High temperatures can negatively affect plant growth and productivity. It is known that heat stress induces significant changes in normal physiological processes and generates reactive oxygen species (ROS). In order to limit the oxidative damage, occurring under stress, plants have developed detoxification systems, able to scavenge the highly toxic ROS. In order to clarify the relationship between cell growth, redox homeostasis and activation of defence mechanisms, the effect of moderate heat stress (exposure to 35°C) has been studied in tobacco BY-2 cells. The data indicates that the block of the cell cycle is an initial defence strategy. A strong increase in the expression of HSPs and an enhancement of antioxidant enzymes also occurs. However, these defence mechanisms seems to be not sufficient to cope with a persistent heat stress. Five-seven days after the start of heat treatment, the activity of antioxidant enzymes declines. The parallel increase in ROS determines oxidative damages and cell death. Interestingly, the pre-treatment of BY-2 cells with antioxidants correlates with a better growth capability, due to the recovery of cell divisions and a decrease in cell death.

Le piante, in quanto organismi privi di movimento, sono spesso esposte a condizioni ambientali avverse che incidono negativamente sulla loro crescita, sviluppo e produttività. tra gli stress di natura abiotica lo stress termico è particolarmente dannoso per gli organismi vegetali, in quanto l’esigenza di esposizione alle radiazioni solari, per lo svolgimento della fotosintesi, può anche comportare un aumento di temperatura dei tessuti. Lo stress termico può avere un effetto devastante sul metabolismo cellulare, poiché non solo induce cambiamenti significativi nei normali processi fisiologici ma porta a sovrapproduzione di specie reattive dell’ossigeno (RoS) con conseguente stress ossidativo (mittLeR, 2002). in queste condizioni la sopravvivenza delle cellule è legata alla loro capacità di potenziare i sistemi antiossidanti. un altro meccanismo di difesa, attivato in presenza di stress ossidativo, consiste nell’arresto del ciclo cellulare, per consentire il riparo del dna. durante l’arresto del ciclo cellulare si osserva un potenziamento dei sistemi antiossidanti, necessario per rendere minimi i danni arrecati al metabolismo cellulare (ReicHHeLd et al., 1999). uno studio recente ha messo in evidenza che le risposte delle piante allo stress termico sono estremamente diverse a seconda dell’intensità dello stress. È stato dimostrato che l’esposizione di cellule tby-2 per 10 minuti a 35 °c, nonostante determini un aumento di RoS, porta ad un potenziamento di sistemi antiossidanti finalizzato al superamento dello stress e alla conseguente sopravvivenza cellulare. al contrario, la breve esposizione a 55 °c determina un abbassamento dei sistemi antiossidanti, con produzione di un burst ossidativo e attivazione di un processo di morte cellulare programmata (Locato et al., 2008). in questo lavoro sono state studiate le risposte delle cellule vegetali ad una esposizione di diversa durata alla temperatura di 35 °c. Le colture cellulari tby- 2, che normalmente crescono alla temperatura di 27 °c, sono state esposte alla temperatura di 35 °c per 6 ore e successivamente riportate alla normale temperatura di crescita (shift) o mantenute alla temperatura di 35 °c per tutta la durata dell’esperimento (7 giorni). i risultati ottenuti hanno messo in evidenza che i due trattamenti determinano risposte cellulari differenti. Lo shift, non ha nessun effetto sulla crescita cellulare che rimane sostanzialmente uguale a quella delle cellule controllo. Queste cellule arrestano solo temporaneamente la divisione cellulare; l’indice mitotico, infatti, torna a valori comparabili a quelli del controllo già al secondo giorno di crescita. contemporaneamente, rafforzano i loro sistemi antiossidanti e ciò le rende in grado di superare lo stress. dopo 7 giorni dal trattamento, infatti, tutti i parametri analizzati ritornano simili a quelli del controllo evidenziando un’acclimatazione delle cellule allo stress. Le stesse cellule esposte in modo continuo a 35 °c presentano un sostanziale rallentamento della crescita cellulare. in questo caso si assiste ad una inibizione persistente delle divisioni cellulari, dovuta al blocco del ciclo cellulare e ad una diminuzione della distensione cellulare. Queste cellule potenziano inizialmente i loro sistemi antiossidanti, ma ciò si dimostra non sufficiente a fronteggiare una situazione di stress termico persistente. dopo 7 giorni dal trattamento, si assiste ad un calo di attività degli enzimi antiossidanti che, probabilmente, contribuisce all’aumento della mortalità cellulare. il pretrattamento delle cellule esposte in modo continuo a 35 °c con glutatione o galattone--lattone, ultimo precursore nella via di biosintesi dell’acido ascorbico, evita il rallentamento delle divisioni cellulari e preserva la vitalità cellulare. il recupero di crescita cellulare, che si osserva in presenza di aumentati livelli di

Artichoke by-products are rich in phenolic compounds although they represent a waste for the food industry. This paper examines the application of ultrasound-assisted extraction (UAE) for obtaining organic solvent-free extracts rich in nutraceuticals from artichoke scraps. Application of ultrasounds for 60 minutes on test samples, using water as a solvent, improved recovery of phenolic substances compared with untreated samples. Among the phenols detected by high performance liquid chromatography, 5-O-caffeoylquinic and 1,5-di-O-caffeoylquinic acids were identified. In vivo treatments of tobacco BY-2 cells with ultrasonic extracts consistently enhanced their antioxidant power, making the cells more resistant to heat stress. UAE applied to artichoke by-products, using water as a solvent, appears to be a powerful eco-friendly technique that can provide extracts rich in nutraceuticals and turn waste products into resources. The extracts could be advantageously utilized in the food industry to produce functional foods.

Plants are not only obligate aerobic organisms requiring oxygen for mitochondrial energy production, but also produce oxygen during photosynthesis Therefore, plant cells have to cope with a hyperoxic cellular environment that determines a production of reactive oxygen species (ROS) higher than the one occurring in animal cells In order to maintain redox homeostasis under control, plants evolved a particularly complex and redundant ROS-scavenging system, in which enzymes and metabolites are linked in a network of reactions This review gives an overview of the mechanisms active in plant cells for controlling redox homeostasis during optimal growth conditions. when ROS are produced in a steady-state low amount, and during stress conditions, when ROS production is increased Particular attention is paid to the aspects of oxygen/ROS management for which plant and animal cells differ. (C) 2010 Elsevier B V All rights reserved

Programmed cell death (PCD) is a genetically controlled process described both in eukaryotic and prokaryotic organisms. Even if it is clear that PCD occurs in plants, in response to various developmental and environmental stimuli, the signalling pathways involved in the triggering of this cell suicide remain to be characterized. In this review, the main similarities and differences in the players involved in plant and animal PCD are outlined. Particular attention is paid to the role of reactive oxygen species (ROS) as key inducers of PCD in plants. The involvement of different kinds of ROS, different sites of ROS production, as well as their interaction with other molecules, is crucial in activating PCD in response to specific stimuli. Moreover, the importance is stressed on the balance between ROS production and scavenging, in various cell compartments, for the activation of specific steps in the signalling pathways triggering this cell suicide process. The review focuses on the complexity of the interplay between ROS and antioxidant molecules and enzymes in determining the most suitable redox environment required for the occurrence of different forms of PCD.

Nitric oxide (NO) is a small redox molecule that acts as a signal in different physiological and stress-related processes in plants. Recent evidence suggests that the biological activity of NO is also mediated by S-nitrosylation, a well-known redox-based posttranslational protein modification. Here, we show that during programmed cell death (PCD), induced by both heat shock (HS) or hydrogen peroxide (H2O2) in tobacco (Nicotiana tabacum) Bright Yellow-2 cells, an increase in S-nitrosylating agents occurred. NO increased in both experimentally induced PCDs, although with different intensities. In H2O2-treated cells, the increase in NO was lower than in cells exposed to HS. However, a simultaneous increase in S-nitrosoglutathione (GSNO), another NO source for S-nitrosylation, occurred in H2O2-treated cells, while a decrease in this metabolite was evident after HS. Consistently, different levels of activity and expression of GSNO reductase, the enzyme responsible for GSNO removal, were found in cells subjected to the two different PCD-inducing stimuli: low in H2O2-treated cells and high in the heat-shocked ones. Irrespective of the type of S-nitrosylating agent, S-nitrosylated proteins formed upon exposure to both of the PCD-inducing stimuli. Interestingly, cytosolic ascorbate peroxidase (cAPX), a key enzyme controlling H2O2 levels in plants, was found to be S-nitrosylated at the onset of both PCDs. In vivo and in vitro experiments showed that S-nitrosylation of cAPX was responsible for the rapid decrease in its activity. The possibility that S-nitrosylation induces cAPX ubiquitination and degradation and acts as part of the signaling pathway leading to PCD is discussed.

Plant programmed cell death (PCD) is a genetically controlled process that plays an important role in development and stress responses. Reactive oxygen species (ROS) are key inducers of PCD. The addition of 50 mM H2O2 to tobacco Bright Yellow-2 (TBY-2) cell cultures induces PCD. A comparative proteomic analysis of TBY-2 cells treated with 50 mM H2O2 for 30 min and 3 h was performed. The results showed early down-regulation of several elements in the cellular redox hub and inhibition of the protein repair–degradation system. The expression patterns of proteins involved in the homeostatic response, in particular those associated with metabolism, were consistently altered. The changes in abundance of several cytoskeleton proteins confirmed the active role of the cytoskeleton in PCD signalling. Cells undergoing H2O2-induced PCD fail to cope with oxidative stress. The antioxidant defence system and the anti-PCD signalling cascades are inhibited. This promotes a genetically programmed cell suicide pathway. Fifteen differentially expressed proteins showed an expression pattern similar to that previously observed in TBY-2 cells undergoing heat shock-induced PCD. The possibility that these proteins are part of a core complex required for PCD induction is discussed.