Institut für Kulturpflanzenwissenschaften

Permanent URI for this collectionhttps://hohpublica.uni-hohenheim.de/handle/123456789/12

Browse

Now showing 1 - 6 of 6

Ammonium uptake, mediated by ammonium transporters, mitigates manganese toxicity in duckweed, Spirodela polyrhiza
(2023) Kishchenko, Olena; Stepanenko, Anton; Straub, Tatsiana; Zhou, Yuzhen; Neuhäuser, Benjamin; Borisjuk, Nikolai
Nitrogen is an essential nutrient that affects all aspects of the growth, development and metabolic responses of plants. Here we investigated the influence of the two major sources of inorganic nitrogen, nitrate and ammonium, on the toxicity caused by excess of Mn in great duckweed, Spirodela polyrhiza. The revealed alleviating effect of ammonium on Mn-mediated toxicity, was complemented by detailed molecular, biochemical and evolutionary characterization of the species ammonium transporters (AMTs). Four genes encoding AMTs in S. polyrhiza, were classified as SpAMT1;1, SpAMT1;2, SpAMT1;3 and SpAMT2. Functional testing of the expressed proteins in yeast and Xenopus oocytes clearly demonstrated activity of SpAMT1;1 and SpAMT1;3 in transporting ammonium. Transcripts of all SpAMT genes were detected in duckweed fronds grown in cultivation medium, containing a physiological or 50-fold elevated concentration of Mn at the background of nitrogen or a mixture of nitrate and ammonium. Each gene demonstrated an individual expression pattern, revealed by RT-qPCR. Revealing the mitigating effect of ammonium uptake on manganese toxicity in aquatic duckweed S. polyrhiza, the study presents a comprehensive analysis of the transporters involved in the uptake of ammonium, shedding a new light on the interactions between the mechanisms of heavy metal toxicity and the regulation of the plant nitrogen metabolism.
Plant ammonium transporter (AMT) integration in regulatory networks
(2016) Straub, Tatsiana; Ludewig, Uwe
Ammonium is a ubiquitous key nutrient in agricultural soils and the preferred nitrogen source for plants. However, excessive ammonium accumulation represses plant growth and development. Ammonium is taken up by plant cells via high-affinity ammonium transporters (AMTs). Six AMT genes were identified in Arabidopsis, which are separated in two distinct clades, five AMT1s and one AMT2. In the plasma membrane, AMT proteins form homo- and heterotrimers with extra-cytoplasmic N-termini and cytoplasmic C-termini. In addition to transcriptional and post-transcriptional control of AMTs by ammonium, phosphorylation in the C-terminus serves as a rapid allosteric switch of the AMT activity and prevents further internal ammonium accumulation. In a physiological screen, a kinase (CIPK23) was identified, which directly regulates ammonium transport activity under high-NH4+ conditions. Interestingly, CIPK23 is already known to regulate nitrate and potassium uptake in roots. Lesion of the CIPK23 gene significantly increased ammonium uptake, but caused growth inhibition. As expected, cipk23 plants were also limited in potassium accumulation, but high potassium availability failed to rescue the cipk23 phenotype. Furthermore, cipk23 plants were more susceptible to methylammonium (MeA), a non-metabolizable analogue of ammonium. The sensitivity to MeA was lost upon genetic suppression of AMT1 genes in the cipk23 background. The data suggest that CIPK23 directly phosphorylates AMT1s in a complex with CBL1 (calcineurin B-like protein) and thereby regulates transport activity. The expression of the CIPK23 and the CBL1 genes were ammonium-dependent and increased when N-starved plants were resupplied with ammonium. Furthermore, cbl1 mutants had enhanced NH4+ accumulation; this phenocopies the larger ammonium uptake in the cipk23 loss-of-function mutant. In vivo experiments demonstrated bimolecular interaction between CIPK23, AMT1;1, and AMT1;2, but not with AMT2;1, suggesting direct phosphorylation of AMT1-type ammonium transporters by CIPK23. However, Western blot analysis with the cipk23 mutant suggested that the loss of the kinase was not sufficient to completely abolish AMT1;1 and AMT1;2 phosphorylation, indicating several independent pathways to regulate ammonium transport activity in AMT trimers. The data identify complex post-translational regulation of ammonium transporters via the CBL1–CIPK23 pathway, which ensures reduction of AMT1 activity and suppression of ammonium uptake under high external NH4+ concentrations.
Role of benzoic acid and lettucenin A in the defense response of lettuce against soil-borne pathogens
(2021) Windisch, Saskia; Walter, Anja; Moradtalab, Narges; Walker, Frank; Höglinger, Birgit; El-Hasan, Abbas; Ludewig, Uwe; Neumann, Günter; Grosch, Rita
Soil-borne pathogens can severely limit plant productivity. Induced defense responses are plant strategies to counteract pathogen-related damage and yield loss. In this study, we hypothesized that benzoic acid and lettucenin A are involved as defense compounds against Rhizoctonia solani and Olpidium virulentus in lettuce. To address this hypothesis, we conducted growth chamber experiments using hydroponics, peat culture substrate and soil culture in pots and minirhizotrons. Benzoic acid was identified as root exudate released from lettuce plants upon pathogen infection, with pre-accumulation of benzoic acid esters in the root tissue. The amounts were sufficient to inhibit hyphal growth of R. solani in vitro (30%), to mitigate growth retardation (51%) and damage of fine roots (130%) in lettuce plants caused by R. solani, but were not able to overcome plant growth suppression induced by Olpidium infection. Additionally, lettucenin A was identified as major phytoalexin, with local accumulation in affected plant tissues upon infection with pathogens or chemical elicitation (CuSO4) and detected in trace amounts in root exudates. The results suggest a two-stage defense mechanism with pathogen-induced benzoic acid exudation initially located in the rhizosphere followed by accumulation of lettucenin A locally restricted to affected root and leaf tissues.
The role of home gardens in mitigating food insecurity and dietary quality : the case of the Mbororo community in the Northwest Region of Cameroon
(2023) Ebile, Pride Anya; Birner, Regina
Despite significant efforts made by development and research organizations to combat global food and nutrition insecurity, many people, especially in sub-Saharan Africa, still struggle with acute food insecurity. Over two billion people also suffer from micronutrient deficiencies or "hidden hunger," which leads to various health problems, particularly in poor communities without access to health infrastructures such as health centers, clinics, and hospitals. Against this backdrop, this dissertation investigated the impact and challenges of home gardens in addressing food and nutrition insecurity in the Mbororo minority community in the Northwest Region of Cameroon. The publications included in this thesis focus on (i) micronutrient deficiencies within the Mbororo community, (ii) assessing the impact of a home garden project on food and nutrition outcomes, and (iii) evaluating agricultural risks within the Mbororo community as a challenge to their food system and the home garden project. The study on micronutrient deficiencies used the 24-hour dietary recall method to collect data on the dietary diversity of Mbororo women in the Northwest Region. Mean dietary diversity scores were used to examine the impact of socio-cultural and economic characteristics on the quality of the Mbororo womens diet. The study found that some characteristics, such as the size of the cooking stove, had a significant impact on the diet, while others, like education, did not. Iron-rich foods were the least consumed, indicating a high risk of nutritional anemia within the community. Members of the Aku sub-tribe were found to be more vulnerable than their Jaafun counterparts. The home garden project aimed to empower Mbororo women by cultivating nutrient-rich vegetables for both income and home consumption. Women from 114 households in seven communities participated in the project, and gardens were built for all participants. The women received materials, educational support, and financial assistance during the implementation of the project. Three groups of vegetables were included in the project: nutrient-rich vegetables like amaranth, high market-value vegetables like chili peppers, and indigenous vegetables like "caricachee." The home garden project was evaluated as a way to mitigate food and nutrition insecurity within the Mbororo community and potentially serve as a model for other minority communities. Qualitative research methods, including in-depth interviews, focus group discussions, and observations, were used to evaluate the outcome of the project. The garden project was found to increase the vegetable variety in the seven communities. The women harvested nutrient-rich vegetables for home consumption, and the high market-value vegetables like chili peppers were sold for extra income. It was noted that the households preferred indigenous vegetables for home consumption, such as okra and eggplant. Although the garden project was successful in mitigating food and nutrition insecurity within the vulnerable communities, it also faced challenges such as a prolonged dry season and political instability in the region. The last study evaluated agricultural risks as a hindrance to the Mbororo communitys food system. The study aimed to assess the types of risks encountered, their frequency and severity, and the management strategies being used to mitigate these risks. The study used an action research approach with interviews, semi-structured questionnaires, and focus group discussions. It was found that the Mbororo communitys food system was fragile due to threats from all risks under consideration. The most severe risks were those related to climatic conditions, followed by pests and diseases, and market fluctuations. The most critical risks were drought, crop and animal diseases, political insecurity, and price variation in the market. It was challenging for the Mbororo people to develop any meaningful mitigation strategies because they lack the required financial resources. However, they mostly sell their cattle as a coping strategy when money is needed to manage financial difficulties. In conclusion, the garden project and the associated research findings provided meaningful information on combating food and nutrition insecurity. The garden project study showed that home gardens can increase vegetable biodiversity, leading to increased availability and accessibility of nutrient-rich vegetables in the Mbororo communities that may help for example to alleviate existing iron-related health deficiencies. However, the assessment of agricultural risks indicates that drought and pests are challenges for implementing and managing home gardens. Nevertheless, home gardens, if well managed, can mitigate food and nutrition insecurity in resource-poor communities such as the Mbororo minority group. However, these gardens should include indigenous vegetables since they are highly preferred to other vegetables among the Mbororo people and could also help to buffer some of the agricultural risks.
The vacuolar transporter LaMTP8.1 detoxifies manganese in leaves of Lupinus albus
(2022) Olt, Philipp; Alejandro‐Martinez, Santiago; Fermum, Johann; Ramos, Edith; Peiter, Edgar; Ludewig, Uwe
Manganese (Mn) is an essential microelement, but overaccumulation is harmful to many plant species. Most plants have similar minimal Mn requirements, but the tolerance to elevated Mn varies considerably. Mobilization of phosphate (P) by plant roots leads to increased Mn uptake, and shoot Mn levels have been reported to serve as an indicator for P mobilization efficiency in the presence of P deficiency. White lupin (Lupinus albus L.) mobilizes P and Mn with outstanding efficiency due to the formation of determinate cluster roots that release carboxylates. The high Mn tolerance of L. albus goes along with shoot Mn accumulation, but the molecular basis of this detoxification mechanism has been unknown. In this study, we identify LaMTP8.1 as the transporter mediating vacuolar sequestration of Mn in the shoot of white lupin. The function of Mn transport was demonstrated by yeast complementation analysis, in which LaMTP8.1 detoxified Mn in pmr1∆ mutant cells upon elevated Mn supply. In addition, LaMTP8.1 also functioned as an iron (Fe) transporter in yeast assays. The expression of LaMTP8.1 was particularly high in old leaves under high Mn stress. However, low P availability per se did not result in transcriptional upregulation of LaMTP8.1. Moreover, LaMTP8.1 expression was strongly upregulated under Fe deficiency, where it was accompanied by Mn accumulation, indicating a role in the interaction of these micronutrients in L. albus. In conclusion, the tonoplast‐localized Mn transporter LaMTP8.1 mediates Mn detoxification in leaf vacuoles, providing a mechanistic explanation for the high Mn accumulation and Mn tolerance in this species.
The wheat AMT2 (AMmonium Transporter) family, possible functions in ammonium uptake and pathogenic/symbiotic interactions
(2023) Porras‐Murillo, Romano; Zhao, Yufen; Hu, Jinling; Ijato, Toyosi; Retamal, Joseline Palafox; Ludewig, Uwe; Neuhäuser, Benjamin
Ammonium uptake into wheat roots relies primarily on two AMmonium Transporters of subfamily one, while the wheat genome comprises 4 to 6 AMT2 type transporters. Plant AMT2s generally show functions in root‐to‐shoot translocation or pathogenic and symbiotic plant–microorganism interactions. We addressed the activity of TaAMT2s in ammonium transport. Nitrogen‐dependent expression implicated a physiological function in ammonium uptake for TaAMT2;1 and in ammonium distribution for TaAMT2;2‐6.

Browse

Browsing Institut für Kulturpflanzenwissenschaften by Classification "570"