Differential Water Deficit in Leaves Is a Principal Factor Modifying Barley Response to Drought Stress.

In response to environmental stress, plants activate complex signalling, including being dependent on reactive oxygen-nitrogen-sulphur species. One of the key abiotic stresses is drought. As a result of drought, changes in the level of hydration of the plant occur, which obviously entails various metabolic alternations. The primary aim of this study was to determine the relationship between the response of barley to drought and the intensity of stress, therefore investigations were performed under various levels of water saturation deficit (WSD) in leaves at 15%, 30%, and 50%. In barley subjected to drought, most significant changes occurred under a slight dehydration level at 15%. It was observed that the gene expression of 9-cis-epoxycarotenoid dioxygenases, enzymes involved in ABA biosynthesis, increased significantly, and led to a higher concentration of ABA. This was most likely the result of an increase in the gene expression and enzyme activity of L-cysteine desulfhydrase, which is responsible for H2S synthesis. Our results suggest that the differential water deficit in leaves underlies the activation of an appropriate defence, with ABA metabolism at the centre of these processes. Furthermore, at 15% WSD, a dominant contribution of H2O2-dependent signalling was noted, but at 30% and 50% WSD, significant NO-dependent signalling occurred.

The Alleviation of Metal Stress Nuisance for Plants-A Review of Promising Solutions in the Face of Environmental Challenges.

Environmental changes are inevitable with time, but their intensification and diversification, occurring in the last several decades due to the combination of both natural and human-made causes, are really a matter of great apprehension. As a consequence, plants are exposed to a variety of abiotic stressors that contribute to their morpho-physiological, biochemical, and molecular alterations, which affects plant growth and development as well as the quality and productivity of crops. Thus, novel strategies are still being developed to meet the challenges of the modern world related to climate changes and natural ecosystem degradation. Innovative methods that have recently received special attention include eco-friendly, easily available, inexpensive, and, very often, plant-based methods. However, such approaches require better cognition and understanding of plant adaptations and acclimation mechanisms in response to adverse conditions. In this succinct review, we have highlighted defense mechanisms against external stimuli (mainly exposure to elevated levels of metal elements) which can be activated through permanent microevolutionary changes in metal-tolerant species or through exogenously applied priming agents that may ensure plant acclimation and thereby elevated stress resistance.

PYR/PYL/RCAR Receptors Play a Vital Role in the Abscisic-Acid-Dependent Responses of Plants to External or Internal Stimuli.

Abscisic acid (ABA) is a phytohormone that plays a key role in regulating several developmental processes as well as in response to stressful conditions such as drought. Activation of the ABA signaling cascade allows the induction of an appropriate physiological response. The basic components of the ABA signaling pathway have been recognized and characterized in recent years. Pyrabactin resistance, pyrabactin resistance-like, and the regulatory component of ABA receptors (PYR/PYL/RCAR) are the major components responsible for the regulation of the ABA signaling pathway. Here, we review recent findings concerning the PYR/PYL/RCAR receptor structure, function, and interaction with other components of the ABA signaling pathway as well as the termination mechanism of ABA signals in plant cells. Since ABA is one of the basic elements related to abiotic stress, which is increasingly common in the era of climate changes, understanding the perception and transduction of the signal related to this phytohormone is of paramount importance in further increasing crop tolerance to various stress factors.

Signal Transduction in Cereal Plants Struggling with Environmental Stresses: From Perception to Response.

Cereal plants under abiotic or biotic stressors to survive unfavourable conditions and continue growth and development, rapidly and precisely identify external stimuli and activate complex molecular, biochemical, and physiological responses. To elicit a response to the stress factors, interactions between reactive oxygen and nitrogen species, calcium ions, mitogen-activated protein kinases, calcium-dependent protein kinases, calcineurin B-like interacting protein kinase, phytohormones and transcription factors occur. The integration of all these elements enables the change of gene expression, and the release of the antioxidant defence and protein repair systems. There are still numerous gaps in knowledge on these subjects in the literature caused by the multitude of signalling cascade components, simultaneous activation of multiple pathways and the intersection of their individual elements in response to both single and multiple stresses. Here, signal transduction pathways in cereal plants under drought, salinity, heavy metal stress, pathogen, and pest attack, as well as the crosstalk between the reactions during double stress responses are discussed. This article is a summary of the latest discoveries on signal transduction pathways and it integrates the available information to better outline the whole research problem for future research challenges as well as for the creative breeding of stress-tolerant cultivars of cereals.

Efficient antioxidant defence systems of spring barley in response to stress induced jointly by the cyst nematode parasitism and cadmium exposure.

Aims: This research aimed to establish how Hordeum vulgare responds to abiotic and biotic stress affecting in tandem. Methods: Plants were inoculated with Heterodera filipjevi and treated with cadmium (Cd) concentration (5 µM) that can occur in the cultivated soil. To verify the hypothesis about participation of increased antioxidative defence in H. vulgare under stress, biochemical and microscopic methods were implemented. Results: The amount of superoxide anions and hydrogen peroxide was diminished in plants that were both nematode-inoculated and cadmium-treated. Superoxide anions were rendered harmless by increased activity of superoxide dismutase, and H2O2 was scavenged via Foyer-Halliwell-Asada pathway. The unique enhanced antioxidant capacity of double stressed plants was also linked with the accumulation of S-nitrosoglutathione as nitrosoglutathione reductase activity was inhibited. Furthermore, stimulated activity of arginase in these plants could promote polyamine synthesis and indirectly enhance non-enzymatic antioxidant mechanism. Results indicate that different antioxidants operating together significantly restricted oxidation of lipids and proteins, thus the integrity of cell membranes and protein functions were maintained. Conclusions: The ROS deactivation machinery in barley leaves showed an unusual response during stress induced by H. filipjevi infection and cadmium treatment. Plants could induce a multi-component model of stress response, to detoxify Cd ions and efficiently repair stress damage.

Reactive oxygen species metabolism and photosynthetic performance in leaves of Hordeum vulgare plants co-infested with Heterodera filipjevi and Aceria tosichella.

KEY MESSAGE: Defence responses of cyst nematode and/or wheat curl mite infested barley engage the altered reactive oxygen species production, antioxidant machinery, carbon dioxide assimilation and photosynthesis efficiency. The primary aim of this study was to determine how barley responds to two pests infesting separately or at once; thus barley was inoculated with Heterodera filipjevi (Madzhidov) Stelter (cereal cyst nematode; CCN) and Aceria tosichella Keifer (wheat curl mite; WCM). To verify hypothesis about the involvement of redox metabolism and photosynthesis in barley defence responses, biochemical, photosynthesis efficiency and chlorophyll a fluorescence measurements as well as transmission electron microscopy were implemented. Inoculation with WCM (apart from or with CCN) brought about a significant suppression in the efficiency of electron transport outside photosystem II reaction centres. This limitation was an effect of diminished pool of rapidly reducing plastoquinone and decreased total electron carriers. Infestation with WCM (apart from or with CCN) also significantly restricted the electron transport on the photosystem I acceptor side, therefore produced reactive oxygen species oxidized lipids in cells of WCM and double infested plants and proteins in cells of WCM-infested plants. The level of hydrogen peroxide was significantly decreased in double infested plants because of glutathione-ascorbate cycle involvement. The inhibition of nitrosoglutathione reductase promoted the accumulation of S-nitrosoglutathione increasing antioxidant capacity in cells of double infested plants. Moreover, enhanced arginase activity in WCM-infested plants could stimulate synthesis of polyamines participating in plant antioxidant response. Infestation with WCM (apart from or with CCN) significantly reduced the efficiency of carbon dioxide assimilation by barley leaves, whereas infection only with CCN expanded photosynthesis efficiency. These were accompanied with the ultrastructural changes in chloroplasts during CCN and WCM infestation.