Impact of Coated Zinc Oxide Nanoparticles on Photosystem II of Tomato Plants

Zinc oxide nanoparticles (ZnO NPs) have emerged as a prominent tool in agriculture. Since photosynthetic function is a significant measurement of phytotoxicity and an assessment tool prior to large-scale agricultural applications, the impact of engineered irregular-shaped ZnO NPs coated with oleylamine (ZnO@OAm NPs) were tested. The ZnO@OAm NPs (crystalline size 19 nm) were solvothermally prepared in the sole presence of oleylamine (OAm) and evaluated on tomato (Lycopersicon esculentum Mill.) photosystem II (PSII) photochemistry. Foliar-sprayed 15 mg L−1 ZnO@OAm NPs on tomato leaflets increased chlorophyll content that initiated a higher amount of light energy capture, which resulted in about a 20% increased electron transport rate (ETR) and a quantum yield of PSII photochemistry (ΦPSII) at the growth light (GL, 600 μmol photons m−2 s−1). However, the ZnO@OAm NPs caused a malfunction in the oxygen-evolving complex (OEC) of PSII, which resulted in photoinhibition and increased ROS accumulation. The ROS accumulation was due to the decreased photoprotective mechanism of non-photochemical quenching (NPQ) and to the donor-side photoinhibition. Despite ROS accumulation, ZnO@OAm NPs decreased the excess excitation energy of the PSII, indicating improved PSII efficiency. Therefore, synthesized ZnO@OAm NPs can potentially be used as photosynthetic biostimulants for enhancing crop yields after being tested on other plant species

Leaf age-dependent effects of foliar-sprayed CuZn nanoparticles on photosynthetic efficiency and ROS generation in <i>Arabidopsis thaliana</i>

Young and mature leaves of Arabidopsis thaliana were exposed by foliar spray to 30 mg L&minus;1 of CuZn nanoparticles (NPs). The NPs were synthesized by a microwave-assisted polyol process and characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). CuZn NPs effects in Arabidopsis leaves were evaluated by chlorophyll fluorescence imaging analysis that revealed spatiotemporal heterogeneity of the quantum efficiency of PSII photochemistry (&Phi;PS&Iota;&Iota;) and the redox state of the plastoquinone (PQ) pool (qp), measured 30 min, 90 min, 180 min, and 240 min after spraying. Photosystem II (PSII) function in young leaves was observed to be negatively influenced, especially 30 min after spraying, at which point increased H2O2 generation was correlated to the lower oxidized state of the PQ pool. Recovery of young leaves photosynthetic efficiency appeared only after 240 min of NPs spray when also the level of ROS accumulation was similar to control leaves. On the contrary, a beneficial effect on PSII function in mature leaves after 30 min of the CuZn NPs spray was observed, with increased &Phi;PS&Iota;&Iota;, an increased electron transport rate (ETR), decreased singlet oxygen (1O2) formation, and H2O2 production at the same level of control leaves.An explanation for this differential response is suggested

Rapid Hormetic Responses of Photosystem II Photochemistry of Clary Sage to Cadmium Exposure

Five-day exposure of clary sage (Salvia sclarea L.) to 100 &mu;M cadmium (Cd) in hydroponics was sufficient to increase Cd concentrations significantly in roots and aboveground parts and affect negatively whole plant levels of calcium (Ca) and magnesium (Mg), since Cd competes for Ca channels, while reduced Mg concentrations are associated with increased Cd tolerance. Total zinc (Zn), copper (Cu), and iron (Fe) uptake increased but their translocation to the aboveground parts decreased. Despite the substantial levels of Cd in leaves, without any observed defects on chloroplast ultrastructure, an enhanced photosystem II (PSII) efficiency was observed, with a higher fraction of absorbed light energy to be directed to photochemistry (&Phi;PS&Iota;&Iota;). The concomitant increase in the photoprotective mechanism of non-photochemical quenching of photosynthesis (NPQ) resulted in an important decrease in the dissipated non-regulated energy (&Phi;NO), modifying the homeostasis of reactive oxygen species (ROS), through a decreased singlet oxygen (1O2) formation. A basal ROS level was detected in control plant leaves for optimal growth, while a low increased level of ROS under 5 days Cd exposure seemed to be beneficial for triggering defense responses, and a high level of ROS out of the boundaries (8 days Cd exposure), was harmful to plants. Thus, when clary sage was exposed to Cd for a short period, tolerance mechanisms were triggered. However, exposure to a combination of Cd and high light or to Cd alone (8 days) resulted in an inhibition of PSII functionality, indicating Cd toxicity. Thus, the rapid activation of PSII functionality at short time exposure and the inhibition at longer duration suggests a hormetic response and describes these effects in terms of &ldquo;adaptive response&rdquo; and &ldquo;toxicity&rdquo;, respectively

Extracts of Non-Microcystin-Producing Cyanobacteria Affect the Plant Cytoskeleton and Cell Cycle

Studies on the toxicity of cyanobacterial products on plant cytoskeleton have so far focused on the effects of microcystins (MCs), cyanobacterial toxins that inhibit protein phosphatases 1 and 2A, enzymes which are involved in plant cytoskeleton (microtubules and F-actin) organization and cell cycle progression. In this study, we investigated the effects of extracts from two non-microcystin-producing (NMP) cyanobacterial strains, Microcystis viridis TAU-MAC 1810 and Planktothrix agardhii TAU-MAC 0514, on the cytoskeleton and cell cycle of Oryza sativa (rice) root cells. Rice seedling roots were exposed for various time periods (1, 12 and 24 h) to aqueous extracts of the aforementioned strains. Treated root tips underwent either immunostaining for α-tubulin or staining of F-actin with fluorescent phalloidin, and DAPI staining of DNA. Fluorescent specimens were observed by confocal laser scanning microscopy (CLSM). Corrected total cell fluorescence (CTCF) was measured to quantify F-actin disorder. To assess cell cycle alterations, cell cycle stage frequencies were calculated. In addition, Evans Blue staining was applied to determine dead cells. Treatment with the extracts affected microtubules and F-actin, as well as the cell cycle. These findings suggest that bioactive cyanobacterial compounds, apart from MCs, can disrupt the cytoskeleton and cell cycle progression in plant cells

Double Puzzle: Morphogenesis of the Bi-Layered Leaf Adaxial Epidermis of Magnolia grandiflora

Anticlinal ordinary epidermal cell wall waviness is a widespread feature found in the leaves of a variety of land plant species. However, it has not yet been encountered in leaves with multiple epidermides. Surprisingly, in Magnolia grandiflora leaves, ordinary epidermal cells in both layers of the bi-layered adaxial epidermis exhibit wavy anticlinal contour. During the development of the above cells, cortical microtubules are organized in anticlinally oriented bundles under the anticlinal walls, and radial arrays extending from the bundles at the edges of anticlinal and external periclinal walls, under the external periclinal walls. This microtubule pattern is followed by cell wall reinforcement with local thickenings, the cellulose microfibrils of which are parallel to the underlying microtubules. This specialized microtubule organization and concomitant cell wall reinforcement is initiated in the external epidermal layer, while hypodermis follows. The waviness pattern of each epidermal layer is unrelated to that of the other. The above findings are discussed in terms of morphogenetic mechanism induction and any implications in the functional significance of ordinary epidermal cell waviness

Plant response mechanisms against the toxicity of tungsten

Tungsten (W) is a rare heavy metal, widely used in a range of industrial, military and household applications, due to its properties. Much work was conducted on W toxicity in animals and humans, less in ecosystems and much less in plants. In plants, W has been used as an inhibitor of the molybdoenzymes since it antagonizes molybdenum (Mo) for the Mo-cofactor (MoCo) of these enzymes. Awareness about the potential environmental toxicity of W is steadily growing. However, its specific subcellular effects remain more or less unknown. In the present study the effects of W on a range of morphological, cytological, subcellular and molecular parameters have been investigated, in combination with the possible antagonism of W for the pathway of Mo. W was applied in the form of tungstate (Na2WO4) at various concentrations in various plants and its effects were analyzed macroscopically, statistically, by molecular techniques etc. Seedlings of Pisum sativum were treated W, Mo or a combination of the two, had W-affected cortical microtubules that were low in number, short, not uniformly arranged and resistant to anti-microtubule drugs. The results indicate that cortical microtubules of plant cells are indirectly affected by W, most probably through a mechanism depending on the in vivo antagonism of W for the Mo-binding site of Cnx1 protein. This has been further established through experimentation on the cnx mutants of Nicotiana plumbaginifolia and Arabidopsis thaliana, and via an in vitro binding assay of W to Cnx1. In particular, null mutants of the Cnx1 protein appeared insensitive to W, especially regarding microtubules or Mo-enzymes. In order to examine the possible universality of this effect (disruption of cortical microtubules), treatments with tungstate were applied in various land plant taxa. W was applied on terrestrial plant representatives of monocots, dicots, gymnosperms, pterophytes and bryophytes, and the microtubules were investigated by tubulin immunofluorescence. However, the mechanism by which W affects the microtubule cytoskeleton remains elusive, and could be a side-effect of programmed cell death (PCD)-related processes, as it was found in Pisum sativum plants. W was also applied on Arabidopsis thaliana roots and several other effects, probably not related with the NO-depleting action of W, were revealed. In particular, W induced cells of the transition and elongation zones to differentiate prematurely, so that development of root hairs in W-treated seedlings took place closer to the root tip than in the controls. Results obtained from the present study indicate that, W is an emerging pollutant having not only the attributes of an inhibitor but also additional toxic effects to plant cells, some of which are similar with that of other heavy metals, including inhibition of seedling growth, reduction of root and shoot biomass, ultrastructural malformations of cell components, aberrations of the cell cycle, disruption of the cytoskeleton and deregulation of gene expression related with PCD.Το βολφράμιο (W) είναι ένα σπάνιο βαρύ μέταλλο, που χρησιμοποιείται ευρέως σε μια σειρά βιομηχανικών, στρατιωτικών και οικιακών εφαρμογών. Οι σχετικές έρευνες έχουν επικεντρωθεί στην τοξικότητα του W στα ζώα και τους ανθρώπους, λιγότερο στα οικοσυστήματα και πολύ λιγότερο στα φυτά. Στα τελευταία, το W έχει χρησιμοποιηθεί πρώτιστα ως ανασταλτικός παράγοντας των μολυβδαινιο-ενζύμων δεδομένου ότι ανταγωνίζεται το μολυβδαίνιο (Mo) για τη σύνδεσή του στο συμπαράγοντα του μολυβδαινίου (MoCo) των ενζύμων αυτών. Στην παρούσα διατριβή διερευνήθηκε η επίδραση του W σε διάφορα επίπεδα, μορφολογικά, κυτταρικά, μοριακά κ.ά., σε σχέση με τον πιθανό ανταγωνισμό του W με το Mo. Το W εφαρμόστηκε υπό τη μορφή του βολφραμικού νατρίου σε διάφορες συγκεντρώσεις και χρόνους επίδρασης σε διάφορα φυτά. Σε αρτίβλαστα Pisum sativum πραγματοποιήθηκαν επιδράσεις W, Mo ή συνδυασμοί των δύο, και οι περιφερειακοί μικροσωληνίσκοι εξετάστηκαν με ανοσοσήμανση σωληνίνης και ηλεκτρονική μικροσκοπία. Οι επηρεασμένοι με W μικροσωληνίσκοι (W-μικροσωληνίσκοι) ήταν περιορισμένοι σε αριθμό, όχι ομοιόμορφα κατανεμημένοι και ανθεκτικοί σε αντι-μιτωτικά δηλητήρια. Η πρωτεΐνη Cnx1 μπορεί να μετέχει στη συγκεκριμένη απόκριση. Αυτό έχει περαιτέρω εδραιωθεί μετά από πειραματισμό σε μεταλλάγματα cnx των Nicotiana plumbaginifolia και Arabidopsis thaliana και μέσω μιας διαδικασίας in vitro δέσμευσης του W στη Cnx1. Ειδικότερα, μεταλλάγματα της πρωτεΐνης Cnx1 εμφανίστηκαν ανθεκτικά στη δράση του W (μικροσωληνίσκοι ή Mo-ένζυμα). Προκειμένου να εξεταστεί η ενδεχόμενη καθολικότητα αυτής της απόκρισης (διαταραχή των περιφερειακών μικροσωληνίσκων), πραγματοποιήθηκαν επιδράσεις W σε διάφορα φυτικά taxa, εκπροσώπους των χερσαίων φυτών, μονοκοτυλήδονων, δικοτυλήδονων, γυμνοσπέρμων, πτεριδοφύτων και βρυοφύτων. Ο μηχανισμός με τον οποίο το W έχει επιπτώσεις στον κυτταρικό σκελετό των μικροσωληνίσκων παραμένει αόριστος, εντούτοις θα μπορούσε η αποδιοργάνωση των μικροσωληνίσκων να είναι μια παρενέργεια της εκδήλωσης προγραμματισμένου κυτταρικού θανάτου (PCD) κυττάρων, όπως παρατηρήθηκε για το Pisum sativum. Το W εφαρμόστηκε επίσης στις ρίζες του φυτού Arabidopsis thaliana. Τα αποτελέσματα έδειξαν ότι η δράση του W σε αυτές πιθανώς δεν σχετίζεται με την ιδιότητά του να λειτουργεί ως αναστολέας του ΝΟ. Tο W μείωσε την αύξηση της ρίζας επάγοντας τα κύτταρα της μεταβατικής ζώνης και της ζώνης επιμήκυνσης να διαφοροποιούνται πρόωρα, έτσι ώστε η ανάπτυξη των ριζικών τριχιδίων στα επηρεασμένα από W αρτίβλαστα να αρχίζει πιο κοντά στην άκρη της ρίζας από ό,τι στο μάρτυρα. Η παρούσα μελέτη δείχνει ότι, πέρα από την παρεμπόδιση των Mo-ενζύμων, το W είναι ένας νέος αναδυόμενος ρύπος που έχει όχι μόνο τις ιδιότητες ενός ανασταλτικού παράγοντα ενζύμων αλλά και τοξικά χαρακτηριστικά ενός μετάλλου, μερικά από τα οποία είναι παρόμοια με αυτά άλλων μετάλλων, συμπεριλαμβανόμενης της αναστολής αύξησης των αρτιβλάστων, δυσμορφίες των κυττάρων, αναστολή της μίτωσης, διαταραχή του κυτταρικού σκελετού και της έκφρασης των γονιδίων που σχετίζονται με τον PCD

Structural Evidence of Programmed Cell Death Induction by Tungsten in Root Tip Cells of Pisum sativum

Previous studies have shown that excess tungsten (W), a rare heavy metal, is toxic to plant cells and may induce a kind of programmed cell death (PCD). In the present study we used transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) to investigate the subcellular malformations caused by W, supplied as 200 mg/L sodium tungstate (Na2WO4) for 12 or 24 h, in root tip cells of Pisum sativum (pea), The objective was to provide additional evidence in support of the notion of PCD induction and the presumed involvement of reactive oxygen species (ROS). It is shown ultrastructurally that W inhibited seedling growth, deranged root tip morphology, induced the collapse and deformation of vacuoles, degraded Golgi bodies, increased the incidence of multivesicular and multilamellar bodies, and caused the detachment of the plasma membrane from the cell walls. Plastids and mitochondria were also affected. By TEM, the endoplasmic reticulum appeared in aggregations of straight, curved or concentric cisternae, frequently enclosing cytoplasmic organelles, while by CLSM it appeared in bright ring-like aggregations and was severely disrupted in mitotic cells. However, no evidence of ROS increase was obtained. Overall, these findings support the view of a W-induced vacuolar destructive PCD without ROS enhancement

Tungsten Toxicity in Plants

Tungsten (W) is a rare heavy metal, widely used in a range of industrial, military and household applications due to its unique physical properties. These activities inevitably have accounted for local W accumulation at high concentrations, raising concerns about its effects for living organisms. In plants, W has primarily been used as an inhibitor of the molybdoenzymes, since it antagonizes molybdenum (Mo) for the Mo-cofactor (MoCo) of these enzymes. However, recent advances indicate that, beyond Mo-enzyme inhibition, W has toxic attributes similar with those of other heavy metals. These include hindering of seedling growth, reduction of root and shoot biomass, ultrastructural malformations of cell components, aberration of cell cycle, disruption of the cytoskeleton and deregulation of gene expression related with programmed cell death (PCD). In this article, the recent available information on W toxicity in plants and plant cells is reviewed, and the knowledge gaps and the most pertinent research directions are outlined

Cortical microtubule orientation in Arabidopsis thaliana root meristematic zone depends on cell division and requires severing by katanin

Abstract Background Transverse cortical microtubule orientation, critical for anisotropic cell expansion, is established in the meristematic root zone. Intending to elucidate the possible prerequisites for this establishment and factors that are involved, microtubule organization was studied in roots of Arabidopsis thaliana, wild-type and the p60-katanin mutants fra2, ktn1-2 and lue1. Transverse cortical microtubule orientation in the meristematic root zone has proven to persist under several regimes inhibiting root elongation. This persistence was attributed to the constant moderate elongation of meristematic cells, prior to mitotic division. Therefore, A. thaliana wild-type seedlings were treated with aphidicolin, in order to prevent mitosis and inhibit premitotic cell elongation. Results In roots treated with aphidicolin for 12 h, cell divisions still occurred and microtubules were transverse. After 24 and 48 h of treatment, meristematic cell divisions and the prerequisite elongation ceased, while microtubule orientation became random. In meristematic cells of the p60-katanin mutants, apart from a general transverse microtubule pattern, cortical microtubules with random orientation were observed, also converging at several cortical sites, in contrast to the uniform transverse pattern of wild-type cells. Conclusion Taken together, these observations reveal that transverse cortical microtubule orientation in the meristematic zone of A. thaliana root is cell division-dependent and requires severing by katanin