Carnivory on demand: phosphorus deficiency induces glandular leaves in the African liana Triphyophyllum peltatum

Triphyophyllum peltatum, a rare tropical African liana, is unique in its facultative carnivory. The trigger for carnivory is yet unknown, mainly because the plant is difficult to propagate and cultivate. This study aimed at identifying the conditions that result in the formation of carnivorous leaves. In vitro shoots were subjected to abiotic stressors in general and deficiencies of the major nutrients nitrogen, potassium and phosphorus in particular, to trigger carnivorous leaves' development. Adventitious root formation was improved to allow verification of the trigger in glasshouse-grown plants. Among all the stressors tested, only under phosphorus deficiency, the formation of carnivorous leaves was observed. These glandular leaves fully resembled those found under natural growing conditions including the secretion of sticky liquid by mature capture organs. To generate plants for glasshouse experiments, a pulse of 55.4 μM α-naphthaleneacetic acid was essential to achieve 90% in vitro rooting. This plant material facilitated the confirmation of phosphorus starvation to be essential and sufficient for carnivory induction, also under ex vitro conditions. Having established the cultivation of T. peltatum and the induction of carnivory, future gene expression profiles from phosphorus starvation-induced leaves will provide important insight to the molecular mechanism of carnivory on demand

Low-cost and automated phenotyping system “Phenomenon” for multi-sensor in situ monitoring in plant in vitro culture

Background: The current development of sensor technologies towards ever more cost-effective and powerful systems is steadily increasing the application of low-cost sensors in different horticultural sectors. In plant in vitro culture, as a fundamental technique for plant breeding and plant propagation, the majority of evaluation methods to describe the performance of these cultures are based on destructive approaches, limiting data to unique endpoint measurements. Therefore, a non-destructive phenotyping system capable of automated, continuous and objective quantification of in vitro plant traits is desirable. Results: An automated low-cost multi-sensor system acquiring phenotypic data of plant in vitro cultures was developed and evaluated. Unique hardware and software components were selected to construct a xyz-scanning system with an adequate accuracy for consistent data acquisition. Relevant plant growth predictors, such as projected area of explants and average canopy height were determined employing multi-sensory imaging and various developmental processes could be monitored and documented. The validation of the RGB image segmentation pipeline using a random forest classifier revealed very strong correlation with manual pixel annotation. Depth imaging by a laser distance sensor of plant in vitro cultures enabled the description of the dynamic behavior of the average canopy height, the maximum plant height, but also the culture media height and volume. Projected plant area in depth data by RANSAC (random sample consensus) segmentation approach well matched the projected plant area by RGB image processing pipeline. In addition, a successful proof of concept for in situ spectral fluorescence monitoring was achieved and challenges of thermal imaging were documented. Potential use cases for the digital quantification of key performance parameters in research and commercial application are discussed. Conclusion: The technical realization of “Phenomenon” allows phenotyping of plant in vitro cultures under highly challenging conditions and enables multi-sensory monitoring through closed vessels, ensuring the aseptic status of the cultures. Automated sensor application in plant tissue culture promises great potential for a non-destructive growth analysis enhancing commercial propagation as well as enabling research with novel digital parameters recorded over time

Genetic analysis of callus formation in a diversity panel of 96 rose genotypes

In a diversity panel of 96 rose genotypes, variation in the capacity to form calluses on leaf explants in vitro was investigated, and a genome-wide association study (GWAS) was performed to identify genetic factors associated with callus formation. Calluses were induced from wounded in vitro leaflets on two media differing in their plant growth regulator composition. Significant differences between genotypes were observed in callus size on the first callus-inducing medium (CIM1, containing 10.7 µM naphthylene acetic acid) using a 0–4 scale, as well as on a second callus-inducing medium (CIM2, containing 4.5 µM dichlorophenoxyacetic acid and 2 µM 6-(γ,γ-dimethylallylaminopurine)) with callus size scales of 0.82–4. GWAS utilizing the WagRhSNP 68K SNP array for callus size induced on either CIM1 or CIM2 enabled the identification of 26 and 13 significantly associated SNPs, respectively. Among these SNPs, we found the SNPs Rh12GR_12098_1092Q (uncharacterized gene) and RhMCRND_2903_1233Q in a gene encoding a pentatricopeptide repeat-containing protein were associated with callus size on CIM1, with large effects being observed between alleles. Two SNPs, RhK5_5473_763P (S-formylglutathione hydrolase) and Rh12GR_37799_568Q (polyglutamine binding protein, WW domain binding protein), were associated with callus size on CIM2 with large effect sizes. The markers associated with callus size on CIM1 form a large cluster on chromosome 3 and minor clusters on other chromosomes and provide the first preliminary indications of candidate genes responsible for the observed phenotypic variation

Expression analysis of candidate genes as indicators for commencing drought stress in starch potatoes

Drought stress is a major problem for potato production and will be of grave importance due to climate change and the resulting temperature peaks along with drought periods in the vegetative growth phase of potato. Plants, as sessile organisms, adapt to their environment morphologically as well as biochemically. To cope better with abiotic stresses like drought, plants developed strategies like reactive oxygen species (ROS) detoxification and fast reacting stomatal closure, as well as signalling cascades leading to a quick response to stress. This study aimed at analysing eight genes of interest, derived from a former proteomic study, and determining their suitability for detection of commencing drought stress in early growth stages of potato. For this aim, six starch potato genotypes, which differed in stress response in previous studies, were examined for plant growth and physiological parameters in two experiments in an open greenhouse after seven and 14 days of stress. Besides lower shoot biomass after drought stress, which was already visible after seven days and became stronger after 14 days, weaker root growth was also detected after 14 days. The observed differences between the experiments can presumably be explained by temperature peaks and high radiation prior to and during the first experiment, which took place earlier in the year. The expression of the eight genes was studied in young leaves of four genotypes after 7 days of water withdrawal. Gene expression patterns were dependent on the studied genes. Three genes, cell wall/vacuolar inhibitor of fructosidase (INH1), peroxidase 51-like (POD) and subtilase family protein (SBT1.7) showed consistent changes in gene expression after seven days of stress between all genotypes. The INH1 gene was found to be upregulated in all genotypes in two independent experiments after drought stress. This correlates with the results at the protein level, where INH1 was also found to be higher abundant in two genotypes of potato (Wellpott et al., DGG-Proceedings 10, 2021). Therefore, this gene might be an appropriate candidate for the detection of commencing drought stress in potato

Transcriptome, carbohydrate, and phytohormone analysis of Petunia hybrida reveals a complex disturbance of plant functional integrity under mild chilling stress

Cultivation of chilling-tolerant ornamental crops at lower temperature could reduce the energy demands of heated greenhouses. To provide a better understanding of how sub-optimal temperatures (12 degrees C vs. 16 degrees C) affect growth of the sensitive Petunia hybrida cultivar 'SweetSunshine Williams', the transcriptome, carbohydrate metabolism, and phytohormone homeostasis were monitored in aerial plant parts over 4 weeks by use of a microarray, enzymatic assays and GC-MS/MS. The data revealed three consecutive phases of chilling response. The first days were marked by a strong accumulation of sugars, particularly in source leaves, preferential up-regulation of genes in the same tissue and down-regulation of several genes in the shoot apex, especially those involved in the abiotic stress response. The midterm phase featured a partial normalization of carbohydrate levels and gene expression. After 3 weeks of chilling exposure, a new stabilized balance was established. Reduced hexose levels in the shoot apex, reduced ratios of sugar levels between the apex and source leaves and a higher apical sucrose/hexose ratio, associated with decreased activity and expression of cell wall invertase, indicate that prolonged chilling induced sugar accumulation in source leaves at the expense of reduced sugar transport to and reduced sucrose utilization in the shoot. This was associated with reduced levels of indole-3-acetic acid and abscisic acid in the apex and high numbers of differentially, particularly up-regulated genes, especially in the source leaves, including those regulating histones, ethylene action, transcription factors, and a jasmonate-ZIM-domain protein. Transcripts of one Jumonji C domain containing protein and one expansin accumulated in source leaves throughout the chilling period. The results reveal a dynamic and complex disturbance of plant function in response to mild chilling, opening new perspectives for the comparative analysis of differently tolerant cultivars.BMBF/AgroCluster/WeGa - Horticulture Research NetworkState of BrandenburgFree State of ThuringiaFederal Republic of German

Editorial: Rhizosphere conversation among the plant-plant microbiome-soil under consecutive monoculture regimes

[no abstract available

Erarbeitung von Grundlagen für die Züchtung neuer Zierpflanzen am Beispiel der Mittagsblumen

For most new ornamentals, fundamental knowledge on the respective species and genera is largely missing that is needed to establish breeding methods, including interspecific and intergeneric hybridization and polyploidization. Using the example of midday flowers (Aizoaceae) which are interesting candidates for new ornamentals due to their special and very intense flower colours and their drought tolerance, investigations on flower development, DNA contents, and crossing compatibility are presented. An obligate photoperiodic reaction was not dectable for any of the genotypes of the genera Cephalophyllum, Lampranthus, and Delosperma, whereas different reactions to daily mean temperatures were observed depending on the genus. In cross pollination experiments within and among the genera Lampranthus and Delosperma, late acting pre-zygotic hybridization barriers were recorded in some interspecific and intergeneric combinations. However, post-zygotic barriers were observed more frequently, resulting in delayed and abnormal development of the zygotic embryo, chlorophyll deficiencies and low vigour of the offspring. By employing in vitro sowing and embryo rescue techniques, few interspecific and intergeneric hybrids were obtained, the hybrid status of which was confirmed by AFLP markers. Aiming at the detection of unreduced gametes pollen grains were analysed. It turned out that flow cytometric analyses may lead to misinterpretation of the data, because pairs of sperm nuclei as well as complete male germ units (MGU) result in peaks at the 2C or 3C position, respectively. Pollen nuclei were useful for the estimation of DNA contents: In Delosperma and Lampranthus, the DNA contents ranged from 1.18 pg/2C to 3.68 pg/2C and from 1.6 pg/2C to 2.36 pg/2C, respectively. The tissues of all analyzed plant organs consisted of cells with up to five different DNA amounts (2C-32C). High proportions of endoreduplicated cells were detected in cotyledons (74-87 %), petals (56-95 %) and older, fully expanded leaves (64-90 %), whereas organs with lower portions, such as roots (23-34 %), internodes (29-45 %) and young leaves (17-56 %) might be well-suited for in vitro shoot regeneration and polyploidization, since endoreduplicated cells are assumed to lose their ability for mitotic cell division.Für die Anwendung von Züchtungsmethoden, wie Art- und Gattungskreuzungen oder Polyploidisierung, für neue Zierpflanzen fehlen in vielen Fällen grundlegende Informationen über die jeweiligen Gattungen und Arten. Am Beispiel der Mittagsblumengewächse (Aizoaceae), die aufgrund ihrer intensiven, strahlenden Blütenfarben und ihrer Trockentoleranz Kandidaten für neue Zierpflanzen darstellen, werden Untersuchungen zur Blütenentwicklung, zur Bestimmung von DNA-Gehalten sowie zu Kreuzungskompatibilitäten vorgestellt. Für keinen der untersuchten Genotypen der Gattungen Cephalophyllum, Lampranthus und Delosperma wurde ein obligater photoperiodischer Einfluss auf die Blühinduktion festgestellt, jedoch waren unterschiedliche Reaktionen auf die Tagesmitteltemperatur für die Vertreter der drei Gattungen nachweisbar. Kreuzungsversuche innerhalb und zwischen den Gattungen Lampranthus und Delosperma zeigten späte präzygotische Hybridisierungsbarrieren bei einigen interspezifischen und intergenerischen Kombinationen. Deutlich häufiger waren postzygotische Kreuzungsbarrieren, die sich in verzögerter und anormaler Entwicklung der zygotischen Embryonen und in Chlorophylldefekten sowie geringer Vitalität der Nachkommen äußerten. Die Überwindung der postzygotischen Barrieren durch In-vitro-Aussaat und Embryo Rescue-Ansätze resultierte in wenigen, durch AFLP-Marker nachgewiesenen intra- und intergenerischen Hybriden. Pollenuntersuchungen mit dem Ziel der Identifikation von unreduzierten Gameten zeigten, dass durchflusszytometrische Analysen zu Fehlinterpretationen führen können, weil zusammenhängende Spermakerne und vollständige „male germ units“ (MGUs) zu Peaks an der 2C- bzw. 3C-Position führen. Pollenkerne waren aber gut zur Abschätzung der DNA-Gehalte nutzbar. Bei Delosperma Genotypen lagen diese zwischen 1,18 pg/2C und 3,68 pg/2C und bei Lampranthus Genotypen zwischen 1,6 pg/2C und 2,36 pg/2C. Die Gewebe fast aller Pflanzenorgane wiesen Zellen mit mindestens fünf unterschiedlichen DNA-Gehalten (2C- 32C) auf. Hohe Anteile endoreplizierter Zellen wurden in Keimblättern (74-87 %), Bluetenblättern (56-95 %) und älteren, voll entfalteten Blättern (64-90 %) nachgewiesen, so dass Organe mit geringen Anteilen, wie Wurzeln (23-34 %), Internodien (29-45 %) und junge Blätter (17-56 %), für die In-vitro-Sprossregeneration und Polyploidisierungsansätze vermutlich geeigneter sind, da sich laut Literatur endoreplizierte Zellen nicht mehr teilen können

Identification of candidate genes associated with tolerance to apple replant disease by genome-wide transcriptome analysis

Apple replant disease (ARD) is a worldwide economic risk in apple cultivation for fruit tree nurseries and fruit growers. Several studies on the reaction of apple plants to ARD are documented but less is known about the genetic mechanisms behind this symptomatology. RNA-seq analysis is a powerful tool for revealing candidate genes that are involved in the molecular responses to biotic stresses in plants. The aim of our work was to find differentially expressed genes in response to ARD in Malus. For this, we compared transcriptome data of the rootstock ‘M9’ (susceptible) and the wild apple genotype M. ×robusta 5 (Mr5, tolerant) after cultivation in ARD soil and disinfected ARD soil, respectively. When comparing apple plantlets grown in ARD soil to those grown in disinfected ARD soil, 1,206 differentially expressed genes (DEGs) were identified based on a log2 fold change, (LFC) ≥ 1 for up– and ≤ −1 for downregulation (p < 0.05). Subsequent validation revealed a highly significant positive correlation (r = 0.91; p < 0.0001) between RNA-seq and RT-qPCR results indicating a high reliability of the RNA-seq data. PageMan analysis showed that transcripts of genes involved in gibberellic acid (GA) biosynthesis were significantly enriched in the DEG dataset. Most of these GA biosynthesis genes were associated with functions in cell wall stabilization. Further genes were related to detoxification processes. Genes of both groups were expressed significantly higher in Mr5, suggesting that the lower susceptibility to ARD in Mr5 is not due to a single mechanism. These findings contribute to a better insight into ARD response in susceptible and tolerant apple genotypes. However, future research is needed to identify the defense mechanisms, which are most effective for the plant to overcome ARD

Stimulation of adventitious root formation by laser wounding in rose cuttings: A matter of energy and pattern

Adventitious root (AR) formation is the basis of vegetative propagation in rose, be it via stem cuttings or via stenting. During this process, wounding plays a pivotal role since cell reprogramming takes place at the tissue adjacent to the wound. We investigated the effects of wounding on AR formation on leafy single-node stem cuttings of the rose rootstock R. canina ‘Pfänder’ (codes R02-3 and R02-6) and the cut rose cultivar Rosa ‘Tan09283’ (Registration name ‘Beluga’). Laser wounding treatments were based on the assisted removal of tissue layers located in the bark. The positioning of wounding was studied based on two marking directions: along the cutting base (strip pattern) and around the cutting base (ring pattern). Additionally, the effects of external supply of indole-butyric acid (IBA 1 mg L-1) on rooting were analyzed. Results showed that in order to remove specific tissue layers, the calculation of the laser energy density (J cm-2) in terms of cutting diameter was necessary. Interestingly, the application of energy densities from 2.5 J cm-2 up to approximately 8.5 J cm-2 were sufficient to expose the tissue layers of epidermis up to regions of phloem. Regarding AR formation for R. canina ‘Pfänder’, characterized by a low rooting response, an increase in the rooting percentage was registered when the laser treatment eliminated the tissue up to phloem proximities. Analysis of the nodal position showed that bud location was a preferential place for AR formation independently of wounding treatment. In case of Rosa ‘Tan09283’, laser treatments did not reduce its high rooting capacity, but an apparent reduction in rooting quality due to an investment in tissue healing was observed when wounding reached deeper layers such as parenchyma and sclerenchyma. Results also showed a strong AR formation directly from wounded regions in case of Rosa ‘Tan09283’ specifically when the wound was located below the axillary bud. In conclusion, wounding by assisted-elimination of layers by laser can induce positive effects on AR formation of single-node stem cuttings of the rose if energy applied is able to expose phloem proximities, a longitudinal orientation, and relative position to the axillary bud are considered

GWAS of adventitious root formation in roses identifies a putative phosphoinositide phosphatase (SAC9) for marker-assisted selection

Rose propagation by cuttings is limited by substantial genotypic differences in adventitious root formation. To identify possible genetic factors causing these differences and to develop a marker for marker-assisted selection for high rooting ability, we phenotyped 95 cut and 95 garden rose genotypes in a hydroponic rooting system over 6 weeks. Data on rooting percentage after 3 to 6 weeks, root number, and root fresh mass were highly variable among genotypes and used in association mappings performed on genotypic information from the WagRhSNP 68 K Axiom SNP array for roses. GWAS analyses revealed only one significantly associated SNP for rooting percentage after 3 weeks. Nevertheless, prominent genomic regions/peaks were observed and further analysed for rooting percentage after 6 weeks, root number and root fresh mass. Some of the SNPs in these peak regions were associated with large effects on adventitious root formation traits. Very prominent were ten SNPs, which were all located in a putative phosphoinositide phosphatase SAC9 on chromosome 2 and showed very high effects on rooting percentage after 6 weeks of more than 40% difference between nulliplex and quadruplex genotypes. SAC9 was reported to be involved in the regulation of endocytosis and in combination with other members of the SAC gene family to regulate the translocation of auxin-efflux PIN proteins via the dephosphorylation of phosphoinositides. For one SNP within SAC9, a KASP marker was successfully derived and used to select genotypes with a homozygous allele configuration. Phenotyping these homozygous genotypes for adventitious root formation verified the SNP allele dosage effect on rooting. Hence, the presented KASP derived from a SNP located in SAC9 can be used for marker-assisted selection in breeding programs for high rooting ability in the future