The Promotive Effect of Purine and Pyrimidine Bases in Rooting Hypocotyl Cuttings of Phaseolus mungo in Relation to Auxin and Nutrition

Exogenously supplied nitrogenous bases in combination with IAA + sucrose hastened the formation of roots on hypocotyl cuttings of Phaseolus mungo L. cv. G31. While purine and pyrimidine bases had little effect when used alone, together with IAA or sucrose they increased the number of roots and the effect was even more pronounced in combination with (IAA + sucrose). By contrast, guanine inhibited rooting completely in higher concentrations even in combination with (IAA + sucrose), and cuttings died within 48–72 h.     

The Effect of IAA on Sugar Accumulation and Basipetal Transport of 14C-labelled Assimilates in Relation to Root Formation in Phaseolus vulgaris Cuttings

The effect of indol-3yl-acetic acid on root formation, accumulation of 80% ethanol-soluble sugars and basipetal transport of ¹⁴C-labelled assimilates has been investigated in Phaseolus vulgaris (cv. Canadian Wonder) hypocotyl cuttings. The removal of leaves reduced root formation in the hypocotyl, while excision of the apical bud was less detrimental. The expression of the IAA effect in inducing more roots was dependent on the area of leaves, and was found to be better when all leaves were present. Sugars accumulated slowly at the base of cuttings during a four-day period after excision, and IAA greatly enhanced this accumulation. By comparing sugar content at the base of green and starved cuttings it was established that IAA greatly increased it concurrently with root formation. IAA applied in solution to the hypocotyl greatly enhanced the basipetal transport of ¹⁴C-labelled assimilates and their accumulation at the hypocotyl during a 24-h period. The IAA-induced accumulation was found to be connected with a greater mobilization of labelled assimilates from upper parts of the cutting. Experiments involving pretreatment with IAA and transport in cuttings already possessing root primordia, suggest a dual effect of IAA: (I) a direct effect on transport, and (2) an increase in the root-“sink”. It is concluded that both may be operating in inducing basipetal accumulation of labelled assimilates. It is suggested that one of the roles of IAA in promoting rooting of cuttings is to increase sugar availability at the site of root formation.     

Polar transport and accumulation of indole-3-acetic acid during root regeneration by Pinus lambertiana embryos

Summary The relation of indoleacetic acid (IAA) transport to accumulation of auxin at the base of cuttings and to polar root formation was investigated with small cuttings from germinating embryos of Pinus lambertiana.The transport of endogenous auxin participates in regeneration of roots. This is shown by the facts that (1) more than 40% of the cuttings rooted without addition of exogenous indoleacetic acid; (2) the first regeneration always occurred at the basal tip of a slanting cut; and (3) 2,3,5-triiodobenzoic acid (TIBA), a specific inhibitor of auxin transport, totally inhibited rooting. Addition of IAA to the medium increased the number of roots formed per rooting hypocotyl.Sections of hypocotyls excised from dormant embryos and tested immediately after 2 h hydration were capable of polar transport of IAA. This polarity increased during the first 3 days of culture because of a marked increase in basipetal transport. Culturing the cuttings in 1 M IAA for 3–5 days doubled both the basipetal transport of 1-¹⁴C-IAA by hypocotyl segments and the accumulation of radioactivity at the base of cuttings.The extent of the accumulation at the base of cuttings was similar at early (2 days, first mitoses) and late stages (5 days, organized meristem) of regeneration and was not affected by removal of the regenerating region immediately prior to uptake and transport of ¹⁴C-IAA. The accumulation was inhibited by TIBA. In terms of increase in wet and dry weight and mitotic activity, the cotyledons rather than the regenerating root meristems were the most actively growing region of the cuttings. The upper part of the hypocotyl elongated more than the region of the slanting cut where regeneration was occurring.These results provide no support for the idea that the regenerating root controls the direction of polar transport by acting as a sink. The results are consistent with the view that polar auxin transport delivers auxin to the base of the cutting and raises the local concentration to levels sufficient to promote root formation.     

Effect of maleic hydrazide on peroxidase isoenzymes in relation to rooting hypocotyl cuttings ofPhaseolus mungo

A time course study of changes in the pattern of peroxidase isoenzymes shows that two new isoenzymesa andb appeared in hypocotyl cuttings cultured either in indolyl-3 acetic acid (IAA) + sucrose or in water but not in maleic hydrazide (MH). Roots were also initiated in the former two cases but not in the last case. That these isoenzymes may be associated with root initiation is also evident from the fact that these appeared when hypocotyl cuttings were transferred from MH to IAA + sucrose. The time of appearance of these isoenzymes in different cultures also synchronized with the time of microscopic root initiation. While the isoenzymea disappeared,b persisted in cuttings transferred from IAA + sucrose to MH. The number of roots produced on cuttings transferred to MH was very low, though their development was normal. It is suggested that isoenzymesa andb may be associated with root initiation andc andd with root development.     

Plant growth regulators and adventitious root development in relation to auxin

Adventitious root formation in stem cuttings of mung bean was enhanced by ethrel, which had an additive effect when employed simultaneously with indolebutyric acid (IBA). Abscisic acid (ABA) did not influence the number of roots per cutting whereas gibberellic acid (GA₃) and kinetin were without effect on rooting at lower concentrations but were inhibitory at higher concentrations. Nevertheless, all three of these chemicals showed synergistic interactions with IBA and/or indol-3-ylacetic acid (IAA) and thereby significantly promoted root formation. A localised application of morphactin to the epicotyl of cuttings totally inhibited root production irrespective of which of the foregoing growth regulators were suppliedvia the hypocotyl. Morphactin application also prevented root formation in cuttings treated with vitamin D₂. The various growth regulators employed had differing effects on growth of roots but there was no simple relationship between their effects on root formation and subsequent root growth.     

Adventitious root initiation in hypocotyl and epicotyl cuttings of eastern white pine (Pinus strobus) seedlings

The present paper reports results of experiments to develop a system for studying adventitious root initiation in cuttings derived from seedlings. Hypocotyl cuttings of 2-week-old eastern white pine (Pinus strobus L.) seedlings were treated for 5 min with 0, 100, 200, 300, 400, 500 or 600 mg l^?1 (0, 0.54, 1.07, 1.61, 2.15, 2.69 or 3.22 mM) 1-naphthaleneacetic acid (NAA) to determine the effect on root initiation. The number of root primordia per cutting was correlated with NAA concentration and the square of NAA concentration. Thus, the number increased from less than one per cutting in the 0 NAA treatment to approximately 40 per cutting at 300 mg l-1 NAA, above which no substantial further increase was observed. The larger number of root primordia formed in response to increasing concentrations of NAA was due to the formation of primordia over a larger proportion of the hypocotyls. Histological analysis of the timing of root primordium formation in hypocotyl cuttings revealed three discernible stages. Progression through these stages was relatively synchronous among NAA-treated hypocotyl cuttings and within a given cutting, but variation was observed in the portion of different cuttings undergoing root formation. Control-treated hypocotyl cuttings formed root primordia at lower frequencies and more slowly than NAA-treated cuttings, with fewer primordia per cutting. Epicotyl cuttings from 11-week-old seedlings also formed adventitious roots, but more slowly than hypocotyl cuttings. NAA treatment of epicotyl cuttings caused more rapid root initiation and also affected the origin of adventitious roots in comparison with nontreated cuttings. NAA-treated epicotyl cuttings formed roots in a manner analogous to that of the hypocotyl cuttings, directly from preformed vascular tissue, while control-treated epicotyl cuttings first formed a wound or callus tissue and subsequently differentiated root primordia within that tissue. This system of inducing adventitious roots in pine stem cuttings lends itself to studying the molecular and biochemical steps that occur during root initiation and development.     

Synergistic interaction between coumarin 1,2-benzopyrone and indole-3-butyric acid in stimulating adventitious root formation in Vigna radiata (L.) Wilczek cuttings: I. Endogenous free and conjugated IAA and basic isoperoxidases

Cuttings from 7-day-old Vigna radiata seedlings were treated for 24 h with various concentrations of coumarin and/or indole-3-butyric acid (IBA), applied either alone or in combination, in order to stimulate adventitious root formation (ARF). The effects of treatment on endogenous free and conjugated indole-3-acetic acid (IAA), basic peroxidase (basic PER) activity and its isoperoxidases analysis and their relation to ARF were then investigated at the potential rooting sites during the first 96 h after application. Simultaneously, combined treatments acted synergistically in inducing more adventitious roots in treated cuttings than in those treated with coumarin or IBA individually, as compared with the control. Endogenous free IAA increased transiently in treated cuttings as compared with the control and the maximum increase occurred with the combined treatment. This suggests that coumarin and IBA may act synergistically in increasing the endogenous free IAA level during the induction phase of rooting to initiate more roots. Likewise, higher level of conjugated IAA was also found in treated cuttings than in untreated ones, during the primary events of ARF, with the maximum level occurring in the combined treatment. Comparison of the dynamics of conjugated IAA and activity of basic PERs led to conclusion that the former but not the latter is responsible for downregulation of endogenous IAA levels significantly during the primary events of ARF. A sharp increases in basic PERs occurred during the secondary events of ARF, suggesting their role in root initiation and development rather than root induction.     

间苯二酚、水杨酸对绿豆下胚轴不定根形成的作用

２０—１００ｍｇＬ（－１）间苯二酚能明显地促进绿豆下胚轴不定根的形成,与２０ｍｇＬ（－１）ＩＢＡ混合处理具加成效应,其作用在于降低生根初期ＩＡＡ氧化酶和多酚氧化酶活性．１０—１００ｍｇＬ（－１）水杨酸抑制下胚轴不定根的形成,随处理浓度的加大,对生根数目、生根范围和根重的抑制作用增加．水杨酸处理后１－３ｄ,能提高ＩＡＡ氧化酶和多酚氧化酶的活性．     

Causes of Centrifugal Root Promotion

Role of water in centrifugal root promotion, effect of centrifugation on ethylene concentration of cuttings, and effect of ethylene on root formation were investigated using Salix jragilis softwood cuttings. When cuttings were centrifuged with water, more roots formed with increasing water depth. Soaking of cuttings upright in water for 24 h stimulated root formation and produced more roots as the depth of water was increased, with submerged cuttings producing the highest number of roots. Soaking of cuttings upright in hot water for 1 h also stimulated root formation with the best root formation occurring at 40°C. Submerging in, or centrifuging with water increased ethylene concentration in cuttings. Ethylene gas and Ethrel treatments stimulated root formation. It is suggested that submerging in water increases the ethylene concentration in Salix fragilis softwood cuttings which in turn stimulates root formation of the cuttings. Centrifuging cuttings with water increased water content of the cuttings. It is suggested that this increase in water content plays a role similar to the submersion of cuttings as described above.     

Auxin effects on rooting in pea cuttings

Light-grown stem cuttingss of Pisum sativum L. cv. Weibull's Marma were rooted in a nutrient solution. The presence of 10 μ M indolylacetic acid (IAA) in the solution for 24 h or longer periods decreased the number of roots subsequently formed to about 50% of control, provided IAA was present in the solution during any of the 4 first 24 h periods. Treatment for 6 h or shorter periods caused no or small response. IAA did not appreciably change the time needed for root formation, the time course of root appearance or the pattern of root distribution along the basal internode. IAA at 100 μ M usually increased the number of roots although variable results were obtained with this IAA concentration.
The number of roots was strongly increased by treatment with indolylbutyric acid (IBA) or 2,4-dichlorophenoxyacetic acid (2,4-D). None of these or other synthetic auxins decreased the number of roots in suboptimal concentrations. Experiments with 10 μ M IBA showed that stimulation of rooting was obtained only if the auxin was present in the rooting solution for several days. Simultaneous treatment with IAA decreased the stimulating effect of IBA to some extent, whereas no such response was obtained if IAA was combined with 2,4-D.
IAA applied in lanolin to the stem of intact cuttings decreased the number of roots formed. Decapitation and debudding of the cuttings decreased the number of roots formed. If at least 2 leaves were left this decrease was efficiently counteracted by an optimal IAA dose applied to the upper part of the stem. A five times higher dose was less effective, indicating a negative effect on rooting also by IAA applied to the shoots.     

Influence of Aryl Esters of Indole-3-acetic and Indole-3-butyric Acids on Adventitious Root Primordium Initiation and Development

Synthetic aryl esters of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) greatly enhanced adventitious root primordium initiation in bean (Phaseolus vulgaris L. cv. Top Crop) and jack pine (Pinus banksiana Lamb.) cuttings, respectively. Bean cuttings produced 95 to 154% more macroscopically visible root primordia in 2 days when treated with phenyl indole-3-acetate (P-IAA), in comparison with an equal concentration of IAA. Substantial but lesser increases occurred when treatment was done with 3-hydroxyphenyl indole-3-acetate (3HP-IAA). On a molar basis, either P-IAA or 3HP-IAA were 10 or more times as efficient as IAA in inducing adventitious root primordium initiation in bean cuttings. Methyl indole-3-acetate was no more effective than IAA in these tests. Phenyl indole-3-butyrate (P-IBA) consistently enhanced the number of rooted jack pine seedling cuttings by 11 to 12% in comparison with a 27% higher concentration of IBA. The number of elongated roots (2 mm or more) after 5 days was 165 to 276% greater for P-IAA than for IAA-treated bean cuttings. Similar but lesser increases occurred as a result of 3HP-IAA treatment. P-IBA in comparison with IBA treatment did not influence either the number of roots or length of the longest root per rooted jack pine cutting. Enzymes in bean and jack pine cuttings hydrolyzed the aryl esters. However, check experiments showed that initial integrity of the esters was required for enhanced activity in inducing root primordium initiation. Treatment of bean cuttings with hydrolysates of P-IAA, or with IAA and phenol, alone or combined, did not influence root primordium initiation or development in a manner different from treatment with IAA alone.     

Adventitious root formation in relation to irradiance and auxin supply

High irradiance during treatment of mung bean cuttings favours root formation in response to supplied auxin, whether the latter is IAA or IBA. On the other hand it is inhibitory towards root formation in the absence of supplied auxin. Light promotes the uptake of¹⁴C-IAA into cuttings and its upward movement into the leaves. When¹⁴C-IAA is applied to leaves of cuttings high irradiance favours movement of radioactivity into the epicotyl and hypocotyl. This movement is also enhanced by concomitant supply of IBA to the base of the cuttings. The irradiance under which stock plants are raised also affects the extent of root formation on cuttings. When cuttings are held in darkness without a supply of exogenous auxin they root best if prepared from seedlings raised under high irradiance. However, transport of¹⁴C-IAA out of leaves of cuttings is favoured when cuttings are prepared from seedlings grown under low irradiance. These observations are discussed in relation to auxin transport, photodestruction and, possibly, metabolism.     

Regulation of root formation by auxin-ethylene interaction in pea stem cuttings

The possibility was investigated that the inhibition of rooting in pea ( Pisum sativum L. cv. Weibull's Marma) cuttings caused by low indol-3yl-acetic acid (IAA) concentrations is due to ethylene produced as a result of IAA treatment. Treatment with 10 uμ IAA reduced the number of roots to about 50% of the control and increased ethylene production in the stem bases by about 20 times the control value during the two first days of treatment. Ethylene-releasing compounds (ethephon and 1-amino-cyclopropane-1-carboxylic acid, ACC), in concentrations giving a similar ethylene release, inhibited rooting to the same extent or more strongly than IAA. These results indicate that IAA-induced ethylene is at least responsible for the negative component in IAA action on root formation in pea cuttings. A higher IAA concentration (100 μ) and indol-3yl-butyric acid efficiently counteracted the negative effect of ethylene on root formation.     

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.     

Evidence for Three Different Systems of Movement of Indoleacetic Acid in Intact Roots of Phaseolus coccineus

Indoleacetic acid (IAA)-5-³H (2 × 10⁻⁹M) was applied to intact roots of Phaseolus coccineus seedlings, at the apex or 2 cm above the apex, at various pHs and in the presence of Cu²⁺ and NaCl. The transport of label in the roots was then examined after 6 h by cutting the roots into 1 mm sections above and below the zone of treatment. Basipetal movement from 2 cm above the apex was unafected by pH, Cu²⁺ or NaCl. Acropetal movement from the same area decreased with increasing pH from 5.4 to 8.0, probably due to an effect of pH on the entry of IAA into the cells. pH had no effect on sucrose transport. Cu²⁺ also inhibited acropetal movement but NaCl had no effect. Basipetal movement of label from the apex was reduced by Cu²⁺ and increasing pH, but not as much as with acropetal movement, and increased by the presence of NaCl. These facts are interpreted as showing 3 different systems of IAA movement in intact roots: basipetal from 2 cm up the root in some extracellular physical system; acropetal from 2 cm up the root, and basipetal from the apex, in a metabolically dependent intracellular system, but in different tissues of the root. It is proposed that endogenous IAA not only moves into the root from the stem but is also synthesized in the root apex, and moves basipetally for a short distance to the root growing zone in a separate system from the IAA descending from the stem.     

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.     

Different Behaviour of Indole-3-Acetic Acid and Indole-3-Butyric Acid in Stimulating Lateral Root Development in Rice (Oryza sativa L.)

The plant hormone auxin has been shown to be involved in lateral root development and application of auxins, indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA), increases the number of lateral roots in several plants. We found that the effects of two auxins on lateral root development in the indica rice (Oryza sativa L. cv. IR8) were totally different from each other depending on the application method. When the roots were incubated with an auxin solution, IAA inhibited lateral root development, while IBA was stimulatory. In contrast, when auxin was applied to the shoot, IAA promoted lateral root formation, while IBA did not. The transport of [³H]IAA from shoot to root occurred efficiently (% transported compared to supplied) but that of [³H]IBA did not, which is consistent with the stimulatory effect of IAA on lateral root production when applied to the shoot. The auxin action of IBA has been suggested to be due to its conversion to IAA. However, in rice IAA competitively inhibited the stimulatory effect of IBA on lateral root formation when they were applied to the incubation solution, suggesting that the stimulatory effect of IBA on lateral root development is not through its conversion to IAA.     

Abscisic acid and auxin accumulation in Catasetum fimbriatum roots growing in vitro with high sucrose and mannitol content

Endogenous contents of indolyl-3-acetic acid (IAA) and abscisic acid (ABA) were quantified in excised roots of Catasetum fimbriatum (Orchidaceae) cultured in vitro on solidified Vacin and Went medium with 1, 2, 4, 6, 8 and 10 % sucrose, as well as 2 % sucrose plus mannitol. Maximum root growth was observed in media with 4 % sucrose and 2 % sucrose plus 2.2 % mannitol, suggesting that a moderate water or osmotic stress promotes orchid root growth. Contents of both ABA and IAA increased in parallel to increasing sucrose concentration and a correlation between root elongation and the ABA/IAA ratio was observed. Incubating isolated C. fimbriatum roots with radiolabeled tryptophan, we showed an accumulation of IAA and its conjugates.     

Juvenile stockplant material enhances root development through higher endogenous auxin level

Stockplants with various physiological characteristics were compared in a propagation experiment with leafy cuttings of ornamental cherry Prunus subhirtella ‘Autumnalis’. At the time of severance, cuttings harvested from juvenile 3-year-old in vitro-derived plants contained in their bases nearly twice as much IAA (indole-3-acetic acid) as cuttings derived from mature 40-year-old trees. Juvenile cuttings showed better rooting success in the propagation season. They developed a significantly higher number of primary roots and grew better than physiologically older cuttings. IAA time-course levels in cutting bases in the days after severance were similar in both cuttings types. They decreased over the first day (rooting late initiation phase) after severance until the third day after severance when the levels increased again (rooting induction phase and beginning of the root developing phase). At the time of severance, juvenile cuttings also contained higher concentrations of IAAasp (indole-3-acetyl aspartic acid) in their bases than mature cuttings. IAAasp time-course levels were similar to those measured for IAA.