Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis II. Morphology and Anatomy of Evolution Forms

Morphological and anatomical parameters which are variable underroot anaerobiosis in Triticum aestivum were checked on fivetaxa of primitive and modern wheats (and the related genus Aegilops).The plants were grown in nutrient solution which was eitheraerated or flushed with nitrogen. When the plants were flushedwith nitrogen a general retardation in longitudinal root growthoccurred in all of them, but only Triticum aestivum showed aclear promotion of growth of later appearing roots enablingit to maintain the same root/shoot ratio even under stress conditions.There was an increase in the volume of intercellular space inthe root cortex of nearly all the plants investigated. The diameterand the lignin content of the roots and the form of their corticalcells also varied. All these changes were expressed in the primitivewheats to a lesser extent than in the advanced Triticum aestivumindicating that there is a clear increase in the adaptive responsein the latter. Triticum species, Aegilops species, wheat, roots, anatomy, anaerobiosis, stress, intercellular space, selection     

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     

The Effect of Mechanically Induced Stress on the Growth of Cauliflower, Lettuce and Celery Seedlings

Brushing cauliflower, lettuce and celery seedlings with paperfor 1.5 min each day for 11–13 d, 10–12 d or 21–28d, respectively resulted in smaller, more compact, plants thanthe unbrushed controls. In all three species shoot fresh anddry weights and leaf area were reduced following brushing. Incauliflower and celery the largest growth reduction was in petiolelength. In lettuce, which has no discernible petioles, the reductionin leaf length caused by brushing was proportionally greaterthan the reduction in leaf width. Brushing reduced hypocotyllength in cauliflowers and to a lesser extent in lettuce. Petioleand hypocotyl thickness was reduced in cauliflower, whereashypocotyl thickness was increased in lettuce following brushing.Brushing increased leaf thickness in cauliflower, celery andto a lesser extent in lettuce and increased the percentage drymatter content of lettuce shoots. The weight of chlorophyllper fresh weight of leaf tissue increased following brushingin celery and lettuce and declined in cauliflowers. Root length and the number of branches per root system werereduced in all three species following brushing. Root dry weightwas reduced and the root:shoot dry weight ratio was increasedin lettuce, reduced in celery and unaffected in cauliflowers. There were different patterns of response to brushing, the reductionin leaf weight being greatest in the youngest leaf of cauliflowerand least in the youngest leaf of lettuce and celery. Growthresponses to brushing were seen several days after brushinghad ceased, noticeably in leaves which were barely visible atthe time of brushing. It is suggested that growth retardation of cauliflowers, lettuceand celery, induced by mechanical stress such as brushing mayprove valuable as a means of ‘conditioning’ theseedlings to withstand both the physical and physiological stresseswhich occur at and during transplanting. Brassica oleracea, cauliflower, Lactuca sativa L., lettuce, Apium graveolens L., celery, mechanical stress, shoot growth, root growth, chlorophyll     

Influence of Genotype and Mineral Nutrition on the Distribution of Growth within Plants of Lolium perenne L. grown in Soil

Genotypes of Lolium perenne were grown with two levels of fertilizerapplication. Using exponential growth-rates and parameters derivedfrom them, the rate of growth of each genotype was partitionedinto the rates of initiation of new roots and tillers, and thegrowth of the individual roots and tillers after initiation.The growth of the individual roots was further analysed by measuringchanges in diameter and length of the main root, and the growthin the branches of the main root. The genotypes varied in their response to additional mineralnutrition. The greater the increase in the rate of shoot growthfor a genotype, the greater was its increase in the rate oftiller initiation, the smaller was the increase in the sizeof its tillers, and the greater was the decrease in its rateof root relative to shoot growth. Within a population of genotypes growing with the same levelof mineral nutrition, the greater the rate of shoot growth ofa genotype, the greater was the rate of initiation of new tillersand, at a low level of mineral nutrition, the smaller the sizeof tillers. With a higher level of mineral nutrition, the higherthe rate of tiller production, the smaller or larger was tillersize, depending upon environmental factors other than mineralnutrition. At both levels of mineral nutrition, the greaterthe rate of shoot growth, the smaller was the rate of root growthrelative to shoot growth, due to relatively less growth takingplace in the branches of the main root.     

Root-Tiller Interrelationships in Spring Barley (Hordeum distichum (L.) Lam.)

Root-tiller relations were investigated in spring barley grownin soil in deep pots. The total dry wt of the root system reachedits maximum 6 weeks from sowing, when the shoot weight was only50 per cent of its value at maturity. Seminal and nodal rootscomprised 40 and 60 per cent, respectively, of the total rootdry wt at maturity; the majority of the nodal root weight wasassociated with the main shoot. The main shoot had approximatelytwice as many nodal roots as either of the first two primarytillers (T1 and T2), and the primary and secondary tillers appearinglater were very poorly rooted. Some tillers, especially secondarytillers that died prematurely, produced no nodal roots. Theweight of the seminal roots and nodal roots attached to themain shoot continued to increase up to maturity but the drywt of nodal roots on tillers declined with time. This patternof growth was closely related to the pattern of ¹⁴C assimilateddistribution within the root system. A very small proportionof ¹⁴C assimilated by the main shoot and T1 and T2 was exported.The majority of the exported assimilate went to the seminalroot system and to nodal roots attached to the main shoot. Individualnodal and seminal roots seemed to have different roles in supplyingnutrients to the shoot system, with the former mainly providing³²P-phosphate to its tiller of origin and the latter generallysupplying the main shoot and primary tillers. Hordeum distichum. (L.) Lam., barley, root growth, nodal roots, seminal roots, tillering, assimilate distribution, ³²P-distribution     

The Reciprocal Transfer of Radiocarbon between a Developing Tiller and its Parent Shoot in Vegetative Plants of Lolium multiflorum Lam.

The transfer of ¹⁴C-labelled assimilates between a tiller andits parent shoot was examined in young plants of Lolium multiflorumLam. Radiocarbon was exported freely from an expanded laminato sinks within the shoot axis from which it originated andto the root system. Lesser amounts of radiocarbon were exportedto the other shoot. It is suggested that the reciprocal exchangeof radiocarbon between tiller and main shoot occurred principallyvia a direct pathway through stem tissues rather than via apathway involving the roots.     

Nitrate Assimilation in Higher Plants with Special Reference to the Cocklebur (Xanthium pennsylvanicum Wallr.)

A soluble NADH-dependent nitrate reductase is described forthe shoot system of Xanthium. Young leaves and immature stemtissues contain high levels of the enzyme. They are relativelyrich in free amino acids and amides but store little free nitrate.The specific activity of the enzyme is lower in fully expandedleaves, although these leaves exhibit higher rates of fixationof carbon in photosynthesis than do younger leaves. Neithernitrate nor free amino acids accumulate in the mesophyll ofthe leaf. Older parts of the stem axis accumulate large amountsof soluble nitrogen, almost entirely as free nitrate. Reservesof nitrate in the shoot and root are rapidly depleted if nitrateis removed from the external medium. Nitrate reductase is apparently absent from roots of Xanthium.This finding is supported by analyses of bleeding sap from nitrate-fedplants which show that 95 per cent of the nitrogen exportedfrom roots is present as free nitrate. However, roots are capableof synthesizing and exporting large amounts of amino nitrogenif supplied with reduced nitrogen such as urea or ammonium. A scheme is presented summarizing the main features of the metabolismof nitrate in Xanthium and this is compared with the situationin nitrate-fed plants of the field pea (Pisum arvense L.), aspecies previously shown to be capable of reducing nitrate inits root system.     

Competition within the root system of rubber seedlings (Hevea brasiliensis) studied by root pruning and blockage

The effects of taproot blocking and pruning on the developmentof the early secondary roots (ESR) of rubber seedlings werestudied in root observation boxes under controlled conditions.During shoot flush, both the mean elongation rate and mean apicaldiameter of the ESR decreased regardless of treatments. Thereafter,the elongation rate of the ESR increased greatly when the taprootwas blocked, slightly for the control and scarcely for the prunedsystems in which fast growing regenerated roots developed. Thedifferences between treatments were related to the proportionof ESR which ceased growing. Following shoot arrest, the apicaldiameter of ESR increased greatly for blocked seedlings andto a lesser extent for pruned seedlings. Branching density ofthe ESR and elongation of tertiary roots were also higher forseedlings without a growing taproot. The dynamics of ESR response was not consistent with activeinhibition of their development by the growing taproot. Moreover,this response was dependent on concurrent development of shootand regenerating roots, hence competition processes were morelikely to be determining. In such an hypothesis, root elongationcan be limited by assimilate availability, but also by eachroot's maximum growth rate in non-limiting conditions, i.e.growth potential. Since the latter is related to apical diameter,a significant acceleration of elongation required a parallelincrease in apical diameter and this may explain the relativeinertia of ESR to taproot alteration. Conversely, regeneratingroots could have a high growth potential because they were initiatedin a favourable context, thus their development competed stronglywith elongation of ESR. Key words: Hevea brasiliensis, root system, development, growth potential, root diameter, competition     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

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     

The Influence of Mineral Nutrition on the Root Development of Trees: I. THE GROWTH OF SITKA SPRUCE WITH DIVIDED ROOT SYSTEMS

Sitka spruce seedlings were grown with their root systems dividedbetween two contrasting nutrient regimes. One half of the rootsystem was supplied with a solution containing N, P, and K ata range of concentrations while the untreated half receivedwater only. High-nutrient treatments induced two flushes ofshoot growth resulting in a large shoot system, whereas plantsin the low-nutrient treatments flushed once only and showedsymptoms of nutrient deficiency. Root growth, assessed in terms of dry weight and diameter ofboth primary and woody tissues, was stimulated in the rootsto which the nutrients were actually applied, whereas in theuntreated roots on treated plants only the primary root diameterwas enhanced. However, internal nutrient concentrations on bothsides of the root system were related to the concentrationsapplied, though to a slightly lesser extent in the untreatedroots. Thus, the nutrients which had been internally translocatedto the untreated roots had little effect on their growth. The localized stimulation of xylem production in the woody rootsextended into the stem along a spiral pathway which was demonstratedby the movement of dye. Possible mechanisms are discussed by which differential rootgrowth is brought about by a localized supply of mineral nutrients.     

Root Respiration and Carbohydrate Status of Two Wheat Genotypes in Response to Hypoxia

To investigate root respiration and carbohydrate status in relationto waterlogging or hypoxia tolerance, root respiration rateand concentrations of soluble sugars in leaves and roots weredetermined for two wheat (Triticum aestivum L.) genotypes differingin waterlogging-tolerance under hypoxia (5% O₂) and subsequentresumption of full aeration. Root and shoot growth were reducedby hypoxia to a larger extent for waterlogging-sensitive Coker9835. Root respiration or oxygen consumption rate declined withhypoxia, but recovered after 7 d of resumption of aeration.Respiration rate was greater for sensitive Coker 9835 than fortolerant Jackson within 8 d after hypoxia. The concentrationsof sucrose, glucose and fructose decreased in leaves for bothgenotypes under hypoxia. The concentration of these sugars inroots, however, increased under hypoxia, to a greater degreefor Jackson. An increase in the ratio of root sugar concentrationto shoot sugar concentration was found for Jackson under hypoxicconditions, suggesting that a large amount of carbohydrate waspartitioned to roots under hypoxia. The results indicated thatroot carbohydrate supply was not a limiting factor for rootgrowth and respiration under hypoxia. Plant tolerance to waterloggingof hypoxia appeared to be associated with low root respirationor oxygen consumption rate and high sugar accumulation underhypoxic conditions.Copyright 1995, 1999 Academic Press Oxygen consumption rate, sugar accumulation, Triticum aestivum L., waterlogging tolerance     

Growth and partitioning of C and fixed N in the shrub legume Acacia littorea in the presence or absence of the root hemiparasite Olax phyllanthi

Nodulated plants of Acacia littorea were pot cultured singlyin minus nitrogen sand culture in the presence or absence ofa transplanted seedling of the root hemiparasite Olax phyllanthiand harvests of cultures made 4 and 8 months after introducingthe parasite. Parasitism decreased host shoot growth while increasingroot growth to a similar extent. Final shoot:root dry weightratio was 2.2 for parasitized versus 4.3 for unparasitized Acacia.Partitioning of fixed N showed 4-fold larger N increments inshoots than roots of unparasitized plants, whereas parasitizedplants lost a small amount of shoot N, made a root gain of Ndouble that of unparasitized plants and lost over half of theirN to Olax. The increment of fixed N in the host:parasite associationwas similar to that of unparasitized Acacia. Data on dry mattergain per unit foliage area and mean CO₂ assimilation rates pershoot of Olax and Acacia (parasitized or unparasitized) werediscussed in relation to an estimated heterotrophic gain ofxylem C from the host equivalent to 40% of the increment ofdry matter C made by the parasite. Growth of Olax was accompaniedby large increases in numbers of haustoria, 9% of which wereattached to root nodules as opposed to roots. Structural andnutritional features of direct parasitism of nodules are described.Models of flow and utilization of C and N in the Acacia:Olaxassociation and unparasitized Acacia are discussed in relationto published data for other host:parasite associations. Key words: Olax phyllanthi, host-parasite relationships, C and N partitioning, Acacia, N₂ fixation     

A Comparison of Dry Matter Partitioning in Seminal and Adventitious Plants of Trifolium repens L

Trifolium repens has two types of root, one derived from theseed and the adventitious roots derived from the stolon nodes.It has been suggested that these two systems have differentpotentials for supporting growth. This paper presents a comparisonof plants grown on single seedling or adventitious roots anddemonstrates that although the shoot: root ratios for the twotypes differ this may be explained by differing shoot morphologies.Comparison of the lamina: root ratios for the two types of plantproduced no statistically significant differences and it isproposed that the two types of root system do not differ intheir relationship with leaf growth. A mechanism for large diameter‘tap’ root formation is suggested. white clover, Trifolium repens L., adventitious roots, seedling roots, shoot: root ratio     

Allometric Root/Shoot Relationships and Predicted Water Uptake for Desert Succulents

Root morphology, shoot morphology, and water uptake for Agavedeserti and Ferocactus acanthodes of various sizes were studiedusing allometric relationships (y = ax^b) and a previously developedwater uptake model. Shoot surface area increased with shootvolume with an exponent b of 0.75 for both species. Root lengthand the ground area explored by the roots increased with shootsurface area with b's of 0.72 for A. deserti and 0.92 for F.acanthodes. Various sized individuals had about the same ratioof root length to explored ground area, with higher values occurringfor A. deserti. Predicted water uptake averaged over the exploredground area was approximately constant over a 10⁴-fold rangein shoot surface area, suggesting that shoot size confers nointraspecific competitive advantage for water uptake. For theroot lengths per explored ground area observed in the field,water uptake was predicted to be 85 per cent of maximal; wateruptake could be increased by the production of more rain roots.When differences in shoot volume were accounted for by allometry,small plants had relatively less shoot surface area and relativelymore root length per shoot volume than did large plants, whichmay be important for the water relations of seedling establishment. Agave deserti, Ferocactus acanthodes, allometry, desert succulents, root distribution, root length, seedling growth, seedling establishment, shoot surface area, shoot volume, water uptake     

Morphogenetic Aspects of a Leafless Mutant in Tomato: III. GROWTH AND PEROXIDASE ACTIVITY OF ROOTS

Using morphological and biochemical criteria, comparisons weremade between intact and excised roots of normal tomato (Lycopersiconesculentum Mill.) and the reduced form of the homozygous lanceolatemutant. Intact normal roots showed greater growth as reflectedin length of the main root axis, number of lateral roots, andprotodermal cell size. Excised normal roots grew more rapidlythan those of the mutant only during the first 24-h intervalof the first week in culture. Intact mutant roots revealed agreater activity of peroxidase, but excised mutant roots showedno increase in enzyme activity. It is concluded that the primarysite of action of the mutant allele is the shoot system, andin particular the leaf marginal meristem. The effects of thelanceolate gene on the root system in tomato are interpretedas being of secondary importance with regard to gene action.     

Root Distribution, Growth, Respiration, and Hydraulic Conductivity for Two Highly Productive Agaves

Cultivated Agave mapisaga and A. salmiana can have an extremelyhigh above-ground dry-weight productivity of 40 Mg ha^–1yr^–1. To help understand the below-ground capabilitiesthat support the high above-ground productivity of these Crassulaceanacid metabolism plants, roots were studied in the laboratoryand in plantations near Mexico City. For approximately 15-year-oldplants, the lateral spread of roots from the plant base averaged1.3 m and the maximal root depth was 0.8 m, both considerablygreater than for desert succulents of the same age. Root andshoot growth occurred all year, although the increase in shootgrowth at the beginning of the wet season preceded the increasein growth of main roots. New lateral roots branching from themain roots were more common at the beginning of the wet season,which favoured water uptake with a minimal biomass investment,whereas growth of new main roots occurred later in the growingseason. The root: shoot dry weight ratio was extremely low,less than 0.07 for 6-year-old plants of both species, and decreasedwith plant age. The elongation rates of main roots and lateralroots were 10 to 17 mm d^–1, higher than for various desertsucculents but similar to elongation rates for roots of highlyproductive C₃ and C₄ agronomic species. The respiration rateof attached main roots was 32 µmol CO₂ evolved kg^–1dry weight s^–1 at 4 weeks of age, that of lateral rootswas about 70% higher, and both rates decreased with root age.Such respiration rates are 4- to 5-fold higher than for Agavedeserti, but similar to rates for C₃ and C₄ agronomic species.The root hydraulic conductivity had a maximal value of 3 x 10^–7ms^–1 MPa^–1 at 4 weeks of age, similar to A. deserti.The radial hydraulic conductivity from the root surface to thexylem decreased and the axial conductivity along the xylem increasedwith root age, again similar to A. deserti. Thus, although rootsof A. mapisaga and A. salmiana had hydraulic properties perunit length similar to those of a desert agave, their highergrowth rates, their higher respiration rates, and the greatersoil volume explored by their roots than for various desertsucculents apparently helped support their high above-groundbiomass productivity Key words: Crassulacean acid metabolism, productivity, root elongation rate, root system, water uptake     

Delivery rates of abscisic acid in xylem sap of Ricinus communis L. plants subjected to part-drying of the soil

Abscisic acid (ABA) moving from roots to shoots in the transpirationstream is a potential hormonal message integrating perceptionof a root stress with adaptive changes in the shoot. A twinroot system was used to study ways of estimating effects ofdroughting the upper roots of Ricinus communis L. on abscisicacid (ABA) transport to the shoot in the transpiration stream.Droughted plants transpired more slowly than controls. Droughtingalso increased concentrations of ABA up to I I-fold in sap inducedto flow from the roots of freshly decapitated plants at ratesof whole plant transpiration. However, because of dilution effectsarising from the different sap flows in control and droughtedplants, these changes in ABA concentration in the xylem sapdid not accurately reflect amounts of ABA transported. To overcomethis problem, delivery rates were calculated by multiplyingconcentration with sap flow rate to generate ABA delivery interms of µmol s–1 per plant. Droughting for 24 hor more increased ABA delivery from roots to shoots by 5-fold.Since droughting can alter the relative sizes of the roots andshoots and also the root:shoot ratio these delivery rates wererefined in several ways to reflect both the amount of root generatingthe ABA message and the size of the recipient shoot system. Key words: Abscisic acid, Ricinus communis L., soil drying, xylem sap     

Changes in the Growth of Roots and Shoots when Perilla frutescens L. Britt. is Induced to Flower

The pattern of root and shoot growth of Perilla frutescens L.Britt. was studied in plants growing either in norally inductivephotoperiods or in non-inductive photoperiods. By the 20th dayof inductive treatment, that is at least 5 d before the firstflowers were pollinated, the rate of dry matter accumulationin the roots was slower in induced than in non-induced plants.The roots of induced plants had both a smaller fresh weightand dry weight per unit length. The rate of root elongationalso became slower in induced plants than in non-induced plants.The frequency of branching was greater in roots of induced plants.Plants exposed to inductive photoperiods showed precocious developmentof axillary buds on the shoot, and a reduction in the rate ofstem elongation. It is suggested that these changes in the shootreflect a decrease in the auxin status of the shoot, which mayin turn be responsible for the decreased rate of root growthin the induced plants.