Effects of Root Temperature and Form of Nitrogen Nutrition on Nitrate Reductase Activity in Oilseed Rape (Brassica napus L.)

The effect of root temperature and form of inorganic nitrogensupply on in vitro nitrate reductase activity (NRA) was studiedin oilseed rape (Brassica napus L. cv. bien venu). Plants weregrown initially in flowing nutrient solution containing 10 µMNH₄NO₃ and then supplied with either nitrate or ammonium for15 d at root temperatures of 3, 7, 11 or 17 °C. Shoot temperatureregime was similar for all plants; 20/15 °C, day/night.Root NRA was highest when roots were grown at 3 and 7 °C.In laminae and petioles NRA was highest when roots were 11 or17 °C. The plants supplied with ammonium had much lowerlevels of NRA in roots after 5 d than the plants supplied onlywith nitrate. NRA in the laminae of plants supplied with ammoniumwas low relative to that in plants supplied with nitrate onlywhen root temperature was 11 or 17 °C. Values of the apparent activation energy (E_a) of NR, calculatedfrom the Arrhenius equation, in laminae and petioles were differentfrom roots suggesting difference in enzyme conformation. Evidencethat the temperature at which roots were growing affected E_awas equivocal. Oilseed rape, Brassica napus L., activation energy, ammonium, Arrhenius equation, nitrate, root temperature, nitrate reductase     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis I. Anatomy and Respiration in Triticum aestivum L.

Anatomical changes in roots of wheat seedlings (Triticum aestivumL. cv. Hatri) following oxygen deficiency in the rooting mediumwere investigated. The response of the plant to stress was testedat a very early developmental stage when the first adventitiousroots had just emerged. In order to analyze the adaptation ofdifferent roots, respiration rates of the roots 1–3 and4–n were compared with the respiration rates of the totalroot system. Oxygen deficiency was induced either by flushingnutrient solution with nitrogen or flooding of sand. In contrast to plants grown in well aerated media, both stressvariants led to a significant increase of the intercellularspace of the root cortex in seminal and first adventitious roots.Radial cell enlargement of cortical cells near the root tip,cell wall thickenings in flooded sand cultures and an increasein phloroglucinol-stainable substances were found to be furtherindicators of low oxygen supply. The roots 4–n which were promoted in growth under hypoxiashowed higher respiration rates; hence the total root respirationwas not restricted. Triticum aestivum L. cv. Hatri, wheat, roots, anatomy, anaerobiosis, stress, root respiration, intercellular space     

Increased Synthesis of ABA in Partially Dehydrated Root Tips and ABA Transport from Roots to Leaves

Zhang, J. and Davies, W. J. 1987. Increased synthesis of ABAin partially dehydrated root tips and ABA transport from rootsto leaves.—J. exp. Bot. 38: 2015–2023. Isolated root tips of pea (Pisum sativum L. cv. Feltham First)and Commelina communis L. were air-dried until they lost between10% and 40% of their fresh weight, followed by a period of incubationat these reduced water contents. These treatments resulted inincreased ABA production, suggesting that root tips of bothspecies have the capacity to synthesize ABA in increased amountswhen water deficits develop in the root. The ABA concentrationin pea roots increased linearly as turgors fell below about0·15 M Pa and relative water contents (R WC) fell below90%. Commelina roots produced more ABA when RWC fell below asimilar value but the threshold turgor for increased ABA productionin Commelina roots was around 0·30 MPa. Roots of intact plants loaded with ABA as a result of incubationin solutions of varying concentrations provided ABA to leaveswhich resulted in increased ABA concentrations in the leaveswhen these were assayed several hours later. This occurred whenthese roots were not contributing substantially to transpirationalflux. Leaves on shoots that were enclosed and darkened and thereforenot transpiring, did not accumulate ABA from ‘loaded’roots. A role for root-sourced ABA in root-to-shoot communication ofthe effects of soil drying is discussed. Key words: ABA, roots, water relations     

Influences of Water Status, Temperature, and Root Age on Daily Patterns of Root Respiration for Two Cactus Species

Daily patterns of root respiration measured as CO₂, efflux werestudied at various soil water potentials, temperatures, androot ages for individual, attached roots of the barrel cactusFerocactus acanthodes and the platyopuntia Opuntia ficus-indica.The daily patterns of root respiration for both establishedroots and rain roots followed the daily patterns of root temperature.Root respiration increased when root temperature was raisedfrom 5 °C to 50 °C for F. acanthodes and from 5 °Cto 55 °C for O. ficus-indica; at 60 °C root respirationdecreased 50° from the maximum for F. acanthodes and decreased25° for O. ficus-indica. Root respiration per unit d. wtdecreased with root age for both species, especially for rainroots. Root respiration rates for rain roots were reduced tozero at a soil water potential (     

Early Effects of Excess Boron on Photosynthesis and Growth of Cucurbita pepo

Summer squash plants {Cucurbita pepo L., cv. ‘Early ProlificStraightneck’) hydroponically cultured under optimal boronnutrition (+ B)³ until age 5 d were transferred to hydroponicsolutions supplemented with excess boron (+ + B)³. As boronaccumulated in the leaves with time, leaf conductance to watervapour, ¹⁴CO₂ fixation, and chlorophyll content of the oldestleaf became significantly less than in the + B-control plantsof the same age; shoot growth essentially ceased. Boron alsoaccumulated in the roots; concomitant inhibition of root elongationand lateral root development resulted. These metabolic changesall occurred prior to the accumulation of sufficient boron tocause the appearance of any symptoms characteristic of borontoxicity. Key words: Boron toxicity, Stomatal conductance, Photosynthesis, Transpiration, Shoot and root growth, Cucurbita pepo     

Effects of Low Temperature on the Development and Morphology of Rye (Secale cereale) and Wheat (Triticum aestivum)

Seedlings of Secale cereale cv. Rheidol and Triticum aestivumcv. Mardler were grown at shoot/root temperatures of 20/20 °C,20/8 °C and 8/8 °C. During vegetative growth both cerealsproduced leaves, tillers and roots in a defined pattern, ata species-specific rate which was linearly related to the temperatureof the shoot meristem. Thus, plant development could be standardizedon a temperature x time (°C d) basis despite contrastinggrowth-temperature treatments. When compared at a similar developmentalstage, the cooling of whole plants or of plant roots resultedin an increase in the d. wt: f. wt ratio of both shoot and roottissues, a decrease in the length of both the longest shootand root, and the development of broader and thicker leaves.Although the effects of temperature on developmental characteristicscould be accurately predicted by an empirical relationship,the effects on morphological characteristics could not. Development, phyllochron, rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Thermal and Water Relations of Roots of Desert Succulents

Two succulent perennials from the Sonoran Desert, Agave desertiEngelm. and Ferocactus acanthodes (Lem.) Britton and Rose, loselittle water through their roots during drought, yet respondrapidly to light rainfall. Their roots tend to be shallow, althoughabsent from the upper 20 mm or so of the soil. During 12–15d after a rainfall, new root production increased total rootlength by 47 per cent to 740 m for A. deserti and by 27 percent to 230 m for F. acanthodes; root dry weight then averagedonly 15 per cent of shoot dry weight. The annual carbon allocatedto dry weight of new roots required 11 per cent of shoot carbondioxide uptake for A. deserti and 19 per cent for F. acanthodes.Elongation of new roots was greatest near a soil temperatureof 30°C, and lethal temperature extremes (causing a 50 percent decrease in root parenchyma cells taking up stain) were56°C and -7°C. Soil temperatures annually exceeded themeasured tolerance to high temperature at depths less than 20mm, probably explaining the lack of roots in this zone. Attached roots immersed in solutions with osmotic potentialsabove -2·6 MPa could produce new lateral roots, with50 per cent of maximum elongation occurring near -1·4MPa for both species. Non-droughted roots lost water when immersedin solutions with osmotic potentials below -0·8 MPa,and root hydraulic conductance decreased markedly below about-1·2 MPa. Pressure-volume curves indicated that, fora given change in water potential, non-droughted roots lostthree to five times more water than droughted roots, non-droughtedleaves, or non-droughted stems. Hence, such roots, which couldbe produced in response to a rainfall, will lose the most tissuewater with the onset of drought, the resulting shrinkage beingaccompanied by reduced root hydraulic conductance, less contactwith drying soil, and less water loss from the plant to thesoil. Agave deserti, Ferocactus acanthodes, roots, soil, temperature, water stress, drought, Crassulacean acid metabolism, succulents     

Hydraulic and osmotic properties of spruce roots

Hydraulic and osmotic properties of roots of 2-year-old Norwayspruce seedlings (Plcea abiea (L.) Karst) were investigatedusing different techniques (steady flow, pressure probe, andstop flow technique). Root pressures were measured using theroot pressure probe. Compared to roots of herbaceous plantsor deciduous trees, excised root systems of spruce did not developappreciable root pressure (-0.001 to 0.004 MPa or -10 to 40cm of water column). When hydrostatic pressure gradients wereused to drive water flows across the roots, hydraulic conductivities(Lp_r) were determined in two types of experiments: (i) rootpressure relaxations (using the root pressure probe) and (ii)steady flow experiments (pneumatic pressures applied to theroot system or xylem or partial vacuum applied to the xylem).Root Lp_r ranged between 0.2 and 810^–8m s^–1 MPa^–1(on average) depending on the conditions. In steady flow experiments,Lpr depended on the pressure applied (or on the flow acrossthe roots) and equalled (0.190.12) to (1.21.7)10^–8m s^–1 MPa^–1 at pressures between 0.2 and 0.4 MPaand (1.51.3)10^–8 m s^–1 MPa^–1 at appliedpressures between 0.8 and 1.0 MPa. When pressures or vacuumwere applied to the xylem, Lp_r values were similar. The hydraulicconductivity measured during pressure relaxations (transientwater flows) was similar to that obtained at high pressures(and water flows). Although there was a considerable scatterin the data, there was a tendency of the hydraulic conductivityof the roots to decrease with increasing size of the root system.When osmotic gradients were used to drive water flows, Lp_r valuesobtained with the root pressure probe were much smaller thanthose measured in the presence of hydrostatic gradients. Onaverage, a root Lp_r=0.01710^–8 was found for osmotic andLp_r=6.410^–8 m s^–1 MPa^–1 in correspondinghydrostatic experiments, i.e. the two values differed by a factorwhich was as large as 380. The same hydraulic conductivity asthat obtained in osmotic experiments using the pressure probewas obtained by the 'stop flow techniquel. In this technique,the suction created by an osmoticum applied to the root wasbalanced by a vacuum applied to the xylem. Lp_r values of rootsystems did not change significantly when measured for up to5 d. In osmotic experiments with different solutes (Na₂S0₄,K₂S0₄, Ca(NO₃)₂, mannitol), no passive uptake of solutes couldbe detected, i.e. the solute permeability was very low whichwas different from earlier findings on roots of herbs. Reflectioncoefficients of spruce roots (O were low for solutes for whichplant cell membranes exhibit values of virtually unity (     

Pea Root Regeneration After Tip Excisions at Different Levels: Polarity of New Growth

The roots of light-grown pea seedlings (Pisum sativum L. cv.Alaska) were excised at 250, 500 or 1500 µm from the body/capjuncture. Tips were sampled for 7 d after excision to monitorthe polarity and structure of the regeneration response. Inroots excised at 250 µm a new single apex regeneratedwithout swelling or any sign of repair. The new root cap appearedidentical to the control. After the 500 µm excision tworesponses occurred. In 45% of the roots examined, a single newapex regenerated, in 55% two or three new apices regeneratedto form a dichotomized or trichotomized root in the same longitudinalaxis as the primary root. In roots excised at 1500 µm,one, two or three lateral roots formed adjacent to the xylemat right angles to the primary root axis. In most instancesthe new roots developed triarch xylem. The discussion concentrateson the relationship of the differentiation state of the vascularcylinder and the pericycle, at the excision site, to the regenerationresponse. Root regeneration, Pisum sativum, Pericycle, Root apex     

Effects of indoleacetic, p-chlorophenoxyisobutyric and 2,4,6-trichlorophenoxyacetic acids on three phases of rooting in Azukia cuttings

In adventitious root formation of disbudded epicotyl cuttingstaken from light-grown, 5-day-old Azukia angularis seedlings,indoleacetic acid (IAA), 1 x 10^–4 M, applied during thefirst day showed no effect, but enhanced the effect of IAA,1 x 10^–4 M, applied during the second day. Treatment duringthe second day promoted rooting by about 70%, and a combinationof treatments for the first and second days promoted rootingsome 200%. p-Chlorophenoxyisobutyric acid (PCIB), 3 x 10^–4M, and2,4,6-trichlorophenoxyacetic acid (2,4,6-T), 2 x 10^–44M, applied the first day also enhanced the effect of IAA, 2x 10^–4 M, applied the second day. When applied the second day, PCIB, 2 x 10^–4M, increasedthe number of root primordia or clusters of small cells, butnot die number of protruded roots. Formation of the cell clusterwas inhibited by 2,4,6-T, 3 x 10^–4M, applied the secondday. Rooting processes in Azukia cuttings seem to include at leastthree phases: the first phase is induced not only by IAA butalso by PCIB or 2,4,6-T, the second phase is induced by IAAor PCIB and the diird phase depends specifically on IAA. (Received October 28, 1970; )     

The Starch Statolith Hypothesis and the Interaction of Amyloplasts and Endoplasmic Reticulum in Root Geotropism

Roots of cress (Lepidium sativum L, ) seedlings continuouslystimulated at an angle of 135°—root tips pointingobliquely upwards—develop a larger final geotropic curvaturethan roots stimulated at 45° or 90°. This well-knownbehaviour has previously been interpreted as support for thestarch statolith hypothesis. In the present experiments two groups of cress and lettuce (Lactucasativa L.) seedlings were used: (a) the control group in whichthe roots were allowed to curve without adjustment of the stimulationangle, and (b) the test group in which the roots were readjustedat different time intervals to the original stimulation angle.They were stimulated continuously at 45°, 90°, or 135°and the development of root curvatures was followed over a periodof 5–8 h. Initially (1–2 h) the rate of curvature was approximatelythe same for 135° and 90° control and tested cress andlettuce roots. Thereafter the test roots stimulated at 135°followed a linear curvature pattern. Seedlings stimulated at45° and 90° did not show the same linearity in curvaturedevelopment in the test group. The rates of curvature in thetest group were generally higher than in the control group atangles less than 135°. Cress seedlings were examined by light and electron microscopyin order to follow the movement of the cell organelles in thestatocytes. In the statocytes of roots of test seedlings thestarch statoliths were located in the position attained beforethe first readjustment of the stimulation angle. In the statocytesof control roots the starch statoliths followed the curvatureof the root tip sliding along the cell walls and attaining therest position as in normally orientated roots. The behaviour of control and readjusted roots is interpretedas a result of interaction between starch statoliths and endoplasmicreticulum membranes.     

Agrobacterium rhizogenes-transformed roots of coffee (Coffea arabica): conditions for long-term proliferation, and morphological and molecular characterization

Background and Aims: The aims of this study were to set up proliferation conditionsfor hairy roots of Coffea arabica regenerated after transformationby Agrobacterium rhizogenes strain A4-RS, and to carry out themorphological and molecular characterization of hairy root clonesmaintained over the long term. Methods: Auxin supply, light conditions and sucrose concentration weremodified with the aim of establishing efficient root proliferationconditions. The morphological variability among 62 establishedhairy root clones was phenotyped by scanning the roots and analysingthe images using ‘whinRHIZO’ software procedures.PCR analysis of integration in transformed root cells of roland aux oncogenes from the T-DNA of the Ri plasmid was usedto study the molecular variability among clones. Key Results: Auxin supply was necessary to obtain and stimulate growth andbranching, and IBA applied at 0·5 µM was the mostefficient auxin. Significant differences were shown among the62 clones for total root length and for the percentage of fineroots. These variables were stable across subcultures and couldhence be used for efficient characterization of hairy root clones.The majority of hairy root clones (86 %) exhibited non-significantphenotype differences with non-transformed roots. Eight cloneswere significantly different from the non-transformed controlsin that they possessed a low proportion of fine roots. Two otherhairy root clones grew significantly faster than the other clones.The PCR analysis revealed a low variability in the integrationof rol and aux oncogenes in transformed root cells. The T_R-DNAwas never integrated as aux1 and aux2 genes were not found,although rolB and rolC genes from the T_L-DNA were always present. Conclusions: The discovery of low morphological variability among coffeehairy roots together with the identification of morphologicalvariables allowing easy identification of phenotypically alteredclones represent two important results. They make hairy rootsa possible, and efficient, tool for functional-genomic studiesof coffee root genes.     

Gravitropism of Primary Roots of Zea mays L. at Different Displacement Angles

Primary roots of Zea mays were oriented at various angles fromthe vertical ranging from 99° to 1° and their subsequentbending analysed from filmed records. The maximum rate of bendingand the time before bending commenced both varied two-fold,but showed no correlation with the initial angle of tip displacement.Roots orientated to small initial angles (< 40°) oftenovershot the vertical and proceeded to oscillate around thisorientation, whereas roots oriented to large initial angles(> 60°) often failed to achieve the vertical. Roots inthis latter group resumed bending after an indeterminate time,or did so immediately after a second displacement of their tip,showing that they were not intrinsically unable to bend. Theapparently spontaneous resumption of bending after a temporaryplagiogravitropic phase is suggested as being due to noise inthe graviperception system in the root cap. The tips of rootsgrowing vertically downwards showed oscillatory bending movementsup to 10° either side of vertical. This angle correspondsto the minimum angle of displacement which induces gravitropicbending. Only when roots were oriented 10-20° from verticaldid they begin unequivocally to show a gravitropism since atsuch angles the deflection of their tips exceeded that due totheir natural oscillation.Copyright 1993, 1999 Academic Press Gravitropism, roots, Zea mays     

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     

Some Effects of Root Anatomy on K, Na and Cl Loading of Citrus Roots and Leaves

Loading of K, Na and Cl into fibrous roots of salt-treated citrusgenotypes, Rangpur lime (Citrus reticulata var. austera hybrid?)and Etrog citron (C. medica L.) was investigated in relationto root anatomy, in particular, the differentiation of the epidermal-hypodermallayers with distance from the root tip. The influence of durationof salinity treatment on the characteristics of K, Na and Claccumulation in leaves of the two genotypes was explored intwo experiments respectively, covering the short term (14 d)and long term (12 weeks). This study focused on two regions of the fibrous root, a segment2–12 mm from the root tip, immediately basipetal to thezone of elongation and a differentiated region of the maturesuberized, fibrous root, 40–50 mm from the root tip. Inthe distal root segment (2–12 mm) the epidermis and hypodermisof both genotypes was observed as two closely packed, uniseriatelayers of living cells. In the proximal root segment (40–50mm) the differentiated hypodermis was evident as a uniseriatelayer of thick-walled lumina interspersed with ‘passagecells’ which were frequently associated with clustersof viable epidermal cells. The characteristics of Na and Cl loading in the two root zonesdiffered profoundly during the short term loading (acclimation)phase. Attainment of quasi-steady-states for Na and Cl in thedistal region (with the exception of Na in Etrog citron) wasrapid as was Na equilibration of the proximal root segmentsin both genotypes. In contrast, Cl loading in the proximal regiontook c. 14 d to reach a quasi-steady-state by which time Cllevels were 2 to 3 times higher in the proximal than in thedistal root segments. The superior tolerance of Rangpur lime to long term salinitywas highly correlated to Cl exclusion from the leaves. However,during the first 14 d of acclimation to 50 mol m^–3 NaClthere was no segregation of the two genotypes based upon leafCl levels. Expression of differential accumulation of Cl inleaves appeared to be a time dependent process and was manifestonly after Cl saturation of the proximal root which representsthe bulk of the fibrous root system. The salt tolerance of Rangpurwas also associated with high selectivity of fibrous roots forK. over Na. A pronounced loss of K from cortical cells in theproximal root segment of salt-stressed Etrog citron was alsoevident by X-ray microanalysis. Key words: Citrus, anatomy, salinity, roots, X-ray microanalysis     

Morphological and physiological characterization of IAA-less-sensitive and IAA-sensitive phases in rooting of Azukia cuttings

In disbudded epicotyl cuttings taken from light grown 5-dayold Azukia angularis Phaseolus angularis) seedlings, all adventitiousrootlets appeared on the second day of incubation. No root primordiawere observed within the first 24 hr and no increase in thenumber of roots occurred after 48 hr. Puromycin (5.5?10^–5M), p-fluorophenylalanine (1?10^–3M),2-thiouracil (2.3?10^–4M) and 2,6-diaminopurine (2?10^–5M)inhibited rooting when applied to cuttings on the second day,but showed no inhibition when applied on the first day. Unlike these inhibitors, pyrithiamine (7.2?10^–5M) inhibitedrooting when it was applied to cuttings on the first day. A rooting promoting effect was observed with actinomycin D (2.4?10^–6M),2,4-dinitrophenol (3?10^–5M) and p-fluorophenylalanine(1?10^–4M) applied to the cuttings on the first day, whereasindoleacetic acid (1.7?10^–4M) showed its promoting effectmost effectively on the second day. ¹Contribution No. 17 from the Botanical Gardens, Faculty ofScience, University of Tokyo, Tokyo, Japan. (Received June 4, 1969; )     

High pH Causes Disintegration of the Root Surface in Lupinus angustifolius L.

The effect of high pH on the morphology and anatomy of the rootsof lupin (Lupinus angustifolius L. cv. Yandee) and pea (Pisumsativum L. cv. Dundale) was examined in buffered solution. Themorphology and anatomy of lupin roots were markedly altered,and root growth was reduced by increasing solution pH from 5·2to 7·5, whereas pea roots were unaffected. In lupin roots,pH 7·5 caused disintegration of the root surface andimpaired root hair formation. Lupin roots grown at pH 7·5also had decreased cell lengths but increased cell diameterin both the epidermis and the cortex in comparison to rootsgrown at pH 5·2. High pH reduced cell volume greatlyin the epidermis, to a lesser extent in the outer cortex andnot at all in the inner cortex. It appears that in lupins, theprimary detrimental effects of growth at pH 7·5 is reducedlongitudinal growth of cells near the root surface with a consequentreduction in elongation of the cells in inner cortex.Copyright1993, 1999 Academic Press Lupinus angustifolius L., Pisum sativum L., high pH, root morphology, root anatomy     

Effects of the Temperature of the Rooting Zone on the Growth and Development of Roots of Potato (Solanum tuberosum)

In solution culture the effect of optimal (20 °C) and supra-optimal(30 °C) root-zone temperatures on root growth and root morphologyof six potato clones (Solanum tuberosum L spp) was studied Growthwas compared with sweet potato (Ipomoea batatas L) and cassava(Manihot esculenta Crantz) Significant genotypical differencesin the responses of potato roots to supra-optimal temperatureswere observed, indicating the potential for selecting heat tolerantpotato clones In both heat tolerant and heat sensitive clones,the size of the root system was reduced by supra-optimal root-zonetemperature This was principally a result of decreased numberand length of lateral roots The first symptom of heat damagewas a reduction in the rate of cell division, followed by cessationof root elongation Bending of the apical root-zone togetherwith the formation of root hairs on the inner (concave) andlateral roots on the outer (convex) side were other symptoms,these coincided with the loss of starch granules in the root-cap Potato, genotypical differences, root morphology, root growth, temperature, Solanum tuberosum L     

Promotion of Plant Cell Division by an Epidermal Growth Factor

In some specified treatments, an epidermal growth factor (EGF)promoted adventitious root formation in epicotyl cuttings ofVigna angularis. The number of the roots induced in cuttingstreated with 0.1 mg liter^-1 EGF during the first 24 h and with210^-4 M IAA during the second 24 h was 15% greater than thatof the roots in cuttings treated without EGF and with IAA. Analysisof the optimum timing of EGF application was performed by dividingthe first 24 h period into three sequential 8 h periods (0–8h, 8–16 h and 16–24 h). The most effective timeperiods in terms of the root formation were 8–16 h and16–24 h. The 0–8 h period was ineffective with respectto the formation. When carrot suspension cells were culturedfor 15 days at a very low cell density (1,000 cells/3 ml Murashigeand Skoog's medium) with more than 0.1 mg liter^-1 EGF, cellnumbers were 72% higher than those cultured without EGF. Theseresults suggest that EGF promotes cell division of plants. (Received October 5, 1992; Accepted May 24, 1993)     

Waterlogging Tolerance Among a Diverse Range of Trifolium Accessions is Related to Root Porosity, Lateral Root Formation and 'Aerotropic Rooting'

Waterlogging tolerance, root porosity and root anatomy wereevaluated for 20 Trifolium accessions (species and sub-species,all annuals) selected from the eight Sections of the genus.Nine accessions were sensitive [relative growth rate (RGR) reducedby up to 80%] to waterlogging, nine accessions were tolerant(RGR not reduced), and in two accessions RGR increased (up to1.9-fold), when compared to drained controls. Growth of themain (i.e. tap) root axis was severely reduced in all accessionswhen waterlogged. Lateral roots formed the bulk of the rootsystem of tolerant accessions when grown in waterlogged soil.Lengths of the longest lateral roots were up to three-timeslonger than the main root axis. Root porosity varied from 0.7–12%among accessions when grown in aerated solution and from 1.1–15.5%in plants grown in hypoxic (0.031–0.045 mol O₂m^-3) solution.In some accessions aerenchyma formed by cell lysigeny; in othersit formed by schizogenous cell separation, or a combinationof both processes. O₂consumption rates of expanded lateral roottissues varied by up to 1.7-fold (on a mass basis) among thesix accessions tested and was reduced by an average of 24% forroots of plants grown in hypoxic solution prior to measurements.Accessions with the highest root porosity tended to have longerroots when grown in waterlogged soil. Three accessions formed‘aerotropic roots’ and the lateral root lengthsof these plants exceeded those of all other accessions, suggestingenhanced O₂movement to the submerged lateral root axis via theaerotropic roots. Waterlogging-tolerant accessions were identifiedin seven of the eight Sections in Trifolium, and the tolerantaccessions tended to be those with extensive lateral root systemsof relatively high porosity. Copyright 2001 Annals of BotanyCompany Waterlogging, Trifolium, aerenchyma, hypoxia, flooding, root respiration, clover, root anatomy, root porosity, pasture, aerotropic roots