The Anchorage Mechanics of Maize, Zea mays

The anchorage system of mature maize Zea mays was investigatedby combining morphological and anatomical study of the rootsystem with mechanical tests on roots and with studies in whichplants were pulled over. The root system is dominated by 20–30adventitious roots which emerge in rings from the stem basepointing radially downwards and outwards, approximately 30°from the vertical. Roots are strengthened near their base bya heavily lignified exodermis which makes them rigid in bending;distally, strength and rigidity both decrease because rootsbecome thinner and less lignified. When plants were pulled over,a maximum anchorage moment of 5–20 Nm was mobilized atangles of 8–10°, larger plants having stronger anchorage.Movement was initially centred on the leeward side of the stem,anchorage being due to the resistance of both windward and leewardroots to axial motion through the soil and to bending. At displacementsover 10°, however, leeward roots buckled under combinedbending and compression and the centre of rotation shifted tothe windward perimeter of the root system; subsequent movementof the cone of roots and soil was resisted only by the bearingstrength of the soil beneath it. The differences between anchorage failure in balsam and sunflowersand that in maize probably results from the lower angular spreadand the weakness in compression of the maize roots which preventsthe leeward side of the root system from bearing large downwardloads. The system behaves more like that of wheat; these resultssuggest that the lodging resistance of both plants may be improvedby increasing the bending strength and angle of spread of theadventitious roots. Key words: Zea mays, roots, anchorage     

The anchorage mechanics of deep rooted larch, Larix europea L. japonica

The anchorage of deep rooted 16-year-old larch trees, Larixeuropea japonica, has been studied by combining winching testswith analyses of strain around the base of the trunk and rootsystem and mechanical tests on individual roots. These showedthat anchorage is provided by the laterals which emerge fromaround the stem base, sinker roots which emerge along theirlength, and tap roots positioned directly underneath the bole.During anchorage failure the leeward laterals are bent and eventuallybreak close to their base, whilst the windward laterals arepulled out of the ground, with their sinker roots intact. Afterinitially being confined by the soil and bending, the tap rootrotates in the soil. Anchorage failure is similar when the soilis dry as when it is wet, but failure occurs closer to the trunk.Strain measurements along the lateral roots revealed that thestresses were highest close to the trunk and that these regionsof the roots contribute most to tree stability. The two major components of anchorage were found to be the resistanceof leeward laterals to bending and the resistance of tap rootsand windward sinkers to uprooting. Bending tests on leewardlaterals revealed that they provide around 25% of tree anchorage.Almost 75% of the anchorage strength must, therefore, be providedby the windward sinkers and tap roots. Anchorage strength ofroots was positively correlated to their cross-sectional area.The vertical orientation of the sinkers makes the anchoragesystem of larch more efficient than the plate system formedby Sitka spruce on waterlogged soils and means that no root-soilplate is formed. Key words: Anchorage, root architecture, sinker roots, root bending strength, windthrow     

The function of buttress roots: a comparative study of the anchorage systems of buttressed (Aglaia and Nephelium ramboutan species) and non-buttressed (Mallotus wrayi) tropical trees

The anchorage mechanics of mature buttressed trees of Aglaiaand Nephelium, and of non-buttressed Mallotus wrayi have beeninvestigated by combining a study of the morphology of theirroot systems with a series of anchorage tests. Both types possessed tap roots, but only buttressed trees possessedsinker roots, which branched from the ends of the buttresses.The anchorage strength of the buttressed trees was almost double(10.6 kNm) that of the unbuttressed ones (4.9 kNm), and themaximum moment was generated at lower angles. In but tressedtrees, the leeward buttresses were pushed into the soil beforebending and eventually breaking towards their tip, whilst thewindward buttresses pulled out of the soil or delaminated ifthey possessed sinker roots. The tap root rotated in the soilto windward. In contrast, during failure of unbuttressed treesthe tap root both moved and bent towards the leeward, the windwardroots were pulled out of the soil, and the leeward lateralssimply buckled. Strains along but tresses were much higher thanalong the laterals of unbuttressed trees. These results suggest that buttresses act in both tension andcompression and make a much larger contribution to anchoragethan the thin laterals of non-buttressed trees. The relativecontribution of the but tresses was determined by carrying outa further series of anchorage tests in which both buttressedand unbuttressed trees were pulled over after all their lateralshad been cut away. These trees were therefore only anchoredby their taproot. Failure of both types was similar to intactunbuttressed trees, and they had similar anchorage strengthstoeach other, 4 kNm, around 80% of the value for intact non-buttressedtrees, but only 40% of the strength of intact buttressed trees.Buttresses therefore contribute around 60% of the anchorageof buttressed trees, producing around six times more anchoragethan the thin laterals of unbuttressed trees. Key words: Anchorage, root architecture, sinker roots, tap roots, root bending strength, buttresses     

The Mechanics of Root Lodging in Winter Wheat, Triticum aestivum L.

The anchorage of winter wheat, Triticum aestivum L., is providedby a cone of rigid coronal roots which emerge from around thestem base. During root lodging this cone rotates at its windwardedge below the soil surface, the soil inside the cone movingas a block and compressing the soil beneath. A theoretical modelof anchorage suggested that lodging resistance should be dependenton the diameter of the root-soil cone, coronal root bendingstrength and soil shear strength. We tested the predictions of the anchorage model by carryingout two series of experiments. In the first, varieties of contrastinglodging resistances were artificially lodged. The moment requiredto rotate plants into the soil, the diameter of the root-soilcone, and the bending strength of the coronal roots were recorded.The lodging moment was correlated with the size of the soilcone, as predicted. Generally, differences in anchorage strengthbetween varieties were due to differences in root-soil conediameter, although coronal root strength was also important. A second series of tests was carried out using model plantsanchored by plastic discs. The behaviour of the models duringartificial lodging supported the anchorage model; the forceresisting lodging was similar to that of plants with root-soilcones of the same size and the resisting force was dependenton the soil strength. These results suggest that root lodging resistance might beimproved by increasing both the angle of spread and the bendingstrength of the coronal roots. Key words: Anchorage, root-soil cone, coronal roots, lodging, wheat     

The Mechanics of Anchorage in Wheat Triticum aestivum L.: II. ANCHORAGE OF MATURE WHEAT AGAINST LODGING

The root system of mature wheat Triticum aestivum Marts Doveis dominated by the 7 to 15 adventitious roots which emergefrom the perimeter of the stem base, pointing radially outwardsand downwards. The basal, coronal region of these roots is thickand unbranched, attached to a rhizosheath of earth by a densecovering of root hairs and stiffened in bending by lignificationof outer layers of the cortex. Root lodging of plants involves bending of the coronal rootsat their base and axial movement of leeward and windward rootsthrough the soil; their resistance to these motions providemoments resisting lodging. A model of anchorage was producedby summing the resistance of each root to both forms of motionto give two anchorage components. The model was tested in aseries of mechanical experiments in which simulated lodgingwas followed by loading of individual roots; results supportedthe anchorage model and suggested that in the experimental conditionsthe two components of anchorage were approximately equal inmagnitude. The stem was about 30% stronger than the anchoragesystem. The coronal anchorage roots made up 4.4% of total dry mass;it is suggested that anchorage could be improved either by increasinginvestment in this region or by altering root orientation. Sequentialdevelopment of seminal and adventitious root systems is relatedto the changes in anchorage requirement with age.     

A Comparative Study of the Anchorage Systems of Himalayan Balsam Impatiens glandulifera and Mature Sunflower Helianthus annuus

The anchorage systems of Himalayan balsam Impatiens glanduliferaand mature sunflowers Helianthus annuus were investigated bycombining morphological and anatomical study of the root systemswith mechanical tests on roots and with studies in which matureplants were pulled over. The root system of balsam is dominated by large numbers of fleshytapering adventitious roots which point downwards from theirorigin at the wide stem base. Sunflowers, in contrast, havea tapering tap-root from which 20–30 well-branched lateralsemerge, pointing radially outwards and downwards. Roots of eachspecies have contrasting anatomy: those of balsam resemble stems,having a central watery pith and being strengthened peripherallyby lignification of vascular tissue; roots of sunflowers arestrengthened by a solid woody stele. Roots of both species arerigid in tension and, towards the base, in bending. Both species exhibited similar behaviour to that known for treessuch as Sitka spruce; when pulled over they rotated about ahinge leeward of the stem base and a root-soil ball was pulledout of the surrounding soil. Anchorage was resolved into threecomponents which, in order of decreasing magnitude, were (i)the resistance to pulling of the roots on the windward sideof the plant (and, for sunflower, the tap-root); (ii) the resistanceof roots and soil at the leeward hinge to rotation; and (iii)the weight of the root-soil ball. Sunflower had stronger anchoragebut achieved it at a greater cost in terms of the dry mass ofits root system. In each species, the morphology, anatomy and mechanical propertiesof the root system can be related to those of the stem. Thewide stem base of balsam allows large numbers of mechanicallyefficient fleshy roots to be attached whereas in sunflowersa woody tap-root system is necessary to anchor the much narrowerstem. Key words: Impatiens, Helianthus, roots, anchorage     

The Increase in Anchorage with Tree Size of the Tropical Tap Rooted TreeMallotus wrayi, King (Euphorbiaceae)

The mechanical development of the anchorage system of the taprooted tropical speciesMallotus wrayiKing (Euphorbiaceae) wasinvestigated by pulling over and examining trees with a diameterat breast height (d_bh) of 4.2 cm to 14.3 cm. The mode of mechanicalfailure depended upon the size of the tree: thicker trees (d_bhapprox.9 cm) failed in the ground with their tap roots pushing intothe soil on the winchward side; in smaller trees (d_bhapprox.7 cm) the trunk snapped before anchorage failure; and in verysmall trees (of d_bh<6 cm) neither type of failure occurredand the trees returned to their original upright position undamagedafter the test. The anchorage strength of the trees was correlatedwith the second power of trunk diameter rather than with thethird power that theory suggests is optimal because tap rootsdid not show an isometric increase in length or diameter. Thereforeas trees grow larger the ‘factor of safety’ againstanchorage failure falls, making them prone to fail in theirroots. These results suggest that only relatively small treespecies can rely solely on the tap root to prevent uprooting.It may be for this reason that most larger trees develop thicklateral roots.Copyright 1998 Annals of Botany Company Anchorage, tap roots, scaling,Mallotus wrayi, isometric growth, functional development, windthrow, root systems.     

The Anchorage of Leek Seedlings: The Effect of Root Length and Soil Strength

The mechanical behaviour of single roots being extracted fromsoil was modelled as a process in which tension is transferredfrom the upper regions of the root to the soil via shear. Quantitativepredictions were made about the extraction forces and the shapeof the uprooting curves, and these were tested using leek radiclesof different lengths in soil of two different strengths. Results of uprooting tests were qualitatively similar to thepredictions. The pullout resistance rose with root length, untilthe breaking strength of the root was reached, at around 30mm: longer roots all broke before the tip was stressed. In wholeroot systems, therefore, failure will occur proximally beforethe line distal roots are mechanically stressed, so these canhave no anchorage function. Resistance to an upward force will be most economically achievedby having many strengthened proximal root axes, as in the adventitiousroot systems of grasses, sedges and stoloniferous dicots. Allium porrum, root, anchorage, shear, tension, soil     

Integrated Control of Nitrate Uptake by Crop Growth Rate and Soil Nitrate Availability under Field Conditions

There is still disagreement about whether crop growth rate orsoil nitrate concentration control nitrogen absorption by cropsunder field conditions. The influence of these factors on thecontrol of N uptake rate was examined in the absence of waterstress, using data on dry matter production, above-ground nitrogenaccumulation and soil nitrate concentration from several N-fertilizerexperiments on winter wheat, winter oilseed rape and maize.The results confirmed that crops can accumulate nitrogen farin excess of the ‘critical dilution curve’, whichdefines the minimum amount of nitrogen needed for maximal growthrate: the N concentration in plants could exceed the criticalN concentration by 70 to 80% for the three species studied.The nitrate uptake rate index (NUI) was calculated as the ratioof actual and critical N uptake rates, at intervals of 1 week.NUI varied with nitrate concentration in the 0–30 cm soillayer according to a Michaelis–Menten equation (with oneor two components). This response was compared with the kineticsof saturation of the nitrate uptake systems: the high affinitytransport system (HATS) and the low affinity transport system(LATS). As a result, it is proposed that there is a criticalN dilution curve delimiting two domains of N use by plants.This is linked to the two nitrate transport systems, with HATSworking at low nitrate concentrations, below the critical dilutioncurve, and LATS at high nitrate concentrations, above the curve.NUI provides another method for calculating the actual nitrateuptake rate, which depends on the maximal crop growth rate (withoutN deficiency) and on the external nitrate concentration. Copyright2000 Annals of Botany Company Nitrate, uptake rate, growth rate, wheat, maize, oilseed rape, soil N availability     

An Experimental Investigation of the Resistance of Model Root Systems to Uprooting

The architecture of a tree root system may influence its abilityto withstand uprooting by wind loading. To determine how theroot branching pattern may alter the anchorage efficiency ofa tree, artificial model root systems with different topologiesand branching angles were built. The root systems were embeddedat various depths in wet sand and the pull-out resistance measured.A model to predict the uprooting resistance from the data collectedwas designed, allowing predictions of anchorage strength withregards to architecture. The dominant factors influencing pull-outresistance were the depth and length of roots in the soil. Themost efficient type of branching pattern predicted by the programwas one with an increased number of roots deep in the soil.The optimum branching angle most likely to resist pull-out isa vertical angle of 90° between a lateral and the main axis.The predicted mechanically optimal radial angle between a lateralbranch and its daughter is between 0 and 20°. Values ofbranching angle are compared with those measured in real woodyroot systems of European larch and Sitka spruce. Root architecture; root anchorage; pull-out resistance; windthrow; Picea sitchensis ; Larix decidua     

A Numerical Investigation into the Influence of Soil Type and Root Architecture on Tree Anchorage

The influence of root morphology and soil type on the mechanical behaviour of tree anchorage was investigated through numerical modelling. We developed a simple computer program to construct three-dimensional virtual root architectural patterns. This tool was used to build four schematic patterns: heart-, tap-, herringbone- and plate-like root systems. Each of these rooting types was characterized by specific branching characteristics. However, the total volume (proportional to the wood biomass) and material properties were kept constant. The finite element method was used to calculate the mechanical response of root/soil systems when the stem was subjected to bending forces. The overturning resistance of the four schematic root patterns was determined in four different idealistic soil types. These soils were based on Mohr–Coulomb plasticity models. Results showed that soil internal friction modified the position of the rotation axis during tilting of the root/soil plate. Rooting depth was a determinant parameter in sandy-like soils. Overturning resistance was greatest in heart- and tap-root systems whatever the soil type. However, the heart root system was more resistant on clay-like soil whereas the tap root system was more resistant on sandy-like soil. Herringbone and plate root systems were twice as less resistant on clay soils and 1.5 times less resistant on sandy soils when compared to heart and tap-like structures.     

Comparative response of wheat and oilseed rape to nitrogen supply: absorption and utilisation efficiency of radiation and nitrogen during the reproductive stages determining yield

We investigated the response of spring wheat and oilseed rape to nitrogen (N) supply, focusing on the critical period for grain number definition and grain filling. Crops were grown in containers under a shelter and treated with five combinations of applied N. Wheat and oilseed rape produced comparable amounts of biomass and yield when corrected for the costs of biomass synthesis (SC). From the responses of biomass and yield to late N applications and the apparent contribution of mobilised biomass to yield, it seems that the yield of oilseed rape was more source-limited during grain filling than that of wheat, particularly at the medium and high N levels. Both species recovered equal amounts of N from the total available N in the soil and had similar N use efficiencies, expressed as yield per unit of N absorbed. However, oilseed rape had higher efficiency to convert absorbed N in biomass, but lower harvest index of N than wheat. Oilseed rape had similar or lower root biomass than wheat, depending on N level, but higher root length per unit soil volume and specific root length. The specific uptake rate of N per unit root dry weight during the critical period for grain number determination was higher in oilseed rape than in wheat. In wheat, N limitation affected growth through a similar or lower reduction in radiation use efficiency corrected for synthesis costs (RUE_SC) than in the cumulative amount of intercepted photosynthetically active radiation (IPARc). In oilseed rape, lower growth due to N shortage was associated more with RUE_SC than IPARc, during flowering while during grain filling both components contributed similarly to decreased growth. RUE_SC and the concentration of N in leaves and inflorescence (LIN%) decreased from flowering to maturity and were curvilinearly related. Oilseed rape tended to have higher RUE_SC than wheat at high N supply during the critical period for grain number determination, and generally lower during grain filling. The reasons for these differences and possibilities to increase yield potential are discussed in terms of the photosynthetic efficiency of the different organs and changes in source–sink ratio during reproductive stages. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of nitrogen and growth regulators on stem and root characteristics associated with lodging in two cultivars of winter wheat

The effects of nitrogen and plant growth regulators (stem shorteners)on root and shoot characteristics associated with lodging resistancewere investigated in two winter wheat (Triticum aestivum L.)cultivars of contrasting lodging resistance: the susceptibleGalahad and the resistant Hereward. The morphology and mechanicalstrength of the stems and anchorage systems grown at two levelsof nitrogen and with or without growth regulators were measuredand related to the incidence of lodging recorded in a fieldtrial. In both cultivars high levels of nitrogen increased theheight of the stem, thereby increasing the ‘self-weight’moment transmitted into the ground and weakened both the stemsand the anchorage coronal roots. As a result, the anchoragestrength was also reduced, plants failing in the root systemin simulated lodging tests. Growth regulators, in contrast,had little effect on the bending strength of the shoots androot systems, but reduced plant height so that the over turningmoments generated by the weight of the shoot were less. Therewere also differences between cultivars: Galahad plants hadweaker anchorage due to the smaller number and lower strengthof the coronal roots. The morphological and mechanical measureswere used to calculate a safety factor against both stem androot lodging. Five factors were found to influence the safetyfactors, these were: cultivar type, the type of lodging, therate of nitrogen and growth regulator application, and time,being lowest in Galahad plants at high levels of nitrogen andwithout growth regulators and at grain filling when the earswere heaviest. This was consistent with the observed patternof lodging: root lodging occurred at grain filling and onlyin Galahad which had been treated with high nitrogen rates,most strongly in plants without growth regulators. Key words: Lodging, safety factors, anchorage, ‘self-weight’ moment     

The Effects of Soil Bulk Density on the Morphology and Anchorage Mechanics of the Root Systems of Sunflower and Maize

The effects of soil bulk density and hence strength on two contrastingspecies of herbaceous annuals, the dicot sunflower (HelianthusannuusL.) and the monocot maize (Zea maysL.), were investigatedby comparing the morphology and mechanics of field-grown plantsin soil with a low and high bulk density. Soil with a low bulkdensity had a significantly lower penetration resistance (118±4.4kPa) than the high bulk density soil (325±12.2 kPa;P<0.0001).Soil strength affected shoot and root systems of both speciesbut had no significant effect on shoot height. In both speciesroots were thicker closer to the stem base in strong soil comparedto those in weaker soil. Sunflower tap-roots growing in strongsoil tapered more rapidly than those in weak soil. Only in maize,however, were roots growing in weak soil stiffer than thosein strong soil. Despite only small absolute differences in thepenetration resistance of the soil both species growing in strongsoil had greater anchorage strength than those in weak soil.As a consequence more plants in weak soil lodged compared withthose growing in strong soil. This study shows that plants can,to a small extent, respond to changes in soil strength, butthat changes do not appear to compensate fully for alterationsin soil conditions. Furthermore it may be possible, by manipulatingsoil strength, to control lodging.Copyright 1999 Annals of BotanyCompany Roots, compaction, soil strength, anchorage mechanics, bulk density, thigmomorphogenesis, lodging,Helianthus annuusL.,Zea maysL.     

Structural development of the shoot and root systems of two winter wheat cultivars, Triticum aestivum L.

The structural development of the stems and basal anchorageroots of Galahad and Hereward winter wheat cultivars (Triticumaestivum L.) were investigated and related to their mechanicalfunction. Stem and root morphology, anatomy and mechanical propertieswere examined from tillering (March) up to maturity (August),together with plant weight distribution. This allowed us tocalculate a ‘factor of safety’ against root andstem failure throughout development. As the plants grew taller the stem and the anchorage ‘coronalroots’ increased in bending strength countering the increasingmechanical demands. The bending strength, in turn, was correlatedwith the amount of lignified material around the stem and rootperimeter. Structural development ceased by ear emergence, whenthe plant was at its tallest, but because the ear weight continuedto rise the ‘self-weight’ moment pushing the plantover continued to increase. This meant that the ‘safetyfactors’ of both cultivars against both root and stemmechanical failure decreased throughout development. In bothcultivars the safety factors against root failure were lowerthan for stem failure, and Galahad had lower factors of safetythan Hereward. All these findings were consistent with resultsof field trials; failure tends to occur late in development,during grain filling, and is localized to the root system, whilstGalahad is more prone to lodging than Hereward. The pattern of mechanical development of winter wheat seemsto be one which would maximize its reproductive success, maintainingits structural integrity especially early in development whileinvesting in a minimum of structural material. Key words: Safety factor, anchorage, lodging, biomechan-ics, structural development     

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     

Understanding the impact of root morphology on overturning mechanisms: a modelling approach

BACKGROUND AND AIMS: The Finite Element Method (FEM) has been used in recent years to simulate overturning processes in trees. This study aimed at using FEM to determine the role of individual roots in tree anchorage with regard to different rooting patterns, and to estimate stress distribution in the soil and roots during overturning. METHODS: The FEM was used to carry out 2-D simulations of tree uprooting in saturated soft clay and loamy sand-like soil. The anchorage model consisted of a root system embedded in a soil block. Two root patterns were used and individual roots removed to determine their contribution to anchorage. KEY RESULTS: In clay-like soil the size of the root-soil plate formed during overturning was defined by the longest roots. Consequently, all other roots localized within this plate had no influence on anchorage strength. In sand-like soil, removing individual root elements altered anchorage resistance. This result was due to a modification of the shape and size of the root-soil plate, as well as the location of the rotation axis. The tap root and deeper roots had more influence on overturning resistance in sand-like soil compared with clay-like soil. Mechanical stresses were higher in the most superficial roots and also in leeward roots in sand-like soil. The relative difference in stresses between the upper and lower sides of lateral roots was sensitive to root insertion angle. Assuming that root eccentricity is a response to mechanical stresses, these results explain why eccentricity differs depending on root architecture. CONCLUSIONS: A simple 2-D Finite Element model was developed to better understand the mechanisms involved during tree overturning. It has been shown how root system morphology and soil mechanical properties can modify the shape of the root plate slip surface as well as the position of the rotation axis, which are major components of tree anchorage.     

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     

Improving of oilseed rape lateral root formation by physiological analogues of auxin

The aim of the present work was to study the effect of auxin physiological analogue TA-12 [1-(2-chloroethoksicarbonylmethyl)-4-naphthalenesulfonic acid calcium salt] on the formation of oilseed rape lateral root and on the mitotic activity of apical meristem cells. Spring oilseed rape (Brassica napus L. ssp. oleifera annua Metzg.) cultivar ‘Mascot’ was chosen as a test object. Anatomical, cytological and histological studies on root development suggest that compound TA-12 induces the activity of parent root pericycle cells, stimulates the formation of lateral roots and enhances the division of apical meristem cells. The auxin transport inhibitor 2,3,5-triiodobenzoic acid suppresses the division of apical meristem cells, while this process is restored by the auxin physiological analogue TA-12 and naphthaleneacetic acid. The compound TA-12, by stimulating primary root growth and lateral root induction, optimised the formation of the oilseed rape root system.     

The Mechanics of Anchorage in Wheat Triticum aestivum L.: I. THE ANCHORAGE OF WHEAT SEEDLINGS

Model of the mechanics of uprooting lead to the identificationof ‘optimal’ anchorage systems which can withstanda given upward force at a minimum construction cost. Such systemshave many downward-pointing fibrous roots which are strengthenedprogressively towards the base. A study of the anchorage systemof 7- and 21-d-old wheat (Triticum aestivum L.) plants showedthat the plants possessed five seminal roots, of which onlythree pointed vertically. Each root was well suited for anchorage,being convered in root hairs and strengthened progressivelytowards the base by lignification of the stele. Strength andstiffiness of roots but not their mass per unit length increasedwith age. There was little interaction between roots when plantswere uprooted; the three vertical roots broke while the twohorizontal ones pulled out, as occurred when roots were pulledout singly, Uprooting forces increased with age and the rootsystem could withstand uprooting forces greater than those requiredto pull out upper leaves, so reducing the chances of the plantbeing uprooted by a herbivore, By 3 weeks a stiff adventitiousroot system, which would later help prevent the wheat lodging,was developing.