Seasonal changes in adventitious root formation in hypocotyl cuttings of Pinus sylvestris: Influence of Photoperiod during stock plant growth and of indolebutyric acid treatment of cuttings

Seedlings of Pinus sylvestris were grown for 6 weeks under natural light conditions in a temperature controlled environment room. Cuttings from these plants were rooted in tap water or in indolebutyric acid (IBA) solutions for 60 days at an irradiance of 16 W m^-2. Experiments were performed at 3-week intervals during two growth seasons. — Seasonal changes in root formation were found in control cuttings as well as in IBA treated cuttings. The number of roots and the percentage of cuttings that rooted were high during early spring and autumn. During the summer period hardly any roots were formed. Stimulation of root formation by IBA occurred manily during spring and autumn when cuttings already possessed the ability to form roots. — The influence of photoperiod during stock plant growth was also investigated. Shorter photoperiod resulted in an increase in the number of roots and rooting percentage. The period during summer where rooting was inhibited under natural light conditions was considerably shortened when stock plants were grown at a photoperiod of only 4 h. The results demonstrate the importance of the growing conditions for stock plants for subsequent root formation. The results are discussed with special reference to the role of irradiance.     

Floral initiation in Rudbeckia hirta (Asteraceae) under limited inductive photoperiodic treatments

Two experiments were conducted to examine the response of Rudbeckia hirta to limited inductive photoperiodic treatments. The first examined the effects on plants grown to an thesis of the second axillary inflorescence, and the second examined the early histological events within the meristem. Plants of Rudbeckia hirta were grown to maturity under short days (SD). At maturity, half the plants were placed in long days (LD). In the first experiment, the plants remained under LD for 0, 8, 16, 24, or 32 days before being returned to SD with an additional group remaining under LD as a control. In the second experiment, the plants remained under LD for 0, 4, 8, 12, 16, 20, 24, or 28 days before being returned to SD. Meristems were sampled 0, 4, 8, or 12 days after return to SD and histologically examined. Four groups of plants receiving 32, 36, 40, or 44 LD were used as a continuous LD control. When grown to anthesis, plant height and branch number increased as the number of inductive cycles increased. Plants receiving 24 or more LD reached anthesis earlier than plants receiving fewer LD. Histological examination of plants receiving only 4 LD showed they never progressed beyond early floral initiation. After 12 LD, the meristems continued to develop even when returned to SD, indicating that enough of the floral stimulus had reached the meristem to initiate flowering. Once involucral bract primordia initiated, floral development continued whether in LD or SD conditions.     

Rooting and vitality of poinsettia cuttings was increased by arbuscular mycorrhiza in the donor plants

In this paper, we provide evidence that the rooting performance of cuttings can be improved by the arbuscular mycorrhizal (AM) symbiosis of donor plants. Poinsettia stock plants were inoculated with the Glomus intraradices isolate H510 and grown in three different cultivation systems (two organic and one conventional). AM colonization was not related to P availability in the substrate. Decay of the excised cuttings in response to unfavorable postharvest storage conditions was significantly reduced by AM colonization of the stock plants. In most cases, AM significantly promoted the formation of adventitious roots in the stored cuttings. The strongest effect of AM was found when donor plants were grown in a modified organic substrate; then AM-conditioned cuttings showed higher leaf sugar levels and a changed kinetic of carbohydrates during storage. Analyses of N, P, and K in cuttings did not indicate a nutritional effect. The results support the idea that an altered carbohydrate metabolism and plant hormones can contribute to improved rooting performance of cuttings excised from mycorrhizal donor plants.     

The role of light and polar auxin transport in root regeneration from hypocotyls of tomato seedling cuttings

A relationship between light conditions, auxin transport and adventitious root formation by hypocotyls of tomato seedling cuttings was demonstrated. Effective rooting of tomato seedling cuttings was observed under continuous white light (WL) irradiation. However, root formation was reduced in darkness or under red (RL) or blue light (BL). At least 3/4-day-long irradiation treatment with (WL) was necessary to increase the number of roots formed in comparison with control cuttings grown in darkness. Light was most effective if applied during the first half of the 13-day-long rooting period. The role of photoreceptor-dependent light perception in the light-regulation of rooting was tested using tomato photomorphogenic mutants: aurea (au) and high pigment (hp). When exposed to WL both mutants generated fewer roots then their isogenic wild type (WT). In darkness or under BL and RL less roots were formed on all plants and no difference was observed between mutants and WT plants. TIBA (2,3,5-triiodobenzoic acid) inhibited rooting in a dose-dependent manner both in darkness and under WL. However, although rooting was suppressed by 0.75 M TIBA in the dark, 8 M TIBA was necessary to block root formation in continuous WL. Inhibition of rooting by TIBA was most efficient when applied at the initial period of rooting, a 1-day-long treatment with TIBA being sufficient to suppress rooting if given during the first 2 days of culture. Later treatment had much less effect on the root formation.     

PHOTOPERIODIC AGING IN ANAGALLIS ARVENSIS CLONES: ITS RELATION TO RNA CONTENT,ROOTING CAPACITY,AND FLOWERING

We investigated the photoperiodic regulation of aging in Anagallis arvensis L. propagated by cuttings. Short-day (SD) conditions caused the persistence of juvenile forms and vegetative growth, as well as high rooting capacity and a high RNA content, through successive vegetative multiplications. SD + 1 long day (LD) every 15th day induced reproductive growth but allowed the persistence of a high rooting capacity and high RNA content through vegetative multiplications. LD conditions caused the persistence of the reproductive stage, the progressive loss of rooting capacity, and a decrease of RNA content. The longevity of the clones seems to be connected to the photoperiodic effects which induce indeterminate growth (SD) and/or determinate and reproductive growth. The loss of propagation capacity and the decrease of RNA content can be considered as indexes of aging not only in plants but also in clones.     

Light effects on root formation in aspen and willow cuttings

The effect of light on rooting of leafy cuttings of aspen (Populus tremula × tremuloides) and a willow hybrid (Salix caprea × viminalis) was investigated under controlled conditions in water culture. Two levels of irradiance were used, 40 and 8 W m^?2. The lower level gave the best rooting of aspen cuttings, both when applied to the stock plants before the cuttings were taken and when given to the cuttings during the rooting period. Irradiation of the cutting base during the rooting period inhibited rooting almost completely in aspen and decreased the number of roots formed in the Salix hybrid. Net photosynthesis in the cuttings of Salix decreased considerably after excision and increased again after formation of roots. Indirect evidence indicated that photosynthesis was even more affected in aspen cuttings. The possible roles of carbohydrates and inhibitors in the light effects are discussed.     

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.     

Induction and floral determination in the terminal bud of Nicotiana tabacum L. cv. Maryland Mammoth,a short-day plant

Floral determination in the terminal bud of the short-day plant Nicotiana tabacum cv. Maryland Mammoth has been investigated. Plants grown continuously in short days flowered after producing 31.4±1.6 (SD) nodes while plants grown continuously in long days did not flower and produced 172.5±9.5 nodes after one year. At various ages, expressed as number of leaves that were at least 1.0 cm in length above the most basal 10-cm leaf, one of three treatments was performed on plants grown from seed in short days: 1) whole plants were shifted from short days to long days, 2) the terminal bud was removed and then rooted and grown in long days, and 3) the terminal bud was removed and then rooted and grown in short days. Whole plants flowered only when shifted from short days to long days at age 15 or later. Only rooted terminal buds from plants at age 15 or older produced plants that flowered when grown in long days. Only terminal buds from plants at age 15 or older that were rooted and grown in short days produced the same number of nodes as they would have produced in their original locations while buds from younger plants produced more nodes than they would have in their original locations. Thus, determination for floral development in the terminal bud, as assayed by rooting, is simultaneous with the commitment to flowering as assayed by shifting whole plants to non-inductive conditions.Abbreviations LD long day(s) - SD short day(s) - DN dayneutral     

Effect of Photoperiod on the Regulation of Wheat Vernalization Genes VRN1 and VRN2

Wheat is usually classified as a long day (LD) plant because most varieties flower earlier when exposed to longer days. In addition to LD, winter wheats require a long exposure to low temperatures (vernalization) to become competent for flowering. Here we show that in some genotypes this vernalization requirement can be replaced by interrupting the LD treatment by 6 weeks of short day (SD), and that this replacement is associated with the SD down-regulation of the VRN2 flowering repressor. In addition, we found that SD down-regulation of VRN2 at room temperature is not followed by the up-regulation of the meristem identity gene VRN1 until plants are transferred to LD. This result contrasts with the VRN1 up-regulation observed after the VRN2 down-regulation by vernalization, suggesting the existence of a second VRN1 repressor. Analysis of natural VRN1 mutants indicated that a CArG-box located in the VRN1 promoter is the most likely regulatory site for the interaction with this second repressor. Up-regulation of VRN1 under SD in accessions carrying mutations in the CArG-box resulted in an earlier initiation of spike development, compared to other genotypes. However, even the genotypes with CArG box mutations required LD for a normal and timely spike development. The SD acceleration of flowering was observed in photoperiod sensitive winter varieties. Since vernalization requirement and photoperiod sensitivity are ancestral traits in Triticeae species we suggest that wheat was initially a SD–LD plant and that strong selection pressures during domestication and breeding resulted in the modification of this dual regulation. The down-regulation of the VRN2 repressor by SD is likely part of the mechanism associated with the SD–LD regulation of flowering in photoperiod sensitive winter wheat. These authors contributed equally to this work     

Seasonal Changes in Auxin Effects on Rooting of Stem Cuttings of Populus nigra and its Relationship with Mobilization of Starch

Stem cuttings of Populus nigra were treated with 10 and 100 mg/1 each of IAA., IBA, 2,4-D and NAA at one month intervals and observations were recorded for the morphophysiological status of the branches, their starch content and their rooting response. — The first phase characterized by delayed, short and scarce roots and the high starch content of cuttings coincided with the onset of winter dormancy in November lasting through February. It was followed by a phase of vigorous rooting and low starch content of cuttings coinciding with the renovation of growth activity in February lasting through October, except in April and May when rooting was more or less completely nullified. — The poor rooting in winter was caused by low activity of hydrolyzing enzymes not mobilizing starch into soluble sugars; and profuse rooting during active growth period by high activity of hydrolyzing enzymes caused by endogenous auxin, resulting in mobilization of reserved food materials necessary for the initiation and development of roots. The low rooting in April and May is ascribed to the fact that bulk of the mobilized food was used up in the growth of sprouted branches leaving very little for rooting when these cuttings were planted. — The seasonal changes in the effectiveness of exogenously applied auxins also appear to be related with the level of endogenous auxin. In June endogenous auxin was high due to high meristematic activity, the exogenously applied auxins raising it to supra-optimal levels that were inhibitory. On the other hand, in October exogenously applied auxins enhanced rooting by raising it to an optimal level as the production of endogenous auxin had been decreasing gradually due to lowering temperatures. — The results demonstrate that auxin effect on differential rooting with season in this plant is determined by the physio-morphological status of the branches that govern the production of endogenous auxin and is mediated primarily through its effect on mobilization of reserve food materials caused by enhanced activity of hydrolytic enzymes.     

The Effect of Photoperiod on Levels of Endogenous Cytokinins in Xanthium strumarium

The cytokinin content of Xanthium strumarium L. plants decreased markedly when they were exposed to short days (SD). There was a significant decrease in the content of the butanol-soluble cytokinins of the mature leaves after only 5 SD cycles, and after 10 SD there was no significant cytokinin activity in butanol extracts; the changes in the young leaves were less marked. Most of the cytokinin activity in mature leaves appears to be present in the aqueous fraction, whereas in young leaves most activity occurs in the butanol-soluble fraction. SD treated plants produced less root exudate than LD plants, but there were no significant differences in the amounts of cytokinin in the root exudates from LD and SD plants collected over an equivalent time period. The cytokinin levels of SD-induced leaves remained low even when transferred back to LD. The observed differences in cytokinin levels did not appear to be the result of photosynthetic differences. Exposure of detached leaves to LD or SD did not result in differences in cytokinin content. It is not clear whether the observed changes in cytokinin levels in the leaves under SD are involved in the flowering response, but they may be causally related to a reduced chlorophyll content observed in SD-induced leaves.     

Influence of Cotyledon Excision and Sucrose on Root Formation in Pea Cuttings

Sucrose was supplied to stock plants of Pisum sativum L. cv. Alaska grown at different levels of irradiance. There was no significant effect on the rooting of the cuttings by sucrose supply to intact plants regardless of the irradiance. However, an increase in the number of roots per cutting was obtained at increasing concentrations of sucrose when the stock plants had been grown at 4 W m^?2 and their cotyledons had been removed two days before the cuttings were excised. Cotyledons were removed from stock plants at different times before the excision of cuttings with the intent to regulate the endogenous supply of carbohydrate. The number of roots per cutting was reduced by removal of the cotyledons and this reduction was correlated to the number of days the stock plants had grown without cotyledons as well as to the irradiance pre-treatment. A greater reduction occurred in cuttings from plants grown under 4 W m^?2 than from those grown under 38 W m^?2. The growth of the stock plants and the subsequent stem growth of the cuttings was determined by the irradiance to the stock plants and by the time of removal of the cotyledons. Exogenous supply of sucrose had no effect on the stem growth of the cuttings.     

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.     

Expression of the <Emphasis Type="Italic">rol</Emphasis>B gene enhances adventitious root formation in hardwood cuttings of aspen

Summary An elite aspen hybrid (Populus × canescens × P. grandidentata) was transformed with Agrobacterium tumefaciens strain EHA105 that harbored a binary vector (pBI121) carrying the nptII gene under the nos promoter and tandem rolB-uidA (GUS) genes with the CaMV 35S or heat shock promoter. Among 32 independent kanamycin-resistant plants, 25 plants were confirmed by polymerase chain reaction and Southern blot analyses to contain all three genes, whereas five plants contained only nptII or/and uidA genes and two plants had both the rolB and nptII or uidA genes. Integration of the rolB gene significantly increased rooting ability of hardwood cuttings. Heat shock-rolB-transformed plants rooted at significantly higher percentage than the CaMV 35S-rolB-transformed plants. Heat shock treatment further enhanced rooting of heat shock-rolB-transformed plants. Exposure to exogenous auxin did not significantly increase the rooting percentage of transgenic hardwood cuttings, but increased the number of roots induced. This research shows great potential to improve rooting of hardwood cuttings of difficult-to-root woody plants which are commercially important to the horticultural and forestry industry. The transgenic plants with gain-of-function in hardwood-cutting rooting can facilitate research in the understanding of adventitious rooting from hardwood cuttings of recalcitrant woody plants.     

Are cuttings suitable for assessing maturity type in potato (Solanum tuberosum)?

Two experiments were carried out to evaluate the potential of single‐node cuttings of potato (Solanum tuberosum) as a tool to assess genotypic differences in maturity type. Plants were exposed to different photoperiodic treatments (different photoperiods, different numbers of photoperiodic cycles), and cuttings were taken at different plant ages. Cuttings from early (and to a lesser extent also late) maturing varieties exposed to short photoperiods showed strong induction to tuberise, irrespective of plant age; the induction increased with an increase in the number of short photoperiodic cycles. The response of cuttings taken from early‐maturing varieties exposed to long photoperiods depended on plant age: cuttings showed stronger induction when mother plants were older; cuttings from late‐maturing varieties hardly tuberised after exposure to long photoperiods. The tuberisation of the cuttings did not depend on the length of the long photoperiod (18 or 24 h) or on the number of cycles of a photoperiod of 18 h. Tuberisation on cuttings did not properly reflect the tuber formation on the mother plants, although within varieties, significant correlations between tuberisation on cuttings and tuber yield per plant 9 weeks after planting were found with different numbers of photoperiodic cycles of 12 h. Our experiments show that the cutting technique cannot be used on older plants to assess the maturity type of potato varieties, as there are interactions between photoperiod, genotype, plant age and number of photoperiodic cycles, in the reflection of the degree of induction to tuberise on single‐node cuttings.     

A relationship between irradiation, carbohydrates and rooting in cuttings of Pisum sativum

Rooting ability was studied for cuttings derived from pea plants ( Pisum sativum , L. cv. Alaska) grown in controlled environment rooms. When the cuttings were rooted at 70 μmol m⁻² s⁻, ¹ (photosynthetic photon flux density) or more, a stock plant irradiance at 100 μmol m⁻² s⁻¹ decreased rooting ability in cuttings compared to 5 μmol m⁻², s⁻¹, However, cuttings rooted at 160 μmol m⁻² s⁻¹ formed more roots compared to 5 (μmol m⁻² s⁻¹. Although a high irradiance increased the number of roots formed, it could not overcome a decreased potential for root formation in stock plants grown at high irradiance. Light compensation point and dark respiration of cuttings decreased by 70% during the rooting period, and the final levels were strongly influenced by the irradiance to the cuttings. Respiratory O₂ uptake decreased in the apex and the base of the cutting from day 2 onwards, whereas a constant level was found in the leaves. Only the content of extractable fructose, glucose, sucrose and starch varied during the early part of the rooting period. We conclude that the observed changes in the cuttings are initiated by excision of the root system, and are not involved in the initiation of adventitious roots.     

Floral morphogenesis in Rudbeckia hirta in relation to polyamine concentration

Changes in polyamine concentration in the long day (LD) plant Rudbeckia hirta were examined over the course of floral initiation and development. Plants of R. hirta were grown to maturity under 9h, non-floral-inductive photoperiods. At maturity, half the plants were placed in ambient day length plus a 4- h night interruption. Plants were sampled at 0, 4, 8, 12 or 16 days for polyamine content and floral initiation. Polyamines were extracted from fully expanded leaves and the meristems were examined histologically. In another experiment, polyamines were extracted from the meristems under paired LD and short day (SD) conditions every 2 days from 0 to 22 days. A rise in free polyamines was linked to important cytological events during floral initiation. Free putrescine and spermidine levels increased after 4 LD and continued until 14 to 16 LD when the levels in the meristem began to decline. Events of floral initiation began between 4 and 8 LD with cell proliferation and the start of stem elongation. Initiation was irreversible after 14 to 16 LD, the period when putrescine and spermidine began to decline. After 4 LD, the polyamine level was consistently higher in the photoinduced plants. Our results from this study, using direct histological comparisons of meristematic development and polyamine concentration, clearly demonstrate a correlation of polyamines and flowering.     

Establishment of willow cuttings grown in porous membrane root envelopes

Small diameter fine, fibrous roots of willow are exceedingly difficult to remove from most soils. Where field retrieval of entire plants including clean roots may be important, porous membrane rooting envelopes are a method of choice.Purple osier willow (Salix purpurea L.) stem cuttings (clone SP3) were field rooted in buried porous membrane envelopes permeable to water and nutrients. Ramets were grown for two and four months, then separated into component parts for dry weight analysis.At two months, cuttings grown in rooting envelopes were no different in shoot dry weight than plants grown in clay pots or in soil. Tests indicated that rooting envelopes may be reused at least once without affecting shoot or total plant dry weight. Likewise, membrane pore sizes of 0.45, 1.2 and 3 m did not affect SP3 dry weight in four month tests. The importance of matching plant material and experiment duration to envelope size was illustrated by the limitation of growth by envelope edges at four months compared to two months.     

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.