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

Molecular and biochemical analyses of germination of cowpea (Vigna unguiculata L.) seeds inhibited by n-propyl gallate reveal a key role of alternative oxidase in germination Re-establishment

n-Propyl gallate (PG) is a phenolic compound that influences enzymatic processes, mostly involving AOX, PTOX, LOX, POD, and PPO. Here, analyses of different PG concentrations (1, 2.5, and 5 mM) during cowpea seed germination at 16, 32, and 48h showed that 2.5 mM PG partially inhibited seed germination at 16 and/or 32h, but by 48h the germination re-established. Thus, this PG concentration was chosen to study the molecular and biochemical mechanisms linked to the PG inhibitory effects and germination recovery. PG inhibition was related to lower H2O2, higher antioxidant activity, and downregulation of genes linked to cell cycle progression, energy status, and the Krebs cycle at 16 and/or 32h, but these changes were reversed at 48h. In general, genes associated with detoxification, germination-related phytohormones, and NAD(P)H metabolism were highly up-regulated across the time points. AOX1 and Pgb1 were continuously up-regulated along the time points, and linked to NR transcript level increase only at 48h. These findings indicated that AOX and the phytoglobin cycle, both systems involved in NO levels regulation, worked efficiently in germination re-establishment. However, genes other than AOX associated with potential target enzymes of PG, such as LOX, POD, PTOX and PPO (except at 48h), were mostly unchanged or down-regulated. Genes linked to glycolysis (PFK and PK) and acetate synthesis (PDC and ALDH) connected with AOX via NAD(P)+ were up-regulated under PG mainly at 48h. The data are discussed in light of AOX's role in cell reprogramming to reverse PG-induced inhibition of germination in cowpea seeds.

Progress in Plant Nitric Oxide Studies: Implications for Phytopathology and Plant Protection

Nitric oxide (NO) is a gaseous free radical known to modulate plant metabolism through crosstalk with phytohormones (especially ABA, SA, JA, and ethylene) and other signaling molecules (ROS, H2S, melatonin), and to regulate gene expression (by influencing DNA methylation and histone acetylation) as well as protein function through post-translational modifications (cysteine S-nitrosation, metal nitrosation, tyrosine nitration, nitroalkylation). Recently, NO has gained attention as a molecule promoting crop resistance to stress conditions. Herein, we review innovations from the NO field and nanotechnology on an up-to-date phytopathological background.

The emerging roles of nitric oxide and its associated scavengers-phytoglobins-in plant symbiotic interactions

A key feature in the establishment of symbiosis between plants and microbes is the maintenance of the balance between the production of the small redox-related molecule, nitric oxide (NO), and its cognate scavenging pathways. During the establishment of symbiosis, a transition from a normoxic to a microoxic environment often takes place, triggering the production of NO from nitrite via a reductive production pathway. Plant hemoglobins [phytoglobins (Phytogbs)] are a central tenant of NO scavenging, with NO homeostasis maintained via the Phytogb-NO cycle. While the first plant hemoglobin (leghemoglobin), associated with the symbiotic relationship between leguminous plants and bacterial Rhizobium species, was discovered in 1939, most other plant hemoglobins, identified only in the 1990s, were considered as non-symbiotic. From recent studies, it is becoming evident that the role of Phytogbs1 in the establishment and maintenance of plant-bacterial and plant-fungal symbiosis is also essential in roots. Consequently, the division of plant hemoglobins into symbiotic and non-symbiotic groups becomes less justified. While the main function of Phytogbs1 is related to the regulation of NO levels, participation of these proteins in the establishment of symbiotic relationships between plants and microorganisms represents another important dimension among the other processes in which these key redox-regulatory proteins play a central role.

Response to Cadmium in Silene vulgaris Ecotypes Is Distinctly Affected by Priming-Induced Changes in Oxidation Status of Macromolecules

This study investigated the impact of several priming agents on metal-tolerant and sensitive Silene vulgaris ecotypes exposed to environmentally relevant cadmium dose. We analyzed how priming-induced changes in the level of lipid, protein, and DNA oxidation contribute to calamine (Cal) and non-calamine (N-Cal) ecotype response to Cd toxicity, and whether the oxidative modifications interrelate with Cd tolerance. In non-primed ecotypes, the levels of DNA and protein oxidation were similar whereas Cal Cd tolerance was manifested in reduced lipid peroxidation. In both ecotypes protective action of salicylic acid (SA) and nitric oxide (NO) priming was observed. SA stimulated growth and reduced lipid and DNA oxidation at most, while NO protected DNA from fragmentation. Priming with hydrogen peroxide reduced biomass and induced DNA oxidation. In N-Cal, priming diminished Cd accumulation and oxidative activity, whereas in Cal, it merely affected Cd uptake and induced protein carbonylation. The study showed that priming did not stimulate extra stress resistance in the tolerant ecotype but induced metabolic remodeling. In turn, the lack of adaptive tolerance made the sensitive ecotype more responsive to the benefits of the primed state. These findings could facilitate priming exploitation with a view of enhancing metallophyte and non-metallophyte suitability for phytoremediation and land revegetation.