Photo-Oxidative Stress during Leaf, Flower and Fruit Development

Effects of reactive oxygen species on fruit ripening and postharvest fruit quality

Reactive oxygen species (ROS) serve as important signaling molecule, involved in numerous biological processes, particularly in the physiological changes associated with fruit ripening and postharvest handing. This review explores ROS key role in plant fruit ripening and postharvest quality. The mechanism of ROS production and degradation in maintaining ROS homeostasis are analyzed in detail. Fruit ripening is a complex and highly coordinated process involving physiological and biochemical changes. Studies have observed that the content of ROS, mainly hydrogen peroxide (H2O2), dynamically changes in various types of fruits during ripening. Furthermore, ROS have significant effects on fruit softening, color change, and other ripening processes. In addition, in the postharvest stage, the abnormal accumulation of ROS isclosely related to the decline in fruit quality and the occurrence of decay browning, which seriously affects the market value and shelf life of fruit. Overall, this review demonstrates the crucial role of ROS in regulating the ripening process and postharvest quality of fruit.

Mechanism of sodium nitroprusside regulating ginseng quality

The roots of Panax ginseng C. A. Meyer (ginseng) are one of the traditional medicinal herbs in Asian countries and is known as the "king of all herbs". The most important active components of ginseng are the secondary metabolite saponins, which are closely related to ecological stress. Unsuitable ecological stress can generate a large amount of reactive oxygen species (ROS), by which the secondary metabolism is regulated, and the quality of herbs can be significantly improved. The purpose of this study was to investigate the effect of sodium nitroprusside (SNP) treatment on the quality of fresh ginseng roots. In this study, 5-year-old fresh ginseng was exposed to 0.1, 0.5, and 2 mmol/L SNP, a nitric oxide (NO) donor for five consecutive days. SNP significantly increased the levels of O2·-, H2O2, malondialdehyde (MDA), NADPH oxidase (NOX), superoxide dismutase (SOD), catalase (CAT), peroxides (POD), ascorbate peroxidase (APX), glutathione reductase (GR), ascorbate (AsA) and GSH/GSSG. The main root treated by 0.5 mmol/L SNP for three days was the best, with the activities of the key enzymes of the ginsenoside synthesis pathway, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), farnesyl pyrophosphate synthase (FPS), squalene synthase (SS), squalene epoxidase (SE), and dammarane diol-II synthase (DS) activities increased markedly; the ginsenosides Rg1 + Re, Rb1, Rf, Rc, Rg2 + Rh1 and the total ginsenoside contents increased by 51.0%, 77.7%, 44.6%, 26.8%, 63.2% and 48.2%, respectively, but only a trace amount of the ginsenoside monomer Rb2 decreased 23.4%. The fibrous roots treated by 0.1 mmol/L SNP for four days showed the best effect, HMGCR, FPS, SS, SE, and DS also increased significantly; ginsenosides Rg1 + Re, Rb1, Ro, Rc, Rf, Rb3, Rb2, and total saponin contents increased 37.6%, 47.8%, 34.2%, 75.1%, 51.0%, 49.4%, 28.3%, and 20.4%, respectively. The 1,3-diphosphoglycerate (1,3-DPG) and phosphoenolpyruvate carboxylase (PEPC), related to primary metabolism, were also significantly elevated. The Morris water maze (MWM), histopathological analysis and oxidative stress indexes in brain tissues were used to evaluate the anti-aging effect, indicating that the SNP-treated ginseng further ameliorated D-gal-induced the impaired memory function and oxidative stress in mice, implying the efficacy of SNP-treated ginseng was better than untreated ginseng's. SNP can build the physiological state of ginseng under ecological stress, stimulate the antioxidant protection mechanism, increase the secondary metabolites, and improve the quality of ginseng.

Introduction of a terminal electron sink in chloroplasts decreases leaf cell expansion associated with higher proteasome activity and lower endoreduplication

Foliar development involves successive phases of cell proliferation and expansion that determine the final leaf size, and is characterized by an early burst of reactive oxygen species generated in the photosynthetic electron transport chain (PETC). Introduction of the alternative PETC acceptor flavodoxin in tobacco chloroplasts led to a reduction in leaf size associated to lower cell expansion, without affecting cell number per leaf. Proteomic analysis showed that the biogenesis of the PETC proceeded stepwise in wild-type leaves, with accumulation of light-harvesting proteins preceding that of electron transport components, which might explain the increased energy and electron transfer to oxygen and reactive oxygen species build-up at this stage. Flavodoxin expression did not affect biogenesis of the PETC but prevented hydroperoxide formation through its function as electron sink. Mature leaves from flavodoxin-expressing plants were shown to contain higher levels of transcripts encoding components of the proteasome, a key negative modulator of organ size. Proteome profiling revealed that this differential accumulation was initiated during expansion and led to increased proteasomal activity, whereas a proteasome inhibitor reverted the flavodoxin-dependent size phenotype. Cells expressing plastid-targeted flavodoxin displayed lower endoreduplication, also associated to decreased organ size. These results provide novel insights into the regulation of leaf growth by chloroplast-generated redox signals, and highlight the potential of alternative electron shuttles to investigate the link(s) between photosynthesis and plant development.

A Novel Sorbitol-Based Flow Cytometry Buffer Is Effective for Genome Size Estimation across a Cypriot Grapevine Collection

Flow cytometry (FCM) is a widely used technique to study genome size (C-value), but recalcitrant metabolites in grapevines often hinder its efficiency in grapevine research. The aim of the present study was (i) to develop a novel buffer tailormade for the nuclei isolation of grapevines and (ii) to characterize a Cypriot germplasm collection based on C-values. A local cultivar "Xinisteri" was used as a pilot test to evaluate a Sorbitol-based buffer, while sprouting, young, and fully matured leaves were examined to evaluate the developmental parameter. The novel Sorbitol buffer was shown to have a coefficient of variation (CV) of 4.06%, indicating improved properties compared to other commonly used FCM buffers [WPB (7.69%), LB01 (6.69%), and LB (7.13%), respectively]. In addition, a significant variation in genome size between genotypes was found in a comprehensive application with 24 grape varieties. Nucleic content (2C) ranged from 0.577/1C pg for the "Assyrtiko" cultivar up to 0.597/1C pg for the "Spourtiko" cultivar, revealing a 17.6/1C Mbp difference. The lowest coefficient of variation (CV) across all entries was found in the variety "Ofthalmo" (2.29%), while the highest was observed in "Pinot Noir" (3.44%). Anova analysis revealed several distinct clusters, showing that in several cases, C-values can be used as a simple method to distinguish grapevine cultivars.

Abscisic acid triggers vitamin E accumulation by transient transcript activation of VTE5 and VTE6 in sweet cherry fruits

Tocopherols are lipophilic antioxidants known as vitamin E and synthesized from the condensation of two metabolic pathways leading to the formation of homogentisate and phytyl diphosphate. While homogentisate is derived from tyrosine metabolism, phytyl diphosphate may be formed from geranylgeranyl diphosphate or phytol recycling from chlorophyll degradation. Here, we hypothesized that abscisic acid (ABA) could induce tocopherol biosynthesis in sweet cherries by modifying the expression of genes involved in vitamin E biosynthesis, including those from the phytol recycling pathway. Hence, the expression of key tocopherol biosynthesis genes was determined together with vitamin E and chlorophyll contents during the natural development of sweet cherries on the tree. Moreover, the effects of exogenously applied ABA on the expression of key tocopherol biosynthesis genes were also investigated during on-tree fruit development, and tocopherols and chlorophylls contents were analyzed. Results showed that the expression of tocopherol biosynthesis genes, including VTE5, VTE6, HPPD and HPT showed contrasting patterns of variation, but in all cases, increased by 2- and 3-fold over time during fruit de-greening. This was not the case for GGDR and VTE4, the first showing constitutive expression during fruit development and the second with marked down-regulation at ripening onset. Furthermore, exogenous ABA stimulated the production of both α- and γ-tocopherols by 60% and 30%, respectively, promoted chlorophyll degradation and significantly enhanced VTE5 and VTE6 expression, and also that of HPPD and VTE4, altogether increasing total tocopherol accumulation. In conclusion, ABA increases promote the transcription of phytol recycling enzymes, which may contribute to vitamin E biosynthesis during fruit development in stone fruits like sweet cherries.

Screening and identification of photoresponse factors in kiwifruit (Actinidia arguta) development

BACKGROUND

Light is essential for kiwifruit development, in which photoresponse factors contributes greatly to the quality formation. 'Light sensitive hypocotyls, also known as light-dependent short hypocotyls' (LSH) gene family can participate in fruit development as photoresponse factor. However, the key LSH gene that determine kiwifruit development remains unclear. This study aim to screen and identify the key gene AaLSH9 in A. arguta.

MATERIALS AND METHODS

Genome-wide identification of the LSH gene family was used to analyse LSH genes in kiwifruit. Homologous cloning was used to confirm the sequence of candidate LSH genes. qRT-PCR and cluster analysis of expression pattern were used to screen the key AaLSH9 gene. Subcellular localization of AaLSH9 in tobacco leaves and overexpression of AaLSH9 in Arabidopsis thaliana hy5 mutant plants were used to define the acting place in cell and identify molecular function, respectively.

RESULTS

We identified 15 LSH genes, which were divided into two sub-families namely A and B. Domain analysis of A and B showed that they contained different domain organizations, which possibly played key roles in the evolution process. Three LSH genes, AaLSH2, AaLSH9, and AaLSH11, were successfully isolated from Actinidia arguta. The expression pattern and cluster analysis of these three AaLSH genes suggested AaLSH9 might be a key photoresponse gene participating in fruit development in A. arguta. Subcellular localization showed AaLSH9 protein was located in the nucleus. The overexpression of AaLSH9 gene in Arabidopsis thaliana hy5 mutant plants partially complemented the long hypocotyls of hy5 mutant, implying AaLSH9 played a key role as photoresponse factor in cells. In addition, the seed coat color of A. thaliana over-expressing AaLSH9 became lighter than the wide type A.thaliana. Finally, AaCOP1 was confirmed as photoresponse factor to participate in developmental process by stable transgenic A. thaliana.

CONCLUSIONS

AaLSH9 can be involved in kiwifruit (A. arguta) development as key photoresponse factor. Our results not only identified the photoresponse factors AaLSH9 and AaCOP1 but also provided insights into their key role in fruit quality improvement in the process of light response.

Impact of individual, combined and sequential stress on photosynthesis machinery in rice (Oryza sativa L)

Abiotic stresses such as heat, drought and submergence are major threats to global food security. Despite simultaneous or sequential occurrence of these stresses being recurrent under field conditions, crop response to such stress combinations is poorly understood. Rice is a staple food crop for the majority of human beings. Exploitation of existing genetic diversity in rice for combined and/or sequential stress is a useful approach for developing climate-resilient cultivars. We phenotyped ~400 rice accessions under high temperature, drought, or submergence and their combinations. A cumulative performance index revealed Lomello as the best performer across stress and stress combinations at the seedling stage. Lomello showed a remarkable ability to maintain a higher quantum yield of photosystem (PS) II photochemistry. Moreover, the structural integrity of the photosystems, electron flow through both PSI and PSII and the ability to protect photosystems against photoinhibition were identified as the key traits of Lomello across the stress environments. A higher membrane stability and an increased amount of leaf chlorophyll under stress may be due to an efficient management of reactive oxygen species (ROS) at the cellular level. Further, an efficient electron flow through the photosystems and, thus, a higher photosynthetic rate in Lomello is expected to act as a sink for ROS by reducing the rate of electron transport to the high amount of molecular oxygen present in the chloroplast. However, further studies are needed to identify the molecular mechanism(s) involved in the stability of photosynthetic machinery and stress management in Lomello during stress conditions.

Experimental approaches in studying active biomolecules modulating fruit ripening: Melatonin as a case study

Phytohormones are naturally occurring small organic molecules found at low concentrations in plants. They perform essential functions in growth and developmental processes, from organ initiation to senescence, including fruit ripening. These regulatory molecules are studied using different experimental approaches, such as performing exogenous applications, evaluating endogenous levels, and/or obtaining genetically modified lines. Here, we discuss the advantages and limitations of current experimental approaches used to study active biomolecules modulating fruit ripening, focusing on melatonin. Although melatonin has been implicated in fruit ripening in several model fruit crops, current knowledge is affected by the different experimental approaches used, which have given different and sometimes even contradictory results. The methods of application and the doses used have produced different results in studies based on exogenous applications, while different measurement methods and ways of expressing results explain most of the variability in studies using correlative analyses. Furthermore, studies on genetically modified crops have focused on tomato (Solanum lycopersicum L.) plants only. However, TILLING and CRISPR methodologies are becoming essential tools to complement the results from the experimental approaches described above. This will not only help the scientific community better understand the role of melatonin in modulating fruit ripening, but it will also help develop technological advances to improve fruit yield and quality in major crops. The combination of various experimental approaches will undoubtedly lead to a complete understanding of the function of melatonin in fruit ripening in the near future, so that this knowledge can be effectively transferred to the field.

Differential tissue-specific accumulation and function of tocochromanols in grape berries

Grape berries have been extensively studied in terms of antioxidant characterization, specifically in anthocyanin, total phenol, and tannin accumulation. However, very little is known about vitamin E composition and contents in this fruit. Aiming to examine the function of vitamin E during grape berries ripening, tocochromanol contents and composition were evaluated in berries and leaves of grapevines (Vitis vinifera L. cv. Merlot), from just before veraison to commercial harvest. We also determined the time-course evolution of tocochromanol accumulation in various fruit tissues, including the skin, pulp, and seeds, and measured the extent of primary and secondary lipid peroxidation, as well as fruit technological maturity parameters. Vitamin E accumulated at higher levels in leaves than in fruits, although the tissue-specific evaluation of tocochromanol contents revealed that berry skin is also rich in α-tocopherol whereas tocotrienols were present in seeds only. α-Tocopherol content decreased during ripening, more specifically in the skin, and it was accompanied by an increase in the extent of lipid peroxidation. Contents and variations in the levels of α-tocopherol, but not those of the other tocochromanols, were inversely related to changes in lipid peroxidation during fruit ripening, as indicated by tissue-specific variations in malondialdehyde contents. In conclusion, α-tocopherol is more abundant in leaves than fruit, yet it apears to exert a role in the modulation of the extent of lipid peroxidation in grape berries, more specifically in the skin, where α-tocopherol depletion and malondialdehyde accumulation may be related to an adequate progression of fruit ripening.

Novel insights into the contribution of plastoglobules and reactive oxygen species to chromoplast differentiation

Plant tissues can be enriched in phytonutrients not only by stimulating their biosynthesis but also by providing appropriate sink structures for their sequestering and storage. In the case of carotenoids, they accumulate at high levels in chromoplasts naturally found in flowers and fruit. Chromoplasts can also be artificially differentiated from leaf chloroplasts by boosting carotenoid production with the bacterial protein crtB. Here we used electron and confocal microscopy together with subplastidial fractionation and transcript, protein and metabolite analyses to analyze the structural and biochemical changes occurring in crtB-induced artificial chromoplasts and their impact on the accumulation of health-related isoprenoids. We show that leaf chromoplasts develop plastoglobules (PG) harboring high levels of carotenoids (mainly phytoene and pro-vitamin A β-carotene) but also other nutritionally relevant isoprenoids, such as tocopherols (vitamin E) and phylloquinone (vitamin K1). Further promoting PG proliferation by exposure to intense (high) light resulted in a higher accumulation of these health-related metabolites but also an acceleration of the chloroplast-to-chromoplast conversion. We further show that the production of reactive oxygen species (ROS) stimulates chromoplastogenesis. Our data suggest that carotenoid accumulation and ROS production are not just consequences but promoters of the chromoplast differentiation process.

Novel insights into the contribution of plastoglobules and reactive oxygen species to chromoplast differentiation

Plant tissues can be enriched in phytonutrients not only by stimulating their biosynthesis but also by providing appropriate sink structures for their sequestering and storage. In the case of carotenoids, they accumulate at high levels in chromoplasts naturally found in flowers and fruit. Chromoplasts can also be artificially differentiated from leaf chloroplasts by boosting carotenoid production with the bacterial protein crtB. Here we used electron and confocal microscopy together with subplastidial fractionation and transcript, protein and metabolite analyses to analyze the structural and biochemical changes occurring in crtB-induced artificial chromoplasts and their impact on the accumulation of health-related isoprenoids. We show that leaf chromoplasts develop plastoglobules (PG) harboring high levels of carotenoids (mainly phytoene and pro-vitamin A β-carotene) but also other nutritionally relevant isoprenoids, such as tocopherols (vitamin E) and phylloquinone (vitamin K1). Further promoting PG proliferation by exposure to intense (high) light resulted in a higher accumulation of these health-related metabolites but also an acceleration of the chloroplast-to-chromoplast conversion. We further show that the production of reactive oxygen species (ROS) stimulates chromoplastogenesis. Our data suggest that carotenoid accumulation and ROS production are not just consequences but promoters of the chromoplast differentiation process.

Solanum dulcamara L. Berries: A Convenient Model System to Study Redox Processes in Relation to Fruit Ripening

The present study provides, for the first time, a physicochemical and biochemical characterization of the redox processes associated with the ripening of Solanum dulcamara L. (bittersweet) berries. Electron Paramagnetic Resonance Spectroscopy (EPRS) and Imaging (EPRI) measurements of reactive oxygen species (ROS) were performed in parallel with the tissue-specific metabolic profiling of major antioxidants and assessment of antioxidant enzymes activity. Fruit transition from the mature green (MG) to ripe red (RR) stage involved changes in the qualitative and quantitative content of antioxidants and the associated cellular oxidation and peroxidation processes. The skin of bittersweet berries, which was the major source of antioxidants, exhibited the highest antioxidant potential against DPPH radicals and nitroxyl spin probe 3CP. The efficient enzymatic antioxidant system played a critical protective role against the deleterious effects of progressive oxidative stress during ripening. Here, we present the EPRI methodology to assess the redox status of fruits and to discriminate between the redox states of different tissues. Interestingly, the intracellular reoxidation of cell-permeable nitroxide probe 3CP was observed for the first time in fruits or any other plant tissue, and its intensity is herein proposed as a reliable indicator of oxidative stress during ripening. The described noninvasive EPRI technique has the potential to have broader application in the study of redox processes associated with the development, senescence, and postharvest storage of fruits, as well as other circumstances in which oxidative stress is implicated.

Nutritional Enrichment of Plant Leaves by Combining Genes Promoting Tocopherol Biosynthesis and Storage

The enrichment of plant tissues in tocochromanols (tocopherols and tocotrienols) is an important biotechnological goal due to their vitamin E and antioxidant properties. Improvements based on stimulating tocochromanol biosynthesis have repeatedly been achieved, however, enhancing sequestering and storage in plant plastids remains virtually unexplored. We previously showed that leaf chloroplasts can be converted into artificial chromoplasts with a proliferation of plastoglobules by overexpression of the bacterial crtB gene. Here we combined coexpression of crtB with genes involved in tocopherol biosynthesis to investigate the potential of artificial leaf chromoplasts for vitamin E accumulation in Nicotiana benthamiana leaves. We show that this combination improves tocopherol levels compared to controls without crtB and confirm that VTE1, VTE5, VTE6 and tyrA genes are useful to increase the total tocopherol levels, while VTE4 further leads to enrichment in α-tocopherol (the tocochromanol showing highest vitamin E activity). Additionally, we show that treatments that further promote plastoglobule formation (e.g., exposure to intense light or dark-induced senescence) result in even higher improvements in the tocopherol content of the leaves. An added advantage of our strategy is that it also results in increased levels of other related plastidial isoprenoids such as carotenoids (provitamin A) and phylloquinones (vitamin K1).

Adjustments in photosynthetic pigments, PS II photochemistry and photoprotection in a tropical C4 forage plant exposed to warming and elevated [CO2]

Global climate change will impact crops and grasslands, affecting growth and yield. However, is not clear how the combination of warming and increased atmospheric carbon dioxide concentrations ([CO₂]) will affect the photosystem II (PSII) photochemistry and the photosynthetic tissue photoinhibition and photoprotection on tropical forages. Here, we evaluated the effects of elevated [CO₂] (∼600 μmol mol^-1) and warming (+2 °C increase temperature) on the photochemistry of photosystem II and the photoprotection strategies of a tropical C4 forage Panicum maximum Jacq. grown in a Trop-T-FACE facility under well-watered conditions without nutrient limitation. Analysis of the maximum photochemical efficiency of PSII (F_v/F_m), the effective PSII quantum yield Y(II), the quantum yield of regulated energy dissipation Y(NPQ), the quantum yield of non-regulated energy dissipation Y(NO), and the malondialdehyde (MDA) contents in leaves revealed that the photosynthetic apparatus of plants did not suffer photoinhibitory damage, and plants did not increase lipid peroxidation in response to warming and [CO₂] enrichment. Plants under warming treatment showed a 12% higher chlorophyll contents and a 58% decrease in α-tocopherol contents. In contrast, carotenoid composition (zeaxanthin and β-carotene) and ascorbate levels were not altered by elevated [CO₂] and warming. The elevated temperature increased both net photosynthesis rate and aboveground biomass but elevated [CO₂] increased only net photosynthesis. Adjustments in chlorophyll, de-epoxidation state of the xanthophylls cycle, and tocopherol contents suggest leaves of P. maximum can acclimate to 2 °C warmer temperature and elevated [CO₂] when plants are grown with enough water and nutrients during tropical autumn-winter season.

Environmentally driven transcriptomic and metabolic changes leading to color differences in "Golden Reinders" apples

Apple is characterized by its high adaptation to diverse growing environments. However, little is still known about how different environments can regulate at the metabolic or molecular level specific apple quality traits such as the yellow fruit peel color. In this study, changes in carotenoids and chlorophylls, antioxidants as well as differences in the transcriptome were investigated by comparing the peel of "Golden Reinders" apples grown at different valley and mountain orchards. Mountain environment favored the development of yellow color, which was not caused by an enhanced accumulation of carotenoids but rather by a decrease in the chlorophyll content. The yellow phenotype was also associated to higher expression of genes related to chloroplast functions and oxidative stress. Time-course analysis over the last stages of apple development and ripening, in fruit from both locations, further revealed that the environment differentially modulated isoprenoids and phenylpropanoid metabolism and pointed out a key role for H₂O₂ in triggering apple peel degreening. Overall, the results presented herein provide new insights into how different environmental conditions regulate pigment and antioxidant metabolism in apple leading to noticeable differences in the apple peel color.

Manipulation of light quality is an effective tool to regulate photosynthetic capacity and fruit antioxidant properties of Solanum lycopersicum L. cv. 'Microtom' in a controlled environment

Light quality plays an essential role in setting plant structural and functional traits, including antioxidant compounds. This paper aimed to assess how manipulating the light spectrum during growth may regulate the photosynthetic activity and fruit bioactive compound synthesis in Solanum lycopersicum L. cv. 'Microtom' to improve plant physiological performance and fruit nutritional value. Plants were cultivated under three light quality regimes: red-green-blue LEDs (RGB), red-blue LEDs (RB) and white fluorescent lamps (FL), from sowing to fruit ripening. Leaf functional traits, photosynthetic efficiency, Rubisco and D1 protein expression, and antioxidant production in fruits were analyzed. Compared to FL, RGB and RB regimes reduced height and increased leaf number and specific leaf area, enhancing plant dwarf growth. The RGB regime improved photosynthesis and stomatal conductance despite lower biomass, favoring Rubisco synthesis and carboxylation rate than RB and FL regimes. The RB light produced plants with fewer flowers and fruits with a lower ascorbic acid amount but the highest polyphenol content, antioxidant capacity and SOD and CAT activities. Our data indicate that the high percentage of the green wavelength in the RGB regime promoted photosynthesis and reduced plant reproductive capacity compared to FL and RB. Conversely, the RB regime was the best in favoring the production of health-promoting compounds in tomato berries.

LcNAC13 Is Involved in the Reactive Oxygen Species-Dependent Senescence of the Rudimentary Leaves in Litchi chinensis

Litchi is an important evergreen fruit tree. Floral formation in litchi is induced by low temperatures (LTs). However, unstable flowering is a challenge for litchi production in times of global warming and climate change. Previous studies have shown that the methyl viologen dichloride hydrate-generated reactive oxygen species (ROS) could promote flowering. Leaves in the panicles may affect the development of the inflorescence in litchi under high-temperature condition. In this study, potted litchi trees were transferred to growth chambers at LT and high temperature (HT). From a previous dataset of the RNA sequencing of the ROS-treated rudimentary leaves, a NAC transcription factor-encoding gene LcNAC13 was identified. By genetic transformation of LcNAC13 to Arabidopsis thaliana and tobacco, it was found that the ROS-induced senescence of the leaves was accelerated. Silencing LcNAC13 by virus-induced gene silencing (VIGS) delayed ROS-dependent senescence. Our results suggested that LcNAC13 regulates rudimentary leaf senescence. Our study provided a new target gene for the future molecular breeding of new cultivars that could flower under global warming conditions.

Biological effects of gamma-ray radiation on tulip (Tulipa gesneriana L.)

Tulip, being an important ornamental plant, generally requires lengthy and laborious procedures to develop new varieties using traditional breeding methods requires. But ionizing radiation potentially accelerates the breeding process of ornamental plant species. The biological effects of γ-ray irradiation on tulip, therefore, were investigated through establishing an irradiation-mediated mutation breeding protocol to accelerate its breeding process. ISSR-PCR molecular marker technique was further used to identify the mutants of phenotypic variation plants. This study showed that low irradiation doses (5 Gy) stimulated bulb germination to improve the survival rate of tulip, while high irradiation doses (20 to 100 Gy) significantly (P < 0.05) inhibited its seed germination and growth, and decreased the flowering rate, petal number, flower stem length and flower diameter. More than 40 Gy significantly (P < 0.05) decreased the total chlorophyll content and increased the malondialdehyde (MDA) content in tulips. Interestingly, three types of both stigma variations and flower pattern variations, and four types of flower colour variations were observed. With increasing the irradiation dose from 5 to 100 Gy, the anthocyanin and flavonoid contents continuously decreased. Scanning electron microscopy (SEM) analysis evidenced that high irradiation doses altered the micromorphology of leaf stomata. Microscopic observations of tulip root apical mitosis further showed the abnormal chromosomal division behaviour occurring at different mitotic phases under irradiation treatment (80 Gy). Increasing the irradiation dose from 20 to 100 Gy enhanced the micronucleus rate. Moreover, the suspected genetic variation in tulips was evaluated by inter-simple sequence repeat (ISSR) analysis, and the percentage of polymorphic bands was 68%. Finally, this study concludes that that 80 Gy may be an appropriate radiation does to better enhance the efficiency of mutagenic breeds in tulip plants. Using γ-ray irradiation, therefore, is expected to offer a theoretical basis for mutation breeding in tulips.

ROS-scavenging-associated transcriptional and biochemical shifts during nectarine fruit development and ripening

ROS are known as toxic by-products but also as important signaling molecules playing a key role in fruit development and ripening. To counteract the negative effects of ROS, plants and fruit own multiple ROS-scavenging mechanisms aiming to ensure a balanced ROS homeostasis. In the present study, changes in specific ROS (i.e. H₂O₂) as well as enzymatic (SOD, CAT, POX, APX) and non-enzymatic (phenylpropanoids, carotenoids and ascorbate) ROS-scavenging systems were investigated along four different stages of nectarine (cv. 'Diamond Ray') fruit development and ripening (39, 70, 94 and 121 DAFB) both at the metabolic (28 individual metabolites or enzymes) and transcriptional level (24 genes). Overall, our results demonstrate a complex ROS-related transcriptome and metabolome reprogramming during fruit development and ripening. At earlier fruit developmental stages an increase on the respiration rate is likely triggering an oxidative burst and resulting in the activation of specific ethylene response factors (ERF1). In turn, ROS-responsive genes or the biosynthesis of specific antioxidant compounds (i.e. phenylpropanoids) were highly expressed or accumulated at earlier fruit developmental stages (39-70 DAFB). Nonetheless, as the fruit develops, the decrease in the fruit respiration rate and the reduction of ERF1 genes leads to lower levels of most non-enzymatic antioxidants and higher accumulation of H₂O₂. Based on available literature and the observed accumulation dynamics of H₂O₂, it is anticipated that this compound may not only be a by-product of ROS-scavenging but also a signaling molecule accumulated during the ripening of nectarine fruit.

Secondary Metabolites Coordinately Protect Grapes from Excessive Light and Sunburn Damage during Development

Sunburn is a physiological disorder that reduces grape quality and vineyard yield. It is the result of excessive sunlight and high temperatures. As climate change continues to increase air temperatures, reports of sunburn damage in vineyards worldwide are becoming more frequent. Grapes produce secondary metabolites (carotenoids, polyphenols and aroma compounds) to counter photooxidative stress and acclimate to higher radiation environments. This study evaluated changes in these compounds in during ripening when grapes were exposed post-flowering (ED) and at véraison (LD), and compared them to a nondefoliated control (ND). ND contained more α-terpineol and violaxanthin, and the defoliated treatments contained more zeaxanthin, β-carotene, C₆ compounds and flavonoids. ED berries adapted better to higher-light environments, displayed larger changes in secondary metabolite concentrations and lower levels of sunburn damage than LD berries did. The composition of berries with increasing sunburn damage was evaluated for the first time. Berries with no damage had the lowest concentrations of flavonoids and oxidized glutathione, and the highest concentrations of chlorophyll and α-terpineol. As damage increased, destruction of photosynthetic pigments, increase in polyphenols and loss of aroma compounds were evidenced. A significant effect of temperature and developmental stage on grape composition was also observed. This study provides a holistic overview of changes in secondary metabolites experienced by grape berries when exposed to excessive light, how these vary along development and how they affect sunburn incidence.

Photosynthesis research under climate change

Increasing global population and climate change uncertainties have compelled increased photosynthetic efficiency and yields to ensure food security over the coming decades. Potentially, genetic manipulation and minimization of carbon or energy losses can be ideal to boost photosynthetic efficiency or crop productivity. Despite significant efforts, limited success has been achieved. There is a need for thorough improvement in key photosynthetic limiting factors, such as stomatal conductance, mesophyll conductance, biochemical capacity combined with Rubisco, the Calvin-Benson cycle, thylakoid membrane electron transport, nonphotochemical quenching, and carbon metabolism or fixation pathways. In addition, the mechanistic basis for the enhancement in photosynthetic adaptation to environmental variables such as light intensity, temperature and elevated CO₂ requires further investigation. This review sheds light on strategies to improve plant photosynthesis by targeting these intrinsic photosynthetic limitations and external environmental factors.

Functional basis of electron transport within photosynthetic complex I

Photosynthesis and respiration rely upon a proton gradient to produce ATP. In photosynthesis, the Respiratory Complex I homologue, Photosynthetic Complex I (PS-CI) is proposed to couple ferredoxin oxidation and plastoquinone reduction to proton pumping across thylakoid membranes. However, little is known about the PS-CI molecular mechanism and attempts to understand its function have previously been frustrated by its large size and high lability. Here, we overcome these challenges by pushing the limits in sample size and spectroscopic sensitivity, to determine arguably the most important property of any electron transport enzyme - the reduction potentials of its cofactors, in this case the iron-sulphur clusters of PS-CI (N0, N1 and N2), and unambiguously assign them to the structure using double electron-electron resonance. We have thus determined the bioenergetics of the electron transfer relay and provide insight into the mechanism of PS-CI, laying the foundations for understanding of how this important bioenergetic complex functions.

Molecular Mechanisms of Nitric Oxide (NO) Signaling and Reactive Oxygen Species (ROS) Homeostasis during Abiotic Stresses in Plants

Abiotic stressors, such as drought, heavy metals, and high salinity, are causing huge crop losses worldwide. These abiotic stressors are expected to become more extreme, less predictable, and more widespread in the near future. With the rapidly growing human population and changing global climate conditions, it is critical to prevent global crop losses to meet the increasing demand for food and other crop products. The reactive gaseous signaling molecule nitric oxide (NO) is involved in numerous plant developmental processes as well as plant responses to various abiotic stresses through its interactions with various molecules. Together, these interactions lead to the homeostasis of reactive oxygen species (ROS), proline and glutathione biosynthesis, post-translational modifications such as S-nitrosylation, and modulation of gene and protein expression. Exogenous application of various NO donors positively mitigates the negative effects of various abiotic stressors. In view of the multidimensional role of this signaling molecule, research over the past decade has investigated its potential in alleviating the deleterious effects of various abiotic stressors, particularly in ROS homeostasis. In this review, we highlight the recent molecular and physiological advances that provide insights into the functional role of NO in mediating various abiotic stress responses in plants.

Photosynthesis and chloroplast redox signaling in the age of global warming: stress tolerance, acclimation, and developmental plasticity

Contemporary climate change is characterized by the increased intensity and frequency of environmental stress events such as floods, droughts, and heatwaves, which have a debilitating impact on photosynthesis and growth, compromising the production of food, feed, and biofuels for an expanding population. The need to increase crop productivity in the context of global warming has fueled attempts to improve several key plant features such as photosynthetic performance, assimilate partitioning, and tolerance to environmental stresses. Chloroplast redox metabolism, including photosynthetic electron transport and CO2 reductive assimilation, are primary targets of most stress conditions, leading to excessive excitation pressure, photodamage, and propagation of reactive oxygen species. Alterations in chloroplast redox poise, in turn, provide signals that exit the plastid and modulate plant responses to the environmental conditions. Understanding the molecular mechanisms involved in these processes could provide novel tools to increase crop yield in suboptimal environments. We describe herein various interventions into chloroplast redox networks that resulted in increased tolerance to multiple sources of environmental stress. They included manipulation of endogenous components and introduction of electron carriers from other organisms, which affected not only stress endurance but also leaf size and longevity. The resulting scenario indicates that chloroplast redox pathways have an important impact on plant growth, development, and defense that goes beyond their roles in primary metabolism. Manipulation of these processes provides additional strategies for the design of crops with improved performance under destabilized climate conditions as foreseen for the future.

Transient photoinhibition and photo-oxidative stress as an integral part of stress acclimation and plant development in a dioecious tree adapted to Mediterranean ecosystems

Mastic trees (Pistacia lentiscus L.) are dioecious perennial plants that are highly adapted to Mediterranean climates but display a high sensitivity to winter periods. In order to understand how sex, leaf phenology and ecological context could condition sensitivity to winter and associated mechanisms to acclimate to these conditions, photoinhibition and photo-oxidative stress markers were examined in mastic trees (P. lentiscus) from a natural population growing in the Garraf Natural Park for a consecutive 12-month period (seasonal study), as well as in three populations naturally growing in the Montseny Natural Park, including the highest altitudes described for this species, during winter (altitudinal study). Results from these studies indicate that both the winter period and higher elevation influenced the degree of photoinhibition, but this was not conditioned by sex. In fact, winter photoinhibition occurred transiently even though it was accompanied by chlorophyll loss and malondialdehyde contents. Stress acclimation was achieved through biochemical adjustments in chloroplasts, characterized by anthocyanin shielding, increased de-epoxidation state of the xanthophyll cycle as well as tocopherol accumulation, and phenological adaptations, the latter allowing a complete resetting of the physiological performance of leaves. Moreover, although females showed higher lipid peroxidation than males during the coldest winter months, at the highest elevation and during flowering in spring, this oxidative stress was mild and transient with no negative consequences for the physiology of plants. It is concluded that evergreen mastic trees acclimate to winter conditions and higher elevations by activation of antioxidant defenses together with phenological adjustments, altogether playing a crucial role in plant survival. Sexual dimorphism in mastic trees appears as a relevant factor when considering sensitivity to photo-oxidative stress in winter and altitudinal conditions.

Several geranylgeranyl diphosphate synthase isoforms supply metabolic substrates for carotenoid biosynthesis in tomato

Geranylgeranyl diphosphate (GGPP) produced by GGPP synthase (GGPPS) serves as a precursor for many plastidial isoprenoids, including carotenoids. Phytoene synthase (PSY) converts GGPP into phytoene, the first committed intermediate of the carotenoid pathway. Here we used biochemical, molecular, and genetic tools to characterise the plastidial members of the GGPPS family in tomato (Solanum lycopersicum) and their interaction with PSY isoforms. The three tomato GGPPS isoforms found to localise in plastids (SlG1, 2 and 3) exhibit similar kinetic parameters. Gene expression analyses showed a preferential association of individual GGPPS and PSY isoforms when carotenoid biosynthesis was induced during root mycorrhization, seedling de-etiolation and fruit ripening. SlG2, but not SlG3, physically interacts with PSY proteins. By contrast, CRISPR-Cas9 mutants defective in SlG3 showed a stronger impact on carotenoid levels and derived metabolic, physiological and developmental phenotypes compared with those impaired in SlG2. Double mutants defective in both genes could not be rescued. Our work demonstrates that the bulk of GGPP production in tomato chloroplasts and chromoplasts relies on two cooperating GGPPS paralogues, unlike other plant species such as Arabidopsis thaliana, rice or pepper, which produce their essential plastidial isoprenoids using a single GGPPS isoform.

Hormonal impact on photosynthesis and photoprotection in plants

Photosynthesis is not only essential for plants, but it also sustains life on Earth. Phytohormones play crucial roles in developmental processes, from organ initiation to senescence, due to their role as growth and developmental regulators, as well as their central role in the regulation of photosynthesis. Furthermore, phytohormones play a major role in photoprotection of the photosynthetic apparatus under stress conditions. Here, in addition to discussing our current knowledge on the role of the phytohormones auxin, cytokinins, gibberellins, and strigolactones in promoting photosynthesis, we will also highlight the role of abscisic acid beyond stomatal closure in modulating photosynthesis and photoprotection under various stress conditions through crosstalk with ethylene, salicylates, jasmonates, and brassinosteroids. Furthermore, the role of phytohormones in controlling the production and scavenging of photosynthesis-derived reactive oxygen species, the duration and extent of photo-oxidative stress and redox signaling under stress conditions will be discussed in detail. Hormones have a significant impact on the regulation of photosynthetic processes in plants under both optimal and stress conditions, with hormonal interactions, complementation, and crosstalk being important in the spatiotemporal and integrative regulation of photosynthetic processes during organ development at the whole-plant level.

Biosynthesis and Cellular Functions of Tartaric Acid in Grapevines

Tartaric acid (TA) is an obscure end point to the catabolism of ascorbic acid (Asc). Here, it is proposed as a "specialized primary metabolite", originating from carbohydrate metabolism but with restricted distribution within the plant kingdom and lack of known function in primary metabolic pathways. Grapes fall into the list of high TA-accumulators, with biosynthesis occurring in both leaf and berry. Very little is known of the TA biosynthetic pathway enzymes in any plant species, although recently some progress has been made in this space. New technologies in grapevine research such as the development of global co-expression network analysis tools and genome-wide association studies, should enable more rapid progress. There is also a lack of information regarding roles for this organic acid in plant metabolism. Therefore this review aims to briefly summarize current knowledge about the key intermediates and enzymes of TA biosynthesis in grapes and the regulation of its precursor, ascorbate, followed by speculative discussion around the potential roles of TA based on current knowledge of Asc metabolism, TA biosynthetic enzymes and other aspects of fruit metabolism.

Genome-wide identification, characterization and expression profile of glutaredoxin gene family in relation to fruit ripening and response to abiotic and biotic stresses in banana (Musa acuminata)

Glutaredoxins (GRXs) are disulfide oxidoreductases that are involved in various biological processes. However, little information on the role of GRXs in the regulation of fruit ripening and the response to stress is available. In this study, we isolated 64 GRX genes from banana genome. Their encoded GRX proteins could be classified into four classes: CC, CGFS, CPYC and GRL types. The distribution and synteny of these GRXs on chromosomes, the gene structures, the promoter sequences, and the possible protein subcellular localizations were characterized. Molecular interaction network analysis suggested that MaGRX might interact with glutathione reductase (GR), sulfiredoxin, peroxiredoxin (Prx), and NADPH-dependent thioredoxin reductase C (NTRC), contributing to the antioxidative defense of banana fruit. MicroRNA prediction showed that MaGRX genes might be targeted by different miRNAs. Transcriptome analysis characterized the expression profiles of different MaGRX genes during banana fruit ripening, and in response to different storage stresses. The results suggested that CC-type, CPYC-type and GRL-type MaGRXs might be more active than CGFS-type MaGRXs during banana fruit ripening and the response to stress. Moreover, MaGRX6/7/9/11/17/23/28 and MaGRL3/16/19 might play important roles in regulating fruit ripening or in response to low and high temperature, or Fusarium proliferatum infection.

Auxins, the hidden player in chloroplast development

Throughout decades of plant research, the plant hormones known as auxins have been found to be of vital importance in most plant development processes. Indole-3-acetic acid (IAA) represents the most common auxin in plants and can be synthesized from its tryptophan precursor, which is synthesized in the chloroplast. The chloroplast constitutes an organelle of great relevance to plants since the photosynthesis process by which plants get most of their energy is carried out there. The role of auxins in photosynthesis has been studied for at least 50 years, and in this time, it has been shown that auxins have an effect on several of the essential components and structure of the chloroplast. In recent decades, a high number of genes have been reported to be expressed in the chloroplast and some of their mutants have been shown to alter different auxin-mediated pathways. Genes in signaling pathways such as IAA/AUX, ARF, GH.3, SAUR and TIR, biosynthesis-related genes such as YUCCA and transport-related genes such as PIN have been identified among the most regulated genes in mutants related to alterations in the chloroplast. This review aims to provide a complete and updated summary of the relationship between auxins and several processes that involve the chloroplast, including chloroplast development, plant albinism, redox regulation and pigment synthesis.

Beyond Ethylene: New Insights Regarding the Role of Alternative Oxidase in the Respiratory Climacteric

Climacteric fruits are characterized by a dramatic increase in autocatalytic ethylene production that is accompanied by a spike in respiration at the onset of ripening. The change in the mode of ethylene production from autoinhibitory to autostimulatory is known as the System 1 (S1) to System 2 (S2) transition. Existing physiological models explain the basic and overarching genetic, hormonal, and transcriptional regulatory mechanisms governing the S1 to S2 transition of climacteric fruit. However, the links between ethylene and respiration, the two main factors that characterize the respiratory climacteric, have not been examined in detail at the molecular level. Results of recent studies indicate that the alternative oxidase (AOX) respiratory pathway may play an essential role in mediating cross-talk between ethylene response, carbon metabolism, ATP production, and ROS signaling during climacteric ripening. New genomic, metabolic, and epigenetic information sheds light on the interconnectedness of ripening metabolic pathways, necessitating an expansion of the current, ethylene-centric physiological models. Understanding points at which ripening responses can be manipulated may reveal key, species- and cultivar-specific targets for regulation of ripening, enabling superior strategies for reducing postharvest wastage.

Effects of ozone treatment on the antioxidant capacity of postharvest strawberry

Strawberries are highly popular around the world because of their juicy flesh and unique taste. However, they are delicate and extremely susceptible to peroxidation of their membrane lipids during storage, which induces water loss and rotting of the fruit. This study investigated the effects of ozone treatment on the physiological traits, active oxygen metabolism, and the antioxidant properties of postharvest strawberry. The results revealed that the weight loss (WL) and respiration rate (RR) of strawberry were inhibited by ozone treatment (OT), while the decline of firmness (FIR) and total soluble solids (TSS) were delayed. Ozone also reduced the generation rate of superoxide radical anions , and the content of hydrogen peroxide (H₂O₂) enhanced the activity of superoxidase (SOD), catalase (CAT), ascorbate peroxidase (APX), and monodehydroascorbate reductase (MDHAR), as well as promoted the accumulation of ascorbic acid (ASA), glutathione (GSH), and ferric reducing/antioxidant power (FRAP). In addition, a total of 29 antioxidant-related proteins were changed between the OT group and control (CK) group as detected by label-free proteomics during the storage time, and the abundance associated with ASA–GSH cycle was higher in the OT group at the later stage of storage, and the qRT-PCR results were consistent with those of proteomics. The improvement of the antioxidant capacity of postharvest strawberry treated with ozone may be achieved by enhancing the activity of the antioxidant enzymes and increasing the expression of the antioxidant proteins related to the ascorbic acid–glutathione (ASA–GSH) cycle.

Strawberries are highly popular around the world because of their juicy flesh and unique taste.

Oxylipins in plastidial retrograde signaling

Oxylipins (compounds derived from the oxidation of polyunsaturated fatty acids) are essential in retrograde signaling emanating from plastids to the nucleus during plant developmental and stress responses. In this graphical review, we provide an overview of the chemical structure, biosynthesis and role of oxylipins, as both redox and hormonal signals, in controlling plant development and stress responses. We also briefly summarize current gaps in the understanding of the involvement of oxylipins in plastidial retrograde signaling to highlight future avenues for research.

A phytotoxicity assessment of the efficiency 2,4-D degradation by different oxidative processes

Highly stable compounds such as dichlorophenoxyacetic acid (2,4-D), which are present in the commercial herbicide Tordon®, are difficult to degrade. Therefore, the objective of this work was to degrade 2,4-D present in Tordon® using different oxidative processes, such as anodic oxidation, Fenton reactions, electro-Fenton, photoelectro-oxidation and photoelectro-Fenton processes. An oxide electrode with the nominal composition Ti/Ru_0.3Ti_0.7O₂ was prepared and inserted into an electrochemical cell containing 100 mL of 0.05 mol L^-1 Na₂SO₄ (pH 3) and 100 mg L^-1 of Tordon®. Electrolysis was performed applying a constant current of 50 mA cm^-2 for 2 h. The concentration of Fenton's reagent was varied from 5 to 10 mg L^-1 (Fe²⁺), and from 50 to 100 mg L^-1 (H₂O₂). Chemical analyses of the total organic carbon (TOC) and the chemical oxygen demand (COD) were performed whilst high-performance liquid chromatography (HPLC) was used to monitor the degradation. A phytotoxicity assessment was performed using cucumber _{seeds as bioindicators. Germination tests were performed using cucumber seeds in the presence of the solutions collected after the application of the oxidative processes. Several analyses were carried out to determine the following: total protein content, the extent of lipid peroxidation, activity of superoxide dismutase, hydrogen peroxide content, catalase activity, and glutathione reductase activity. Oxidation of 2,4-D was observed in all of the oxidative processes, and significant results for the removal of TOC and COD were obtained. Anodic oxidation, and the Fenton and photoelectro-oxidation processes were the least efficient, affording 2,4-dichlorophenol, 2-chlorohydroquinone, and 2-chlorobenzoquinone as by-products. The electro-Fenton and photoelectro-Fenton processes were the most efficient, giving short-chain acids as the main by-products. The formation of these by-products directly affected the phytotoxicity results. The processes that formed short-chain by-products did not generate significant oxidative stress during seed growth, and therefore, seed germination tests were successful.}

Plant Origin, but Not Phylogeny, Drive Species Ecophysiological Response to Projected Climate

Knowledge of the relationship between environmental conditions and species traits is an important prerequisite for understanding determinants of community composition and predicting species response to novel climatic conditions. Despite increasing number of studies on this topic, our knowledge on importance of genetic differentiation, plasticity and their interactions along larger sets of species is still limited especially for traits related to plant ecophysiology. We studied variation in traits related to growth, leaf chemistry, contents of photosynthetic pigments and activity of antioxidative enzymes, stomata morphology and photosynthetic activity across eight Impatiens species growing along altitudinal gradients in Himalayas cultivated in three different temperature regimes and explored effects of among species phylogenetic relationships on the results. Original and target climatic conditions determine trait values in our system. The traits are either highly plastic (e.g., APX, CAT, plant size, neoxanthin, β-carotene, chlorophyll a/b, DEPSC) or are highly differentiated among populations (stomata density, lutein production). Many traits show strong among population differentiation in degree of plasticity and direction in response to environmental changes. Most traits indicate that the species will profit from the expected warming. This suggests that different processes determine the values of the different traits and separating the importance of genetic differentiation and plasticity is crucial for our ability to predict species response to future climate changes. The results also indicate that evolution of the traits is not phylogenetically constrained but including phylogenetic information into the analysis may improve our understanding of the trait-environment relationships as was apparent from the analysis of SLA.

Light Activates the Translational Regulatory Kinase GCN2 via Reactive Oxygen Species Emanating from the Chloroplast

Cytosolic mRNA translation is subject to global and mRNA-specific controls. Phosphorylation of the translation initiation factor eIF2α anchors a reversible regulatory switch that represses cytosolic translation globally. The stress-responsive GCN2 kinase is the only known kinase for eIF2α serine 56 in Arabidopsis (Arabidopsis thaliana). Here, we show that conditions that generate reactive oxygen species (ROS) in the chloroplast, including dark-light transitions, high light, and the herbicide methyl viologen, rapidly activated GCN2 kinase, whereas mitochondrial and endoplasmic reticulum stress did not. GCN2 activation was light dependent and mitigated by photosynthesis inhibitors and ROS quenchers. Accordingly, the seedling growth of multiple Arabidopsis gcn2 mutants was retarded under excess light conditions, implicating the GCN2-eIF2α pathway in responses to light and associated ROS. Once activated, GCN2 kinase preferentially suppressed the ribosome loading of mRNAs for functions such as mitochondrial ATP synthesis, the chloroplast thylakoids, vesicle trafficking, and translation. The gcn2 mutant overaccumulated transcripts functionally related to abiotic stress, including oxidative stress, as well as innate immune responses. Accordingly, gcn2 displayed defects in immune priming by the fungal elicitor, chitin. Therefore, we provide evidence that reactive oxygen species produced by the photosynthetic apparatus help activate the highly conserved GCN2 kinase, leading to eIF2α phosphorylation and thus affecting the status of the cytosolic protein synthesis apparatus.

Evaluation of Antioxidant Systems and Ascorbate-Glutathione Cycle in Feijoa Edible Flowers at Different Flowering Stages

Background: Feijoa (Acca sellowiana (O. Berg)) was initially introduced as an ornamental plant, but nowadays, it is widely cultivated for the numerous beneficial properties of its edible fruits. Feijoa flowers have been included in the list of edible flowers, but despite this, they are still considered niche products due to consumer skepticism and lack of publicity. Methods: This study evaluated the physicochemical traits, antioxidant system, and ascorbate-glutathione cycle in feijoa flowers at five flowering stages based on the Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie (BBCH) scale. Results: The results showed that the optimal stage to harvest feijoa flower is the F2 stage characterized by high bioactive compounds content. Furthermore, the enzymes involved in oxidative stress and the ascorbate-glutathione cycle showed different trends during the flowering stages. Conclusions: This study provides new evidence to understand the possible role of bioactive compounds and ascorbate-glutathione cycle in the regulation of flower development, defining the optimal stage to harvest flowers.

Distinctive Gene Expression Patterns Define Endodormancy to Ecodormancy Transition in Apricot and Peach

Dormancy is a physiological state that plants enter for winter hardiness. Environmental-induced dormancy onset and release in temperate perennials coordinate growth cessation and resumption, but how the entire process, especially chilling-dependent dormancy release and flowering, is regulated remains largely unclear. We utilized the transcriptome profiles of floral buds from fall to spring in apricot (Prunus armeniaca) genotypes with contrasting bloom dates and peach (Prunus persica) genotypes with contrasting chilling requirements (CR) to explore the genetic regulation of bud dormancy. We identified distinct gene expression programming patterns in endodormancy and ecodormancy that reproducibly occur between different genotypes and species. During the transition from endo- to eco-dormancy, 1,367 and 2,102 genes changed in expression in apricot and peach, respectively. Over 600 differentially expressed genes were shared in peach and apricot, including three DORMANCY ASSOCIATED MADS-box (DAM) genes (DAM4, DAM5, and DAM6). Of the shared genes, 99 are located within peach CR quantitative trait loci, suggesting these genes as candidates for dormancy regulation. Co-expression and functional analyses revealed that distinctive metabolic processes distinguish dormancy stages, with genes expressed during endodormancy involved in chromatin remodeling and reproduction, while the genes induced at ecodormancy were mainly related to pollen development and cell wall biosynthesis. Gene expression analyses between two Prunus species highlighted the conserved transcriptional control of physiological activities in endodormancy and ecodormancy and revealed genes that may be involved in the transition between the two stages.

Leaf Senescence: The Chloroplast Connection Comes of Age

Leaf senescence is a developmental process critical for plant fitness, which involves genetically controlled cell death and ordered disassembly of macromolecules for reallocating nutrients to juvenile and reproductive organs. While natural leaf senescence is primarily associated with aging, it can also be induced by environmental and nutritional inputs including biotic and abiotic stresses, darkness, phytohormones and oxidants. Reactive oxygen species (ROS) are a common thread in stress-dependent cell death and also increase during leaf senescence. Involvement of chloroplast redox chemistry (including ROS propagation) in modulating cell death is well supported, with photosynthesis playing a crucial role in providing redox-based signals to this process. While chloroplast contribution to senescence received less attention, recent findings indicate that changes in the redox poise of these organelles strongly affect senescence timing and progress. In this review, the involvement of chloroplasts in leaf senescence execution is critically assessed in relation to available evidence and the role played by environmental and developmental cues such as stress and phytohormones. The collected results indicate that chloroplasts could cooperate with other redox sources (e.g., mitochondria) and signaling molecules to initiate the committed steps of leaf senescence for a best use of the recycled nutrients in plant reproduction.

Enhancement of COD removal in constructed wetlands treating saline wastewater: Intertidal wetland sediment as a novel inoculation

This study investigated intertidal wetland sediment (IWS) as a novel inoculation source for saline wastewater treatment in constructed wetlands (CWs). Samples of IWS (5-20 cm subsurface sediment), which are highly productive and rich in halophilic and anaerobic bacteria, were collected from a high-salinity natural wetland and added to CW matrix. IWS-supplemented CW microcosms that are planted and unplanted Phragmites australis were investigated under salty (150 mM NaCl: PA+(S) and CT+(S)) and non-salty (0 mM NaCl: PA+ and CT+) conditions. The chemical oxygen demand (COD) removal potential of IWS-supplemented CWs was compared with that of conventional CWs without IWS (PA(S) and CT(S), PA, and CT). Results showed that the COD removal rate was higher in PA+(S) (51.80% ± 3.03%) and CT+(S) (29.20% ± 1.26%) than in PA(S) (27.40% ± 3.09%) and CT(S) (27.20% ± 3.06%) at 150 mM NaCl. The plants' chlorophyll content and antioxidant enzyme activity indicated that the addition of IWS enhanced the resistance of plants to salt. Microbial community analysis showed that the dominant microorganisms in PA+(S) and CT+(S), namely, Anaerolineae, Desulfobacterales, and Desulfuromonadales, enhanced the organic removal rates via anaerobic degradation. IWS-induced Dehalococcoides, which is a key participant in ethylene formation, improved the plants' stress tolerance. Several halophilic/tolerant microorganisms were also detected in the CW system with IWS. Thus, IWS is a promising inoculation source for CWs that treat saline wastewater.

Melatonin as an inhibitor of sweet cherries ripening in orchard trees

Although melatonin effects on postharvest fruit ripening have been studied in some detail, information is still scarce during pre-harvest. Here, we examined whether or not melatonin may exert a regulatory role during sweet cherries ripening in orchard trees. We evaluated (i) the endogenous variations in melatonin contents, in comparison to those of well-known phytohormones such as ABA, salicylic acid and jsamonic acid, by ultrahigh performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) during fruit ripening over two consecutive years, and (ii) to what extent melatonin treatments at low and high concentrations (at 10^-4 M and 10^-5 M, respectively) influence fruit ripening on the tree. Endogenous melatonin contents decreased in parallel to those of salicylic acid and jasmonic acid, while ABA contents increased as fruit ripening progressed, thus suggesting an inhibitory role for melatonin in fruit ripening. Furthermore, melatonin treatment at 10^-5 M, which transiently increased endogenous melatonin contents at physiological concentrations, delayed anthocyanin accumulation, thus confirming an inhibitory regulatory role for melatonin in fruit ripening. We also found that the endogenous contents of cytokinins, but not those of ABA were transiently affected by melatonin treatment at 10^-5 M. It is concluded that melatonin may delay sweet cherries ripening in orchard trees, probably exerting a modulatory role through a hormonal cross-talk. These results have important implications for the use of melatonin in the control of the timing of sweet cherries ripening in orchard trees.

The zinc-finger transcription factor CcLOL1 controls chloroplast development and immature pepper fruit color in Capsicum chinense and its function is conserved in tomato

Chloroplast development and chlorophyll content in the immature fruit has a major impact on the morphology and quality in pepper (Capsicum spp.) fruit. Two major quantitative trait loci (QTLs), pc1 and pc10 that affect chlorophyll content in the pepper fruit by modulation of chloroplast compartment size were previously identified in chromosomes 1 and 10, respectively. The pepper homolog of GOLDEN2-LIKE transcription factor (CaGLK2) has been found as underlying pc10, similar to its effect on tomato chloroplast development. In the present study, we identified the pepper homolog of the zinc-finger transcription factor LOL1 (LSD ONE LIKE1; CcLOL1) as the gene underlying pc1. LOL1 has been identified in Arabidopsis as a positive regulator of programmed cell death and we report here on its role in controlling fruit development in the Solanaceae in a fruit-specific manner. The light-green C. chinense parent used for QTL mapping was found to carry a null mutation in CcLOL1. Verification of the function of the gene was done by generating CRISPR/Cas9 knockout mutants of the orthologous tomato gene resulting in light-green tomato fruits, indicating functional conservation of the orthologous genes in controlling chlorophyll content in the Solanaceae. Transcriptome profiling of light and dark-green bulks differing for pc1, showed that the QTL affects multiple photosynthesis and oxidation-reduction associated genes in the immature green fruit. Allelic diversity of three known genes CcLOL1, CaGLK2, and CcAPRR2 that influence pepper immature fruit color, was found to be associated with variation in chlorophyll content primarily in C. chinense.

The Roles of Environmental Factors in Regulation of Oxidative Stress in Plant

Exposure to a variety of environmental factors such as salinity, drought, metal toxicity, extreme temperature, air pollutants, ultraviolet-B (UV-B) radiation, pesticides, and pathogen infection leads to subject oxidative stress in plants, which in turn affects multiple biological processes via reactive oxygen species (ROS) generation. ROS include hydroxyl radicals, singlet oxygen, and hydrogen peroxide in the plant cells and activates signaling pathways leading to some changes of physiological, biochemical, and molecular mechanisms in cellular metabolism. Excessive ROS, however, cause oxidative stress, a state of imbalance between the production of ROS and the neutralization of free radicals by antioxidants, resulting in damage of cellular components including lipids, nucleic acids, metabolites, and proteins, which finally leads to the death of cells in plants. Thus, maintaining a physiological level of ROS is crucial for aerobic organisms, which relies on the combined operation of enzymatic and nonenzymatic antioxidants. In order to improve plants' tolerance towards the harsh environment, it is vital to reinforce the comprehension of oxidative stress and antioxidant systems. In this review, recent findings on the metabolism of ROS as well as the antioxidative defense machinery are briefly updated. The latest findings on differential regulation of antioxidants at multiple levels under adverse environment are also discussed here.

Expression of a Chloroplast-Targeted Cyanobacterial Flavodoxin in Tomato Plants Increases Harvest Index by Altering Plant Size and Productivity

Tomato is the most important horticultural crop worldwide. Domestication has led to the selection of highly fruited genotypes, and the harvest index (HI), defined as the ratio of fruit yield over total plant biomass, is usually employed as a biomarker of agronomic value. Improvement of HI might then result from increased fruit production and/or lower vegetative growth. Reduction in vegetative biomass has been accomplished in various plant species by expression of flavodoxin, an electron shuttle flavoprotein that interacts with redox-based pathways of chloroplasts including photosynthesis. However, the effect of this genetic intervention on the development of reproductive organs has not been investigated. We show herein that expression of a plastid-targeted cyanobacterial flavodoxin in tomato resulted in significant reduction of plant size affecting stems, leaves, and fruit. Decreased size correlated with smaller cells and was accompanied by higher pigment contents and photosynthetic activities per leaf cross-section. Flavodoxin accumulated in green fruit but declined with ripening. Significant increases in HI were observed in flavodoxin-expressing lines due to the production of higher fruit number per plant in smaller plants. Therefore, overall yields can be enhanced by increasing plant density in the field. Metabolic profiling of ripe red fruit showed that levels of sugars, organic acids, and amino acids were similar or higher in transgenic plants, indicating that there was no trade-off between increased HI and fruit metabolite contents in flavodoxin-expressing plants. Taken together, our results show that flavodoxin has the potential to improve major agronomic traits when introduced in tomato.

Get the Balance Right: ROS Homeostasis and Redox Signalling in Fruit

Plant central metabolism generates reactive oxygen species (ROS), which are key regulators that mediate signalling pathways involved in developmental processes and plant responses to environmental fluctuations. These highly reactive metabolites can lead to cellular damage when the reduction-oxidation (redox) homeostasis becomes unbalanced. Whilst decades of research have studied redox homeostasis in leaves, fundamental knowledge in fruit biology is still fragmentary. This is even more surprising when considering the natural profusion of fruit antioxidants that can process ROS and benefit human health. In this review, we explore redox biology in fruit and provide an overview of fruit antioxidants with recent examples. We further examine the central role of the redox hub in signalling during development and stress, with particular emphasis on ascorbate, also referred to as vitamin C. Progress in understanding the molecular mechanisms involved in the redox regulations that are linked to central metabolism and stress pathways will help to define novel strategies for optimising fruit nutritional quality, fruit production and storage.

Photoinhibition and photoprotection during flower opening in lilies

Although most studies to extend vase life in cut flowers have focused on flower senescence thus far, flower opening is a complex process of major biological significance in the determination of flower commercialization. In order to better understand flower opening, this study evaluated to what extent photoinhibition and photo-oxidative stress are associated with tepal de-greening during flower opening in lilies (Lilium "Litouwen"). We estimated the degree of photoinhibition, the capacity for photo- and antioxidant protection, and the extent of lipid peroxidation at four flower opening stages, from closed flowers to anthesis. Additionally, we evaluated to what extent and by which mechanisms related to photo- and antioxidant protection, Promalin® (a combination of gibberellins and cytokinins) delays flower opening. Results showed that chlorophyll content decreased progressively during flower opening, while a sharp decrease of the maximum PSII efficiency (Fv/Fm ratio) was observed just before anthesis. Moreover, content of secondary lipid peroxidation products (malondialdehyde and jasmonic acid) increased just before anthesis, which was preceded by an enhanced production of primary lipid peroxidation products (lipid hydroperoxides). While both tocopherols and tocotrienols (vitamin E) increased during flower opening, β-carotene and xanthophyll content decreased sharply, which may be associated with the sharp decline in the Fv/Fm ratio before anthesis. Flowers treated with Promalin®, which showed delayed opening, experienced transient increases of lipid hydroperoxide and jasmonic acid contents at early stages of flower opening, together with reduced vitamin E and malondialdehyde contents just prior to anthesis. We conclude that the extent of photoinhibition, the capacity of photo- and antioxidant protection and the production of primary and secondary products of lipid peroxidation are finely controlled in a time-dependent manner to allow a correct development of lily flowers.