Effects of 3-Indolylacetic Acid and 3-Indolylacetonitrile on the Growth of Excised Tomato Roots

1. The inhibition by IAA (3-indolylacetic acid) and by IAN (3-indolylacetonitrile)of the growth of excised tomato roots cultured for 7 days at27 C. in a modified White's medium is described. 510^–9g./ml, IAA or 510^–6 g./ml, IAN cause approx, 50 per cent,inhibition of the linear growth of the main axis. With IAA decreasein number of laterals closely parallels the decrease in lineargrowth of the main axis; with IAN reduction in linear growthof the main axis occurs at concentrations above 10^–8 whereasnumber of laterals does not decrease until the concentrationexceeds 10^–6.
2. Study of the course of cell elongationin the exodermal cellsshowed that in the standard medium andin media containing 510^–9IAA or 510^–6 IAN theprocess takes about 7 hours; thefinal cell lengths in IAA andIAN media are lower than in standardmedium owing to a slowerrate of elongation. The decrease inlinear growth of the mainaxis in presence of IAA could be accountedfor by the decreasein cell length; this was not the case withIAN. The implicationsof this are considered.
3. Determinations of the distance (mm.)between, and of the numberof exodermal cells separating, theadjacent laterals in oneorthostichy showed that IAN enhancesthe frequency of lateralswhereas this is either unaffectedor decreased by IAA. The enhancementof lateral frequency inIAN arises from shortening of the cellsof the main axis anddecrease in the number of cells separatingadjacent laterals.
4. The results are considered to support the view that IAN haseffects on root growth different from those of IAA. Study ofthe degree of inhibition of main axis growth and of alterationsin lateral frequency resulting from treatment with mixturesof IAA and IAN provided data which could also be most easilyexplained on this hypothesis.

     

Nutrient Supply and the Growth of the Seminal Root System in Barley: I. THE EFFECT OF NITRATE CONCENTRATION ON THE GROWTH OF AXES AND LATERALS

A method was devised by which different zones along a singleseminal axis of an intact plant could be exposed for extendedperiods to contrasting concentrations of nitrate (either 0.01or 1.0 mM) in continuous flow, the supply of all other nutrientsbeing favourable throughout. The concentration of nitrate wasfound to exert a direct and strictly localized effect upon thegrowth of lateral roots which, depending upon the supply ofassimilates from the shoot, resulted in marked modificationsto the form of the root system. Zones receiving 1.0 mM nitrateshowed an increase in the number and extension rate of bothfirst- and second-order laterals, associated with a preferentialaccumulation of dry matter, compared with zones in 0.01 mM nitrate.The average number of laterals (both first and second order)per cm of parent root was 4.4 in the presence of 1.0 mM nitrateand 2.2 in 0.01 mM. The average extension rates of first-orderlaterals were 0.61 and 0.26 cm d^–1 and second-order laterals,0.10 and 0.05 cm d^–1 for nitrate concentrations of 1.0and 0.01 mM respectively. The precise numbers and extensionrates of laterals in any one zone were affected, however, bythe rate of growth of laterals in other parts of the root system.In contrast, the extension rates of axes were little affectedby the concentration of nitrate to which their apical meristemswere exposed and approached 2.0 cm d^–1 provided the plantswere not nitrogen-starved. The significance of these resultsto the physiology of root growth and soil-plant relations isdiscussed.     

The Uptake of Nitrate by Lolium perenne from Flowing Nutrient Solution: I. EFFECT OF CONCENTRATION

Experiments with simulated swards of perennial ryegrass (Loliumperenne L.) show the relationship between concentration in flowing nutrient solution, nitrate uptake,plant growth, and the chemical composition of roots and shoots.Rates of uptake exceeding 1 g N m^–2 d^–1 were maintainedat concentrations in solution down to 0•02 mg N l^–1. Short-term studies confirmed that at such lowconcentrations the plants were able to maintain rates of uptakeof about 85% of maximum. Between 0•2 and 200 mg N l^–1the concentration of in solution had little effect on rate of uptake or plant growth. With at 1000 and 2000 mg N l^–1 there was a marked reductionin weight of the shoots and, more particularly, in the lengthand tensile strength of the roots. There were several significanttrends in mineral composition of the plants (notably in S, Ca,Mg) which were apparently correlated with increasing concentrationof in solution.     

Turgor, Growth and Rheological Gradients of Wheat Roots Following Osmotic Stress

The growth rate of hydroponically grown wheat roots was reducedby mannitol solutions of various osmotic pressures. For example,following 24 h exposure to 0·96 MPa mannitol root elongationwas reduced from 1· mm h^–1 to 0·1 mm h^–1 Mature cell length was reduced from 290 µm in unstressedroots to 100 µm in 0·96 MPa mannitol. This indicatesa reduction in cell production rate from about 4 per h in theunstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4·5 mm in unstressedroots but became shorter as growth ceased in the proximal regionsat higher levels of osmotic stress. The turgor pressure along the apical 5·0 mm of unstressedroots was between 0·5 and 0·6 MPa but declinedto 0·41 MPa over the next 50 mm. Following 24 h in 0·48(200 mol m^–3) or 0·72 MPa (300 mol m^–) mannitol,turgor along the apical 50 mm was indistinguishable from thatof unstressed roots but turgor declined more steeply in theregion 5·10 mm from the tip. At the highest level ofstress (0·96 MPa or 400 mol m^–3 mannitol) turgordeclined steeply within the apical 20 mm. Key words: Growth, turgor pressure, wall rheology, osmotic stress, osmotic adjustment     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: IV. TRANSLOCATION AND REMOBILIZATION OF NITROGEN

Barley (Hordeum vulgare L., cvs Golf and Laevigatum) was grownunder nitrogen limitation in solution culture until near maturity.Three different nitrogen addition regimes were used: in the‘HN’ culture, the relative rate of nitrate-N additionwas 0·08 d^–1 until day 48 and then stepwise decreasedto, finally, 0·005 d^–1 during late grain-filling;the ‘LN’ culture received 45% of the nitrogen addedin HN; the ‘CN’ culture was maintained at RA 0·0375d^–1 throughout growth. At four different growth stages(vegetative,anthesis, and twice during grain-filling), ¹⁵N-nitrate was fedto the plants. In some cases (‘split root cultures’),label was fed only to one-half of the root system. These wereharvested directly after labelling, whereas ‘standardcultured’ plants were harvested at termination of theexperiment (day 148). Absorption of added nitrate was nearlycomplete in the HN and LN cultures, and translocation of nitrogenwithin the plants could thus be studied independently of differencesin nitrate absorption. Cycling of nitrogen absorbed by vegetativeplants accounted for up to 50% of the nitrogen recovered inthe roots. The sink strength of the roots for cycling nitrogen,however, declined during post-anthesis growth, and net lossof nitrogen from both roots and vegetative shoot tissue occurredconcomitantly with incorporation of labelled ¹⁵N-nitrogen. Thenitrogen of the vegetative shoot tissue was substantially lesslabelled than the nitrogen entering the ears, indicating thattranslocation of recently absorbed nitrogen to ears occurs withminor prior exchange with the bulk nitrogen of shoots. In caseswhere the sink strength of the ears was weak, as in LN-culturedLaevigatum (due to high frequency of sterile flowers) and inCN-cultured Golf, nitrogen translocated from roots appearedto be incorporated into the vegetative shoot tissue. There werealso indications that a fraction of the remobilized nitrogenwas actually lost from the plants in these cases. It is concludedthat the root remains efficient in translocation of nitrogento the aerial parts throughout ontogeny and that nitrogen takenup during grain–filling is preferentially directly translocatedto the developing grains. The further translocation of nitrogenreceived by vegetative shoot parts to ears appears mainly relatedto the potential of the ear to accumulate nitrogen. Nitrogenabsorbed/remobilized in excess of the sink strength of the earsis either invested in continued shoot growth, or is irreversiblylost from the plants. Key words: Barley, ¹⁵N-labelling, post-anthesis, remobilization, translocation     

Nutrient Supply and the Growth of the Seminal Root System in Barley: II. LOCALIZED, COMPENSATORY INCREASES IN LATERAL ROOT GROWTH AND RATES OP NITRATE UPTAKE WHEN NITRATE SUPPLY IS RESTRICTED TO ONLY PART OF THE ROOT SYSTEM

The development of the seminal root system, its ability to absorbnitrate, and effects on shoot growth were studied in barleyplants in nutrient solution. The roots received either a uniformsupply of 1.0 mM nitrate (controls), or a supply of the samesolution restricted to a 4-cm length of only one of the mainseminal roots (axes) on each plant, the remainder of the rootsystem receiving a solution containing a low concentration (0.01mM). Marked increases took place in both the growth of lateralroots and the absorption and transport of ¹⁵N-labelled nitrate(per unit root weight) from the zone locally supplied with 1.0mM nitrate. These effects appear largely to compensate for thedeficient supply of nitrate to the remainder of the root system,since after 14 d the relative growth rate (g g^–1d^–1)of the total plant equals that of the controls. Rates of ¹⁵N-nitrateuptake (per unit root weight) remain relatively uniform throughoutthe 29-d experiment, during which root axes develop from theirinitial unbranched form to a complex system of laterals. Theresults are discussed in relation to possible mechanisms bywhich coordination is maintained between root growth, ion uptake,and shoot growth.     

Acid phosphatase role in chickpea/maize intercropping

• Background and aims Organic P comprises 30–80 %of the total P in most agricultural soils. It has been proventhat chickpea facilitates P uptake from an organic P sourceby intercropped wheat. In this study, acid phosphatase excretedfrom chickpea roots is quantified and the contribution of acidphosphatase to the facilitation of P uptake by intercroppedmaize receiving phytate is examined. • Methods For the first experiment using hydroponics, maize(Zea mays ‘Zhongdan No. 2’) and chickpea (Cicerarietinum ‘Sona’) were grown in either the sameor separate containers, and P was supplied as phytate, KH₂PO₄at 0·25 mmol P L^–1, or not at all. The second experimentinvolved soil culture with three types of root separation betweenthe two species: (1) plastic sheet, (2) nylon mesh, and (3)no barrier. Maize plants were grown in one compartment and chickpeain the other. Phosphorus was supplied as phytate, Ca(H₂PO₄)₂at 50 mg P kg^–1, or no P added. • Key results In the hydroponics study, the total P uptakeby intercropped maize supplied with phytate was 2·1-foldgreater than when it was grown as a monoculture. In the soilexperiment, when supplied with phytate, total P uptake by maizewith mesh barrier and without root barrier was 2·2 and1·5 times, respectively, as much as that with solid barrier.In both experiments, roots of both maize and chickpea suppliedwith phytate and no P secreted more acid phosphatase than thosewith KH₂PO₄ or Ca(H₂PO₄)₂. However, average acid phosphataseactivity of chickpea roots supplied with phytate was 2–3-foldas much as maize. Soil acid phosphatase activity in the rhizosphereof chickpea was also significantly higher than maize regardlessof P sources. • Conclusions Chickpea can mobilize organic P in both hydroponicand soil cultures, leading to an interspecific facilitationin utilization of organic P in maize/chickpea intercropping.     

Environmental Control of Flower Number in Multi-flowered Cultivars of Pisum sativum L.

Pea cultivars capable of regularly producing more than two flowersper node were grown at temperatures ranging from 10 to 25 °C.There was positive correlation between flower number per nodeand air temperature. Genotypic variation in the size of thisresponse to temperature was observed. For example, those cultivarswitha mean of 3•0 flowers per node at 10 °C gave meansof 6•2, 5•7 and 3•5 at 25 °C. The concentrationof soluble sugars in the shoot at flower initiation was negativelycorrelated with air temperature and flower number per node.An increase in radiation intensity from 60 to 120 J m^–2s^–1 however, resulted in increased numbers of flowersper node. These environmental effects are contrasted with effectson cultivars regularly producing fewer than two flowers pernode and possible control mechanisms are indicated.     

Nutrient Supply and the Growth of the Seminal Root System in Barley: III. COMPENSATORY INCREASES IN GROWTH OF LATERAL ROOTS, AND IN RATES OF PHOSPHATE UPTAKE, IN RESPONSE TO A LOCALIZED SUPPLY OF PHOSPHATE

Responses to a localized supply of phosphate were studied inbarley grown in continuous flow solution culture. Root systemswere either uniformly supplied with 50 µM phosphate (controls)or the same solution was supplied to only a 4 cm or 2 cm lengthof a seminal root (localized supply), the remainder of the rootsystem receiving a nutrient solution lacking phosphate. Little development of laterals occurred on those parts of theroot system receiving no phosphate from the external solution,while an increase in the number and extension of laterals tookplace in the 4 cm zone enriched with phosphate. Compared withsimilar zones on controls, the total length of laterals wasincreased 15-fold in 21 d plants. In addition, rates of ³²P-phosphateuptake and translocation to shoots per unit root weight werehigher than in controls by a factor of 2?5–5?0. Furtherincreases in the growth of lateral roots, and rates of phosphateuptake, were induced when the segment initially supplied withphosphate was restricted to only 2 cm. These localized modifications to root growth and uptake of phosphatelargely compensated for the deficient supply of phosphate tothe remainder of the root system. After an early period of retardedgrowth and phosphate stress, the relative growth rate of plantsand the concentration of phosphate in shoots were restored tolevels similar to that of the controls. The manner in which the supply of phosphate may control rootdevelopment, and the nature of the co-ordination between rootgrowth, phosphate uptake, and shoot growth, are discussed.     

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     

The Effects of Mechanical Impedance to Growth on the Levels of ABA and IAA in Root Tips of Zea mays L.

Extraction and analytical methods have been refined and newones devised to allow precise determinations by GC-EC of thelevels of abscisic acid (ABA) and indol-3ylacetic acid (IAA)in samples of maize root tips as small as 1.0 g fr. wt. Seminalroots of 5-d-old maize seedlings grown in normal (bulk density1200 kg m^–3) and compacted (bulk density 1600 kg m^–3)sand/garden loam mixtures have been examined. Seminal rootsfrom compacted soil had an average length of about 40% of thatof control roots and were much thicker. The ABA levels in 10mm tips of impeded roots (c. 25–35 ng g^–1 fr.wt.)did not differ significantly from those of normal root tipson both a fresh and dry weight basis. The levels in 0–1mm tips were approximately double those in the remaining 1–10mm zones. IAA levels were increased by about 3 times in impededroots (176.3 as compared with 52.4 ng g^–1 fr.wt) and itis concluded that this response is likely to be the main causeof the morphological and growth changes brought about by soilcompaction.     

Anatomy, Ultrastructure and Assimilate Concentrations of Roots of Citrus Genotypes Differing in Ability for Salt Exclusion

Seedlings of Rangpur lime (Citrus reticulata var. austera hybrid?)and Etrog citron (C. medica) were treated in water culture with0, 25, 50 or 100 mol m^–3 NaCl, and in sand culture with0 or 100 mol m^–3 NaCl. Leaf chloride analyses indicatedthat Etrog citron accumulated the most chloride at all levelsof salinity. The structure, ultrastructure and concentrationsof chloride and reserve assimilates of the primary root up to50 mm back from the tip were compared between genotypes andbetween salt treatments. There were no differences in root anatomy in the absence ofsalt between the two genotypes. The hypodermal cells developedlignified and suberized walls which blocked the plasmodesmataand resulted in degeneration of the cell contents. Frequentthin-walled passage cells in the hypodermis had living contentsand may represent major sites of ion uptake into the symplasm,which was connected with the stele via plasmodesmatal connectionswith and between the cortical cells. The primary endodermalcells had lignified casparian strips and plasmodesmata in othercell wall areas. These connections were blocked by secondarysuberization of all except the endodermal passage cells oppositethe protoxylem arcs. Suberization of the hypodermis and endodermis and the appearanceof granular deposits in the vacuole occurred closer to the roottip of both genotypes after treatment with 100 mol m^–3NaCl. Levels of starch and triglyceride in 10 mm serial segmentswere similar between roots of control and salt-treated plantsand increased with distance back from the root tip. Chlorideconcentrations increased with salt treatment but values (ona tissue water basis) were similar between genotypes and betweenthe apical and proximal ends of the root. Reducing sugar concentrationsdecreased with salt treatment to a similar extent in roots ofboth genotypes. Key words: Citrus, Roots, Salinity     

Respiration and Phloem Translocation in the Roots of Chickpea (Cicer arietinum)

Root growth in chickpea (Cicer arietinum) has been studied fromthe early vegetative phase to the reproductive stage in orderto elucidate its growth and maintenance respiration and to quantifythe translocation of assimilates from shoot to root. A carbonbalance has been drawn for this purpose using the growth andrespiration data. The increase in the sieve tube cross-sectionalarea was also followed simultaneously. Plants growing in a nutrient culture medium were studied todetermine the relative growth rate (RGR) 5–60 d aftergermination. RGR declined from 113 to 41 mg d^–1 g^–1during the measurement period. Simultaneous with the RGR analysis,respiration rate was also measured using an oxygen electrode.The respiration rate declined as the plants aged and a drasticreduction was recorded following anthesis. The relationshipbetween RGR and respiration rate was used to extrapolate themaintenance respiration (m) and growth respiration (1/Y_EG).The respiration quotient (r.q.) of the roots was 1.2 and theQ₁₀ in the range 20–25 °C was 2·2. A carbon balance for the roots was constructed by subtractingthe carbon lost during respiration from that gained during growth.The roots were found to respire no less than 80% of the carbontranslocated. The increase in the cross-sectional area composed of sieve tubeswas measured near the root-shoot junction as the plants grew.Chickpea has storied sieve plates which simplifies these measurements.Their cross-sectional area increased during growth mainly becauseof an increase in sieve tube number. The diameter of individualsieve tubes remained constant. Specific mass transfer (SMT) values for seive tubes into theroots have been computed during various stages of growth. SMTvalues were relatively constant before anthesis (approx. 6·5g h^–1 cm^–2), but decreased following anthesis. Wedid not evaluate possible retranslocation from roots: any suchretranslocation would have the effect of increasing our SMTvalues. Chickpea, Cicer arietinum, legume, root, respiration, phloem, translocation, carbon balance, specific mass transfer, sieve-tube dimensions     

Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina (Forsk.) Vierh.)

The roots of young plants of Avicennia marina (Forsk.) Vierh.grown under simulated tidal conditions were harvested so asto obtain the entire root system. The roots were subdividedand weighed and subsamples taken for manometric determinationof respiration rates at different temperatures. The supply capacityof the above-ground portion of the root system was determinedand the results compared in terms of supply and demand. Theoxygen consumption rate of the roots at 15°C was found tobe 1·69±0·07 µmol kg^–1 s^–1for cable roots and 3·27±0·12 µmolkg^–1 s^–1 for fine roots. The Q₁₀ for respirationwas 2·55 for oxygen consumption in both fine and cableroots, and for carbon dioxide production was 2·66 forfine roots and 3·04 for cable roots. The respiratoryquotient varied with temperature but was less than unity. Concentrationdifferences of between 1·8 mol m^–3 and 3·4mol m^–3 between the inside of root and the air were sufficientto permit aeration of the root system by diffusion alone, andthe aerenchyma contained sufficient oxygen to maintain aerobicconditions while the roots were covered with water. The effectof tide and seasonal temperature change on gas exchange, togetherwith the possibility of some form of carbon dioxide fixationwithin the root, are examined and the implications of theseeffects on growth and development are discussed. Key words: Mangrove, root aeration, respiration, aerenchyma     

Effects of Kinetin on Growth of the Apical Meristem and Floral Differentiation in Chenopodium rubrum L.

Kinetin (1•10^–4 M and 1•10^–3 M) was appliedto the plumules of 6-day-old Chenopodium rubrum plants. Effectson growth, anatomical structure and organogenesis in the apicalmeristem were followed. Floral differentiation as affected bykinetin was also investigated in plants induced to flower byshort-day treatment. Kinetin increased mitotic activity in the apical meristems inboth induced and non-induced plants. The effect was most pronouncedin the peripheral and subcentral zone. An increase in nucleolussize and a higher degree of pyroninophilia in the peripheralzone was also observed, indicating a localized promotion ofRNA synthesis. A higher rate of leaf initiation and a stimulationof leaf and stem growth was subse quentiy recorded. The growthof axillary meristems and of bud primordia was promoted onlyat the lower concentration of kinetin (1•^10–4 M),in both photoperiodically-induced and non-induced plants. However,the pattern of lateral bud growth differed from that found innormal floral differentiation. In kinetintreated plants, thebud primordia are isolated from the summit of the shoot apexby a succession of rapidly growing leaves. The enhancement ofleaf growth leads to correlative inhibition of axillary budpriniordia and results, finally, in a suppression of floraldifferentiation. The inhibitory effect of kinetin on floweringwas compared with that of auxin. Inhibition of flowering occurredin both cases but is achieved in two different ways.     

Growth and Development of Roots of Grapevine (Vitis vinifera L.) in Relation to Water Uptake from Soil

Developmental patterns of lateral roots and their vascular differentiationwere investigated for Vitis vinifera L. cv. Shiraz to assessthe likely contribution of lateral roots to total water uptakeof plants subjected to different irrigation regimes. Correlationanalyses showed a significant positive correlation between mainroot diameter and the diameter of first order lateral rootsof well-watered plants, but in water-stressed plants the twowere not significantly correlated. The correlations betweendiameters of first order lateral roots and the diameters ofmain roots were greater than correlations between the lengthsof first order laterals and the diameters of main roots. Thesuberised surface area of well-watered main roots increasedfrom 4% of total surface area at 0·25 cm to 100% at 10cm from the tip, whereas that of stressed plants increased from15% at 0·25 cm to 100% at 5 cm from the tip. In all treatmentsthe highest linear density of first order laterals was about7 laterals cm^-1 of main root. More than 50% of first order lateralshad diameters less than 0·05 cm, and more than 90% ofthem had lengths less than 5 cm. Calculations of axial resistancesbased on xylem diameter measurements suggest that the axialresistances of root segments may not be uniform along rootsas is often assumed in models of water uptake. Water flow intothe main roots via the lateral root pathway is likely to bemuch smaller than that via the direct radial flow pathway asonly about 1% of surface area of main roots is directly occupiedby lateral roots, leaving the other 99% of main root surfacearea available for the direct radial flow pathway.Copyright1994, 1999 Academic Press Axial resistance, grapevine (Vitis vinifera L. cv. Shiraz) roots, root diameter, root length, xylem vessels     

The Uptake and Distribution of Copper in Some Forage Grasses as Affected by Nitrate-nitrogen Supply in Flowing Solution Culture

The effect of changes in nitrate-nitrogen supply on the absorptionand distribution of copper was examined in grasses grown inflowing solution culture with a maintained concentration ofcopper. Absorption by roots (µg Cu g^–1 dry root)decreased markedly when nitrogen had been depleted or was maintainedat 0.1 mg l^–1 N, but there was an immediate increase whennitrogen was maintained at 1.0 or 10.0 mg l^–1. There werealso large increases in the concentration of copper in the shootsof plants grown with 1.0 and 10.0 mg 1^–1 N. The rootsof plants grown with 0.1 or 1.0 mg 1^–1 N retained similarproportions of uptake, but a lower proportion was retained whenthe plants were grown with 10.0 mg 1^–1. Although a lowerproportion of the copper was associated with cell walls in theplants grown at 10.0 mg 1^–1 N this was the result of alower content of cell walls rather than an effect on copperitself. In a longer-term experiment in conventional solutionculture with a range of nitrogen concentration, the concentrationof copper in shoots was largely determined by shoot growth. Dactylis glomerata, Festuca arundinacea, Lolium perenne, cell walls, copper absorption, copper distribution, flowing solution culture, nitrate-nitrogen     

Ion Transport in Suaeda maritima: Its Relation to Growth and Implications for the Pathway of Radial Transport of Ions across the Root

The ion relations of the halophytc Suaeda maritima are described.When plants grew in 340 mol m^–3 sodium chloride (—1•76MPa) leaf solute potentials decreased, and were sustained around—2•5 MPa Inorganic ion concentration (mostly of sodiumchloride) accounted for this. Comparable shoot ion concentrationsof potassium, nitrate and sulphate occurred when plants grewon different salinity types characterized by these ions. Netsodium transport and shoot sodium concentration increased dramaticallywith increases in external sodium chloride concentration upto 85 mol m^–3; thereafter, further increases in externalsodium chloride concentration had relatively little effect uponeither shoot sodium concentration or upon net transport of sodiumto the shoot. The net transport of sodium plus potassium onlydoubled when the external concentration of sodium plus potassiumincreased from 24 to 687 mol m^–3 Shoot ion concentrationswere remarkably constant with time, external concentration andsalinity type. The membrane flux rates and symplasmic ion concentrations neededto sustain the observed net transport of sodium (of some 10mmol g^–1 dry wt. of roots d^–1) are calculated fromanatomical and stereological data for the root system of thisspecies. The minimum net sodium chloride flux to load the symplasmwould be 260 nmol m^–2s^–1 if the whole cortical andepidermal plasmalemmal surface area were used uniformly, butthe flux rate required would be 3000 nmol m^–2s^–1if uptake took place only at the root surface. A flux rate ofat least 1000 nmol m^–2s^–1 is needed between symplasmand xylem. The symplasmic concentration of NaCl would be atleast 80 mol m^–3. It is argued (1), that both symplasmicand xylem loading are likely to be passive processes mediatedby ion channels rather than active carriers, (2), that net iontransport at 340 mol m^–3 sodium chloride is close to themaximum which is physiologically sustainable and (3), that growthof this halophyte is limited by NaCl supply from the root. Key words: Suaeda maritima, halophyte, salinity, roots, radial ion transport     

Studies on the Formation of Roots and Shoots in Wheat Callus Cultures

Callus tissues were initiated from root, embryo and inflorescenceexplants of wheat. These callus cultures were used to studythe formation of roots and shoots in the absence and presenceof selected plant hormones. On a basal medium alone, only newly-initiatedembryo callus formed both roots and shoots while root callusonly formed roots. Inflorescence callus showed no signs of differentiation.The regenerative capacity of root and embryo callus tissueson medium lacking hormones decreased with increasing periodsof culture. Calluses which failed to differentiate in the absenceof hormones were selected for studies on hormone-mediated differentiation.NAA (1 mg 1^–1) was effective in inducing roots from allcalluses irrespective of their origin or age. In contrast, shootformation was elicited by incubating newly-formed callus onbasal medium supplemented with kinetin (5 mg 1^–1) andNAA (1 mg 1^–1) but rapidly decreased with longer periodsof culture. The differences observed in differentiation of thecallus in the absence and presence of hormones is discussed.     

Effects of Aluminium on Honeylocust (Gleditsia triacanthos L.) Seedlings in Solution Culture

Honeylocust (Gleditsia triacanthos L.) seedlings were grownin solution culture at pH 4.0) with 50, 150, 600 and 1500 mmolm^–3 aluminium. All levels of aiuminium reduced the sizeand weight of roots, shoots and leaves with the exception ofroot elongation at 50 mmol m^–3 Al. Aluminium content ofroots was 50 to 100 times that of shoots. With increasing concentrationof aluminium, aluminium content of leaves and roots increasedexponentially while a linear increase was observed for stems.The nutrient content of seedlings was improved in 50 mmol m^–3where increases in shoot calcium, magnesium, and phosphorusconcentrations were observed. Aluminium concentrations greaterthan 50 mmol m^–3 reduced shoot nutrient content. Presenceof aluminium increased the root phosphorus and calcium levelsbut had no effect on potassium and magnesium concentrations.Results show that honeylocust is an aluminium sensitive treespecies whose growth may be reduced by high soil Al levels. Key words: Aluminium toxicity, Gleditsia triacanthos, nutrient solution