Distinct modes of adventitious rooting in Arabidopsis thaliana

The literature describes different rooting protocols for Arabidopsis thaliana as models to study adventitious rooting, and results are generally perceived as comparable. However, there is a lack of investigations focusing on the distinct features, advantages and limitations of each method in the study of adventitious rooting with both wild-type (WT) ecotypes and their respective mutants. This investigation was undertaken to evaluate the adventitious rooting process in three different experimental systems, all using A. thaliana, analysing the same rooting parameters after transient exposure to auxin (indole-3-acetic acid) and control conditions: excised leaves, de-rooted plants and etiolated seedlings. The founding tissues and sites of origin of roots differed depending on the system used, whereas all rooting patterns were of the direct type (i.e., without callus formation). None of the systems had an absolute requirement for exogenous auxin, although rooting was enhanced by this phytohormone, with the exception of de-rooted plants, which had adventitious rooting strongly inhibited by exogenous auxin. Root elongation was much favoured in isolated leaves. Auxin-overproducing mutants could not be used in the detached leaf system due to precocious senescence; in the de-rooted plant system, these mutants had a WT-like rooting response, whereas the expression of the 'rooty' phenotype was only evident in the etiolated seedling system. Adventitious rooting of etiolated WT seedlings in the presence of exogenous auxin was inhibited by exogenous flavonoids, which act as auxin transport inhibitors; surprisingly, the flavonoid-deficient mutant chs had a lower rooting response compared to WT. Although Arabidopsis is an excellent model system to study adventitious rooting, physiological and developmental responses differed significantly, underlining the importance of avoiding data generalisation on rooting responses derived from different experimental systems with this species.     

Strigolactones promote nodulation in pea

Strigolactones are recently defined plant hormones with roles in mycorrhizal symbiosis and shoot and root architecture. Their potential role in controlling nodulation, the related symbiosis between legumes and Rhizobium bacteria, was explored using the strigolactone-deficient rms1 mutant in pea (Pisum sativum L.). This work indicates that endogenous strigolactones are positive regulators of nodulation in pea, required for optimal nodule number but not for nodule formation per se. rms1 mutant root exudates and root tissue are almost completely deficient in strigolactones, and rms1 mutant plants have approximately 40% fewer nodules than wild-type plants. Treatment with the synthetic strigolactone GR24 elevated nodule number in wild-type pea plants and also elevated nodule number in rms1 mutant plants to a level similar to that seen in untreated wild-type plants. Grafting studies revealed that nodule number and strigolactone levels in root tissue of rms1 roots were unaffected by grafting to wild-type scions indicating that strigolactones in the root, but not shoot-derived factors, regulate nodule number and provide the first direct evidence that the shoot does not make a major contribution to root strigolactone levels.     

Identification of pectin methylesterase 3 as a basic pectin methylesterase isoform involved in adventitious rooting in Arabidopsis thaliana

? Here, we focused on the biochemical characterization of the Arabidopsis thaliana pectin methylesterase 3 gene (AtPME3; At3g14310) and its role in plant development. ? A combination of biochemical, gene expression, Fourier transform-infrared (FT-IR) microspectroscopy and reverse genetics approaches were used. ? We showed that AtPME3 is ubiquitously expressed in A. thaliana, particularly in vascular tissues. In cell wall-enriched fractions, only the mature part of the protein was identified, suggesting that it is processed before targeting the cell wall. In all the organs tested, PME activity was reduced in the atpme3-1 mutant compared with the wild type. This was related to the disappearance of an activity band corresponding to a pI of 9.6 revealed by a zymogram. Analysis of the cell wall composition showed that the degree of methylesterification (DM) of galacturonic acids was affected in the atpme3-1 mutant. A change in the number of adventitious roots was found in the mutant, which correlated with the expression of the gene in adventitious root primordia. ? Our results enable the characterization of AtPME3 as a major basic PME isoform in A. thaliana and highlight its role in adventitious rooting.     

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.     

Heritability of adventitious rooting of grapevine dormant canes

One of the most important viticultural characteristics of a grapevine rootstock is the ability to form roots on dormant lignified canes (rootstrike). North American species of Vitis are the primary source of germplasm for grapevine rootstocks and vary widely in their rate of rootstrike. Breeders have hybridized grape species in order to introgress traits to produce commercial rootstocks. A combination of 26 parents consisting of improved and wild accessions of Vitis spp. was used to generate 27 families. The percentage of rootstrike of dormant canes was observed over several years for 552 individuals. A logistic generalized linear mixed model (GLMM) method was used to estimate the narrow sense heritability (h ²) of rootstrike. Heritability was found to be moderate (h ²?=?0.307?±?0.050). The model also estimated breeding values of all parents and progeny. A GLMM method can be used to estimate breeding values of germplasm to identify individuals with commercially acceptable rates of rootstrike with a defined probability of transmitting this trait to progeny. This is useful for the introgression of traits into potentially new commercial rootstocks. The pattern of normal distribution of rooting indicates that it is possible to identify individuals with good rootstrike from Vitis species that are generally considered to have low rootstrike. Selection of individuals with a higher breeding value will increase the efficiency of rootstock breeding.     

Efficient adventitious shoot regeneration and somatic embryogenesis in pea

A rapid and simple method for adventitious shoot regeneration and somatic embryogenesis from immature cotyledon explants of pea (Pisum sativum L.) is described. Cotyledon size and the explant orientation to the medium surface were shown to have a clear effect on shoot regeneration. The highest frequency of shoot regeneration was achieved when the distal end of the greenest cotyledons (7–8 mm in size) were placed in contact with the agar surface. Shoots rooted at a frequency of 80–90% and grew into normal fertile plants. Somatic embryos were induced in cultures of immature cotyledons on modified MS medium containing high levels of -naphthaleneacetic acid (27–215 M) and 2,4-dichlorophenoxyacetic acid (23–181 M). A higher frequency of somatic embryos with a normal morphology were induced using -naphthaleneacetic acid.Abbreviations BA 6-benzyladenine - 2,4-d dichlorophenoxyacetic acid - IBA indole-3-butyric acid - NAA -naphthaleneacetic acid     

Strigolactones affect lateral root formation and root-hair elongation in Arabidopsis

Strigolactones (SLs) have been proposed as a new group of plant hormones, inhibiting shoot branching, and as signaling molecules for plant interactions. Here, we present evidence for effects of SLs on root development. The analysis of mutants flawed in SLs synthesis or signaling suggested that the absence of SLs enhances lateral root formation. In accordance, roots grown in the presence of GR24, a synthetic bioactive SL, showed reduced number of lateral roots in WT and in max3-11 and max4-1 mutants, deficient in SL synthesis. The GR24-induced reduction in lateral roots was not apparent in the SL signaling mutant max2-1. Moreover, GR24 led to increased root-hair length in WT and in max3-11 and max4-1 mutants, but not in max2-1. SLs effect on lateral root formation and root-hair elongation may suggest a role for SLs in the regulation of root development; perhaps, as a response to growth conditions.     

Stimulation of adventitious rooting of Taxus species by thiamine

Summary Results obtained from using root inducing compounds on Taxus species cuttings suggested that rooting could be significantly enhanced by the presence of thiamine. This observation was verified using a root inducing solution containing a set concentration of IBA (0.2%), NAA (0.1%), and supplemented with various concentrations of thiamine. The best rooting response for Taxus cuspidata stem cuttings was found using this solution supplemented with 0.08% thiamine. Rooted cuttings were easily established and developed into vigorous plants. In addition, Taxus brevifolia shoots obtained from tissue cultures via in vitro organogenesis also responded favorably to this 0.08% thiamine supplemented rooting solution.     

The lose of juvenility elicits adventitious rooting recalcitrance in apple rootstocks

For perennial woody plants, softwood cutting is an efficient technique for larger scale propagation and adventitious rooting of cuttings is one of the most crucial steps. To evaluate the significance of juvenility on adventitious rooting, rooting rates was compared between softwood cuttings collected from apomictic seedlings (juvenile), in vitro cultured plants (rejuvenated), suckers (juvenile like) and canopy shoots (adult) of reproductively mature trees in Malus xiaojinensis. After pre-treatment with indole-3-butytric acid (IBA) (3,000 mg L^?1) + H₂O₂ (50 mM), rooting rates in cutting from juvenile, juvenile like and rejuvenated donor plants were significantly higher (>90 %) than that from adult trees. The effects of IBA on adventitious rooting were enhanced significantly by exogenous H₂O₂. After 15 passages of in vitro subculture, the micro-shoots from adult phase explants were rejuvenated successfully, marked by the elevated expression of miR156 in the leaflets of the micro-shoots. But the rooting ability of rejuvenated micro-shoots was recovered delayed at the 18th or 21st passage of subculture. During the process of rejuvenation, the leaf indole-3-acetic acid contents and the expressions of rooting related genes CKI1, ARRO-1, ARF7 and ARF19 increased significantly. In contrary, the leaf abscisic acid contents decreased. A lack of juvenility is the most important limiting factor governing adventitious rooting of softwood cuttings in apple rootstocks.     

Early changes in auxin and ethylene production in vine cuttings before adventitious rooting

Node cuttings of in vitro cultured grapevine were rooted in absence of any growth regulator, before the onset of the axillary bud. There were two peaks of ethylene production at 2 and 10–12 h, well marked in the top and bottom portions of the cuttings for the former. The level of IAA increased in the basal portions of the cuttings only, from the 4th hour, and culminated at the 24th hour. The wound ethylene of the first rise might be initiating the sequence of reactions leading to root formation. The second ethylene rise might result from the beginning of the increase of the IAA level.     

Nitric oxide modulates specific steps of auxin-induced adventitious rooting in sunflower

Present work on indole-3-acetic acid (IAA)-induced adventitious rooting in sunflower hypocotyl highlights a clear demarcation of nitric oxide (NO)-dependent and NO-independent roles of auxin in this developmental process. Of the three phases of adventitious rooting, induction is strictly auxin-dependent though initiation and extension are regulated by an interaction of IAA with NO. A vital role of auxin-efflux transporters (PIN) is also evident from 1-napthylphthalamic acid (NPA)-triggered suppression of adventitious roots (AR). Use of actin depolymerizing agent, latrunculin B (Lat B), has demonstrated the necessity of functional actin filaments in auxin-induced AR response, possibly through its effect on actin-mediated recycling of auxin transporter proteins. Thus, evidence for a linkage between IAA, NO and actin during AR formation has been established.Key words: adventitious roots, auxin, sunflowerAdventitious roots (AR) are post-embryonic roots known to originate from stem, leaf petiole and non-pericycle tissue of old roots. In young stem, AR commonly arise from the interfascicular parenchyma while they appear from vascular rays near the cambium in older stem. Formation of AR begins with re-differentiation of predetermined cells which switch from their morphogenetic path to act as mother cells for initiation of root primordia.¹ The process of AR formation consists of three physiologically interdependent phases: induction, initiation and extension.¹ Induction phase comprises of various molecular and biochemical events but no morphologically visible changes appear during this phase. Formation of multilayered cells and conception of root primordia occurs during initiation phase. During expression phase, root primordia exhibit intra-stem growth and their emergence through epidermis. Various environmental and endogenous factors, such as temperature, light, hormones (particularly auxin), sugars and mineral salts, act as cues for promoting redifferentiation of predetermined cells resulting in root induction.The three phases of AR formation are known to be regulated by alterations in the endogenous level of auxin.² A transient increase in auxin concentration has been reported during induction phase, which is followed by a decrease and again an increase during expression phase.³ Auxin transport to and from the responding region is essential for root organogenesis. Acropetal transport of auxin occurs through the vascular cylinder and the basipetal transport takes place through the epidermal and subtending cortical cells.⁴ Polar transport of auxin from the shoot apical meristem to the rooting region is primarily facilitated by auxin-influx (AUX1) and -efflux (PIN) transporters. Asymmetric localization of these transporter proteins in the vascular cambium cells is responsible for differential distribution of auxin in a particular zone of cells.⁵ Polar auxin transport is known to be inhibited by 1-napthylphthalamic acid (NPA, a phytotropin). This inhibition is mediated through a binding of NPA molecule to putative NPA-binding protein (NBP), which is functionally associated with PIN proteins.⁶ Efflux transporters exhibit rapid turnover in plasma membrane.⁷ High affinity of NBP for actin filaments,^8,9 suggests its involvement in the cycling and polar distribution of PIN proteins.¹⁰ Organization of actin filaments is known to be rapidly, reversibly and specifically disrupted by Latrunculin B (Lat B), a macrolide toxin isolated from Latrunculia magnificia, a red sea sponge.¹¹ Lat B associates with actin monomers in 1:1 ratio, thereby preventing their repolymerization into filaments, resulting in a complete shift from F-actin to G-actin.¹² Owing to its well-understood and simple mode of action and low effective dosage, Lat B has supplanted the classic actin-depolymerizing drug cytochalasin D¹³ in pharmacological investigations. In the past few years, significant work has been done on NO as a signaling molecule in a variety of plant developmental processes.¹⁴ Nitric oxide is known to play a crucial role in root development.¹⁵Using sunflower as a model system, present work has been undertaken to investigate the possible role of NO during IAA-induced adventitious rooting in hypocotyl explants. Since auxin action is principally based on PIN-regulated polar transport of IAA molecules, and PIN proteins are known to exhibit actin-asssisted rapid recycling in the target cells, attempts have been made in the present work to find a correlation between auxin transport, actin and NO, using specific pharmacological agents. Additionally, effect of Cyclosporin A (CsA), an inhibitor of nitric oxide synthase (NOS) in animal systems,¹⁶ has also been investigated. These specific agents have been used to monitor root initiation at the target sites in our attempts to decipher a signaling cascade for AR.Seeds of Sunflower (Helianthus annuus L. cv. Morden) were germinated on moist germination sheets at 25 ± 2°C under continuous illumination of 4.3 Wm⁻². Hypocotyls from 4 d old seedlings and with similar growth rate, were excised up to 6 cm below the cotyledonary node. Hypocotyl explants with apical meristem intact but cotyledons excised were selected for the present work with a view to provide a continuity of the endogenous auxin source. Similar explants were also recently used by Huang et al.¹⁷ to investigate indole-3-butyric acid (IBA)-induced AR formation in mung bean (Phaseolus radiatus L.). Using IAA instead of IBA for such investigations was preferred for the present work keeping in view that the two auxins seem to employ different transport proteins for their polar transport.¹⁸ Freshly harvested explants were put upright in glass vials with their proximal cut ends dipped in 1 ml of different concentrations (1, 5, 10 and 15 µM) of IAA, thus bathing the hypocotyls up to 5 mm of their lower ends. Explants were maintained in dark during the course of experiments. The number of AR visible on hypocotyl surface was recorded daily up to 4 days of incubation. Concentration of IAA thus observed optimal for rooting (10 µM) was used for all further experiments. Similarly, various concentrations of other test solutions, namely NPA (auxin efflux blocker; 1 and 10 µM), Lat B (an inducer of actin depolymerization; 25, 50 and 100 nM), CsA (an inhibitor of cyclophilins; 1, 5 and 10 µM), sodium nitroprusside (SNP; NO donor; 1, 5, 10 and 100 µM) and 2-phenyl-4,4,5,5-tetramethyllimidazoline-1-oxyl-3-oxide (PTIO; NO scavenger; 1 and 1.5 mM), were initially used to select their respective optimal concentrations. Based on these preliminary experiments NPA, Lat B, CsA, SNP and PTIO were used at 10 µM, 100 nM, 10 µM, 100 µM and 1.5 mM, respectively, for all subsequent experiments. Some other treatment combinations, namely NPA (10 µM) + IAA (10 µM); LatB (100 nM) + IAA (10 µM); CsA (10 µM) + IAA (10 µM); SNP (100 µM) + NPA (10 µM) and PTIO (1.5 mM) + IAA (10 µM) were also used to investigate their effects on adventitious rooting. Hypocotyl explants incubated in distilled water served as control. Morphological observations of rooting response were imaged after 7 days of incubation, using Nikon digital camera fitted on a stereomicroscope (Stemi 2000, Zeiss, Germany). Detailed evaluation of root initiation was observed after clearing by immersing the explants in a 3:1 solution of ethanol: acetic acid overnight. They were then transferred to 2 N NaOH solution, left overnight, washed once with distilled water and stained with safranin solution for 2–3 min. Excess stain was removed by repeated washing in distilled water. The lower 2 cm region of hypocotyl explants was then cut and mounted on a glass slide to examine endogenous root initials, using a stereomicroscope (Stemi 2000, Zeiss, Germany) fitted with a Nikon camera.Root initiation and extension in the basal region of hypocotyl explants maintained in distilled water indicates the expected basipetal transport of the inducing factor (endogenous IAA) from the intact meristem, as also reported earlier.¹⁹ Treatment with IAA (10 µM) elicited two effects on hypocotyl explants in comparison to those subjected to distilled water treatment: (1) Formation of greater number of root initials, (2) Greater extension of the initiated roots (Figs. 1 and ​and22). A response similar to that evoked by IAA is also evident in hypocotyl explants treated with 100 µM of SNP (Figs. 1 and ​and22). Recently SNP (NO donor) has been reported to evoke dose-dependent response on AR formation in marigold.²⁰ In the present work, treatment with variable concentrations of SNP, ranging from 1–100 µM, lead to a gradual increase in the number and extension growth of AR till 100 µM. Pagnussat et al.²¹ and Liao et al.²⁰ have used 10 µM and 50 µM as effective SNP concentration in cucumber and marigold, respectively. Thus, optimal concentration of SNP for AR formation is species-dependent. In presence of PTIO (1.5 mM; a specific NO scavenger), complete suppression of AR was evident in sunflower, as also reported earlier in mung bean.¹⁷ Combination of PTIO with IAA lead to root initiation only (no extension growth). NPA (10 µM) blocked AR initiation by endogenous (distilled water treatment) and exogenous IAA (Fig. 1). Application of NPA inhibits polar auxin transport, thus reducing the optimal concentration of IAA required for AR formation at the hypocotyl base (zone of AR formation). Thus, no evidence of root initials was evident in presence of NPA, which is also reported in cucumber²² and loblolly pine,²³ respectively. Though NO is expected to act downstream of IAA²⁴ but a treatment of SNP in combination with NPA (present work) lead to complete suppression of AR formation. Our unpublished observations have indicated the expression of NO in the interfascicular cells after induction phase (i.e., during AR iniation and extension). Thus, it can be proposed that IAA is involved in induction phase of adventitious rooting independent of NO, while initiation and extension phases appear to involve IAA-NO interaction. CsA-cyclophilin complex is known to inhibit calcineurin (a protein phosphatase) and NOS activity in animal systems.²⁵ Treatment of hypocotyl explants with CsA (10 µM) lead to formation of fewer number of roots which exhibited extension growth. Oh et al.²⁶ reported a significant reduction in the number of roots in the presence of CsA in hypocotyl explants from tomato. Subjecting hypocotyl explants with a combination of CsA and IAA lead to formation of fewer number of root initials, reaffirming the involvement of NO in auxin action in the developmental process under investigation (AR). However, further investigations on the role of cyclophilins and NOS in auxin-modulated AR formation are required to pinpoint their specific sites of action in this developmental process. Treatment with Lat B (+ and − IAA) lead to complete AR suppression in sunflower hypocotyl explants. Actin-mediated polar localization of PIN proteins is responsible for polar auxin transport and disruption of microfilaments by Lat-B would thus, directly affect IAA transport leading to the observed AR suppression. These observations indicate a convergence of the effect of IAA with that of NO and a role of a well organized actin in the responding cells.Open in a separate windowFigure 1Effect of IAA and various other pharmacological agents on adventitious rooting in hypocotyl explants. Morphological observations of rooting response (A and C). Evaluation of endogenous root initiation and elongation observed in cleared explants stained with safranin (B and D). Scale bar represents 3 mm.Open in a separate windowFigure 2Quantitative analysis of AR initiation in presence of distilled water, IAA and various pharmacological agents in hypocotyl explants of sunflower. Each datum presents a mean and standard error from at least three observations.To sum up, present investigations provide evidence for a linkage between auxin-induced AR response in seedling hypocotyls and NO (Fig. 3). Both endogenous and exogenous IAA-mediated AR induction seem to depend on actin. Significance of actin in this developmental response has become evident via its role in the cycling of auxin efflux proteins (PIN). The three phases of AR formation can be differentiated from each other in terms of their sensitivities to IAA and NO. AR induction phase seems to be governed by auxin alone, independent of NO. NO seems to become operative in this auxin-modulated response (AR) during initiation and extension phase only. Investigations are being undertaken in the author''s laboratory to visualize and quantitate the NO signal in the IAA-responding hypocotyl explants so that the phasing of the role of NO during AR formation can be precisely predicted.Open in a separate windowFigure 3Schematic presentation of the probable events associated with NO-mediated adventitious rooting.     

Strigolactones interact with ethylene and auxin in regulating root-hair elongation in Arabidopsis

Strigolactones (SLs) or derivatives thereof have been identified as phytohormones, and shown to act as long-distance shoot-branching inhibitors. In Arabidopsis roots, SLs have been suggested to have a positive effect on root-hair (RH) elongation, mediated via the MAX2 F-box. Two other phytohormones, auxin and ethylene, have been shown to have positive effects on RH elongation. Hence, in the present work, Arabidopsis RH elongation was used as a bioassay to determine epistatic relations between SLs, auxin, and ethylene. Analysis of the effect of hormonal treatments on RH elongation in the wild type and hormone-signalling mutants suggested that SLs and ethylene regulate RH elongation via a common regulatory pathway, in which ethylene is epistatic to SLs, whereas the effect of SLs on RH elongation requires ethylene synthesis. SL signalling was not needed for the auxin response, whereas auxin signalling was not necessary, but enhanced RH response to SLs, suggesting that the SL and auxin hormonal pathways converge for regulation of RH elongation. The ethylene pathway requirement for the RH response to SLs suggests that ethylene forms a cross-talk junction between the SL and auxin pathways.     

Induction,growth and direct rooting of adventitious shoots of Begonia x hiemalis

The efficiency of commercial micropropagation programs for Begonia x hiemalis depends on the production of large adventitious shoots for easy handling and on effective rooting and acclimatization procedures. Maximum induction of adventitious buds on petiole segments occurred in response to NAA (0.1 mg, l^-1) and BA (0.5 mg l^-1), but continued shoot growth was limited. With a lower concentration of BA (0.1 mg l^-1) fewer shoots were produced but shoot growth was enhanced. With a combined agar/liquid culture program the low BA (0.1 mg l^-1) medium produced 50 percent more shoots larger than 1 cm than did the high BA (0.5 mg l^-1) medium. In vitro rooted explants developed weak root systems and acclimatization losses occurred during adaptation to greenhouse conditions. Adventitious shoots treated with commercial rooting powder and placed directly in mist frames produced much stronger root systems and could be adapted to greenhouse conditions without loss. The elimination of the in vitro rooting stage also simplifies the micropropagation program.Contribution No. 743     

Adventitious rooting of detached Arabidopsis thaliana leaves

Arabidopsis thaliana Heyhn is a model species in biochemical, physiological and molecular studies for which a plethora of mutants is available. This work aimed at developing a system for rooting of detached leaves, and evaluating time course of several relevant biochemical parameters during rooting assays with and without auxins. The rooting pattern was of the direct type (without callus formation) in all of the treatments and ecotypes analyzed and was rather stable. Considering the different parameters examined, peroxidase activity and contents of phenolic compounds and soluble sugars appeared as the most distinct biochemical markers of the rooting process in this system.     

Endogenous auxin levels in terminal stem cuttings of Chrysanthemum morifolium during adventitious rooting

Free and ester-bound IAA were determined in Chrysanthemum morifolium Ramat cv. 'Yellow Galaxy' by means of a solid phase enzyme immunoassay. In shoots, free auxin decreases basipetally whereas ester IAA reaches a maximum in the middle part. After making the cuttings, a strong increase in both free and ester IAA (or total IAA, respectively) is found up to the time when the first adventitious roots become visible. Only prolonged irradiance of stock plants at high light intensities (40 W m⁻²) delays this increase in the cuttings, concomitantly with a lower number of roots compared to the controls (4.5 W m⁻²), although root growth as determined by measuring root length or fresh weight is not affected. A distinct relation is found between IAA content of stock plants at the time when cuttings are taken and the number of adventitious roots formed by the cuttings 20 days later.     

Weakly cytokinin-active diphenylurea derivatives influence adventitious rooting in M26 Malus pumila microcuttings

The cytokinin activity of 8 previously unstudied diphenylurea (DPU)derivatives, differing in either type or position of the substituents of thephenyl rings, was investigated. Cytokinin activity was assessed using thebetacyanin (so-called amaranthin) accumulation test and the tomato regenerationtest. We also assayed their capacity to enhance adventitious root formation inmicrocuttings of apple rootstock M26 and in a tomato cotyledon rooting test,while their possible auxin-like activity was tested using the pea stemelongation test. All the compounds showed weak cytokinin activity, and thismight be responsible for the enhanced adventitious rooting which is induced bysome of the compounds. None of the DPU derivatives showed auxin-like activity.