Involvement of nitrate reductase in auxin-induced NO synthesis

Nitric Oxide Alters the Pattern of Auxin Maxima and PIN-FORMED1 During Shoot Development

Hormone patterns tailor cell fate decisions during plant organ formation. Among them, auxins and cytokinins are critical phytohormones during early development. Nitric oxide (NO) modulates root architecture by the control of auxin spatial patterns. However, NO involvement during the coordination of shoot organogenesis remains unclear. Here, we explore the effect of NO during shoot development by using a phenotypic, cellular, and genetic analysis in Arabidopsis thaliana and get new insights into the characterization of NO-mediated leaf-related phenotypes. NO homeostasis mutants are impaired in several shoot architectural parameters, including phyllotactic patterns, inflorescence stem elongation, silique production, leaf number, and margin. Auxin distribution is a key feature for tissue differentiation and need to be controlled at different levels (i.e., synthesis, transport, and degradation mechanisms). The phenotypes resulting from the introduction of the cue1 mutation in the axr1 auxin resistant and pin1 backgrounds exacerbate the relationship between NO and auxins. Using the auxin reporter DR5:GUS, we observed an increase in auxin maxima under NO-deficient mutant backgrounds and NO scavenging, pointing to NO-ASSOCIATED 1 (NOA1) as the main player related to NO production in this process. Furthermore, polar auxin transport is mainly regulated by PIN-FORMED 1 (PIN1), which controls the flow along leaf margin and venations. Analysis of PIN1 protein levels shows that NO controls its accumulation during leaf development, impacting the auxin mediated mechanism of leaf building. With these findings, we also provide evidence for the NO opposite effects to determine root and shoot architecture, in terms of PIN1 accumulation under NO overproduction.

Nitric oxide production in plants: an update

Nitric oxide (NO) is a key signaling molecule in plant physiology. However, its production in photosynthetic organisms remains partially unresolved. The best characterized NO production route involves the reduction of nitrite to NO via different non-enzymatic or enzymatic mechanisms. Nitrate reductases (NRs), the mitochondrial electron transport chain, and the new complex between NR and NOFNiR (nitric oxide-forming nitrite reductase) described in Chlamydomonas reinhardtii are the main enzymatic systems that perform this reductive NO production in plants. Apart from this reductive route, several reports acknowledge the possible existence of an oxidative NO production in an arginine-dependent pathway, similar to the nitric oxide synthase (NOS) activity present in animals. However, no NOS homologs have been found in the genome of embryophytes and, despite an increasing amount of evidence attesting to the existence of NOS-like activity in plants, the involved proteins remain to be identified. Here we review NO production in plants with emphasis on the presentation and discussion of recent data obtained in this field.

Nitric Oxide Analyzer Quantification of Plant S-Nitrosothiols

Nitric oxide (NO) is a small diatomic molecule that regulates multiple physiological processes in animals, plants, and microorganisms. In animals, it is involved in vasodilation and neurotransmission and is present in exhaled breath. In plants, it regulates both plant immune function and numerous developmental programs. The high reactivity and short half-life of NO and cross-reactivity of its various derivatives make its quantification difficult. Different methods based on calorimetric, fluorometric, and chemiluminescent detection of NO and its derivatives are available, but all of them have significant limitations. Here we describe a method for the chemiluminescence-based quantification of NO using ozone-chemiluminescence technology in plants. This approach provides a sensitive, robust, and flexible approach for determining the levels of NO and its signaling products, protein S-nitrosothiols.

The role of nitric oxide signalling in response to salt stress in Chlamydomonas reinhardtii

Nitric oxide signal and GSNOR activity play an essential role for Chlamydomonas reinhardtii response to salt stress. The unicellular alga Chlamydomonas reinhardtii is one of the most important model organisms phylogenetically situated between higher plants and animals. In the present study, we used comparative proteomics and physiological approaches to study the mechanisms underlying the response to salt stress in C. reinhardtii. We identified 74 proteins that accumulated differentially after salt stress, including oxidative enzymes and enzymes associated with nitric oxide (NO) metabolism, cell damage, and cell autophagy processes. A set of antioxidant enzymes, as well as S-nitrosoglutathione reductase (GSNOR) activity, were induced to balance the cellular redox status during short-term salt stress. Enzymes involved in DNA repair and cell autophagy also contribute to adaptation to short-term salt stress. However, under long-term salt stress, antioxidant enzymes and GSNOR were gradually inactivated through protein S-nitrosylation, leading to oxidative damage and a reduction in cell viability. Modulating the protein S-nitrosylation levels by suppressing GSNOR activity or adding thioredoxin affected the plant's adaptation to salt stress, through altering the redox status and DNA damage and autophagy levels. Based on these data, we propose that unicellular algae use multiple strategies to adapt to salt stress, and that, during this process, GSNOR activity and protein S-nitrosylation levels play important roles.

Nitric oxide and phytohormone interactions: current status and perspectives

Nitric oxide (NO) is currently considered a ubiquitous signal in plant systems, playing significant roles in a wide range of responses to environmental and endogenous cues. During the signaling events leading to these plant responses, NO frequently interacts with plant hormones and other endogenous molecules, at times originating remarkably complex signaling cascades. Accumulating evidence indicates that virtually all major classes of plant hormones may influence, at least to some degree, the endogenous levels of NO. In addition, studies conducted during the induction of diverse plant responses have demonstrated that NO may also affect biosynthesis, catabolism/conjugation, transport, perception, and/or transduction of different phytohormones, such as auxins, gibberellins, cytokinins, abscisic acid, ethylene, salicylic acid, jasmonates, and brassinosteroids. Although still not completely elucidated, the mechanisms underlying the interaction between NO and plant hormones have recently been investigated in a number of species and plant responses. This review specifically focuses on the current knowledge of the mechanisms implicated in NO-phytohormone interactions during the regulation of developmental and metabolic plant events. The modifications triggered by NO on the transcription of genes encoding biosynthetic/degradative enzymes as well as proteins involved in the transport and signal transduction of distinct plant hormones will be contextualized during the control of developmental, metabolic, and defense responses in plants. Moreover, the direct post-translational modification of phytohormone biosynthetic enzymes and receptors through S-nitrosylation will also be discussed as a key mechanism for regulating plant physiological responses. Finally, some future perspectives toward a more complete understanding of NO-phytohormone interactions will also be presented and discussed.

Indole-3-butyric acid induces lateral root formation via peroxisome-derived indole-3-acetic acid and nitric oxide

Controlled plant growth requires regulation through a variety of signaling molecules, including steroids, peptides, radicals of oxygen and nitrogen, as well as the 'classical' phytohormone groups. Auxin is critical for the control of plant growth and also orchestrates many developmental processes, such as the formation of new roots. It modulates root architecture both slowly, through actions at the transcriptional level and, more rapidly, by mechanisms targeting primarily plasma membrane sensory systems and intracellular signaling pathways. The latter reactions use several second messengers, including Ca(2+) , nitric oxide (NO) and reactive oxygen species (ROS). Here, we investigated the different roles of two auxins, the major auxin indole-3-acetic acid (IAA) and another endogenous auxin indole-3-butyric acid (IBA), in the lateral root formation process of Arabidopsis and maize. This was mainly analyzed by different types of fluorescence microscopy and inhibitors of NO production. This study revealed that peroxisomal IBA to IAA conversion is followed by peroxisomal NO, which is important for IBA-induced lateral root formation. We conclude that peroxisomal NO emerges as a new player in auxin-induced root organogenesis. In particular, the spatially and temporally coordinated release of NO and IAA from peroxisomes is behind the strong promotion of lateral root formation via IBA.

Nitric oxide enhances development of lateral roots in tomato (Solanum lycopersicum L.) under elevated carbon dioxide

Elevated carbon dioxide (CO₂) has been shown to enhance the growth and development of plants, especially of roots. Amongst them, lateral roots play an important role in nutrient uptake, and thus alleviate the nutrient limitation to plant growth under elevated CO₂. This paper examined the mechanism underlying CO₂ elevation-induced lateral root formation in tomato. The endogenous nitric oxide (NO) in roots was detected by the specific probe 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM DA). We suggest that CO₂ elevation-induced NO accumulation was important for lateral root formation. Elevated CO₂ significantly increased the activity of nitric oxide synthase in roots, but not nitrate reductase activity. Moreover, the pharmacological evidence showed that nitric oxide synthase rather than nitrate reductase was responsible for CO₂ elevation-induced NO accumulation. Elevated CO₂ enhanced the activity of nitric oxide synthase and promoted production of NO, which was involved in lateral root formation in tomato under elevated CO₂.

Variation characteristics of the nitrate reductase gene of key inbred maize lines and derived lines in China

Key inbred lines have played a fundamental role in maize genetics and breeding. Research on variation characteristics of key genes from key inbred lines and from derived lines is important for early identification and evaluation of inbred maize lines. The nitrate reductase (NR) gene, which plays a central role in nitrate acquisition, was the target gene for this research. Forty-one inbred maize lines were investigated, including four key inbred lines: Huangzaosi, Mo17, Dan340, and Ye478. Through multiple sequence alignment with the NR gene from B73, used as a control, we found that: 1) the NR gene of most inbred lines from Huangzaosi and from derived lines had two insertion fragments and two replacement fragments; 2) the NR gene of most inbred lines from Mo17 and derived lines had one insertion fragment and one replacement fragment; 3) there were two common variations and eight common SNPs in the NR gene of the four key lines. Huangzaosi and Mo17 also had three common variations compared with the other key lines. Moreover, Mo17 had some unique variations; there were no unique variations in the other key lines, even for SNPs, and 4) phylogenetic tree analysis showed that the NR gene of the derived lines from the same key line had higher sequence homology. Based on the above NR gene variation characteristics and sequence homology of key inbred lines and derived lines, a candidate inbred line can be preliminarily selected and evaluated by marker development and/or sequence alignment of the NR gene.