Nitric Oxide in Plant Functioning: Metabolism, Signaling, and Responses to Infestation with Ecdysozoa Parasites.

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological processes in plants, including responses to biotic and abiotic stresses. Changes in endogenous NO concentration lead to activation/deactivation of NO signaling and NO-related processes. This paper presents the current state of knowledge on NO biosynthesis and scavenging pathways in plant cells and highlights the role of NO in post-translational modifications of proteins (S-nitrosylation, nitration, and phosphorylation) in plants under optimal and stressful environmental conditions. Particular attention was paid to the interactions of NO with other signaling molecules: reactive oxygen species, abscisic acid, auxins (e.g., indole-3-acetic acid), salicylic acid, and jasmonic acid. In addition, potential common patterns of NO-dependent defense responses against attack and feeding by parasitic and molting Ecdysozoa species such as nematodes, insects, and arachnids were characterized. Our review definitely highlights the need for further research on the involvement of NO in interactions between host plants and Ecdysozoa parasites, especially arachnids.

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.

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.