Molecular and physiological responses to salt stress in salinity-sensitive and tolerant Hibiscus rosa-sinensis cultivars.

Ornamental plants are used to decorate urban and peri-urban areas, and during their cultivation or utilisation, they can be exposed to abiotic stress. Salinity is an abiotic stress factor that limits plant growth and reduces the ornamental value of sensitive species. In this study, transcriptomic analysis was conducted to identify genes associated with tolerance or sensitivity to salinity in two hibiscus (Hibiscus rosa-sinensis L.) cultivars, 'Porto' and 'Sunny wind'. The physiological and biochemical parameters of plants exposed to 50, 100, or 200 mM NaCl and water (control) were monitored. Salinity treatments were applied for six weeks. After four weeks, differences between cultivars were clearly evident and 'Porto' was more tolerant than 'Sunny wind'. The tolerant cultivar showed lower electrolyte leakage and ABA concentrations, and higher proline content in the leaves. Accumulation of Na in different organs was lower in the flower organs of 'Porto'. At the molecular level, several differential expressed genes were observed between the cultivars and flower organs. Among the highly expressed DEGs, coat protein, alcohol dehydrogenase, and AP2/EREBP transcription factor ERF-1. Among the downregulated genes, GH3 and NCED were the most interesting. The differential expression of these genes may explain the salt stress tolerance of 'Porto'.

The Role of Blue and Red Light in the Orchestration of Secondary Metabolites, Nutrient Transport and Plant Quality.

Light is a fundamental environmental parameter for plant growth and development because it provides an energy source for carbon fixation during photosynthesis and regulates many other physiological processes through its signaling. In indoor horticultural cultivation systems, sole-source light-emitting diodes (LEDs) have shown great potential for optimizing growth and producing high-quality products. Light is also a regulator of flowering, acting on phytochromes and inducing or inhibiting photoperiodic plants. Plants respond to light quality through several light receptors that can absorb light at different wavelengths. This review summarizes recent progress in our understanding of the role of blue and red light in the modulation of important plant quality traits, nutrient absorption and assimilation, as well as secondary metabolites, and includes the dynamic signaling networks that are orchestrated by blue and red wavelengths with a focus on transcriptional and metabolic reprogramming, plant productivity, and the nutritional quality of products. Moreover, it highlights future lines of research that should increase our knowledge to develop tailored light recipes to shape the plant characteristics and the nutritional and nutraceutical value of horticultural products.

LED Lighting to Produce High-Quality Ornamental Plants.

The flexibility of LED technology, in terms of energy efficiency, robustness, compactness, long lifetime, and low heat emission, as well as its applications as a sole source or supplemental lighting system, offers interesting potential, giving the ornamental industry an edge over traditional production practices. Light is a fundamental environmental factor that provides energy for plants through photosynthesis, but it also acts as a signal and coordinates multifaceted plant-growth and development processes. With manipulations of light quality affecting specific plant traits such as flowering, plant architecture, and pigmentation, the focus has been placed on the ability to precisely manage the light growing environment, proving to be an effective tool to produce tailored plants according to market request. Applying lighting technology grants growers several productive advantages, such as planned production (early flowering, continuous production, and predictable yield), improved plant habitus (rooting and height), regulated leaf and flower color, and overall improved quality attributes of commodities. Potential LED benefits to the floriculture industry are not limited to the aesthetic and economic value of the product obtained; LED technology also represents a solid, sustainable option for reducing agrochemical (plant-growth regulators and pesticides) and energy inputs (power energy).

Diversification of petal monoterpene profiles during floral development and senescence in wild roses: relationships among geraniol content, petal colour, and floral lifespan.

Wild roses store and emit a large array of fragrant monoterpenes from their petals. Maximisation of fragrance coincides with floral maturation in many angiosperms, which enhances pollination efficiency, reduces floral predation, and improves plant fitness. We hypothesized that petal monoterpenes serve additional lifelong functions such as limiting metabolic damage from reactive oxygen species (ROS), and altering isoprenoid hormonal abundance to increase floral lifespan. Petal monoterpenes were quantified at three floral life-stages (unopened bud, open mature, and senescent) in 57 rose species and 16 subspecies originating from Asia, America, and Europe, and relationships among monoterpene richness, petal colour, ROS, hormones, and floral lifespan were analysed within a phylogenetic context. Three distinct types of petal monoterpene profiles, revealing significant developmental and functional differences, were identified: Type A, species where monoterpene abundance peaked in open mature flowers depleting thereafter; Type B, where monoterpenes peaked in senescing flowers increasing from bud stage, and a rare Type C (8 species) where monoterpenes depleted from bud stage to senescence. Cyclic monoterpenes peaked during early floral development, whereas acyclic monoterpenes (dominated by geraniol and its derivatives, often 100-fold more abundant than other monoterpenes) peaked during floral maturation in Type A and B roses. Early-diverging roses were geraniol-poor (often Type C) and white-petalled. Lifetime changes in hydrogen peroxide (H2O2) revealed a significant negative regression with the levels of petal geraniol at all floral life-stages. Geraniol-poor Type C roses also showed higher cytokinins (in buds) and abscisic acid (in mature petals), and significantly shorter floral lifespan compared with geraniol-rich Type A and B roses. We conclude that geraniol enrichment, intensification of petal colour, and lower potential for H2O2-related oxidative damage characterise and likely contribute to longer floral lifespan in monoterpene-rich wild roses.

Differential submergence tolerance between juvenile and adult Arabidopsis plants involves the ANAC017 transcription factor.

Plants need to attune their stress responses to the ongoing developmental programmes to maximize their efficacy. For instance, successful submergence adaptation is often associated with a delicate balance between saving resources and their expenditure to activate measures that allow stress avoidance or attenuation. We observed a significant decrease in submergence tolerance associated with ageing in Arabidopsis thaliana, with a critical step between 2 and 3 weeks of post-germination development. This sensitization to flooding was concomitant with the transition from juvenility to adulthood. Transcriptomic analyses indicated that a group of genes related to abscisic acid and oxidative stress response was more highly expressed in juvenile plants than in adult ones. These genes are induced by the endomembrane tethered transcription factor ANAC017 that was in turn activated by submergence-associated oxidative stress. A combination of molecular, biochemical and genetic analyses showed that these genes are located in genomic regions that move towards a heterochromatic state with adulthood, as marked by lysine 4 trimethylation of histone H3. We concluded that, while the mechanisms of flooding stress perception and signal transduction were unaltered between juvenile and adult phases, the sensitivity that these mechanisms set into action is integrated, via epigenetic regulation, into the developmental programme of the plant.

Borage extracts affect wild rocket quality and influence nitrate and carbon metabolism.

Market is increasingly demanding vegetables with high quality and nutraceutical characteristics. It was demonstrated that leafy vegetables can get benefit from biostimulants, for the reduction of nitrate concentration and the increment of antioxidants, with potential benefit for human health. The research purpose was to investigate on the role of a novel plant-based biostimulant in affecting nitrogen and carbon metabolism in wild rocket (Diplotaxis tenuifolia L.). Foliar spray treatments were performed with extracts obtained from borage (Borago officinalis L.) leaves and flowers. To evaluate the treatments effect, in vivo determinations (chlorophyll a fluorescence and chlorophyll content) were performed. At harvest, nitrate concentration, sucrose, total sugars, chlorophyll, and carotenoids levels were measured in leaves. In order to characterize the mechanism of action also at molecular level, a set of genes encoding for some of the key enzymes implicated in nitrate and carbon metabolism was selected and their expression was measured by qRT-PCR. Interesting results concerned the increment of sucrose, coherent with a high value of Fv/Fm, in addition to a significant reduction of nitrate and ABA than control, and an enhanced NR in vivo activity. Also, genes expression was influenced by extracts, with a more pronounced effect on N related genes.

"Help is in the air": volatiles from salt-stressed plants increase the reproductive success of receivers under salinity.

MAIN CONCLUSION: Salinity alters VOC profile in emitter sweet basil plants. Airborne signals by emitter plants promote earlier flowering of receivers and increase their reproductive success under salinity. Airborne signals can prime neighboring plants against pathogen and/or herbivore attacks, whilst little is known about the possibility that volatile organic compounds (VOCs) emitted by stressed plants alert neighboring plants against abiotic stressors. Salt stress (50 mM NaCl) was imposed on Ocimum basilicum L. plants (emitters, namely NaCl), and a putative alerting-priming interaction was tested on neighboring basil plants (receivers, namely NaCl-S). Compared with the receivers, the NaCl plants exhibited reduced biomass, lower photosynthesis, and changes in the VOC profile, which are common early responses of plants to salinity. In contrast, NaCl-S plants had physiological parameters similar to those of nonsalted plants (C), but exhibited a different VOC fingerprint, which overlapped, for most compounds, with that of emitters. NaCl-S plants exposed later to NaCl treatment (namely NaCl-S + NaCl) exhibited changes in the VOC profile, earlier plant senescence, earlier flowering, and higher seed yield than C + NaCl plants. This experiment offers the evidence that (1) NaCl-triggered VOCs promote metabolic changes in NaCl-S plants, which, finally, increase reproductive success and (2) the differences in VOC profiles observed between emitters and receivers subjected to salinity raise the question whether the receivers are able to "propagate" the warning signal triggered by VOCs in neighboring companions.

Hormone profile changes occur in roots and leaves of Micro-Tom tomato plants when exposing the aerial part to low doses of UV-B radiation.

During the last decades, many studies investigated the effects of UV-B on the above-ground organs of plants, directly reached by the radiation but, to the best of our knowledges, the influence of mild UV-B doses on root hormones was not explored. Consequently, this research aimed at understanding whether low, not-stressful doses of UV-B radiation applied above-ground influenced the hormone concentrations in leaves and roots of Micro-Tom tomato (Solanum lycopersicum L.) plants during 11 days of treatment and after 3 days of recovery. In particular, ethylene, abscisic acid, jasmonic acid, salicylic acid and indoleacetic acid were investigated. The unchanged levels of chlorophyll a and b, lutein, total xanthophylls and carotenoids, as well as the similar H2O2 concentration between control and treated groups suggest that the UV-B dose applied was well tolerated by the plants. Leaf ethylene emission decreased after 8 and 11 days of irradiation, while no effect was found in roots. Conversely, indoleacetic acid underwent a significant reduction in both organs, though in the roots the decrease occurred only at the end of the recovery period. Salicylic acid increased transiently in both leaves and roots on day 8. Changes in leaf and root hormone levels induced by UV-B radiation were not accompanied by marked alterations of plant architecture. The results show that irradiation of above-ground organs with low UV-B doses can affect the hormone concentrations also in roots, with likely implications in stress and acclimation responses mediated by these signal molecules.

Transcriptional Regulation in Rocket Leaves as Affected by Salinity.

Salinity is one of the major abiotic stress causing yield losses and decreasing product quality. The beneficial effects of biostimulant products to enhance plant tolerance to abiotic stresses have been reported in several crops, but their mode of action is poorly understood. This work aims to better understand the effect of salt stress on wild rocket treated with a borage extract. The expression of some of the transcription factors (TFs) typically involved in salt stress response was studied within a 24 h period. Physiological parameters such as chlorophyll, chlorophyll a fluorescence, carotenoids, phenols, and anthocyanin were analyzed. Results obtained showed that salt stress induced a general increase in the expression levels of almost all TFs studied, whereas the treatment with the plant-base extract only induced an increase at specific time points. Moreover, the approach adopted allowed indagating the change in gene expression during time. Different pathways such as sugars metabolism, cuticular wax biosynthesis, and brassinosteroids signaling took part in plant responses.

UV-B Physiological Changes Under Conditions of Distress and Eustress in Sweet Basil.

UV-B radiation has been previously reported to induce protective or deleterious effects on plants depending on the UV-B irradiation doses. To elucidate how these contrasting events are physiologically coordinated, we exposed sweet basil plants to two UV-B doses: low (8.5 kJ m-2 day-1, 30 min exposure) and high (68 kJ m-2 day-1, 4 h exposure), with the plants given both doses once continuously in a single day. Physiological tests during and after both UV-B exposures were performed by comparing the stress-induced damage and adverse effects on photosynthetic activity, the concentration and composition of photosynthetic and non-photosynthetic pigments, and stress-related hormones biosynthesis in basil plants. Our results showed that upon receiving a high UV-B dose, a severe inactivation of oxygen evolving complex (OEC) activity at the PSII donor side and irreversible PSII photodamage caused primarily by limitation of the acceptor side occurred, which overloaded protective mechanisms and finally led to the death of the plants. In contrast, low UV-B levels did not induce any signs of UV-B stress injuries. The OEC partial limitation and the inactivation of the electron transport chain allowed the activation of photoprotective mechanisms, avoiding irreversible damage to PSII. Overall results indicate the importance of a specific response mechanisms regulating photoprotection vs irreversible photoinhibition in basil that were modulated depending on the UV-B doses.

Effect of Preharvest Abiotic Stresses on the Accumulation of Bioactive Compounds in Horticultural Produce.

The quality of horticultural products is the result of the interaction of different factors, including grower's crop management ability, genotype, and environment. Sub-optimal environmental conditions during plant growth can induce abiotic stresses and reduce the crop performance with yield reduction and quality losses. However, abiotic stresses can induce several physiological, biochemical, and molecular responses in plants, aiming to cope with the stressful conditions. It is well known that these abiotic stresses are also elicitors of the biosynthesis of many metabolites in plants, including a wide range of bioactive compounds, which firstly serve as functional molecules for crop adaptation, but they have also a great interest for their beneficial effects on human health. Nowadays, the consumer is oriented to low-energy foods with low fat content, but at the same time, growing attention is paid to the presence of bioactive molecules, which are recognized as health-related compounds and concur to the nutraceutical value of plant-derived foods. In this context, fruit and vegetables play an important role as sources of bioactive ingredients in the diet. At the cultivation level, the understanding of crop responses to abiotic stresses and how they act in the biosynthesis/accumulation of these bioactive compounds is crucial. In fact, controlled abiotic stresses can be used as tools for improving the nutraceutical value of fruit and vegetables. This review focuses on the quality of vegetables and fruits as affected by preharvest abiotic stressors, with particular attention to the effect on the nutraceutical aspects.

When "thirsty" means "less able to activate the signalling wave trigged by a pulse of ozone": A case of study in two Mediterranean deciduous oak species with different drought sensitivity.

There is a lack of knowledge about the possibility that plants facing abiotic stressors, such as drought, have an altered perception of a pulse of O3 and incur in alterations of their signalling network. This poses some concerns as to whether defensive strategy to cope episodic O3 peaks in healthy plants may fail under stress. In this study, a set of saplings of two Mediterranean deciduous species, Quercus cerris and Q. pubescens, was subjected to water withholding (20% of daily evapotranspiration for 15 days) while another set was kept well-watered. Saplings were then subjected to a pulse of O3 (200 nl l-1 for 5 h) or maintained in filtered air. Q. pubescens had a more severe decline of photosynthesis and leaf PDΨw (about -65% and 5-fold lower than in well-watered ones) and events of cell death were observed under drought when compared to Q. cerris, which is supportive for a higher sensitivity to drought exhibited by this species. When O3 was applied after drought, patterns of signalling compounds were altered in both species. Only in Q. pubescens, the typical O3-induced accumulation of apoplastic reactive oxygen species, which is the first necessary step for the activation of signalling cascade, was completely lost. In Q. cerris the most frequent changes encompassed the weakening of peaks of key signalling molecules (ethylene and salicylic acid), whereas in Q. pubescens both delayed (salicylic and jasmonic acid) or weakened (ethylene and salicylic acid) peaks were observed. This is translated to a higher ability of Q. cerris to maintain a prompt activation of defensive reaction to counteract oxidative damage due to the pollutant. Our results reveal the complexity of the signalling network in plants facing multiple stresses and highlight the need to further investigate possible alteration of defensive mechanism of tree species to predict their behavior.

How Quercus ilex L. saplings face combined salt and ozone stress: a transcriptome analysis.

BACKGROUND: Similar to other urban trees, holm oaks (Quercus ilex L.) provide a physiological, ecological and social service in the urban environment, since they remove atmospheric pollution. However, the urban environment has several abiotic factors that negatively influence plant life, which are further exacerbated due to climate change, especially in the Mediterranean area. Among these abiotic factors, increased uptake of Na + and Cl - usually occurs in trees in the urban ecosystem; moreover, an excess of the tropospheric ozone concentration in Mediterranean cities further affects plant growth and survival. Here, we produced and annotated a de novo leaf transcriptome of Q. ilex as well as transcripts over- or under-expressed after a single episode of O3 (80 nl l-1, 5 h), a salt treatment (150 mM for 15 days) or a combination of these treatments, mimicking a situation that plants commonly face, especially in urban environments. RESULTS: Salinity dramatically changed the profile of expressed transcripts, while the short O3 pulse had less effect on the transcript profile. However, the short O3 pulse had a very strong effect in inducing over- or under-expression of some genes in plants coping with soil salinity. Many differentially regulated genes were related to stress sensing and signalling, cell wall remodelling, ROS sensing and scavenging, photosynthesis and to sugar and lipid metabolism. Most differentially expressed transcripts revealed here are in accordance with a previous report on Q. ilex at the physiological and biochemical levels, even though the expression profiles were overall more striking than those found at the biochemical and physiological levels. CONCLUSIONS: We produced for the first time a reference transcriptome for Q. ilex, and performed gene expression analysis for this species when subjected to salt, ozone and a combination of the two. The comparison of gene expression between the combined salt + ozone treatment and salt or ozone alone showed that even though many differentially expressed genes overlap all treatments, combined stress triggered a unique response in terms of gene expression modification. The obtained results represent a useful tool for studies aiming to investigate the effects of environmental stresses in urban-adapted tree species.

Effects of Two Doses of Organic Extract-Based Biostimulant on Greenhouse Lettuce Grown Under Increasing NaCl Concentrations.

The enhancement of plant tolerance toward abiotic stresses is increasingly being supported by the application of biostimulants. Salinity represents a serious problem in the Mediterranean region. To verify the effects deriving from the application of biostimulants, trials on Romaine lettuce plants under salt exposure were performed, in greenhouse. Plants were subjected to three NaCl solutions with 0.8, 1.3, and 1.8 dS/m of electrical conductivity. The volume of the solution was 200 mL/plant and delivered every 3 days. Biostimulant treatments started after crop establishment and were: control (water) and two doses (0.1 or 0.2 mL/plant) of the commercial biostimulant Retrosal® (Valagro S.p.A), containing calcium, zinc, and specific active ingredients. Four Retrosal® treatments were applied, every 7 days, directly to the substrate. Non-destructive analyses were conducted to assess the effects on leaf photosynthetic efficiency. At harvest, plants fresh weight (FW) and dry weight were determined, as well as the concentration of chlorophylls, carotenoids, total sugars, nitrate, proline, and abscisic acid (ABA). The biostimulant tested increased significantly the FW of lettuce (+65% in the highest dose) compared to controls. Results indicate that treatments positively affected the chlorophyll content measured in vivo (+45% in the highest dose) and that a general positive effect was observable on net photosynthesis rate. Retrosal® seems to improve the gas exchanges under our experimental conditions. The total sugars levels were not affected by treatments. Biostimulant allowed maintaining nitrate concentration similar to the untreated and unstressed controls. The increasing levels of water salinity caused a raise in proline concentration in control plants (+85%); biostimulant treatments at 0.2 mL/plant dose kept lower the proline levels. All plants treated with the biostimulant showed lower value of ABA (-34%) compared to controls. Results revealed that Retrosal® is able to stimulate plant growth independently from the salinity exposure. However, treated plants reached faster the commercial maturity stage. The fresh biomass of control at the end of experiment, after 30 days, ranged from 15 to 42 g/head, while in biostimulant treated plants ranged from 45 to 94 g/head. The product applied at maximum dose seems to be the most effective in our experimental conditions.

Losing the Warning Signal: Drought Compromises the Cross-Talk of Signaling Molecules in Quercus ilex Exposed to Ozone.

Understanding the interactions between drought and acute ozone (O3) stress in terms of signaling molecules and cell death would improve the predictions of plant responses to climate change. The aim was to investigate whether drought stress influences the responses of plants to acute episodes of O3 exposure. In this study, the behavior of 84 Mediterranean evergreen Quercus ilex plants was evaluated in terms of cross-talk responses among signaling molecules. Half of the sample was subjected to drought (20% of the effective daily evapotranspiration, for 15 days) and was later exposed to an acute O3 exposure (200 nL L-1 for 5 h). First, our results indicate that in well-water conditions, O3 induced a signaling pathway specific to O3-sensitive behavior. Second, different trends and consequently different roles of phytohormones and signaling molecules (ethylene, ET; abscisic acid, ABA; salycilic acid, SA and jasmonic acid, JA) were observed in relation to water stress and O3. A spatial and functional correlation between these signaling molecules was observed in modulating O3-induced responses in well-watered plants. In contrast, in drought-stressed plants, these compounds were not involved either in O3-induced signaling mechanisms or in leaf senescence (a response observed in water-stressed plants before the O3-exposure). Third, these differences were ascribable to the fact that in drought conditions, most defense processes induced by O3 were compromised and/or altered. Our results highlight how Q. ilex plants suffering from water deprivation respond differently to an acute O3 episode compared to well-watered plants, and suggest new effect to be considered in plant responses to environmental changes. This poses the serious question as to whether or not multiple high-magnitude O3 events (as predicted) can change these cross-talk responses, thus opening it up possible further investigations.

Ethylene Role in Plant Growth, Development and Senescence: Interaction with Other Phytohormones.

The complex juvenile/maturity transition during a plant's life cycle includes growth, reproduction, and senescence of its fundamental organs: leaves, flowers, and fruits. Growth and senescence of leaves, flowers, and fruits involve several genetic networks where the phytohormone ethylene plays a key role, together with other hormones, integrating different signals and allowing the onset of conditions favorable for stage progression, reproductive success and organ longevity. Changes in ethylene level, its perception, and the hormonal crosstalk directly or indirectly regulate the lifespan of plants. The present review focused on ethylene's role in the development and senescence processes in leaves, flowers and fruits, paying special attention to the complex networks of ethylene crosstalk with other hormones. Moreover, aspects with limited information have been highlighted for future research, extending our understanding on the importance of ethylene during growth and senescence and boosting future research with the aim to improve the qualitative and quantitative traits of crops.

The harsh life of an urban tree: the effect of a single pulse of ozone in salt-stressed Quercus ilex saplings.

Ozone (O3) and salinity are usually tested as combined factors on plant performance. However, the response to a single episode of O3 in plants already stressed by an excess of NaCl as occurs in the natural environment has never been investigated, but is important given that it is commonly experienced in Mediterranean areas. Three-year-old Quercus ilex L. (holm oak) saplings were exposed to salinity (150 mM NaCl, 15 days), and the effect on photosynthesis, hydric relations and ion partitioning was evaluated (Experiment I). In Experiment II, salt-treated saplings were exposed to 80 nl l-1 of O3 for 5 h, which is a realistic dose in a Mediterranean environment. Gas exchanges, chlorophyll fluorescence and antioxidant systems were characterized to test whether the salt-induced stomatal closure limited O3 uptake and stress or whether the pollutant represents an additional stressor for plants. Salt-dependent stomatal closure depressed the photosynthetic process (-71.6% of light-saturated rate of photosynthesis (A380)) and strongly enhanced the dissipation of energy via the xanthophyll cycle. However, salt-treated plants had higher values of net assimilation rate/stomatal conductance (A/gs) than the controls, which was attributable to a greater mesophyll conductance gm/gs and carboxylation efficiency (higher gm/maximal rate of Rubisco carboxylation (Vcmax)), thus suggesting no damage to chloroplasts. O3 did not exacerbate the effect of salinity on photosynthesis, however a general enhancement of the Halliwell-Asada cycle was necessary to counteract the O3-triggered oxidative stress. Despite the 79.4% gs reduction in salt-stressed plants, which strongly limited the O3 uptake, a single peak in the air pollutant led to an additional burden for the antioxidant system when plants had been previously subjected to salinity.

Spatial and temporal transcriptome changes occurring during flower opening and senescence of the ephemeral hibiscus flower, Hibiscus rosa-sinensis.

Flowers are complex systems whose vegetative and sexual structures initiate and die in a synchronous manner. The rapidity of this process varies widely in flowers, with some lasting for months while others such as Hibiscus rosa-sinensis survive for only a day. The genetic regulation underlying these differences is unclear. To identify key genes and pathways that coordinate floral organ senescence of ephemeral flowers, we identified transcripts in H. rosa-sinensis floral organs by 454 sequencing. During development, 2053 transcripts increased and 2135 decreased significantly in abundance. The senescence of the flower was associated with increased abundance of many hydrolytic genes, including aspartic and cysteine proteases, vacuolar processing enzymes, and nucleases. Pathway analysis suggested that transcripts altering significantly in abundance were enriched in functions related to cell wall-, aquaporin-, light/circadian clock-, autophagy-, and calcium-related genes. Finding enrichment in light/circadian clock-related genes fits well with the observation that hibiscus floral development is highly synchronized with light and the hypothesis that ageing/senescence of the flower is orchestrated by a molecular clock. Further study of these genes will provide novel insight into how the molecular clock is able to regulate the timing of programmed cell death in tissues.

Role of ethylene in responses of plants to nitrogen availability.

Ethylene is a plant hormone involved in several physiological processes and regulates the plant development during the whole life. Stressful conditions usually activate ethylene biosynthesis and signaling in plants. The availability of nutrients, shortage or excess, influences plant metabolism and ethylene plays an important role in plant adaptation under suboptimal conditions. Among the plant nutrients, the nitrogen (N) is one the most important mineral element required for plant growth and development. The availability of N significantly influences plant metabolism, including ethylene biology. The interaction between ethylene and N affects several physiological processes such as leaf gas exchanges, roots architecture, leaf, fruits, and flowers development. Low plant N use efficiency (NUE) leads to N loss and N deprivation, which affect ethylene biosynthesis and tissues sensitivity, inducing cell damage and ultimately lysis. Plants may respond differently to N availability balancing ethylene production through its signaling network. This review discusses the recent advances in the interaction between N availability and ethylene at whole plant and different organ levels, and explores how N availability induces ethylene biology and plant responses. Exogenously applied ethylene seems to cope the stress conditions and improves plant physiological performance. This can be explained considering the expression of ethylene biosynthesis and signaling genes under different N availability. A greater understanding of the regulation of N by means of ethylene modulation may help to increase NUE and directly influence crop productivity under conditions of limited N availability, leading to positive effects on the environment. Moreover, efforts should be focused on the effect of N deficiency or excess in fruit trees, where ethylene can have detrimental effects especially during postharvest.

Functional Leaf Traits and Diurnal Dynamics of Photosynthetic Parameters Predict the Behavior of Grapevine Varieties Towards Ozone.

A comparative study on functional leaf treats and the diurnal dynamics of photosynthetic processes was conducted on 2-year-old potted plants of two grape (Vitis vinifera L.) varieties (Aleatico, ALE, and Trebbiano giallo, TRE), exposed under controlled conditions to realistic concentrations of the pollutant gas ozone (80 ppb for 5 h day(-1), 8:00-13:00 h, + 40 ppb for 5 h day(-1), 13:00-18:00 h). At constitutive levels, the morphological functional traits of TRE improved leaf resistance to gas exchange, suggesting that TRE is characterized by a potential high degree of tolerance to ozone. At the end of the treatment, both varieties showed typical visible injuries on fully expanded leaves and a marked alteration in the diurnal pattern of photosynthetic activity. This was mainly due to a decreased stomatal conductance (-27 and -29% in ALE and TRE, in terms of daily values in comparison to controls) and to a reduced mesophyllic functioning (+33 and +16% of the intercellular carbon dioxide concentration). Although the genotypic variability of grape regulates the response to oxidative stress, similar detoxification processes were activated, such as an increased content of total carotenoids (+64 and +30%, in ALE and TRE), enhanced efficiency of thermal energy dissipation within photosystem II (+32 and +20%) closely correlated with the increased de-epoxidation index (+26 and +22%) and variations in content of some osmolytes. In summary, we can conclude that: the daily photosynthetic performance of grapevine leaves was affected by a realistic exposure to ozone. In addition, the gas exchange and chlorophyll a fluorescence measurements revealed a different quali-quantitative response in the two varieties. The genotypic variability of V. vinifera and the functional leaf traits would seem to regulate the acclimatory response to oxidative stress and the degree of tolerance to ozone. Similar photoprotective mechanisms were activated in the two varieties, though to a different extent.