Inhibition of sulfur assimilation by S-benzyl-L-cysteine: Impacts on growth, photosynthesis, and leaf proteome of maize plants.

Sulfur is an essential nutrient for various physiological processes, including protein synthesis and enzyme activation. We aimed to evaluate how S-benzyl-L-cysteine (SBC), an inhibitor of the sulfur assimilation pathway, affects maize plants' growth, photosynthesis, and leaf proteomic profile. Thus, maize plants were grown for 14 days in vermiculite supplemented with SBC. Photosynthesis was assessed using light and CO2 response curves and chlorophyll a fluorescence. Leaf proteome analysis was conducted to evaluate photosynthetic protein biosynthesis, and ROS content was quantified to assess oxidative stress. Applying SBC resulted in a significant decrease in the growth of maize plants. The gas exchange analysis revealed that maize plants exhibited a diminished rate of CO2 assimilation attributable to both stomatal and non-stomatal limitations. Furthermore, SBC suppressed the activity of important elements involved in the photosynthetic electron transport chain (including photosystems I and II, cytochrome b6f, and ATP synthase) and enzymes responsible for the Calvin cycle, some of which have sulfur-containing prosthetic groups. Consequently, the diminished electron flow rate resulted in a substantial increase in the levels of ROS within the leaves. Our research highlights the crucial role of SBC in disrupting maize photosynthesis by limiting L-cysteine and assimilated sulfur availability, which are essential for the synthesis of protein and prosthetic groups and photosynthetic processes, emphasizing the potential of OAS-TL as a new herbicide site of action.

Fluorescence and Hyperspectral Sensors for Nondestructive Analysis and Prediction of Biophysical Compounds in the Green and Purple Leaves of Tradescantia Plants.

The application of non-imaging hyperspectral sensors has significantly enhanced the study of leaf optical properties across different plant species. In this study, chlorophyll fluorescence (ChlF) and hyperspectral non-imaging sensors using ultraviolet-visible-near-infrared shortwave infrared (UV-VIS-NIR-SWIR) bands were used to evaluate leaf biophysical parameters. For analyses, principal component analysis (PCA) and partial least squares regression (PLSR) were used to predict eight structural and ultrastructural (biophysical) traits in green and purple Tradescantia leaves. The main results demonstrate that specific hyperspectral vegetation indices (HVIs) markedly improve the precision of partial least squares regression (PLSR) models, enabling reliable and nondestructive evaluations of plant biophysical attributes. PCA revealed unique spectral signatures, with the first principal component accounting for more than 90% of the variation in sensor data. High predictive accuracy was achieved for variables such as the thickness of the adaxial and abaxial hypodermis layers (R2 = 0.94) and total leaf thickness, although challenges remain in predicting parameters such as the thickness of the parenchyma and granum layers within the thylakoid membrane. The effectiveness of integrating ChlF and hyperspectral technologies, along with spectroradiometers and fluorescence sensors, in advancing plant physiological research and improving optical spectroscopy for environmental monitoring and assessment. These methods offer a good strategy for promoting sustainability in future agricultural practices across a broad range of plant species, supporting cell biology and material analyses.

Effects of Salicylic Acid on Physiological Responses of Pepper Plants Pre-Subjected to Drought under Rehydration Conditions.

Capsicum annuum L. has worldwide distribution, but drought has limited its production. There is a lack of research to better understand how this species copes with drought stress, whether it is reversible, and the effects of mitigating agents such as salicylic acid (SA). Therefore, this study aimed to understand the mechanisms of action of SA and rehydration on the physiology of pepper plants grown under drought conditions. The factorial scheme adopted was 3 × 4, with three water regimes (irrigation, drought, and rehydration) and four SA concentrations, namely: 0 (control), 0.5, 1, and 1.5 mM. This study evaluated leaf water percentage, water potential of shoots, chlorophylls (a and b), carotenoids, stomatal conductance, chlorophyll a fluorescence, and hydrogen peroxide (H2O2) concentration at different times of day, water conditions (irrigation, drought, and rehydration), and SA applications (without the addition of a regulator (0) and with the addition of SA at concentrations equal to 0.5, 1, and 1.5 mM). In general, exogenous SA application increased stomatal conductance (gs) responses and modified the fluorescence parameters (ΦPSII, qP, ETR, NPQ, D, and E) of sweet pepper plants subjected to drought followed by rehydration. It was found that the use of SA, especially at concentrations of 1 mM in combination with rehydration, modulates gs, which is reflected in a higher electron transport rate. This, along with the production of photosynthetic pigments, suggests that H2O2 did not cause membrane damage, thereby mitigating the water deficit in pepper plants. Plants under drought conditions and rehydration with foliar SA application at concentrations of 1 mM demonstrated protection against damage resulting from water stress. Focusing on sustainable productivity, foliar SA application of 1 mM could be recommended as a technique to overcome the adverse effects of water stress on pepper plants cultivated in arid and semi-arid regions.

Comparative Insights into Photosynthetic, Biochemical, and Ultrastructural Mechanisms in Hibiscus and Pelargonium Plants.

Understanding photosynthetic mechanisms in different plant species is crucial for advancing agricultural productivity and ecological restoration. This study presents a detailed physiological and ultrastructural comparison of photosynthetic mechanisms between Hibiscus (Hibiscus rosa-sinensis L.) and Pelargonium (Pelargonium zonale (L.) L'Hér. Ex Aiton) plants. The data collection encompassed daily photosynthetic profiles, responses to light and CO2, leaf optical properties, fluorescence data (OJIP transients), biochemical analyses, and anatomical observations. The findings reveal distinct morphological, optical, and biochemical adaptations between the two species. These adaptations were associated with differences in photochemical (AMAX, E, Ci, iWUE, and α) and carboxylative parameters (VCMAX, ΓCO2, gs, gm, Cc, and AJMAX), along with variations in fluorescence and concentrations of chlorophylls and carotenoids. Such factors modulate the efficiency of photosynthesis. Energy dissipation mechanisms, including thermal and fluorescence pathways (ΦPSII, ETR, NPQ), and JIP test-derived metrics highlighted differences in electron transport, particularly between PSII and PSI. At the ultrastructural level, Hibiscus exhibited optimised cellular and chloroplast architecture, characterised by increased chloroplast density and robust grana structures. In contrast, Pelargonium displayed suboptimal photosynthetic parameters, possibly due to reduced thylakoid counts and a higher proportion of mitochondria. In conclusion, while Hibiscus appears primed for efficient photosynthesis and energy storage, Pelargonium may prioritise alternative cellular functions, engaging in a metabolic trade-off.

Biostimulant Response of Foliar Application of Rare Earth Elements on Physiology, Growth, and Yield of Rice.

Rare earth elements (REEs) have been intentionally used in Chinese agriculture since the 1980s to improve crop yields. Around the world, REEs are also involuntarily applied to soils through phosphate fertilizers. These elements are known to alleviate damage in plants under abiotic stresses, yet there is no information on how these elements act in the physiology of plants. The REE mode of action falls within the scope of the hormesis effect, with low-dose stimulation and high-dose adverse reactions. This study aimed to verify how REEs affect rice plants' physiology to test the threshold dose at which REEs could act as biostimulants in these plants. In experiment 1, 0.411 kg ha-1 (foliar application) of a mixture of REE (containing 41.38% Ce, 23.95% La, 13.58% Pr, and 4.32% Nd) was applied, as well as two products containing 41.38% Ce and 23.95% La separately. The characteristics of chlorophyll a fluorescence, gas exchanges, SPAD index, and biomass (pot conditions) were evaluated. For experiment 2, increasing rates of the REE mix (0, 0.1, 0.225, 0.5, and 1 kg ha-1) (field conditions) were used to study their effect on rice grain yield and nutrient concentration of rice leaves. Adding REEs to plants increased biomass production (23% with Ce, 31% with La, and 63% with REE Mix application) due to improved photosynthetic rate (8% with Ce, 15% with La, and 27% with REE mix), favored by the higher electronic flow (photosynthetic electron transport chain) (increase of 17%) and by the higher Fv/Fm (increase of 14%) and quantum yield of photosystem II (increase of 20% with Ce and La, and 29% with REE Mix), as well as by increased stomatal conductance (increase of 36%) and SPAD index (increase of 10% with Ce, 12% with La, and 15% with REE mix). Moreover, adding REEs potentiated the photosynthetic process by increasing rice leaves' N, Mg, K, and Mn concentrations (24-46%). The dose for the higher rice grain yield (an increase of 113%) was estimated for the REE mix at 0.72 kg ha-1.

Physiological and Biochemical Aspects of Silicon-Mediated Resistance in Maize against Maydis Leaf Blight.

Maydis leaf blight (MLB), caused by the necrotrophic fungus Bipolaris maydis, has caused considerable yield losses in maize production. The hypothesis that maize plants with higher foliar silicon (Si) concentration can be more resistant against MLB was investigated in this study. This goal was achieved through an in-depth analysis of the photosynthetic apparatus (parameters of leaf gas exchange chlorophyll (Chl) a fluorescence and photosynthetic pigments) changes in activities of defense and antioxidative enzymes in leaves of maize plants with (+Si; 2 mM) and without (-Si; 0 mM) Si supplied, as well as challenged and not with B. maydis. The +Si plants showed reduced MLB symptoms (smaller lesions and lower disease severity) due to higher foliar Si concentration and less production of malondialdehyde, hydrogen peroxide, and radical anion superoxide compared to -Si plants. Higher values for leaf gas exchange (rate of net CO2 assimilation, stomatal conductance to water vapor, and transpiration rate) and Chl a fluorescence (variable-to-maximum Chl a fluorescence ratio, photochemical yield, and yield for dissipation by downregulation) parameters along with preserved pool of chlorophyll a+b and carotenoids were noticed for infected +Si plants compared to infected -Si plants. Activities of defense (chitinase, ß-1,3-glucanase, phenylalanine ammonia-lyase, polyphenoloxidase, peroxidase, and lipoxygenase) and antioxidative (ascorbate peroxidase, catalase, superoxide dismutase, and glutathione reductase) enzymes were higher for infected +Si plants compared to infected -Si plants. Collectively, this study highlights the importance of using Si to boost maize resistance against MLB considering the more operative defense reactions and the robustness of the antioxidative metabolism of plants along with the preservation of their photosynthetic apparatus.

Past environmental changes: using sedimentary photosynthetic pigments to enhance subtropical reservoir management.

The historical impacts of eutrophication processes were investigated in six subtropical reservoirs (São Paulo, Brazil) using a paleolimnological approach. We questioned whether the levels of pigment indicators of algal biomass could provide information about trophic increase and whether carotenoid pigments could offer additional insights. The following proxies were employed: organic matter, total phosphorus, total nitrogen, photosynthetic pigments (by high-performance liquid chromatography), sedimentation rates, and geochronology (by 210 Pb technique). Principal component analysis indicated a gradient of eutrophication. In eutrophic reservoirs (e.g., Rio Grande and Salto Grande), levels of lutein and zeaxanthin increased over time, suggesting growth of Chlorophyta and Cyanobacteria. These pigments were significantly associated with algal biomass, reflecting their participation in phytoplankton composition. In mesotrophic reservoirs, Broa and Itupararanga, increases and significative linear correlations (r > 0.70) between pigments and nutrients are mainly linked to agricultural and urban activities. In the oligotrophic reservoir Igaratá, lower pigment and nutrient levels reflected lesser human impact and good water quality. This study underscores eutrophication's complexity across subtropical reservoirs. Photosynthetic pigments associated with specific algal groups were informative, especially when correlated with nutrient data. The trophic increase, notably in the 1990s, may have been influenced by neoliberal policies. Integrated pigment and geochemical analysis offers a more precise understanding of eutrophication changes and their ties to human factors. Such research can aid environmental monitoring and sustainable policy development.

A non-invasive method to predict drought survival in Arabidopsis using quantum yield under light conditions.

BACKGROUND: Survival rate (SR) is frequently used to compare drought tolerance among plant genotypes. While a variety of techniques for evaluating the stress status of plants under drought stress conditions have been developed, determining the critical point for the recovery irrigation to evaluate plant SR often relies directly on a qualitative inspection by the researcher or on the employment of complex and invasive techniques that invalidate the subsequent use of the tested individuals. RESULTS: Here, we present a simple, instantaneous, and non-invasive method to estimate the survival probability of Arabidopsis thaliana plants after severe drought treatments. The quantum yield (QY), or efficiency of photosystem II, was monitored in darkness (Fv/Fm) and light (Fv'/Fm') conditions in the last phase of the drought treatment before recovery irrigation. We found a high correlation between a plant's Fv'/Fm' value before recovery irrigation and its survival phenotype seven days after, allowing us to establish a threshold between alive and dead plants in a calibration stage. This correlation was maintained in the Arabidopsis accessions Col-0, Ler-0, C24, and Kondara under the same conditions. Fv'/Fm' was then applied as a survival predictor to compare the drought tolerance of transgenic lines overexpressing the transcription factors ATAF1 and PLATZ1 with the Col-0 control. CONCLUSIONS: The results obtained in this work demonstrate that the chlorophyll a fluorescence parameter Fv'/Fm' can be used as a survival predictor that gives a numerical estimate of the Arabidopsis drought SR before recovery irrigation. The procedure employed to get the Fv'/Fm' measurements is fast, non-destructive, and requires inexpensive and easy-to-handle equipment. Fv'/Fm' as a survival predictor can be used to offer an overview of the photosynthetic state of the tested plants and determine more accurately the best timing for rewatering to assess the SR, especially when the symptoms of severe dehydration between genotypes are not contrasting enough to identify a difference visually.

How does shading mitigates the water deficit in young Hymenaea courbaril L. plants?

Information on tolerance to isolated or combined abiotic stresses is still scarce for tree species, although such stresses are normal in nature. The interactive effect of light availability and water stress has been reported for some native tree species in Brazil but has not been widely investigated. To test the hypothesis that shading can mitigate the stressful effect of water deficit on the photosynthetic and antioxidant metabolism and on the growth of young Hymenaea courbaril L. plants, we evaluated the following two water regimes: a) continuous irrigation - control (I) - 75% field capacity. and b) water deficit (S), characterized by irrigation suspension associated the two following periods of evaluation: P0 - when the photosynthetic rate of plants subjected to irrigation suspension reached values ​​close to zero, with the seedlings being re-irrigated at that moment, and REC - when the photosynthetic rate of the re-irrigated plants of each shading levels reached values ​​similar to those of plants in the control treatment, totaling four treatments: IP0, SP0, IREC, and SREC. The plants of these four treatments were cultivated under the four following shading levels: 0, 30, 50, and 70%, constituting 16 treatments. Intermediate shading of 30 and 50% mitigates the water deficit and accelerates the recovery of H. courbaril. Water deficit associated with cultivation without shading (0%) should not be adopted in the cultivation or transplantation of H. courbaril. After the resumption of irrigation in the REC, the other characteristics presented a recovery under all cultivation conditions. Key message: Intermediate shading of 30 and 50% mitigates the water deficit and accelerates the recovery of H. courbaril.

Alkaloids (emetine and cephalin) production - affected by full sunlight stress in Carapichea ipecacuanha.

This study evaluated the responses of Carapichea ipecacuanha to sunlight stress-induced changes in the electron transport chain and its extended effects on alkaloid production (emetine and cephalin). The treatments consisted of: (i). 50, 70, and 90% shading (controls) and their respective exposure to full sunlight; besides, full sunlight (55 days of direct sun exposure). Photosynthetic pigments, chlorophyll a fluorescence transient, antioxidant enzymatic system, and quantification of cephalin and emetine were analyzed. Several changes in the Chl a fluorescence induction were observed, such as a decline in the quantum yield of the conversion of photochemical energy and photosynthetic performance and; an increase in emetine production of plants exposed to full sunlight. These results demonstrated that ipecac plants are extremely sensitive to full exposure to solar radiation, especially in periods with high temperatures, such as in summer, however with increment in emetine production.

Adjustments in photosynthetic pigments, PS II photochemistry and photoprotection in a tropical C4 forage plant exposed to warming and elevated [CO2].

Global climate change will impact crops and grasslands, affecting growth and yield. However, is not clear how the combination of warming and increased atmospheric carbon dioxide concentrations ([CO2]) will affect the photosystem II (PSII) photochemistry and the photosynthetic tissue photoinhibition and photoprotection on tropical forages. Here, we evaluated the effects of elevated [CO2] (∼600 µmol mol-1) and warming (+2 °C increase temperature) on the photochemistry of photosystem II and the photoprotection strategies of a tropical C4 forage Panicum maximum Jacq. grown in a Trop-T-FACE facility under well-watered conditions without nutrient limitation. Analysis of the maximum photochemical efficiency of PSII (Fv/Fm), the effective PSII quantum yield Y(II), the quantum yield of regulated energy dissipation Y(NPQ), the quantum yield of non-regulated energy dissipation Y(NO), and the malondialdehyde (MDA) contents in leaves revealed that the photosynthetic apparatus of plants did not suffer photoinhibitory damage, and plants did not increase lipid peroxidation in response to warming and [CO2] enrichment. Plants under warming treatment showed a 12% higher chlorophyll contents and a 58% decrease in α-tocopherol contents. In contrast, carotenoid composition (zeaxanthin and ß-carotene) and ascorbate levels were not altered by elevated [CO2] and warming. The elevated temperature increased both net photosynthesis rate and aboveground biomass but elevated [CO2] increased only net photosynthesis. Adjustments in chlorophyll, de-epoxidation state of the xanthophylls cycle, and tocopherol contents suggest leaves of P. maximum can acclimate to 2 °C warmer temperature and elevated [CO2] when plants are grown with enough water and nutrients during tropical autumn-winter season.

Shading minimizes the effects of water deficit in Campomanesia xanthocarpa (Mart.) O. Berg seedlings / Sombreamento minimiza o efeito do déficit hídrico em mudas de Campomanesia xanthocarpa (Mart.) O. Berg

Abstract The objective of this study was to evaluate the activity of antioxidant enzymes, the functioning of the photosystem II and quality of C. xanthocarpa seedlings cultivated under intermittent water deficit and shading levels and the influence of shading on recovery potential after suspension of the stress conditions. The seedlings were subjected to three levels of shading (0, 30, and 70%), six periods of evaluation (start: 0 days; 1st and 2nd photosynthesis zero: 1st and 2nd P0; 1st and 2nd recovery: 1stand 2nd REC; and END), and two forms of irrigation (control: periodically irrigated to maintain 70% substrate water retention capacity, and intermittent irrigation: suspension of irrigation). The plants subjected to intermittent irrigation conditions at 0% shading showed a reduction in water potential (Ψw) and potential quantum efficiency of photosystem II (Fv/Fm) and maximum efficiency of the photochemical process (Fv/F0) and an increase in basal quantum production of the non-photochemical processes (F0/Fm). Superoxide dismutase (SOD) activity was higher in the leaves than in the roots. The C. xanthocarpa is a species sensitive to water deficit but presents strategies to adapt to an environment under temporary water restriction, which are more temporary are most efficient under shading. The seedlings with water deficit at all levels of shading exhibited higher protective antioxidant activity and lower quality at 0% shading. The shading minimizes prevents permanent damage to the photosystem II and after the re-irrigation, the evaluated characteristics showed recovery with respect to the control group, except POD and SOD activities in the leaves.

Resumo O objetivo deste estudo foi avaliar a atividade de enzimas antioxidantes, o funcionamento do fotossistema II e a qualidade de mudas de C. xanthocarpa cultivadas sob déficit hídrico intermitente e níveis de sombreamento e a influência do sombreamento sobre o potencial de recuperação após suspensão das condições de estresse. As mudas foram submetidas a três níveis de sombreamento (0, 30 e 70%), seis períodos de avaliação (início: 0 dias; 1ª e 2ª fotossíntese zero: 1ª e 2ª P0; 1ª e 2ª recuperação: 1ª e 2ª REC; e final), e duas formas de irrigação (controle: periodicamente irrigado para manter 70% da capacidade de retenção de água do substrato, e irrigação intermitente: suspensão da irrigação). As plantas submetidas às condições de irrigação intermitente a 0% de sombreamento apresentaram redução do potencial hídrico (Ψw) e eficiência quântica potencial do fotossistema II (Fv/Fm) e máxima eficiência do processo fotoquímico (Fv/F0) e aumento da produção quantica basal dos processos não fotoquímicos (F0/Fm). A atividade da superóxido dismutase (SOD) foi maior nas folhas do que nas raízes. C. xanthocarpa é uma espécie sensível ao déficit hídrico, mas apresenta estratégias para se adaptar a um ambiente com restrição hídrica temporária, sendo mais eficientes sob sombreamento. As mudas com déficit hídrico em todos os níveis de sombreamento exibiram maior atividade antioxidante protetora e menor qualidade no sombreamento 0%. O sombreamento minimiza danos permanentes ao fotossistema II e após a re-irrigação, as características avaliadas apresentaram recuperação em relação ao grupo controle, exceto atividades de POD e SOD nas folhas.

Shading minimizes the effects of water deficit in Campomanesia xanthocarpa (Mart) O Berg seedlings / Sombreamento minimiza o efeito do déficit hídrico em mudas de Campomanesia xanthocarpa (Mart) O Berg

The objective of this study was to evaluate the activity of antioxidant enzymes, the functioning of the photosystem II and quality of C. xanthocarpa seedlings cultivated under intermittent water deficit and shading levels and the influence of shading on recovery potential after suspension of the stress conditions. The seedlings were subjected to three levels of shading (0, 30, and 70%), six periods of evaluation (start: 0 days; 1st and 2nd photosynthesis zero: 1st and 2nd P0; 1st and 2nd recovery: 1stand 2nd REC; and END), and two forms of irrigation (control: periodically irrigated to maintain 70% substrate water retention capacity, and intermittent irrigation: suspension of irrigation). The plants subjected to intermittent irrigation conditions at 0% shading showed a reduction in water potential (Ψw) and potential quantum efficiency of photosystem II (Fv/Fm) and maximum efficiency of the photochemical process (Fv/F0) and an increase in basal quantum production of the non-photochemical processes (F0/Fm). Superoxide dismutase (SOD) activity was higher in the leaves than in the roots. The C. xanthocarpa is a species sensitive to water deficit but presents strategies to adapt to an environment under temporary water restriction, which are more temporary are most efficient under shading. The seedlings with water deficit at all levels of shading exhibited higher protective antioxidant activity and lower quality at 0% shading. The shading minimizes prevents permanent damage to the photosystem II and after the re-irrigation, the evaluated characteristics showed recovery with respect to the control group, except POD and SOD activities in the leaves.(AU)

O objetivo deste estudo foi avaliar a atividade de enzimas antioxidantes, o funcionamento do fotossistema II e a qualidade de mudas de C. xanthocarpa cultivadas sob déficit hídrico intermitente e níveis de sombreamento e a influência do sombreamento sobre o potencial de recuperação após suspensão das condições de estresse. As mudas foram submetidas a três níveis de sombreamento (0, 30 e 70%), seis períodos de avaliação (início: 0 dias; 1ª e 2ª fotossíntese zero: 1ª e 2ª P0; 1ª e 2ª recuperação: 1ª e 2ª REC; e final), e duas formas de irrigação (controle: periodicamente irrigado para manter 70% da capacidade de retenção de água do substrato, e irrigação intermitente: suspensão da irrigação). As plantas submetidas às condições de irrigação intermitente a 0% de sombreamento apresentaram redução do potencial hídrico (Ψw) e eficiência quântica potencial do fotossistema II (Fv/Fm) e máxima eficiência do processo fotoquímico (Fv/F0) e aumento da produção quantica basal dos processos não fotoquímicos (F0/Fm). A atividade da superóxido dismutase (SOD) foi maior nas folhas do que nas raízes. C. xanthocarpa é uma espécie sensível ao déficit hídrico, mas apresenta estratégias para se adaptar a um ambiente com restrição hídrica temporária, sendo mais eficientes sob sombreamento. As mudas com déficit hídrico em todos os níveis de sombreamento exibiram maior atividade antioxidante protetora e menor qualidade no sombreamento 0%. O sombreamento minimiza danos permanentes ao fotossistema II e após a re-irrigação, as características avaliadas apresentaram recuperação em relação ao grupo controle, exceto atividades de POD e SOD nas folhas.(AU)

Shading minimizes the effects of water deficit in Campomanesia xanthocarpa (Mart) O Berg seedlings / Sombreamento minimiza o efeito do déficit hídrico em mudas de Campomanesia xanthocarpa (Mart) O Berg

The objective of this study was to evaluate the activity of antioxidant enzymes, the functioning of the photosystem II and quality of C. xanthocarpa seedlings cultivated under intermittent water deficit and shading levels and the influence of shading on recovery potential after suspension of the stress conditions. The seedlings were subjected to three levels of shading (0, 30, and 70%), six periods of evaluation (start: 0 days; 1st and 2nd photosynthesis zero: 1st and 2nd P0; 1st and 2nd recovery: 1stand 2nd REC; and END), and two forms of irrigation (control: periodically irrigated to maintain 70% substrate water retention capacity, and intermittent irrigation: suspension of irrigation). The plants subjected to intermittent irrigation conditions at 0% shading showed a reduction in water potential (Ψw) and potential quantum efficiency of photosystem II (Fv/Fm) and maximum efficiency of the photochemical process (Fv/F0) and an increase in basal quantum production of the non-photochemical processes (F0/Fm). Superoxide dismutase (SOD) activity was higher in the leaves than in the roots. The C. xanthocarpa is a species sensitive to water deficit but presents strategies to adapt to an environment under temporary water restriction, which are more temporary are most efficient under shading. The seedlings with water deficit at all levels of shading exhibited higher protective antioxidant activity and lower quality at 0% shading. The shading minimizes prevents permanent damage to the photosystem II and after the re-irrigation, the evaluated characteristics showed recovery with respect to the control group, except POD and SOD activities in the leaves.

O objetivo deste estudo foi avaliar a atividade de enzimas antioxidantes, o funcionamento do fotossistema II e a qualidade de mudas de C. xanthocarpa cultivadas sob déficit hídrico intermitente e níveis de sombreamento e a influência do sombreamento sobre o potencial de recuperação após suspensão das condições de estresse. As mudas foram submetidas a três níveis de sombreamento (0, 30 e 70%), seis períodos de avaliação (início: 0 dias; 1ª e 2ª fotossíntese zero: 1ª e 2ª P0; 1ª e 2ª recuperação: 1ª e 2ª REC; e final), e duas formas de irrigação (controle: periodicamente irrigado para manter 70% da capacidade de retenção de água do substrato, e irrigação intermitente: suspensão da irrigação). As plantas submetidas às condições de irrigação intermitente a 0% de sombreamento apresentaram redução do potencial hídrico (Ψw) e eficiência quântica potencial do fotossistema II (Fv/Fm) e máxima eficiência do processo fotoquímico (Fv/F0) e aumento da produção quantica basal dos processos não fotoquímicos (F0/Fm). A atividade da superóxido dismutase (SOD) foi maior nas folhas do que nas raízes. C. xanthocarpa é uma espécie sensível ao déficit hídrico, mas apresenta estratégias para se adaptar a um ambiente com restrição hídrica temporária, sendo mais eficientes sob sombreamento. As mudas com déficit hídrico em todos os níveis de sombreamento exibiram maior atividade antioxidante protetora e menor qualidade no sombreamento 0%. O sombreamento minimiza danos permanentes ao fotossistema II e após a re-irrigação, as características avaliadas apresentaram recuperação em relação ao grupo controle, exceto atividades de POD e SOD nas folhas.

Shading minimizes the effects of water deficit in Campomanesia xanthocarpa (Mart.) O. Berg seedlings

Abstract The objective of this study was to evaluate the activity of antioxidant enzymes, the functioning of the photosystem II and quality of C. xanthocarpa seedlings cultivated under intermittent water deficit and shading levels and the influence of shading on recovery potential after suspension of the stress conditions. The seedlings were subjected to three levels of shading (0, 30, and 70%), six periods of evaluation (start: 0 days; 1st and 2nd photosynthesis zero: 1st and 2nd P0; 1st and 2nd recovery: 1stand 2nd REC; and END), and two forms of irrigation (control: periodically irrigated to maintain 70% substrate water retention capacity, and intermittent irrigation: suspension of irrigation). The plants subjected to intermittent irrigation conditions at 0% shading showed a reduction in water potential (w) and potential quantum efficiency of photosystem II (Fv/Fm) and maximum efficiency of the photochemical process (Fv/F0) and an increase in basal quantum production of the non-photochemical processes (F0/Fm). Superoxide dismutase (SOD) activity was higher in the leaves than in the roots. The C. xanthocarpa is a species sensitive to water deficit but presents strategies to adapt to an environment under temporary water restriction, which are more temporary are most efficient under shading. The seedlings with water deficit at all levels of shading exhibited higher protective antioxidant activity and lower quality at 0% shading. The shading minimizes prevents permanent damage to the photosystem II and after the re-irrigation, the evaluated characteristics showed recovery with respect to the control group, except POD and SOD activities in the leaves.

Resumo O objetivo deste estudo foi avaliar a atividade de enzimas antioxidantes, o funcionamento do fotossistema II e a qualidade de mudas de C. xanthocarpa cultivadas sob déficit hídrico intermitente e níveis de sombreamento e a influência do sombreamento sobre o potencial de recuperação após suspensão das condições de estresse. As mudas foram submetidas a três níveis de sombreamento (0, 30 e 70%), seis períodos de avaliação (início: 0 dias; 1ª e 2ª fotossíntese zero: 1ª e 2ª P0; 1ª e 2ª recuperação: 1ª e 2ª REC; e final), e duas formas de irrigação (controle: periodicamente irrigado para manter 70% da capacidade de retenção de água do substrato, e irrigação intermitente: suspensão da irrigação). As plantas submetidas às condições de irrigação intermitente a 0% de sombreamento apresentaram redução do potencial hídrico (w) e eficiência quântica potencial do fotossistema II (Fv/Fm) e máxima eficiência do processo fotoquímico (Fv/F0) e aumento da produção quantica basal dos processos não fotoquímicos (F0/Fm). A atividade da superóxido dismutase (SOD) foi maior nas folhas do que nas raízes. C. xanthocarpa é uma espécie sensível ao déficit hídrico, mas apresenta estratégias para se adaptar a um ambiente com restrição hídrica temporária, sendo mais eficientes sob sombreamento. As mudas com déficit hídrico em todos os níveis de sombreamento exibiram maior atividade antioxidante protetora e menor qualidade no sombreamento 0%. O sombreamento minimiza danos permanentes ao fotossistema II e após a re-irrigação, as características avaliadas apresentaram recuperação em relação ao grupo controle, exceto atividades de POD e SOD nas folhas.

Morphoanatomical, Physiological, and Biochemical Indicators in Lactuca sativa L. Germination and Growth in Response to Fluoride.

Fluoride is one of the main phytotoxic environmental pollutants, and high concentrations (10-30 mg L-1) are commonly detected in surface and groundwater. Little, however, is known about the effects of this pollutant on crops that require irrigation during their development, which, in addition to phytotoxicity, may cause negative human health effects. Thus, the aim of this study was to characterize the effects of potassium fluoride (KF) on the germination of lettuce seeds and identify the physiological and anatomical markers of this pollutant's action on plants exposed to it during growth. Initially, lettuce seeds were sown in gerboxes and soaked in solutions containing 0 mg L-1, 10 mg L-1, 20 mg L-1, and 30 mg L-1 KF. Plants grown in a greenhouse were treated daily with KF irrigation at the same KF concentrations for 40 days. KF exposure reduced the germination rate and germination speed index of lettuce seeds at 20 mg L-1 and 30 mg L-1, resulting in compromised root development at the highest KF concentration. Lettuce plants displayed a slight photosynthesis reduction and a significant photochemical efficiency decrease after exposures to all KF concentrations. Lower chlorophyll contents and nitrogen balance indices were observed in plants exposed to 30 mg L-1 KF. On the other hand, increases in phenolic compounds and malondialdehyde were noted with increasing KF concentrations. Lettuce plants can, therefore, accumulate fluoride in leaves when irrigated with KF-rich water. The investigated physiological and biochemical variables were proven to be adequate fluoride action biomarkers in lettuce plants and may become an important tool in the study of olericulture contaminants.

Roles of Calcium Signaling in Gene Expression and Photosynthetic Acclimatization of Solanum lycopersicum Micro-Tom (MT) after Mechanical Damage.

A momentary increase in cytoplasmic Ca2+ generates an oscillation responsible for the activation of proteins, such as calmodulin and kinases, which interact with reactive oxygen species (ROS) for the transmission of a stress signal. This study investigated the influence of variations in calcium concentrations on plant defense signaling and photosynthetic acclimatization after mechanical damage. Solanum lycopersicum Micro-Tom was grown with 0, 2 and 4 mM Ca2+, with and without mechanical damage. The expression of stress genes was evaluated, along with levels of antioxidant enzymes, hydrogen peroxide, lipid peroxidation, histochemistry, photosynthesis and dry mass of organs. The ROS production generated by mechanical damage was further enhanced by calcium-free conditions due to the inactivation of the oxygen evolution complex, contributing to an increase in reactive species. The results indicated that ROS affected mechanical damage signaling because calcium-free plants exhibited high levels of H2O2 and enhanced expression of kinase and RBOH1 genes, necessary conditions for an efficient response to stress. We conclude that the plants without calcium supply recognized mechanical damage but did not survive. The highest expression of the RBOH1 gene and the accumulation of H2O2 in these plants signaled cell death. Plants grown in the presence of calcium showed higher expression of SlCaM2 and control of H2O2 concentration, thus overcoming the stress caused by mechanical damage, with photosynthetic acclimatization and without damage to dry mass production.

Binding Properties of Photosynthetic Herbicides: Photosynthetic Activity and Molecular Docking Approach towards 1,4-Dihydropyridines Derivatives.

In the current work, we describe the synthesis of 1,4-dihydropyridine (1,4-DHP) derivatives via Hantzsch multicomponent reaction and their evaluation as photosystem II (PSII) inhibitors through chlorophyll a fluorescence bioassay. Among all the compounds tested, 1,1'-(2,4,6-trimethyl-1,4-dihydropyridine-3,5-diyl)bis(ethan-1-one) (4b) showed best results, reducing the parameters performance index on absorption basis (PIabs ) and electron transport per reaction center by 61 % and 49 %, respectively, as compared to the control. These results indicate the inhibitory activity of PSII over the electron transport chain. Additionally, a molecular docking approach using the protein D1 (PDB code 4V82) was performed in order to assess the structure-activity relationship among the 1,4-DHP derivatives over the PSII, which revealed that both, size of the group at position 4 and the carbonyl groups at the dihydropyridine ring are important for the ligand's interaction, particularly for the hydrogen-bonding interaction with the residues His215, Ser264, and Phe265. Thus, the optimization of these molecular features is the aim of our research group to extend the knowledge of PSII electron chain inhibitors and the establishment of new potent bioactive molecular scaffolds.

Cowpea: A low-cost quality protein source for food safety in marginal areas for agriculture.

Cowpea is a low-cost protein source for human nutrition for the world's impoverished regions. Therefore, the yield and total grain protein content (TGPC) of two modern commercials genotypes, Novaera and Gurguéia, and two traditional local genotypes, Paulistinha and EPACE-10, were studied. Also, leaf area and dry weight, leaf soluble protein content, and chlorophyll a fluorescence, parameters related to photosynthetic capacity, were used to evaluate genotypes. Under optimal conditions, the yield of EPACE-10 and Paulistinha, with higher TGPC, was lower than for Gurguéia and Novaera, which showed lower TGPC. The four cowpea genotypes showed high lysine content and low methionine and cysteine. The results revealed a negative correlation between yield and TGPC. The modern commercial genotype Novaera showed a high yield with low TGPC but a higher globulin and albumin content than Gurguéia. Thus, it can be used in high-input agriculture. In contrast, the traditional local genotype EPACE-10, with high TGPC and higher amino acid content than Paulistinha, is indicated for low-input agriculture in marginal areas for food safety under climate changes.

Photodynamic Inactivation of Microorganisms Using Semisynthetic Chlorophyll a Derivatives as Photosensitizers.

In this study, we describe the semisynthesis of cost-effective photosensitizers (PSs) derived from chlorophyll a containing different substituents and using previously described methods from the literature. We compared their structures when used in photodynamic inactivation (PDI) against Staphylococcus aureus, Escherichia coli, and Candida albicans under different conditions. The PSs containing carboxylic acids and butyl groups were highly effective against S. aureus and C. albicans following our PDI protocol. Overall, our results indicate that these nature-inspired PSs are a promising alternative to selectively inactivate microorganisms using PDI.