPa to between–O.93 and –2.04 MPa. The decrease was less in theyoung leaves than in the old leaves. Polyethylene glycol inducedosmotic stress resulted in a drop in leaf water potential from–0.20 MPa to between –1.05 and –1.20 MPa alongwith a loss of 40-85% of leaf nitrate reductase activity after48 h. It is suggested that maintenance of nitrate reductase activityin field grown barley and durum wheat plants reflects an acclimationto water deficit Maintenance of nitrate assimilation duringwater stress may allow continued synthesis of nitrogenous compatiblesolutes using the excess photochemical energy available duringstomatal closure. Key words: Nitrate reductase, water stress, barley, durum wheat     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: II. METHOD FOR MONITORING GENERATIVE GROWTH AND DEVELOPMENT IN SOLUTION CULTURE

Growth of barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)under N-limitation was investigated in solution culture, withspecial emphasis on the generative growth stage. Three differentregimes for limiting nitrate-N availability while keeping otherelements in surplus were employed. In the ‘high, decreasingnitrogen’ (HN) treatment, the relative nitrogen additionrate (RA) was maintained at 0.08 d^–1 until the ears startedto develop and was then decreased stepwise to, finally, RA 0·005d^–1. In the ‘low, decreasing nitrogen’ (LN)treatment, plants received 45% of the nitrogen added in HN.In the ‘constant nitrogen’ (CN) treatment, RA washeld constant at 0·0375 d^–1. Cumulative nitrogenadditions at termination of the experiment (day 147 after sowing)were 192, 179 and 87 mg plant^–1 for HN, CN, and LN cultures,respectively. Nitrogen availability limited nitrogen acquisitionin all treatments except in the CN culture at plant ages above110 d. Stepwise decrease of RA largely synchronized transitionsin developmental stages in the different cultivars and nitrogenregimes (HN and LN), and eventually yielded plants that wereclose to completing their life cycle. Normal maturation wasnot obtained in the CN treatment. The HN and LN treatments wereused for formal analysis of post-anthesis growth. A sigmoidfunction was fitted to growth data and from this, organ weightsand nitrogen concentrations at maturity (defined as cessationof growth) were derived. The two modern cultivars, Golf andMette, clearly outperformed the more primitive cv. Laevigatumin terms of allocation of nitrogen to ears, particularly inthe LN culture. The stepwise decrease of RA appears suitablefor studies of post-anthesis growth and nitrogen relations inbarley, with regard to both genotypic variation and variationcaused by differences in cumulative amounts of nitrogen added. Key words: Barley, development, growth, nitrogen concentration, post-anthesis     

Respiratory Efflux of Carbon Dioxide from Mature and Meristematic Tissue of Uniculm Barley During Eighty Hours of Continuous Darkness

Young plants of uniculm barley were grown singly in pots ina growth room at 23/21 °C, and an irradiance of 655 µEm^–2s^–1 during each 12 h photoperiod. At the fifth leaf stage,they were subjected to 80 h of continuous darkness during whichthe rates of CO₂ efflux of vegetative shoot meristems, and maturefully expanded leaves, were separately monitored. Respiratoryefflux from the meristematic tissue was initially high, 12–15mg CO₂ g^–1 h^–1, equivalent to a daily loss in weightof 20–25 per cent. It remained high, or even rose slightly,during what would have been the normal dark period, but thenfell sharply. Even so, it was still three times that of themature tissue at the end of the experimental period. The rateof CO₂ efflux of the mature tissue began low, and fell evenfurther during the first 12 h of darkness. It then levelledoff at a rate of 2·0–2·5 mg CO2 g^–1h^–1, equivalent to a daily loss in weight of about 3 percent. It is suggested that the rate of ‘mature tissue’respiration, established after 12–24 h of darkness, mightbe a useful selection criterion to employ in attempts to increasethe total dry matter yield of the grass crop by breeding. Hordeum vulgare L., barley, respiration, synthetic respiration, maintenance respiration, meristem, mature tissue respiration, simulated sward