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Compact plant growth is an economically important trait for many crops. In practice, compactness is frequently obtained by applying chemical plant growth regulators. In view of sustainable and environmental-friendly plant production, the search for viable alternatives is a priority for breeders. Co-cultivation and natural transformation using rhizogenic agrobacteria result in morphological alterations which together compose the Ri phenotype. This phenotype is known to exhibit a more compact plant habit, besides other features. In this review, we highlight the use of rhizogenic agrobacteria and the Ri phenotype with regard to sustainable plant production and plant breeding. An overview of described Ri lines and current breeding applications is presented. The potential of Ri lines as pre-breeding material is discussed from both a practical and legal point of view.

Indoor potted plants are able to remove volatile organic compounds (VOC) from air, but only few studies have investigated the removal of compounds in mixtures. Here, we present a non-targeted pixel-based fingerprinting analysis documenting the removal of a complex mixture of gasoline VOCs by Hedera helix under dynamic chamber conditions allowing for air exchange and continuous gasoline exposure. For 15 days, the entire potted plant was exposed to gasoline; subsequently, the epigeous plant parts were removed and the soil microcosm (i.e. soil, plant roots and microorganisms) was exposed to gasoline for another eight days. Quantitative analysis was performed for heptane, 3-methylhexane, toluene, ethylbenzene and m,p-xylenes, and the CHEMSIC method (CHEMometric analysis of Selected Ion Chromatograms) was used for non-targeted pixel-based fingerprinting analysis. The quantitative analysis demonstrated that the presence of potted plants or pots without epigeous plant parts led to a reduction of selected VOCs by 16.7-22.6%. The CHEMSIC method confirmed this and revealed that all gasoline VOCs were reduced in concentration when H. helix was present. The estimate for the total VOC removal was in the range of 11-32%. The removal was highest for samples where the epigeous plant parts were absent and compounds known to be hard to degrade by microorganisms such as dimethylcyclopentanes were removed the least compared to compounds more easily degraded by microorganisms such as heptane when epigeous plant parts were removed. All findings support the conclusion that the soil microcosm was the main responsible for the removal of VOCs.

Rhizobium rhizogenes exploits horizontal gene transfer as part of its mechanism of pathogenesis. In this respect, genetic material, transfer DNA (T-DNA) from the bacterium, is transferred transiently to the host plant genome. However, plant species within Nicotiana, Linaria and Ipomea genera contain genomic traces of ancient bacterial T-DNA. To determine if ancient bacterial T-DNA is present in uncultivated plants of European genera within Scrophulariaceae, seeds of Linaria, Antirrhinum, Digitalis, and Veronica were analysed for the presence of one of the root oncogenic loci genes; rolC of R. rhizogenes. This study discloses remnants of ancient rolC haplotypes in several species of Linaria, Antirrhinum, Digitalis and Veronica. The distribution of plant species harbouring rolC sequences within each genus was not uniform. In total, 7 of the 16 investigated species were found to be positive for at least one of the rolC haplotypes, where 6 of these are new additions to the group of naturally transformed plants. Sequence alignment showed high interspecies homology of rolC. Five unique rolC haplotypes (rolCa-rolCe) were found in several plant species. The most abundant, rolCa, was identified in all the plant species holding ancient bacterial DNA. Transcripts of rolC were not detected in leaves, which indicates that rolC may not have a function in leaves under non-stress conditions. This study adds Antirrhinum, Digitalis and Veronica to the list of plant genera within Scrophulariaceae which have been subjected to ancient transformation events via horizontal gene transfer from bacteria to plants.

Increasing agricultural losses due to biotic and abiotic stresses caused by climate change challenge food security worldwide. A promising strategy to sustain crop productivity under conditions of limited water availability is the use of plant growth promoting rhizobacteria (PGPR). Here, the effects of spore forming Bacillus licheniformis (FMCH001) on growth and physiology of maize (Zea mays L. cv. Ronaldinho) under well-watered and drought stressed conditions were investigated. Pot experiments were conducted in the automated high-throughput phenotyping platform PhenoLab and under greenhouse conditions. Results of the PhenoLab experiments showed that plants inoculated with B. licheniformis FMCH001 exhibited increased root dry weight and plant water use efficiency compared to uninoculated plants. In greenhouse experiments, root and shoot dry weight significantly increased by more than 15% in inoculated plants compared to uninoculated control plants. Also, the water use efficiency increased in FMCH001 plants up to 46% in both well-watered and drought stressed plants. Root and shoot activities of 11 carbohydrate and 8 antioxidative enzymes were characterised in response to FMCH001 treatments. This showed a higher antioxidant activity of catalase in roots of FMCH001 treated plants compared to uninoculated plants. The higher catalase activity was observed irrespective of the water regime. These findings show that seed coating with gram positive spore forming B. licheniformis could be used as biostimulants for enhancing plant water use efficiency under both normal and drought stress conditions.

Kalanchoe pinnata from the stonecrop family (Crassulaceae) is a medicinal plant with high content of bioactive compounds. The plant is known for its anti-allergic, antioxidant, anti-inflammatory, antimicrobial and antibacterial activities, which are mainly attributed to flavonoids. Low yields of bioactive compounds in medicinal plants have led to new strategies for enhancing their biosynthetic capacity in order to increase the content of specialized metabolites. Herein, the accumulation of specialized metabolites in plants can be triggered by elicitation methods. In the current study, different elicitation strategies were conducted towards the enhancement of bioactive compounds in K. pinnata leaves. We investigated the effect of natural transformation with the Agrobacterium rhizogenes strain A4 as means of biological elicitation on the total content of flavonoids in the leaves of K. pinnata. Furthermore, the effect of supplemental UV-B radiation, as physical elicitor, was assessed on the total flavonoid content of both wild-type (WT) and rol-transformed plants. The combined effect of the two mentioned elicitation methods was also examined. The data showed that presence of rol genes resulted in an increase of 24% in the total flavonoid content compared to WT plants. The supplemental UV-B radiation increased the total content of flavonoids with 95% and 89% in the WT and the rol+ plants, respectively. Collectively, a synergistic effect was shown as the combination of the two factors dramatically increased (133%) the total flavonoid content in K. pinnata leaves.

The PEBP family comprises proteins that function as key regulators of flowering time throughout the plant kingdom and they also regulate growth and plant architecture. Within the PEBP protein family, three subfamilies can be distinguished in angiosperms: MOTHER OF FT AND TFL1-like (MFT), FLOWERING LOCUS T-like (FT-like), and TERMINAL FLOWER1-like (TFL1-like). Taking advantage of the genome sequences available from K. fedtschenkoi and K. laxiflora, we performed computational analysis to identify the members of the PEBP gene family in these species. The analyses revealed the existence of 11 PEBP genes in K. fedtschenkoi and 18 in K. laxiflora, which are clustered in two clades: FT-like and TFL1-like. The PEBP genes had conserved gene structure and the proteins had highly conserved amino acid sequences in the positions crucial for the protein functions. The analysis of Ka/Ks ratio revealed that most recently duplicated genes are under positive selection. Despite being an economically important genus, the genetics underlying the regulation of flowering in Kalancho&euml, is poorly understood. The results of this study may provide a new insight into the molecular control of flowering that will allow further studies on flowering control in Kalancho&euml

Plant transformation with the wild type Ri plasmid T-DNA of Agrobacterium rhizogenes is a promising method for breeding of compact plants and has been the subject of numerous studies. However, knowledge concerning the isolated functions of single genes and ORFs from the plasmid is limited. The rolB and ORF13 oncogenes of A. rhizogenes show considerable promise in plant breeding, but have not been comprehensively studied. Detailed information regarding the morphological impact of specific genes of the Ri plasmid will allow for optimized targeted breeding of plants transformed with the wild type Ri plasmid T-DNA. rolB and ORF13 were recombined into the genome of Arabidopsis thaliana using Gateway® cloning and the effect on plant growth was assessed biometrically throughout the plants' life cycle. rolB-lines exhibited dwarfing, early necrosis of rosette leaves, altered leaf and flower morphology, and developed an increased number of inflorescences per rosette area compared to the wild type. ORF13-lines were extremely dwarfed, attaining only ca. 1% of the rosette area of the wild type, leaf and flower size was reduced, and the shape modified. The study documents that the traits inferred by the rolB oncogene yield plants with increased formation of generative shoots, but also result in some degree of premature senescence of vegetative organs. The extreme dwarfism seen in ORF13-lines indicate that this oncogene may be more important in the dwarfing response of plants transformed with the wild type Ri plasmid T-DNA than previously assumed and that transformation with this oncogene induces a very compact phenotype.

Compactness is a desirable trait in ornamental plant breeding because it is preferred by producers, distributors and consumers. Presently, in ornamental plant production growth of many potted plants is regulated by application of chemical growth retardants, several of which are harmful to both the environment and human health. With the aim to develop an alternative to chemical growth regulators, a biotechnological approach without the use of recombinant DNA technology has been developed. In this method, the soil borne bacterium Agrobacterium rhizogenes inserts T-DNA, containing four root oncogenic loci (rol)-genes rolA, rolB, rolC and rolD among 18 ORFs, into the plant genome. Infection of plants by A. rhizogenes induces hairy roots, from which shoots containing rol-genes can be regenerated. Natural transformation with A. rhizogenes reveals very promising results in several plant species and can be useful in a broader range of application than ornamental breeding. One important aspect of this technology is that the hairy roots can be used directly in the selection process as a primary indicator of a successful transformation. Thus the technology avoids use of undesired antibiotic resistance marker genes. Noteworthy, in Denmark the authorities have confirmed that plant products developed using natural transformation by unmodified strains of A. rhizogenes are not considered as genetically modified (GM) plants according to the European legislation. Generally, rol-genes cause increased rooting, decreased plant height, short internodes, reduced apical dominance and changes in flower characteristics. Several of these traits improve ornamental plant quality and may also benefit characteristics useful in agricultural field crops. In addition, a number of regenerated plants derived from hairy roots contain higher contents of secondary metabolites compared to wild type plants. Hence, this method also has potential as a tool for boosting high value compounds in medicinal plants.

Kalanchoe blossfeldiana and its cultivars are important worldwide as potted plants. Their improvement relies mainly on cross-breeding and interspecific hybridization, although the use of the resource of wild species was limited. The present study aimed to characterize novel features of interspecific hybrids that can increase attractiveness of these commercially important ornamental plants. We investigated the new traits of selected hybrids resulting from hybridization between K. blossfeldiana and three wild Kalanchoe species, namely K. nyikae, K. pubescens and K. marnieriana. The selected qualitative and quantitative traits of plant growth and flowering were analyzed in hybrids and parental species. The analysis demonstrated generally intermediate character of hybrids. Following principal component analysis, clear separation among plants forming three distinct clusters was observed, where hybrids were situated between the two parental species. The plants were clearly grouped according to flower characteristics, plant height and timing of flowering in all investigated groups. Quantitative analysis also revealed significant differences among parental plants and hybrids for all examined characteristics. Transgressive segregation and heterosis were observed in relation to specific traits such as days until first open flower, plant height, number of inflorescences, flower diameter and number of flowers. Pollen analysis of the interspecific hybrids revealed low viability of pollen or complete sterility. The interspecific hybrids exhibited novel features valuable for breeders. Thus, wide hybridization can contribute to the development of new cultivars and this study clearly demonstrates the usefulness of interspecific crosses in the improvement of Kalanchoe cultivars.

Brassica napus (oilseed rape) is a major oil crop worldwide. Due to the short domestication period of oilseed rape the genetic variability is limited compared to other crops. Transfer of rol and aux genes from Agrobacterium rhizogenes is used in horticulture to increase genetic variability. In the current study, we explore transformation by A. rhizogenes as a biotechnological approach in breeding for more branched and shorter oilseed rape. In the 2nd generation of transformed oilseed rape, branch numbers increased significantly by 49% from 7.7 ± 0.4 to 11.5 ± 1.9 when comparing rol+/aux+ plants with WT. Simultaneously, the apical height of plants was reduced by 25% from 81.3 ± 1.9 cm to 62.4 ± 6.7 cm in rol+/aux+ plants at the onset of flowering. Reproductive parameters affecting yield as seed size and number were negatively affected in rol+/aux+ plants. Interestingly, oil composition was changed in rol+/aux+ seeds. Oleic acid (ω9) contents were reduced by more than 3% whereas α-linolenic acid (ω6) increased by more than 25% in mature seeds. To obtain shorter and more branched breeding material of oilseed rape we suggest crossing plants with the rol+/aux+ genotype back into the parental breeding line. This could reduce the negative impact of rol+/aux+ on yield.

Volatile organic compounds (VOCs) are found in indoor air, and many of these can affect human health (e.g. formaldehyde and benzene are carcinogenic). Plants affect the levels of VOCs in indoor environments, thus they represent a potential green solution for improving indoor air quality that at the same time can improve human health. This article reviews scientific studies of plants' ability to remove VOCs from indoor air. The focus of the review is on pathways of VOC removal by the plants and factors affecting the efficiency and rate of VOC removal by plants. Laboratory based studies indicate that plant induced removal of VOCs is a combination of direct (e.g. absorption) and indirect (e.g. biotransformation by microorganisms) mechanisms. They also demonstrate that plants' rate of reducing the level of VOCs is influenced by a number of factors such as plant species, light intensity and VOC concentration. For instance, an increase in light intensity has in some studies been shown to lead to an increase in removal of a pollutant. Studies conducted in real-life settings such as offices and homes are few and show mixed results.

© The Author(s)., Black carrot (Daucus carota L. ssp. sativus var. atroburens) is a root vegetable with anthocyanins as major phenolic compounds. The accumulation of phenolic compounds is a common response to UV-B exposure, acting as protective compounds and as antioxidants. In the present study, black carrot plants grown under a 12-h photoperiod were supplemented with UV-B radiation (21.6 kj m−2 day−1) during the last two weeks of growth. Carrot taproots and tops were harvested separately, and the effect of the UV-B irradiance was evaluated in terms of size (biomass and length), total monomeric anthocyanin content (TMC), total phenolic content (TPC), and phytohormones levels. The results showed that UV-B irradiance promoted plant growth, as shown by the elevated root (30%) and top (24%) biomass, the increased TMC and TPC in the root (over 10%), and the increased TPC of the top (9%). A hormone analysis revealed that, in response to UV-B irradiance, the levels of abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA) decreased in tops while the level of the cytokinins cis-zeatin (cZ) and trans-zeatinriboside (tZR) increased in roots, which correlated with an amplified growth and the accumulation of anthocyanins and phenolic compounds. Beyond the practical implications that this work may have, it contributes to the understanding of UV-B responses in black carrot, This research was funded by the Danish Ministry of Science, Innovation, and Education grant number 6111-00240B and “Fundación Séneca” of the Agency of Science and Technology of the Region of Murcia grant number 20405/SF/17.

Compact growth is an important quality criterion in horticulture. Many Campanula species and cultivars exhibit elongated growth which is suppressed by chemical retardation and cultural practice during production to accommodate to the consumer’s desire. The production of compact plants via transformation with wild type Agrobacterium rhizogenes is an approach with great potential to produce plants that are non-GMO. Efficient transformation and regeneration procedures vary widely among both plant genera and species. Here we present a transformation protocol for Campanula. Hairy roots were produced on 26–90% of the petioles that were used for transformation of C. portenschlagiana (Cp), a C. takesimana × C. punctata hybrid (Chybr) and C. glomerata (Cg). Isolated hairy roots grew autonomously and vigorously without added hormones. The Cg hairy roots produced chlorophyll and generated plantlets in response to treatments with cytokinin (42 µM 2iP) and auxin (0.67 µM NAA). In contrast, regeneration attempts of transformed Cp and Chybr roots lead neither to the production of chlorophyll nor to the regeneration of shoots. Agropine A. rhizogenes strains integrate split T-DNA in TL- and TR-DNA fragments into the plant genome. In this study, regenerated plants of Cg did not contain TR-DNA, indicating that a selective pressure against this T-DNA fragment may exist in Campanula.

The gaseous plant hormone ethylene plays a central role in numerous physiological and developmental processes, such as germination, growth and development, flower initiation and opening, senescence of leaves and flowers, organ abscission and fruit ripening. Ethylene is often termed the senescence hormone and has a crucial role in rose flower senescence. The so called climacteric plants are ethylene sensitive and flowers of these plants deteriorate rapidly in the presence of the hormone. The senescence of flowers belonging to this category is associated with a climacteric rise in ethylene production and increase in respiration. The climacteric plant rose is regarded as one of the most important ornamental plants worldwide and is produced in vast numbers both as cut flowers and potted ornamental plants. This chapter describes principles of postharvest biology and handling of roses with focus on differences in postharvest characteristics among several cultivars. The effects of exogenous ethylene on flower longevity and the endogenous production of the hormone in rose flowers at different developmental stages are addressed. The principles of the ethylene biosynthesis pathway are depicted and ethylene biosynthesis inhibitors are presented. Furthermore, the mode of action and the effect of inhibitors of ethylene action to improve rose display life are discussed including the significant compounds silver thiosulfate and 1-methylcyclopropene. The ethylene signal transduction pathway in plants is reviewed, with particular focus on rose, followed by studies of expression of ethylene signal transduction genes in rose flowers. Finally, strategies for improvement of postharvest quality in roses and future prospects are discussed.

Background Black carrots (Daucus carota ssp. sativus var. atrorubens Alef.) constitute a valuable source of anthocyanins, which are used as natural red, blue and purple food colourants. Anthocyanins and phenolic compounds are specialised metabolites, accumulation of which often requires elicitors, which act as molecular signals in plant stress responses. In the present study, ethephon, an ethylene-generating compound was explored as enhancer of anthocyanin and phenolic contents during growth of ‘Deep Purple’ black carrots. The effects of ethephon on several parameters were investigated, and the expression of biosynthetic anthocyanin genes was studied during growth and anthocyanin accumulation. Results Roots of ethephon-treated carrot plants exhibited an increase in anthocyanin content of approximately 25%, with values ranging from 2.25 to 3.10 mg g−1 fresh weight, compared with values ranging from 1.50 to 1.90 mg g−1 fresh weight in untreated roots. The most rapid accumulation rate for anthocyanins, phenolic compounds, soluble solids and dry matter was observed between 10 and 13 weeks after sowing in both untreated and ethephon-treated carrots. The differences in anthocyanin contents between untreated and treated carrots increased for several weeks after the ethephon treatment was terminated. Five cyanidin-based anthocyanin forms were identified, with variable relative abundance values detected during root growth. Overall, the expression of the anthocyanin biosynthetic genes analysed (PAL1, PAL3, F3H1, DFR1, LDOX2) increased in response to ethephon treatment, as did the expression of the MYB1 transcription factor, which is associated with activation of the phenylpropanoid pathway under stress conditions. In addition, a correlation was proposed between ethylene and sugar contents and the induction of anthocyanin synthesis. Conclusions This study presents a novel method for enhancing anthocyanin content in black carrots. This finding is of economic importance as increased pigment concentration per unit of biomass implies improved profitability parameters in food colour production. We provide new insight into the accumulation patterns of the different cyanidin-based anthocyanins and phenolic compounds during root growth. Moreover, we show that enhanced anthocyanin content in ethephon-treated carrots is accompanied by increased expression of anthocyanin biosynthetic genes. Electronic supplementary material The online version of this article (doi:10.1186/s12870-017-1021-7) contains supplementary material, which is available to authorized users.

Transformation of Kalanchoe blossfeldiana ‘Molly’ using the naturally occurring bacterium Agrobacterium rhizogenes is a non-GMO strategy to breed compact plants. In the present study, crosses resembling a commercial breeding strategy were made to determine if the improved ornamental quality observed in the T1 generation was inherited to the offspring. F1 lines were produced by crossing the commercial Kalanchoe cultivar ‘Sarah’ with a selected T1 line. Subsequently, F2 populations were produced by self-pollination of individual selected lines. The rol-genes were inherited to the progeny and the presence of rol-genes was confirmed in all F1 and many F2 plant lines exhibiting dwarfism. Screening of F1 and F2 plants showed that the rol-genes were inherited together. Besides decreased plant height, several F1 and F2 lines containing rol-genes exhibited changes in plant diameter, number of branches, flower diameter and time to first open flower and duration of flowering compared to the WT ‘Molly’. Furthermore, increased ethylene tolerance was observed in several lines containing rol-genes compared to the WT ‘Sarah’. Screening of three selected F2 populations derived from self-pollination of F1 lines containing rol-genes indicated a shift in distribution towards a lower mean plant height within the entire plant population compared to a control population of plants without rol-genes. Moreover, one of these F2 populations also exhibited earlier flowering compared to the control population. Compact potted plants and lines without delayed flowering and with improved ethylene tolerance were obtained and are valuable in commercial breeding programmes without using recombinant DNA technology.

Through the last decades, environmentally and health-friendly production methods and conscientious use of resources have become crucial for reaching the goal of a more sustainable plant production. Protection of the environment requires careful consumption of limited resources and reduction of chemicals applied during production of ornamental plants. Numerous chemicals used in modern plant production have negative impacts on human health and are hazardous to the environment. In Europe, several compounds have lost their approval and further legal restrictions can be expected. This review presents the more recent progress of genetic engineering in ornamental breeding, delivers an overview of the biological background of the used technologies and critically evaluates the usefulness of the strategies to obtain improved ornamental plants. First, genetic engineering is addressed as alternative to growth retardants, comprising recombinant DNA approaches targeting relevant hormone pathways, e.g. the gibberellic acid (GA) pathway. A reduced content of active GAs causes compact growth and can be facilitated by either decreased anabolism, increased catabolism or altered perception. Moreover, compactness can be accomplished by using a natural transformation approach without recombinant DNA technology. Secondly, metabolic engineering approaches targeting elements of the ethylene signal transduction pathway are summarized as a possible alternative to avoid the use of chemical ethylene inhibitors. In conclusion, molecular breeding approaches are dealt with in a way allowing a critical biological assessment and enabling the scientific community and public to put genetic engineering of ornamental plants into a perspective regarding their usefulness in plant breeding.

The isolation and expression analysis of four partial gene sequences from rose (Rosa hybrida cv. Linda) belonging to the receptor-like kinase gene superfamily are reported. These genes have been designated RhSERK1 to RhSERK4 (Accession No. EF631967 to EF631970) as they exhibit high sequence identities with genes from the somatic embryogenesis receptor-like kinase (SERK) family in other plant species. The RhSERK genes are differentially expressed in non-embryogenic callus, embryogenic callus, mature somatic embryos and a range of tissues from intact plants, indicating a broad role in plant growth and development. However, the expressions of RhSERK3 and RhSERK4 were approximately fivefold higher in embryogenic callus than in non-embryogenic callus, and they are even higher when compared to tissues from intact plants. In addition, RhSERK4 expression was approximately eightfold higher in somatic embryos than in embryogenic callus. These results suggest that the expression pattern of RhSERK3 and RhSERK4 may be used as a marker of somatic embryogenesis.

Phalaenopsis frequently exhibits bud drop during production and in response to adverse postharvest conditions. The effect of exogenous ethylene on bud drop of mini Phalaenopsis was studied and ethylene sensitivity of four cultivars was compared. Water content, membrane permeability and ABA (abscisic acid) content in floral buds and flowers were determined after ethylene treatment. Exogenous ethylene induced flower bud drop in all tested Phalaenopsis cultivars and the different cultivars showed distinct differences in ethylene sensitivity. The cultivar Sogo ‘Vivien’ exhibited the highest bud drop, water loss and change in membrane permeability in floral petals, while Sogo ‘Berry’ showed the lowest sensitivity. The ethylene inhibitor 1-MCP (1-methylcyclopropene) reduced ethylene-induced floral bud drop in the cultivar Sogo ‘Yenlin’. ABA content in floral buds was increased in response to ethylene and 1-MCP pretreatment inhibited the ethylene-induced increase in ABA levels efficiently. This finding suggests that the observed increase in ABA content during bud drop was mediated by ethylene. The interaction between ABA and ethylene is discussed.

Kalanchoe blossfeldiana transformed with rol genes, termed root-inducing (Ri) lines, which had been produced through transformation using Agrobacterium rhizogenes wild-type strain ATCC15834, were tested for their postharvest performance. Flower longevity, ethylene sensitivity and display quality varied among control and chemical growth retarded plants and the Ri lines. Both chemical growth retardation and transformation with rol genes reduced the number of flowers in comparison to control plants. Detached single flowers of the two Ri lines tested, Ri line 306 and 331, had a longevity, defined as the stage where the flowers were 70% open, of 32 and 34 d, respectively, whereas chemical growth retarded and control plants had a longevity of 28 and 26 d, respectively. Ri line 331 had the significantly longest display life of 34 d to reach the stage of losing the ornamental value of the whole plant, defined as 10% wilted flowers. The corresponding display life of control and chemical retarded plants and plants of Ri line 306 was 25 d. The opening of the flowers was more synchronous in the Ri lines than control plants. Exposed to ethylene, the flowers of the Ri lines exhibited reduced responsiveness whereas chemical growth retarded and control plants were sensitive. Possible mechanisms behind the improved postharvest performance of plants transformed with rol genes are discussed.

SummaryTransgenic hairy roots were induced from leaf, petiole, and shoot explants of in vitro-raised plantlets of potted Hibiscus rosa-sinensis L. ‘Cassiopeia Wind Yellow’ plants after co-cultivation with three different wild-type strains of Agrobacterium rhizogenes. The highest infection rate (56.4%) was obtained in explants inoculated with A. rhizogenes strain ATCC43057, followed by ATCC15834 (44.0%), and NCPPB8196 (34.4%). The highest infection rate (60.5%) was obtained using leaf basal segments, followed by petioles (44.0%), leaf tips (40.0%), and shoots (20%). A total of 102 putative transgenic root lines were produced. The hairy root lines did not grow without applying 0.2 mg l−1 indole-3-butryric acid (IBA) and 0.2 mg l−1 α-naphthaleneacetic acid (NAA). The presence of T-DNA was confirmed in six hairy root lines, and no A. rhizogenes contamination was detected by polymerase chain reaction.

Dwarf genotypes of the economically important flowering potted plant Kalanchoe blossfeldiana were developed by molecular breeding. Root inducing (Ri)-lines were regenerated by applying CPPU to the hairy roots, which were produced by inoculating leaf explants with a wild-type Agrobacterium rhizogenes strain ATCC15834. Amplification by polymerase chain reaction (PCR) and Southern blot analysis confirmed the presence of T-DNA in the Ri-lines. Six Ri-lines were characterised in a greenhouse trial revealing that several morphological traits changed with respect to ornamental value such as plant height, number of lateral shoots, leaf size, leaf number, flower size and number of flowers. The Ri-lines differed in their degree of Ri-phenotype, and the internodes of the Ri-lines were clearly shorter, giving a compact growth habit compared to control plants. Time to anthesis was the same in Ri-line 331 as in control plants and delayed by only 3 days in Ri-line 306 as compared to control plants. A compact plant without delayed flowering can be assumed to be valuable for further breeding.

Some factors influencing in vitro cultures of potted Hibiscus rosa-sinensis L. using nodal cuttings were investigated. A protocol using a modified MS medium helped to overcome chlorosis, shoot tip necrosis (STN) and leaf drop. These disorders have been caused by mineral imbalance associated with calcium and iron deficiency. STN and leaf drop were overcome by increasing calcium level from 3 mM (MS standard concentration) to 9 mM, and this increase, in addition, enhanced shoot dry weight and shoot extension. The chlorophyll content and leaf area increased by increasing the iron concentration 3-fold from 98 μM to 295 μM. Furthermore, substituting Fe-EDTA with Fe-EDDHA resulted in an increase in chlorophyll content, leaf area and shoot extension. The most suitable multiplication medium for H. rosa-sinensis L. was demonstrated to be a modified MS medium containing 2.2 μM BAP and increased concentrations of calcium at 9 mM and iron at 295 μM provided as Fe-EDDHA. The shoots were rooted in half-strength modified MS medium containing 2.7 μM NAA. Acclimatization was successful with all shoots with or without roots.

Background The phytohormone ethylene plays a central role in development and senescence of climacteric flowers. In ornamental plant production, ethylene sensitive plants are usually protected against negative effects of ethylene by application of chemical inhibitors. In Campanula, flowers are sensitive to even minute concentrations of ethylene. Results Monitoring flower longevity in three Campanula species revealed C. portenschlagiana (Cp) as ethylene sensitive, C. formanekiana (Cf) with intermediate sensitivity and C. medium (Cm) as ethylene insensitive. We identified key elements in ethylene signal transduction, specifically in Ethylene Response Sensor 2 (ERS2), Constitutive Triple Response 1 (CTR1) and Ethylene Insensitive 3- Like 1 and 2 (EIL1 and EIL2) homologous. Transcripts of ERS2, CTR1 and EIL1 were constitutively expressed in all species both throughout flower development and in response to ethylene. In contrast, EIL2 was found only in Cf and Cm. We identified a natural mutation in Cmeil2 causing a frameshift which resulted in difference in expression levels of EIL2, with more than 100-fold change between Cf and Cm in young flowers. Conclusions This study shows that the naturally occurring 7 bp frameshift discovered in Cmeil2, a key gene in the ethylene signaling pathway, correlates with ethylene insensitivity in flowers. We suggest that transfer of the eil2 mutation to other plant species will provide a novel tool to engineer ethylene insensitive flowers. Electronic supplementary material The online version of this article (doi:10.1186/s12870-016-0786-4) contains supplementary material, which is available to authorized users.

SummaryThe transcription factor EIN3 is part of the ethylene signal transcription pathway in Arabidopsis. To investigate the genes involved in ethylene induced leaf and flower senescence in Rosa hybrida, a cDNA fragment encoding part of a transcription factor EIN3 homologue, termed RhEIN3, was isolated. The deduced proteinEIN3-fragment has 83% and 88% identity to the corresponding region of Arabidopsis EIN3 and EIL1, respectively. The gene RhEIN3 was constitutively and stably expressed in leaves of two cultivars, and during flower senescence in two rose cultivars with differences in flower life, even after ABA or ethylene treatment.

To analyze differences in flower longevity and ethylene sensitivity, we isolated Rosa hybrida gene fragments with sequence similarity to the Arabidopsis thaliana ethylene receptor gene-family. A rose gene (RhETR1) highly similar to AtERS1 had been previously sequenced. Here, we report the isolation of three additional partial rose genes (RhETR2-4) belonging to different sub-groups of ethylene receptor genes. RhETR2 clusters with AtETR1, RhETR4 with AtERS1 and RhETR1, whereas RhETR3 shows high sequence similarity to AtETR2 and AtERS2. Expression analysis of RhETR2 and RhETR3 revealed that they are differentially expressed. RhETR2 is expressed at a constitutive level throughout flower development whereas RhETR3 expression increases in senescing flowers of the cultivar Bronze which has a short floral life while it remains at low levels in the long-lasting flowers of the cultivar Vanilla. Expression of both genes was increased by ABA and ethylene treatment, but transcript abundance differed between rose cultivars with different postharvest performance. These results indicate that differences in flower life among rose cultivars could be due to differences in receptor levels.

Exogenous application of ABA (abscisic acid) to intact miniature potted rose plants (Rosa hybrida L.) resulted in deterioration of postharvest quality of two cultivars. Spraying with ABA increased leaf drop and accelerated flower senescence in ‘Vanilla’ and ‘Bronze’, while bud drop was only induced in ‘Bronze’. Application of ABA to detached rose flowers accelerated their senescence, indicating that the observed senescence promoting effect was not a secondary response resulting from ABA-induced leaf senescence and abscission. ABA-treatment increased ethylene production in ‘Bronze’ flowers, while no ethylene production was measured in flowers of ‘Vanilla’, or in the leaves of both cultivars. Pre-treatment with 1-MCP (1-methylcyclopropene) delayed ABA promoted flower senescence in ‘Bronze’, suggesting that the effect of ABA is at least partly mediated by ethylene. The senescence promoting effect of ABA on leaf drop and flower life of ‘Vanilla’ flowers was not counteracted by 1-MCP pre-treatment. The cultivar ‘Vanilla’ had a low ABA level at all flower stages, while ABA content of the ‘Bronze’ petals was high in buds, lower in open flowers, and increased during flower senescence. An increased ABA content after ethylene treatment in ‘Vanilla’ suggests that ethylene, natural or exogenous, can increase ABA levels of flowers.

Commercial miniature potted rose cultivars ( Rosa hybrida L.) varied dramatically in their postharvest life. In some short-lived cultivars such as `Bronze,' 100% of the flowers faded after 12 days. In long-lived cultivars like `Vanilla' or `Charming,' less than 10% loss in display quality took place after the same period. Flower senescence in some cultivars was accompanied by a clear climacteric rise in ethylene production, in others there was only moderate or very low ethylene production. Leaf, bud abscission and flower senescence were accelerated when plants were exposed to exogenous ethylene, and there were marked differences in sensitivity and response to ethylene among cultivars. Longevity in the absence of ethylene was apparently related to timing of the onset of ethylene production. One cultivar with excellent longevity in air was also almost insensitive to exogenous ethylene, and indicates the potential for a breeding approach to increasing postharvest longevity of these plants.

KEY MESSAGE : The P ( SAG12 ) -ipt gene was transferred to miniature rose, as the first woody species, resulting in increased ethylene resistance due to specific up-regulation of the ipt gene under senescence promoting conditions. Transgenic plants of Rosa hybrida 'Linda' were obtained via transformation with Agrobacterium tumefaciens strain harboring the binary vector pSG529(+) containing the P( SAG12 )-ipt construct. A. tumefaciens strains AGL1, GV3850 and LBA4404 (containing P(35S)-INTGUS gene) were used for transformation of embryogenic callus, but transgenic shoots were obtained only when AGL1 was applied. The highest transformation frequency was 10 % and it was achieved when half MS medium was used for the dilution of overnight culture of Agrobacterium. Southern blot confirmed integration of 1-6 copies of the nptII gene into the rose genome in the tested lines. Four transgenic lines were obtained which were morphologically true-to-type and indistinguishable from Wt shoots while they were in in vitro cultures. Adventitious root induction was more difficult in transgenic shoots compared to the Wt shoots, however, one of the transgenic lines (line 6) was rooted and subsequently analyzed phenotypically. The ipt expression levels were determined in this line after exposure to exogenous ethylene (3.5 μl l(-1)) and/or darkness. Darkness resulted in twofold up-regulation of ipt expression, whereas darkness combined with ethylene caused eightfold up-regulation in line 6 compared to Wt plants. The transgenic line had significantly higher content of chlorophyll at the end of the treatment period compared to Wt plants.

Growth retardation is an important breeding aim and an essential part of horticultural plant production. Here, the potential of transferring the Arabidopsis short internode (shi) mutant phenotype was explored by expressing the AtSHI gene in the popular ornamental plant Kalanchoe. A 35S-AtSHI construct was produced and transferred into eight genetically different cultivars of Kalanchoe by Agrobacterium tumefaciens. The resulting transgenic plants showed dwarfing phenotypes like reduced plant height and diameter, and also more compact inflorescences, as a result of increased vegetative height. The shi phenotype was stable over more than five vegetative subcultivations. Compared with Arabidopsis, the ectopic expression of AtSHI in Kalanchoe showed several differences. None of the Kalanchoe SHI-lines exhibited alterations in leaf colour or morphology, and most lines were not delayed in flowering. Moreover, continuous treatment of lines delayed in flowering with low concentrations of gibberellins completely restored the time of flowering. These features are very important as a delay in flowering would increase plant production costs significantly. The effect of expression controlled by the native Arabidopsis SHI promoter was also investigated in transgenic Kalanchoe and resulted in plants with a longer flowering period. Two AtSHI like genes were identified in Kalanchoe indicating a widespread presence of this transcription factor. These findings are important because they suggest that transformation with the AtSHI gene could be applied to several species as a tool for growth retardation, and that this approach could substitute the use of conventional chemical growth regulation in plant production.

The expression of two CTR-gene homologues was investigated during flower senescence in two Rosa hybrida cultivars. A fragment of a gene for a protein kinase, termed RhCTR1 (GenBank Acc. No. AF271206), was amplified by PCR and used to isolate the corresponding full-length cDNA (Acc. No. AY032953) from a rose petal cDNA library. The protein RhCTR1 has 66% amino acid identity to Arabidopsis CTR1. A fragment of a second CTR homologue, termed RhCTR2 (Acc. No. AY029067) is 69% identical to the corresponding region of RhCTR1. RhCTR1 expression increased during flower senescence, while RhCTR2 was constitutively expressed during flower development. The expression of both RhCTR1 and RhCTR2 was increased in response to exogenous ethylene.

Miniature potted roses (Rosa hybrida L.) are an important horticultural crop in Denmark. Leaf yellowing, flower, bud and leaf abscission can be important quality problems in miniature roses during marketing [2]. Selected cultivars were characterized with respect to natural ethylene production, endogenous ethylene in response to postharvest stress, ethylene sensitivity and/or ethylene binding in petal tissue.

An unknown antibiotic, ophiocordin, C21H22N2O8, MW: 430, was isolated from submerged cultures of Cordyceps ophioglossoides, strain TU 276, grown in a glycerol soybean meal medium at 27 degrees C. The antibiotic was extracted from acidified culture fluids with n-butanol and purified by subsequent column chromatography on DEAE-Sephadex and cellulose. Studies including nuclear magnetic resonance and mass spectrometry resulted in proposals of partial structures of the molecule. Inhibition by ophiocordin could be demonstrated for a small number of fungi belonging to different taxonomic groups. Bacteria were not inhibited. The antifungal effect was antagonized by ammonia and nitrate ions and by certain amino acids.

Kalanchoe blossfeldiana transformed with Agrobacterium rhizogenes exhibited marked alterations in morphology and biomass distribution. Plants termed root-inducing (Ri) lines were regenerated from hairy roots produced by inoculating leaf explants with Agrobacterium rhizogenes wild-type strain ATCC15834. Six Ri lines were characterized in a greenhouse trial and all Ri lines had reduced dry weights of main shoot, lateral shoots, leaves, and flowers compared with control plants. The reduction in dry weights of these organs correlated with reduced plant height, shoot length, leaf area, and number of flowers per plant. Furthermore, an altered distribution of dry matter was evident in the Ri plants, where the greater part of dry matter was allocated into leaves and secondly into flowers, whereas the majority of dry matter in control plants was allocated into flowers and secondly into leaves. Furthermore, a higher percentage of dry matter was allocated into the main shoot of the Ri lines in comparison with that of control plants. Increased dry matter in leaves and in the main shoot in the Ri lines appeared to be at the expense of dry matter allocated into flowers. Moreover, an increased number of vegetative lateral shoots was recorded in the Ri lines, whereas the number of reproductive lateral shoots was decreased. Possible mechanisms behind the altered resource distribution are discussed.

The miniature rose cultivar ‘Vanilla Kordana’ is a useful genetic resource for improving display life and ethylene resistance of miniature potted roses. To investigate the significance of ethylene production and sensitivity as determinants of display life two mutants (‘Goldy, Safari’) selected on external traits and one offspring (‘Champagner’) of ‘Vanilla’ were analysed. All cultivars exhibited a shorter postharvest life and higher ethylene sensitivity than ‘Vanilla’. The cultivar ‘Amber’, which was crossed with ‘Vanilla’ to produce ‘Champagner’, had the shortest display life of the investigated cultivars and was highly ethylene sensitive. In response to exogenous ethylene, ‘Vanilla’ and the related cultivars exhibited differences in display life, chlorophyll loss, leaf and bud drop. The two mutants had a clearly higher ethylene production than ‘Vanilla’, suggesting that this is the main reason for their shorter flower life. ‘Vanilla’ and the mutants did not show autocatalytic stimulation of ethylene production. The ethylene production in ‘Champagner’, which results from crossing of ‘Vanilla’ and ‘Amber’, was lower than in both parents and in the mutants. Ethylene exposure induced increased ethylene production in leaves and partly in flowers of the cultivars ‘Amber’ and ‘Champagner’. This autocatalytic ethylene production may be a major reason for the short display life of these two cultivars. The results indicate that not only initial ethylene production but also degree of autocatalytic stimulation is a major factor determining display life.

In an interior environment, the display life of miniature potted roses ( Rosa hybrida L.) ‘Bronze’ was 7 days, while that of ‘Vanilla’ was 23 days. Although there was a substantial difference in ethylene production between flowers from two cultivars, there was no difference in binding site activity ( k d = 0.14 nl l −1 ). Pre-treatment with the ethylene action inhibitor 1-methylcyclopropene (1-MCP) did not have a clear effect on display life without preceding transport stress. When the plants were subjected to simulated transportation stress, post-harvest life of both cultivars was reduced (to 6 days for ‘Bronze’, and to 17 days for ‘Vanilla’). In ‘Bronze’ the stress resulted in a modest increase in ethylene production, but there was no effect of stress on the low ethylene production by ‘Vanilla’ flowers. Nevertheless, pretreatment with 1-MCP before transport simulation improved display life of both cultivars.

Expression of phosphate starvation inducible genes was studied during recovery from phosphate starvation of Arabidopsis thaliana. Genes analysed were ACPS (encoding an acid phosphatase), RNS1 (encoding an RNase), At4 and IPS1 (both of unknown function), Phtl;7 and Pht2;1 (encoding phosphate transporters). Plants grown at limiting phosphate exhibited reduced growth rate and accumulated anthocyanins, soluble sugars, and starch. Re-supply of phosphate resulted in dramatic uptake of phosphate, increased growth rate and decreased levels of anthocyanins, soluble sugars, and starch in leaf tissue. In both shoots and roots re-supplied with P i , transcript levels decreased rapidly, and first changes were observed within 30 min. These alterations in gene expression occurred before the content of carbohydrates decreased, indicating that transcriptional regulation was due to phosphate sensing, and not a secondary effect of carbon accumulation. The data reveal different response rates for individual genes and demonstrate that roots and shoots can differ with respect to both timing and genes responding. In general, the changes in transcriptional activity in roots preceded the changes in shoots. Furthermore, transcriptional regulation was observed in isolated roots and shoots. This implies that roots do not strictly require a signal from the shoot, and vice versa, in order to respond to phosphate starvation.