Enhanced Superoxide Radical Production in Roots of Zinc-Deficient Plants

The production of superoxide radical () was studied in roots of cotton (Gossypium hirsutum L. cv. Deltapine15/21), bean (Phaseolus vulgaris L. var. Pr?lude) and tomato(Lycopersicon esculentum L. cv. Super marmande) plants grownin nutrient solution with different Zn concentrations. UsingTiron as a spin-probe, electron spin resonance (ESR) was employedfor the measurements of levels. In the 48 000 g and 140 000 g supernatants of cotton root extracts theamplitude of the Tiron ESR signals reflecting production steeply increased with the appearance of visual Zndeficiency symptoms in the shoots. The changes in the amplitudeof the Tiron ESR signals were closely correlated with an NADPH-dependent generating oxidase activity with a high pH optimum. Increases in NADPH-dependent generation were also found in root extracts of Zn-deficientbean and tomato plants. In all experiments re-supply of Zn todeficient plants for 12 h or 24 h markedly decreased generation. Further, with advancing Zn deficiencyrates of NADPH oxidation increased and the activities of superoxidedismutase (SOD) and catalase decreased. The results suggest that cotton, bean and tomato roots possessan NADPH-dependent generating activity which is affected by the Zn nutritional status of the plants. UnderZn deficiency, enhanced generation and impaired detoxification of Of and H₂O₂ could lead to elevated levelsof and -derived oxidizing O₂ species and thus to increased peroxidation of membrane lipids. Key words: NADPH oxidase, superoxide radical, zinc deficiency     

Effect of Nitrogen Form and Counterion on Establishment of the Rhizobium trifolii-Trifolium repens Symbiosis

The effect of level of different counterion forms of or or both, on establishment of the Rhizobium trifolii-Trifolium repens symbiosis was evaluatedin plants cultured under bacteriologically controlled conditions. Ammonium had little effect on nodule formation, and even after exhaustion there was little compensatory nodule formation. Plant growth, nodule mass and acetylene reductionactivity all declined with increasing levels of . Except for , different counterion forms had little effect on plant growth, nodule numberand mass, and acetylene reduction activity. Ammonium markedlydecreased pH, the extent being dependent upon level and counterion present. Nitrate inhibited nodulation while levels remained in excessof plant uptake. Compensatory nodulation followed exhaustionof or at lower or levels. Nodule mass and acetylene reduction activity decreased, but plant growth increased withincreasing or levels. Nitrate raised the pH of the nutrient solution by one unit orless. Different or counterion forms had little effect on the symbiosis or plant growth. Ammonium nitrate severely inhibited nodulation but on exhaustionmarked compensatory nodulation occurred. The patterns of nodulemass, acetylene reduction activity and plant growth with increasingNH₄NO₃ levels were similar to or alone. Plants provided with NH₄NO₃ or no nitrogenwere similar in only slightly decreasing pH. Key words: Ammonium, Nitrate, Ammonium nitrate, Nitrogen fixation, Rhizobium trifolii, Trifolium repens, Symbiosis establishment, Nodulation     

ATP Synthesis Coupled to Nitrate Photoreduction in the Alga Hydrodictyon africanum

The presence of exogenous stimulates O₂evolution in illuminated H. africanum cells at the CO₂ compensationpoint, and it is likely that reduction in the light uses reductant produced in non-cyclic electron flow.When sources of ATP other than fermentation are absent, thepresence of , light, and a functional non-cyclic electron transport pathway stimulates active, ATP-dependentH₂ influx. This is consistent with non-cyclic electron flow associated with reduction being coupled to ATP synthesis. This -dependent ATP synthesis may be quantitatively important as a source ofATP during photolithotrophic growth with as N source in H. africanum and other algal unicells.     

Compensatory Changes in Ion Fluxes into Barley (Hordeum vulgare L. cv. Betzes) Seedlings in Response to Differential Root/Shoot Growth Temperature

The effect of growth temperature on the short term influx of⁸⁶Rb⁺/K⁺, ³⁶Cl^–/Cl^–, , ⁴⁵Ca²⁺/Ca²⁺and into barley plants (Hordeum vulgareL. cv. Betzes) has been examined. When barley plants were grownwith a differential root: shoot temperature (15 ?C/25 ?C) therewas a marked stimulation of influx of all ions except Ca²⁺.Q₁₀ measurements were close to 2.0 for all ions except Ca²⁺,where Q₁₀ 1.0 was found. Kinetics of ion influx showed thatthere had been almost complete compensation for the lower growingtemperature over a range of concentrations. The regulation of uptake was affected by growth temperature. On exposure to 15?C efflux/influx fell initially but was restored after 5 d. Sensitivity of net uptake to was increased by growth at a lower temperature. The importance of these observations in relationto application to field experiments and the proposed mechanismfor uptake is discussed. Key words: Growth temperature, Nitrate, Ammonium     

Interactions Between the Uptake and Assimilation of Inorganic Nitrogen and Carbon in Amphidinium spp. (Dinophyceae)

The rate of exponential growth of Amphidinium carterae Hulburtwas the same (0.025 h^–1) with either or as sole N-source. Nevertheless, in short-term experiments, cells growing exponentially with as N-source took up added 5–6 times faster than . accumulated in the cells. Addition of inhibited, reversibly, disappearance of from the medium; prior N-deprivation of the cells did not affect this inhibition. N-repIetecells, grown with as N-source, took up for several hours both in light and darkness, butthe uptake by such cells soon ceased in darkness although it continued in light. When uptake ceased, the cells could still take up rapidly in darkness. Ammonium taken up was assimilated rapidly into organic-N includingglutamine, other amino acids and protein. Ammonium uptake in darkness was accompanied by the utilizationof cellular polysaccharide, mainly glucose polysaccharide. Mostof this carbon was unavailable for the dark assimilation of. Addition of the analogue, methylammonium, did not initiate polysacchande catabolism. Itis suggested that a control mechanism is in operation, througha product of assimilation, which operates on one or more of the enzymes concerned with polysaccharidebreakdown, for example, -amylase or phosphorylase. Uptake of was accompanied by a high rate of dark ¹⁴CO₂ fixation and with both Amphidintum klebsii Kof.et Swezy and A. carterae N-deprivation led to a marked increasein this rate following addition of ; addition of had much less effect. The possible implications of these findings for the eco-physiology of marine dinoflagellatesare discussed. Key words: Ammonium, nitrate, CO₂ fixation     

Nitrate Transport into Chara corallina Cells using as an Analogue for Nitrate: III. INTERACTIONS BETWEEN CHLORIDE AND NITRATE TRANSPORT PROCESSES

The effects of Cl^– and pretreatment on ³⁶Cl^–influx and influx into Characorallina cells were examined. Both treatments reduced ³⁶Cl^–influx into C. corallina cells in the acid pH range (4.5–7.0). pretreatment stimulated influx into C. corallina cells, but Cl^– pretreatment hadno effect. There was a direct inhibitory effect of CI on influx into C. corallina cells, but no apparenteffect on net NO uptake. The time course of ³⁶Cl accumulation into cytoplasmic and vacuolarcompartments during incubation of the cells with showed that significant radioactivity appeared in the vacuolarsap after 30 min. There was a linear increase in the percentageof total ³⁶CI which crossed the tonoplast (_c-v). There was noeffect of Cl^– or pretreatment on accumulation of radioactivity in the vacuole. Thin layer chromatography ofthe vacuolar sap showed that after 2 h only one component waspresent which had an R_F which was similar to ³⁶CI^–. Therate of accumulation of ³⁶C1^– in the vacuole could beused to estimate rates of reduction. Key words: Chloride, Chlorate, Chara, Nitrate     

Relative Uptake Rates of Inorganic Nutrients by NO3- and NH4+ Grown Ricinus communis and by two Plantago Species

Allen, S., Thomas, G. E. and Raven, J. A. 1986. Relative uptakerates of inorganic nutrients by and grown Ricinus communis and by two Plantago species.—J. exp. Bot. 37: 419–428. The relative rates of uptake and assimilation of C, N, P, S,Cl^–, K⁺ , Na⁺ Ca²⁺ and Mg²⁺ by and grown Ricinus conimunisand by NH₄NO₃- grown Plantago lanceolata and P. major were calculatedfrom data presented elsewhere. Results showed that for grown Ricinus the short term relativeuptake rates, for each nutrient X did not change significantly over the steady-state periodof exponential growth. The average gave , the mean relative uptake rate during exponential growth, for each nutrient. The amountof each nutrient taken up from a nutrient solution over a periodof time could, therefore, be calculated. For and -grown R. communis,the relative uptake rate of each nutrient was a constant fractionof the relative rate of carbon assimilation. It is suggestedthat this is typical of plants of cauline habit. For both Plantago spp., the relative rates of nitrogen uptakeand assimilation fell significantly during the exponential growthphase It is suggested that this could be a characteristic ofthe growth habit of the rosette plant. Key words: Relative uptake rates, Ricinus, Plantago, ammonium, nitrate, cauline, rosette     

Differential rates of inhibition of N2 fixation by sustained low concentrations of NH4+ and NO3- in northern ecotypes of white clover (Trifolium repens L.)

An experimental study in flowing solution culture compared threeNorwegian ecotypes (from Saerheim, Pasvik and Bod) and a commercialcultivar (Ac51) of white clover (Trifolium repens L.) and demonstrateddifferences with respect to the rate and intensity with whichN₂ fixation was affected when or were supplied at 20 mmol m^–3 over 14 d. Plants were nodulated and N₂ fixation wasestablished over 17 d prior to supplying mineral N, with shoottemperature 25/15 C day/night and root temperature adjustedprogressively to 12C. Control plants received no mineral Nthroughout, and did not grow as rapidly as those supplied with or . Mineral N generally depressed the total N₂ fixation per plantrelative to control plants, with two exceptions. The effectof on N₂ fixation was moresevere than that of and, over the 14 d, -fed plants fixed more N₂ than the comparable -fed plants. Interpolated daily rates of N₂ fixation per plant andnodule dry wts were used to calculate specific rates of N₂ fixation.These showed that (1) addition of either or initially stimulated fixation relative to control plants and to mineral N uptake;(2) this stimulation was greatest and was delayed by 1-2 d in-fed plants; and (3) nutrition sustained higher residualrates of N₂ fixation after 8 d compared with nutrition, under which fixation all but ceased after10 d in three of the genotypes. Ecotype Bode showed by far themost severe induced depression of N₂ fixation. Key words: N₂ fixation, nitrate, ammonium, white clover, northern ecotypes     

Calcification in the Green Alga Halimeda: III. THE SOURCES OF INORGANIC CARBON FOR PHOTOSYNTHESIS AND CALCIFICATION AND A MODEL OF THE MECHANISM OF CALCIFICATION

Calcification and photosynthetic rates in Halimeda tuna weremeasured by the ¹⁴C method under conditions of differing pHand total inorganic carbon (CO₂) concentrations. The effectsof pH and CO₂ on photosynthesis and respiration were also monitoredwith a polarographic O₂ electrode. The results obtained indicatethat the intercellular pH and CO₂ differ from those of the externalmedium. Experiments carried out over a range of pH values show thatHalimeda can use for photosynthesis. Photosynthesis appears to stimulate calcification by removing CO₂ from theintercellular spaces. As these spaces are isolated from theexternal sea water by the layer of cell wall of the adpressedperipheral utricles, the removal of CO₂ results in a rise in[] and a rise in pH. This results in an increased rate of CaCO₃ precipitation. Respiratory CO₂ evolution has aninhibitory effect on calcification by decreasing the pH and[]. A model for calcification in Halimeda is proposed based on theresults of this and previous papers. Calcification in Halimedais seen to be a result of the anatomy of the thallus in whichthe sites of calcification are within a semi-isolated chamberwhere removal or addition of CO₂ due to photosynthesis or respirationcan effectively change [CO] thereby resulting in precipitation of CaCO₃. In the Appendix to this paper theoreticalcalculations illustrate the effects of CO₂, , and removal or addition in a closed system on the relative concentrations of the other inorganic carbonspecies.     

Nitrate Nutrition of Grasses from Steady-State Supplies in Flowing Solution Culture following Nitrate Deprivation and/or Defoliation: I RECOVERY OF UPTAKE AND GROWTH AND THEIR INTERACTIONS

Two Lolium genotypes, i.e. Lolium perenne cv. S23 and a L. perenne? L. multiflorum hybrid cv. Augusta were, in one treatment,grown in flowing solution culture with a maintained supply of at 10 mmol m–3 throughout. In another treatment, the plants were deprived of for 11 d, was then re-supplied and both control and N-deprived plants were either defoliatedor left entire. Effects of the stresses imposed by N deprivationor defoliation on subsequent net uptake of , shoot and root growth and their interactions were examined.There were no major differences in the behaviour of the twogenotypes throughout. The removal of NO3 supply did not altertotal dry matter production during the 11 d period of deprivationbut the rate of root growth accelerated markedly. There waslittle effect of N deprivation on the specific growth ratesof the recovering defoliated shoots. Cumulative net uptake of closely paralleled the pattern of growth and there were obvious and marked effects of both N deprivationand defoliation. Effects on uptake were more distinctly demonstrated when uptake was expressed on aper unit root or shoot basis, i.e. specific unit absorptionrates (S_NO3). In the control plants with sustained supply, there was a progressive decline with time in S_NO3, inspite of an increasing shoot: root ratio. After both N deprivationand defoliation treatments there was a rapid initial increasein S_NO3, followed by an oscillatory cycle of increasing anddecreasing rates with a 10–11 d period. The relationshipsbetween growth and uptake were complex and did not conform to a previously predicted linear relationshipbetween S_NO3, and the ratio total fresh plant weight: root freshweight. The results are discussed in relation to the possiblemechanisms involved. It is suggested that the oscillations inunit absorption rate indicated that the roots of N-deprivedor defoliated plants retained a high capacity for absorptionimmediately after re-supply or defoliation and that the stressedplants were unable to assimilate or utilize taken up; net uptake then decreased through a shift in favourof efflux over influx until the influx mechanism was able todominate and the pattern was then repeated. Key words: Lolium, genotypes, N deprivation, nitrate uptake, defoliation, unit absorption, growth     

Nitrate Transport Characteristics in Hordeum vulgare L. Seedlings using Three Different Tracer Techniques

Deane-Drummond, C. E. and Thayer, J.R. 1986. Nitrate transportcharacteristics in Hordeum vulgare L. seedlings using threedifferent tracer techniques.—J. exp. Bot. 37: 429–439. and have been used to investigate various properties of nitrate uptake and translocation intoHordeum vulgare L seedlings. Short term / influx into seed lings grown in CaSO⁴ was stimulated by after a lag of 2 h. The apparent kinetics of shortterm / influx over the concentration range 0?0–0?7mol m fitted Michaelis-Menten equations The apparent V_max didnot change when seedlings were used that had been pretreatedin 10 or 100 mmol m^–3 and V^max=3.77 and 3?56µmol g^–1 fr. wt. h^–1respectively. The apparent Michaelis constants were also similarand K_m=0?47 and 0?45 mol m^–3 respectively. Longer term pulse chase experiments with the heavy isotope ¹⁵Nhave shown that feeding roots with resulted in the preferential appearance of ¹⁵N labelled aminoacids in the xylem sap. Pulse chase experiments with the radioisotope¹³N have shown that feeding shoots with resulted in a radial pattern of distnbution of labelin the leaf veins, which can be detected using autoradiography. The limitations and advantages of all three techniques are comparedby reference to other known experimental data. Key words: ³⁶Chlorate, ¹³nitrate, ¹⁵nitrate, Hordeum vulgare     

Comparison of the Effects of Root Temperature on Nitrate and Ammonium Nutrition of Oilseed Rape (Brassica napus L.) in Flowing Solution Culture: I. GROWTH UPTAKE OF NITROGEN

Oilseed rape plants (Brassica napus L. cv. Bien venu) were grownin flowing nutrient solution and acclimatized over 49 d to lowroot temperature (5 ?C) prior to treatment at root temperaturesof 3, 7, 11 or 17?C for 14 d, with common air temperature of20/15?C day/night and solution pH 6.0. The effects of root temperatureon growth, uptake and assimilation of N were compared with Nsupplied either as or at 10 mmol m^–3. Plant fresh weight, dry weight and leafarea increased with root temperature. Q₁₀ values for specificgrowth rates between 7?C and 17?C were 1.10 and 1.33, respectively,under and nutrition. Fresh weight and leaf area were favoured by nutrition, particularly at 11 ?C and 17 ?C. At each temperaturethe net uptake of over 14 d was similar to that of , increasing 4-fold between 3?C and 17 ?C. Unit absorption rates of increased over the first 3 or 4 d, to an extent that increased with roottemperature. Thereafter, near constant values were maintainedat 3, 7 and 11 ?C. Unit absorption rates of at 3 ?C and 7 ?C did not increase over the first 3 or 4 d. Plantsat 17?C responded differently from those at other temperatures,with steep increases in unit absorption rates of and after day 8. The tendency for plants to adjust unit absorption rates of N over 14 d to become independentof root temperature was limited to the range 7–11 ?C.Q¹⁰ values between 7 ?C and 17 ?C for unit absorption rateswere 1.7—1.8 and 1.4—1.5, respectively, for and . Plants at 7, 11 and 17?C absorbed more than was subsequently assimilated, but at 3 ?C the absorption of was insufficient to meet the assimilatory demand. The results are discussed comparativelyfor and and in terms of the factors that determine unit absorption rates of N inresponse to a change in root temperature. Key words: Brassica napus, oilseed rape, root temperature, nitrate, ammonium, ion uptake rate     

Nitrate Metabolism in Alfalfa Root Nodules under Water Stress

Three-month-old plants (vegetative stage) of alfalfa (Medicagosaliva L cv. Aragon) were supplied for one week with 1.0dm³(uniformly distributed) nutrient solutions containing 0 or 20mol m^–3 . One week after initiation of treatment, the plants were subjected to drought by withholding water. Bacteroidsand cytosol of nodules were obtained at different stages ofstress, and used for enzyme assays and for determination of, and . Proteins of bacteroids were more stable than cytosolic proteinswith respect to the detrimental effects of water stress and. Protein contents of bacteroids and cytosol were inversely related to proteolytic activitiesagainst azocasein in both nodule fractions. Specific nitrate reductase activity (NRA) and nitrite reductaseactivity (NiRA) of bacteroids from -treated plants were inhibited by c. 70% and 45%, respectively, as leafwater potential (_w) declined from –0.5 MPa (control) to–1.8 MPa. At still lower _w both activities began to increase:NRA was doubled, whereas NiRA only returned to its control level.Cytosolic NRA was strongly inhibited by drought, but the correspondingNiRA remained constant. Ammonia concentration in bacteroids and nodule cytosol keptbasically constant, whereas accumulated in the cytosol at severe stress, due to the activationof bacteroid nitrate reductase. Results indicate that nitrate and nitrite reductases of thebacteroids and the nodule cytosol act in different form: assimilatory,the cytosolic enzymes; and dissimilatory, the enzymes of bacteroidsat low _w The possibility that assimilation of also occurs in bacteroids at control or mild waterstress conditions is suggested. Key words: Assimilatory and dissimilatory reduction, bacteroids, Medicago saliva, nodule cytosol, water stress     

Effects of Light on Transport by Azolla pinnata

Effects of light flux density (LFD) during growth and uptakeassay on induction of transport system and kinetics of transport were studied using the Azolla pinnata-Anabaena azollae association (Azolla). Theinduction and uptake kinetics of the transport system were determined using an automated system that measuredthe NO₃ concentration in the growth medium as a function oftime, using an on-line high performance liquid chromatograph(HPLC) with a UV-VIS detector. Full induction of the transport system required about 1.5 to 2.0 h and occurred without any apparent lag phase,regardless of the LFD provided. The level of induction of transport of Azolla grown at 600 µmol m^–2s^–1 LFD was higher than for that grown at 100 µmolm^–2 s^–1. Similarly, 600 µmol m^–1 s^–1LFD during the assay resulted in a higher level of inductionthan did 100 umol m^–2 s^–1. An increase in the LFDeither during the growth or the assay period increased the uptake rate; however, an increase in LFD duringthe latter period had greater effect. Azolla grown and assayedat 600 umol m^–2 s^–1 had the highest uptake rate. The uptake rate at 50 cm³ m^–3ambient CO₂ concentration was initially higher than at 305 cm³m^–3, but the uptake rate decreased rapidly with time andeventually dropped below that at 305 cm³ m^–3 CO₂. Thesedata suggest that the energy required for transport in Azolla may bypass the photosynthetic CO₂ fixationand carbon-cycling. Key words: carbon dioxide, concentration dependence, light flux density, uptake     

Uptake of Methylammonium Ions by Hydrodictyon africanum

Methylamine influx into Hydrodictyon has been measured with[^l4C]methylamine. The influx increases with rising externalpH up to about pH 8. Between pH 8 and 9 influx remains quiteconstant, with a further increase above pH 9. Influx is light-dependent,temperature-sensitive, and is decreased by . During short-term influx (less than 4 h) metabolism of methylamineappears negligible. Prolonged influx results in CH₃ accumulation, and efflux of K⁺, Na⁺, and H⁺. There is no effecton Cl^– influx. Methylamine decreases the membrane electricp.d. by 60–120 mV at external concentrations of 0?2–1?0mM. The results indicate that, below pH 9, methylamine enters thecell almost entirely as CH₃. It is suggested that a passive electrogenic uniporter is involved, and thatby analogy uniport of may also be expected in Hydrodictyon. The results are discussed in relation to theevidence for uptake of CH₃ and by other plant cells.     

Relationship between Inhibition of CO2 Fixation and Glutamine Synthetase Inactivation in Lemna gibba L. Treated with L-Methionine-D,L-Sulphoximine (MSO)

The rate of net CO₂ fixation in Lemna gibba L. was decreasedto 50% by 100–150 min incubation in the presence of 0•5mol m^–3 L-methionine-D,L-Sulphoximine (MSO), an irreversibleinhibitor of glutasnine synthetase (GS). The pattern of inhibitionwas similar in both 21% O₂ and 2% O₂. The inhibition was accompaniedby increased intracellular levels. Incubation with 10 mol m^–3 under the same conditions, but without MSO, resulted in even higher levels but the rate of CO₂ fixation was unaffected. Additions of glutamine, glutamate, glycine or serine delayedthe MSO-induced inhibition of CO₂ fixation. The same amino acidsdelayed the inactivation of GS by MSO. Thus inhibition of CO₂ fixation by MSO in Lemna is neither causedby elevated levels nor closely related to photorespiration. Possibly, MSO causes shortage of amino-N formaintenance of the functional integrity of the photosyntheticapparatus. Key words: Methionine sulphoximine, CO₂, fixation, Lemna     

Salt-Stimulated Bicarbonate-Dependent Photosynthesis in the Marine Angiosperm Zostera muelleri

Millhouse, J. and Strother, S. 1986. Salt-stimulated bicarbonate-dependentphotosynthesis in the marine angiosperm Zostera muelleri.—J.exp. Bot. 37: 965–976. Photosynthetic oxygen evolution in the seagrass Zostera muelleriIrmisch ex Aschers. was inhibited in iso-osmotic sucrose. Theapparent affinity of the leaves for CO₂ in seawater increasesfrom pH 8?2 to 8?9 indicating that as well as CO₂ may act as a substrate for photosynthesis. Theaffinity for CO₂ was lower in iso-osmotic sucrose and was notaffected by pH. Under these conditions was not a substrate for photosynthesis. The differencebetween the photosynthetic rate in seawater and iso-osmoticsucrose at the same concentration of CO₂ was used to estimate assimilation. The Briggs-Maskell equation, which allows for an unstirred layer around the tissuewas more appropriate than the Michaelis-Menten theory for calculatingthe apparent affinity of the leaf slices for CO₂. The apparentK_m CO₂ was calculated as 116 mmol m^–3 at pH 8?2 by Michaelis-Mentenkinetics but only 8?10 mmol m^–3 by the Briggs-Maskellequation. The stimulation by various ions in Seawater of use was investigated. The cations,in decreasing order of effectiveness were Ca²⁺, Mg²⁺, K⁺ andNa⁺ Anions were ineffective. No single cation at its concentrationin seawater was capable of supporting use at the rate observed in seawater. Acetazolamide,an inhibitor of carbonic anhydrase, inhibited the use of for photosynthesis but had littleeffect on CO₂ photosynthesis. Thus, carbonic anhydrase activityis required for -dependent photosynthesis. Key words: Zostera muelleri, photosynthesis, salinity     

Abscisic Acid Accumulation and Water Relations of Four Cultivars of Phaseolus vulgaris L. under Drought

Larqué-Saavedra, A., Rodriguez, M. T., Trejo, C. andNava, T. 1985. Abscisic acid accumulation and water relationsof four cultivars of Phaseolus vulgaris L. under drought.—J.exp. Bot 36: 1787–1792. Plants of four cultivars of Phaseolus vulgaris L. differingin drought resistance were grown in pots under greenhouse conditionsand prior to flowering water was withheld from the pots untilthe mid-day transpiration rate reached values below 1.0 µgH₂O cm^–2 s^–1 (designated the ‘drought’stage). At this point leaves were harvested on 3 or 4 occasionsover 24 h to determine the abscisic acid (ABA) concentration,total water potential (), solute potential (₁) and turgor potential(_p). Results showed that values of , ₁, and _p differed between cultivarswhen they reached the ‘drought’ stage. The stomatalsensitivity to changes in and _p, was as follows: Michoacán12A3 > Negro 150 Cacahuate 72 > Flor de Mayo. These datacorrelated well with the pattern of drought resistance reportedfor the cultivars. ABA accumulation at the ‘drought’ stage differedbetween cultivars at each sampling time, but overall differencesin ABA level between cultivars were not significant. ABA levelsdid not, therefore, correlate with the drought resistance propertiesreported for the cultivars. Results are discussed in relationto and hour of the day when bean samples were taken for ABAanalysis. Key words: Phaseolus vulgaris L., drought resistance, abscisic acid     

Interspecific Grafts Demonstrate Root System Control of Leaf Water Status in Water-Stressed Phaseolus

We examined the importance and the mechanisms of the root systems'effect on leaf water status in two bean species: Phaseolus vulgarisL. cv. Redcloud (Pv) and P. acutifolius Gray MN cultivatedaccession 258/78 (Pa). Pa maintains a higher leaf water potential(₁) than Pv. We used reciprocal grafts between the two species.We grew four plants (one of each graft combination) in one potso they experienced the same soil water potential. Shoot genotypedetermined ₁ of well-watered plants. Root genotype determined₁ of the most stressed plants. Stressed Pa root systems increased₁ of Pv shoots by 0·1 MPa over Pv shoots on Pv roots.Pa roots did not maintain by affecting stomatal conductancenor by simply having more dry weight. Pa roots may have greaterhydraulic conductivity than Pv roots. Key words: Phaseolus acutifolius, Phaseolus vulgaris, leaf water potential, root-shoot communication     

Growth and 2, 4-Diaminobutyric Acid Composition of Flatpea (Lathyrus sylvestris L.) as Influenced by Mineral- and Symbiotically Fixed-Nitrogen

Flatpea (Lathyrus sylvestris L. cv. ‘Lathco’) plants,grown hydroponically, were inoculated with rhizobia (Rhizobiumleguminosarum strain 92F2), supplied with nitrate nitrogen (2meq 1^–1), or provided with both rhizobia and . Nodulated plants supplied with had the highest biomass and the highest level of free amino acids in leavesand roots. Nitrogen fixation was depressed 80% in inoculatedplants supplemented with . Compared to plants whose nitrogen requirement was satisfied either partially orfully by , plants that were totally dependent upon biological nitrogen fixation had fewer lateral shoots andlower concentrations of nitrogen, soluble protein, and totalfree amino acids in the shoots, especially in the leaves. Thesymbiotic association between plants and rhizobia for nitrogenfixation was not essential to the production and accumulationof 2,4-diaminobutyric acid (A₂bu) and other non-protein aminoacids in flatpea. Levels of A₂bu, and most of the other freeamino acids quantified, were significantly lower in the nodulatedplants grown in the absence of than in the inoculated or noninoculated plants supplied with . Arginine and glutamic acid were exceptions in that levels ofthese two amino acids were higher in roots bearing effectivenodules. Plant responses to the different treatments are attributedto the amount of nitrogen available to the plant, rather thanthe method or form of nitrogen supplied. Key words: 2,4-Diaminobutyric acid, Lathyrus, nitrogen