Root-Shoot Interactions in Peach: The Function of the Root

Peach seedlings were grown in aerated nutrient solution in small(15 cm³) or large (500 cm³) containers. Subsequently, some plantswere removed from the small containers to the large, or werestressed by root pruning. Half the plants received a foliarspray of synthetic cytokinin 6-benzylaminopurine (BAP) every4 days. Analysis of all the results enabled correlations between functionand growth measurements to be made. Irrespective of the treatmentthe total water and the total nutrient uptake by the roots wasdirectly related to the total dry weight increment. This suggeststhat for both water and nutrient uptake a functional equilibriumexisted between the root and the shoot. Where BAP treatmentincreased the top: root ratio there was a corresponding increasein the rate of water uptake per unit length of root. The relationship between root number and leaf number and thecomplementary action of BAP suggests that the root tip and itsproduction of cytokinins exerts considerable control over topgrowth.     

Root-Shoot Interactions: Functional Equilibria for Nutrient Uptake in Peach (Prunuspersica L. Batsch.)

Peach seedlings were grown in aerated nutrient solution in small(15 cm³) or large (500 cm³) containers. Subsequently, some plantswere transferred from the small containers to the large, orwere stressed by root pruning. Half the plants received a foliarspray of 6-benzylaminopurine (BAP) every 4 days. Analysis of all the results enabled correlations between growthand nutrient uptake to be made. These relationships supportedthe hypothesis that for nutrient uptake a functional equilibriumexisted between the root and the shoot systems. Data for individual nutrients showed that treatment with BAPaltered the functional equilibrium for some nutrients. In particularit was suggested that indirectly BAP depressed calcium uptakewhereas potassium uptake was increased. Prunus persica, peach, growth, nutrient uptake, root-shoot interactions     

Root Development and Source-Sink Relations in Carrot, Daucus carota L: II. EFFECTS OF ROOT PRUNING ON CARBON ASSIMILATION AND THE PARTITIONING OF ASSIMILATES

Physiological responses to root pruning were investigated bycomparing ¹⁴CO₂ fixation rates, the partitioning of ¹⁴C-labelledassimilate, and soluble and insoluble carbohydrate levels inthe leaves of carrot plants following the removal of some ofthe fibrous roots, or fibrous roots and part of the tap root.Root pruning reduced ¹⁴CO₂ fixation by 28–45% but leafspecific activity (¹⁴C assimilation g-¹ leaf fresh weight) wasunchanged. The proportion of total assimilate exported to theroot system increased following root pruning and this was atthe expense of the developing leaves. In younger plants (wherethe tap root received 10% of the assimilate) the supply of ¹⁴Cto the tap root was maintained in spite of root pruning. However,shortening the tap root to 3 cm in older plants (in which 30%of the fixed 14C was normally exported to the developing storageorgan), reduced its sink capacity and resulted in slightly greaterretention of ¹⁴C in the mature leaves. Greater concentrationsof insoluble carbohydrate were found in the mature leaves followingroot pruning but soluble sugar content was unaffected. Onlysmall differences were observed in the distribution of ¹⁴C betweensoluble and insoluble carbohydrate fractions when plants werefed ¹⁴CO₂ several days after the root pruning operations. Thesephysiological responses were mainly associated with the removalof fibrous roots and support the view that the fibrous rootsystem is more important than the developing storage organ inregulating growth in young carrot plants.     

Suppression of Calcium Transport to Shoots by Root Restriction in Tomato Plants

Restriction of tomato roots by growth in small containers stronglysuppressed transport of ⁴⁵Ca²⁺ ions to new leaves and apices.Water transport, expressed on a leaf area basis, was marginallyreduced by root restriction, an indication that calcium transportwas more severely limited than water transport. (Received October 11, 1996; Accepted January 27, 1997)     

Tomato (Lycopersicon esculentum Mill., cv. 'Better Bush') Plant Response to Root Restriction

Observations presented here describe changes in the growth ofLycopersicon esculentum Mill., cv. ‘Better Bush’,at the onset of root-restriction stress. Plants were grown ineither 1500 cm³ (control) or 25 cm³ (treated) containers ina flow-through hydroponic culture system (FTS). Seeds were imbibed,germinated, held for 13 d in sterile germination bags, thenplaced into the FTS and designated day zero plants. Plants grownin the FTS were harvested, every 7 d, from day 11 to day 46.Plant height, root and shoot weights, leaf areas, leaf lengths,branching and flowering were measured to illustrate morphologicalchanges that occurred in response to root-restriction stress.Plants restricted to a 25 cm³ root volume experienced a markedstress after 18 d in the FTS. A reduction in leaf elongationwas evident and preceded the time (prior to day 25) when maximumdry weights were attained by restricted root systems. Controlplants had greater leaf areas and plant dry weights than thoseof root-restricted plants after day 18. Treated plants showedno significant increase in dry weights from day 32 to the endof the experiment. Between day 18 and 25 the root: shoot ratiofor the treated plants dropped below that of the controls. Adventitiousrooting was evident in treated plants by day 25. Roots of thetreated plants showed an apparent waterlogging indicated bybrowning of roots by day 32. Root turnover followed as the primaryroot system was replaced by adventitious roots. The number ofbranches or flowers did not differ between control and treatedplants. The timing of the events described here can be usedto further the study of specific physiological responses oftomato plants to root-restriction stress.     

Root Confinement and its Effects on the Water Relations, Growth and Assimilate Partitioning of Tomato (Lycopersicon esculentum Mill)

Although it is well established that the root growth in manyspecies is very sensitive to mechanical impedance or to confinementin small volumes, little is known about the consequent effectson growth of the whole plant and the mechanisms involved. Thiswork investigated the effects of root confinement on the waterrelations, growth and assimilate partitioning of tomato (Lycopersiconesculentum Mill) grown in solution culture. Six-week old plants were transferred to either 4500 ml or 75ml containers filled with nutrient solution, and allowed togrow for 14 d. Transpiration, leaf-air temperature differences,and leaf diffusive resistances were measured frequently. Leaf,stem and shoot dry masses, leaf area and root length, were estimatedwhen the treatments were imposed and at the end of the experiment.After 14 d growth the root and shoot hydraulic resistances wereestimated from measurements of leaf water potential and transpirationrate, using a steady-state technique. Confining root growth to the small containers substantiallyreduced shoot and root growth and increased the proportion oftotal dry matter present in the stems. These effects were dueto drought stress. The hydraulic resistance of the root systemwas greatest in the confined plants. This led to more negativeleaf water potentials, increased leaf diffusive resistance,and reduced the net assimilation rate by a factor of 2.5. Transpirationper unit leaf area was less affected. However, cumulative transpirationwas also reduced by a factor of 2.5. mostly because of the smallerleaf area on the confined plants. Root hydraulic resistivitywas measured at 3.1 x 10¹²s m^–1 in the control treatment,but increased to 3.9 x 10¹² s m^–1 for roots in the smallcontainer. The mechanisms by which root confinement caused drought stressand disrupted the pattern of assimilate partitioning are discussedin detail. Assimilate partitioning, Lycopersicon esculentum, root confinement, plant growth, root growth, root resistance, shoot resistance, tomato, transpiration, water-use efficiency     

Water relations and abscisic acid levels of watermelon as affected by rooting volume restriction

Rooting volume restriction (RVR) reduces shoot growth of plantsprovided with sufficient water or nutrients. The effects ofRVR on water status, abscisic acid (ABA) levels in leaves, roots,or xylem sap from detopped plants of watermelon [Citrullus lanatus(Thunb.) Matsum. and Nakai ‘StarBrite’] seedlingswere evaluated with five rooting volumes (18, 26, 36, 46, or80 cm3). Shoot water potential increased with increasing rootingvolume, with no difference between plants from 18 and 26 cm³cells or between plants from 36 and 46 cm³ cells. Stomatal conductancewas not consistently affected by RVR; at 10 and 20 DAE, stomatalconductance in plants grown in 36 cm³ cells was higher thanthat of plants grown in any other cell volume. Severe RVR (18and/or 26 cm³) tended to produce plants with higher ABA levelsin roots (15 DAE only), xylem sap (all dates), and leaves (5and 10 DAE). Plants grown in 18 and 26 cm³ cells had higherroot ABA levels than those from 46 and 80 cm³ cells at 15 DAE.Plants grown in 18 cm³ cells had the highest xylem sap ABA levelat all dates, but ABA levels did not differ among plants grownin the other cell volumes. Plants grown in 18 cm³ cells at 5DAE and 18 and 26 cm³ cells at 10 DAE also had higher leaf ABAlevels than those from other rooting volumes. The results suggestthat ABA may act as a signal for reduced growth of plants underRVR conditions. Key words: Abscisic acid, ABA, root signals, root volume restriction, water relations     

Effects of Root Zone Restriction on Amino Acid Status and Bean Plant Growth

The possibility that the suppression of shoot growth in restrictedroot zone plants (RRZP) is caused by a deficiency in N-aminocompounds (NAC) in the shoot, possibly due to an insufficientsupply from the roots, was studied in bean (Phaseolus vulgarisL.). Root zone restriction to 10 cm³ in an aerated nutrientsolution resulted in suppressed plant growth, as compared withcontrol plants grown in a non-limiting root zone volume. Rootxylem exudation of solution and N-amino compunds (NAC) followingdecapitation was much greater in the control, as compared withRRZP, both per plant and per unit root fresh weight (FWT). Inboth treatments, asparagine comprised more than 52% of the NACfraction in the root xylem exudate (RE). Its reduced exudationin the RRZP was of a proportion similar to the combined fractionof NAC left over in both treatments. Asparagine accumulationin leaves of the control plants was very high, comprising 73%of the total NAC pool, while in RRZP, it was much smaller anddid not exceed 25%. The total NAC amount per unit of leaf FWTwas 3·3 times smaller for the RRZP, as compared withthe control, resulting mainly from the dramatic drop in asparagineaccumulation. In the roots, RRZP accumulated more NAC per unitroot FWT than the control. Raising both treatments in distilledwater reduced considerably the accumulation of NAC, includingasparagine, in their leaves. RRZP was relatively more suppressedby the absence of nutrients than control plants. This phenomenondid occur, despite the fact that NAC and asparagine concentrationsin the root and shoot of RRZP were greater than in the controlwhen grown in distilled water; Therefore, it was concluded thatroot zone restriction might affect the accumulation of NAC andasparagine in the leaves, but that deficiency in these compoundsis not the primary or the major cause of growth suppressionin RRZP. Key words: Root zone restriction, asparagine, amino-acids, Phaseolus vulgaris     

The Effects of Partially Drying Part of the Root System of Helianthus annuus on the Abscisic Acid Content of the Roots, Xylem Sap and Leaves

Plants of Helianthus annuus were grown in soil in pots suchthat approximately 30% of the root system protruded throughthe base of the pot. After 7 d further growth in aerated nutrientsolution, the attached, protruding roots were air-dried for10–15 min and thereafter surrounded with moist still air,in the dark, for 49 h, whilst the soil was kept at field capacity.The roots of the control plants remained in the nutrient solutionthroughout the experiment. This treatment rapidly reduced the water content of protrudingroots from 20.5 to 17.8 g g^–1 dry mass (DM), which remainedless than that of the control roots for the rest of the experiment.This treatment also reduced root turgor and water potential.The abscisic acid (ABA) concentrations in the protruding roots,xylem sap and leaves of the treated plants increased significantly,compared to values recorded for control plants. In treated roots, the ABA concentration was significantly increased4 h after treatment, with a maximum of 4.4+0.1 nmol g^–1(DM) after 25 h. The ABA concentration in the xylem sap of thetreated plants was significantly greater than in the controls25 h, 30 h, and 49 h after the partial drying of the roots,with a maximum concentration of approximately 970 pmol ABA cm-3at 49 h. Initially, the ABA concentration in the leaves was0.45 nmol g^–1 (DM) which increased significantly to 1.1±0.1 nmol g^–1 at 25 h, to 1.7±0.3 nmol g^–1at 49 h. Leaf conductance was significantly less in plants with air-driedroots than in the controls 8 h after the start of the treatmentand thereafter. The water relations of the leaves of the treatedplants did not differ from those of the control plants. These results confirm previous reports that ABA is rapidly generatedin partially-dried and attached root systems and demonstratesa concomitant large increase in the ABA content of the xylemsap. It is suggested that partial dehydration of some of theroots of Helianthus annuus, increases ABA concentration in thetranspiration stream and decreases leaf conductance in the absenceof changes in leaf water status. As these responses were initiatedin free-growing roots the stimulus is independent of any increasesin soil shear strength that are associated with soil drying. Key words: Soil drying, roots, ABA, leaf conductance, water relations     

Effect of Restricted Root Growth on Carbohydrate Metabolism and Whole Plant Growth of Cucumis sativus L

The effects of varied rooting volumes on root growth and source leaf carbohydrate metabolism were studied in greenhouse-grown cucumber (Cucumis sativus L cv Calypso) plants. Plants were grown for 7 weeks in container volumes that ranged from 0.4 to 5.9 liters. Plants grown in the smaller containers exhibited less leaf expansion, lower root and shoot weight, and fewer lateral stems than plants grown in the 5.9 liter containers. Shoot/root ratio was not altered by the container volume, suggesting coordination of root and shoot growth due to rooting volume. Source leaf carbon exchange rates, assimilate export rates, and starch accumulation rates for plants grown in 0.4 liter containers were approximately one-half or less in comparison to those for plants grown in 5.9 liter containers. Starch concentrations per unit leaf area were maintained at high levels in source leaves of plants grown in 0.4 liter containers over the entire day/night cycle. Lower extractable galactinol synthase activities and higher galactinol concentrations occurred in leaves of plants grown in 0.4 liter container volumes. The reduced sink demand, induced by restricted root growth, may have led to increased starch concentrations and to a reduction in stachyose biosynthesis in cucumber source leaves.     

Root growth of wetland plants with different root types

A wastewater culture system was designed to study the root growth of eight species of wetland plants with two different root types. The system included a plastic barrel for holding the wastewater and a foam plate for holding the plant. The results indicated that the root growth of the plants with fibril roots was faster than that of the plants with rhizomatic roots. The species with fibril roots had higher root number (1349 per plant) than species with rhizomatic roots (549 per plant) after ten weeks of cultivation. The average root biomass of plants with fibril roots was 11.3 g per plant, whereas that of plants with rhizomatic roots was 7.4 g per plant. Fine root biomass of diameter ≤ 1 mm constituted 51.9% of the total root biomass in plants with fibril roots, whereas it accounted for only 25.1% in plants with rhizomatic roots. The root surface area of the plants with fibril roots (6933 cm² per plant) was markedly larger than that of the species with rhizomatic roots (1897 cm² per plant). The species with rhizomatic roots showed a longer root lifespan (46.6 days) than those with fibril roots (34.8 days).     

The Effect of Nitrogen on the Growth and Sugar Content of Sugar-beet

Nitrogen fertilizer applied to sugar-beet increased plant androot dry weight and leaf area, and decreased the sugar contentof the roots per cent of both fresh and dry weight. Change inleaf area accounted wholly for the increase in plant dry weightproduced by nitrogen, because net assimilation rate was unaffected.Nitrogen did not alter the partition of the total assimilatebetween roots and shoots, but increased the fraction of totalassimilate entering the roots that was used in growth, at theexpense of that stored as sugar. Thus, plants with more nitrogenhad a smaller proportion of their root dry weight as sugar becausemore was metabolized in growth of the roots, and not becauseless entered the roots. The heavier roots of plants given more nitrogen were largerin cross-sectional area because the areas of both parenchymaand vascular zones of each peripheral ring within the root werelarger; the number of rings was not increased. Nitrogen increasedthe areas of the tissues in these zones by enlarging cell volumes,not by increasing the number of cells within the tissues. Increasein cell volume was accompanied by proportional increases inthe weights of non-sugar dry matter per cell and water per cell,but the amount of sugar per cell was proportional to cell volumeonly during the initial stage of cell expansion up to cell volumesof about 15x10^–8 cm²; thereafter it was less than proportional,so that sugar per cent of both fresh and dry weight decreasedas cell size increased beyond 15x10^–8 cm². The relationof sugar per cell to cell volume was the same with both amountsof nitrogen given. This implies that increase in nitrogen supplymade the sugar concentration of the root less by increasingthe size of the root cells and not by a specific effect on sugarstorage.     

Growth Responses of Sweet Orange Seedlings to Shoot and Root Pruning

Following combined shoot- and root-pruning treatments the growthof Citrus sinensis (L.) Osbeck seedlings was analysed into responsesto post-pruning size and to the part pruned. The treatmentswere shoots pruned by removing O, , or of their estimated weightin all combinations with roots pruned by removing O, , or oftheir estimated weight. Responses were measured a year laterand are discussed in terms of the mechanisms controlling increment.Total increment was linearly related to initial pruned weightboth within and between treatments and there were no interactionsbetween shoot and root pruning in increment of leaf, new stem,old stem, thorn, fibre-root, or tap-root. Root pruning, pergramme of pruned material, reduced increment more than did shootpruning. With increasing shoot pruning the ratio of new stem to old stemincreased while with increasing root pruning the ratio of fibre-rootto tap-root increased. Following shoot pruning the new-stemincrement was disproportionately large while following rootpruning the increment of top growth was proportionately largerthan that of roots. The results suggest that pruning citrus trees to a constantsize at planting could lead to a uniform tree size in the subsequentorchard but that maximum growth would occur on un-pruned trees.     

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     

Root Development and Source-Sink Relations in Carrot, Daucus carota L.

Growth analysis and ¹⁴CO₂ feeding experiments have shown thatthe developing storage organ became an increasingly importantsink for assimilates, accumulating 40% of the dry matter producedby the carrot plant within 9 weeks of sowing. The relative importanceof each leaf in fixing and exporting ¹⁴C was assessed at twostages of development. Morphogenetic responses indicated thatan absence of thickening in the lateral roots was associatedwith continued meristematic activity in the tap root, in theform of an elongating apex or a vascular cambium. Source-sink relations were examined by observing plant growthfollowing the removal of part of the tap root and/or lateralroots. Pruning the roots at 35 d reduced the subsequent growthof the plant by reducing the AGR of the remaining root systemand the shoot. The reduction in leaf growth was associated witha loss of fibrous roots, removal of part of the tap root havingvery little additional effect on shoot growth although the AGRof the root system was reduced by a further 78%. Increased fibrousroot RGRs following pruning soon re-established the normal fibrousroot/shoot ratio. These experiments demonstrated the importanceof the root system in controlling dry matter production in thecarrot plant, but suggested that the sink activity of the developingstorage organ was less significant than other root functions.     

Pattern and Control of Distribution of 14C-assimilates in Reproductive Plants of Lolium multiflorum Lam. var. Westerwoldicum

The distribution of ¹⁴C-assimilates was examined in reproductiveplants of Lolium multiflorum Lam. var. Westerwoldicum (cv. Tama)from which all emerged tillers had been removed, leaving themain tiller with two expanding leaves, one of them the flagleaf, and two expanded leaves. Export of ¹⁴C from the lowerexpanded leaf was mainly to the tiller in its axil, the steminternode below its node and the roots, whereas the upper expandedleaf supplied predominantly the expanding leaves, the ear, steminternodes, roots and the tiller bud in the axil of the lowerleaf. Defoliation and root-pruning showed that expanding leaveswere able to compete successfully for assimilates, probablythrough the production of substances capable of mobilizing supply.Local application of 1-naphthaleneacetic acid (NAA), gibberellicacid (GA₃) and 6-benzylaminopurine (BAP) to small tiller budsshowed that GA³ and BAP promoted bud growth and ¹⁴C accumulation,but that addition of NAA reduced these effects.     

Dependence of Net Assimilation Rate on Root Growth of Isolated Leaves

The phenomenon of inhibition of assimilation by carbohydrateaccumulation has been reinvestigated using single rooted leavesof dwarf bean. Such a system has the advantage that assimilatingarea remains constant and carbohydrate is translocated to asingle sink-the root system. The net assimilation rate of thesystem did not vary with season and was small compared withintact plants in the summer, suggesting that an internal factorcontrols assimilation rate. Evidence is given that this factoris the rate of translocation of carbohydrate from source tosink (from lamina to root) which in turn depends on growth-rateof the root system. The evidence came from experiments in whichroot growth was stimulated by increasing vessel size, by preliminarytreatment with IAA or by raising the root temperature, or wasretarded by kinetin treatment. In experiments at glasshouse temperature, lamina dry matterincreased by 0.75 mg. per cm.² per week. The maximum valuesattained depended on the time of the experiment. In August itwas greater than 7.0 mg. per cm.¹, but there was a seasonaltrend. In experiments with roots at 24?C, carbohydrate accumulatedin the lamina more slowly than at lower temperatures.     

The Movement of 2,4-dichlorophenyl methanesulfonate 35S in Plants

Movement of 2,4-dichlorophenyl methanesulfonate ³⁵S in plant roots was investigated using plastic containers which physically isolated portions of the plant root system. Results with bean and cotton plants showed that this compound can be absorbed in one part of the root system and distributed to other parts of the root system and also to the top of the plant. These tests confirm field observations of nematode control on roots outside a treated zone which indicated lateral movement of this compound in the roots. There was no evidence of its downward movement from treated leaves to stems or roots of cotton or beans.     

Root growth and nitrate uptake by wheat (Triticum aestivum L.) following wetting of dry surface soil

The nitrate uptake capacity of surface roots of spring wheat(Triticum aestivum L. cv. Kulin) was investigated followingwetting of dry surface soil. Plants were grown to stem elongationstage with adequate watering at depth while the surface soilwas allowed to dry. Eight weeks after sowing, water or a ¹⁵N-nitratesolution was added to the surface soil to simulate rainfall.Root growth and nitrate uptake were measured up to 4 d afterwetting on plants with unconfined nodal root growth and on plantswith the majority of nodal roots confined within small vials.Prior to wetting, plants from both nodal treatments had seminalroots with collapsed cortices along the upper 10 cm and manyshort, viable lateral roots. Nodal roots, where present, wereonly a few cm long and unbranched. Only plants with unconfinednodal roots were able to take up nitrate within the 24 h beforeany new root growth. By 2 d after wetting there was significantgrowth of the seminal lateral roots, and rapid growth and branchingof nodal roots. From 2 d after wetting, plants with confinednodal roots also took up nitrate, presumably due to the growthof the seminal lateral roots. Hence it appears as though thenodal roots in the unconfined treatment could immediately takeup nitrate, but the seminal roots required new lateral rootgrowth to become active in nitrate uptake. The plants with confinednodal roots had a lower nitrate uptake than those with unconfinednodal roots 4 d after wetting, indicating that the seminal rootsystem was not able to compensate for lack of nodal roots. Insufficientnitrate was taken up after 4 d, by plants from either nodalroot treatment, to increase the shoot N concentration significantly. Key words: Triticum aestivum, nitrate uptake, drought, seminal roots, nodal roots     

Effects of Growth Hormone Application on the Secondary Growth of Roots and Stems in Picea sitchensis (Bong.) Carr

Indol-3-ylacetic acid (IAA), gibberellin A3 (GA) and 6 benzylaminopurine(BAP) were applied factorially each at 3x10^–2 M in lanolinto the roots and stems of Sitka spruce seedlings and the activityof the two secondary meristems, the vascular cambium and phellogen,and of the parenchymatous tissues between them, was examined.All the treatments, with the exception of GA produced a localizedstimulation of radial growth at the point of application andthere was a similarity in the response of the various tissuesin both the root and stem. Radial growth of the xylem was notsignificantly affected in the roots whereas in the stems BAPand IAA stimulated growth. In the phloem BAP produced significantstimulation in both roots and stems and IAA stimulated growthin the roots. Growth of the parenchyma and periderm externalto the phloem was also strongly stimulated by both BAP, andIAA in roots and stems. In roots and stems the application of BAP altered the derivativesproduced by the vascular cambium, resulting in the productionof large multiseriate rays in the xylem, and giving rise toan overall increase in the proportion of ray tissue. Picea sitchensis (Bong.) Carr, Sitka spruce, secondary growth, xylem, phloem, periderm, wood rays, Indol-3-ylacetic acid, gibberellin A3, 6 benzylaminopurine, growth hormones