Search Results (228)

We investigated diel physiological responses of the leafy aquatic liverwort Jungermannia eucordifolia under natural field conditions during two consecutive days. Photosynthetically active radiation (PAR), UV-A and UV-B radiation, together with water temperature, were monitored throughout the study. Physiological responses included: (1) chlorophyll fluorescence assessed through steady-state fluorescence parameters and fast chlorophyll fluorescence induction kinetics (OJIP approach); (2) UV-absorbing phenolic compounds in the methanol-soluble and methanol-insoluble fractions, mainly representing vacuolar and cell wall-bound compounds, respectively, thereby covering different functional modalities of UV protection; both the bulk UV absorption capacity of UV-absorbing compounds and seven individual phenolic compounds were analyzed; and (3) DNA damage. Photosynthetic performance parameters, including the effective photochemical quantum yield of photosystem II (Φ_PSII), the maximum photochemical quantum yield of photosystem II (F_v/F_m), and the Performance Index (PI), together with the photoprotection parameter non-photochemical quenching (NPQ), showed pronounced diel fluctuations closely associated with changes in ambient irradiance. Φ_PSII, F_v/F_m, and PI were negatively related to irradiance, whereas NPQ exhibited the opposite trend. These responses were consistent with those previously observed in this liverwort under controlled laboratory conditions, suggesting dynamic photoinhibition accompanied by efficient photoprotection of photosystem II (PSII) against excess radiation, probably involving the xanthophyll cycle. Nevertheless, the strong covariation among PAR, UV-A, and UV-B wavebands prevented a clear distinction of their individual contributions. In contrast to chlorophyll fluorescence parameters, most variables associated with UV photoprotection through UV-absorbing compounds did not display consistent diel patterns under field conditions, although some individual compounds showed significant temporal fluctuations. This finding contrasted with previous laboratory experiments, where several UV-absorbing compounds increased under enhanced UV-B. DNA damage was not detected in any sample, consistent with previous field studies conducted under ambient UV-B levels but contrasting with experiments using enhanced UV-B exposure under either field or laboratory conditions. These results contribute to a better understanding of short-term physiological dynamics in aquatic bryophytes and may help improve UV biomonitoring protocols based on these organisms. Full article

The genus Euterpe, which includes açaí palm (Euterpe oleracea) and juçara palm (Euterpe edulis), plays an important socioeconomic and environmental role in Brazil. However, soil and water salinization is a global issue that compromises agricultural productivity by affecting plant physiological and metabolic processes. This study aimed to evaluate the physiological responses of young açaí and juçara plants under salt stress. The experiment was conducted in a randomized complete block design in a 5 × 2 factorial arrangement, consisting of five irrigation water salinity levels (0.1, 1.0, 2.0, 3.0, and 5.0 dS m⁻¹) and two Euterpe species (açaí and juçara), with four replicates. After 104 days of stress exposure, gas exchange, chlorophyll ‘a’ fluorescence, relative chlorophyll index (SPAD), and sodium, chloride, and phenolic compounds were evaluated. Increasing salinity caused linear reductions in the maximum quantum yield and potential photochemical efficiency of PSII, accompanied by an increase in F₀/Fm, indicating impaired PSII photochemical performance and photoinhibition. Stomatal conductance and transpiration also decreased significantly with increasing salinity, with reductions of up to 41.33% and 35.48%, respectively, at the highest salinity level. Salt stress negatively affected the physiological performance of both palm species through stomatal limitation and reduced photosystem II efficiency. However, açaí plants exhibited greater tolerance to salt stress than juçara plants. Full article

Microalgae biophotovoltaic (BPV) systems convert solar energy into electricity through photosynthetic electron transfer (PET) and have emerged as a promising solar-integrated bioenergy technology. However, high-density tubular arrays suffer from the “canyon effect” at low solar angles and from photoinhibition under peak irradiance (>450 W/m²), where non-photochemical quenching (NPQ) and reactive oxygen species (ROS) dissipate bioelectric potential as heat. To address this, a hysteresis-based dual-mode PID controller with hysteresis switching is proposed within an optical–mechanical–biological co-optimization framework, integrating array self-shading, nonlinear microalgal photoresponse, and tracking parasitic losses. In low-light mode, the system actively tracks the sun to minimize shading; in peak-light mode, it defocuses the incident angle to limit irradiance near the saturation threshold, mitigating the risk of photoinhibition. Structural control boundaries, including tube spacing and connecting rod length, are determined numerically. Under the nominal clear-sky design day, the defocusing mode reduces the daily exposure of the culture to irradiance above the saturation threshold (450 W/m²) from 5.28 h to 3.08 h. Numerical simulations indicate a daily net energy yield improvement of +14.9% over continuous dual-axis tracking and +6.3% over the latitude-based fixed-tilt baseline under idealized clear-sky design-day conditions. These values are simulation-derived estimates; experimental validation with a physical prototype is required before the framework can be interpreted as a validated system-level performance gain. Full article

Singlet oxygen (¹O₂), a highly reactive oxygen species generated in illuminated chloroplasts, is a major contributor to photooxidative damage in plants, particularly under high-light stress. This review summarizes the major sites of ¹O₂ production, its damage mechanisms, and the antioxidant defense and scavenging strategies that limit ¹O₂ accumulation. Particular emphasis is placed on recent advances in ¹O₂-mediated signal transduction. EX1 and β-carotene-derived oxidation products have been proposed to act as key components in ¹O₂ perception and signaling, mediating signal transmission from distinct subchloroplast locations and contributing to a spatially coordinated ¹O₂ signaling network. Plants counteract ¹O₂-induced damage through a multilayered defense–perception–signal transduction system. The functional partitioning of ¹O₂ signaling between grana margins and grana cores, together with the coordinated action of multiple signaling molecules, provides important insights into the mechanisms of plant photoprotection and offers potential strategies for improving crop tolerance to photooxidative stress. Full article

Some mutants of the green alga Chlamydomonas reinhardtii, including the cia3 mutant deficient in the carbonic anhydrase CAH3 in the thylakoid lumen, strongly require high CO₂ supplementation for survival, which is usually explained by disruption at some step(s) of the carbon-concentrating mechanism. This study aimed to determine whether CAH3 contributes to photosystem II (PSII) functional stability under low CO₂ conditions. Two wild-type C. reinhardtii strains and the cia3 mutant were compared for PSII photoinhibition sensitivity, D1 protein stability, pigment content, and PSII photoprotective responses before and after short-term acclimation to low CO₂ growth conditions. Compared with the two wild-type strains, the cia3 mutant exhibited greater PSII sensitivity to increased light intensity after acclimation to low CO₂. In addition, this was accompanied by more pronounced degradation of the D1 protein of PSII, indicating that the absence of CAH3 also affects the structural stability of PSII. At the same time, no differences in pigment content were observed between the strains, and a low contribution of PSII photoprotective mechanisms was detected, indicating that the growth light conditions used were non-stressful for the algal photosynthetic apparatus. The observed data indicate that CAH3 contributes to maintaining the functional and structural stability of PSII under low CO₂, even under non-stressful light growth conditions. Full article

Across much of the Arctic, climate warming has reduced the extent of thicker and more persistent sea ice and increased the prevalence of thinner first-year ice. Thin first-year landfast sea ice is ecologically important because reduced ice thickness can increase light transmission to the ice–water interface, while the associated brine conditions, including salinity and permeability, can strongly influence algal biomass accumulation and photophysiology. This thin (0.24–0.55 m), short-lived, seasonal, first-year landfast sea ice already dominates Nuup Kangerlua fjord, southwest Greenland, making it a useful natural example of ice conditions that may become more common in parts of the future Arctic. We focused on late February–early March because this period captures the seasonal transition from very low winter irradiance toward increasing spring light, when sea ice algal communities begin photosynthetic acclimation prior to the main bloom period. Using this site as an example of future Arctic-like conditions, we investigated chlorophyll a (Chl a) concentration and the photobiology of sea ice algal communities during five sampling events between 2017 and 2022. The vertical distribution of Chl a concentration and photobiological parameters measured with variable chlorophyll fluorescence differed between years, as did Chl a concentrations, with integrated biomass ranging from 0.08 to 0.78 mg Chl a m⁻². Direct under-ice PAR measurements showed transmittance values ranging from 0.013 to 0.29. Bottom-ice communities were acclimated to relatively high light intensities, with E_k often exceeding 200 µmol photons m⁻² s⁻¹, and we detected no clear evidence of photoinhibition in the fluorescence data. Boosted regression tree models identified brine salinity as the main predictor of both Chl a concentration, explaining 42.0% of the variation, and, Φ_{PSII_max}, the maximum dark-adapted photosynthetic efficiency, explaining 86.1% of the variation. Both parameters decreased exponentially with increasing sea ice brine salinity (p < 0.0001), indicating that higher brine salinity was associated with reduced algal biomass and lower photosynthetic efficiency. These results show that short-lived first-year landfast sea ice can support physiologically active sea ice algal communities despite relatively low biomass, and suggest that algal performance in this ice type was more strongly associated with brine salinity during the late-winter to early spring sampling period, while light availability also varied substantially among years. As thin and short-lived sea ice conditions become more common in parts of the Arctic, this habitat may represent an increasingly important, though temporally variable, component of Arctic marine primary production. Full article

Low temperature and low irradiance (LTLI) stress severely limits strawberry growth and productivity during winter protected cultivation. This study investigated the physiological responses of the short-day strawberry cultivar ‘Benihoppe’ to individual and combined LTLI stress and developed a quantitative damage evaluation index. Seedlings were exposed to four treatments for 20 d: control (25/15 °C, 600 μmol m⁻² s⁻¹), single low temperature (LT: 15/5 °C), single low irradiance (LI: 100 μmol m⁻² s⁻¹), and combined stress (LTLI: 15/5 °C, 100 μmol m⁻² s⁻¹). Compared to isolated stress factors, combined LTLI treatment exhibited a statistically verified synergistic damaging effect (two-factor ANOVA, LT × LI p < 0.01) on leaf structure and function. LTLI-treated plants showed severe reductions in leaf area, palisade tissue thickness, chlorophyll content, and net photosynthetic rate (Pn), alongside elevated malondialdehyde (MDA) accumulation. Chlorophyll a fluorescence (OJIP) analysis revealed that LTLI stress strongly blocked the electron transport chain at the PSII acceptor side, increasing the J-step relative variable fluorescence (Vj) and suppressing the performance index (PI). To quantify these impacts, a Low Temperature and Low Irradiance Damage Index (LTLDI) was derived from 12 core physiological and morphological variables. The LTLDI scores demonstrated that LTLI induced severe damage by day 10 (score: 0.69) and extremely severe damage by day 20 (0.87), which were substantially higher than the damage caused by LT (0.58 at 20 d) and LI (0.63 at 20 d) alone. The index reliability was confirmed by its strong correlation (r > 0.9) with key stress markers (Fv/Fm, Pn, and MDA). Overall, combined LTLI stress exacerbates structural degradation and PSII photoinhibition in strawberry leaves. The proposed LTLDI offers a practical, standardized tool for evaluating stress severity, facilitating timely environmental management in greenhouse strawberry production. Full article

Although soybean is vital to the global economy, this crop faces productivity losses due to photoinhibition of photosystem II (PSII), which is worsened by heat and drought. Carbon dots (Cdots) offer a strategy to mitigate this stress by acting as light-harvesting and UV-protective agents. This study evaluated the foliar application of Cdots on soybean (Glycine max L. Merr. cv. BRS 1054 IPRO) exposed to high light intensity. In a greenhouse experiment with a completely randomized design, plants received deionized water (Control), synthesized Cdots at three concentrations (0.02, 0.05, and 0.20 mg mL⁻¹), or a commercial Cdot product. Plants were grown under 50% shade and, at 24 days after sowing, transferred to a high-light greenhouse (20% attenuation). Measurements included PSII fluorescence (maximum quantum yield, potential activity, basal fluorescence, and dynamic photoinhibition) and leaf gas exchange (stomatal conductance, net photosynthesis, transpiration, intercellular CO₂ concentration, intrinsic water use efficiency, and carboxylation efficiency), as well as chlorophyll index and growth traits. Cdots at 0.05 mg mL⁻¹ and the commercial product maintained higher morning PSII maximum activity (+16% vs. Control), indicating enhanced photoprotection. Conversely, 0.20 mg mL⁻¹ Cdots reduced PSII maximum activity by 62% at noon. At day 14, the 0.05 mg mL⁻¹ treatment improved stress acclimation, reducing stomatal conductance and transpiration, while sustaining photosynthesis. Growth was significantly enhanced at this concentration, increasing chlorophyll content by 14%, shoot length by 26%, and total dry mass by up to 41% compared to controls. In conclusion, Cdots at 0.05 mg mL⁻¹ alleviated chronic photoinhibition without increasing dynamic photoinhibition, thus acting as a promising nanobiostimulant that promotes soybean early growth under high-light stress. Full article

Sapling survival and growth depend on photosynthetic assimilates. Therefore, improving physiological performance during early stages may enhance subsequent performance and nursery production. This study evaluated whether exogenous oxidized glutathione (GSSG), reported to enhance photosynthesis, improves the photosynthetic, physiological, and growth-related traits of Larix gmelinii var. japonica saplings. Sixteen saplings were assigned to four treatments: GSSG, 5-aminolevulinic acid, Hyponex, and a water control. Photosynthetic, nitrogen-related, and growth traits were measured before treatment and at 3, 6, 13, and 31 days after treatment, and biomass was assessed after three months. The GSSG treatment showed no difference in the net CO₂ assimilation rate (A_max) compared with the control, but exhibited a significantly earlier peak at 6 days than the other treatments. This response was supported by the stability of GSSG-treated saplings against photoinhibition (F_v/F_m) and a tendency toward greater resilience to midday light stress (Φ_PSII). Enhanced photosynthetic performance was associated with reduced carbon and nitrogen fluctuations and was accompanied by numerically greater root and stem biomass in the 2024 terminal shoots. Although fertilization effects were generally weak and transient, GSSG elicited notable responses, suggesting that the immediate enhancement of photosynthesis underlies its impact. However, its antioxidant properties under stressful conditions warrant further investigation. Full article

The protection of leaves from photoinhibition and berries from dehydration and sunburn has become an increasingly important objective in response to the rising frequency and intensity of heat waves worldwide. This research investigated the effect of a white nonwoven geotextile sheet (TNT) installed in the fruiting zone in the white cultivar ‘Verdicchio’ (Vitis vinifera L.) during critical summer periods with the aim of protecting leaves and berries from extreme heat. The study was conducted over two seasons (2020–2021) in a rainfed vineyard in central Italy using a randomized block design. Physiological and yield parameters were recorded. Vines protected with TNT did not show any changes in net photosynthesis, stomatal conductance, and water use efficiency, compared to unshielded vines. However, TNT reduced leaf temperature and increased berry total acidity and malic acid concentration while reducing sugar content, leading to wines with higher freshness and reduced alcohol levels. The use of TNTs shows significant potential as a practical tool for viticulturists to mitigate the effects of excessive heat, allowing for better management of berry ripening and ultimately improving final wine characteristics. Additionally, TNT is economically feasible, especially if applied only to the afternoon-exposed side of the canopy, and its cost can be amortized, especially in vineyards affected by frequent heat waves and/or dedicated to the production of premium wines. Full article

The damage caused by herbivores is generally measured as the amount of leaf tissue consumed, without accounting for the fate of the leftover tissue. As a result, the plant defense mechanisms that promote resistance to herbivore feeding by photosynthetically acclimating the rest of the plant to the feeding spot leaf area have not been well exploited. Plant-insect interactions are now becoming better defined with the development of visualization methods that permit spatial whole-leaf assessment of photosynthetic efficiency after herbivore attack. The purpose of our study was to evaluate the spatial heterogeneity of photosystem II (PSII) function at the whole-leaf level before and after herbivory by the Colorado potato beetles. Twenty minutes after Colorado potato beetle (Leptinotarsa decemlineata) feeding, the maximum efficiency of PSII photochemistry (Fv/Fm) decreased significantly, suggesting photoinhibition due to reduced efficiency of the oxygen-evolving complex (OEC). The decreased quantum yield of PSII photochemistry (Φ_PSII) after feeding, at the neighboring area of the feeding spot and at the rest of the leaf area, was attributed to the reduced efficiency of the open PSII reaction centers (Fv′/Fm′), since there was no change in the fraction of open PSII reaction centers (qp). Nevertheless, plant defense elicitation was activated by the photoprotective mechanism of non-photochemical quenching (NPQ) that reduced the singlet oxygen (¹O₂) formation in potato plants in the neighboring area of the feeding spot and at the rest of the leaf area. In addition, the increased production of hydrogen peroxide (H₂O₂) triggered by this increase suggests that it acted as a signaling molecule in the biotic stress defense response. Full article

Achieving high morphological uniformity and mechanical strength is critical for the automation of watermelon grafting; yet, specific light protocols targeting these traits are lacking. This study employed LED lighting to regulate the morphological development of watermelon scion seedlings in a controlled plant factory environment. Using the watermelon cultivar ‘Heimeiling’ as the experimental material, three sequential experiments were conducted: (1) Under conditions of 95 μmol·m⁻²·s⁻¹ light intensity and a 12 h photoperiod, seven red/blue light ratios and a white light control were tested to identify the appropriate light quality. (2) Under the R3B1 light quality, gradients of the daily light integral (DLI) ranging from 2.88 to 17.28 mol·m⁻²·d⁻¹ were established by adjusting the light intensity and photoperiod to determine the optimal DLI. (3) Based on the above results, an orthogonal experiment was designed, with factors including the light quality (R7B1, R3B1, R1B1; where R7B1 represents 87.5% red light and 12.5% blue light), light intensity (120, 160, 200 μmol·m⁻²·s⁻¹), and photoperiod (16 h, 20 h, 24 h) to identify the optimal light environment combination for mechanical grafting. Results indicated that while monochromatic red light induced excessive elongation and suppressed metabolism, the R3B1 spectrum significantly enhanced the stem diameter, mechanical strength, and carbon–nitrogen accumulation while maintaining hormonal balance. Regarding the daily light integral (DLI), seedlings exhibited an optimal performance at 11.52 mol·m⁻²·d⁻¹. Lower DLI levels led to etiolation, whereas higher levels caused photoinhibition and PSII damage. Furthermore, orthogonal analysis revealed that light intensity was the dominant factor driving stem thickening and biomass accumulation, while light quality primarily regulated plant height. Consequently, a combination of R3B1 light quality, 200 μmol·m⁻²·s⁻¹ intensity, and a 20 h photoperiod was identified as the optimal strategy to satisfy the stringent morphological requirements for mechanical grafting. Full article

Hosta ‘So Sweet’, a shade-tolerant Asparagaceae species, displays remarkable high-light tolerance in open-field full-sun cultivation without photoinhibition symptoms. To clarify its growing-season photosynthetic dynamics and adaptive strategies, this study measured diurnal photosynthetic variations from May to September, determined chlorophyll fluorescence parameters and pigment contents in May, July and September, and analyzed the data alongside the light and CO₂ response curves for July. The results showed that the high temperatures combined with high-light conditions in July lowered P_n relative to May and September, but the light saturation point (LSP) reached 1508.99 μmol m⁻² s⁻¹, and the CO₂ compensation point (CCP) was 75.46 μmol mol⁻¹, highlighting the robust light energy utilization and carbon assimilation potential. Meanwhile, PSII maximum photochemical efficiency (Fv/Fm) remained stable under these conditions, indicating undamaged photosystems. Mechanistically, its photosynthetic limitation strategies showed seasonal plasticity: a tight coupling between P_n, stomatal conductance, and humidity in May shifted to a strong association between P_n and photoprotective dissipation (qN) in July, followed by an optimization of light capture linked to increased chlorophyll content and adjusted Chl a/b ratios in September. Taken together, H. ‘So Sweet’ synergistically adapts to growing-season light and temperature fluctuations by integrating light utilization potential, photosystem stability and pigment adjustment strategies. This study preliminarily delineated its photosynthetic physiological profile, revealed core light-adaptive strategies, and provided a theoretical basis for the ecological application of this excellent ornamental cultivar. Full article

Drought stress critically constrains plant development and morphogenesis, representing a substantial challenge to crop production systems. Dehydrins (DHNs), belonging to the late embryogenesis abundant (LEA) protein superfamily, play crucial roles in plant adaptation to environmental stress conditions. Nevertheless, the capacity of Suaeda salsa SsDHN protein to confer drought resistance has not been adequately investigated. In the present study, transgenic tobacco lines with constitutive SsDHN expression (SsDHN-OE) were employed to examine its influence on seedling development under water-limited conditions. Results indicated that constitutive SsDHN expression enhanced biomass accumulation, foliar expansion, root elongation, and root surface dimensions in water-stressed seedlings. Moreover, transformed lines demonstrated elevated proline (Pro) accumulation and abscisic acid (ABA) content, augmented antioxidant enzyme activity, and intensified stomatal regulation under stress conditions. Conversely, photoinhibition intensity, chloroplast structural degradation, malondialdehyde (MDA) accumulation, electrolyte leakage, hydrogen peroxide (H₂O₂), and superoxide radical (O₂⁻) concentrations were diminished. Furthermore, transcript abundance of stress-responsive genes—encompassing NtNCED3, NtSnRK2.2, NtRD26, NtLEA5, NtPOD, NtSOD, NtCAT, and NtAPX1—was markedly increased in SsDHN-OE lines experiencing drought stress. Taken together, these findings establish that SsDHN functions as a positive regulator of drought resilience in plants. Full article

The APETALA2/Ethylene Response Factor (AP2/ERF) family of transcription factors (TF) is characterized by their participation in various biological processes related to growth, development, and response to stress. ERFs are ideal candidates for crop improvement because they regulate defense genes like JERF1, JERF3, LeERF2, NtERF5, and Tsil which confer tolerance to drought, salinity, osmotic stress, and pathogen attack, respectively. The ERF subfamily includes the TF Pti4, whose activity is regulated by different signaling pathways, thus providing tolerance response to multiple factors such as drought, salinity, cold, and pathogen attack in tomato. In this work we evaluated the effect of overexpression of TF SlPti4 from Solanum lycopersicum in transgenic tobacco plants when subjected to saline, osmotic, and drought stress. Our results from this study demonstrated that transgenic lines overexpressing Pti4 tolerate abiotic stress during germination and in plants. The transgenic lines showed improvements in photoinhibition, electron transport rate, chlorophyll content, and biomass, as well as a reduction in malondialdehyde content. Full article