In the recent years, the rapid advancement in the field of nanomaterials (NMs) increased their development, production and commercialization. Among NMs, the carbon-based ones are the most widely researched because of their potential on the most diverse fields, with a predominant role occupied by Graphene-Related Materials (GRMs). Graphene is a two-dimensional, single layer sheet of carbon atoms organized in a honeycombed network with six-membered rings. Since its discovery, the attention of researchers was focused on its unique and exceptional properties, such as mechanical stiffness, strength, elasticity, very high electrical and thermal conductivity, which led to the development of numerous applications. Even if GRMs-enabled products have undeniable advantages, an involuntary release of GRMs nanoparticles (NPs) into the environment should be expected during their life cycle. Moreover, applications involving a direct release of GRMs-composites in the environment are under development, such us pesticides, fertilizers and paintings. Thus, GRMs have all the traits of emerging persistent pollutants: they have (i) increasing production volumes, (ii) a broad range of applications, and (iii) potentially harmful effects on organisms. GRM particles of micro- and nanometric size are extremely lightweight and, thus, could easily be aerodispersed for long distances, being intercepted by the aboveground organs of seed plants, i.e., leaves, stems, and flowers, which are natural traps for airborne particulate matter. So far, widely varying effects of GRMs on seed plants have been reported, from positive to negative, possibly owing to different experimental conditions (materials, concentrations, exposure time, protocols, etc.) and/or species tested. Unfortunately, there are only few in vitro studies focusing on the effects of these materials on the sexual reproduction of seed plants. The main aim of this PhD project is to assess the in vivo effect of GRMs on the sexual reproduction of seed plants. The effect of few-layer graphene (FLG) was compared with muscovite mica, a natural 2D NM, on pollen viability, stigma integrity and on their interaction in terms of pollen adhesion and germination on the stigma of the economically important and model plant Cucurbita pepo L (summer squash). Then, in two similar study, graphene oxide (GO) and purified-GO (PGO) were tested on pollen stigma interaction and fruit and seed production and development of C. pepo. First using amount far from a realistic scenario and then applying environmental-compatible dry depositions of the two materials. A fourth study focused on anemophilous species, because they might be the most exposed to airborne GRMs. A dedicated set-up was used to verify if airborne GO and PGO can be entrapped by anemophilous stigmas, and if they affects the pollen-stigma system or interact with liquid water possibly present on stigmas. Finally, the hypothesis of a stigmatic buffer capability was tested on four species selected for their pollination biology and stigmatic features. Stigmas were soaked in NaNO3 solutions. pH variations of solutions with or without stigmas were monitored progressively adding GRMs, while acid solutions were used as positive control. The stigmatic exudates were analysed to verify the presence of substances with buffering properties. According to the results obtained, GRM NPs released in atmosphere can be considered per se no more hazardous than similar layered naturally occurring NMs. On the other hand, the phytotoxic substances (i.e., strong acids and oxidants) used to produce GO and still adherent to its flakes can hinder the finely tuned communication between pollen and stigma, altering the reproduction process. Therefore, the application of accurate purification procedures before the use of GRMs should be considered in view of a "safer-by-design" approach
La ricerca sui nanomateriali (NMs) è avanzata molto recentemente. Tra i NMs, quelli a base di carbonio sono i maggiormente studiati per le loro applicazioni in vari campi, con un ruolo predominante occupato dai materiali a base di grafene (GRMs). Il grafene è un materiale bidimensionale, formato da uno strato monoatomico di atomi di carbonio, disposti in un reticolo a nido d’ape. Dalla sua scoperta, l’attenzione si è focalizzata sulle su proprietà quali rigidità, resistenza, elasticità e conducibilità elettrica e termica, che hanno portato allo sviluppo di molte applicazioni. Anche se i prodotti basati su GRMs hanno innegabili vantaggi, è prevedibile un rilascio involontario di nanoparticelle (NPs) di GRMs nell’ambiente durante tutta la loro vita. Inoltre, sono al vaglio applicazioni con rilascio diretto nell’ambiente di composti contenenti GRMs, per esempio pesticidi, fertilizzanti e pitture. Perciò, i GRMs hanno tutti i tratti di inquinanti emergenti: (i) sono prodotti in grandi volumi, (ii) hanno una grande varietà d’applicazioni, e (iii) sono potenzialmente dannosi per gli organismi. Particelle di GRMs sono estremamente leggere, perciò possono essere facilmente aerodisperse, venendo, poi, intercettate dagli organi aerei delle piante a seme, i.e., foglie, fusti e fiori, che sono trappole naturali per il particolato sospeso. Ad ora, gli effetti dei GRMs riportati per le piante sono vari, probabilmente a causa delle diverse condizioni sperimentali (materiali, concentrazioni, tempi di esposizione, protocolli, etc.) e/o delle specie usate. Purtroppo, ci sono pochi studi in vitro sugli effetti di questi materiali sulla riproduzione sessuale delle piante a seme. Lo scopo principale di questo progetto di dottorato è quello di verificare l’effetto in vivo dei GRMs sulla riproduzione sessuale delle piante a seme. L’effetto del few-layer grafene (FLG) è stato comparato con quello della muscovite, un NM bidimensionale, su vitalità del polline, integrità dello stigma e sulla loro interazione in termini di adesione e germinazione del polline sullo stigma nella pianta modello Cucurbita pepo L. (zucchina). In seguito, due studi similari sono stati condotti testando grafene ossido (GO) e GO-purificato (PGO) sull’interazione polline-stigma e sulla produzione e sviluppo di frutti e semi in C. pepo. Prima usando quantitativi dei due materiali lontani da uno scenario realistico e poi applicando deposizioni secche a possibili livelli ambientali. Un quarto studio si è focalizzato su specie anemofile, poiché queste potrebbero essere maggiormente esposte a GRMs aero-sospesi. Un set-up dedicato è stato sviluppato per verificare se GO e PGO aero-sospesi possano essere intercettati da stigmi di piante anemofile, danneggiare la comunicazione tra polline e stigma o interagire con acqua liquida presente sugli stigmi. Infine, l’ipotesi di una capacità tamponante stigmatica è stata testata su quattro specie scelte per la loro biologia dell’impollinazione e per le loro caratteristiche stigmatiche. Gli stigmi sono stati immersi in una soluzione di NaNO3 e le variazioni di pH sono state monitorate con lo stigma immerso o meno aggiungendo quantitativi crescenti di GRMs, mentre soluzioni acide sono state usate come controllo positivo. Inoltre, gli essudati stigmatici sono stati analizzati per verificare la presenza di sostanze con proprietà tamponati. Sulla base dei risultati ottenuti, le NP di GRMs rilasciate in atmosfera possono essere considerate di per sé non più pericolose di NM naturali con simile struttura. D’altro lato, gli acidi e ossidanti usati per la produzione del GO, rimanendone adesi possono danneggiare la comunicazione finemente regolata tra polline e stigma, alterando il processo riproduttivo. Quindi, l’applicazione di accurate procedure di purificazione dei GRMs prima del loro uso dovrebbe essere considerata nel contesto di un approccio "safer-by-design".
Effetti di Materiali a Base di Grafene sulla Biologia dell'Impollinazione delle Piante / Zanelli, Davide. - (2022 Mar 25).
Effetti di Materiali a Base di Grafene sulla Biologia dell'Impollinazione delle Piante
ZANELLI, DAVIDE
2022-03-25
Abstract
In the recent years, the rapid advancement in the field of nanomaterials (NMs) increased their development, production and commercialization. Among NMs, the carbon-based ones are the most widely researched because of their potential on the most diverse fields, with a predominant role occupied by Graphene-Related Materials (GRMs). Graphene is a two-dimensional, single layer sheet of carbon atoms organized in a honeycombed network with six-membered rings. Since its discovery, the attention of researchers was focused on its unique and exceptional properties, such as mechanical stiffness, strength, elasticity, very high electrical and thermal conductivity, which led to the development of numerous applications. Even if GRMs-enabled products have undeniable advantages, an involuntary release of GRMs nanoparticles (NPs) into the environment should be expected during their life cycle. Moreover, applications involving a direct release of GRMs-composites in the environment are under development, such us pesticides, fertilizers and paintings. Thus, GRMs have all the traits of emerging persistent pollutants: they have (i) increasing production volumes, (ii) a broad range of applications, and (iii) potentially harmful effects on organisms. GRM particles of micro- and nanometric size are extremely lightweight and, thus, could easily be aerodispersed for long distances, being intercepted by the aboveground organs of seed plants, i.e., leaves, stems, and flowers, which are natural traps for airborne particulate matter. So far, widely varying effects of GRMs on seed plants have been reported, from positive to negative, possibly owing to different experimental conditions (materials, concentrations, exposure time, protocols, etc.) and/or species tested. Unfortunately, there are only few in vitro studies focusing on the effects of these materials on the sexual reproduction of seed plants. The main aim of this PhD project is to assess the in vivo effect of GRMs on the sexual reproduction of seed plants. The effect of few-layer graphene (FLG) was compared with muscovite mica, a natural 2D NM, on pollen viability, stigma integrity and on their interaction in terms of pollen adhesion and germination on the stigma of the economically important and model plant Cucurbita pepo L (summer squash). Then, in two similar study, graphene oxide (GO) and purified-GO (PGO) were tested on pollen stigma interaction and fruit and seed production and development of C. pepo. First using amount far from a realistic scenario and then applying environmental-compatible dry depositions of the two materials. A fourth study focused on anemophilous species, because they might be the most exposed to airborne GRMs. A dedicated set-up was used to verify if airborne GO and PGO can be entrapped by anemophilous stigmas, and if they affects the pollen-stigma system or interact with liquid water possibly present on stigmas. Finally, the hypothesis of a stigmatic buffer capability was tested on four species selected for their pollination biology and stigmatic features. Stigmas were soaked in NaNO3 solutions. pH variations of solutions with or without stigmas were monitored progressively adding GRMs, while acid solutions were used as positive control. The stigmatic exudates were analysed to verify the presence of substances with buffering properties. According to the results obtained, GRM NPs released in atmosphere can be considered per se no more hazardous than similar layered naturally occurring NMs. On the other hand, the phytotoxic substances (i.e., strong acids and oxidants) used to produce GO and still adherent to its flakes can hinder the finely tuned communication between pollen and stigma, altering the reproduction process. Therefore, the application of accurate purification procedures before the use of GRMs should be considered in view of a "safer-by-design" approachFile | Dimensione | Formato | |
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Effects of Graphene-Related Materials on Plant Pollination Biology_Davide Zanelli_XXXIV PhD cycle.pdf
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Descrizione: Effect of graphene-related materials on plant pollination biology
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