Qualitative and Quantitative Analysis of Endogenous Jasmonic Acid in Bulbing and Non-Bulbing Onion Plants

Bulb development in onion plants (Allium cepa L.) is consideredto be regulated by bulbing and anti-bulbing hormones. Sincebulbing involves the disruption of microtubules, both jasmonicacid (JA) and methyl jasmonate (JAMe) are candidates for thebulbing hormone because of their microtubule-disrupting activitiesand wide distribution in higher plants. To survey JA and JAMein onion plants, we developed a radioimmunoassay (RIA) for JAMethat is sensitive enough to detect femtomole amounts of JAMe.Using this RIA, we detected JA in leaf blades, leaf sheathsand roots of onion plants, but no JAMe was detected in any tissue.The endogenous levels of JA in leaf blades, leaf sheaths androots of 4-week-old bulbing and non-bulbing onion plants weredetermined by gas chromatography/selected ion monitoring with[²H₂]JA as an internal standard. The amount of JA per plantin leaf sheaths of bulbing onion plants was about three timeshigher than that of non-bulbing onion plants, although the differencein levels of JA in leaf blades between bulbing and non-bulbingonion plants was quite small, and the level of JA in roots ofbulbing onion plants was lower than that of non-bulbing onionplants. However, the relationship between endogenous JA andthe development of onion bulbs remains to be clarified. (Received June 3, 1992; Accepted October 1, 1992)     

Studies in the Nutrition of Apple Rootstocks The Effect on Growth and Mineral Composition of Supplying Iron Through the Leaves

Apple rootstocks were grown with either 0.02 ppm Fe (Fe₀) or5 ppm (Fe₃), to give very chlorotic or dark-green plants. Toinvestigate whether iron can be supplied through leaves insteadof roots the shoots of half the plants in each treatment weredipped periodically in solutions of iron. This prevented chlorosisin Fe₀ plants and increased their growth, which did not, however,equal that of Fe₃ plants supplied with iron through the roots.Growth of Fe₃ plants was reduced by dipping. Iron was not translocated from leaves to roots, although theconcentration in leaves was greatly increased by dipping. Dippingreduced the amount of manganese in Fe₀ roots to one-quarterof that in roots of undipped Fe₀ plants. Effects of treatmentson nitrogen, potassium, calcium, magnesium, and copper levelsare also described.     

Inductive Flood Tolerance in Swamp Tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.)

Under flooding or anoxia the newly initiated roots of swamptupelo produce et hanol and lactio acid and oxidize their rhizosphere.Unflooded roots produce less ethanol than flood roots and donot oxidize their rhizosphere. Oxygen enters the stem via thelenticels and appears to be diffused or transported via thecortex or phloem. Flood roots have less suberization in theepidermis in the terminal 2-cm section and casparian stripswere less evident than in the same sections in unflooded roots.Swamp tupelo roots tolerated 10 per cent CO₂ without adverseeffects but 31 per cent CO₂ reduced the initiation of new roots,rate of O₂ uptake, and transpiration rate. Tolerance to highCO₂ around the root seemed to be related to the oxidation ofthe rhizosphere by new roots. The combined adaptations of acceleratedanaerobic respiration in the absence of O₂, oxidation of therhizosphere, and CO₂ tolerance of new roots appear to be sufficientconditions to account for flood tolerance in this species.     

Interaction of Gibberellin A3 and Ancymidol in the Growth and Cell-Wall Extensibility of Dwarf Pea Roots

Effects of ancymidol (Anc) and gibberellin A₃ (GA₃) on rootgrowth, osmotic concentration and cell-wall extensibility ofthe root were investigated in the gibberellin-sensitive cultivarof dwarf pea, Little Marvel. Anc strongly suppressed elongationof both shoots and roots in darkness. Although the elongationof shoots of this dwarf cultivar was severely retarded in thelight, it was repressed still further by Anc. GA₃ promoted elongationof shoots both in the presence and in the absence of Anc, whereasit reversed suppression of root elongation by Anc. The concentrationof GA₃ required for the recovery of root elongation was lowerthan that required for the promotion of shoot elongation. Treatmentwith Anc led to increased thickening of roots with increasednumbers of cells per cross section and lateral expansion ofcells in the cortex. GA₃ had little effect on the osmotic concentration of cell sapobtained from root segments. Anc-treated roots did not respondto acid solutions by elongation, whereas GA₃-treated roots respondednormally to such solutions. Anc suppressed but GA₃ enhancedthe cell-wall extensibility of roots as measured in vivo andin vitro. These results indicate that a low concentration of gibberellinplays a role in normal elongation of roots by maintaining theextensibility of the cell wall in this gibberellin-sensitivedwarf pea. (Received January 17, 1994; Accepted July 15, 1994)     

Water Influx Characteristics and Hydraulic Conductivity for Roots of Agave deserti Engelm.

Various plant and environmental factors influence the hydraulicproperties for roots, which were examined using negative hydrostaticpressures applied to the proximal ends of individual excisedroots of a common succulent perennial from the Sonoran Desert,Agave deserti Engelm. The root hydraulic conductivity, L^p, increasedsubstantially with temperature, the approximately 4-fold increasefrom 0.5°C to 40°C representing a Q¹⁰ of 1.45. Suchvariations in L_p with temperature must be taken into accountwhen modelling water uptake, as soil temperatures in the rootzone of such a shallow-rooted species vary substantially bothdaily and seasonally. At 20°C, L_p was 2.3 x 10^–7 ms^{macron}1MPa^{macron}1for 3-week-old roots, decreasing to abouthalf this value at 10 weeks and then becoming approximatelyhalved again at 6 months. For a given root age, L_p for rainroots that are induced by watering as lateral branches on theestablished roots (which arise from the stem base) was aboutthe same as L_p for established roots. Hence, the conventionalbelief that rain roots have a higher L_p than do establishedroots is more a reflection of root age, as the rain roots tendto be shed following drought and thus on average are much youngerthan are established roots. Unlike previous measurements onroot respiration, lowering the gas-phase oxygen concentrationfrom 21% to 0% or raising the carbon dioxide concentration from0.1% to 2% had no detectable effect on L_p for rain roots andestablished roots. L_p for rain roots and established roots wasdecreased by an average of 11% and 35% by lowering the soilwater potential from wet conditions (_soil=0 kPa) to {macron}40kPa and {macron}80 kPa, respectively. Such decreases in L_p mayreflect reduced water contact between soil particles and theroot surface and should be taken into account when predictingwater uptake by A. deserti. Key words: Gas phase, rain roots, root age, soil, temperature, water potential     

Studies on the change of the respiratory system in roots in relation to the growth of plants II. Activity of iron-containing oxidases in roots of cereal crops with the aging of plants

Distribution of iron-containing oxidases in aging nodal rootsof rice and wheat was studied. Activities of cytochrome c oxidase(1.9.3.1 [EC] , cytochrome c : O₂ oxidoreductase), catalase (1.11.1.6 [EC] ,H₂O₂: H₂O₂ oxidoreductase) and peroxidase (1.11.1.7 [EC] , donor:H₂O₂ oxidoreductase) in wheat roots were comparatively higherthan were those in rice roots at corresponding stages. Cytochromec oxidase in roots remained active throughout the lives of therice and wheat crops. In rice roots, catalase seemed to playa distinct role around the panicle formation stage. Decay ofcatalase activity took place earlier than did that of peroxidaseand cytochrome c oxidase activities. In wheat roots similarenzyme activity changes were not observed. Data may suggestthat the high activity of iron containing oxidases at the panicleformation stage (I) may be chiefly due to catalase activityin rice roots. ¹Paper presented at the 14th Annual Meeting of the Society ofthe Science of Soil and Manure, Japan (1968). (Received November 21, 1968; )     

The Production of the Striga and Orobanche Germination Stimulants by Maize Roots: I. THE NUMBER AND VARIETY OF STIMULANTS

By means of paper partition chromatography and a suitable biologicaltest, the number and variety of the Orobanche and Striga germinationstimulants produced by maize roots have been assessed. It isshown that extracts of maize roots and aqueous solutions inwhich roots have been suspended (diffusate solutions) containa complex of stimulating substances consisting of, at least,one water-soluble and a number of ether-soluble stimulants.Germination of O. minor is promoted by the water-soluble stimulantand one of the ether-soluble stimulants (M_o). Germination ofS. hermonthica is promoted by another ether-soluble stimulant(M_s). Aqueous extracts are rich in M_s and the water-solublematerial, whereas the diffusate contains a higher proportionof M_o and only a trace of the water-soluble stimulant. The complex of ether-soluble stimulants, but not the water-solublestimulant, accumulates in a solution of glucose when it is exposedto fragments of maize roots. These solutions contain a highproportion of M_o which is synthesized by the fragments and passesout into the sugar solution. It is suggested that the water-solublestimulant is a precursor of M_o. The effects of the water-soluble stimulant and of M_s and M_oare greatly enhanced if a trace of the diffusate solution fromlinseed roots is mixed with them. The significance of the enhancementis discussed.     

Above- and Below-ground Production of Young Scots Pine (Pinus sylvestris L.) Trees after Three Years of Growth in the Field under Elevated CO2

Scots pine (Pinus sylvestris L.) seedlings were grown for 3years in the ground in open top chambers and exposed to twoconcentrations of atmospheric CO₂(ambient or ambient + 400 µmol mol^-1) without addition of nutrients and water. Biomassproduction (above-ground and below-ground) and allocation, aswell as canopy structure and tissue nitrogen concentrationsand contents, were examined by destructive harvest after 3 years.Elevated CO₂increased total biomass production by 55%, reducedneedle area and needle mass as indicated, respectively, by lowerleaf area ratio and leaf mass ratio. A relatively smaller totalneedle area was produced in relation to fine roots under elevatedCO₂. The proportion of dry matter in roots was increased byelevated CO₂, as indicated by increased root-to-shoot ratioand root mass ratio. Within the root system, there was a significantshift in the allocation towards fine roots. Root litter constituteda much higher fraction of fine roots in trees grown in the elevatedCO₂than in those grown in ambient CO₂. Growth at elevated CO₂causeda significant decline in nitrogen concentration only in theneedles, while nitrogen content significantly increased in branchesand fine roots (with diameter less than 1 mm). There were nochanges in crown structure (branch number and needle area distribution).Based upon measurements of growth made throughout the 3 years,the greatest increase in biomass under elevated CO₂took placemainly at the beginning of the experiment, when trees grownin elevated CO₂had higher relative growth rates than those grownunder ambient CO₂; these differences disappeared with time.Symptoms of acclimation of trees to growth in the elevated CO₂treatmentwere observed and are discussed. Copyright 2000 Annals of BotanyCompany Elevated CO₂, Pinus sylvestris, biomass production, allocation, fine roots, root litter, crown structure, nitrogen, C/N ratio     

Studies in the Nutrition of Apple Rootstocks: IV. The Effect on Growth and Mineral Coomposition of Supplying Magnesium through the Leaves

One-year rooted shoots of M.VII apple rootstock were grown fora single season by spraying their roots continuously with nutrientsolutions containing either < 3 ppmMg(Mg₍₀₎) or 45 ppm(Mg₍₀₎)to give, respectively, potentially very deficient or healthyplants. The new shoots of half the plants in each of these treatmentswere dipped periodically in a 2 per cent solution of MgSO₄.₇H₂O plus ‘wetter’. Mg₍₀₎ undipped plants developed severe symptoms of Mg deficiency,growth was poor, and the shoot/root dry-weight increment ratiowas high; none of these characteristics was found in Mg₍₀₎ dippedplants, whose growth was not appreciably less than that of Mg₍₂₎undipped controls. There was little translocation of Mg from leaves to roots: theconcentration of Mg in roots of Mg(0) dipped plants was as lowas that of the undipped. The large accumulation of Mn and, toa less extent, of Fe in Mg₍₀₎ dipped roots was not apparentlydetrimental to growth. Growth of Mg⁽²⁾ dipped plants was similar to that of the undipped. Dipping had little effect on the chemical composition of leaves,except to raise the concentration of Mg.     

Effects Produced on Tomato Plants, Lycopersicum esculentum, by Seed or Root Treatment with Gibberellic Acid and Indol-3yl-Acetic Acid

Growth in lengths of tomato stems and leaves was acceleratedby 5.0 µg gibberellic acid (GA₂) applied to the seed,or by 5.0, 0.5, and 0.05 µg given to the roots. Treatmentwith 5.0 µg also decreased bud number and lengthened thetime between bud appearance and fruit formation on the firsttruss by 1–8 days. Smaller amounts applied to roots shortenedthis time by 1–4 days. Indol-3yl-acetic acid at 0.5 µghad no effect, nor was simultaneous application of GA₃ and IAAto the roots more effective than GA₃, alone. Single applicationsof very small amounts of GA₃ to seeds or seedling roots thusproved capable of changing growth-rates of stems, leaves, andtrusses.The effects of treating tomatoes with GA₂ and with culturesof Azotobacter chroococcum, which contain small amounts of GA₃,and IAA, are compared.     

Effect of GA3 on the Molecular Mass of Polyuronides in the Cell Walls of Alaska Pea Roots

The role of cell wall matrix polysaccharides in gibberellin-regulatedroot growth is unknown. We examined pectic polysaccharides frompea roots treated with or without gibberellin A₃ (GA₃) in thepresence of ancymidol, an inhibitor of gibberellin biosynthesis.Pectic polymers solubilized by CDTA (trans-l,2-cyclohexanediamine-N,N,N',N'-tetraaceticacid) at 23°C and subjected to gel permeation analysis exhibitedhigh polydispersity with a molecular mass in excess of 500 kDa.Subsequent extraction of cell walls with CDTA at 100°C solubilizedpolymers with an average mol mass of 10 to 40 kDa. Subjectingthe high molecular mass pectic polymers extracted at 23°Cto 70–100°C for 2h generated 10 to 40 kDa fragments,similar in size distribution to those solubilized directly fromcell walls by CDTA solutions at 100°C. Pectic polymers from(GA₃+Anc)-treated roots were of higher average mol mass thanthose from Anc-treated roots in both the elongation zone andin the basal maturation zone. Since (GA₃+Anc)-treated rootselongate more quickly than Anc-treated roots [Tanimoto (1994)Plant Cell Physiol. 35:1019], the slender, GA₃-treated rootsmay produce and deposit highly integrated pectins more rapidlythan the thicker, Anc-treated roots in the elongating or elongatedcell walls. ²Present address: Horticultural Sciences Department, POB 110690IFAS, University of Florida, Gainesville, FL 32611-0690 U.S.A.     

Ion Distribution in Salt-stressed Mature Zea mays Roots in Relation to Ultrastructure and Retention of Sodium

Ultrastructural features and the distribution of soluble ionshave been examined in mature roots of Zea mays plants grownin both NaCl and Na₂SO₄ salinities. When the plants were grown in either salt, the Na concentrationincreased proximally along the root with a concomitant declinein the K concentration. Both trends were reversed in the shoot. X-ray microanalysis of deep-frozen, fully hydrated specimensshowed that in salt-treated roots Na, and Cl, or S were distributedabout stoichiometrically in the cortex and endodermis. Na wasusually less concentrated than the anion in the lumens of thevessels, but was concentrated markedly relative to either Clor S in the adjoining xylem parenchyma cells. In the older, proximal parts of seminal roots of plants grownboth without salt (controls) and in the presence of either NaClor Na₂SO₄, wall developments occurred in xylem parenchyma cellsat the half-bordered pits in which the cell wall became markedlythicker and possessed a loosely packed fibrillar structure.These structures were not comparable with the transfer-celltype of protuberances reported in the roots of other species. In the xylem parenchyma of plants grown in the presence of Na₂SO₄there were dramatic increases in the quantities of rough endoplasmicreticulum, ribosomes, and mitochondria relative both to controlsand NaCl treatments. The results are discussed in relation to the possible functionof the xylem parenchyma of the mature root in the reabsorptionof Na from the xylem sap, which may mitigate adverse effectsof salinity in salt-sensitive glycophytes.     

褐飞虱侵害后不同水稻品种根及地上部氮、磷、钾含量的变化

利用浓硫酸-过氧化氢消煮法,研究了不同耐、感虫品种水稻分蘖期在褐飞虱侵害胁迫后根及地上部间营养成分含量的变化情况。结果表明：褐飞虱侵害协优963后3天,根及地上部N、P、K含量、6天根及地上部N含量、9天地上部N含量在60、120头/株侵害后变化不明显;6天根及地上部P含量、6天根K含量、9天地上部P含量、9天根及地上部K含量在120头/株侵害后显著下降,60头/株侵害后变化不明显;6天地上部K含量、9天根N含量在60、120头/株侵害后均显著下降。对于协优63,3天地上部N含量、3天根及地上部P含量、6天及9天地上部N、P含量在60、120头/株侵害后变化不明显;6天根N、P含量、根及地上部K含量、9天根N含量在120头/株侵害后显著下降,60头/株侵害后下降不明显;3天、9天根及地上部K含量、9天根部P含量在60、120头/株侵害后均显著下降。表明不同水稻品种体内不同营养物质含量在褐飞虱侵害后变化不同,协优63较协优963敏感;K含量变化最明显,其次为P,最后为N;而且根比地上部对褐飞虱的反应敏感。     

碱胁迫对黑麦草幼苗根系活性氧代谢和渗透溶质积累的影响

为了探讨牧草对碱胁迫的耐受程度,采用营养液砂培方法,研究了不同浓度NaHCO3（0、50、100、150和200 mmol·L^-1）胁迫对黑麦草幼苗根系生长、活性氧代谢和渗透溶质积累的影响。结果表明：NaHCO3胁迫显著抑制黑麦草幼苗根系的生长,其抑制程度随胁迫浓度提高而增强,黑麦草可耐受的最高NaHCO₃浓度约为150 mmol·L^-1。随着NaHCO₃胁迫浓度的增加,黑麦草根中超氧阴离子(O^-·₂)、过氧化氢(H₂O₂)和丙二醛(MDA)含量明显上升,超氧化物歧化酶(SOD)活性和谷胱甘肽(GSH)含量显著下降,过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)活性及抗坏血酸(ASA)含量先升后降。黑麦草根中Na⁺含量随NaHCO₃浓度增大而增加,K⁺含量和K⁺/Na⁺比降低,可溶性糖含量先升后降,脯氨酸含量则先降后升,游离氨基酸含量呈先升后降再升高变化。表明碱胁迫导致的活性氧代谢失调和Na⁺、K⁺失衡及积累有机溶质进行渗透调节时更多能量的消耗可能是黑麦草根系生长受抑的重要因素。     

Soil O2 and CO2 Effects on Apparent Cell Viability for Roots of Desert Succulents

Roots of desert succulents occupy the upper layers of porous,well-aerated soils. However, roots of Agave deserti, Ferocactusacanthodes, and Opuntia ficus-indica all tolerated many daysof soil anoxia; 0% O₂ in the soil gas phase for 30 d reducedthe fraction of cells taking up the vital stain neutral red,an average of only 18% for the cortex and 6% for parenchymacells within the stele of perennial established roots. Ephemeralrain roots, induced by watering as branches on the establishedroots, were more susceptible to 0% O₂ in the soil gas phase;19 d abolished stain uptake for cortical cells and 32 d forstelar parenchyma cells. Soil CO₂ levels above the 0.1% observedin the root zone in the field rapidly reduced uptake of neutralred; the fraction of cortical cells taking up the stain decreased30% in 10 h at 0.5% CO₂ and was abolished in 9 h at 2% and 7h at 10% CO₂ averaged for the three species. Rain roots weresomewhat more susceptible than established roots to elevatedsoil CO₂ levels, and stelar parenchyma cells were much lesssusceptible than were cortical cells. When uptake of the vitalstain was abolished by elevated soil CO₂, no anatomical evidenceof cellular damage was observed. For A. deserti exposed to 2%CO₂, the pH of macerated root tissue decreased about 0.35 pHunit over 10 h; CO₂ apparently entered the cells, lowered theintracellular and/or cell wall pH, and prevented the accumulationof neutral red. Elevated soil CO₂ also inhibits root respirationfor the three desert succulents considered. Hence, the restrictionof such species to porous soils may reflect the relatively rapidinhibiting effects of elevated soil CO₂ levels rather than arequirement for high soil O₂ levels, consistent with the observationthat desert soils tend to have low gas-phase CO₂ levels near0.1% compared with 1% or more in the root zone of non-desertspecies. Key words: Agave deserti, Ferocactus acanthodes, neutral red, Opuntia ficus-indica, pH     

Mode of Action of IAA and GA3 on Root and Shoot Growth of Epiphyllous Buds of Bryophyllum tubiflorum

Darkness and GA₃ stimulate the elongation of the first internodebut inhibit the production of roots while IAA inhibits internodalelongation but promotes the production of roots on epiphyllousbuds of Bryophylhum tubiflorum. Cycloheximide inhibits both,implicating the synthesis of proteins in the growth of bothroot and shoot. Even pre-treatment of buds with cycloheximidefor 4 h inhibits rooting as well as internodal elongation whenthese are subsequently transferred to IAA or GA₃. On the otherhand, pre-treatment with IAA or GA₃ even for 8 h does not alleviatethe inhibitory effect of cycloheximide suggesting that thereis a lag period between the application of these regulatorsand the synthesis of proteins caused by them.     

Cyanamide mode of action during inhibition of onion (Allium cepa L.) root growth involves disturbances in cell division and cytoskeleton formation

Cyanamide is an allelochemical produced by hairy vetch (Vicia villosa Roth.). Its phyotoxic effect on plant growth was examined on roots of onion (Allium cepa L.) bulbs. Water solution of cyanamide (2-10 mM) restricted growth of onion roots in a dose-dependent manner. Treatment of onion roots with cyanamide resulted in a decrease in root growth rate accompanied by a decrease in accumulation of fresh and dry weight. The inhibitory effect of cyanamide was reversed by its removal from the environment, but full recovery was observed only for tissue treated with this chemical at low concentration (2-6 mM). Cytological observations of root tip cells suggest that disturbances in cell division may explain the strong cyanamide allelopathic activity. Moreover, in cyanamide-treated onion the following changes were detected: reduction of mitotic cells, inhibition of proliferation of meristematic cells and cell cycle, and modifications of cytoskeleton arrangement.     

Mycorrhizal associations between Tuber melanosporum mycelia and transformed roots of Cistus incanus

We set out to establish root cultures of a host plant with the aim of obtaining dual cultures of Tuber melanosporum mycorrhiza on transformed roots. Seedlings of Cistus incanus germinated under sterile conditions from seeds collected in the wild were treated with Agrobacterium rhizogenes. Nine hairy roots collected from different seedlings were cultured individually by repeated subculturing. The hairy root clones differed in growth rates and in morphology (branching frequency and distance between side roots). Root growth in a liquid medium exhibited a lag phase of about 2 weeks and an exponential phase lasting about 12 days before the start of the stationary phase. Hairy roots could be kept alive on medium M, a special solid minimal medium (low in Fe²⁺, BO₄^3-, Ca²⁺, Cu²⁺ and Zn²⁺, very low in PO₄^3- and lacking MoO₄^2-, NH₄⁺ and Co²⁺), for more than 7 months. T. melanosporum could be grown on the same medium for long periods only by subculturing the fungus with the roots. A mycorrhizal association developed between the roots and the T. melanosporum mycelium within 3 months. The association consisted of elongated roots with a mantle and a Hartig net surrounding two to three layers of cortical cells. Swollen, club-like root tips were discernible 5 months after inoculation. The mycorrhized roots could be subcultured and propagated on medium M and maintain the mycorrhizal association.     

Genotypic, Developmental and Drought-Induced Differences in Root Hydraulic Conductance of Contrasting Sugarcane Cultivars

Hydraulic properties of entire root systems and isolated rootsof three contrasting sugarcane clones were evaluated using transpiration-induceddifferences in hydrostatic pressure across intact root systems,root pressure-generated xylem sap exudation, and pressure-fluxrelationships. Regardless of the measurement technique employed,the clones were ranked in the same order on the basis of theirleaf area–specific total root system hydraulic conductance(C_root). All methods employed detected large developmental changesin G_rootroot with maximum values occurring in plants with approximately02 m₂ total leaf area. Genotypic ranking according to G_root,was reflected as a similar ranking according to root length-specifichydraulic conductance (L) of individual excised roots. Genotypicdifferences in G_root and L were consistent with anatomical characteristicsobserved in individual roots. Patterns of G_root, during soildrying and following re-irrigation suggested that the declinein G_root, observed during soil drying occurred within the rootsrather than at the soil–root interface and may have beencaused in part by xylem cavitation in the roots. Key words: Root hydraulic conductance, Saccharum spp, transpiration, root pressure, pressure-flux     

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