Effect of NaCI Salinity on Flows and Partitioning of C, N, and Mineral Ions in Whole Plants of White Lupin, Lupinus albusL.

Plants of Lupinus albus L., cv. Ultra, were grown hydroponicallywith NO₃^–-nutrition for 51 d under control (0.05 mol m^–3Na⁺ and 10 mol m^–3 Cl^–) and saline (40 mol m^–3NaCI) conditions. Plants were harvested 41 and 51 d after germinationand analysed for content and net increment of C, N and the mineralcations K⁺, Na⁺, Mg²⁺, and Ca²⁺ and the anions Cl^–, NOJ,malate, phosphate, and SO₄^2–. Roots, stem interaodes,petioles and leaflets were analysed separately. During the studyperiod net photosynthesis, respiratory losses of CO₂ from shootand root and the composition of the spontaneously bleeding phloemsap and the root pressure xylem exudate were also determined.Using molar ratios of C over N in the transport fluids, incrementsof C and N, and photosynthetic gains as well as respiratorylosses of C, the net flows of C and N in the xylem and phloemwere then calculated as in earlier studies (Pate, Layzell andMcNeill, 1979a). Knowing the carbon flows, the ratios of ionto carbon in the phloem sap, and ion increments in individualorgans, net flows of K⁺, Na⁺, and Cl^– over the study periodwere also calculated. Salt stress led to a general decrease of all partial componentsof C and N partitioning indicating that inhibitions were notdue to specific effects of NaCI salinity on photosynthesis oron NO₃ uptake. However, there were differences between variouslyaged organs, and net phloem export of nitrogenous compoundsfrom ageing leaves was substantially enhanced under saline conditions.In addition, NO₃^–reduction in the roots was specificallyinhibited. Uptake and xylem transport of K⁺ was more severelyinhibited than photosynthetic carbon gain or NO₃^– uptakeby the root. K⁺ transport in the phloem was even more severelyrestricted under saline conditions. Na⁺ and Cl^– flowsand uptake, on the other hand, were substantially increasedin the presence of salt and, in particular, there were thenmassive flows of Na^– in the phloem. The results are discussedin relation to the causes of salt sensitivity of Lupinus albus.The data suggest that both a restriction of K⁺ supply and astrongly increased phloem translocation of Na⁺ contribute tothe adverse effects of salt in this species. Restriction ofK⁺ supply occurs by diminished K⁺ uptake and even more by reducedK⁺ cycling within the plant. Key words: Lupinus albus, salt stress, phloem transport, xylem transport, partitioning, carbon, nitrogen, K⁺, Na⁺, CI^–     

The Sensitivity of Net Photosynthesis in Several Plant Species to Short-term Fumigation with Sulphur Dioxide

The effects of exposure of up to 2 h with sulphur dioxide ona range of plant species was observed by measuring changes inthe rate of net photosynthesis under closely controlled environmentalconditions. Ryegrass, Lolium perenne ‘S23’ was thespecies most sensitive to SO₂; significant inhibition was detectedat 200 nl l^–1. Fumigations at 300 nl l^–1 also inhibitedphotosynthesis in field bean (Vicia faba cv. ‘Three FoldWhite’ and ‘Blaze’) and in barley (Hordeumvulgare cv. ‘Sonja’). No effect was detected inwheat (Triticum aestivum cv. ‘Virtue’) at concentrationsup to 600 nl l^–1 SO₂, or in oil-seed rape (Brassica napuscv. ‘Rafal’) except at 800 nl l^–1 SO₂). Recoverycommenced immediately after the fumigation was terminated andwas complete within 2 h when inhibition had not exceeded 20%during the SO₂ treatment. Key words: Sulphur dioxide, short-term fumigation, photosynthesis     

Effects of Sulphur Dioxide and Nitrogen Dioxide on Growth and Translocation in Winter Wheat

Gould, R. P. and Mansfield, T. A. 1988. Effects of sulphur dioxideand nitrogen dioxide on growth and translocation in winter wheat.—J. exp. Bot 39: 389–99 Winter wheat (Triticum aestivum L. cv. Avalon) was grown undersimulated autumn conditions for 4 weeks and exposed to a mixtureof SO₂ and NO₂. Biomass was measured after 2, 3 and 4 weeksand the flag leaves of sample plants were labelled with ¹⁴CO₂.Biomass yields revealed an increase in shoot-to-root ratiosunder polluted conditions. The labelling experiments showedthat less assimilate was transported to the roots, whilst morewas allocated to the younger components of the plant. It appearedthat NO₂ and SO₂ also caused labelled photosynthate to be retainedin the labelled leaf. Reducing the photon flux exacerbated theeffects of SO₂ and NO₂ as indicated by changes in biomass andby the distribution of ¹⁴C. Key words: Wheat, SO₂, NO₂, growth, translocation     

Effects of elevated CO2 concentrations on three montane grass species: III. Source leaf metabolism and whole plant carbon partitioning

Agrostis capillaris L.⁵, Festuca vivipara L. and Poaalpina L.were grown in outdoor open-top chambers at either ambient (340 3µmol mol^–1) or elevated (6804µmol mol^–1)concentrations of atmospheric carbon dioxide (CO₂) for periodsfrom 79–189 d. Photosynthetic capacity of source leaves of plants grown atboth ambient and elevated CO₂ concentrations was measured atsaturating light and 5% CO₂. Dark respiration of leaves wasmeasured using a liquid phase oxygen electrode with the buffersolution in equilibrium with air (21% O₂, 0.034% CO₂). Photo-syntheticcapacity of P. alpina was reduced by growth at 680 µmolmol^–1 CO₂ by 105 d, and that of F. vivipara was reducedat 65 d and 189 d after CO₂ enrichment began, suggesting down-regulationor acclimation. Dark respiration of successive leaf blades ofall three species was unaltered by growth at 680 relative to340 µmol mol^–1 CO₂. In F. vivipara, leaf respirationrate was markedly lower at 189 d than at either 0 d or 65 d,irrespective of growth CO₂ concentration. There was a significantlylower total non-structural carbohydrate (TNC) concentrationin the leaf blades and leaf sheaths of A. capillaris grown at680µmol mol^–1 CO₂. TNC of roots of A. capillariswas unaltered by CO₂ treatment. TNC concentration was increasedin both leaves and sheaths of P. alpina and F. vivipara after105 d and 65 d growth, respectively. A 4-fold increase in thewater-soluble fraction (fructan) in P. alpina and in all carbohydratefractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosyn-theticcapacity and leaf carbohydrate concentration was such that therewas a strong positive correlation between photosynthetic capacityand total leaf N concentration (expressed on a per unit structuraldry weight basis), and total nitrogen concentration of successivemature leaves reduced with time. Multiple regression of leafphotosynthetic capacity upon leaf nitrogen and carbohydrateconcentrations further confirmed that leaf photosynthetic capacitywas mainly determined by leaf N concentration. In P. alpina,leaf photosynthetic capacity was mainly determined by leaf CHOconcentration. Thus there is evidence for down-regulation ofphotosynthetic capacity in P. alpina resulting from increasedcarbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positivelycorrelated in P. alpina and F. vivipara. Leaf dark respirationand soluble carbohydrate concentration of source leaves werepositively correlated in A. capillaris. Changes in source leafphotosynthetic capacity and carbohydrate concentration of plantsgrown at ambient or elevated CO₂ are discussed in relation toplant growth, nutrient relations and availability of sinks forcarbon. Key words: Elevated CO₂, Climate change, grasses, carbohydrate partitioning, photosynthesis, respiration     

Modification of Stomatal Conductance by Sulphur Dioxide

The mechanism of SO₂-induced changes in stomatal conductance(g) of alder was examined to determine if SO₂ affects guardcell function directly or indirectly through the SO₂-inducedchanges in photosynthesis. During experimental fumigations at SO₂ concentrations of 3–3µmol m^–3 (0.08 µl l^–1), stomatal closurepreceded declines in net photosynthetic rate (A), indicatingthat SO₂ can directly affect guard cells. From these and otherstudies it appears that the sequence of A and g responses maybe influenced by SO₂ concentration as well as by species. Fumigation with SO₂ did not cause increases in g, even whenthe intercellular substomatal CO₂ concentration (c_i) was reducedby 50 µmol mol^–1. Increases in g are not attributableto SO₂ effects on the CO₂-based stomatal control system. Key words: Air pollution, Alnus serrulata, gas exchange, stomata, sulphur dioxide     

Proton Neutralization in the Leaves of English Oak (Quercus robur L.) Exposed to Sulphur Dioxide

Reactions to the input of acidic gases were investigated inleaves of Quercus robur L. exposed to different concentrationsof SO₂ (80, 120, and 160 nl I^–1) for 32 to 70 d. Two-year-oldoaks were grown in nutrient solutions with varied nitrogen formand were fumigated in closed chambers. An attempt was made toidentify the mechanisms of proton neutralization by consideringthe uptake of nitrogen, the increase in sulphur and carboxylatecontents, and the excretion of hydroxyl ions or protons. Inaddition, nitrate reductase activity was determined in the leaves. The reduction of sulphur was not involved in the neutralizationof protons generated by SO₂-uptake, whereas organic acid metabolismplayed a decisive role. Depending on SO₂-concentration, durationof fumigation and nitrogen supply, oaks reacted with a reductionin the size of the carboxylate pool in the leaves, and/or withan increase in proton excretion (or a decrease in hydroxyl ionexcretion). Nitrate reductase activity increased in the leavesof nitrate-grown oaks exposed to the highest SO₂-concentration(160 nl l^–1) for 42 d. The capacity of the mechanismsconsidered is sufficient for the neutralization of the calculatedamounts of protons resulting from SO₂-uptake. Key words: Leaves, neutralization, protons, Quercus, sulphur dioxide     

Leaf Abscission and Stem Lesions (Intumescences) on Poplar Clones after SO2 and O3 Fumigation: A Link with Ethylene Release?

Differences in premature leaf abscission and in visible steminjury in genetic lines of poplar followed continuous fumigationswith air pollutant levels of SO₂ (90–100 nl l^–1)and O₃ (70–80 nl l^–1) either separately or together.The clones used were: Populus deltoides var. missiouriensisMarsh., P. nigra cv. ‘italicd’ L., and the hybridsP. nigra cv. ‘italica’ xP. deltoides (He-X/3) andP. nigra cv.‘italica’ x P. nigra cv. ‘Serres’(He-K/7). While most leaf abscission occurred within 20 d fromthe start of fumigation, stem lesions (intumescences), appearedonly after 72 d. Their anatomical characteristics include theformation of lysigenous aerenchyma in the lower parts of theintumescence, the sloughing of superficial cells from the injuredarea, and the development of crystalline formations on the surfaceof the lesions. P. deltoides exhibited the least morphologicalresponse to the gases. Ethylene released from fumigated leaves was determined at thesame gas concentration of SO₂ (100 nl l^–1), O₃ (75 nll^–1) and their mixture. Leaves of P. deltoides consistentlyshowed the lowest ethylene production after the gas treatments.P. ‘italica’ production was higher but was littlealtered by the treatments. The two hybrids He-X/3 and He-K/7showed the greatest increases in ethylene evolution with time.With He-K/7 exposed to the gas mixture the production of ethylenedecreased after the initial sharp rise during days 1–2,and reflected the considerable leaf damage observed after day3. The results suggest that sensitivity to air pollution, (as shownby leaf abscission and the formation of stem intumescences)can be correlated with the level of pollutant-induced ethyleneevolution from leaves. Initially high levels could induce abscission,whilst prolonged production could be responsible for intumescenceinitiation. The discussion proposes a series of events fromSO₂ and/or O₃ entry into the leaf and the physiological reasonsfor the clonal differences. Key words: Sulphur dioxide, ozone, ethylene, poplar, leaf abscission, stem lesions     

Active oxygen participation in chlorophyll destruction and lipid peroxidation in SO2-fumigated leaves of spinach

Chlorophyll a and carotenoids of spinach began to be destroyed2 to 3 hr after fumigation with 2 ppm SO₂ under light, whereaschlorophyll b was undamaged during 8 hr of exposure to SO₂.Pheophytin a was not affected by the fumigation. When disks excised from leaves fumigated with SO₂ at 2 ppm for2 hr were illuminated, chlorophyll a and carotenoids were brokendown, while they were not destroyed in darkness. The destructionof these pigments was suppressed under nitrogen. Chlorophylla destruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate(tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-[2,2,2]-octane(DABCO), methio-nine, histidine, benzoate and formate. Chlorophylla destruction was inhibited by phenazine methosulfate but stimulatedby methyl viologen. Addition of superoxide dismutase (SOD) tothe homogenate of SO₂-fumigated leaves inhibited the chlorophylla destruction. The activity of endogenous SOD was reduced to40% by 2-hr fumigation before the loss of chlorophyll was observed.These results suggest that chlorophyll a destruction by SO₂was due to superoxide radicals (O₂^–). Moreover, malondialdehyde (MDA), a product of lipid peroxidation,was formed in SO₂-fumigated leaves. MDA formation was inhibitedby tiron, hydroquinone and DABCO but not by benzoate and formate.MDA formation was increased by D₂O. These results suggest thatlipid peroxidation in SO₂-fumigated leaves was due to singletoxygen ¹O₂ produced from O_2^–. (Received May 15, 1980; )     

Active oxygen participation in chlorophyll destruction and lipid peroxidation in SO2-fumigated leaves of spinach

Chlorophyll a and carotenoids of spinach began to be destroyed2 to 3 hr after fumigation with 2 ppm SO₂ under light, whereaschlorophyll b was undamaged during 8 hr of exposure to SO₂.Pheophytin a was not affected by the fumigation. When disks excised from leaves fumigated with SO₂ at 2 ppm for2 hr were illuminated, chlorophyll a and carotenoids were brokendown, while they were not destroyed in darkness. The destructionof these pigments was suppressed under nitrogen. Chlorophylla destruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate(tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-[2,2,2]-octane(DABCO), methio-nine, histidine, benzoate and formate. Chlorophylla destruction was inhibited by phenazine methosulfate but stimulatedby methyl viologen. Addition of superoxide dismutase (SOD) tothe homogenate of SO₂-fumigated leaves inhibited the chlorophylla destruction. The activity of endogenous SOD was reduced to40% by 2-hr fumigation before the loss of chlorophyll was observed.These results suggest that chlorophyll a destruction by SO₂was due to superoxide radicals (O₂^–). Moreover, malondialdehyde (MDA), a product of lipid peroxidation,was formed in SO₂-fumigated leaves. MDA formation was inhibitedby tiron, hydroquinone and DABCO but not by benzoate and formate.MDA formation was increased by D₂O. These results suggest thatlipid peroxidation in SO₂-fumigated leaves was due to singletoxygen ¹O₂ produced from O_2^–. (Received May 15, 1980; )     

Assimilation of gaseous ammonia and the transport of its products in barley and spinach leaves

The interactions between the assimilation and transport of nitrogenand carbon were investigated in barley and spinach leaves. Bothplants were fumigated with NH₃ (1 mg m^–3 and the contentof amino acids, sucrose and carbon intermediates of amino acidmetabolism were analysed in the leaves, apoplast and phloemsap. The following changes took place in the C- and N-metabolismof barley leaves during 5 h of fumigation with NH₃ (a) The contentsof amino acids, especially glutamine, largely increased andthe contents of sucrose, 2-oxoglutarate, phosphoenolpyruvate,and glycerate-3-phosphate declined. (b) A decrease in the phophoenolpyruvatecontent was accompanied by an increased activity of phosphoenolpyruvatecarboxylase. (c) The altered cytosolic concentrations of aminoacids and sucrose during NH₃ fumigation correlated with similarchanges in the apoplast and phloem sap. The altered percentageof each amino acid relative to the total amino acid concentrationin the cytosol, caused by NH₃ fumigation, is reflected in theapoplast and the phloem sap. The results indicate that the concentrations of amino acids in the cytosol determine their concentrationsin the phloem. Key words: Amino acids, ammonia fumigation, barley leaves, C: N partitioning, phosphoenolpyruvate carboxylase, phloem sap, spinach leaves     

Some Experimental and Theoretical Observations Concerning Mass Flow in the Vascular Bundles of Heracleum

The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, L_EE = 5 ? 10–⁴ mho cm^–1,L_pE = 9 ? 10^–6 cm³ s^–1 cm^–2 volt^–1 cm,and L_PP = 0.16 cm³ s^–1 cm^–2 (J cm^–3)^–1cm. In uncut phloem strands L_EE is about 1 ? 10^–3 mhocm^–1. In xylem in 2 x 10^–3 N KCI, L_pp = 50 to 225,L_PE = 2 ? 10^–4, and L^EE = 4 ? 10^–3. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga ‘long distance’ current pathway can be the majormotive ‘force’ for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm^–1endogenous in the phloem.     

The Effect of Sulphur Dioxide on the Growth of Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L., and Phleum pratense L.

Lockyer, D. R. 1985. The effect of sulphur dioxide on the growthof Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerataL., and Phleum pratense L.?J. exp. Bot. 36: 1851-1859. Fouragriculturally important grasses, Lolium perenne L., Loliummultiflorum Lam., Dactylis glomerata L. and Phleum pratenseL. were exposed to sulphur dioxide (SO₂) in a system of exposurechambers. The plants were exposed for a total of 43 d to meanconcentrations of SO₂ in the air of 0,87 or 448 (µg m^–3and herbage was harvested twice. All four grasses showed chloroticlesions after exposure to the highest concentration of SO₂.The effect of SO₂ on the yield of herbage was statisticallysignificant only at the second harvest and at the highest concentration;the dry weights of shoots of D. glomerata and L. perenne werereduced by 33% and 16% respectively. Significant effects ofSO₂ were also found on the 'transpiration coefficients' measuredfor D. glomerata and P. pratense. The grasses differed in theiruptake of sulphur from the atmosphere but this was not relatedto their sensitivity to SO₂. Total–S concentration inthe shoots of L. perenne, L. multiflorum and D. glomerata increasedalmost linearly in response to increasing SO₂ concentration;with P. pratense only the highest SO₂ concentration raised total-Sabove the level in control plants. These increases were almostentirely due to the accumulation of sulphate–S. Key words: Sulphur diozide, Lolium perenne, Lolium multiflorum, Dactylis glomerata, Phleum pratense     

Sectorial Patterns in Leaves on Fruit Tree Shoots Produced by Radioactive Assimilates and Solutions

In vigorously growing shoots of apple and plum ¹⁴C-assimilateswere translocated from a ‘fed’ leaf to particularsectors of other leaves in a distribution pattern associatedwith the phyllotaxis; the same sectorial and distribution patternswere produced by ³²P phosphate solution taken into the shootthrough a cut petiole. The frequency with which a given sectorialpattern occurred at a particular position on the phyllotacticspiral was ascertained. Such patterns were not observed abovethe third rolled leaf in the apple shoot apex. Killing the phloem in the petiole prevented egress of labelledassimilate but not of ³²P solution. Barkringing above the sourceleaf reduced, but did not completely prevent, assimilate movementup the stem, suggesting some translocation in the xylem. Distribution of label from ⁴⁵CaCl₂, ⁸⁶RbCl and [³H]asparagine,incorporated through cut petioles, did not follow the same patternas label from ³²P solutions. Malus pumila Mill., apple, Prunus domestica L., Prunus insititia. L., leaf plum, patterns, transport of radioisotopes, vascular phyllotaxis     

The Effect of SO2 on Lolium perenne L. Grown at Different Levels of Sulphur and Nitrogen Nutrition

The effects of exposure to SO₂ (55 m^–3) on the growthand sulphur nutrition of perennial ryegrass (Lolium perenneL.) cv. S23 were examined using a system of specially constructedgrowth chambers. The plants were grown in soil with two ratesof added nitrogen, either with or without added sulphate. Theywere harvested twice during the exposure period of 85 d. The high rate of added nitrogen gave a four-fold increase inthe yield of plants given added sulphate but resulted in sulphurdeficiency, with reduced yield and number of tillers, when nosulphate was given. Exposure to SO₂ alleviated the effects ofdeficiency but was without effect on the yield of plants givensulphate. With the low rate of added nitrogen, the yield ofplants and the number of tillers were unaffected by the additionof sulphate to the soil or of SO₂ to the air. The only indicationof possible injury through exposure of these plants to SO₂ wasa small increase in the proportion of dead leaves at the secondharvest. Analysis of the leaves for total S and sulphate-S gave valuesconsistent with sulphur deficiency and its alleviation throughexposure to SO₂; the contents of 0?045% S and 42 parts 10^–6sulphate-S in deficient plants were raised to 0?102% and 153parts 10^–6 respectively. The organic-S content of theleaves was always increased through exposure to SO₂. There wasno evidence that exposure to SO₂ increased the ‘transpirationcoefficient’ for plants having an adequate supply of sulphurfrom the soil.     

Effects of elevated carbon dioxide on three montane grass species: I. Growth and dry matter partitioning

Upland grasslands are a major component of natural vegetationwithin the UK. Such grasslands support slow growing relativelystable plant communities. The response of native montane grassspecies to elevated atmospheric carbon dioxide concentrationshas received little attention to date. Of such studies, mosthave only focused on short-term (days to weeks) responses, oftenunder favourable controlled environment conditions. In thisstudy Agrostis caplllaris L.⁵, Festuca vivipara L. and Poa alpinaL. were grown under semi-natural conditions in outdoor open-topchambers at either ambient (340µmol mol^–1) or elevated(680µmol mol^–1) concentrations of atmospheric carbondioxide (CO₂ for periods from 79 to 189 d, with a nutrient availabilitysimilar to that of montane Agrostis-Fescue grassland in Snowdonia,N. Wales. Whole plant dry weight was increased for A. capillarisand P. alpina, but decreased for F. vivipara, at elevated CO₂.Major components of relative growth rate (RGR) contributingto this change at elevated CO₂ were transient changes in specificleaf area (SLA) and leaf area ratio (LAR). Despite changes ingrowth rate at 680 µmol mol^–1 CO₂, partitioningof dry weight between shoot and root in plants of A. capillarisand P. alpina was unaltered. There was a significant decreasein shoot relative to root growth at elevated CO₂ in F. viviparawhich also showed marked discoloration of the leaves and increasedsenescence of the foliage. Key words: Allometry, growth analysis, elevated CO₂, grasses     

Nutrient Solution pH Control using Dipolar Buffers in Studies of Trifolium repens L. Nitrogen Nutrition

In studies of Trifolium repens nitrogen nutrition, the controlof nutrient solution pH using dipolar buffers, was evaluatedin tube culture under sterile conditions. Five buffers; MES,ADA, ACES, BES and MOPS with pK₂s (20 °C) of 6.15, 6.60,6.90, 7.15 and 7.20 respectively, at a concentration of 2.0mol m^–3, were provided to inoculated Trifolium repensgrowing in nutrient solution containing 7.13 mol m^–3 nitrogenas (NH₄)₂SO₄. Initial pH of each solution was adjusted to theappropriate buffer pK₂ Two buffers, ADA and ACES completelyinhibited plant growth. The remaining buffers had little effectin limiting pH change, although plant dry matter was higherand nodule numbers lower in the presence of these buffers. MESand MOPS were supplied to nutrient solutions with and without7.13 mol m^–3 (NH₄)₂SO₄, at concentrations ranging from0–12 mol m^–3. MES at 9 mol m^–3 and 12 molm^–3 reduced growth of plants reliant on the symbiosisfor providing nitrogen. The provision of MES to plants providedwith NH₄⁺ significantly increased plant yield and reduced nodulenumber at all concentrations. MOPS did not affect plant yieldor nodule number. The use of dipolar buffers in legume nitrogennutrition studies is considered in terms of buffering capacity,and the side effects on plant growth and symbiotic development. Key words: Ammonium, Dipolar buffer, Nitrogen nutrition, pH control, Symbiosis, Trifolium repens     

Temporal Patterns of Uptake, Flow and Utilization of Nitrate, Reduced Nitrogen and Carbon in a Leaf of Salt-Treated Castor Bean (Ricinus communis L.)

Changes in net photosynthesis, respiration, transpiration andcontents of total C, NO₃-N and reduced N were followed throughoutthe life of leaf 6 of nitrate-dependent plants of castor beanexposed to moderate salinity stress (71 mol m^–3 NaCl).Salt treatment was applied for measuring mineral flows in aparallel study (Jeschke and Pate, 1991b). Concurrent measurementswere made of solute composition and C: N molar ratios and concentrationsof reduced N and collected NO₃-N in phloem sap bleeding fromshallow incisions in the top and at the base of petioles andin xylem exudates from flaps of proximal leaf midribs followingpressurization of the root system. The resulting data were usedto construct empirical models of the respective economies ofC, total N, NO₃ and reduced N for a sequence of defined phasesof leaf life. Water use efficiency increased 3-fold from emergenceto a maximum of 1·5 mmol CO₂ mol^–1 H₂O before decliningto 0·5 mmol CO₂ mol^–1 H₂O at senescence. Xylemmolar ratios of C:N varied from 1·2–2·8,with nitrate always a smaller component than reduced N. Phloemsap C:N increased from 10–40 with leaf expansion and wasthen maintained in the range of 40–50 until falling steeplyto 20 at leaf senescence. Nitrate comprised less than 1% oftotal N in all phloem sap samples. The models of C uptake, flow,and utilization showed a major role of phloem import and thenincreasingly of laminar photosynthesis in providing C for leafgrowth. The carbon budget was thereafter characterized by ratesof phloem export closely matched to net rates of CO₂ fixationby the lamina. Corresponding data for total N depicted an earlymajor role of both xylem and phloem import, but the eventualdominance of xylem import as the N source for leaf growth. Cyclingof N by xylem to phloem exchange commenced before the leaf hadachieved maximum N content, and was the major contributor tophloem export until leaf senescence when mobilized N providedmost exported N. The nitrate economy of the leaf was characterizedby early establishment of tissue pools of the ion in the petioleand to a lesser extent in the lamina, continued high rates ofnitrate reduction in the lamina but negligible assimilationin the petiole, and a release through xylem of previously accumulatedNO₃ from petiole to lamina. Related data for reduced N illustratedthe much greater importance of this form of N than nitrate intransport, storage and cycling of N at all stages of leaf andpetiole life. Xylem to phloem interchanges of reduced N in petiolewere minimal in comparison with cycling through the lamina.The ratio of CO₂ reduction to NO₃ reduction in the lamina wasat first low (57 mol mol^–1) increasing to a peak valueof 294 during mature leaf functioning before declining to 190during the presenescence phase of leaf development. This patternreflected age-related effects on water use efficiency, changesin NO₃ levels in the xylem stream entering the lamina, and therelatively low photosynthetic performances of very young andsenescent laminae. Key words: Ricinus communis, leaf development, phloem transport, xylem transport, carbon, nitrogen, nitrate, reduced nitrogen, nitrate reduction, partitioning     

Effects of sulfite and pH on abscisic acid-dependent transpiration and on stomatal opening

In rice, alday, wheat and tobacco (Nicotiana tabacum L. Samsunand Samsun NN) plants which contained large amounts of ABA,the transpiration rate decreased rapidly with 2 ppm SO₂ fumigationand reached 20 to 65% of the initial level after 5- to 30-minexposure depending on their ABA contents. In the cases of broadbean and tobacco (N. glutinosa L.) with low ABA contents, therate slightly increased for 20 and 40 min, respectively, afterthe start of the fumigation and then decreased gradually. Thetranspiration rates of corn and sorghum, in spite of their extremelylow ABA contents, pronouncedly decreased with SO₂ fumigationand reached 65 and 50%, respectively, of the initial levelsafter 40-min exposure. Foliar application of 0.04 N HC1 to N.tabacum L. Samsun NN leaves remarkably depressed the transpirationrate, while the application of 0.04 M Na₂SO₃ decreased the rateonly to the same level as water treatment. Foliar applicationof either HCl or Na₂SO₃ to N. glutinosa L. leaves exerted littlechange in the transpiration rate. When 10^–4M ABA was appliedto broad bean leaves prior to HCl and Na₂SO₃ treatment, theirtranspiration rate was decreased by HCl, but not by Na₂SO₃ application.In sonicated epidermal strips peeled from broad bean leaves,Na₂SO₃ produced a slight increase in the stomatal aperture sizein the absence of ABA, but showed no effect in the presenceof ABA. The aperture size was identical in the pH range of 3.0to 7.0 in the incubation medium. In the presence of ABA in themedium, the aperture size was small in the acidic region ofpH with a minimal value at pH 4.0. ABA decreased the aperturesize at concentrations above 10^–9 M at pH 4.0 and 10^–6M at pH 7.0 in the medium. [2_–14C] ABA uptake by epidermalstrips was large in the acidic region, especially at pH 4.0. (Received February 28, 1980; )     

Influence of Wind Speed on the Sensitivity of Ryegrass to SO2

The sensitivity of S23 Lolium perenne L. to 11 parts 10^–8SO₂ was investigated at two different wind speeds. At the higherwind speed of 25 m min^–8, SO₂ caused significant reductionsin leaf area, root/shoot ratio, and all dry weight fractionsmeasured. At the lower wind speed of 10 m min^–1 growthreductions were not found. The differences in sensitivity ofplants to SO₂ at different wind speeds is discussed in relationto boundary layer resistances of leaves. It is concluded thatthe sensitivity of a plant to a particular pollutant shouldno longer be measured in terms of only the concentration andlength of exposure.     

The Import and Redistribution of Several Cations and Anions in Tomato Leaves

Wolterbeek, H. Th. and De Bruin, M. 1986. The import and redistributionof several cations and anions in tomato leaves.—J. exp.Bot. 37: 331–340. The upward movements in the xylem and redistribution from theleaf of Na⁺ , K⁺ , Rb⁺, Cs⁺ and four anions were examined insub-systems of tomato plants (Lycopersicon esculentum, Mill.cv. Tiny Tim). There was a delay with respect to the redistributionof newly imported elements from the source leaf of about 16–20h for all four alkali ions. This is considerably less than theapparent delay for the anions Sb(SO₄)^– WO₄^2– Mo₇O₂₄^6–and AsO₄^3– The prolonged delay for the anions is suggestedto be a consequence of metabolic transformation in the leaf.Reduction of the source-sink activity ratio did not decreasethe delay period from the source leaf, but apparently causedincreased Na⁺ transfer from the xylem. It is concluded thatthe application of a detailed mathematical descnption of upwardelement movement has considerable potential possibilities forunderstanding circulation of nutrients in the plant. Key words: Alkali ions, anions, xylem, phloem, redistribution, tomato