Ultraviolet-B radiation exposure lowers the antioxidant capacity in the Arabidopsis thaliana pdx1.3-1 mutant and leads to glucosinolate biosynthesis alteration in both wild type and mutant

A synchronized, large-scale field experiment using Arabidopsis thaliana reveals the significance of the UV-B photoreceptor UVR8 under natural conditions

This study determines the functional role of the plant ultraviolet-B radiation (UV-B) photoreceptor, UV RESISTANCE LOCUS 8 (UVR8) under natural conditions using a large-scale 'synchronized-genetic-perturbation-field-experiment'. Laboratory experiments have demonstrated a role for UVR8 in UV-B responses but do not reflect the complexity of outdoor conditions where 'genotype × environment' interactions can mask laboratory-observed responses. Arabidopsis thaliana knockout mutant, uvr8-7, and the corresponding Wassilewskija wild type, were sown outdoors on the same date at 21 locations across Europe, ranging from 39°N to 67°N latitude. Growth and climatic data were monitored until bolting. At the onset of bolting, rosette size, dry weight, and phenolics and glucosinolates were quantified. The uvr8-7 mutant developed a larger rosette and contained less kaempferol glycosides, quercetin glycosides and hydroxycinnamic acid derivatives than the wild type across all locations, demonstrating a role for UVR8 under field conditions. UV effects on rosette size and kaempferol glycoside content were UVR8 dependent, but independent of latitude. In contrast, differences between wild type and uvr8-7 in total quercetin glycosides, and the quercetin-to-kaempferol ratio decreased with increasing latitude, that is, a more variable UV response. Thus, the large-scale synchronized approach applied demonstrates a location-dependent functional role of UVR8 under natural conditions.

Phase-Selective Synthesis of Anatase and Rutile TiO2 Nanocrystals and Their Impacts on Grapevine Leaves: Accumulation of Mineral Nutrients and Triggering the Plant Defense

Titanium dioxide nanocrystals (TiO₂ NCs), through their photocatalytic activity, are able to generate charge carriers and induce the formation of various reactive oxygen species (ROS) in the presence of O₂ and H₂O. This special feature makes TiO₂ an important and promising material in several industrial applications. Under appropriate antioxidant balancing, the presence of ROS is crucial in plant growth and development, therefore, the regulated ROS production through the photocatalytic activity of TiO₂ NCs may be also exploited in the agricultural sector. However, the effects of TiO₂ NCs on plants are not fully understood and/or phase-pure TiO₂ NCs are rarely used in plant experiments. In this work, we present a phase-selective synthesis of TiO₂ NCs with anatase and rutile crystal phases. The nanomaterials obtained were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance UV-Vis spectroscopy, and electron paramagnetic resonance spectroscopy (EPR). In field experiments, Vitis vinifera cv. Cabernet Sauvignon leaves developed under natural sunlight were treated with aqueous dispersions of TiO₂ NCs at concentrations of 0.001, 0.01, 0.1, and 1 w/v%. The effect of the applied nanocrystals was characterized via leaf photochemistry, mineral nutrient contents, and pyridoxine levels. We found that stress responses of grapevine to anatase and rutile NCs treatments are different, which can be related to the different ROS profiles of the two polymorphs. Our results indicate that TiO₂ NCs may be utilized not only for direct pathogen inactivation but also for eliciting plant defense mechanisms.

UV-B Radiation as Abiotic Elicitor to Enhance Phytochemicals and Development of Red Cabbage Sprouts

Background: The main objective of this study was to evaluate the effect of periodical UV-B illumination during red cabbage germination on morphological development and the phenolics and carotenoid accumulation. Methods: During a sprouting period of 10 days at 20 °C in darkness, seedlings received 5, 10, or 15 kJ m−2 UV-B (T5, T10, and T15) applied in four steps (25% on days 3, 5, 7, and 10). UV untreated sprouts were used as control (CTRL). After 10 days of germination, the sprouts were harvested and stored 10 days at 4 °C as a minimally processed product. Phenolic and carotenoid compounds were analysed 1 h after each UV-B application and on days 0, 4, 7, and 10 during cold storage. Results: The longest hypocotyl length was observed in T10-treated sprouts. The total phenolic content (TPC), total flavonoid content (TFC), and total antioxidant capacity (TAC) increased during germination following a sigmoidal kinetic, especially in the UV-B-treated samples, which reported a dose-dependent behaviour. In this way, T10-treated sprouts increased the TPC by 40% after 10 days at 4 °C compared to CTRL, while TAC and TFC increased by 35 and 30%, respectively. Carotenoids were enhanced with higher UV-B doses (T15). Conclusions: We found that UV-B stimulated the biosynthesis of bioactive compounds, and a dose of 10 kJ m−2 UV-B, proportionally applied on days 3, 5, 7, and 10 days, is recommended.

In through the out door: Biochemical mechanisms affecting flavonoid glycoside catabolism in plants

Plants are the sole source of flavonoids, a chemical category that includes flavonols. For the most part, flavonols occur as glycosides with numerous postulated biological roles in plants, including photoprotection, modulation of hormone translocation, and sequestration of reactive oxygen species. Flavonol glycosides are often considered as dead-end metabolites because related flavonoids (i.e., anthocyanins) occur in terminal tissues such as flowers and fruit, but recent evidence points to their turnover in planta, including developing photosynthetic tissues. Although microbial degradation pathways for flavonol glycosides of plant origin are well described, plant catabolic pathways are little studied by comparison. This review will address our current understanding of biochemical processes leading to the loss of flavonol glycosides in plants, with a specific emphasis on the evidence for flavonol-specific β-glucosidases. Complete elucidation of these catabolic pathways is dependent on the identification of regiospecific modifying steps, including enzymes associated with the hydrolysis of rhamnosylated flavonols, as well as flavonol peroxidation and their encoding genes. Herein, we highlight challenges for the identification of hypothetical plant α-rhamnosidases and peroxidases involved in flavonol glycoside degradation, and the potential biological role of this catabolism in mitigating oxidative stress in developing and postharvest plant tissues.

β-Sitosterol differentially regulates key metabolites for growth improvement and stress tolerance in rice plants during prolonged UV-B stress

BACKGROUND

Elevated ultraviolet-B (UV-B) radiation is potentially deleterious to many organisms specifically crop plants and has become a global challenge. Rice is an exceptionally important staple food which is grown worldwide, and many efforts have been done recently to improve rice varieties against UV-B stress. This current study aims to investigate the effects of exogenous application of β-sitosterol (βSito) on growth improvement and tolerance level of rice plants against prolonged UV-B stress. The physiological and metabolic responses were evaluated in rice plants not supplemented with βSito (Nβ) and those supplemented with βSito (Sβ).

RESULTS

The Nβ and Sβ plants were grown under non-stress (ns) and under prolonged UV-B stress (uvs) conditions and termed as Nβ^ns, Sβ^ns and Nβ^uvs, Sβ^uvs, respectively. The application of βSito contributes positively under non-stress and specifically to UV-B stress in terms of improving numerous physiological parameters associated with growth and development such as shoot and root length, RWC, whole plant biomass, chlorophyll pigments, and photosynthetic-related parameters (Pn, Gs, Tr, WUEi, Fv/Fm, and NPQ) in Sβ compared with Nβ plants. Moreover, enhanced oxidative stress tolerance of Sβ^uvs vs. Nβ^uvs plants under stress was attributed to low levels of ROS and substantial trigger in activities of antioxidant enzymes (SOD, POD, CAT, and APX). Metabolic analysis was performed using GC-TOFMS, which revealed higher accumulation of several key metabolites including organic acids, sugars, amino acids, and others in Sβ^uvs vs. Nβ^uvs plants, which were mainly reduced in Nβ plants under stress vs. non-stress conditions.

CONCLUSION

These results provide useful data regarding the important role of βSito on growth maintenance and modulation of several metabolites associated with osmotic and redox adjustments during UV-B stress tolerance in rice plants. Importantly, βSito-regulated plasticity could further be explored specifically in relation to different environmental stresses in other economically useful crop plants.