Institut für Kulturpflanzenwissenschaften

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The functional diversity of the high-affinity nitrate transporter gene family in hexaploid wheat: Insights from distinct expression profiles
(2023) Sigalas, Petros P.; Buchner, Peter; Kröper, Alex; Hawkesford, Malcolm J.
High-affinity nitrate transporters (NRT) are key components for nitrogen (N) acquisition and distribution within plants. However, insights on these transporters in wheat are scarce. This study presents a comprehensive analysis of the NRT2 and NRT3 gene families, where the aim is to shed light on their functionality and to evaluate their responses to N availability. A total of 53 NRT2s and 11 NRT3s were identified in the bread wheat genome, and these were grouped into different clades and homoeologous subgroups. The transcriptional dynamics of the identified NRT2 and NRT3 genes, in response to N starvation and nitrate resupply, were examined by RT-qPCR in the roots and shoots of hydroponically grown wheat plants through a time course experiment. Additionally, the spatial expression patterns of these genes were explored within the plant. The NRT2s of clade 1, TaNRT2.1-2.6, showed a root-specific expression and significant upregulation in response to N starvation, thus emphasizing a role in N acquisition. However, most of the clade 2 NRT2s displayed reduced expression under N-starved conditions. Nitrate resupply after N starvation revealed rapid responsiveness in TaNRT2.1-2.6, while clade 2 genes exhibited gradual induction, primarily in the roots. TaNRT2.18 was highly expressed in above-ground tissues and exhibited distinct nitrate-related response patterns for roots and shoots. The TaNRT3 gene expression closely paralleled the profiles of TaNRT2.1-2.6 in response to nitrate induction. These findings enhance the understanding of NRT2 and NRT3 involvement in nitrogen uptake and utilization, and they could have practical implications for improving nitrogen use efficiency. The study also recommends a standardized nomenclature for wheat NRT2 genes, thereby addressing prior naming inconsistencies.
Functional traits shape plant–plant interactions and recruitment in a hotspot of woody plant diversity
(2023) Cooksley, Huw; Dreyling, Lukas; Esler, Karen J.; Griebenow, Stian; Neumann, Günter; Valentine, Alex; Schleuning, Matthias; Schurr, Frank M.
Understanding and predicting recruitment in species‐rich plant communities requires identifying functional determinants of both density‐independent performance and interactions. In a common‐garden field experiment with 25 species of the woody plant genus Protea, we varied the initial spatial and taxonomic arrangement of seedlings and followed their survival and growth during recruitment. Neighbourhood models quantified how six key functional traits affect density‐independent performance, interaction effects and responses. Trait‐based neighbourhood models accurately predicted individual survival and growth from the initial spatial and functional composition of species‐rich experimental communities. Functional variation among species caused substantial variation in density‐independent survival and growth that was not correlated with interaction effects and responses. Interactions were spatially restricted but had important, predominantly competitive, effects on recruitment. Traits increasing the acquisition of limiting resources (water for survival and soil P for growth) mediated trade‐offs between interaction effects and responses. Moreover, resprouting species had higher survival but reduced growth, likely reinforcing the survival–growth trade‐off in adult plants. Resource acquisition of juvenile plants shapes Protea community dynamics with acquisitive species with strong competitive effects suffering more from competition. Together with functional determinants of density‐independent performance, this makes recruitment remarkably predictable, which is critical for efficient restoration and near‐term ecological forecasts of species‐rich communities.
High-throughput field phenotyping reveals genetic variation in photosynthetic traits in durum wheat under drought
(2021) Zendonadi dos Santos, Nícolas; Piepho, Hans‐Peter; Condorelli, Giuseppe Emanuele; Licieri Groli, Eder; Newcomb, Maria; Ward, Richard; Tuberosa, Roberto; Maccaferri, Marco; Fiorani, Fabio; Rascher, Uwe; Muller, Onno
Chlorophyll fluorescence (ChlF) is a powerful non‐invasive technique for probing photosynthesis. Although proposed as a method for drought tolerance screening, ChlF has not yet been fully adopted in physiological breeding, mainly due to limitations in high‐throughput field phenotyping capabilities. The light‐induced fluorescence transient (LIFT) sensor has recently been shown to reliably provide active ChlF data for rapid and remote characterisation of plant photosynthetic performance. We used the LIFT sensor to quantify photosynthesis traits across time in a large panel of durum wheat genotypes subjected to a progressive drought in replicated field trials over two growing seasons. The photosynthetic performance was measured at the canopy level by means of the operating efficiency of Photosystem II (Fq′/Fm′) and the kinetics of electron transport measured by reoxidation rates (Fr1′ and Fr2′). Short‐ and long‐term changes in ChlF traits were found in response to soil water availability and due to interactions with weather fluctuations. In mild drought, Fq′/Fm′ and Fr2′ were little affected, while Fr1′ was consistently accelerated in water‐limited compared to well‐watered plants, increasingly so with rising vapour pressure deficit. This high‐throughput approach allowed assessment of the native genetic diversity in ChlF traits while considering the diurnal dynamics of photosynthesis.
Impact of harvest time and pruning technique on total CBD concentration and yield of medicinal cannabis
(2022) Crispim Massuela, Danilo; Hartung, Jens; Munz, Sebastian; Erpenbach, Federico; Graeff-Hönninger, Simone
The definition of optimum harvest and pruning interventions are important factors varying inflorescence yield and cannabinoid composition. This study investigated the impact of (i) harvest time (HT) and (ii) pruning techniques (PT) on plant biomass accumulation, CBD and CBDA-concentrations and total CBD yield of a chemotype III medical cannabis genotype under indoor cultivation. The experiment consisted of four HTs between 5 and 11 weeks of flowering and three PTs-apical cut (T); removal of side shoots (L) and control (C), not pruned plants. Results showed that inflorescence dry weight increased continuously, while the total CBD concentration did not differ significantly over time. For the studied genotype, optimum harvest time defined by highest total CBD yield was found at 9 weeks of flowering. Total CBD-concentration of inflorescences in different fractions of the plant’s height was significantly higher in the top (9.9%) in comparison with mid (8.2%) and low (7.7%) fractions. The T plants produced significantly higher dry weight of inflorescences and leaves than L and C. Total CBD yield of inflorescences for PTs were significantly different among pruned groups, but do not differ from the control group. However, a trend for higher yields was observed (T > C > L).
Impacts of carbon dioxide enrichment on landrace and released Ethiopian barley (Hordeum vulgare L.) cultivars
(2021) Gardi, Mekides Woldegiorgis; Malik, Waqas Ahmed; Haussmann, Bettina I. G.
Barley (Hordeum vulgare L.) is an important food security crop due to its high-stress tolerance. This study explored the effects of CO2 enrichment (eCO2) on the growth, yield, and water-use efficiency of Ethiopian barley cultivars (15 landraces, 15 released). Cultivars were grown under two levels of CO2 concentration (400 and 550 ppm) in climate chambers, and each level was replicated three times. A significant positive effect of eCO2 enrichment was observed on plant height by 9.5 and 6.7%, vegetative biomass by 7.6 and 9.4%, and grain yield by 34.1 and 40.6% in landraces and released cultivars, respectively. The observed increment of grain yield mainly resulted from the significant positive effect of eCO2 on grain number per plant. The water-use efficiency of vegetative biomass and grain yield significantly increased by 7.9 and 33.3% in landraces, with 9.5 and 42.9% improvement in released cultivars, respectively. Pearson’s correlation analysis revealed positive relationships between grain yield and grain number (r = 0.95), harvest index (r = 0.86), and ear biomass (r = 0.85). The response of barley to eCO2 was cultivar dependent, i.e., the highest grain yield response to eCO2 was observed for Lan_15 (122.3%) and Rel_10 (140.2%). However, Lan_13, Land_14, and Rel_3 showed reduced grain yield by 16, 25, and 42%, respectively, in response to eCO2 enrichment. While the released cultivars benefited more from higher levels of CO2 in relative terms, some landraces displayed better actual values. Under future climate conditions, i.e., future CO2 concentrations, grain yield production could benefit from the promotion of landrace and released cultivars with higher grain numbers and higher levels of water-use efficiency of the grain. The superior cultivars that were identified in the present study represent valuable genetic resources for future barley breeding.
Loss of LaMATE impairs isoflavonoid release from cluster roots of phosphorus‐deficient white lupin
(2021) Zhou, Yaping; Olt, Philipp; Neuhäuser, Benjamin; Moradtalab, Narges; Bautista, William; Uhde‐Stone, Claudia; Neumann, Günter; Ludewig, Uwe
White lupin (Lupinus albus L.) forms brush‐like root structures called cluster roots under phosphorus‐deficient conditions. Clusters secrete citrate and other organic compounds to mobilize sparingly soluble soil phosphates. In the context of aluminum toxicity tolerance mechanisms in other species, citrate is released via a subgroup of MATE/DTX proteins (multidrug and toxic compound extrusion/detoxification). White lupin contains 56 MATE/DTX genes. Many of these are closely related to gene orthologs with known substrates in other species. LaMATE is a marker gene for functional, mature clusters and is, together with its close homolog LaMATE3, a candidate for the citrate release. Both were highest expressed in mature clusters and when expressed in oocytes, induced inward‐rectifying currents that were likely carried by endogenous channels. No citrate efflux was associated with LaMATE and LaMATE3 expression in oocytes. Furthermore, citrate secretion was largely unaffected in P‐deficient composite mutant plants with genome‐edited or RNAi‐silenced LaMATE in roots. Moderately lower concentrations of citrate and malate in the root tissue and consequently less organic acid anion secretion and lower malate in the xylem sap were identified. Interestingly, however, less genistein was consistently found in mutant exudates, opening the possibility that LaMATE is involved in isoflavonoid release.
Membrane transport and long-distance translocation of urea in Arabidopsis thaliana
(2011) Bohner, Anne; von Wirén, Nicolaus
Urea is a soil nitrogen (N) form available to plant roots and a secondary N metabolite liberated in plant cells by protein degradation, especially during senescence. Despite the fact that urea also represents the most widespread form in N fertilizers used in agricultural plant production, membrane transporters that might contribute to urea uptake in plant roots or urea retranslocation in senescent leaves have so far been characterized only in heterologous systems. The first part of the thesis investigated a role of the H+/urea cotransporter AtDUR3 in N nutrition of Arabidopsis thaliana plants. T-DNA insertion lines with a defective expression in AtDUR3 showed impaired growth on urea as a sole nitrogen source. In transgenic lines expressing an AtDUR3-promoter-GFP construct, promoter activity was upregulated under N deficiency and localized to the rhizodermis, including root hairs, as well as to the cortex in more basal root zones. The AtDUR3 protein accumulated in plasma membrane-enriched protein fractions, and AtDUR3 gene expression in N-deficient roots was repressed by ammonium and nitrate but induced after supply of urea. Higher urea accumulation in roots of wild-type plants relative to the T-DNA insertion lines confirmed that urea was the transported substrate of AtDUR3. Influx of 15N-labeled urea allowed the calculation of an affinity constant of 4 µM. These results indicated that AtDUR3 is the major transporter for high-affinity urea uptake in Arabidopsis roots and suggested that the high substrate affinity of AtDUR3 reflects an adaptation to the low urea levels usually found in unfertilized soils. A physiological function of urea and its transporters in leaves was investigated in the second part of the thesis. Currently it is unclear whether transport and metabolism of urea might limit the overall retranslocation of N during senescence. AtDUR3 transcript levels were only slightly de-repressed under N starvation, but strongly increased in senescent leaves. Urea concentrations in leaf samples of different plant and leaf age showed a strong increase after plants turned into generative growth. In parallel, mRNA as much as the protein abundance of AtDUR3 increased with leaf age. The analysis of leaf petiole exudates revealed that urea was indeed a translocated N form and urea-N represented approx. 13% of the total amino acid-N irrespective of the N status of the plant. Urea concentrations determined in apoplastic wash fluids supported a role of AtDUR3 in urea retrieval from the leaf apoplast, and transgenic AtDUR3-promoter-GUS lines indicated a localization of AtDUR3 promoter activity in the vasculature of old leaves. Thus, AtDUR3 might keep internal urea in the cytosol by urea retrieval from the apoplast, allowing urea to be transported to the vascular bundle, where it is either passively loaded to the phloem or converted into amino acids for long-distance N translocation. A strong daytime-dependent phenotype with shorter leaf petioles of an Arabidopsis line overexpressing AtDUR3 led to an in silico analysis of the AtDUR3 promoter sequence revealing that salicylic acid (SA) appears to induce AtDUR3 gene expression in senescent leaves. SA is well known for its involvement in the initiation of senescence. A strongly enhanced uptake capacity for 15N-labeled urea in N-sufficient Arabidopsis roots after SA pretreatment indicated that SA might be able to mimic N-deficiency conditions, paving the way to the possibility that SA builds a regulatory link between developmental and N deficiency-induced senescence.
Molecular regulation of components of root development and nutrient uptake in white lupin (Lupinus albus L.)
(2023) Olt, Philipp; Ludewig, Uwe
White lupin (Lupinus albus L.) is specially adapted to sites with low availability of plant-available phosphorus (P), which is of particular agricultural importance because of chemical P fixation in the soil and limited reserves of P fertilizer resources. With special root structures, the cluster roots (syn. proteoid roots), it considerably increases the root surface area and excretes root exudates such as anions of organic acids, which make it possible to release phosphate ions from poorly soluble phosphate compounds in the soil and make them available to plants. The characteristic structure of these cluster roots usually consists of a lateral root with certain sections that have a significantly higher density of further lateral roots (rootlets) than the rest of the lateral root. In addition, the rootlets are evenly limited in length and, as they grow bundled in the cluster sections, the structure of cluster roots is reminiscent of a bottle brush. Cluster roots are also formed by other plant species such as some species from the Proteaceae family, but in contrast to these slow- growing and perennial woody plants, white lupin with its short life cycle and small size is an ideal model organism for the study of these special root structures. In addition to the mechanisms involved in the function of cluster roots, the regulation of formation and development of cluster roots is also of great importance for basic research in this field. Three studies were carried out as part of this thesis to examine these aspects in more detail. In order to better understand the functional mechanisms involved in the excretion of exudates, the hypothesis that the METAL AND TOXIN EXTRUSION (MATE) transport proteins LaMATE and LaMATE3 transport citrate was tested in the first study. The similarity of the gene sequences of these white lupin proteins with proteins from the MATE/DTX family, of which citrate transport is already known, as well as the increased gene expression of LaMATE and LaMATE3 in mature cluster roots led to this assumption. However, electrophysiological studies of the proteins with 13C- labeled citrate showed that LaMATE and LaMATE3 probably do not transport citrate and also the analysis of root exudates from transient loss-of-function mutants could not confirm the involvement of LaMATE in the transport of citrate. However, the excretion of the isoflavonoid genistein was found to be significantly reduced in the transient loss-of-function mutants, leading to the hypothesis that LaMATE may be involved in the exudation of isoflavonoids in mature cluster roots. As a result of the mobilization of phosphates through the excretion of organic acids, other cations such as manganese (Mn) also dissolve, which leads to increased Mn concentrations in the soil solution. As manganese uptake in the roots is not actively regulated, Mn accumulates in the plant, which has a toxic effect in higher concentrations. For this reason, white lupin needs a strategy to counteract toxic manganese accumulation, which was investigated in more detail in the second study. The observation that a greater increase in Mn concentration could be measured in the leaves than in the roots after elevated Mn exposure of white lupin indicates an actively regulated transport of excess Mn in the plant. The METAL TOLERANCE PROTEIN (MTP) AtMTP8 is involved in the detoxification of excess Mn in Arabidopsis and the increased gene expression of the corresponding white lupin homolog LaMTP8.1 in plants exposed to elevated Mn concentration suggested that LaMTP8.1 also fulfills a detoxification function. In further experiments, the ability of the LaMTP8.1 protein to transport Mn was demonstrated by heterologous expression of LaMTP8.1 in yeast cells. Furthermore, the high Mn concentrations in the leaves already indicated that the sink of Mn sequestration is located there and since AtMTP8 transports Mn into the vacuole, it was assumed that LaMTP8.1 could be localized in the tonoplast of the leaf cells to transport excess Mn into the vacuoles. This hypothesis was confirmed by homologous expression of LaMTP8.1 combined with a fluorescent marker in white lupin protoplasts. In summary, this study demonstrated that LaMTP8.1 is a vacuolar Mn transporter that mediates the transport of Mn into the vacuoles of leaf cells to detoxify excess Mn. While the first two studies addressed functional and physiological aspects of cluster roots, the third study focused on the mechanisms of formation and development of these root structures. To this end, the main focus was on the CLAVATA3/ EMBRYO SURROUNDING REGION (ESR)- RELATED (CLE) peptide family, of which some members regulate root growth in other plant species and enable more precise control of regulation compared to the known growth regulators auxin and cytokinin. In a comprehensive analysis, 30 known and further 25 new, putative CLE peptides were identified in Lupinus albus. Several of the CLE peptides were tested in a hydroponic system on young white lupins for their effects on root development and cluster root formation. The two CLE peptides LaCLE35 (RGVHyPSGANPLHN) and LaCLE55 (RRVHyPSCHyPDPLHN) showed striking inhibitory effects and altered both root growth and cluster root development in an inhibitory manner. The peptide LaCLE35 stood out in particular because it was the only CLE peptide detected in white lupin xylem sap and was therefore investigated in more detail. It was shown that LaCLE35 influences both the density and the length of cluster rootlets, and thus has an effect on the two crucial factors of cluster root formation. The inhibitory effect of CLE35 could be attributed to a suppression of cell elongation and further experiments with split-root setups showed that the externally added synthetic peptide LaCLE35 has a local but not a systemic effect. The investigations of the LaMATE transport proteins and LaMTP8.1-mediated Mn detoxification as well as the overview of the detected CLE peptides in white lupin and the analysis of the inhibitory influences of LaCLE35 on cluster roots form the basis of this thesis and aim to contribute to the understanding of the function, effects and formation of these special root structures.
Nutritional and climatic effects on berry shrivel of grapevines in Southern Germany
(2012) Bachteler, Kristina; Wünsche, Jens Norbert
Berry shrivel (BS) is one of the economically most important physiological disorders in grapevine, but it is also one of the least studied ones. At the beginning of the ripening process, berries stop accumulating sugars and lose their turgescence. The must weight remains low, the berries taste sour and bitter. During the last ten years, several studies were conducted to narrow eliciting factors. As a result, an unbalanced ratio of K and Mg in the soil was considered likely to induce BS. To verify this hypothesis, two fertilization trials with two different varieties each, one via the soil and one foliar fertilization trial, were initiated. Within two years, no effect on the incidence of BS was evident. In the foliar fertilization trials, Mg, K and Ca fertilizers were tested with their effect on BS. For the first year, no significant differences could be observed. In the second year, more berries were affected by BS in the plots treated with Ca fertilizer. The plots with Mg fertilizer showed significantly less berries affected by BS than the untreated control in one variety. Extensive analysis of concentrations of Ca, Mg and K in berries illustrate that berries affected by BS show significantly higher concentrations of Ca compared to healthy berries. The loss of quality of wines made of berries affected by BS was demonstrated by must and wine analysis as well as by a consumer preference analysis. Phenolic compounds (in particular resveratrol) that are often used as indicators of abiotic stress were analysed as well. It was supposed that BS is caused or increased by abiotic stress so that the concentration of resveratrol in berries affected by BS is increased as well. However, in all varieties analysed, the concentration of resveratrol was higher in healthy berries than in affected ones. A direct connection between weather condition at bloom and especially at ripening was examined. Observations at monitoring sites and reports from other countries seem to show that cool and wet weather at these phenological stages might increase the risk of BS. It was only possible to statistically prove a connection between the precipitation at bloom and the incidence of BS.
Potential of impedance flow cytometry to assess the viability and quantity of Cannabis sativa L. pollen
(2021) Rafiq, Hamza; Hartung, Jens; Burgel, Lisa; Röll, Georg; Graeff-Hönninger, Simone
Over the last decade, efforts to breed new Cannabis sativa L. cultivars with high Cannabidiol (CBD) and other non-psychoactive cannabinoids with low tetrahydrocannabinol (THC) levels have increased. In this context, the identification of the viability and quantity of pollen, which represents the fitness of male gametophytes, to accomplish successful pollination is of high importance. The present study aims to evaluate the potential of impedance flow cytometry (IFC) for the assessment of pollen viability (PV) and total number of pollen cells (TPC) in two phytocannabinoid-rich cannabis genotypes, KANADA (KAN) and A4 treated with two different chemical solutions, silver thiosulfate solution (STS) and gibberellic acid (GA3). Pollen was collected over a period of 8 to 24 days after flowering (DAF) in a greenhouse experiment. Impedance flow cytometry (IFC) technology was used with Cannabis sativa to assess the viability and quantity of pollen. The results showed that the number of flowers per plant was highest at 24 DAF for both genotypes, A4 (317.78) and KAN (189.74). TPC induced by STS was significantly higher compared to GA3 over the collection period of 8 to 24 DAF with the highest mean TPC of 1.54 × 105 at 14 DAF. STS showed significantly higher viability of pollen compared to GA3 in genotype KAN, with the highest PV of 78.18% 11 DAF. Genotype A4 also showed significantly higher PV with STS at 8 (45.66%), 14 (77.88%), 18 (79.37%), and 24 (51.92%) DAF compared to GA3. Furthermore, counting the numbers of flowers did not provide insights into the quality and quantity of pollen; the results showed that PV was highest at 18 DAF with A4; however, the number of flowers per plant was 150.33 at 18 DAF and was thus not the maximum of produced flowers within the experiment. IFC technology successfully estimated the TPC and differentiated between viable and non-viable cells over a period of 8 to 24 DAF in tested genotypes of Cannabis sativa. IFC seems to be an efficient and reliable method to estimate PV, opening new chances for plant breeding and plant production processes in cannabis.

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