The Effects of Indole-3-Acetic Acid and 2:4-Dichlorophenoxyacetic Acid on the Growth Rate and Endogenous Rhythm of Intact AvenaColeoptiles

The rates of elongation of the coleoptiles of Avena seedlings,subjected to intermittent immersion in solutions of IAA or 2:4-Dfor various total periods, were determined from measurementsof photographs taken every hour by infra-red radiation. Immersion in 17·5 mg./l. IAA for 1–5 hours causeda large increase in the growth rate followed by a depression.When the seedlings were immersed in 8·75 mg./l. IAA forperiods of 12 or 24 hours the depression was partially overcomeso long as the treatment was continued. Absorption of additionalIAA by the coleoptiles reduced their geotropic sensitivity. Penetration of 2:4-D (sodium salt) into the coleoptiles wasslower than that of IAA and the resulting stimulation of thegrowth rate was less, particularly in unbuffered solutions.After the treatment the growth rate declined slowly to aboutthe normal value. Results with coleoptiles were very similar to those previouslyobtained with rhizomes of Aegopodium and suggest that inhibitionof growth following stimulation by IAA may be of general occurrence.Possible causes of the inhibition are discussed and a comparisonis made between the results with intact coleoptiles and observationsmade by others on coleoptile sections. Temporary immersion of the seedlings in auxin solutions depressedthe rate of elongation of the primary leaf while it increasedthat of the coleoptile. It caused little disturbance of theendogenous rhythm induced by change from light to darkness.The suggestion that such rhythms can be explained in terms ofvariation in concentration of IAA-oxidase is not supported.     

Epidermal Growth Factor Interacts with Indole-3-Acetic Acid and Promotes Coleoptile Growth

We used coleoptile sections of Avena sativa, Sorghum bicolor,and Zea mays seedlings to examine interactions between epidermalgrowth factor (EGF) and indole-3-acetic acid (IAA) that mayaffect plant growth and development. Our 24-h bioassays employedthree controls ranging in dilution from 10^–4 to 10^–8g ml^–1: (1) 50 mM potassium-phosphate buffer solution(pH=6.0), (2) bovine serum albumin, a nonspecific protein; and(3) IAA; plus two treatments: (1) mouse epidermal growth factor(EGF) ranging from 10^–6 to 10^–10gml^–1, and(2) EGF + IAA. In all three species growth in IAA, EGF, andEGF + IAA treatments showed significant increases over controls;EGF+IAA showed significant increases in growth over IAA alone.As the concentrations of IAA decreased, the EGF and IAA interactionbecame more pronounced. At the highest IAA concentrations, EGF+ IAA increased growth rates ca. 2% to 39%, whereas at lowerIAA concentrations EGF + IAA promoted growth as much as 121%,thereby lowering the normal IAA physiological set point up tothree or four orders of magnitude. Our data suggest that aninteraction between EGF and IAA may allow plants to recognizeand respond to animal biochemical messengers, resulting in changesin plant cell elongation that ultimately may alter plant growthpatterns. (Received April 27, 1994; Accepted September 5, 1994)     

Studies on the Geotropism of Roots:II.THE EFFECTS OF THE AUXIN ANTAGONIST {alpha}-(I-NAPHTHYLMETHYLSULPHIDE)PROPIONIC ACID (NMSP) AND ITS INTERACTIONS WITH APPLIED AUXINS

Previous experiments on the effects of auxins on the geotropicresponses of seedling pea roots (Audus and Brownbridge, 1957)have been extended using the ‘anti-auxin’ -(I-naphthylmethylsulphide)propionicacid (NMSP) alone and in combination with indole-3-acetic acid(IAA) and 2:4-dichlorophenoxyacetic acid (2:4-D). NMSP action differs from that of the auxins in that it reducesthe rate of curvature progressively as the concentration isincreased, irrespective of whether the overall extension growthof the roots is being stimulated (10 and 30 p.p.m.) or inhibited(100 p.p.m.). Correspondingly the reaction time is lengthenedby 25–50 per cent. in all concentrations. Studies of responsesin mixtures of growth-stimulating concentrations of NMSP (30p.p.m.) and growth-inhibiting concentrations of IAA (10^–8)and 2:4-D (3 x 10^–8) show that auxins and ‘antiauxins’are mutually antagonistic in most, if not all, their actionson growth and curvature. The results suggest that the anti-auxin NMSP may stimulate rootgrowth and inhibit curvature by interfering with the synthesisor distribution of a natural endogenous inhibitor, which isnot IAA. NMSP inhibition of root growth in high concentrationsmust, however, be exerted independently of this natural inhibitor.The mutual antagonisms shown between the auxins and NMSP arebest explained in terms of an interference with access to thegrowth centres; competitive action at the growth centres themselvesseems not to be involved.     

Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean     

Effects of Auxin and Gibberellin on Elongation of Young Hyphae in Neurospora crassa

IAA, 2,4-D and GA₃ promoted the elongation of young hyphae inNeurospora crassa at the optimum concentrations of 10^–6,10^–6 and 10^–4 M, respectively. The effects of IAAand GA₃ were additive. (Received June 17, 1983; Accepted December 22, 1983)     

Cooperation of Ethylene and Auxin in the Growth Regulation of Rice Coleoptile Segments

Elongation of coleoptile segments, having or not having a tip,excised from rice (Oryza sativa L. cv. Sasanishiki) seedlingswas promoted by exogenous ethylene above 0.3 µl l^–1as well as by IAA above 0.1 µM. Ethylene production ofdecapitated segments was stimulated by IAA above 1.0µM,and this was strongly inhibited by 1.0 µM AVG. AVG inhibitedthe IAA-stimulated elongation of the decapitated segment witha 4 h lag period, and this was completely recovered by ethyleneapplied at the concentration of 0.03 µl l^–1, whichhad no effect on elongation without exogenous IAA. The effectsof IAA and ethylene on elongation were additive. These factsshow that ethylene produced in response to IAA promotes ricecoleoptile elongation in concert with IAA, probably by prolongingthe possible duration of the IAA-stimulated elongation, butthat they act independently of each other. Moreover, AVG stronglyinhibited the endogenous growth of coleoptile segments withtips and this effect was nullified by the exogenous applicationof 0.03 µl l^–1 ethylene. These data imply that theelongation of intact rice coleoptiles may be regulated cooperativelyby endogenous ethylene and auxin in the same manner as foundin the IAA-stimulated elongation of the decapitated coleoptilesegments. Key words: oryza sativa, Ethylene, Auxin, Coleoptile growth     

The Uptake of Growth Substances: I. FACTORS CONTROLLING THE UPTAKE OF PHENOXYACETIC ACIEDS BY LEMNA MINOR

An analysis has been made of the factors controlling the uptakeof 2:4-dichloro-phenoxyacetic acid (2:4-D) and related compoundsby Lemna minor, grown under controlled conditions. All compoundswere labelled with ¹⁴C in the carboxyl group and the ¹⁴C inthe plants, after liquid combustion, assayed as barium carbonate. With 2:4-D the rate of entry from concentrations of 8 to 32mg./l. is maximal in the first 20 minutes, then falls progressivelyuntil the rate is zero between 1 and 2 hours and in the thirdphase (up to 24 hours) there is a net loss from the plants dueto an outward movement of the compound back into the externalsolution. When the chlorine substitutions are in the 2:6-positionthe course of uptake is similar, save that loss to the solutiontakes place later. For the 2-chloro-substitution, after theinitial phase of uptake there is some loss but this is followedby a period of recovery and uptake again proceeds, but slowly.In contrast, the course of uptake over 24 hours of phenoxyaceticacid is normal, i.e. there is a steady accumulation. When plants are pretreated with labelled 2:4-D for 30–60minutes and transferred to water or culture solution then over90 per cent. of the ¹⁴C is found in the external medium after4:5 hours and this release cannot be accounted for in termsof exchange processes since the addition of unlabelled compoundto the medium retards the rate of loss. This loss is slowedbut not stopped at 1.25°C. and up to 22.5°C. the rangeof the Q₁₀ is 1.6–1.9. Uptake in the first 30 minutes is temperature sensitive between7.5 and 30°C. (Q₁₀ 2.3–2.6) and in general is positivelyand curvilinearly related to the external concentration. Pretreatmentwith unlabelled compound up to 2 hours progressively depressesthe subsequent initial uptake of labeled growth regulator. Itis concluded that initially the rate of entry greatly exceedsthe rate of loss but that with time the ratio steadily diminishesto less than unity. Initial uptake of 2:4-D is markedly dependent on the pH of thesolution and closely but not completely correlated with theexternal concentration of undissociated molecules. On the otherhand, the outward movement is relatively unaffected by the externalpH. Combinations of concentration and time of exposure which bringabout loss to the solution need not cause any permanent retardationof growth. In fact, exposure for 1 hour to 8 mg./l. significantlyaccelerated growth in the next 8 days. These results are discussed in relation to previous findingsand it is concluded that the pattern of uptake is determinedon the one hand by the chemical structure of the growth substanceand on the other by specific physiological differences at celllevel.     

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; )     

Factors Affecting Growth and Aggregate Dissociation in Batch Suspension Cultures of Datura innoxia (Miller)

Growth kinetics of Datura innoxia batch suspension cultureswen monitored by a Klett-turbidimetric technique. While cultured. wt varied linearly with Klett units, f. wt and packed cellvolume did not. Turbidimetrically determined doubling timeswere highly reproducible. The method proved to be useful inthe determination of acutely lethal conantrations of a seriesof anti-metabolites. In certain circumstances, aggregate dissociation in batch suspensioncultures of D. innoxia was found to be coupled to growth rate.Suspensions maintained with 10^–5 M 2,4-D exhibited a relativelyslow growth rate with a high degree of aggregate dissociation:10^–4 M 2,4-D promoted a maximum growth rate, but dramaticallysuppressed aggregate dissociation. At 10^–5 M 2,4-D, themitotic index of smaller-aggregate fractions was greater thanthe mitotic index of the large-aggregate fraction. At 10^–5M 2,4-D the converse was observed. Supraoptimal 2,4-D concentrationsthus enhanced both aggregate dissociation and the growth ofsmaller aggregates. When present in concentrations promoting optimal growth. malicand succinic acids caused a decrease in aggregate dissociation.Casein hydrolysate dramatically enhanced growth, but did notaffect aggregate dissociation to the same degree as 2,4-D orthe Krebs cycle organic acids. Suggestions are made concerningmedium composition to be used in future mutant selection schemesusing D. innoxia. Datura innoxia (Miller), suspension culture, growth kinetics, mitotic index, 2,4-dichorophenoxy acetic acid     

Spatial and Temporal Aspects of Growth in the Primary Root of Cotton Seedlings: Effects of NaCl and CaCl2

Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) weregrown in modified Hoagland nutrient solution with various combinationsof NaCl and CaCl₂. Marking experiments and numerical analysiswere conducted to characterize the spatial and temporal patternsof cotton root growth at varied Na/Ca ratios. At 1 mol m^–3Ca, 150 mol m^–3 NaCl reduced overall root elongation rateto 60% of the control, while increasing Ca to 10 mol m^–3at the same NaCl concentration restored the elongation rateto 80% of the control. Analysis of the spatial distributionof elongation revealed that the presence of 150 mol m^–3NaCl in the medium shortened the growth zone by about 2 mm fromthe approximate 10 mm in the control and also reduced the relativeelemental elongation rate (i.e. the longitudinal strain rate,defined as the derivatives of displacement velocity of a cellularparticle with respect to position on root axis). Supply of 10mol m^–3 Ca at the high salt condition restored partiallythe relative elemental elongation rate, but not the length ofthe growth zone. Compared to the control, the growth trajectoriesshowed that at 1 mol m^–3 CaCl2 it took more time for acellular particle to move through the growth zone at 150 molm^–3 NaCl, while at 10 mol m^–3 CaCl it took lesstime and there was no difference between the NaCl treatments Key words: Gossypium hirsutum, salinity stress, root growth kinematics     

Studies on the Geotropism of Roots: I.GROWTH-RATE DISTRIBUTION DURING RESPONSE AND THE EFFECTS OF APPLIED AUXINSI

Experiments are described in which the normal geotropic responsesof the roots of Pisum sativum seedlings have been compared withthose obtained in the presence of auxins (indole-3-acetic acidand 2:4-dichlorophenoxyacetic acid) in the external medium.The courses of positive curvature resulting from short exposures(40 minutes) and also subsequent recovery phenomena on a horizontalklinostat have been followed. A photographic recording techniqueallowed the determination of absolute growth-rates of both upperand lower sides of the root during the course of each experiment. Positive curvature started at its maximum rate (0.30–0.32deg./min.) after a reaction time of 11.5 minutes and continuedconstant at that rate for about 60 minutes after stimulationceased. Recovery took place at a similar rate of curvature andwas complete after a further 150–200 minutes. During thephase of positive curvature overall root growth-rates were considerablyreduced and were slowly restored to normal during recovery. Low concentrations (1 part in 10¹¹) of both auxins increasedthe rate of positive curvature by 30–40 per cent. andshortened the reaction time roughly in proportion. The growth-ratesof both sides of the root were increased to the same extentduring both curvature and recovery. High concentrations (10^–8IAA and 3.10^–8 2: 4-D)reduced the rates of curvature by 50 per cent., lengthened thereaction time, and inhibited the growth of both sides of theroot during both curvature and recovery. Neither concentration of either auxin otherwise affected thetime course of response and recovery. It is suggested that geotropic response is due to the de novoproduction of an endogenous inhibitor in the extending cellsof the lower side of the root whence it may later spread tothe upper side. The complete independence of the growth actionsof this inhibitor and of the applied auxins suggests that itis not indole-3-acetic acid or any similar compound. Recoverymay be very largely independent of both inhibitor and auxinsand due to the action of another growth factor limiting celllength. The implications of these findings and of the attendant theoriesare fully discussed.     

Effect of Indoleacetic Acid on Growth and Dinitrogen Fixation in Cyanobacteria

The effect of IAA on growth, dinitrogen fixation, and heterocystsfrequency of Anabaena PCC 7119 and Nodularia sp. have been investigated.Concentrations of IAA ranging from 10^–10 to 10^–4M did not change the growth of Anabaena PCC 7119. Concentrationshigher than 10^–4 M were inhibitory. Similar results werefound in Nodularia sp. although in this case the inhibitoryeffect appeared with 10^–5M of IAA. Neither the nitrogenaseactivity nor the heterocysts frequency were enhanced by IAAtreatment. (Received June 17, 1986; Accepted January 22, 1987)     

Effect of {alpha}-Tomatine on the Response of Wheat Coleoptile Segments to Exogenous Indole-3-acetic Acid

A concentration of 10^–5 M tomatine had no effect on leakagefrom, or elongation of, wheat coleoptile segments, but consistentlyreduced IAA-enhanced extension growth by c. 50 per cent. Therewas no evidence of chemical interaction between the alkaloidand the auxin in solution, and IAA action was not affected bypre-treatment for up to 3 h with 10^–5 M tomatine. Studieswith [2-¹⁴C]IAA revealed that 10^–5 M tomatine did notinhibit uptake of auxin into segments. The effect of pre-treatingsegments for up to 3 h with IAA could be virtually nullifiedby 10^–5 M tomatine, as could also IAA-induced changesin properties of coleoptile cell walls. Results are discussedin relation to the ability of tomatine to disrupt membrane functionand to current hypotheses implicating membranes in the primaryaction of auxin.     

Effect of Some Known Growth Regulators on Growth and Fertility in Male Clones of the Moss Microdus brasiliensis (Dub.) Ther.

Among the auxins (IAA, 2,4-D, NAA and NOA) LAA proves inhibitoryfor antheridial formation. The rest promote this response, andNAA is most effective. Cytokinin (2iP) stimulates vegetativegrowth as well as antheridial formation, but the effect is morepronounced on the former. Interaction of kinetin and IAA provesbetter for antheridial production as compared to IAA alone.Gibberellic acid enhances gametangial induction as well as vegetativegrowth at lower levels (10^–8–10^–8 mol dm^–3).With abscisic acid both the responses are markedly reduced.Anti-auxins and cycocel promote antheridial production and vegetativegrowth. Testosterone is more potent than progesterone in promotingantheridial formation and vegetative growth. Key words: Fertility, growth hormones, moss     

Hormonal Regulation of Phototropism in the Light-grown Sunflower Seedling, Helianthus annuus L.: Immobility of Endogenous Indoleacetic Acid and Inhibition of Hypocotyl Growth by Illuminated Cotyledons

Light-grown sunflower seedlings contain 10^–7–3 x10^–7 M indoleacetic acid (IAA). The even distributionof this endogenous IAA in straight hypocotyls does not changeduring phototropic curvature. The diffusate from hypocotylscontains substance(s) influencing the elongation rate of Avenacoleoptile segments but hardly any IAA. Phototropic curvature of the hypocotyl requires the presenceof illuminated cotyledons. Illumination of cotyledons inhibitshypocotyl growth. It is concluded that the phototropic response of the sunflowerhypocotyl is regulated by factors promoting and inhibiting cellelongation other than IAA.     

Ethylene and 1 -Aminocyclopropane-1-Carboxylic Acid Production in flacca, a Wilty Mutant of Tomato, Subjected to Water Deficiency and Pre-treatment with Abscisic Acid

Neill, S. J., McGaw, B. A. and Horgan, R. 1986. Ethylene and1-aminocyclopropane-l-carboxylic acid production in flacca,a wilty mutant of tomato, subjected to water deficiency andpretreatment with abscisic acid —J. exp. Bot. 37: 535–541. Plants of Lycoperstcon esculentum Mill. cv. Ailsa Craig wildtype and flacca (flc) were sprayed daily with H²O or 2?10^–2mol m^–3 abscisic acid (ABA). ABA treatment effected apartial phenotypic reversion of flc shoots; leaf areas wereincreased and transpiration rates decreased. Leaf expansionof wild type shoots was inhibited by ABA. Indoleacetic acid (IAA), ABA and l-aminocyclopropane-l-carboxylicacid (ACC) concentrations were determined by combined gas chromatography-massspectrometry using deuterium-labelled internal standards ABAtreatment for 30 d resulted in greatly elevated internal ABAlevels, increasing from 1?0 to 4?3 and from 0?45 to 4?9 nmolg^–1 fr. wt. in wild type and flc leaves respectively.Endogenous IAA and ACC concentrations were much lower than thoseof ABA. IAA content ranged from 0?05 to 0?1 nmol g^–1 andACC content from 0?07 to 0?24 nmol g^–1 Ethylene emanationrates were similar for wild type and flc shoots. Wilting of detached leaves induced a substantial increase inethylene and ACC accumulation in all plants, regardless of treatmentor type. Ethylene and ACC levels were no greater in flc leavescompared to the wild type. ABA pretreatment did not preventthe wilting-induced increase in ACC and ethylene synthesis. Key words: ABA, ACC, ethylene, wilting, wilty mutants     

Resemblance of growth substances to metal chelators with respect to their actions on duckweed growth

Action patterns of IAA, KIN and GA on the growth of Lemna gibbaG3 are similar to those reported for agents chelating both cupricand ferric ions. Relatively high doses of growth substances,e.g.10^–6 M IAA or KIN and ^–4 M GA, inhibit developmentof photoperiodically induced flower buds and antagonisticallypromote frond multiplication; whereas, at relatively low doses,e.g. 10^–9 M IAA or KIN and ^–5 M GA, they acceleratethe process occurring in the latter half of the induction periodto enhance flower induction. Complex forming abilities of IAA,KIN and GA with cupric and ferric ions are demonstrated spectrophotometrically.Moreover, the ferrous ion-dependent oscillatory change in reproductiveand vegetative photophilies of duckweed is eliminated by KINbut not by IAA and GA. Of the three growth substances tried,KIN alone shows an affinity for ferrous ions. (Received April 5, 1971; )     

Involvement of cellulose synthesis in actions of gibberellin and kinetin on cell expansion. Gibberellin-coumarin and kinetin-coumarin interactions on stem elongation

In azuki bean (Azukia angularis = Vignia angularis) epicotylsections, 5 ? 10^–4 M coumarin inhibited the incorporationof radioactivity from [U^–14C]glucose into the cellulosefraction by 35% in the absence of indole-3-acetic acid (IAA)and by 40% in the presence of 1 ? 10^–4 M IAA. There wasno inhibitory effect on the incorporation of radioactivity intothe other fractions. Coumarin at 5 ? 10^–4 M reversed thepromoting effect of 1 ? 10^–5 M gibberellin A₃ (GA) andthe inhibitory effect of 1 ? 10^–5 M kinetin on IAA-inducedelongation of sections with no significant effects on IAA-inducedelongation. Neither GA nor kinetin had any appreciable effectson cellulose synthesis. No inhibition of cellulose syntheiswas observed with 1 ? 10^–3 M colchichine, which has beenreported to have effects similar to those of coumarin on GA-or kinetin-affected stem elongation. Coumarin at 5 ? 10^–4M was ineffectual in breaking up wall microtubules, while adisrupting effect on wall microtubules was clearly demonstratedwith 3 ? 10^–4M colchicine. From these results, the possible involvement of cellulose synthesisin cell expansion controlled by GA or kinetin was suggested. (Received August 3, 1973; )     

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