Seasonal Changes in the Effects of Auxin on Rooting in Stem Cuttings of Ficus infectoria

Ficus infectoria stem cuttings were treated with 10 and 100 μg/ml each of IAA, IBA, 2,4, -D and NAA at monthly intervals and planted to study their rooting response after recording morphophysiological status and cambial activty of the parent branches. Attempts were also made to surgically expose the cambium before auxin treatment to determine the relationship of seasonal variation in auxin effectivity to cambial activity. The results show that: (1) there are two distinct phases in the sensitivity of Ficus infectoria stem cuttings to auxin-induced rooting; (2) the high rooting phase coincides with renovation of growth and high cambial activity starting in March and lasting through August and the low rooting phase coincides with winter dormancy and low cambial activity; (3) roots emerge in longitudinal rows in slitted auxin-treated cuttings; (4) slitted auxin-treated cuttings root profusely in June when cambial activity is high but not in October when cambial activity is low suggesting a close correspondence of seasonal variation between the rooting activity of auxin and cambial activity.     

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.     

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     

Auxin and Ethylene-stimulated Adventitious Rooting in Relation to Tissue 9

We have previously shown that both endogenous auxin and ethylenepromote adventitious root formation in the hypocotyls of derootedsunflower (Helianthus annuus) seedlings. Experiments here showedthat promotive effects on rooting of the ethylene precursor,1-aminocyclopropane-l-carboxylic acid (ACC) and the ethylene-releasingcompound, ethephon (2-chloro-ethylphosphonic acid), dependedon the existence of cotyledons and apical bud (major sourcesof auxin) or the presence of exogenously applied indole-3-aceticacid (IAA). Ethephon, ACC, aminoethoxyvinylglycine (an inhibitorof ethylene biosynthesis), and silver thiosulphate (STS, aninhibitor of ethylene action), applied for a length of timethat significantly influenced adventitious rooting, showed noinhibitory effect on the basipetal transport of [³H]IAA. Theseregulators also had no effect on the metabolism of [³H]IAA andendogenous IAA levels measured by gas chromatography-mass spectrometry.ACC enhanced the rooting response of hypocotyls to exogenousIAA and decreased the inhibition of rooting by IAA transportinhibitor, N-1-naphthylphthalamic acid (NPA). STS reduced therooting response of hypocotyls to exogenous IAA and increasedthe inhibition of rooting by NPA. Exogenous auxins promotedethylene production in the rooting zone of the hypocotyls. Decapitationof the cuttings or application of NPA to the hypocotyl belowthe cotyledons did not alter ethylene production in the rootingzone, but greatly reduced the number of root primordia. We concludethat auxin is a primary controller of adventitious root formationin sunflower hypocotyls, while the effect of ethylene is mediatedby auxin. Key words: Auxin, ethylene, adventitious rooting, sunflower     

Early steps of adventitious rooting: morphology,hormonal profiling and carbohydrate turnover in carnation stem cuttings

The rooting of stem cuttings is a common vegetative propagation practice in many ornamental species. A detailed analysis of the morphological changes occurring in the basal region of cultivated carnation cuttings during the early stages of adventitious rooting was carried out and the physiological modifications induced by exogenous auxin application were studied. To this end, the endogenous concentrations of five major classes of plant hormones [auxin, cytokinin (CK), abscisic acid, salicylic acid (SA) and jasmonic acid] and the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid were analyzed at the base of stem cuttings and at different stages of adventitious root formation. We found that the stimulus triggering the initiation of adventitious root formation occurred during the first hours after their excision from the donor plant, due to the breakdown of the vascular continuum that induces auxin accumulation near the wounding. Although this stimulus was independent of exogenously applied auxin, it was observed that the auxin treatment accelerated cell division in the cambium and increased the sucrolytic activities at the base of the stem, both of which contributed to the establishment of the new root primordia at the stem base. Further, several genes involved in auxin transport were upregulated in the stem base either with or without auxin application, while endogenous CK and SA concentrations were specially affected by exogenous auxin application. Taken together our results indicate significant crosstalk between auxin levels, stress hormone homeostasis and sugar availability in the base of the stem cuttings in carnation during the initial steps of adventitious rooting.     

The Effects of Ascorbate on Root Regeneration in Seedling Cuttings of Tomato

The changes in ascorbate (ASC) and dehydroascorbate (DHA) levels and the activities of ascorbate metabolising enzymes were examined during adventitious root formation in cuttings of tomato (Lycopersicon esculentum Mill. cv. Paw) seedlings. The effects of ASC, DHA and the immediate ascorbate precursor – galactono-γ-lactone (GalL) supplemented to the culture medium on the rooting response, ascorbate content and the activities of the ASC-metabolising enzymes were also investigated. The cuttings treated with abovementioned compounds formed more roots then control plants. However, in contrast to the number of regenerated organs, the elongation of newly formed roots was markedly inhibited. Treatment with auxin (IAA) resulted in a similar phenotype. The inhibitor of auxin polar transport-TIBA (2,3,5-triiodobenzoic acid) effectively blocked rooting. The inhibitory effect of TIBA was reversed by auxin and ASC treatments, while DHA and GalL were ineffective. Both auxin and ASC stimulated cell divisions in an area of pericycle layer of TIBA-treated rooting zones, that enabled cuttings to form roots in the presence of the inhibitor of auxin polar transport. It has been found that the first stages of rooting, preceding the emergence of roots, are accompanied by an increase in endogenous content of ASC with a peak in the 3rd day of rooting. Subsequent stages, when elongation of newly formed roots occurs, are characterised by low level of ASC. The activities of the ascorbate peroxidase (APX), ascorbate oxidase (AOX), ascorbate free radical reductase (AFRR) and dehydroascorbate reductase (DHR) increased in the first 3 days of root formation. The initial period of rooting was also accompanied by the increase of the hydrogen peroxide content and the activities of catalase (CAT) and guaiacol peroxidase (GPX) in the rooting zones. IAA, ASC, DHA as well as Gal stimulated the APX activity, however the rise of the enzyme's activity induced by ASC, DHA and Gal was reversed by TIBA, which was found to inhibit APX. Only exogenous IAA was able to maintain the high level of APX activity in the TIBA-treated cuttings. AOX was strongly affected by ASC and GalL – treatments, its activity increased in the cuttings grown on the media containing ASC in the absence as well as in the presence of TIBA. On the other hand, GalL-dependent stimulation of its activity was suppressed if TIBA was present in a rooting medium.     

The influence of branches and leaf area on rooting and development of Cotinus coggygria cv. Royal Purple cuttings

The influence of branches and mature leaves on the rooting and subsequent development of cuttings was examined, using Cotinus coggygria cv. Royal Purple. A model system was developed, whereby branched cuttings could be harvested from stock hedges and manipulated to alter leaf area, the number of actively‐growing, lateral branches and thus the source: sink ratio for photoassimilates. Highest percentage rooting ((80%) was promoted by retention of branches and a full leaf area. Reducing leaf area resulted in a lower rooting percentage (44%); however, greatest reductions in rooting were associated with the removal of lateral branches ((22%). Applying exogenous auxin (indole‐3‐butyric acid) at the excision point where branches had been removed significantly improved rooting potential, but did not fully substitute for the presence of branches with active shoot tips. Negative effects associated with removing a proportion of mature leaves appeared to relate to alterations in carbon balance rather than an influence on the supply of endogenous auxin to the potential rooting zone. The use of branched cuttings accelerated root and shoot development and resulted in a finished plant being produced more rapidly than is achieved from conventional, non‐branched cuttings. The results presented indicate a means for improving the efficiency of production of Cotinus coggygria, which may be applicable to a wider range of ornamental plants.     

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.

     

Effect of auxins on adventitious rooting from stem cuttings of candidate plus tree Pongamia pinnata (L.), a potential biodiesel plant

Pongamia pinnata, commercially important tree species used to produce biofuels, is known for its multipurpose benefits and its role in agro-forestry. Present study examines the amenability of vegetative propagation and effect of maturation in candidate plus tree P. pinnata through rooting of stem cuttings treated with varying concentrations and combinations of auxins. The performance of the cuttings was evaluated using SAS GLM software and the data were analyzed as a one-way classified data with and without sub sampling for inferring auxin concentration that can be included in programmes aimed at genetic improvement of the tree species. All auxin treatments promoted sprouting and at lower concentrations triggered/enhanced rooting of cuttings. The effectiveness was in the order of IBA > NAA > IAA when applied singly. IBA at 4.92 mM was found to be most effective where rooting percentage and number of roots were significantly higher (P < 0.01) than in control. However higher concentrations of auxins above 7 mM in general inhibited the rooting of cuttings. The interaction among auxins was found to be effective in root induction and differentiation and the most stimulating effects were observed in three-component mixture. The effect of other cutting characteristics such as juvenility and cutting position on rooting is also discussed.     

Fluctuations of different endogenous phenolic compounds and cinnamic acid in the first days of the rooting process of cherry rootstock 'GiSelA 5' leafy cuttings

The relationship between the phenol composition of rooting zones and rootability was studied in the first days after the establishment of cuttings. The trial included two different types of cuttings (basal and terminal). Additionally, the influence of exogenously applied auxin (IBA) was observed. The best rooting results (55.6%) were achieved with terminal IBA treated cuttings, while only 1.9% of basal cuttings formed roots. The auxin treatment increased the root formation in terminal, but not in basal cuttings. Low rooting rate of basal cuttings was probably due to higher lignification rate of the basal tissue which can represent a mechanical barrier for root emergence. When measuring phenolic compounds and cinnamic acid, terminal cuttings contained higher (rutin, vanillic acid, (-)-epicatechin, caffeic acid and sinapinic acid) or equal concentrations of detected phenols as basal cuttings, while applied auxin did not influence the level of any of discussed phenolics, neither of cinnamic acid. It is to assume that cuttings for starting of root induction phase should contain certain levels of several phenolic compounds, but higher influence on rooting success is to be ascribed to the impact of the auxin level. During the time of the experiment concentrations of monophenols sinapinic acid and vanillic acid rapidly decreased. This decrease was more pronounced in terminal cuttings, which might have a better mechanism of lowering those two compounds to which a negative influence on rooting is ascribed. Fluctuations and differences between treatments of other phenolics were not significant enough to influence the rooting process.     

Maturation-related loss in rooting competence by loblolly pine stem cuttings: The role of auxin transport, metabolism and tissue sensitivity

A comparison of rooting ability of stem cuttings made from hypocotyls and epicotyls from 50-day-old seedlings of loblolly pine ( Pinus taeda L. ) reveals a dramatic decline by epicotyl cuttings, which do not root at all in 20–30 days in the presence or absence of auxin. In contrast, almost all the hypocotyls root during this time, but only in the presence of exogenously applied auxin. The failure of epicotyls to root does not appear to be due to differences in [¹⁴C]-labeled auxin uptake, transport, metabolism, or tissue distribution in the two types of cuttings. At the cellular level, initial responses to auxin, such as differentiation of the cambium into parenchyma, occur in both types of cuttings, but localized rapid cell division and root meristem organization are not observed in epicotyls. Autoradiography revealed that radioactivity from a -naphthalene acetic acid is bound in the cortex but not concentrated at sites of root meristem organization prior to the organization of the meristem in hypocotys. During the development of the epicotyl. cellular competence to form roots appears to be lost. Although this loss in competence is not associated with a concurrent loss in ability to transport auxin polarly, the latter process appears to play a key role in rooting other than to move auxin to the site of root formation. The phytotropin N-(1-naphthyl)phthalamic acid inhibits rooting if applied during the first 3 days after the cutting is made, but does not affect auxin concentration or metabolism at the rooting site.     

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.     

Endogenous Levels of Growth Regulators and Their Relationship to the Rooting of Dahlia Cuttings

The relationship between the level of endogenous growth regulators and the rooting ability of dahlia cuttings was investigated. Easy-to-root vegetative cuttings were compared with difficult-to-root, flower bud bearing cuttings and the easy-to-root cv. Choot Hashani was compared with the difficnlt-to-root cv. Orpheo. No differences in the level of extracted or diffusable auxin, nor in the level of rooting cofactors, were found between easy-to-root and difficult-to-root cuttings. No activity could be found at the R_f zone corresponding to Cofactor 4 which is considered the main rooting cofactor in other plants. Higher inhibitor activity levels (assayed by the wheat coleoptile test and the mung bean rooting test) were found in difficult-to-root than in easily rooted cuttings. Furthermore, the inhibitor activity level in exadates from decapitated plants, was higher in esodates from plants which bore difficult-to-root cuttings than from plants bearing easy-to-root ones. Grafting of an easy-to-root plant onto a difficult-to-root stock caused inhibition of rooting in the cuttings taken from the scion. Results suggest that inhibitors formed in the root system, move upwards and accumulate in the plant, there causing the inhibition of rooting. Evidence from chromatographic comparisons and exogenous treatments with ABA indicate that the main inhibitor involved in the inhibition of rooting in dahlia cuttings is not ABA.     

Peroxidase genes differentially respond to auxin during the formation of adventitious roots in soybean hypocotyl

In our investigation, auxins (IAA, IBA and NAA) effectively promoted rooting in soybean hypocotyls. The activity of anionic peroxidase (POX) (pI 3.7) and cationic POX (pI 8.5) was significantly suppressed by exogenous auxins on day 2 (the inductive phase). Some particular anionic POXs (pI 4.0 and pI 5.3) significantly increased in IBA-treated tissues as compared with the control when the incubation time was prolonged to day 3 and day 4 (the initiation phase). We sequenced 5′-flanking region of pI 8.5 and pI 5.3 POX genes using the PLACE and PlantCARE databases to identify several potential cis-regulatory elements. The pI 8.5 POX gene promoter contained two sites that were homologous to sequences commonly found in auxin response elements; motifs ARF/AuxRE and CATATGGMSAUR. During the inductive phase, the activity of pI 8.5 POX was significantly suppressed by the exogenously applied auxins. The pI 8.5 POX gene promoter contained both ARF/AuxRE and CATATGGMSAUR motifs that responded to auxins earlier than the pI 5.3 POX gene. Hence, the pI 8.5 POX gene might belong to primary auxin response genes. The pI 5.3 POX gene, which responded to auxins a day or two later, contained only ARF/AuxRE motif. Moreover, unlike pI 8.5 and pI 3.7 POXs that were suppressed by auxins, the pI 5.3 POX was induced or enhanced by the applied auxins, especially IBA. The pI 5.3 POX might generate H₂O₂ which caused the auxin-induced growth at the initiation phase during the formation of adventitious root in soybean hypocotyls.     

Adventitious rooting in hypocotyls of sunflower (Helianthus annuus) seedlings. IV. The role of changes in endogenous free and conjugated indole‐3‐acetic acid

We have studied the role of endogenous auxin on adventitious rooting in hypocotyls of derooted sunflower (Helianthus annuus L. var. Dahlgren 131) seedlings. Endogenous free and conjugated indole-3-acetic acid (IAA) were measured in three segments of hypocotyls of equal length (apical, middle, basal) by using gas chromatography-mass spectrometry with [¹³C₆]-IAA as an internal standard. At the time original roots were excised (0 h), the free IAA level in the hypocotyls showed an acropetally decreasing gradient, but conjugated IAA level increased acropetally; i.e. free to total IAA ratio was highest in the basal portion of hypocotyls. The basal portion is the region where most of root primordia were found. Some primordia were seen in this region within 24 h after the roots were excised. The quantity of free IAA in the middle portion of the hypocotyl increased up to 15 h after excision and then decreased. In this middle region there were fewer root primordia, and they could not be seen until 72 h. In the apical portion the amount of free IAA steadily increased and no root primordia were seen by 72 h. Surgical removal of various parts of the hypocotyl tissues caused adventitious root formation in the hypocotyl regions where basipetally transported IAA could accumulate. Reduction in the basipetal flow of auxin by N-1-naphthylphthalamic acid and 2,3,5-tri-iodobenzoic acid resulted in fewer adventitious roots. The fewest root primordia were seen if the major sources of endogenous auxin were removed by decapitation of the cotyledons and apical bud. Exogenous auxins promoted rooting and were able to completely overcome the inhibitory effect of 2,3,5-tri-iodobenzoic acid. Exogenous auxins were only partially able to overcome the inhibitory effect of decapitation. We conclude that in sunflower hypocotyls endogenously produced auxin is necessary for adventitious root formation. The higher concentrations of auxin in the basal portion may be partially responsible for that portion of the hypocotyl producing the greatest number of primordia. In addition to auxins, other factors such as wound ethylene and lowered cytokinin levels caused by excision of the original root system cuttings must also be important.     

Juvenility and endogenous rooting substances inCastanea sativa Mill

The rooting response to exogenous auxin of cuttings in a juvenile phase of growth from plants ofCastanea sativa Mill. was determined and simultaneously the rooting potential of the water extracts was evaluated in presence of IAA by a bean rooting test. The level of the extractable rooting promoters was high in the cuttings which exhibited the highest percentage of rooting. An inhibition of the effect of IAA on rooting was detected in the cuttings which showed the lowest rooting response, the histogram differing not much from that of the adult plant. The results indicate that in chestnut the juvenile condition, easy rooting, is associated with high levels of endogenous rooting promoters.     

Auxin stability and accumulation during in vitro shoot morphogenesis influences subsequent root induction and development in <Emphasis Type="Italic">Eucalyptus grandis</Emphasis>

Recent results showed that after 16 months in the field, micropropagated eucalyptus plants have an inferior root system to cuttings. Such differences may be due to the plant growth regulators supplied during the culture stages of standard protocols, which are targeted at optimising plantlet yields and not root quality. This study investigated such a proposal, focusing on auxins in an easy-to-root clone. Initial results showed that the auxin provided in the standard protocol (NAA for multiplication and IBA for elongation) enabled 100% rooting in auxin-free medium, where rooting was faster than on IBA-rooting media. When auxin supply was omitted from multiplication and restricted to NAA or IAA during elongation, rooting in an auxin-free medium was reduced to 68 and 31%, respectively, reflecting the stabilities of these auxins in plant tissues. Additionally, 15% of shoots from the NAA-medium and 65% from the IAA-medium produced roots with altered graviperception. GC–MS analysis of these shoots revealed a relationship between free IAA-availability and altered graviperception. This was further tested by adding the IAA-specific transport inhibitor 2,3,5-triiodobenzoic acid to rooting media with IBA, IAA or NAA, which resulted in 100, 70.9 and 20.6% rooting, respectively. At least 40% of the sampled root tips had atypical starch grain deposition and abnormal graviperception. It is proposed that, at least in this clone, while IBA and NAA can be used for in vitro root induction, IAA is necessary for development of graviresponse.     

Growth-regulating activity of N-benzyl- and O-benzyl-containing compounds belonging to a new group of synthetic analogues of natural auxins

We studied the effect of benzylamine, benzyl alcohol, and their derivatives (constituting a new group of synthetic analogues of natural auxins) on rooting of leaf and stem cuttings, rhizogenesis and growth of barley plantlets and tomato seedlings, and tomato plant productivity. These compounds promoted rooting of leaf and stem bean cuttings, increased rhizogenic activity, and stimulated the development of root systems in barley and tomato seeds. The activity of the compounds studied was similar to that of standard substances (3-indoleacetic acid potassium salt and 2-naphthylacetic acid). The benzyl group attached to the oxygen or nitrogen atom was shown to be the smallest molecular structure which provided auxin activity of the compounds. Derivatives of benzyl alcohol containing the quaternary ammonium fragment possessed auxin and anti-gibberellin (retardant) properties. They were selected by chemical synthesis of low-molecular-weight bioregulators with desired properties (a combination of chemical fragments with complementary physiological activity in the molecule). Auxin and anti-gibberellin (retardant) activities produced a synergistic effect. Germination of seeds treated with these compounds was accompanied by a more significant increase in the weight and length of roots (compared to standard auxins). The rate of seedling establishment reached 100%. The development of fruits and accumulation of reserve nutrient substances were synchronized and accelerated after spraying vegetating plants with solutions of studied compounds. The synergistic effect underlay a significant increase in the amount and quality of the crop (e.g., tomatoes).     

Response to auxin changes during maturation-related loss of adventitious rooting competence in loblolly pine (Pinus taeda) stem cuttings

Hypocotyl cuttings (from 20- and 50-day-old Pinus taeda L. seedlings) rooted readily within 30 days in response to exogenous auxin, while epicotyl cuttings (from 50-day-old seedlings) rarely formed roots within 60 days. Responses to auxin during adventitious rooting included the induction of cell reorganization and cell division, followed by the organization of the root meristem. Explants from the bases of both epicotyl and hypocotyl cuttings readily formed callus tissue in response to a variety of auxins, but did not organize root meristems. Auxin-induced cell division was observed in the cambial region within 4 days, and later spread to the outer cortex at the same rate in both tissues. Cells at locations that would normally form roots in foliated hypocotyl cuttings did not produce callus any differently than those in other parts of the cortex. Therefore, auxin-induced root meristem organization appeared to occur independently of auxin-induced cell reorganization/division. The observation that N-(1-naphthyl)phthalamic acid (NPA) promoted cellular reorganization and callus formation but delayed rooting implies the existence of an auxin signal transduction pathway that is specific to root meristem organization. Attempts to induce root formation in callus or explants without foliage were unsuccessful. Both the cotyledon and epicotyl foliage provided a light-dependent product other than auxin that promoted root meristem formation in hypocotyl cuttings.     

Isolation, Purification, and Characterization of an Endogenous Root-promoting Factor Obtained from Basal Sections of Pear Hardwood Cuttings

Basal segments taken from Old Home and Bartlett pear hardwood cuttings collected at intervals during the rooting period in September were extracted with ethanol and fractionated by paper chromatography in different solvent systems. Different zones on the chromatograms were bioassayed by the mung bean rooting test, which showed high levels of promotion in Old Home basal extracts when the cuttings were obtained during the period of maximum rooting. Extracts from Bartlett cuttings, however, showed considerably less promotion activity in the bioassay but did show high levels of inhibitory activity.

After the easily-rooted Old Home cuttings had been in the rooting medium for 10 days, a highly active endogenous root-promoting material was found in extracts from basal segments of cuttings having buds and which had been treated with indolebutyric acid. Similar extracts obtained from disbudded cuttings, or from cuttings with buds but not treated with indolebutyric acid, lacked this rooting-factor. Extracts obtained from all types of the difficult-to-root Bartlett cuttings also lacked this rooting-factor. The latter is believed to be produced by physiologically active Old Home buds, and is very effective in the mung bean bioassay, even at extremely low concentrations.

From paper chromatographic studies, tests with spray reagents, solubility determinations, biological tests, UV spectrum analysis, and infrared spectroscopy, it is believed that this rooting factor could be a condensation product between exogenous auxin (indolebutyric acid) and a phenolic compound produced by physiologically active Old Home pear buds.