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

Heavy Metal Toxicity Effects on Plants

Although heavy metals are naturally present in the soil, geologic and anthropogenic activities increase the concentration of these elements to amounts that are harmful to plants [...

Photosynthetic and metabolic responses of Arabidopsis thaliana to drought stress

In the present work, the photosynthetic and metabolic responses of the model plant Arabidopsis thaliana to drought stress were studied. Using chlorophyll fluorescence imaging, the effect of mild, moderate and severe drought stress on photosystem II (PSII) photochemistry was examined. Spatio-temporal heterogeneity in all chlorophyll fluorescence parameters was maintained throughout drought stress. It was found that under mild and severe drought stress, the quantum yield of PSII was decreased, while under moderate stress the function of PSII was maintained. Under moderate drought stress, the antioxidant mechanism of A.thaliana leaves seemed to be sufficient in scavenging reactive oxygen species (ROS), as was evident by the decreased lipid peroxidation. After exposure to drought stress, the quantum yield of PSII photochemistry decreased less in the proximal (base) leaf than in the distal (tip) leaf. The non-uniform photosynthetic pattern under drought stress may reflect different zones of leaf anatomy and mesophyll development. It was also observed that the exogenous application of proline on A.thaliana plants under drought stress, increased the quantum yield of PSII, contributed to ROS scavenging and caused an increase of soluble sugars, suggesting a possible interaction between the signal pathway of proline and that of soluble sugars. The synergistic action of proline and soluble sugars is possibly part of a redox system that helps scavenging ROS and contributes to drought stress tolerance, with proline having a dual function as an osmolyte and as an antioxidant. However, the exogenous application of proline under normal growth conditions led to an imbalance of the photosynthetic redox state and caused a decrease of the quantum yield of PSII in young and mature leaves. The decrease of the quantum yield of PSII was higher in mature leaves with exogenous application of proline than in young leaves. It seems that, under normal growth conditions, the capacity of mature leaves to catabolize proline is greater than that of young leaves, as was evident by the lower concentration of proline in the former, which led to a more reduced state of the first electron acceptor of PSII, quinone A (QA), as well as to an increased susceptibility of mature leaves to photoinhibition. The photoprotective mechanisms of mature and young leaves of A.thaliana plants under drought stress was also studied. As young leaves managed to dissipate excess light energy, excitation pressure was lower and QA was in a more oxidized state. Thus, the redox state of the photosynthetic electron transport chain probably functioned as signal for the increased induction of anthocyanin biosynthesis in young leaves. Soluble sugar concentration was also higher in young leaves and was possibly responsible for increased biosynthesis of anthocyanins. Flavonoids and anthocyanins seem to offer a long-term protection by contributing to ROS scavenging. The higher accumulation of all the above metabolites provided a better photoprotective mechanism for young leaves, which resulted in higher drought tolerance compared to mature leaves.Στην παρούσα εργασία, μελετήθηκαν οι φωτοσυνθετικές και μεταβολικές αποκρίσεις του φυτού μοντέλου Arabidopsis thaliana στο στρες ξηρασίας. Συγκεκριμένα, με τη μέθοδο της απεικόνισης του φθορισμού της χλωροφύλλης, μελετήσαμε την επίδραση του ήπιου, του μέτριου και του έντονου στρες ξηρασίας στη λειτουργία του φωτοσυστήματος ΙΙ (PSII). Παρατηρήθηκε ότι οι επιδράσεις του στρες ξηρασίας στις παραμέτρους φθορισμού χλωροφύλλης εμφανίζουν χρονική και χωρική ετερογένεια. Βρέθηκε ότι το ήπιο και το έντονο στρες ξηρασίας μείωσαν την απόδοση του PSII, ενώ σε συνθήκες μέτριου στρες ξηρασίας παρατηρήθηκε βελτίωση στη λειτουργία του, η οποία οφειλόταν στην επαρκή αντιοξειδωτική προστασία από την παραγωγή ενεργών μορφών οξυγόνου (ROS), όπως προέκυψε από τον προσδιορισμό της υπεροξείδωσης των λιπιδίων. Η λειτουργικότητα του PSII βρέθηκε ότι μειώνεται παραπάνω στην άκρη του φύλλου σε σχέση με τη βάση του, γεγονός που πιθανόν αντανακλά διαφορετικές ανατομικές ζώνες του φύλλου, οι οποίες αντικατοπτρίζουν διαφορετικό αναπτυξιακό στάδιο. Επιπλέον, βρήκαμε ότι η εξωγενής επίδραση προλίνης σε φυτά A. thaliana με στρες ξηρασίας βελτίωσε την απόδοση του PSII, συνετέλεσε στη μείωση των ROS και προκάλεσε την αύξηση της συγκέντρωσης των υδατανθράκων, γεγονός που συνηγορεί στη διαπίστωση ότι το σηματοδοτικό μονοπάτι της προλίνης αλληλεπιδρά με το σηματοδοτικό μονοπάτι των υδατανθράκων. Η συνεργιστική δραση προλίνης και υδατανθράκων αποτελεί πιθανόν μέρος ενός αντιοξειδωτικού συστήματος που συντελεί στην απομάκρυνση των ROS και συμβάλλει στην ανθεκτικότητα στο στρες ξηρασίας, με την προλίνη να εμφανίζει μια διττή λειτουργία, ως ωσμωλύτης και ως αντιοξειδωτική ένωση. Ωστόσο, η εξωγενής επίδραση προλίνης σε φυσιολογικές συνθήκες ανάπτυξης οδήγησε σε διαταραχή της φωτοσυνθετικής οξειδοαναγωγικής ομοιόστασης και προκάλεσε μείωση στην απόδοση του PSII, τόσο σε νεαρά, όσο και σε ώριμα φύλλα. Συγκεκριμένα, η μείωση της απόδοσης του PSII ήταν μεγαλύτερη στα ώριμα φύλλα με εξωγενή επίδραση προλίνης συγκριτικά με τα νεαρά. Φαίνεται ότι, υπό φυσιολογικές συνθήκες, η ικανότητα των ώριμων φύλλων να καταβολίζουν την προλίνη περισσότερο σε σχέση με τα νεαρά, όπως φάνηκε από τη μικρότερη συγκέντρωση προλίνης στα πρώτα, οδήγησε σε περισσότερο ανηγμένη κατάσταση του πρώτου δέκτη ηλεκτρονίων του PSII, την κινόνη Α (QA) και σε μία αυξημένη ευαισθησία των ώριμων φύλλων στη φωτοαναστολή. Μελετήσαμε, επίσης, τους φωτοπροστατευτικούς μηχανισμούς ώριμων και νεαρών φύλλων A. thaliana σε στρες ξηρασίας. Καθώς τα νεαρά φύλλα μπόρεσαν να αποβάλουν τη μη-φωτοχημικά αξιοποιήσιμη ενέργεια, η ενέργεια αποδιέγερσης σε αυτά ήταν μικρότερη σε σχέση με τα ώριμα φύλλα και η QA βρισκόταν σε περισσότερο οξειδωμένη κατάσταση. Αυτό πιθανόν συνετέλεσε, ώστε η οξειδοαναγωγική κατάσταση της φωτοσυνθετικής αλυσίδας μεταφοράς ηλεκτρονίων να λειτουργήσει ως σήμα για την επαγωγή αυξημένης βιοσύνθεσης ανθοκυανινών στα νεαρά φύλλα. Επιπλέον, η μεγαλύτερη συγκέντρωση υδατανθράκων στα νεαρά φύλλα πιθανόν λειτούργησε σηματοδοτικά για την αυξημένη βιοσύνθεση ανθοκυανινών σε αυτά. Tα φλαβονοειδή και οι ανθοκυανίνες φαίνεται να συνεισφέρουν στην αποτελεσματικότερη φωτοπροστασία μακροπρόθεσμα, συντελώντας στη μείωση των ROS. Η μεγαλύτερη συσσώρευση όλων των παραπάνω μεταβολιτών προσέφερε καλύτερη φωτοπροστασία στα νεαρά φύλλα, με αποτέλεσμα τη μεγαλύτερη ανθεκτικότητα στο στρες ξηρασίας συγκριτικά με τα ώριμα

Harnessing Chlorophyll Fluorescence for Phenotyping Analysis of Wild and Cultivated Tomato for High Photochemical Efficiency under Water Deficit for Climate Change Resilience

Fluctuations of the weather conditions, due to global climate change, greatly influence plant growth and development, eventually affecting crop yield and quality, but also plant survival. Since water shortage is one of the key risks for the future of agriculture, exploring the capability of crop species to grow with limited water is therefore fundamental. By using chlorophyll fluorescence analysis, we evaluated the responses of wild tomato accession Solanum pennellii LA0716, Solanum lycopersicum cv. Μ82, the introgression line IL12-4 (from cv. M82 Χ LA0716), and the Greek tomato cultivars cv. Santorini and cv. Zakinthos, to moderate drought stress (MoDS) and severe drought stress (SDS), in order to identify the minimum irrigation level for efficient photosynthetic performance. Agronomic traits (plant height, number of leaves and root/shoot biomass), relative water content (RWC), and lipid peroxidation, were also measured. Under almost 50% deficit irrigation, S. pennellii exhibited an enhanced photosynthetic function by displaying a hormetic response of electron transport rate (ETR), due to an increased fraction of open reaction centers, it is suggested to be activated by the low increase of reactive oxygen species (ROS). A low increase of ROS is regarded to be beneficial by stimulating defense responses and also triggering a more oxidized redox state of quinone A (QA), corresponding in S. pennellii under 50% deficit irrigation, to the lowest stomatal opening, resulting in reduction of water loss. Solanumpennellii was the most tolerant to drought, as it was expected, and could manage to have an adequate photochemical function with almost 30% water regime of well-watered plants. With 50% deficit irrigation, cv. Μ82 and cv. Santorini did not show any difference in photochemical efficiency to control plants and are recommended to be cultivated under deficit irrigation as an effective strategy to enhance agricultural sustainability under a global climate change. We conclude that instead of the previously used Fv/Fm ratio, the redox state of QA, as it can be estimated by the chlorophyll fluorescence parameter 1 - qL, is a better indicator to evaluate photosynthetic efficiency and select drought tolerant cultivars under deficit irrigation

Early Drought Stress Warning in Plants: Color Pictures of Photosystem II Photochemistry

Drought, the major limiting factor for plant growth and crop productivity, affecting several physiological and biochemical processes, is expected to increase in duration, intensity, and frequency as a consequence of climate change. Plants have developed several approaches to either avoid or tolerate water deficit. Plants as a response to drought stress (DS), close stomata, reducing carbon dioxide (CO2) entry in the leaf, thus decreasing photosynthesis which results in reduced synthesis of essential organic molecules that sustain the life on earth. The reduced CO2 fixation, decreases electron transport rate (ETR), while the absorbed light energy overdoes what can be used for photochemistry resulting in excess reactive oxygen species (ROS) and oxidative stress. Current imaging techniques allow non-destructive monitoring of changes in the physiological state of plants under DS. Thermographic visualization, near-infrared imaging, and chlorophyll a fluorescence imaging are the most common verified imaging techniques for detecting stress-related changes in the display of light emission from plant leaves. Chlorophyll a fluorescence analysis, by use of the pulse amplitude modulation (PAM) method, can principally calculate the amount of absorbed light energy that is directed for photochemistry in photosystem II (PSII) (ΦPSII), dissipated as heat (ΦNPQ), or dissipated by the non-radiative fluorescence processes (ΦNO). The method of chlorophyll a fluorescence imaging analysis by providing colour pictures of the whole leaf PSII photochemistry, can successfully identify the early drought stress warning signals. Its implementation allowed visualization of the leaf spatial photosynthetic heterogeneity and discrimination between mild drought stress (MiDS), moderate drought stress (MoDS), and severe drought stress (SDS). The fraction of open reaction centers of PSII (qp) is suggested as the most sensitive and suitable indicator of an early drought stress warning and also for selecting drought tolerant cultivars

Photochemical changes and oxidative damage in the aquatic macrophyte Cymodocea nodosa exposed to paraquat-induced oxidative stress

The non-selective herbicide paraquat (Pq) is being extensively used for broad-spectrum weed control. Through water runoff and due to its high water solubility it contaminates aquatic environments. Thus, the present study was carried out to investigate the photochemical changes and oxidative damage in the aquatic macrophyte Cymodocea nodosa to short- (2 h) and long-term (24 h) exposure to 2,20, 200 and 1000 mu M paraquat (Pq) toxicity by using chlorophyll fluorescence imaging and H2O2 real-time imaging. The effective quantum yield of PSII (Phi(PSII)) show a tendency to increase at 2 mu M Pq after 2 h exposure, and increased significantly at 20 and 200 mu M Pq. The maximum oxidative effect on C. nodosa leaves was observed 2 h after exposure to 200 mu M Pq concentration when the highest increases of (Phi(PSII) due to high electron transport rate (ETR) resulted in a significant increase of H2O2 production due to the lowest non-photochemical quenching (NPQ) that was not efficient to serve as a protective mechanism, resulting in photooxidation. Prolonged exposure (24 h) to 200 mu M Pq resulted in a decreased Phi(PSII) not due to an increase of the photoprotective mechanism NPQ but due to high quantum yield of non-regulated energy loss in PSII (Phi(NO)), resulting to the lowest fraction of open PSII reaction centers (q(p)). This decreased Phi(PSII) has resulted to less Pq radicals to be formed, with a consequence of a small increase of H2O2 production compared to control C. nodosa leaves, but substantial lower than that of 2 h exposure to 200 mu M Pq. Exposure of C. nodosa leaves to 1000 mu M Pq toxicity had lower effects on the efficiency of photochemical reactions of photosynthesis under both short- (2 h) and long-term (24 h) exposure than 200 mu M Pq. This was evident by an almost unchanged Phi(PSII) and q(p), that remained unchanged even at a longer exposure time (48 h), compared to control C. nodosa leaves. Thus, the response of C. nodosa leaves to Pq toxicity fits the "Threshold for Tolerance Model", with a threshold concentration of 200 mu M Pq required for initiation of a tolerance mechanism, by increasing H2O2 production for the induction of genes encoding protective processes in response to Pq-induced oxidative stress. Overall, it is concluded that chlorophyll fluorescence imaging constitutes a promising basis for investigating herbicide mode of action in aquatic plants and for detecting their protective mechanisms. (C) 2015 Elsevier Inc. All rights reserved

Photosystem II Is More Sensitive than Photosystem I to Al3+ Induced Phytotoxicity

Aluminium (Al) the most abundant metal in the earth&rsquo;s crust is toxic in acid soils (pH &lt; 5.5) mainly in the ionic form of Al3+ species. The ability of crops to overcome Al toxicity varies among crop species and cultivars. Here, we report for a first time the simultaneous responses of photosystem II (PSII) and photosystem I (PSI) to Al3+ phytotoxicity. The responses of PSII and PSI in the durum wheat (Triticum turgidum L. cv. &lsquo;Appulo E&rsquo;) and the triticale (X Triticosecale Witmark cv. &lsquo;Dada&rsquo;) were evaluated by chlorophyll fluorescence quenching analysis and reflection spectroscopy respectively, under control (&minus;Al, pH 6.5) and 148 &mu;M Al (+Al, pH 4.5) conditions. During control growth conditions the high activity of PSII in &lsquo;Appulo E&rsquo; led to a rather higher electron flow to PSI, which induced a higher PSI excitation pressure in &lsquo;Appulo E&rsquo; than in &lsquo;Dada&rsquo; that presented a lower PSII activity. However, under 148 &mu;M Al the triticale &lsquo;Dada&rsquo; presented a lower PSII and PSI excitation pressure than &lsquo;Appulo E&rsquo;. In conclusion, both photosystems of &lsquo;Dada&rsquo; displayed a superior performance than &lsquo;Appulo E&rsquo; under Al exposure, while in both cultivars PSII was more affected than PSI from Al3+ phytotoxicity

Copper bioaccumulation, photosystem II functioning, and oxidative stress in the seagrass Cymodocea nodosa exposed to copper oxide nanoparticles

Photosynthetic activity, oxidative stress, and Cu bioaccumulation in the seagrass Cymodocea nodosa were assessed 4, 12, 24, 48, and 72 h after exposure to two copper oxide nanoparticle (CuO NP) concentrations (5 and 10 mg L-1). CuO NPs were characterized by scanning electron microscopy (SEM) and dynamic light scattering measurements (DLS). Chlorophyll fluorescence analysis was applied to detect photosystem II (PSII) functionality, while the Cu accumulation kinetics into the leaf blades was fitted to the Michaelis-Menten equation. The uptake kinetics was rapid during the first 4 h of exposure and reached an equilibrium state after 10 h exposure to 10 mg L-1 and after 27 h to 5 mg L-1 CuO NPs. As a result, 4-h treatment with 5 mg L-1 CuO NPs, decreased the quantum yield of PS II photochemistry (Phi (PSI (TM) I (TM)) ) with a parallel increase in the regulated non-photochemical energy loss in PSII (Phi(NPQ) ). However, the photoprotective dissipation of excess absorbed light energy as heat, through the process of non-photochemical quenching (NPQ), did not maintain the same fraction of open reaction centers (q(p) ) as in control plants. This reduced number of open reaction centers resulted in a significant increase of H2O2 production in the leaf veins serving possibly as an antioxidant defense signal. Twenty-four-hour treatment had no significant effect on Phi (PSI (TM) I (TM)) and q(p) compared to controls. However, 24 h exposure to 5 mg L-1 CuO NPs increased the quantum yield of non-regulated energy loss in PSII (Phi (NO) ), and thus the formation of singlet oxygen (O-1(2)) via the triplet state of chlorophyll, possible because the uptake kinetics had not yet reached the equilibrium state as did 10 mg L-1. Longer-duration treatment (48 and 72 h) had less effect on the allocation of absorbed light energy at PSII and the fraction of open reaction centers, compared to 4-h treatment, suggesting the function of a stress defense mechanism. The response of C. nodosa leaves to CuO NPs fits the "Threshold for Tolerance Model" with a threshold time (more than 4 h) required for induction of a stress defense mechanism, through H2O2 production