Induction of phenolic compounds by UV and PAR is modulated by leaf ontogeny and barley genotype

Antiviral Activity of Biosynthesized Silver Nanoparticles from Pomegranate (Punica granatum L.) Peel Extract against Tobacco Mosaic Virus

Tobacco mosaic virus (TMV) is a major pathogen affecting tomato plants worldwide. The efficacy of silver nanoparticles (Ag-NPs) mediated by Punica granatum biowaste peel extract in mitigating the negative impact of TMV infection on tomato growth and oxidative stress was investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Visible (UV-Vis) spectrophotometer, X-ray Diffraction (XRD), dynamic light scattering (DLS), zeta potential, energy-dispersive X-ray spectroscopy (EDX), and Fourier-transform infrared spectra (FTIR). Results of SEM analysis of green Ag-NPs revealed the presence of condensed spherical or round NPs with diameters ranging between 61 and 97 nm. TEM confirmed the SEM results and showed round-shaped Ag-NPs with an average size of 33.37 ± 12.7 nm. The elemental analysis (EDX) of prepared Ag-NPs revealed the presence of elemental Ag as a major peak (64.43%) at 3-3.5 KeV. The FTIR revealed several functional groups on the prepared Ag-NPs, for which three treatment strategies for Ag-NP applications were evaluated in the greenhouse study and compared to inoculated TMV and control plants: pre-infection treatment (TB), post-infection treatment (TA), and dual treatment (TD). The results showed that the TD strategy is the most effective in improving tomato growth and reducing viral replication, whereas all Ag-NP treatments (TB, TA, and TD) were found to significantly increase expression of the pathogenesis-related (PR) genes PR-1 and PR-2, as well as polyphenolic compounds, HQT, and C4H genes compared to control plants. In contrast, the flavonoid content of tomato plants was not affected by the viral infection, while the phenolic content was significantly reduced in the TMV group. Furthermore, TMV infection led to a significant increase in oxidative stress markers MDA and H₂O₂, as well as a reduction in the enzymatic activity of the antioxidants PPO, SOD, and POX. Our results clearly showed that the application of Ag-NPs on TMV-infected plants reduces virus accumulation, delays viral replication in all treatments, and greatly enhances the expression of the CHS gene involved in flavonoid biosynthesis. Overall, these findings suggest that treatment with Ag-NPs may be an effective strategy to mitigate the negative impact of TMV infection on tomato plants.

Biochemical and Epigenetic Modulations under Drought: Remembering the Stress Tolerance Mechanism in Rice

A plant, being a sessile organism, needs to modulate biochemical, physiological, and molecular responses to the environment in a quick and efficient manner to be protected. Drought stress is a frequently occurring abiotic stress that severely affects plant growth, development, and productivity. Short- and long-term memories are well-known phenomena in animals; however, the existence of such remembrance in plants is still being discovered. In this investigation, different rice genotypes were imposed with drought stress just before flowering and the plants were re-watered for recovery from the stress. Seeds collected from the stress-treated (stress-primed) plants were used to raise plants for the subsequent two generations under a similar experimental setup. Modulations in physio-biochemical (chlorophyll, total phenolics and proline contents, antioxidant potential, lipid peroxidation) and epigenetic [5-methylcytosine (5-mC)] parameters were analyzed in the leaves of the plants grown under stress as well as after recovery. There was an increase in proline (>25%) and total phenolic (>19%) contents, antioxidant activity (>7%), and genome-wide 5-mC level (>56%), while a decrease (>9%) in chlorophyll content was recorded to be significant under the stress. Interestingly, a part of the increased proline content, total phenolics content, antioxidant activity, and 5-mC level was retained even after the withdrawal of the stress. Moreover, the increased levels of biochemical and epigenetic parameters were observed to be transmitted/inherited to the subsequent generations. These might help in developing stress-tolerant crops and improving crop productivity under the changing global climate for sustainable food production and global food security.

Variation of the Antioxidative Defense in Elaeis guineensis Jacq. Facing Bud Rot Disease in the Coastal Area of Ecuador

Elaeis guineensis Jacq. has gained a reputation in the food industry as an incredible crop capable of supplying the world's largest edible oil production. In Ecuador, an important oil palm-producing country, this crop is affected in a high percentage by the bud rot disease, which is responsible for palm death. The main objective of the investigation was dedicated to understanding the palm defense mechanism facing bud rot disease, translated in the induction of reactive oxygen species, activation of defensive machinery comprising enzymatic and non-enzymatic antioxidative components, secondary metabolites, carotenoids accumulation in the palm during all stages of disease infection. For this, a survey was conducted in different oil palm plantations in the Esmeraldas province, one of the most representative for its highest incidence of bud rot disease. The survey completed DPPH, FRAP, ABTS, and other spectrophotometric analyses to underline the biochemical, biological, and physiological palm response front of bud rot incidence. The palm defense strategy in each disease stage could be represented by the phenolic compound's involvement, an increment of antioxidant activity, and the high enzymatic activity of phenylalanine ammonia-lyase (PAL). The results of the investigation made understandable the palm defense strategy front of this disease, respectively, the antioxidative defense and the palm secondary compounds involved.

Outer and internal cuticle in the leaves of Malus (Rosaceae) in mountains and plains

The outer and internal cuticles in apple (Malus domestica Borkh.) leaves on the plain and in the mountains was studied using transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). The outer cuticle consisted of lamellate and homogeneous layers of the cuticle proper and cuticular layer containing electron-transparent plates and electron-dense dendrites. Blue fluorescence predominated in the cell wall. The cuticle fluoresced green and red. The intensity of the red part of the spectrum in the cuticle increased with altitude, and the number of electron-transparent plates increased within the cuticular layer. The cell wall on both leaf sides was the thinnest in the arid conditions (300 m). At an altitude of 600 m, under favorable temperature and rainfall conditions, the cuticle thickness increased due to the cuticular layer adjacent to the cell wall. The internal cuticle was distinguished by intense yellow or red autofluorescence, similar in color and spectrum to the outer cuticle. The outer and internal cuticles had cuticular folds. The average distance between the ridges of the internal cuticle was almost the same in the samples at different altitudes. The ridge height was maximum at 600 m.

Regulation of Phenolic Compound Production by Light Varying in Spectral Quality and Total Irradiance

Photosynthetically active radiation (PAR) is an important environmental cue inducing the production of many secondary metabolites involved in plant oxidative stress avoidance and tolerance. To examine the complex role of PAR irradiance and specific spectral components on the accumulation of phenolic compounds (PheCs), we acclimated spring barley (Hordeum vulgare) to different spectral qualities (white, blue, green, red) at three irradiances (100, 200, 400 µmol m⁻² s⁻¹). We confirmed that blue light irradiance is essential for the accumulation of PheCs in secondary barley leaves (in UV-lacking conditions), which underpins the importance of photoreceptor signals (especially cryptochrome). Increasing blue light irradiance most effectively induced the accumulation of B-dihydroxylated flavonoids, probably due to the significantly enhanced expression of the F3′H gene. These changes in PheC metabolism led to a steeper increase in antioxidant activity than epidermal UV-A shielding in leaf extracts containing PheCs. In addition, we examined the possible role of miRNAs in the complex regulation of gene expression related to PheC biosynthesis.

Interactive effects of nitrogen, UV and PAR on barley morphology and biochemistry are associated with the leaf C:N balance

Environmental conditions to which plants acclimate prior exposure to abiotic or biotic stressors can greatly affect their subsequent resilience. This may have a significant impact on the response to ongoing climate change and can be useful for increasing the food security under adverse weather conditions associated with climate change.Within this study, we tested the hypothesis that plant morphological and biochemical acclimation to radiation conditions and nitrogen (N) availability is closely linked with carbon (C) and N balance. Four barley (Hordeum vulgare) varieties, differing in their morphological characteristics and sensitivity to photooxidative stress, were grown at two levels of N supply and four radiation regimes combining distinct levels of ultraviolet (UV) and photosynthetically active radiation (PAR). Changes in root and shoot morphology, accumulation of phenolic compounds, amino acids, and sugars were studied together with the analysis of C and N content in leaves. Both UV and PAR reduced leaf length and increased root-to-shoot ratio (R:S). Such effect was more pronounced under high N availability. High N supply reduced R:S, but this effect showed significant interactions with UV and PAR, and also with barley variety. Changes in R:S were positively related to C:N ratio in leaves that varied in response to both N availability and radiation treatments. UV radiation, particularly in combination with high PAR intensity, led to increases in most phenolic compounds (particularly flavones such as saponarin, homoorientin and isovitexin) which was also closely associated with changes in C:N ratio, while specifically phenolic acids (vanillic and syringic acids) decreased under high levels of UV and PAR, and hydroxycinnamic acids responded positively mainly to PAR. Although high N availability generally reduced the accumulation of phenolic compounds, this effect was genotype-specific and modulated by the radiation regime. A similar antagonistic effect of radiation treatment and N availability was also found for the accumulation of sugars (pentoses), resulting in a close relationship between the accumulation of pentoses and C:N ratio. The accumulation of most amino acids, in contrary to phenolic compounds, increases at high N and is also stimulated by high PAR and UV intensities. We conclude that radiation conditions and N availability have opposite effects on plant morphology and accumulation of most phenolic compounds and modulate the amino acid and sugar metabolism. Strong associations of these responses with changes in C:N ratio indicates that plant stoichiometry integrates acclimation processes and induction of relevant defence mechanisms.

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

In agro-ecosystem, plant pathogens hamper food quality, crop yield, and global food security. Manipulation of naturally occurring defense mechanisms in host plants is an effective and sustainable approach for plant disease management. Various natural compounds, ranging from cell wall components to metabolic enzymes have been reported to protect plants from infection by pathogens and hence provide specific resistance to hosts against pathogens, termed as induced resistance. It involves various biochemical components, that play an important role in molecular and cellular signaling events occurring either before (elicitation) or after pathogen infection. The induction of reactive oxygen species, activation of defensive machinery of plants comprising of enzymatic and non-enzymatic antioxidative components, secondary metabolites, pathogenesis-related protein expression (e.g. chitinases and glucanases), phytoalexin production, modification in cell wall composition, melatonin production, carotenoids accumulation, and altered activity of polyamines are major induced changes in host plants during pathogen infection. Hence, the altered concentration of biochemical components in host plants restricts disease development. Such biochemical or metabolic markers can be harnessed for the development of "pathogen-proof" plants. Effective utilization of the key metabolites-based metabolic markers can pave the path for candidate gene identification. This present review discusses the valuable information for understanding the biochemical response mechanism of plants to cope with pathogens and genomics-metabolomics-based sustainable development of pathogen proof cultivars along with knowledge gaps and future perspectives to enhance sustainable agricultural production.

Light and CO2 Modulate the Accumulation and Localization of Phenolic Compounds in Barley Leaves

Barley (Hordeum vulgare) accumulates phenolic compounds (PhCs), which play a key role in plant defense against environmental stressors as antioxidants or UV screening compounds. The influence of light and atmospheric CO2 concentration ([CO2]) on the accumulation and localization of PhCs in barley leaves was examined for two varieties with different tolerances to oxidative stress. PhC localization was visualized in vivo using fluorescence microscopy. Close relationships were found between fluorescence-determined localization of PhCs in barley leaves and PhC content estimated using liquid chromatography coupled with mass spectroscopy detection. Light intensity had the strongest effect on the accumulation of PhCs, but the total PhC content was similar at elevated [CO2], minimizing the differences between high and low light. PhCs localized preferentially near the surfaces of leaves, but under low light, an increasing allocation of PhCs in deeper mesophyll layers was observed. The PhC profile was significantly different between barley varieties. The relatively tolerant variety accumulated significantly more hydroxycinnamic acids, indicating that these PhCs may play a more prominent role in oxidative stress prevention. Our research presents novel evidence that [CO2] modulates the accumulation of PhCs in barley leaves. Mesophyll cells, rather than epidermal cells, were most responsive to environmental stimuli in terms of PhC accumulation.

Developmental Stage Determines the Accumulation Pattern of UV-Absorbing Compounds in the Model Liverwort Marchantia polymorpha subsp. ruderalis under Controlled Conditions

The liverwort Marchantia polymorpha subsp. ruderalis is an emerging model plant, and some data are available on its responses to ultraviolet (UV) radiation. However, it is unknown if the developmental stage of the thalli modulates the effects of UV radiation on the contents of potentially protecting phenolic compounds. To fill this gap, liverwort samples were exposed or non-exposed to UV radiation for 38 days under controlled conditions, using three developmental stages: gemmae (G), one-month thalli (T1), and two-month thalli (T2). Then, the bulk level of methanol-soluble UV-absorbing compounds and the contents of six flavones (apigenin and luteolin derivatives) were measured. The UV responsiveness decreased with thallus age: G and T1 plants were the most UV-responsive and showed a strong increase in all the variables, with G plants more responsive than T1 plants. In UV-exposed T2 plants, only apigenin derivatives increased and more modestly, probably due to a lower acclimation capacity. Nevertheless, the thalli became progressively tougher due to a decreasing water content, representing a possible structural protection against UV. In UV-exposed plants, the temporal patterns of the accumulation of phenolic compounds were compound-specific. Most compounds decreased with thallus age, but di-glucuronide derivatives showed a bell-shaped pattern, with T1 plants showing the highest contents. A Principal Components Analysis (PCA) ordination of the different samples summarized the results found. The patterns described above should be taken into account to select thalli of an adequate developmental stage for experiments investigating the induction of phenolic compounds by UV radiation.

Temporal Changes in Ozone Concentrations and Their Impact on Vegetation

Tropospheric concentrations of phytotoxic ozone (O3) have undergone a great increase from preindustrial 10–15 ppbv to a present-day concentration of 35–40 ppbv in large parts of the industrialised world due to increased emissions of O3 precursors including NOx, CO, CH4 and volatile organic compounds. The rate of increase in O3 concentration ranges between 1 ppbv per decade in remote locations of the Southern hemisphere and 5 ppbv per decade in the Northern hemisphere, where largest sources of O3 precursors are located. Molecules of O3 penetrating into the leaves through the stomatal apertures trigger the formation of reactive oxygen species, leading thus to the damage of the photosynthetic apparatus. Accordingly, it is assumed, that O3 increase reduces the terrestrial carbon uptake relative to the preindustrial era. Here we summarise the results of previous manipulative experiments in laboratory growth cabinets, field open-top chambers and free-air systems together with O3 flux measurements under natural growth conditions. In particular, we focus on leaf-level physiological responses in trees, variability in stomatal O3 flux and changes in carbon fluxes and biomass production in forest stands. As the results reported in the literature are highly variable, ranging from negligible to severe declines in photosynthetic carbon uptake, we also discuss the possible interactions of O3 with other environmental factors including solar radiation, drought, temperature and nitrogen deposition. Those factors were found to have great potential to modulate stomata openness and O3 fluxes.

Quantitative Analysis of UV-B Radiation Interception and Bioactive Compound Contents in Kale by Leaf Position According to Growth Progress

UV-B (280-315 nm) radiation has been used as an effective tool to improve bioactive compound contents in controlled environments, such as plant factories. However, plant structure changes with growth progress induce different positional distributions of UV-B radiation interception, which cause difficulty in accurately evaluating the effects of UV-B on biosynthesis of bioactive compounds. The objective of this study was to quantitatively analyze the positional distributions of UV-B radiation interception and bioactive compound contents of kales (Brassica oleracea L. var. acephala) with growth progress and their relationships. Short-term moderate UV-B levels did not affect the plant growth and photosynthetic parameters. Spatial UV-B radiation interception was analyzed quantitatively by using 3D-scanned plant models and ray-tracing simulations. As growth progressed, the differences in absorbed UV-B energy between leaf positions were more pronounced. The concentrations of total phenolic compound (TPC) and total flavonoid compound (TFC) were higher with more cumulative absorbed UV-B energy. The cumulative UV energy yields for TFC were highest for the upper leaves of the older plants, while those for TPC were highest in the middle leaves of the younger plants. Despite the same UV-B levels, the UV-B radiation interception and UV-B susceptibility in the plants varied with leaf position and growth stage, which induced the different biosynthesis of TFC and TPC. This attempt to quantify the relationship between UV-B radiation interception and bioactive compound contents will contribute to the estimation and production of bioactive compounds in plant factories.

Physiological, transcriptional, and metabolic alterations in spaceflight-subjected Senna obtusifolia

Senna obtusifolia is a widely used medicinal herb in Asian countries. To select elite cultivars, S. obtusifolia seeds were carried by "ShenZhou Ⅷ" recoverable satellite to space. Three spaceflight-subjected lines (SP-lines), namely QC10, QC29, QC46, and their ground control line (GC-line) were cultivated on the ground. Previous studies demonstrated that biological traits and secondary metabolites are different between SP-lines and GC-line. Here, we combined physiological, transcriptional, and metabolic studies to compare the differences between SP-lines and GC-line. The results showed that activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and monodehydroascorbate reductase (MDHAR) were dramatically increased in SP-lines as compared to that of GC-line. Transcript levels of SOD, POD, CAT, APX, and MDHAR were significantly up-regulated in SP-lines. Malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents decreased in SP-lines. Seed yields of QC29 and QC46 were considerably higher than that of GC-line. Besides, QC29 had significantly higher aurantio-obtusin content. Pearson correlation coefficient analysis revealed positive relationships between POD and aurantio-obtusin, as well as APX and aurantio-obtusin. In conclusion, SP-lines have higher antioxidant gene expression level and antioxidant enzyme activity as compared to that of GC-line. With higher seed yield and aurantio-obtusin content, QC29 can be used to breed elite S. obtusifolia cultivars. This study provides a new insight in SP-lines and paves the way to breed elite S. obtusifolia cultivars in the future.