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Common duckweed ( Lemna minor L.) is ideally suited to test the impact of metals on freshwater vascular plants. Literature on cadmium (Cd) and uranium (U) oxidative responses in L. minor are sparse or, for U, non-existent. It was hypothesised that both metals impose concentration-dependent oxidative stress and growth retardation on L. minor. Using a standardised 7-day growth inhibition test, the adverse impact of these metals on L. minor growth was confirmed, with EC50 values for Cd and U of 24.1 ± 2.8 and 29.5 ± 1.9 μ m, respectively, and EC10 values of 1.5 ± 0.2 and 6.5 ± 0.9 μ m, respectively. The metal-induced oxidative stress response was compared through assessing the activity of different antioxidative enzymes [catalase, glutathione reductase, superoxide dismutase ( SOD), ascorbate peroxidase ( APOD), guaiacol peroxidase ( GPOD) and syringaldizyne peroxidase ( SPOD)]. Significant changes in almost all antioxidative enzymes indicated their importance in counteracting the U- and Cd-imposed oxidative burden. However, some striking differences were also observed. For activity of APODs and SODs, a biphasic but opposite response at low Cd compared to U concentrations was found. In addition, Cd (0.5-20 μ m) strongly enhanced plant GPOD activity, whereas U inhibited it. Finally, in contrast to Cd, U up to 10 μ m increased the level of chlorophyll a and b and carotenoids. In conclusion, although U and Cd induce similar growth arrest in L. minor, the U-induced oxidative stress responses, studied here for the first time, differ greatly from those of Cd. [ABSTRACT FROM AUTHOR]

The uptake of ascorbate into protoplasts isolated from a Nicotiana tabacum Bright Yellow-2 (BY-2) cell suspension culture was investigated. Addition of14C-labelled ascorbate to freshly isolated protoplasts resulted in a time- and substrate-dependent association of radioactive molecules with the protoplasts. The kinetic characterisation of this presumptive uptake revealed kinetics of Michaelis-Menten type with an apparent maximal uptake activity of 24 pmol/min·106 protoplasts and an apparent affinity constant of 139 μM. The amount of ascorbate molecules transported intoN. tabacum protoplasts decreased when nonlabelled dehydroascorbate or iso-ascorbate were added but was not affected by addition of 5,6- o-cyclohexylidene ascorbate or ascorbate-2-sulfate. These data indicate a carrier-mediated uptake of ascorbate into the protoplasts that shows a high structural specificity. To investigate which redox status of ascorbate is preferentially taken up by the N. tabacum protoplasts, transport was tested in the presence of various compounds that can affect the redox status of ascorbate. Testing uptake in the presence of a reductant, dithiothreitol, resulted in a significant and concentration-dependent inhibition of the amount of ascorbate molecules transported into the protoplasts. On the other hand, ascorbate uptake was significantly stimulated in the presence of the enzyme ascorbate oxidase. Ferricyanide did not affect ascorbate transport. Inhibition studies revealed that ascorbate uptake in the protoplasts is sensitive to addition of sulfhydryl reagents N-ethyl maleimide and p-chloro-mercuribenzenesulfonic acid and to a disruption of the proton gradient by the protonophore carbonylcyanide-3-chlorophenylhydrazone. The uptake of ascorbate was also inhibited by addition of cytochalasin B but not sensitive to addition of phloretin or sulfinpyrazone. Taken together these data indicate the presence of an ascorbate transport system in the plasma membrane of N. tabacum protoplasts and suggest dehydroascorbate as the preferentially transported redox species. The putative presence of different carriers for reduced and oxidised ascorbate in the plasma membrane is discussed. [ABSTRACT FROM AUTHOR]

Incubation of bean hook plasma membrane vesicles in the presence of L-[C]ascorbate (ASC) resulted in a specific recovery of significant levels of the ligand with the vesicles. The strong decrease in radioactive ASC detected after hypotonic disruption of the vesicles or after an assay at 4 °C indicated that ASC was probably transported from the medium into the lumen of the membrane vesicles. The concentration kinetics of this presumptive transport process revealed a saturation curve which best fitted a biphasic model. Each phase in this model showed Michaelis-Menten type kinetics. The kinetic parameters for the different phases were calculated to be 14 and 79 μM ( K and K) and 26 and 53 pmol/min · mg protein ( V and V). High concentrations of iso-ascorbate, dehydroascorbate (DHA) or non-labelled ASC significantly reduced the uptake of the radioactive vitamin. It was demonstrated that sugar or amino acid carriers are not involved in the ASC transport reaction. Generation of transmembrane cation gradients (H, K, Ca, Na) or addition of sulfhydryl reagents (pCMBS or NEM) did not affect the ASC uptake in any way. It is suggested that ASC is taken up by a facilitated diffusion mechanism. [ABSTRACT FROM AUTHOR]

Higher plant plasma membranes contain a b-type cytochrome that is rapidly reduced by ascorbic acid. The affinity towards ascorbate is 0.37 mM and is very similar to that of the chromaffin granule cytochrome b. High levels of cytochrome b reduction are reached when ascorbic acid is added either on the cytoplasmic or cell wall side of purified plasma membrane vesicles. This result points to a transmembrane organisation of the heme protein or alternatively indicates the presence of an effective ascorbate transport system. Plasma membrane vesicles loaded by ascorbic acid are capable of reducing extravesicular ferricyanide. Addition of ascorbate oxidase or washing of the vesicles does not eliminate this reaction, indicating the involvement of the intravesicular electron donor. Absorbance changes of the cytochrome b α-band suggest the electron transfer is mediated by this redox component. Electron transport to ferricyanide also results in the generation of a membrane potential gradient as was demonstrated by using the charge-sensitive optical probe oxonol VI. Addition of ascorbate oxidase and ascorbate to the vesicles loaded with ascorbate results in the oxidation and subsequent re-reduction of the cytochrome b. It is therefore suggested that ascorbate free radical (AFR) could potentially act as an electron acceptor to the cytochrome-mediated electron transport reaction. A working model on the action of the cytochrome as an electron carrier between cytoplasmic and apoplastic ascorbate is discussed. [ABSTRACT FROM AUTHOR]

To reach the estimated food demands for 2050 in decreasingly suiting climates, current agricultural techniques have to be complemented by sustainably intensified practices. The current study repurposed wheat crop residues into biochar, and investigated its potential in different plant cultivation systems, including a hydroponic cultivation of wheat. Biochars resulting from varying pyrolysis parameters including feedstock composition (straw and chaff) and temperature (450°C and 600°C), were tested using a fast plant screening method. Biochar WBC450, produced from a combination of chaff and straw at 450°C, was selected for further plant experiments, and used in a static leaching experiment in the Arabidopsis thaliana cultivation medium. Increased pH and EC were observed, together with an increase of most macronutrient (K, Mg, P, S) and a decrease of most micronutrient (Fe, Mn, Zn) concentrations. Considering plant growth, application of biochar resulted in concentration-dependent effects in both tested plant species ( A. thaliana and wheat). It improved the vegetative yield across all tested cultivation systems. Increases in K and S, and concentration-dependent decreases in Fe and Na content in wheatgrass were observed. Biochar influenced the reproduction of hydroponically cultivated wheat by increasing the number of spikes and the number of seeds per spike. The antioxidative capacity of wheat grass, and the seed sugar and starch contents remained unaffected by biochar application. This study contributes to innovation in soilless cultivation approaches of staple crops, within the framework of closing waste loops for a circular bioeconomy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Kunnen, Ali, Lataf, Van Hees, Nauts, Horemans, Vandamme and Cuypers.)

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)