Chemical induction of adventitious root formation in Taxus baccata cuttings

The effect of some auxins (IBA and NAA), phenolic compounds (phloroglucinol, gentisic acid and coumarin), a combination of auxins and phenolics, and a systemic fungicide (Bavistin) have been examined for stimulatory effects on adventitious root formation in stem cuttings (current season's growth) of Taxus baccata L. In general lower concentration (0.25 mM) of both IBA and NAA was more effective in inducing rooting of cuttings taken from both male and female trees. The combined treatment of IBA+NAA (0.25 mM each) showed some success in cuttings from male trees only (55%, compared to 15% rooting in cuttings from female trees). Generally, the callus formation was quite high (70%) in all auxin treatments (alone or in combination). Among the phenolics, 40% rooting success was achieved with phloroglucinol only, while coumarin and gentisic acid were ineffective. The combined treatment of auxins and phenolics also failed to promote rooting. On the other hand, Bavistin was extremely effective for callusing (90%) as well as rooting (80%). The effectiveness of various compounds tested for rooting of young stem cuttings declined in the order: 0.25 mM IBA>0.05% Bavistin>0.25 mM NAA>1.25 mM IBA>15 mM phloroglucinol>IBA+NAA (0.25 mM each). In addition to the auxins, IBA and NAA that are widely used for commercial propagation, the auxin-like properties of the fungicide Bavistin could be exploited for adventitious rooting in T. baccata, and in other plant species.     

Removal of the stem terminal and application of auxin change carbohydrates in Pinus banksiana cuttings during propagation

This study determined how surgical removal of the stem terminal, with indole-3-butyric acid (IBA) treatment, influenced concentrations and partitioning of carbohydrates in Pinus banksiana Lamb, cuttings during propagation. Seedlings and cuttings that originated from 90-day-old stock plants were untreated or treated by removing the stem terminal, followed by application of IBA to the severed apical or basal (cuttings only) stem. Fresh and dry weights of the basal 1-cm stems of cuttings were determined daily for the first 10 days of propagation (i.e., before roots were visible). In addition, basal 1-cm stems, upper (ca 9-cm) stems and needles of seedlings and cuttings were analyzed for sucrose, soluble reducing sugar and total non-structural carbohydrate. Net concentrations of each carbohydrate in cuttings were obtained by subtracting corresponding concentrations for similarly treated seedlings, yielding data directly related to only the physiology of rooting. Data for cuttings indicated that presence of the stem terminal combined with applied IBA positively influenced rooting through processes that increased basal stem fresh and dry weights before root emergence. Removal of the stem terminal influenced accumulation of net total carbohydrate in cuttings, but the major effect was on carbohydrate partitioning. Either type of IBA treatment after removal of the stem terminal usually resulted in different net carbohydrate concentrations in each tissue source of cuttings, compared with only removal of the terminal. Neither basal nor apical IBA treatment of cuttings without stem terminals yielded results for carbohydrate accumulation and partitioning like those obtained with intact cuttings. Removal of the stem terminal, even if followed by IBA treatment, may have lessened rooting potential of cuttings because it resulted in greater reducing sugarstarch concentration ratios in basal stems compared with those in intact cuttings.     

Metabolic changes during rooting in stem cuttings of Casuarina equisetifolia L.: effects of auxin, the sex and the type of cutting on rooting

Rooting in terminal shoot and lateral shoot cuttings from 10-year-old elite trees of Casuarina equisetifolia L. in different sex groups was achieved after 20 days when the basal ends of the cuttings were dipped for 3 h in 20 ppm indole-3-butyric acid (IBA). Shoots derived from male plants rooted better than their female and monoecious counterparts, and the lateral shoots were more responsive to rooting than the terminal shoots. During rooting, the metabolic activities varied in both lateral shoot and terminal shoot cuttings derived from plants under different sex groups. Peroxidase and polyphenoloxidase activities were high during root initiation and showed a sharp decline thereafter. The polyphenoloxidase activity was higher in the lateral shoot than the terminal shoot cuttings. The rooted plantlets survived and established well in the field.Abbreviations IAA indole-3-acetic acid - IBA indole-3-butyric acid - NAA 1-naphthaleneacetic acid - PVP polyvinylpyrrolidone     

Morpho-anatomical and biochemical changes associated with rooting of micropropagated ninebark cuttings

Ninebark (Physocarpus opulifolius) is an attractive ornamental shrub with poor rooting characteristics in some cultivars, which is a limiting factor in commercial production This study was designed to optimize rooting conditions of ninebark cuttings and to observe the effect of exogenous auxin IBA on some morpho-anatomical and biochemical changes associated with rhizogenesis in the in vitro conditions. Both auxins under study: the indole-3-butyric acid (IBA) and 1-naphthalene acetic acid (NAA) gave comparable effects but the combination of ½ MS?+?1 mg·L^?1 IBA was the most cost effective for all rooting parameters. Anatomical changes at the cuttings’ bases during root formation were typical for woody plants and they were accelerated by auxin in the culture medium. High levels of the endogenous indole acid and hydrogen peroxide were temporarily associated with intensive cell divisions in cuttings, and the polyphenolic acid contents kept increasing during rooting above the initial levels and those in controls.

     

The effect of etiolation and shading of stock plants on rhizogenesis in stem cuttings of <Emphasis Type="Italic">Cotinus coggygria</Emphasis>

In order to improve vegetative propagation of a difficult to root Cotinus coggygria the stock plants were subjected to: etiolation, shading and spraying with IBA, combined with the application of two commercially available rooting powders. The IBA treatment was more suitable for rooting of C. coggygria cuttings than the NAA application and it enhanced rhizogenesis regardless of the form of auxin application (foliar application to a stock plant or a rooting powder used directly on cuttings) and the amount of light provided to stock plants. Etiolation did not improve rhizogenesis in stem cuttings, however, reduction of light intensity by 50% and 96% of the ambient prior to harvest of cuttings affected rooting positively. Positive effects of shading can be ascribed to changes in shoot anatomy, i.e. a weaker sclerenchyma development. Synergistic effect of shading and foliar auxin application can result from the increase in leaf blade area and/or thinner lower epiderm. Enhanced rooting in cuttings from shoots grown out under reduced light intensity was accompanied by decrease in the contents of total soluble sugars, soluble proteins and free ABA and by increase in total chlorophyll, free amino acids, polyphenolic acids and free IAA contents.     

Stimulation of adventitious root formation in non-woody stem cuttings by uridine

Uridine strongly stimulated adventitious root formation in stem cuttings of sunflower (Helianthus annuus L.), mung bean (Vigna radiata L.) and common bean (Phaseolus vulgaris L.). A dose response curve of uridine induced rooting showed that the optimum concentration of uridine was 0.1 µM. At all concentrations employed, uridine had no significant effect on root elongation. The rooting response of stem cuttings to the optimal concentration of indole-3-butyric acid (10 µM) in combination with 0.1 µM uridine did not significantly differ from their response to either of these compounds when applied alone. However, the rooting response of the cuttings to sub-optimal IBA (0.01 µM) was significantly stimulated by uridine. These findings suggested that uridine may have stimulated rooting by increasing the sensitivity of the rooting tissue to auxin.     

Changes in auxin protectors and IAA oxidases during the rooting of chestnut shoots in vitro

Auxin protectors and IAA oxidase activity were comparatively analyzed in the upper and the lower parts of shoots of chestnut ( Castanea sativa Mill.) cultivated in vitro with indolebutyric acid (IBA) pretreatment. Rhizogenesis of the shoots is accompanied by an increase in auxin protectors in the lower parts and by a decrease of these protectors in the upper parts. Besides, the IAA oxidase activity declines in the basal parts during the rooting process while it increases in the upper ones. These biochemical events would enhance the IAA level in the rooting region of the shoots. In untreated, non-rooted cuttings, the IAA oxidase activity remains low in the upper parts and high in the basal parts of the shoots. The results thus indicate that the IBA treatment may control the endogenous auxin level of the cuttings, either through a direct regulation of the IAA oxidase system or more indirectly through the transport of auxin protectors.     

Effect of Auxins and Light on Rooting Stem Cuttings of Populus nigra Salix tetrasperma, Ipomea fistulosa and Hibiscus notodus in Relation to Polarity

The apical and basal ends of stem cuttings of Populus nigra, Salix tetrasperma, Ipomoea fistulosa and Hibiscus notodus were treated with 10 mg/l solutions of IAA and IBA for 24 hours and were planted either erect or inverted both in light and dark. Observations for the number of cuttings that rooted and the roots produced on them were recorded at weekly intervals. In Salix, Ipomoea and Hibiscus rooting was more on cuttings planted erect, while in populus it did not differ much with the manner of planting. The reduced rooting in inverted cuttings may be ascribed to the low level of endogenous auxin at the apex due to polar transport. An exogenous application of auxins enhanced rooting on inverted cuttings. In dark, roots on Populus and Salix cuttings were produced both above and within the rooting medium. The weak polarity of these two plants may be due to the potential root primordia reported in their stem. The formation of callus occurred on the top of Populus cuttings whether planted erect or inverted but it differentiated into branches on erect cuttings only. In those planted in an inverted position the callus failed to differentiate in spite of the application of kinetin, auxins, TIBA, coumarin and sucrose, and dried ultimately.     

Assigning a Role to the Endogenous Phenolic Compounds on Adventitious Root Formation of Olive Stem Cuttings

The objective of this study was to role the effect of phenolic compounds on the rooting potential of leafy cuttings of the recalcitrant to root olive cultivar ‘Kalamata’ and the easy to root ‘Arbequina’. Subsamples of cuttings were taken for analysis before planting (day 0) in the mist system and during the early phases of rhizogenesis (EPR). ‘Kalamata’ presented higher initial (day 0) total phenols in summer and total o-diphenols in autumn and spring compared to ‘Arbequina’, while ‘Arbequina’ had significantly higher initial total flavonoids and flavanols in autumn. A positive correlation was found between initial total phenols and rooting ability of ‘Arbequina’. In ‘Kalamata’ a positive correlation was established between initial total o-diphenols and rooting percentage while total flavonoids were negatively correlated with rooting. Generally, total phenols, o-diphenols, flavanols and flavonoids did not differ between the two cultivars and their concentration reduced significantly 15 days after planting. Furthermore, ‘Arbequina’ presented higher initial tyrosol, chlorogenic acid, luteolin-7-glucoside, rutin, quercetin and luteolin in summer and autumn compared to ‘Kalamata’. The above phenolics were positively correlated with the rooting of ‘Arbequina’. Significant changes were observed in the concentration of the individual phenolics during the EPR, whereas chlorogenic acid, rutin, quercetin and luteolin concentration increased significantly from day 1 to 5. In conclusion, there is a clear relationship between the phenolic profile and adventitious rooting of the two olive cultivars and in fact chlorogenic acid and rutin can be proposed as olive rooting enhancers.

     

Auxin Synergists in Rooting of Cuttings

Leafy cuttings of Eranthemum tricolor were treated with tannic acid, gallic acid, p-hydroxybenzoic acid and salicylic acid at the concentrations of 1000, 100, 10 and 1 nig/1 for 24 hours, whereafter they were dipped quickly in a 1000 mg/l solution of IAA, IBA and NAA for ten seconds. None of the phenolics showed any root promoting effect when used singly. In combination with NAA and IBA tannic acid promoted rooting, however, with IAA there was no effect to be seen. Gallic acid also markedly increased the number of roots of cuttings treated with NAA and IBA. Even in this case there was no effect with IAA. Synergism was also recorded between p-hydroxybenzoic acid and IAA or NAA but not with IBA. Salicylic acid greatly promoted rooting in combination with both IAA, IBA and NAA.     

Adventitious Root Formation in Young Shoots of Cedrus Deodara

The effect of auxins [indole-3-butyric acid (IBA) and -naphthaleneacetic acid (NAA)], phenolics (phloroglucinol and coumarin), a combination of auxins and phenolics, and a systemic fungicide (Bavistin, containing 50% carbendazim) on adventitious root formation in stem cuttings (current season's growth) of Cedrus deodara L. during winter and monsoon (rainy) seasons has been examined. Significant stimulation of rooting due to treatments was observed in cuttings planted in winter in the following order: 0.25 mM IBA (87.5% rooting) > 5 mM coumarin (70.8%) > IBA (0.5 mM) + coumarin (5 mM) (50.0%). In cuttings planted in monsoon only 0.05% Bavistin was found to be effective in inducing rooting (83.3%). Other treatments were ineffective and in some treatments drying of cuttings was noticed.     

Indole-3-butyric acid in plants: occurrence, synthesis, metabolism and transport

Indole-3-butyric acid (IBA) was recently identified by GC/MS analysis as an endogenous constituent of various plants. Plant tissues contained 9 ng g^?1 fresh weight of free IBA and 37 ng g^?1 fresh weight of total IBA, compared to 26 ng g^?1 and 52 ng g^?1 fresh weight of free and total indole-3-acetic acid (IAA), respectively. IBA level was found to increase during plant development, but never reached the level of IAA. It is generally assumed that the greater ability of IBA as compared with IAA to promote rooting is due to its relatively higher stability. Indeed, the concentrations of IAA and IBA in autoclaved medium were reduced by 40% and 20%, respectively, compared with filter sterilized controls. In liquid medium, IAA was more sensitive than IBA to non-biological degradation. However, in all plant tissues tested, both auxins were found to be metabolized rapidly and conjugated at the same rate with amino acids or sugar. Studies of auxin transport showed that IAA was transported faster than IBA. The velocities of some of the auxins tested were 7. 5 mm h^?1 for IAA, 6. 7 mm h^?1 for naphthaleneacetic acid (NAA) and only 3. 2 mm h^?1 for IBA. Like IAA, IBA was transported predominantly in a basipetal direction (polar transport). After application of ³H-IBA to cuttings of various plants, most of the label remained in the bases of the cuttings. Easy-to-root cultivars were found to absorb more of the auxin and transport more of it to the leaves. It has been postulated that easy-to-root, as opposed to the difficult-to-root cultivars, have the ability to hydrolyze auxin conjugates at the appropriate time to release free auxin which may promote root initiation. This theory is supported by reports on increased levels of free auxin in the bases of cuttings prior to rooting. The auxin conjugate probably acts as a ‘slow-release’ hormone in the tissues. Easy-to-root cultivars were also able to convert IBA to IAA which accumulated in the cutting bases prior to rooting. IAA conjugates, but not IBA conjugates, were subject to oxidation, and thus deactivation. The efficiency of the two auxins in root induction therefore seems to depend on the stability of their conjugates. The higher rooting promotion of IBA was also ascribed to the fact that its level remained elevated longer than that of IAA, even though IBA was metabolized in the tissue. IAA was converted to IBA by seedlings of corn and Arabidopsis. The K_m value for IBA formation was low (approximately 20 μM), indicating high affinity for the substrate. That means that small amounts of IAA (only a fraction of the total IAA in the plant tissues) can be converted to IBA. It was suggested that IBA is formed by the acetylation of IAA with acetyl-CoA in the carboxyl position via a biosynthetic pathway analogous to the primary steps of fatty acid biosynthesis, where acetyl moieties are transferred to an acceptor molecule. Incubation of the soluble enzyme fraction from Arabidopsis with ³H-IBA, IBA and UDP-glucose resulted in a product that was identified tentatively as IBA glucose (IBGIc). IBGIc was detected only during the first 30 min of incubation, showing that it might be converted rapidly to another conjugate.     

Auxin metabolism and rooting in young and mature clones of Sequoia sempervirens

The capacity of young and mature Sequoia sempervirens clones to produce roots in vitro was studied after wounding and indole-3-butyric acid (IBA) treatments. Rooting was not observed in mature or in young cuttings cultivated for 30 days in medium without IBA. The presence of 25 μ M IBA in the medium resulted in the appearance of roots at the base of the cuttings. More roots appeared and grew faster on cuttings of the young than on the mature clone. This difference in rooting capacity between young and mature cuttings may be related to differences in the hormone levels at the base of the 5 mm long cuttings during the first 4 days of the root inductive period. After HPLC fractionation. IAA. IBA and related compounds, including indole-3-aspartic acid (IAAsp) and IBA-glucose ester (IBA-GE), were determined by MS and MS-MS and their levels measured by ELISA. Another immunoreactive compound was also found and determined to be N,N-dimethyltryptophan (DMT), a compound previously reported to inhibit auxin-enhanced ethylene production. Wounding of the stem without IBA treatment revealed a transient increase in IAA, IAAsp and DMT levels in young cuttings while a dramatic increase in the levels of DMT was observed in mature cuttings. Following IBA treatment. IAA levels increased in both clones, but higher levels were measured in the young than in the mature clone. IBA and IBA-GE were also found but in higher levels in the mature clone. Thus, the difficult-to-root mature clone differs from the young clone in its auxin metabolism.     

N,N′-bis-(2,3-Methylenedioxyphenyl)urea and N,N′-bis-(3,4-methylenedioxyphenyl)urea enhance adventitious rooting in Pinus radiata and affect expression of genes induced during adventitious rooting in the presence of exogenous auxin

We have analyzed the effect of N,N′-bis-(2,3-methylenedioxyphenyl)urea (2,3-MDPU) and N,N′-bis-(3,4-methylenedioxyphenyl)urea (3,4-MDPU), two symmetrically substituted diphenylurea derivatives with no auxin or cytokinin-like activity, on the rooting capacity of Pinus radiata stem cuttings. Results indicate that both diphenylurea derivatives enhance adventitious rooting in the presence of exogenous auxin (indole-3-butyric acid, IBA), even at low auxin concentration, in rooting-competent cuttings, but have no effect on the adventitious rooting of low or null competent-to-root cuttings. Histological analyses show that, in the simultaneous presence of MDPUs and low concentration of exogenous auxin, adventitious root formation is induced in the cell types that retain intrinsic competence to form adventitious roots in response to auxin. The time course of cellular events leading to root formation and the time of root emergence are closely similar to that observed in cuttings treated only with higher auxin concentration. In addition, the mRNA level of a P. radiata SCARECROW-LIKE gene, which is significantly induced in the presence of the optimal concentration (10 μM) of exogenous auxin needed for cuttings to root, is increased in the presence of MDPUs and low concentration of exogenous auxin (1 μM). The expression of a P. radiata SHORT-ROOT gene in rooting-competent cuttings during adventitious rooting is also affected by the presence of MDPUs when combined with auxin. As MDPUs do not affect the expression of either gene in the absence of exogenous auxin, but only in its presence, we suggest that MDPUs could interact, directly or indirectly, with the auxin-signalling pathways in rooting-competent cuttings during adventitious rooting.     

Comparative effect of IBA, BSAA and 5,6-Cl2-IAA-Me on the rooting of hypocotyl in mung bean

Mung bean hypocotyl cuttings were treated with indole-3-butyric acid (IBA), 3-(benzo[b]selenienyl)acetic acid (BSAA) and 5,6-dichloroindole-3-acetic acid methyl ester (5,6-Cl2-IAA-Me) at different concentrations, respectively. Each chemical produced the maximum number of adventitious roots at a different concentration. Compared with IBA treatment, 5,6-Cl2-IAA-Me and BSAA treatments significantly increased root numbers on hypocotyl cuttings at lower concentration, particularly of 5,6-Cl2-IAA-Me treatment. Combinations of paclobutrazol (PB) with either 5,6-Cl2-IAA-Me or BSAA significantly stimulated the production of more adventitious roots than either chemical alone or combined. Capillary electrophoresis analysis have shown that the levels of IAA, IBA and BSAA in IBA plus PB or BSAA plus PB treatments were higher than those of IBA or BSAA alone. It was suggested that the cause of the synergistic effect of IBA (or BSAA) plus PB treatment might be due to increased endogenous auxin level. The activities of peroxidase and IAA oxidase in the rooting zone coincided with root development, indicating that the activities of these two enzymes were positively correlated to rooting. Peroxidase and IAA oxidase activity in all treatments started 24 h and 12 h after cutting, respectively. It is suggested that the major role of IAA oxidase differed from that of peroxidase in adventitious root formation.     

Metabolic changes during rooting in stem cuttings of five mangrove species

Vegetative propagation through rooting in stem cuttings in five tree mangroves namely Bruguiera parviflora, Cynometra iripa, Excoecaria agallocha, Heritiera fomes, and Thespesia populnea using IAA, IBA and NAA was reported. Spectacular increase in the root number was noted in the cuttings of H. fomes and C. iripa treated together with IBA (5000 ppm) and NAA (2500 ppm). The highest number of roots was obtained with IBA (2500 ppm) and NAA (500 ppm) in E. agallocha. B. parviflora and T. populnea responded better to IAA and IBA treatment. The species specific variation in the rooting response to exogenous application of auxins was reflected in the metabolic changes during initiation and development of roots in cuttings. Biochemical analysis showed increase of reducing sugar in the above-girdled tissues at initiation as well as subsequent development of roots which was further enhanced by the use of auxins. Decreases in the total sugar, total carbohydrate and polyphenols and increase in total nitrogen were recorded in the girdled tissues and the high C/N ratio at the initial stage helped in initiation of roots in all the species. Interaction of IBA and NAA promoted starch hydrolysis better than IAA and IBA during root development and subsequently reduced the C/N ratio and increased the protein-nitrogen activity during root development which suggest the auxin influenced mobilization of nitrogen to the rooting zone.Abbreviations IAA Indole-3-acetic acid - IBA Indole-butyric acid - NAA A-naphthalene acetic acid     

Effect of Auxins on Adventitious Root Development from Single Node Cuttings of Camellia sinensis (L.) Kuntze and Associated Biochemical Changes

An attempt was made to induce rooting from single node cuttings of Camellia sinensis var. TV-20 under controlled conditions and study its biochemical changes during rooting. The nodal cuttings were pretreated with different concentrations of IAA, NAA and IBA and kept in a growth chamber (25 ±2 °C, 16 h photoperiod (55 μ mol m⁻² s⁻¹) with cool, white fluorescent lamps and 65% relative humidity) for 12 h. Among the three auxins used for pretreatment, IBA showed more positive response on rooting as compared to IAA and NAA within 2 weeks of transfer to potting medium. Among four concentrations of IBA tested, 75 ppm gave maximum percentage of rooting, number of roots and root length. Therefore, IBA was used further in experiments for biochemical investigation. The adventitious rooting was obtained in three distinct phases i.e. induction (0–12 days), initiation (12–14 days) and expression (14–18 days). IAA-oxidase activity of IBA-treated cuttings increased slightly as compared to control. The activity was found to decrease during induction and initiation phases and increase during expression phase. The peroxidase activity in IBA-treated cuttings increased up to initiation phase and declined at the expression phase. Polyphenoloxidase activity increased both in IBA-treated and control cuttings during induction and initiation phase but declined slowly during expression phase. Total phenolic content was higher in IBA-treated cuttings, particularly in initiation and expression phases and it also correlated with peroxidase activity. Phenolics might be playing key role for induction of adventitious rooting, and phenolic compounds can be used as rooting enhancer in tea plant.     

Caffeic acid affects early growth, and morphogenetic response of hypocotyl cuttings of mung bean (Phaseolus aureus)

Caffeic acid (CA) is one of the most common cinnamic acids ubiquitously present in plants and implicated in a variety of interactions including allelopathy among plants and microbes. This study investigated the possible interference of CA with root growth and the process of rhizogenesis in hypocotyl cuttings of mung bean (Phaseolus aureus=Vigna radiata). Results indicated that CA (0-1000 microM) significantly suppressed root growth of mung bean, and impaired adventitious root formation and root length in the mung bean hypocotyl cuttings. Further investigations into the role of CA in hampering root formation indicated its interference with the biochemical processes involved in rooting process at the three stages - root initiation (third day; RI), root expression (fifth day; RE), and post-expression (seventh day; PE) - of rhizogenesis. CA caused significant changes in the activities of proteases, peroxidases (PODs), and polyphenol oxidases (PPOs) during root development and decreased the content of total endogenous phenolics (TP) in the hypocotyl cuttings. The enhanced activity of PODs and PPOs, though, relates to lignification and/or phenolic metabolism during rhizogenesis; yet their protective role to CA-induced stress, especially during the PE phase, is not ruled out. At 1000 microM CA, where rooting was significantly affected, TP content was very high during the RI phase, thus indicating its non-utilization. The study concludes that CA interferes with the rooting potential of mung bean hypocotyl cuttings by altering the activities of PODs and PPOs and the endogenous TP content that play a key role in rhizogenesis.     

Shoot RNA, cambrial activity and indolebutyric acid effectivity in seasonal rooting of juvenile and mature Ficus pumila cuttings

The seasonal influence on adventitious root formation was studied in woody leaf bud cuttings of Ficus pumila L., creeping fig. Juvenile cuttings rooted easily, whereas only mature cuttings treated with indolebutyric acid (IBA) exceeded 30% rooting. Greater rooting occurred in IBA-treated juvenile and mature cuttings than controls, regardless of the month each experiment was initiated. Seasonal changes influenced rooting in all treatments except IBA treated juvenile cuttings where percentage rooting was not affected. Higher vascular cambial activity and shoot RNA levels occurred in juvenile and mature forms during peak rooting periods. Highest RNA was recorded with juvenile materials during maximum rooting periods, while lowest RNA was observed in mature shoots during low rooting intervals.     

Characterization and Rooting Ability of Indole-3-Butyric Acid Conjugates Formed during Rooting of Mung Bean Cuttings

Indole-3-butyric acid (IBA) is rapidly metabolized by mung bean cuttings during rooting. Twenty-four hours after application, less than 20% of the applied IBA remained in the free form and its level decreased continuously in the later stages of rooting. Indole-3-butyrylaspartic acid (IBAsp) and at least two high molecular weight conjugates were the major metabolites in IBA-treated cuttings. In the latter conjugates, at least part of the IBA moiety is attached to a high molecular weight constituent in an amide linkage. IBAsp level peaked 24 hours after application of IBA to the cuttings and then declined. The level of the high molecular weight conjugates increased continuously throughout the rooting process. The conjugates were active in inducing rooting of cuttings, with IBAsp being superior to free IBA. It is suggested that IBA conjugates, and particularly IBAsp, serve as the source of auxin during the later stages of rooting.