Post-harvest quality and sensory analysis of 'Prata' bananas produced in different cultivation field locations.

Banana 'Prata' has a significant demand in the Brazilian market, and Minas Gerais is one of the largest banana producers in the country. Scientific studies that evaluate the bananas quality produced in different cultivation regions are still incipient. Thus, this study evaluated the physical, biochemical and sensory attributes of banana 'Prata' from south and north of Minas Gerais and Vale do Ribeira (SP). Bananas from south were also cultivated in different production systems, organic and conventional. Data were submitted to multivariate analysis that provided the discrimination of the samples according to the cultivation regions. Bananas from southern presented higher levels of soluble solids and acidity, better taste, higher diameter and overall acceptance, where in the organic bananas were the most preferred by consumers. Fruit from northern stood out in appearance, texture, aroma and color, in addition to greater length. Fruit from Vale do Ribeira had higher levels of total phenolics and antioxidant activity. With these results we can assume that fruit quality is highly related to the specific climatic conditions from each producing region. Bananas from the south of Minas Gerais showed superiority for most of the evaluated traits, reflecting on consumer preference.

A putative bifunctional CPD/ (6-4) photolyase from the cyanobacteria Synechococcus sp. PCC 7335 is encoded by a UV-B inducible operon: New insights into the evolution of photolyases.

Photosynthetic organisms are continuously exposed to solar ultraviolet radiation-B (UV-B) because of their autotrophic lifestyle. UV-B provokes DNA damage, such as cyclobutane pyrimidine dimers (CPD) or pyrimidine (6-4) pyrimidone photoproducts (6-4 PPs). The cryptochrome/photolyase family (CPF) comprises flavoproteins that can bind damaged or undamaged DNA. Photolyases (PHRs) are enzymes that repair either CPDs or 6-4 PPs. A natural bifunctional CPD/(6-4)- PHR (PhrSph98) was recently isolated from the UV-resistant bacteria Sphingomonas sp. UV9. In this work, phylogenetic studies of bifunctional CPD/(6-4)- photolyases and their evolutionary relationship with other CPF members were performed. Amino acids involved in electron transfer and binding to FAD cofactor and DNA lesions were conserved in proteins from proteobacteria, planctomycete, bacteroidete, acidobacteria and cyanobacteria clades. Genome analysis revealed that the cyanobacteria Synechococcus sp. PCC 7335 encodes a two-gene assembly operon coding for a PHR and a bifunctional CPD/(6-4) PHR- like. Operon structure was validated by RT-qPCR analysis and the polycistronic transcript accumulated after 15 min of UV-B irradiation. Conservation of structure and evolution is discussed. This study provides evidence for a UV-B inducible PHR operon that encodes a CPD/(6-4)- photolyase homolog with a putative bifunctional role in the repair of CPDs and 6-4 PPs damages in oxygenic photosynthetic organisms.

Selection and optimization of reference genes for RT-qPCR normalization: A case study in Solanum lycopersicum exposed to UV-B.

Quantitative RT- PCR is one of the most common methods to study gene expression in response to stress. Therefore, it is crucial to have suitable reference genes (RGs) for result normalization. Although several reports describe UV-B-modulated gene expression in Solanum lycopersicum, there are no suitable RGs identified until now. The aim of this work was to evaluate the suitability of seven traditional genes: actin (ACT), tubulin (TUB), ubiquitin (UBI), glyceraldehyde- 3 phosphate dehydrogenase (GAPDH), elongation factor 1α (EF1α), phosphatase 2A catalytic subunit (PP2A) and GAGA binding transcriptional activator (GAGA); and two non-traditional genes: thioredoxin h1 (TRX h1) and UV-B RESISTANCE LOCUS 8 (UVR8), as candidate RGs for their potential use as reliable internal controls in leaves, stems and roots of tomato seedlings exposed to acute and chronic UV-B. The stability of these genes expression was evaluated using five statistical algorithms: geNorm, NormFinder, BestKeeper, Delta Ct and ANOVA. Considering the comprehensive stability ranking, we recommend ACT+TUB as the best pair of RGs for leaves, PP2A+GAPDH+TRX h1 for stems and TUB+UVR8 for roots. The reliability of the selected RGs for each tissue was verified amplifying tomato chalcone synthase 1 (CHS1) and cyclobutane pyrimidine dimer (CPD) photolyase (PHR1-LIKE). Under UV-B treatment, CHS1 was upregulated in leaves, stems and roots whereas PHR1-LIKE was only upregulated in leaves and stems. This interpretation differs when the most and least stable RGs are chosen. This is the first report regarding suitable RGs selection for accurate normalization of gene expression in tomato seedlings exposed to UV-B irradiation.

The era of nitric oxide in plant biology: Twenty years tying up loose ends.

Nitric oxide (NO) is an essential signal molecule to maintain cellular homeostasis in uni and pluricellular organisms. Conceptually, NO intervenes as much in sustaining basal metabolic processes, as in firing cellular responses to changes in internal and external conditions, and also in guiding the return to basal conditions. Behind these unusual capabilities of NO is the chemistry of this molecule, an unstable, reactive, free radical and short half-life gas. It is a lipophilic molecule that crosses all the barriers that biological membranes can impose. The extraordinary impact that the elucidation of physiological processes regulated by NO has had on plants, is comparable to the consequences of the discovery in 1986 that NO is present in animal tissues, and the following deep studies that demonstrated its biological activity regulating blood pressure. In this review, we have summarized and discuss the main discoveries that have emerged at Mar del Plata University over the past 20 years, and that have contributed to understand part of the biology of NO in plants. Besides, these findings are put in context with the progress made by other research groups, and in perspective, emphasizing that the history of NO in plants has just begun.

Climate Change and the Impact of Greenhouse Gasses: CO2 and NO, Friends and Foes of Plant Oxidative Stress.

Here, we review information on how plants face redox imbalance caused by climate change, and focus on the role of nitric oxide (NO) in this response. Life on Earth is possible thanks to greenhouse effect. Without it, temperature on Earth's surface would be around -19°C, instead of the current average of 14°C. Greenhouse effect is produced by greenhouse gasses (GHG) like water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxides (NxO) and ozone (O3). GHG have natural and anthropogenic origin. However, increasing GHG provokes extreme climate changes such as floods, droughts and heat, which induce reactive oxygen species (ROS) and oxidative stress in plants. The main sources of ROS in stress conditions are: augmented photorespiration, NADPH oxidase (NOX) activity, ß-oxidation of fatty acids and disorders in the electron transport chains of mitochondria and chloroplasts. Plants have developed an antioxidant machinery that includes the activity of ROS detoxifying enzymes [e.g., superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX), and peroxiredoxin (PRX)], as well as antioxidant molecules such as ascorbic acid (ASC) and glutathione (GSH) that are present in almost all subcellular compartments. CO2 and NO help to maintain the redox equilibrium. Higher CO2 concentrations increase the photosynthesis through the CO2-unsaturated Rubisco activity. But Rubisco photorespiration and NOX activities could also augment ROS production. NO regulate the ROS concentration preserving balance among ROS, GSH, GSNO, and ASC. When ROS are in huge concentration, NO induces transcription and activity of SOD, APX, and CAT. However, when ROS are necessary (e.g., for pathogen resistance), NO may inhibit APX, CAT, and NOX activity by the S-nitrosylation of cysteine residues, favoring cell death. NO also regulates GSH concentration in several ways. NO may react with GSH to form GSNO, the NO cell reservoir and main source of S-nitrosylation. GSNO could be decomposed by the GSNO reductase (GSNOR) to GSSG which, in turn, is reduced to GSH by glutathione reductase (GR). GSNOR may be also inhibited by S-nitrosylation and GR activated by NO. In conclusion, NO plays a central role in the tolerance of plants to climate change.

A Comprehensive Phylogeny Reveals Functional Conservation of the UV-B Photoreceptor UVR8 from Green Algae to Higher Plants.

Ultraviolet-B (UV-B) is present in sunlight (280-315 nm) and has diverse effects on living organisms. Low fluence rate of exposure induces a specific photomorphogenic response regulated by the UV-B response locus 8 (UVR8) receptor. UVR8 was first described in Arabidopsis thaliana. In the absence of stimuli it is located in the cytoplasm as a homodimer. However, upon UV-B irradiation, it switches to a monomer and interacts with the ubiquitin ligase E3 COP1 via the UVR8 ß-propeller domain and the VP core. This induces the expression of the transcription factor HY5 leading to changes in the expression of genes associated with UV-B acclimation and stress tolerance. UVR8 senses UV-B through tryptophan residues being Trp233 and 285 the most important. Based on the comparison and analysis of UVR8 functionally important motifs, we report a comprehensive phylogeny of UVR8, trying to identify UVR8 homologs and the ancestral organism where this gene could be originated. Results obtained showed that Chlorophytes are the first organisms from the Viridiplantae group where UVR8 appears. UVR8 is present in green algae, bryophytes, lycophytes, and angiosperms. All the sequences identified contain tryptophans 233 and 285, arginines involved in homodimerization and the VP domain suggesting they are true UVR8 photoreceptors. We also determined that some species from bryophytes and angiosperms contain more than one UVR8 gene copy posing the question if UVR8 could constitute a gene family in these species. In conclusion, we described the functional conservation among UVR8 proteins from green algae to higher plants.

A bioassay for brassinosteroid activity based on the in vitro fluorimetric detection of nitric oxide production.

Recent studies have shown that low concentrations of brassinolide induce a rapid generation of nitric oxide in mesophyll cells of maize leaves, which can be easily detected by fluorimetric methods. In this work we describe a series of natural and synthetic brassinosteroids that are able to trigger in vitro NO production in tomato cells that exhibits dose-response behavior. We propose that this effect can be used to develop a new rapid and very sensitive bioassay for brassinosteroid activity that offers several advantages when compared to the current methodologies.

Ultraviolet-B-induced stomatal closure in Arabidopsis is regulated by the UV RESISTANCE LOCUS8 photoreceptor in a nitric oxide-dependent mechanism.

UV RESISTANCE LOCUS8 (UVR8) signaling involves CONSTITUTIVELY PHOTOMORPHOGENIC1, the ELONGATED HYPOCOTYL5 (HY5) transcription factor, and the closely related HY5 HOMOLOG. Some UV-B responses mediated by UVR8 are also regulated by nitric oxide (NO), a bioactive molecule that orchestrates a wide range of processes in plants. In this study, we investigated the participation of the UVR8 pathway and its interaction with NO in UV-B-induced stomatal movements in Arabidopsis (Arabidopsis thaliana). Stomata in abaxial epidermal strips of Arabidopsis ecotype Landsberg erecta closed in response to increasing UV-B fluence rates, with maximal closure after 3-h exposure to 5.46 µmol m⁻² s⁻¹ UV-B. Both hydrogen peroxide (H2O2) and NO increased in response to UV-B, and stomatal closure was maintained by NO up to 24 h after the beginning of exposure. Stomata of plants expressing bacterial NO dioxygenase, which prevents NO accumulation, did not close in response to UV-B, although H2O2 still increased. When the uvr8-1 null mutant was exposed to UV-B, stomata remained open, irrespective of the fluence rate. Neither NO nor H2O2 increased in stomata of the uvr8-1 mutant. However, the NO donor S-nitrosoglutathione induced closure of uvr8-1 stomata to the same extent as in the wild type. Experiments with mutants in UVR8 signaling components implicated CONSTITUTIVELY PHOTOMORPHOGENIC1, HY5, and HY5 HOMOLOG in UV-B-induced stomatal closure. This research provides evidence that the UVR8 pathway regulates stomatal closure by a mechanism involving both H2O2 and NO generation in response to UV-B exposure.

S-nitrosylation influences the structure and DNA binding activity of AtMYB30 transcription factor from Arabidopsis thaliana.

MYB proteins are a family of transcription factors that play an important role in plant development and regulatory defense processes. Arabidopsis thaliana MYB30 (AtMYB30), a member of this protein family, is involved in cell death processes during the hypersensitive response (HR) of plants. HR is characterized by a vast production of reactive oxygen species (ROS) and nitric oxide (NO). NO may thus influence the binding of AtMYB30 to DNA. In this work we evaluated the effect of NO on AtMYB30 DNA binding activity, and also in the protein structural properties. A fully active minimal DNA-binding domain (DBD) of AtMYB30 (residues 11-116) containing two cysteine residues (C49 and C53) was overexpressed and purified. Site-directed mutagenesis was used to obtain AtMYB30 DBD mutants C49A and C53A. The DNA binding activity of AtMYB30 DBD, and Cys single mutants is clearly inhibited upon incubation with a NO donor, and S-nitrosylation was confirmed by the biotin switch assay. Finally, in order to understand the mechanism of NO effect on AtMYB30 DNA binding activity we performed circular dichroism analysis, to correlate the observed protein function inhibition and a potential structural impairment on AtMYB30 DBD. Indeed, NO modification of C49 and C53 residues promotes a subtle modification on the secondary structure of this transcription factor. We thus demonstrated, using various techniques, the in vitro effect of NO on AtMYB30 DBD, and thus the potential consequences of NO activity on plant metabolism influenced by this transcription factor.

Pharmacological and genetical evidence supporting nitric oxide requirement for 2,4-epibrassinolide regulation of root architecture in Arabidopsis thaliana.

Brassinosteroids (BRs) regulate various physiological processes, such as tolerance to stresses and root growth. Recently, a connection was reported between BRs and nitric oxide (NO) in plant responses to abiotic stress. Here we present evidence supporting NO functions in BR signaling during root growth process. Arabidopsis seedlings treated with BR 24-epibrassinolide (BL) show increased lateral roots (LR) density, inhibition of primary root (PR) elongation and NO accumulation. Similar effects were observed adding the NO donor GSNO to BR-receptor mutant bri1-1. Furthermore, BL-induced responses in the root were abolished by the specific NO scavenger c-PTIO. The activities of nitrate reductase (NR) and nitric oxide synthase (NOS)-like, two NO generating enzymes were involved in BR signaling. These results demonstrate that BR increases the NO concentration in root cells, which is required for BR-induced changes in root architecture.

RETRACTED: Nitric oxide and flavonoids are systemically induced by UV-B in maize leaves.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of Cristina Lombardo, Lorenzo Lamattina, Raul Cassia. Several figures in the article by Tossi et al appear to have been intentionally manipulated and, therefore, representing results that are not accurate. The specific concerns are 1) the NO/-UVB panel in Fig. 1B is an apparent duplication of the Fig. 4 NO/PC panel; 2) the Flavonoid/UVB panel in Fig. 1B is an apparent duplication of the Fig. 4 Flavonoid/U panel; and 3), many of the RT-PCR bands in Fig. 5 are apparently identical. The apparent duplications of the panels in Fig. 1B and Fig. 4 appears to have been done intentionally. The brightness of the published Fig. 1B NO/-UVB panel was decreased and rotated 180 degrees relative to the NO/PC panel in Fig. 4. The two images are identical when the brightness of Fig. 1B is enhanced and the Fig. 4 panel rotated 180 degrees as shown in the attachment. Likewise, Fig. 1B Flavonoid/UVB panel was manipulated to disguise it from the Flavonoid/U panel in Fig. 4. We thank Dr Elisabeth Bik for drawing the irregularities to the authors' attention.

ABA says NO to UV-B: a universal response?

Abscisic acid (ABA) signaling pathways have been widely characterized in plants, whereas the function of ABA in animals is less well understood. However, recent advances show ABA production by a wide range of lower animals and higher mammals. This enables a new evaluation of ABA signaling pathways in different organisms in response to common environmental stress, such as ultraviolet (UV)-B. In this opinion article, we propose that the induction of common signaling components, such as ABA, nitric oxide (NO) and Ca(2+), in plant and animal cells in response to high doses of UV-B, suggests that the evolution of a general mechanism activated by UV-B is conserved in divergent multicellular organisms challenged by a changing common environment.

Autocrine abscisic acid mediates the UV-B-induced inflammatory response in human granulocytes and keratinocytes.

UV-B is an abiotic environmental stress in both plants and animals. Abscisic acid (ABA) is a phytohormone regulating fundamental physiological functions in plants, including response to abiotic stress. We previously demonstrated that ABA is an endogenous stress hormone also in animal cells. Here, we investigated whether autocrine ABA regulates the response to UV-B of human granulocytes and keratinocytes, the cells involved in UV-triggered skin inflammation. The intracellular ABA concentration increased in UV-B-exposed granulocytes and keratinocytes and ABA was released into the supernatant. The UV-B-induced production of NO and of reactive oxygen species (ROS), phagocytosis, and cell migration were strongly inhibited in granulocytes irradiated in the presence of a monoclonal antibody against ABA. Moreover, presence of the same antibody strongly inhibited release of NO, prostaglandin E2 (PGE(2)), and tumor necrosis factor-α (TNF-α) by UV-B irradiated keratinocytes. Lanthionine synthetase C-like protein 2 (LANCL2) is required for the activation of the ABA signaling pathway in human granulocytes. Silencing of LANCL2 in human keratinocytes by siRNA was accompanied by abrogation of the UV-B-triggered release of PGE(2), TNF-α, and NO and ROS production. These results indicate that UV-B irradiation induces ABA release from human granulocytes and keratinocytes and that autocrine ABA stimulates cell functions involved in skin inflammation.

Nitric oxide enhances plant ultraviolet-B protection up-regulating gene expression of the phenylpropanoid biosynthetic pathway.

The link between ultraviolet (UV)-B, nitric oxide (NO) and phenylpropanoid biosynthetic pathway (PPBP) was studied in maize and Arabidopsis. The transcription factor (TF) ZmP regulates PPBP in maize. A genetic approach using P-rr (ZmP+) and P-ww (ZmP⁻) maize lines demonstrate that: (1) NO protects P-rr leaves but not P-ww from UV-B-induced reactive oxygen species (ROS) and cell damage; (2) NO increases flavonoid and anthocyanin content and prevents chlorophyll loss in P-rr but not in P-ww and (3) the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) blocks the UV-B-induced expression of ZmP and their targets CHS and CHI suggesting that NO plays a key role in the UV-B-regulated PPBP. Involvement of endogenous NO was studied in Arabidopsis nitric oxide dioxygenase (NOD) plants that express a NO dioxygenase gene under the control of a dexamethasone (DEX)-inducible promoter. Expression of HY5 and MYB12, TFs involved in PPBP regulation, was induced by UV-B, reduced by DEX in NOD plants and recovered by subsequent NO treatment. C4H regulates synapate esters synthesis and is UV-B-induced in a NO-independent pathway. Data indicate that UV-B perception increases NO concentration, which protects plant against UV-B by two ways: (1) scavenging ROS; and (2) up-regulating the expression of HY5, MYB12 and ZmP, resulting in the PPBP activation.

A possible mechanism for the apocynin-induced nitric oxide accumulation in plants.

Nitric oxide (NO) is a small, ubiquitous bioactive molecule, postulated as a broad spectrum anti-stress compound. The NADPH oxidase inhibitor apocynin induces the accumulation of endogenous NO in leaves of maize seedlings through a nitric oxide synthase (NOS)-like activity, and confers an augmented tolerance to UV-B-induced oxidative damage. Here we propose a mechanism for the apocynin-induced NO increase in plants. NOS catalyzes the oxidation of arginine to citrulline and NO. It is suggested that apocynin inhibits arginase, the enzyme that hydrolyzes L-arginine to urea and L-ornithine, increasing the arginine availability for arginine-dependent NO synthesis. Superoxide (O(2)(-)) is a strong NO scavenger due to its high reactivity with NO to give peroxynitrite (ONOO(-)). Superoxide is mainly produced by plant NADPH oxidase (pNOX). Inhibition of pNOX by apocynin at relatively high NO concentration, could reduces the formation of O(2)(-) and ONOO(-), increasing the availability of a huge amount of NO. We consider apocynin as a very attractive compound for studying NO-regulated processes in plants since it can replace the use of NO donors and overcome the subsequent technical problems.

Apocynin-induced nitric oxide production confers antioxidant protection in maize leaves.

The effect of apocynin on nitric oxide (NO) synthesis and oxidative stress was studied in corn (Zea mays) seedlings. After treatment with 100 microM apocynin, strongly increased amounts of NO were detected in the leaves. This NO production was reduced by more than 70% by N(G)-nitro-l-arginine methyl ester (L-NAME), a NO synthase (NOS) inhibitor, but there was no reduction in NO production when apocynin was applied in combination with diphenylene iodonium (a plant NOX inhibitor). When maize seedlings were UV-B-irradiated, cellular damage occurred and reactive oxygen species (ROS) were found widely distributed in chloroplasts and mesophyll cells. Pre-treatment with apocynin and coinciding NO accumulation prevented this damage. However, the protective effect was averted by L-NAME application. Leaf discs placed in 1M H(2)O(2) for 24h showed a reduction in chlorophyll content that could also be avoided by apocynin treatment. Our results show that apocynin induces the accumulation of NO in leaves of maize seedlings through a NOS-like activity, a mechanism alternative to NOX inhibition, and confers an augmented tolerance to different types of abiotic oxidative stress. Indeed, we propose the use of apocynin as an alternative approach to study NO functionality in plants.

An increase in the concentration of abscisic acid is critical for nitric oxide-mediated plant adaptive responses to UV-B irradiation.

Here, the link between UV-B stimulus and the abscisic acid (ABA)-induced nitricoxide (NO) synthesis pathway was studied in leaves of maize (Zea mays).The ABA concentration increased by 100% in UV-B irradiated leaves. Leaves of viviparous 14 (vp14), a mutant defective in ABA synthesis, were more sensitive to UV-B-induced damage than those of the wild type (wt). ABA supplementation attenuated UV-B-induced damage in both the wt and vp14. The hydrogen peroxide(H2O2) concentration increased in the irradiated wt, but changed only slightly in vp14. This increase was prevented by diphenylene iodonium (DPI), an inhibitor of NADPH oxidase (pNOX).NO was detected using the fluorophore 4,5-diamino-fluorescein diacetate(DAF-2DA). DAF-2DA fluorescence increased twofold in UV-B-irradiated wt leaves but not in vp14 leaves. H2O2 and NO production was restored in vp14 plants supplied with 100 µM ABA. Catalase, DPI and the NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) partially blocked UV-B-induced NO accumulation, suggesting that H2O2 as well as NOS-like activity is required for a full plant response to UV-B. NO protects against UV-B-induced cell damage.Our results suggest that UV-B perception triggers an increase in ABA concentration,which activates pNOX and H2O2 generation, and that an NOS-like-dependent mechanism increases NO production to maintain cell homeostasis and attenuate UV-B-derived cell damage.