Magnesiummangel bei Mais und Effektivität einer Nährstoffversorgung mittels MgSO4-Blattapplikation

The plant nutrient magnesium (Mg) is of fundamental importance for optimal plant growth and development. However, Mg nutrition of crops is frequently overlooked and Mg deficiency is increasingly becoming an important limiting production factor in both industrialized crop production and rural subsistence agriculture. This work aimed at providing new insight into the metabolic adaptation to Mg undersupply of maize (Zea mays L.). Moreover, the suitability of a chlorophyll fluorescence-based method for Mg deficiency detection was tested and the effectiveness and efficiency of foliar Mg fertilization for ameliorating Mg deficiency in maize were evaluated. It was shown that neither the glutamine synthetase-mediated ammonium assimilation nor the protein biosynthesis in maize leaves are growth limiting steps in response to low Mg supply in this crop. These findings are in contrast to previous reports in other crops and contradict the assumption that disturbed polypeptide synthesis is the primary effect of Mg shortage and the concomitant growth inhibition. Furthermore, Mg deficiency-induced accumulation of foliar flavonols was shown for the first time. This knowledge can contribute to the future development of devices for rapid early-stage diagnosis of nutrient deficiency in agriculture and plant research. The results of the conducted sugar analysis argue against the prevalent hypothesis that anthocyanins synthesized in response to abiotic stress act as carbon storage compounds in maize leaves. Foliar MgSO4 application proved to be effective and efficient in ameliorating physiological constraints caused by severe Mg deficiency such as decreased photosynthesis and transpiration rate, disturbed homeostasis of potassium and manganese, and reduced overall growth. The results can contribute to the development of environmentally and economically beneficial fertilization strategies for instantaneous amelioration of an acute Mg deficiency.Der Pflanzennährstoff Magnesium (Mg) ist von essentieller Bedeutung für optimales Pflanzenwachstum. Dennoch wird die Mg-Versorgung von Nutzpflanzen vielfach unzureichend beachtet und Mg-Mangel wird zunehmend zum Wachstum-limitierenden Faktor sowohl in industrialisierter Landwirtschaft als auch ländlicher Selbstversorgerwirtschaft. Diese Arbeit zielte darauf ab, neue Einblicke in die physiologischen Anpassungen von Mais (Zea mays L.) an Mg-Mangel zu gewähren. Darüber hinaus wurden die Eignung einer Chlorophyll-Fluoreszenz-basierten Messmethode zur Diagnose von Mg-Mangel getestet und die Effektivität und Effizienz von Mg-Blattdüngung zur Abmilderung von starkem Mg-Mangel in Mais bewertet. Es wurde gezeigt, dass weder die Glutaminsynthetase-vermittelte Ammoniumassimilation noch die Proteinsynthese das Maiswachstum bei Mg-Mangel limitieren. Diese Erkenntnisse stehen im Widerspruch zu vorherigen Berichten in anderen Nutzpflanzen und widerlegen die Annahme, dass eine gestörte Polypeptidsynthese der primäre Effekt von Mg-Mangel und der damit einhergehenden Wachstumsdepression ist. Des Weiteren wurde in dieser Arbeit erstmalig Mg-Mangel-induzierte Flavonolakkumulation im Blatt gezeigt. Dieses Wissen kann zur Entwicklung von Messgeräten zur schnellen Früherkennung von Nährstoffmangel für landwirtschaftliche und wissenschaftliche Zwecke genutzt werden. Die Ergebnisse der durchgeführten Zuckeranalysen widersprachen der Hypothese, dass infolge von abiotischem Stress akkumulierte Anthocyane zum Zwecke der Kohlenstoffspeicherung synthetisiert werden. Blattapplikation von MgSO4 erwies sich als effektive und effiziente Methode, um mit Mg-Mangel einhergehende Stoffwechseleinschränkungen wie verminderte Fotosynthese- und Transpirationsrate, gestörte Homöostase von Kalium und Mangan sowie reduziertes Gesamtwachstum von Mais zu beheben. Diese Ergebnisse können zur Entwicklung ökologisch und ökonomisch vorteilhafter Düngestrategien zur sofortigen Behebung von akutem Mg-Mangel beitragen

A constraint-relaxation-recovery mechanism for stomatal dynamics

Models of guard cell dynamics, built on the OnGuard platform, have provided quantitative insights into stomatal function, demonstrating substantial predictive power. However, the kinetics of stomatal opening predicted by OnGuard models were threefold to fivefold slower than observed in vivo. No manipulations of parameters within physiological ranges yielded model kinetics substantially closer to these data, thus highlighting a missing component in model construction. One well‐documented process influencing stomata is the constraining effect of the surrounding epidermal cells on guard cell volume and stomatal aperture. Here, we introduce a mechanism to describe this effect in OnGuard2 constructed around solute release and a decline in turgor of the surrounding cells and its subsequent recovery during stomatal opening. The results show that this constraint–relaxation–recovery mechanism in OnGuard2 yields dynamics that are consistent with experimental observations in wild‐type Arabidopsis, and it predicts the altered opening kinetics of ost2 H+‐ATPase and slac1 Cl− channel mutants. Thus, incorporating solute flux of the surrounding cells implicitly through their constraint on guard cell expansion provides a satisfactory representation of stomatal kinetics, and it predicts a substantial and dynamic role for solute flux across the apoplastic space between the guard cells and surrounding cells in accelerating stomatal kinetics

Acute SIV Infection in Sooty Mangabey Monkeys Is Characterized by Rapid Virus Clearance from Lymph Nodes and Absence of Productive Infection in Germinal Centers

Lymphoid tissue immunopathology is a characteristic feature of chronic HIV/SIV infection in AIDS-susceptible species, but is absent in SIV-infected natural hosts. To investigate factors contributing to this difference, we compared germinal center development and SIV RNA distribution in peripheral lymph nodes during primary SIV infection of the natural host sooty mangabey and the non-natural host pig-tailed macaque. Although SIV-infected cells were detected in the lymph node of both species at two weeks post infection, they were confined to the lymph node paracortex in immune-competent mangabeys but were seen in both the paracortex and the germinal center of SIV-infected macaques. By six weeks post infection, SIV-infected cells were no longer detected in the lymph node of sooty mangabeys. The difference in localization and rate of disappearance of SIV-infected cells between the two species was associated with trapping of cell-free virus on follicular dendritic cells and higher numbers of germinal center CD4+ T lymphocytes in macaques post SIV infection. Our data suggests that fundamental differences in the germinal center microenvironment prevent productive SIV infection within the lymph node germinal centers of natural hosts contributing to sustained immune competency

Guard cell endomembrane Ca2+-ATPases underpin a ‘carbon memory’ of photosynthetic assimilation that impacts on water-use efficiency

Stomata of most plants close to preserve water when the demand for CO2 by photosynthesis is reduced. Stomatal responses are slow compared with photosynthesis, and this kinetic difference erodes assimilation and water-use efficiency under fluctuating light. Despite a deep knowledge of guard cells that regulate the stoma, efforts to enhance stomatal kinetics are limited by our understanding of its control by foliar CO2. Guided by mechanistic modelling that incorporates foliar CO2 diffusion and mesophyll photosynthesis, here we uncover a central role for endomembrane Ca2+ stores in guard cell responsiveness to fluctuating light and CO2. Modelling predicted and experiments demonstrated a delay in Ca2+ cycling that was enhanced by endomembrane Ca2+-ATPase mutants, altering stomatal conductance and reducing assimilation and water-use efficiency. Our findings illustrate the power of modelling to bridge the gap from the guard cell to whole-plant photosynthesis, and they demonstrate an unforeseen latency, or ‘carbon memory’, of guard cells that affects stomatal dynamics, photosynthesis and water-use efficiency

Anthocyanin management in fruits by fertilization

Anthocyanins are water-soluble vacuolar plant pigments that are mainly synthesized in epidermal layers and the flesh of fruits such as apples, cherries, grapes, and other berries. Because of their attractive red to purple coloration and their health-promoting potential, anthocyanins are significant determinants for the quality and market value of fruits and fruit-derived products. In crops, anthocyanin accumulation in leaves can be caused by nutrient deficiency which is usually ascribed to insufficient nitrogen or phosphorus fertilization. However, it is a little-known fact that the plant’s nutrient status also impacts anthocyanin synthesis in fruits. Hence, strategic nutrient supply can be a powerful tool to modify the anthocyanin content and consequently the quality and market value of important agricultural commodities. Here we summarize the current knowledge of the influence of plant nutrients on anthocyanin synthesis in fruits of major global market value and discuss the underlying cellular processes that integrate nutrient signaling with fruit anthocyanin formation. It is highlighted that fertilization that is finely tuned in amount and timing has the potential to positively influence the fruit quality by regulating anthocyanin levels. We outline new approaches to enrich plant based foods with health-promoting anthocyanins

The membrane transport system of the guard cell and its integration for stomatal dynamics

Stomatal guard cells are widely recognized as the premier plant cell model for membrane transport, signaling, and homeostasis. This recognition is rooted in half a century of research into ion transport across the plasma and vacuolar membranes of guard cells that drive stomatal movements and the signaling mechanisms that regulate them. Stomatal guard cells surround pores in the epidermis of plant leaves, controlling the aperture of the pore to balance CO2 entry into the leaf for photosynthesis with water loss via transpiration. The position of guard cells in the epidermis is ideally suited for cellular and subcellular research, and their sensitivity to endogenous signals and environmental stimuli makes them a primary target for physiological studies. Stomata underpin the challenges of water availability and crop production that are expected to unfold over the next 20 to 30 years. A quantitative understanding of how ion transport is integrated and controlled is key to meeting these challenges and to engineering guard cells for improved water use efficiency and agricultural yields

What can mechanistic models tell us about guard cells, photosynthesis, and water use efficiency?

No abstract available

Why do plants blush when they are hungry?

Foliar anthocyanins, as well as other secondary metabolites, accumulate transiently under nutritional stress. A misconception that only nitrogen or phosphorus deficiency induces leaf purpling/reddening has led to over-use of fertilizers that burden the environment. Here we emphasize that several other nutritional imbalances induce anthocyanin accumulation, and nutrient-specific differences in this response have been reported for some deficiencies. A range of ecophysiological functions have been attributed to anthocyanins. We discuss the proposed functions and signalling pathways that elicit anthocyanin synthesis in nutrient-stressed leaves. Knowledge from the fields of genetics, molecular biology, ecophysiology, and plant nutrition are combined to deduce how and why anthocyanins accumulate under nutritional stress. Future research to fully understand the mechanisms and nuances of foliar anthocyanin accumulation in nutrient-stressed crops could be utilized to allow these leaf pigments to act as bio-indicators for demand-oriented application of fertilizers. This would benefit the environment, being timely due to the increasing impact of the climate crisis on crop performance

Fast responses of metabolites in Vicia faba L. to moderate NaCl stress

Geilfus C-M, Niehaus K, Goedde V, et al. Fast responses of metabolites in Vicia faba L. to moderate NaCl stress. Plant Physiology and Biochemistry. 2015;92:19-29.Salt stress impairs global agricultural crop production by reducing vegetative growth and yield. Despite this importance, a number of gaps exist in our knowledge about very early metabolic responses that ensue minutes after plants experience salt stress. Surprisingly, this early phase remains almost as a black box. Therefore, systematic studies focussing on very early plant physiological responses to salt stress (in this case NaCl) may enhance our understanding on strategies to develop crop plants with a better performance under saline conditions. In the present study, hydroponically grown Vicia faba L. plants were exposed to 90 min of NaCl stress, whereby every 15 min samples were taken for analyzing short-term physiologic responses. Gas chromatography-mass spectrometry-based metabolite profiles were analysed by calculating a principal component analysis followed by multiple contrast tests. Follow-up experiments were run to analyze downstream effects of the metabolic changes on the physiological level. The novelty of this study is the demonstration of complex stress-induced metabolic changes at the very beginning of a moderate salt stress in V. faba, information that are very scant for this early stage. This study reports for the first that the proline analogue trans-4-hydroxy-L-proline, known to inhibit cell elongation, was increasingly synthesized after NaCl-stress initiation. Leaf metabolites associated with the generation or scavenging of reactive oxygen species (ROS) were affected in leaves that showed a synchronized increase in ROS formation. A reduced glutamine synthetase activity indicated that disturbances in the nitrogen assimilation occur earlier than it was previously thought under salt stress. (C) 2015 Elsevier Masson SAS. All rights reserved