Vasileios Ziogas

Polyamines reprogram oxidative and nitrosative status and the proteome of citrus plants exposed to salinity stress

The interplay among polyamines (PAs) and reactive oxygen and nitrogen species (RNS and ROS) is emerging as a key issue in plant responses to salinity. To address this question, we analysed the impact of exogenous PAs [putrescine (Put), spermidine (Spd) and spermine (Spm)] on the oxidative and nitrosative status in citrus plants exposed to salinity. PAs partially reversed the NaCl-induced phenotypic and physiological disturbances. The expression of PA biosynthesis (ADC, SAMDC, SPDS and SPMS) and catabolism (DAO and PAO) genes was systematically up-regulated by PAs. In addition, PAs altered the oxidative status in salt-stressed plants as inferred by changes in ROS production and redox status accompanied by regulation of transcript expression and activities of various antioxidant enzymes. Furthermore, NaCl-induced up-regulation of NO-associated genes, such as NR, NADde, NOS-like and AOX, along with S-nitrosoglutathione reductase and nitrate reductase activities, was partially restored by PAs. Protein carbonylation and tyrosine nitration are depressed by specific PAs whereas protein S-nitrosylation was elicited by all PAs. Furthermore, we identified 271 S-nitrosylated proteins that were commonly or preferentially targeted by salinity and individual PAs. This work helps improve our knowledge on the plants response to environmental challenge.

Nitrosative responses in citrus plants exposed to six abiotic stress conditions

Nitrosative status has emerged as a key component in plant response to abiotic stress; however, knowledge on its regulation by different environmental conditions remains unclear. The current study focused on nitrosative responses in citrus plants exposed to various abiotic stresses, including continuous light, continuous dark, heat, cold, drought and salinity. Morphological observations and physiological analysis showed that abiotic stress treatments were sensed by citrus plants. Furthermore, it was revealed that nitrosative networks are activated by environmental stress factors in citrus leaves as evidenced by increased nitrite (NO) content along with the release of NO and superoxide anion (O₂⁻) in the vascular tissues. The expression of genes potentially involved in NO production, such as NR, AOX, NADHox, NADHde, PAO and DAO, was affected by the abiotic stress treatments demonstrating that NO-derived nitrosative responses could be regulated by various pathways. In addition, S-nitrosoglutathione reductase (GSNOR) and nitrate reductase (NR) gene expression and enzymatic activity displayed significant changes in response to adverse environmental conditions, particularly cold stress. Peroxynitrite (ONOO⁻) scavenging ability of citrus plants was elicited by continuous light, dark or drought but was suppressed by salinity. In contrast, nitration levels were elevated by salinity and suppressed by continuous light or dark. Finally, S-nitrosylation patterns were enhanced by heat, cold or drought but were suppressed by dark or salinity. These results suggest that the nitrosative response of citrus plants is differentially regulated depending on the stress type and underscore the importance of nitrosative status in plant stress physiology.

Involvement of AsA/DHA and GSH/GSSG Ratios in Gene and Protein Expression and in the Activation of Defence Mechanisms Under Abiotic Stress Conditions

In a persistently changing environment there are many adverse abiotic stress conditions such as cold, heat, drought, salinity, heavy metal toxicity and oxygen deprivation, which remarkably influence plant growth and crop production. Plant cells produce oxygen radicals and their derivatives, so-called reactive oxygen species (ROS) during various processes associated with abiotic stress. Moreover, the generation of ROS is the main means for higher plants to transmit cellular signalling information concerning the changing environmental conditions. Therefore, plants have evolved inducible redox state-based sensing mechanisms that are activated or amplified in response to adverse environmental conditions. Ascorbate and glutathione, the key cellular redox buffers, are used for both detoxification of ROS and transmission of redox signals. In recent years, it has become clear that abiotic stress conditions induce changes in the reduction/oxidation (redox) state of signalling molecules, which in turn modulate gene and protein expression to increase plant acclimation to abiotic stress. This important redox state-related branch of science has given several clues in understanding the adaptive plant responses to different stressful regimes. In this chapter, an overview of the literature is briefly presented in terms of the main function of ascorbate and glutathione in plant cells. Further more, we describe how important forms of abiotic stress regulate the expression of genes and proteins involved in the ascorbate and glutathione redox sensing system.

Citrus Plants: A Model System for Unlocking the Secrets of NO and ROS-Inspired Priming Against Salinity and Drought

Plants treated with chemical compounds can develop an enhanced capacity to resist long after being subjected to (a)biotic stress, a phenomenon known as priming. Evidence suggests that reactive oxygen species (ROS) and reactive nitrogen species (RNS) coordinately regulate plant stress responses to adverse environmental conditions; however, the mechanisms underlying this function remain unknown. Based on the observation that pre-exposure of citrus (Citrus aurantium L.) roots to the NO donor sodium nitroprusside (SNP) or to H2O2 prior to NaCl application can induce acclimation against subsequent stress we characterized the changes occurring in primed citrus tissues using several approaches. Herein, using this experimental model system, we provide an overview of our current knowledge of the possible mechanisms associated with NO and H2O2 priming to abiotic stresses, particularly concerning salinity and drought. The data and ideas presented here introduce six aspects of priming behavior in citrus under abiotic stress that provide knowledge necessary to exploit priming syndrome in the context of sustainable agriculture.

Hydrogen Sulfide: A Potent Tool in Postharvest Fruit Biology and Possible Mechanism of Action

Hydrogen sulfide (H2S), an endogenous gaseous molecule, is considered as a signaling agent, in parallel with other low molecular weight reactive substances, mainly hydrogen peroxide (H2O2) and nitric oxide (NO), in various plant systems. New studies are now revealing that the postharvest application of H2S, through H2S donors such as sodium hydrosulfide (NaSH) or sodium sulfide (Na2S), can inhibit fruit ripening and senescence programs in numerous fruits. We discuss here current knowledge on the impact of H2S in postharvest physiology of several climacteric and non-climacteric fruits such as banana, apple, pear, kiwifruit, strawberry, mulberry fruit, and grape. Although there is still a considerable lack of studies establishing the mechanisms by which H2S signaling is linked to fruit metabolism, we highlight several candidate mechanisms, including a putative cross-talk between H2S and ethylene, reactive oxygen and nitrogen species, oxidative/nitrosative stress signaling, sulfate metabolism, and post-translational modification of protein cysteine residues (S-sulfhydration) as being functional in this H2S postharvest action. Understanding H2S metabolism and signaling during postharvest storage and the interplay with other key player molecules would therefore provide new, improved strategies for better fruit postharvest storage. To achieve this understanding, postharvest fruit physiology research will need to focus increasingly on the spatial interaction between H2S and ethylene perception as well as on the interplay between S-sulfhydration/desulfhydration and S-nitrosylation/denitrosylation under several postharvest conditions.

Foliar Nutrition, Biostimulants and Prime-Like Dynamics in Fruit Tree Physiology: New Insights on an Old Topic

Despite the fact that the usage of foliar nutrients has long history, many aspects of fertilization through leaves are still unknown. Herein, we review the current knowledge regarding the canopy fertilization putting special emphasis on Fe nutrition and briefly provide insights into the nanofertilizer technology of the foliar feeding of fruit crops. In addition, this paper discusses the main aspects of the foliar application of biostimulants regarding crucial factors of fruit cropping systems, such as fruit yield/size, tolerance to environmental stresses, and nutrient availability. Also, we specifically discuss the role of hydrogen peroxide (H2O2) and nitric oxide (NO) as priming molecules and their possible cross-talk with biostimulants in fruit tree physiology. Finally, a view of the key issues for future fundamental and applied research in the topic is put forward.

Nitric Oxide Action in the Improvement of Plant Tolerance to Nutritional Stress

Nitric oxide (NO) is a chemical messenger that actively operates in the plant kingdom. In recent years, NO has been shown to be involved in many growth, developmental, and physiological processes in plants. NO has been also shown to be involved in the metabolic reactions evoked by abiotic stresses, including mineral nutrients-associated stressful conditions. This chapter presents an overview of the present knowledge on the involvement of NO in plant response to nutritional stress, with special emphasis to salinity, calcium and iron homeostasis, and heavy metal stress.