Ann Cuypers

Cadmium stress: an oxidative challenge

At the cellular level, cadmium (Cd) induces both damaging and repair processes in which the cellular redox status plays a crucial role. Being not redox-active, Cd is unable to generate reactive oxygen species (ROS) directly, but Cd-induced oxidative stress is a common phenomenon observed in multiple studies. The current review gives an overview on Cd-induced ROS production and anti-oxidative defense in organisms under different Cd regimes. Moreover, the Cd-induced oxidative challenge is discussed with a focus on damage and signaling as downstream responses. Gathering these data, it was clear that oxidative stress related responses are affected during Cd stress, but the apparent discrepancies observed in between the different studies points towards the necessity to increase our knowledge on the spatial and temporal ROS signature under Cd stress. This information is essential in order to reveal the exact role of Cd-induced oxidative stress in the modulation of downstream responses under a diverse array of conditions.

Normalisation of real-time RT-PCR gene expression measurements in Arabidopsis thaliana exposed to increased metal concentrations

Accurate quantification by real-time RT-PCR relies on normalisation of the measured gene expression data. Normalisation with multiple reference genes is becoming the standard, but the best reference genes for gene expression studies within one organism may depend on the applied treatments or the organs and tissues studied. Ideally, reference genes should be evaluated in all experimental systems. A number of candidate reference genes for Arabidopsis have been proposed, which can be used as a starting point to evaluate their expression stability in individual experimental systems by available computer algorithms like geNorm and NormFinder. Using this approach, we identified the best three reference genes from a set of ten candidates, which included three traditional “housekeeping” genes, for normalisation of gene expression when roots and leaves of Arabidopsis thaliana are exposed to cadmium (Cd) and copper (Cu). The expression stabilities of AT5G15710 (F-box protein), AT2G28390 (SAND family protein) and AT5G08290 (mitosis protein YLS8) were the highest when considering the effect to the roots and shoots of Cd and Cu treatments. Even though the effect of Cd and excess Cu on the plants is very different, the same best reference genes were identified when considering Cd or Cu treatments separately. This suggests that these three genes may also be suitable when studying the gene expression after exposure of Arabidopsis thaliana to increased concentrations of other metals.

Glutathione Is a Key Player in Metal-Induced Oxidative Stress Defenses

Since the industrial revolution, the production, and consequently the emission of metals, has increased exponentially, overwhelming the natural cycles of metals in many ecosystems. Metals display a diverse array of physico-chemical properties such as essential versus non-essential and redox-active versus non-redox-active. In general, all metals can lead to toxicity and oxidative stress when taken up in excessive amounts, imposing a serious threat to the environment and human health. In order to cope with different kinds of metals, plants possess defense strategies in which glutathione (GSH; γ-glu-cys-gly) plays a central role as chelating agent, antioxidant and signaling component. Therefore, this review highlights the role of GSH in: (1) metal homeostasis; (2) antioxidative defense; and (3) signal transduction under metal stress. The diverse functions of GSH originate from the sulfhydryl group in cysteine, enabling GSH to chelate metals and participate in redox cycling.

The cellular redox state as a modulator in cadmium and copper responses in Arabidopsis thaliana seedlings.

The cellular redox state is an important determinant of metal phytotoxicity. In this study we investigated the influence of cadmium (Cd) and copper (Cu) stress on the cellular redox balance in relation to oxidative signalling and damage in Arabidopsis thaliana. Both metals were easily taken up by the roots, but the translocation to the aboveground parts was restricted to Cd stress. In the roots, Cu directly induced an oxidative burst, whereas enzymatic ROS (reactive oxygen species) production via NADPH oxidases seems important in oxidative stress caused by Cd. Furthermore, in the roots, the glutathione metabolism plays a crucial role in controlling the gene regulation of the antioxidative defence mechanism under Cd stress. Metal-specific alterations were also noticed with regard to the microRNA regulation of CuZnSOD gene expression in both roots and leaves. The appearance of lipid peroxidation is dual: it can be an indication of oxidative damage as well as an indication of oxidative signalling as lipoxygenases are induced after metal exposure and are initial enzymes in oxylipin biosynthesis. In conclusion, the metal-induced cellular redox imbalance is strongly dependent on the chemical properties of the metal and the plant organ considered. The stress intensity determines its involvement in downstream responses in relation to oxidative damage or signalling.

Plant sugars are crucial players in the oxidative challenge during abiotic stress: extending the traditional concept

Plants suffering from abiotic stress are commonly facing an enhanced accumulation of reactive oxygen species (ROS) with damaging as well as signalling effects at organellar and cellular levels. The outcome of an environmental challenge highly depends on the delicate balance between ROS production and scavenging by both enzymatic and metabolic antioxidants. However, this traditional classification is in need of renewal and reform, as it is becoming increasingly clear that soluble sugars such as disaccharides, raffinose family oligosaccharides and fructans--next to their associated metabolic enzymes--are strongly related to stress-induced ROS accumulation in plants. Therefore, this review aims at extending the current concept of antioxidants functioning during abiotic stress, with special focus on the emanate role of sugars as true ROS scavengers. Examples are given based on their cellular location, as different organelles seem to exploit distinct mechanisms. Moreover, the vacuole comes into the picture as important player in the ROS signalling network of plants. Elucidating the interplay between the mechanisms controlling ROS signalling during abiotic stress will facilitate the development of strategies to enhance crop tolerance to stressful environmental conditions.

Phytoextraction of toxic metals: a central role for glutathione

Phytoextraction has a promising potential as an environmentally friendly clean-up method for soils contaminated with toxic metals. To improve the development of efficient phytoextraction strategies, better knowledge regarding metal uptake, translocation and detoxification in planta is a prerequisite. This review highlights our current understanding on these mechanisms, and their impact on plant growth and health. Special attention is paid to the central role of glutathione (GSH) in this process. Because of the high affinity of metals to thiols and as a precursor for phytochelatins (PCs), GSH is an essential metal chelator. Being an important antioxidant, a direct link between metal detoxification and the oxidative challenge in plants growing on contaminated soils is observed, where GSH could be a key player. In addition, as redox couple, oxidized and reduced GSH transmits specific information, in this way tuning cellular signalling pathways under environmental stress conditions. Possible improvements of phytoextraction could be achieved by using transgenic plants or plant-associated microorganisms. Joined efforts should be made to cope with the challenges faced with phytoextraction in order to successfully implement this technique in the field.

The need for transparency and good practices in the qPCR literature

Two surveys of over 1,700 publications whose authors use quantitative real-time PCR (qPCR) reveal a lack of transparent and comprehensive reporting of essential technical information. Reporting standards are significantly improved in publications that cite the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, although such publications are still vastly outnumbered by those that do not.

The redox status of plant cells (AsA and GSH) is sensitive to zinc imposed oxidative stress in roots and primary leaves of Phaseolus vulgaris

Abstract The ascorbate-glutathione cycle has been shown to be of great importance in multiple stress reactions. In the present study, alterations in the antioxidant pools combined with the evolution of the capacities of enzymes involved in defence against oxidative stress was investigated in roots and primary leaves of Phaseolus vulgaris L. after a 50-μM Zn application to roots. A difference has to be made between both plant organs. In roots, an overall oxidation of ascorbate occurred immediately after the start of the zinc treatment. This was accompanied by a decrease in ascorbate peroxidase (APOD; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) capacities, the latter resulting in an increase of glutathione disulphide (GSSG). In addition, in the primary leaves ascorbate was strongly affected by zinc toxicity and an immediate increase in the total amount could be observed. Whereas enhancement of the capacities constituting the ascorbate-glutathione pathway was observed, it only limited the effects of oxidative stress in primary leaves. At the end of the experiment, a strong increase in ascorbate oxidation was noticed suggesting that an excess of zinc can cause oxidative stress.

Bacterial seed endophytes: genera, vertical transmission and interaction with plants

Summary Although the importance of plant-associated microorganisms for plant growth and health was getting more recognition recently, the role of seed-associated microorganisms, and especially seed endophytic bacteria, still is underestimated. Nevertheless, these associations could be beneficial for germination and seedling establishment as seed endophytic bacteria are already present in these very early plant growth stages. Moreover, bacteria with beneficial characteristics can be selected by the plants and could be transferred via the seed to benefit the next generation. In this paper, the current literature concerning bacterial endophytes that have been isolated from seeds of different plant species is reviewed. Their colonization routes, localization inside seeds and mode of transmission as well as their role and fate during germination and seedling development are discussed. At the end, some examples of bacterial seed endophytes with applications as a plant growth-promoting or biocontrol agent are given.

Physiological Responses to Heavy Metals in Higher Plants; Defence against Oxidative Stress

Depending on the physiological process investigated heavy metal phytotoxicity can be either inhibitory or stimulatory. Photosynthesis and its partial light and dark reactions are inhibited; the activity of various enzymes, located in several cell compartiments, is increased. These enzymes are mostly induced since metals affect the transcription activity. They appear to be related to the plant defence against oxidative stress caused by metal phytotoxicity. Careful examination of the time course of this induction reveals differences in response between the metals applied