1,720,986 research outputs found
Effects of chilling on the photosynthetic performance of the CAM orchid Phalaenopsis
No full textINTRODUCTION: Crassulacean acid metabolism (CAM) is one of the three main metabolic adaptations for CO2 fixation found in plants. A striking feature for these plants is nocturnal carbon fixation and diurnal decarboxylation of malic acid to feed Rubisco with CO2 behind closed stomata, thereby saving considerable amounts of water. Compared to the effects of high temperatures, drought, and light, much less information is available about the effects of chilling temperatures on CAM plants. In addition a lot of CAM ornamentals are grown in heated greenhouses, urging for a deeper understanding about the physiological responses to chilling in order to increase sustainability in the horticultural sector. METHODS: The present study focuses on the impact of chilling temperatures (10°C) for 3 weeks on the photosynthetic performance of the obligate CAM orchid Phalaenopsis 'Edessa'. Detailed assessments of the light reactions were performed by analyzing chlorophyll a fluorescence induction (OJIP) parameters and the carbon fixation reactions by measuring diel leaf gas exchange and diel metabolite patterns. RESULTS AND DISCUSSION: Results showed that chilling already affected the light reactions after 24h. Whilst the potential efficiency of photosystem II (PSII) (Fv/Fm) was not yet influenced, a massive decrease in the performance index (PIabs) was noticed. This decrease did not depict an overall downregulation of PSII related energy fluxes since energy absorption and dissipation remained uninfluenced whilst the trapped energy and reduction flux were upregulated. This might point to the presence of short-term adaptation mechanisms to chilling stress. However, in the longer term the electron transport chain from PSII to PSI was affected, impacting both ATP and NADPH provision. To avoid over-excitation and photodamage plants showed a massive increase in thermal dissipation. These considerations are also in line with carbon fixation data showing initial signs of cold adaptation by achieving comparable Rubisco activity compared to unstressed plants but increasing daytime stomatal opening in order to capture a higher proportion of CO2 during daytime. However, in accordance with the light reactions data, Rubisco activity declined and stomatal conductance and CO2 uptake diminished to near zero levels after 3 weeks, indicating that plants were not successful in cold acclimation on the longer term.sponsorship: KU Leuvenstatus: Publishe
How to resolve the enigma of diurnal malate remobilization from the vacuole in plants with crassulacean acid metabolism?
No full textOpening of stomata in plants with crassulacean acid metabolism (CAM) is mainly shifted to the night period when atmospheric CO2 is fixed by phosphoenolpyruvate carboxylase and stored as malic acid in the vacuole. As such, CAM plants ameliorate transpirational water losses and display substantially higher water-use efficiency compared with C3 and C4 plants. In the past decade significant technical advances have allowed an unprecedented exploration of genomes, transcriptomes, proteomes and metabolomes of CAM plants and efforts are ongoing to engineer the CAM pathway in C3 plants. Whilst research efforts have traditionally focused on nocturnal carboxylation, less information is known regarding the drivers behind diurnal malate remobilisation from the vacuole that liberates CO2 to be fixed by RuBisCo behind closed stomata. To shed more light on this process, we provide a stoichiometric analysis to identify potentially rate-limiting steps underpinning diurnal malate mobilisation and help direct future research efforts. Within this remit we address three key questions: Q1 Does light-dependent assimilation of CO2 via RuBisCo dictate the rate of malate mobilisation? Q2: Do the enzymes responsible for malate decarboxylation limit daytime mobilisation from the vacuole? Q3: Does malate efflux from the vacuole set the pace of decarboxylation?sponsorship: The authors would like to thank Internal Funds KU Leuven for financial support. (Internal Funds KU Leuven)status: Published onlin
pH modulation of the environment by <i>Stagonosporopsis cucurbitacearum</i>, an important pathogen causing fruit rot in <i>Cucurbitaceae</i>
No full textThe Cucurbitaceae is a genetically diverse group of plants containing several important commodity crops in many parts of the world such as cucumber, pumpkin and melon. In the last decades, fruit rot caused by Stagonosporopsis spp. became a major disease in both field grown and greenhouse grown cucurbits. Yield losses due to Stagonosporopsis can show seasonal peaks up to 30%. Despite its economic importance, only limited information is available about growth characteristics of Stagonosporopsis cucurbitacearum. Our in vitro studies with different media indicated an optimal growth rate of the fungus within the range of pH 5 to pH 6. Independent of the carbon source (sucrose, glucose, dextrose, fructose) alkalization of 1–3, 5 pH units was noticed under both carbon deprivation and excess. The observed pH modulation could not always be related with a more favourable growth environment. The key factor influencing both pH modulating capacity and growth showed to be the nitrogen source. Supplying nitrate, ammonium or a combination of both, the environmental pH respectively increased, decreased or remained stable. In addition to a pH-elevating effect, nitrate supply also stimulated growth whilst growth on ammonium containing media was seriously affected. This research highlights the importance of the nitrogen source in the growth and regulation of environmental pH by fungi and adds in our understanding of S. cucurbitacearum pathogenicity.sponsorship: This work was funded by the Agency for Innovation by Science and Technology in Flanders (IWT-LA-140982). (Agency for Innovation by Science and Technology in Flanders|IWT-LA-140982)status: Publishe
Possibilities of modified atmosphere packaging to prevent the occurrence of internal fruit rot in bell pepper fruit (Capsicum annuum) caused by Fusarium spp
No full textBell pepper (Capsicum annuum L.), with its wide array of colors and flavors, plays an important role in many different cuisines around the world. Yet once harvested, it is a highly perishable fruit and needs appropriate post-harvest handling. Recently, post-harvest internal rotting (IFR) by Fusarium lactis species complex isolates (FLASC), became an additional challenge to maintain shelf-life and quality of bell pepper fruit. Therefore, modified atmosphere packaging (MAP) was explored as a possible technique to postpone symptom development of infected bell peppers. Four artificially infected bell pepper cultivars with different susceptibility towards IFR were stored under MAP conditions for a maximum of 14 d at challenging conditions of 20 degrees C resembling unrefrigerated shelf life conditions. Each week, 5 fruit of each object were analyzed for IFR symptom development and additional physicochemical and quality parameters. For all cultivars, MAP packaged fruit showed less severe fungal proliferation compared to controls after 14 d. As total titratable acid (TA), total soluble solids (TSS) and vitamin C concentrations in fruit remained rather stable throughout the experiment, fungal development was likely to be postponed directly due to reduced oxygen levels in the pouches rather than a decreased host susceptibility by influencing fruit metabolism. Since no significant differences of disease development were observed between sensitive and less sensitive cultivars for both colors, sensitivity for IFR seems not likely to be caused by different post-harvest disease development patterns but rather by differences in the initial susceptibility for flower infection under normal growth conditions. Based on our results, MAP can indeed be considered a useful tool to ameliorate IFR development during post-harvest storage of bell pepper under conventional temperatures of 7-16 degrees C
Metabolic modelling identifies mitochondrial Pi uptake and pyruvate efflux as key aspects of daytime metabolism and proton homeostasis in crassulacean acid metabolism leaves
No full textCrassulacean acid metabolism (CAM) leaves are characterized by nocturnal acidification anddiurnal deacidification processes related with the timed actions of phosphoenolpyruvate carbox-ylase and Rubisco, respectively. How CAM leaves manage cytosolic proton homeostasis, particu-larly when facing massive diurnal proton effluxes from the vacuole, remains unclear. A 12-phase flux balance analysis (FBA) model was constructed for a mature malicenzyme-type CAM mesophyll cell in order to predict diel kinetics of intracellular proton fluxes. The charge- and proton-balanced FBA model identified the mitochondrial phosphate carrier(PiC, Pi/H+symport), which provides Pi to the matrix to sustain ATP biosynthesis, as a majorconsumer of cytosolic protons during daytime (>50%). The delivery of Pi to the mitochon-drion, co-transported with protons, is required for oxidative phosphorylation and allows suffi-cient ATP to be synthesized to meet the high energy demand during CAM Phase III.Additionally, the model predicts that mitochondrial pyruvate originating from decarboxylationof malate is exclusively exported to the cytosol, probably via a pyruvate channel mechanism,to fuel gluconeogenesis. In this biochemical cycle, glyceraldehyde 3-phosphate dehydrogen-ase (GAPDH) acts as another important cytosolic proton consumer. Overall, our findings emphasize the importance of mitochondria in CAM and uncover ahitherto unappreciated role in metabolic proton homeostasis.Funding was provided by the Research Fund KU Leuven. Figures were created with BioRender.com
Characteristics of Residues from Heathland Restauration and Management: Implications for Their Sustainable Use in Agricultural Soils or Growing Media.
No full textsponsorship: This research was funded by iCleantech Flanders and MIP (Milieu- en Energie Innovatie Platform/Platform for Environmental Innovation-Project IWT140635). The authors would like to acknowledge the support of KU Leuven, PCS Ornamental Plant Research, the Flemish Research Institute for Agriculture, Fisheries and Food and Greenyard Group. Moreover, special thanks goes to the professionals and volunteers from Kwanten & co bvba, Belgian Agency for Forest and Nature (ANB), Natuurpunt and Heylen bvba for their input and time and to those that participated in the interviews. Finally, we would like to thank Kim Vekemans for her intensive help, and master student Lorean Van Rensbergen for his collaboration in sample collection and lab analyses. (iCleantech Flanders, MIP (Milieu- en Energie Innovatie Platform/Platform for Environmental Innovation-Project)|IWT140635, KU Leuven, PCS Ornamental Plant Research, Flemish Research Institute for Agriculture, Fisheries and Food, Greenyard Group)status: Published onlin
Elucidating the microbiome of the sustainable peat replacers composts and nature management residues
No full textSustainable peat alternatives, such as composts and management residues, are considered to have beneficial microbiological characteristics compared to peat-based substrates. Studies comparing microbiological characteristics of these three types of biomass are, however, lacking. This study examined if and how microbiological characteristics of subtypes of composts and management residues differ from peat-based substrates, and how feedstock and (bio)chemical characteristics drive these characteristics. In addition, microbiome characteristics were evaluated that may contribute to plant growth and health. These characteristics include: genera associated with known beneficial or harmful microorganisms, microbial diversity, functional diversity/activity, microbial biomass, fungal to bacterial ratio and inoculation efficiency with the biocontrol fungus Trichoderma harzianum. Bacterial and fungal communities were studied using 16S rRNA and ITS2 gene metabarcoding, community-level physiological profiling (Biolog EcoPlates) and PLFA analysis. Inoculation with T. harzianum was assessed using qPCR. Samples of feedstock-based subtypes of composts and peat-based substrates showed similar microbial community compositions, while subtypes based on management residues were more variable in their microbial community composition. For management residues, a classification based on pH and hemicellulose content may be relevant for bacterial and fungal communities, respectively. Green composts, vegetable, fruit and garden composts and woody composts show the most potential to enhance plant growth or to suppress pathogens for non-acidophilic plants, while grass clippings, chopped heath and woody fractions of compost show the most potential for blends for calcifuge plants. Fungal biomass was a suitable predictor for inoculation efficiency of composts and management residues.sponsorship: This work was supported by Flanders Innovation & Entrepreneurship (HBC.2017.0815) (Bi-o-ptimal@work - Sustainable cultivation in container and open field by using innovative and local materials with enhanced microbial life, ready for use and implementation by ornamental growers). CT received a grant of the Research Foundation Flanders (FWO) with application number (12S9418N). KV received an FWO sabbatical bench fee (number VWH-E1313-SAB/22/016). (Flanders Innovation & Entrepreneurship|HBC.2017.0815, Research Foundation Flanders (FWO)|12S9418N, FWO|VWH-E1313-SAB/22/016)status: Publishe
De invloed van sucrose op de koolhydratendynamiek en fotosynthese vanGuzmania 'Hilda' tijdens weefselkweek
No full textTissue culture is a widely applied technology for the production of ornamental plants. During the in vitro phase, plants are exposed to lower light intensities and limited gas exchange, both associated with poor photosynthesis. For that reason, another carbon source is needed for adequate growth and development. Sucrose is generally supplied to culture media, stimulating heterotrophic behavior of the in vitro plants. As a consequence, transfer of the plants to an ex vitro environment implies acclimation to an autotrophic way of energy providing. To achieve excellent ex vitro performance, delivery of qualitative in vitro plants with improved carbon utilization is required. In this work, the interaction between heterotrophic and autotrophic growth is investigated by determining the influence of sucrose in the medium on carbohydrate dynamics ina culture vessel and their relation with photosynthesis. As a study object, the bromeliad hybrid Guzmania ‘Hilda’ is used. This ornamental plant is commercially produced by tissue culture and its in vitro part consists of three phases: multiplication, elongation and rooting. For the experiments the rooting medium is supplied with four different sucrose concentrations: 15, 37, 73 and 117 µmol g-1medium. After an 8 week culture period on this medium, plants are transferred to the greenhouse for further growth.
When sucrose is added to the culture medium, almost all sucrose is depleted after four weeks, both by uptake and hydrolysis in glucose and fructose. The remaining part of the culture period, G. ‘Hilda’ plants are depending for sustaining growth on hexose uptake (preferably glucose), photosynthesis and degradation of storage (starch) molecules.
It is clear that increasing the sucroselevel results in a higher carbohydrate uptake from the medium and a stimulated heterotrophic growth (bigger plants containing a higher number of roots and shoots) at the end of the in vitro culture. About 50% of thesugars available at the start of the rooting phase remain in the mediumduring eight weeks of culture. Only for plants grown on the lowest sucrose concentration a more efficient use of the available resources is observed, since 65% was metabolized.
Autotrophic behavior is mainly dependent on the accumulated CO2 levels in the headspace of the culture vessel, originating from dark respiration. Plants grown on increased sucrose release more CO2 during night and improved CO2 uptake rates are noticed. This way autotrophic behavior is indirectly influenced by sucrose and the negative effects of sucrose on the chlorophyll levels and activity of Rubisco are covered by the accumulated CO2 levels in the headspace of the culture vessels. At the onset of the day CO2 is depleted (by photosynthesis) in less than 90 minutes, resulting in only limited CO2 concentrations during the remaining part of the day. If photosynthesis of the plants is measured under a constant CO2 flow (no accumulation), the inhibitory effect of sugars on the photosynthetic capacity of G. ‘Hilda’ emerges as lower CO2 uptake rates are measured in plants grown at increased sucrose in their medium. So it is suggested that quality improvement of the in vitro plants is possible by a combination of reducing sucrose and CO2 enrichment to stimulate a more efficient carbon utilization.
The leaves act as storage organs since the carbohydrates (mainly starch) are degraded when sucrose is no longer available. After three months of transfer to the greenhouse, plants supplied initiallywith lower sucrose concentrations resembles the starch content of the in vitro leaves. On the other hand, plants cultivated in vitro on increased sucrose show a starch breakdown during these first three months ex vitro. This indicates the plants grown on lower sucrose need to engage more in photosynthesis for further growth, which is confirmed by higher Rubisco activities. After four months of ex vitro culture, the observed differences in plant growth at the end of the in vitro period (bigger plants when more sucrose was supplied) are no longer noticed ex vitro as the lower treated plants equals the growth of plants cultivated with increased sucrose levels. These are indications that reducing the sucrose concentration in the medium improves carbon utilization after transfer to thegreenhouse.
It is believed that improvement of G. ‘Hilda’ tissue culture is possible by optimizing carbon utilization. The photosynthetic capacity of in vitro plants is not fully exploited and can be enhanced by CO2 enrichment. Under these conditions it is recommended to reduce the sucrose concentrations, because they show a negative effect on the photosynthetic capacity of the plants. Lowering sucrose in the medium is also recommended since a more efficient use of the available resources occurs.status: Publishe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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