Photoprotective Role of Photosynthetic and Non-Photosynthetic Pigments in Phillyrea latifolia: Is Their "Antioxidant" Function Prominent in Leaves Exposed to Severe Summer Drought?

Spatiotemporal metabolic responses to water deficit stress in distinct leaf cell-types of poplar

The impact of water-deficit (WD) stress on plant metabolism has been predominantly studied at the whole tissue level. However, plant tissues are made of several distinct cell types with unique and differentiated functions, which limits whole tissue 'omics'-based studies to determine only an averaged molecular signature arising from multiple cell types. Advancements in spatial omics technologies provide an opportunity to understand the molecular mechanisms underlying plant responses to WD stress at distinct cell-type levels. Here, we studied the spatiotemporal metabolic responses of two poplar (Populus tremula× P. alba) leaf cell types -palisade and vascular cells- to WD stress using matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI). We identified unique WD stress-mediated metabolic shifts in each leaf cell type when exposed to early and prolonged WD stresses and recovery from stress. During water-limited conditions, flavonoids and phenolic metabolites were exclusively accumulated in leaf palisade cells. However, vascular cells mainly accumulated sugars and fatty acids during stress and recovery conditions, respectively, highlighting the functional divergence of leaf cell types in response to WD stress. By comparing our MALDI-MSI metabolic data with whole leaf tissue gas chromatography-mass spectrometry (GC-MS)-based metabolic profile, we identified only a few metabolites including monosaccharides, hexose phosphates, and palmitic acid that showed a similar accumulation trend at both cell-type and whole leaf tissue levels. Overall, this work highlights the potential of the MSI approach to complement the whole tissue-based metabolomics techniques and provides a novel spatiotemporal understanding of plant metabolic responses to WD stress. This will help engineer specific metabolic pathways at a cellular level in strategic perennial trees like poplars to help withstand future aberrations in environmental conditions and to increase bioenergy sustainability.

Physiological and proteomic changes of Castanopsis fissa in response to drought stress

Castanopsis fissa is a native, broadleaf tree species in Guangdong with characteristics of barrenness and fast growth and is often used as a pioneer species for vegetation restoration with excellent ecological benefits. To explore the response of C.fissa to drought, this study investigated the drought tolerance mechanism of C.fissa using physiological and proteomic assessments. Using a potted continuous drought experimental method with normal water supply as a control, we measured photosynthetic parameters, antioxidant enzyme activities, and osmoregulatory substances of C. fissa in response to drought stress for 1 to 4 weeks, respectively. In addition, we used TMT quantitative proteomics to identify differentially expressed proteins (DEPs) between the drought-stress-treated C. fissa leaves and the control leaves. With the extension of drought stress time, the photosynthetic indexes and peroxidase (POD) activity of C. fissa leaves showed a decreasing trend. The malondialdehyde (MDA) content; superoxide Dismutase (SOD) and catalase (CAT) activities; and proline (Pro), soluble sugar (SS) and soluble protein (SP) contents showed an overall increasing trend, all of which reached significant differences at 4 w of stress. We identified 177 and 529 DEPs in the 2 and 4 weeks drought-stress leaves, respectively, in reference to the control leaves. These DEPs were closely related to physiological metabolic processes such as photosynthesis, energy and carbohydrate metabolism, stress response and defense, transcriptional regulation, and signal ion transduction. Drought stress mainly affects photosynthesis, carbohydrate metabolism, and protein synthesis and degradation in C. fissa leaves. At 2 weeks of stress, the expression of carbon metabolism, pyruvate metabolism and ribosome-related proteins was significantly changed, however, and at 4 weeks of stress, protein processing in the endoplasmic reticulum and spliceosome-related proteins were significantly increased in plant leaves. To alleviate the effect of water unavailability, the drought-stressed C.fissa leaves increased its oxidative protective enzyme system to eliminate excess reactive oxygen species (ROS) and also increased its Pro and SP contents to maintain the intracellular osmotic potential balance.

Phytochemicals from Phillyrea latifolia L. leaves and fruit extracted with various solvents: Their identification and quantification by LC-MS and antihyperglycemic effects

Phillyrea latifolia L. is a type of shrubland, which is widely known as mock privet, and belongs to the Oleaceae family. The objective of this study was to compare and assess the phytochemical composition, antioxidant and antidiabetic activities of ethyl acetate, methanol and aqueous extracts of the fruit and leaves of P. latifolia L. Phenolics were analysed by detecting individual bioactive compounds using an LCMS-2020 quadrupole mass spectrometer and by calculating total phenolic content (TPC). For the first time, the antioxidant and antidiabetic activities of both leaves and fruit were determined using DPPH radical scavenging. The aqueous extract was indicated to have higher antioxidant activities than ethyl acetate and methanol extracts. The individual constituents within the different extracts for both fruit and leaves were detected as the luteolin-7-O-glucoside in the ethyl acetate (854 μg · g–1 and 1,098 μg · g–1), methanol (1,241 μg · g–1 and 2,136.43 μg · g–1) and aqueous (509 μg · g–1 and 898.23 μg · g–1) extracts, respectively. Extractions of ethyl acetate and methanol demonstrated stronger inhibitory activity against human salivary α-amylase than the aqueous extract of both parts of the mock privet. Similarly, extraction of ethyl acetate from the leaves and fruit of the mock privet indicated significantly better inhibitory activity than the methanol and aqueous extracts, respectively, for the inhibition of α-glucosidase activity. This study indicates that both fruit and leaves of mock privet may use as a potential source of natural biomolecules to promote healthy activities.

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.

Morphological and physiological changes in Artemisia selengensis under drought and after rehydration recovery

Changes in global climate and precipitation patterns have exacerbated the existing uneven distribution of water, causing many plants to face the alternate situation of drought and water flooding. We studied the growth and physiological response of the wetland plant Artemisia selengensis to drought and rehydration. In this study, Artemisia selengensis seedlings were subjected to 32.89% (SD), 47.36 % (MD), 60.97% (MID), and 87.18 % (CK) field water holding capacity for 70 days, followed by 14 days of rehydration. The results showed that drought inhibited the increase of plant height, basal diameter, and biomass accumulation under SD and MD, but the root shoot ratio (R/S) increased. Drought stress also decreased the content of total chlorophyll (Chl), chlorophyll a (Chl-a), chlorophyll b (Chl-b), and carotenoid (Car). Soluble sugar (SS) and proline (Pro) were accumulated rapidly under drought, and the relative water content (RWC) of leaves was kept at a high level of 80%. After rehydration, the plant height, basal diameter, biomass, and R/S ratio could not be recovered under SD and MD, but these indicators were completely recovered under MID. The RWC, Chl, Chl-a, Chl-b, Car, and osmotic substances were partially or completely recovered. In conclusion, Artemisia selengensis not only can improve drought resistance by increasing the R/S ratio and osmotic substances but also adopt the compensatory mechanism during rehydration. It is predictable that A. selengensis may benefit from possible future aridification of wetlands and expand population distribution.

Photoprotective Potential, Cytotoxicity, and UPLC-QTOF/MS Analysis on Bioactive Solvent Fractions of Moringa concanensis Nimmo Bark

Moringa concanensis Nimmo (Moringaceae) belongs to the same family of M. oleifera (miracle tree) and is a medicinal plant traditionally used by Indians to treat various ailments related to diabetes, tumours, inflammation, and blood pressure. Despite its versatility, the photoprotective properties of the plant remain unclear. This study revealed the UV-protective properties of its methanol bark extract and respective subfractions, chloroform, hexane, and ethyl acetate through total phenolic and flavonoid content (TPC & TFC), antioxidant (DPPH), sun protecting factor (SPF) value, and UV absorption spectra analysis. This study also investigated on the inhibitory effect of the tested samples on collagenases and elastase, which are well-known for their role in the skin. The cytotoxic and H2O2 scavenging properties of M. concanensis in 3T3-L1 cells were explored. Finally, the phytochemical profiling of the active fraction was conducted through UPLC-QTOF/MS analysis. Among the tested fractions, the chloroform fraction of M. concanensis showed the highest TPC (30.92 ± 0.71 mg GAE/DW), TFC (29.05 ± 0.09 mg QE/DW), and antioxidant properties (IC50-6.616 ± 1.90 μgml−1). Additionally, chloroform fraction demonstrated the highest SPF value, 10.46 at 200 μgml−1, compared to the other tested fractions. All the fractions showed a broad absorption spectrum covering both UVA and UVB ranges. The chloroform fraction of M. concanensis also showed collagenase (50%) and elastase (IC50-2.95 ± 1.23 μgml−1) inhibition properties similar to the positive control. Cytotoxic results revealed that the chloroform fraction of M. concanensis prevented the H2O2-induced oxidative damage in 3T3-L1 cells even at lower concentrations (1.56 μgml−1). UPLC-QTOF/MS analysis tentatively identified the presence of bioactive flavonoids and phenolics such as astragalin, quercetin, isoquercetin, and caffeic acid in the active fraction of M. concanensis bark. Overall, it is suggested that the chloroform fraction of M. concanensis bark has the potency to be used as an active ingredient in sunscreen products.