Photosynthetic Variables Research Articles

GasanalyzeR: advancing reproducible research using a new R package for photosynthesis data workflows.

The analysis of photosynthetic traits has become an integral part of plant (eco-)physiology. Many of these characteristics are not directly measured, but calculated from combinations of several, more direct, measurements. The calculations of such derived variables are based on underlying physical models and may use additional constants or assumed values. Commercially available gas-exchange instruments typically report such derived variables, but the available implementations use different definitions and assumptions. Moreover, no software is currently available to allow a fully scripted and reproducible workflow that includes importing data, pre-processing and recalculating derived quantities. The R package gasanalyzer aims to address these issues by providing methods to import data from different instruments, by translating photosynthetic variables to a standardized nomenclature, and by optionally recalculating derived quantities using standardized equations. In addition, the package facilitates performing sensitivity analyses on variables or assumptions used in the calculations to allow researchers to better assess the robustness of the results. The use of the package and how to perform sensitivity analyses are demonstrated using three different examples.

Oxidative stress as markers in identification of aluminum-tolerant peach tree rootstock cultivars and clonal selections

ABSTRACT Peach rootstock and scion cultivars are selected in breeding programs considering resistance to pests and diseases, salt tolerance, drought tolerance, and vigor. However, rootstock tolerance to aluminum (Al), which is markedly present in tropical and subtropical soils of the world, is not considered. Thus, it is essential to define potential markers that can contribute to the selection of Al-resistant or Al-tolerant peach rootstocks. The objective of this study was to identify Al-tolerant peach tree rootstock cultivars and clonal selections using physiological and oxidative stress variables. A completely randomized experimental design was used in a 13 (rootstock cultivars and clonal selections) × 2 (with and without Al) factorial arrangement, with three replications. Nursery peach trees of own-rooted ‘BRS Mandinho’ (without rootstock) and nursery trees of ‘BRS Mandinho’ grafted on different rootstock cultivars and clonal selections were grown in a hydroponic system, consisting of two treatments, with and without 100 mg L -1 of Al. Dry biomass, photosynthetic variables, pigment concentration, hydrogen peroxide content, membrane lipid peroxidation, and activity of the antioxidant enzymes were evaluated. The total dry matter production of the own-rooted ‘BRS Mandinho’ trees and the SS-CHI-09-39 and SS-CHI-09-40 selections is affected by the Al presence, representing a decline of 35.4, 37.2, and 24.4 %, respectively, compared to the treatment with Al. The highest total dry matter production in Al presence was observed for the ‘Sharpe’ rootstock. ‘Capdeboscq’, DB-SEN-09-23, FB-ESM-09-43, JB-ESM-09-13, JAH-MAC-09-77, SAS-SAU-09-71, and VEH-GRA-09-55 rootstock selections are tolerant to Al. The use of physiological and biochemical variables shows potential for the selection of clonal rootstocks tolerant or resistant to Al.

Zinc toxicity and tolerance-related responses in Inga marginata and Allophylus edulis seedlings

Although zinc (Zn) is a micronutrient, excessive amounts in the soil can have toxic effects on plants. Fertilizers, limestone materials, pesticides, and fungicides added with Zn have contributed to increasing the concentration of this element in agricultural soils. Accordingly, it is necessary to find Zn-tolerant plant species to be properly used in degraded soil restoration programs. Thus, the current study aims to investigate the influence of different Zn concentrations on photosynthetic variables, antioxidant activity, and growth of I. marginata and A. edulisseedlings to determine their potential to be used as phytoremediation species. The experiment was installed in a 2×5 factorial scheme, with the first factor being two species (Allophylus edulis and Inga marginata), and the second factor: five concentrations of Zn (2, 75, 150, 225, and 300 μM), with three replications per treatment. Each sampling unit consisted of a pot with five plants. Photosynthetic, morphological variables of the shoot and root systems, chlorophyll a fluorescence, photosynthetic pigments, antioxidant enzyme activity, lipid peroxidation, hydrogen peroxide concentration, and Zn accumulated in the roots and shoot were evaluated. Zn stress has activated an efficient antioxidant system, which reduced oxidative damage in the leaves of both species; consequently, it did not decrease shoot biomass production in Inga marginata and Allophylus edulis seedlings. High Zn accumulation in plant tissues and lack of negative effects on Inga marginata and Allophylus edulis shoot have suggested that these plant species are tolerant to Zn and may be indicated for Zn-polluted soil phytoremediation purposes.

CADMIUM STRESS-INDUCED SENSITIVITY RESPONSES IN Peltophorum dubium

Cadmium (Cd) ranks prominent position among issues observed worldwide due to its increased bioavailability that results from several polluting activities. Thus, it is necessary conducting studies focused on investigating the association between this metal and the flora, since species capable of tolerating toxic Cd levels can be indicated for the phytoremediation of contaminated areas. The aim of the present study is to investigate the tolerance of species Peltophorum dubium to excess Cd, based on the assessment of morphophysiological and biochemical variables. P. dubium seedlings were cultivated in nutrient solution with five different Cd concentrations (0, 25, 50, 75 and 100 µM) and four repetitions. Each sampling unit comprised a tray with 16 plants, and it totaled 64 plants per treatment. Morphophysiological features such as dry biomass, roots’ morphological variables, and photosynthetic variables were analyzed. In addition, photosynthetic pigment concentration, antioxidant enzymes, hydrogen peroxide (H2O2), and lipid peroxidation (MDA) concentrations were investigated. P. dubium seedlings showed toxicity symptoms, such as reduced pigment concentration and photosynthetic rate, as well as root growth and biomass production inhibition. Based on these findings, P. dubium seedlings have shown sensitivity to Cd. Therefore, this species can be used as bioindicators of cadmium-contaminated areas.

Biostimulatory Effects of Chlorella fusca CHK0059 on Plant Growth and Fruit Quality of Strawberry.

Green algae have been receiving widespread attention for their use as biofertilizers for agricultural production, but more studies are required to increase the efficiency of their use. This study aimed to investigate the effects of different levels of Chlorella fusca CHK0059 application on strawberry plant growth and fruit quality. A total of 800 strawberry seedlings were planted in a greenhouse and were grown for seven months under different Chlorella application rates: 0 (control), 0.1, 0.2, and 0.4% of the optimal cell density (OCD; 1.0 × 107 cells mL-1). The Chlorella application was conducted weekly via an irrigation system, and the characteristics of fruit samples were monitored monthly over a period of five months. The growth (e.g., phenotype, dry weight, and nutrition) and physiological (e.g., Fv/Fm and chlorophylls) parameters of strawberry plants appeared to be enhanced by Chlorella application over time, an enhancement which became greater as the application rate increased. Likewise, the hardness and P content of strawberry fruits had a similar trend. Meanwhile, 0.2% OCD treatment induced the highest values of soluble solid content (9.3-12 °Brix) and sucrose content (2.06-2.97 g 100 g-1) in the fruits as well as fruit flavor quality indices (e.g., sugars:acids ratio and sweetness index) during the monitoring, whilst control treatment represented the lowest values. In addition, the highest anthocyanin content in fruits was observed in 0.4% OCD treatment, which induced the lowest incidence of grey mold disease (Botrytis cinerea) on postharvest fruits for 45 days. Moreover, a high correlation between plants' nutrients and photosynthetic variables and fruits' sucrose and anthocyanin contents was identified through the results of principal component analysis. Overall, C. fusca CHK0059 application was found to promote the overall growth and performance of strawberry plants, contributing to the improvement of strawberry quality and yield, especially in 0.2% OCD treatment.

Effects of Cadmium, Thallium, and Vanadium on Photosynthetic Parameters of Three Chili Pepper (Capsicum annuum L.) Varieties.

Photosynthesis is a crucial process supporting life on Earth. However, unfavorable environmental conditions including toxic metals may limit the photosynthetic efficiency of plants, and the responses to those challenges may vary among genotypes. In this study, we evaluated photosynthetic parameters of the chili pepper varieties Jalapeño, Poblano, and Serrano exposed to Cd (0, 5, 10 µM), Tl (0, 6, 12 nM), and V (0, 0.75, 1.5 µM). Metals were added to the nutrient solution for 60 days. Stomatal conductance (Gs), transpiration rate (Tr), net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), instantaneous carboxylation efficiency (Pn/Ci), instantaneous water use efficiency (instWUE), and intrinsic water use efficiency (iWUE) were recorded. Mean Pn increased with 12 nM Tl in Serrano and with 0.75 µM V in Poblano. Tl and V increased mean Tr in all three cultivars, while Cd reduced it in Jalapeño and Serrano. Gs was reduced in Jalapeño and Poblano with 5 µM Cd, and 0.75 µM V increased it in Serrano. Ci increased in Poblano with 6 nM Tl, while 12 nM Tl reduced it in Serrano. Mean instWUE increased in Poblano with 10 µM Cd and 0.75 µM V, and in Serrano with 12 nM Tl, while 6 nM Tl reduced it in Poblano and Serrano. Mean iWUE increased in Jalapeño and Poblano with 5 µM Cd, in Serrano with 12 nM Tl, and in Jalapeño with 1.5 µM V; it was reduced with 6 nM Tl in Poblano and Serrano. Pn/Ci increased in Serrano with 5 µM Cd, in Jalapeño with 6 nM Tl, and in Poblano with 0.75 µM V. Interestingly, Tl stimulated six and inhibited five of the seven photosynthetic variables measured, while Cd enhanced three and decreased two variables, and V stimulated five variables, with none inhibited, all as compared to the respective controls. We conclude that Cd, Tl, and V may inhibit or stimulate photosynthetic parameters depending on the genotype and the doses applied.

Effects of increasing soil phosphorus and association with ectomycorrhizal fungi (Pisolithus microcarpus) on morphological, nutritional, biochemical, and physiological parameters of Pinus taeda L

Phosphorus (P) is the macronutrient that most limits the growth of forest plantations. Pinus taeda L., has shown divergent responses when subjected to phosphate fertilization, probably by association with mycorrhizal fungi activity, in relation to morphological parameters, nutritional, physiological, and oxidative stress. The study aimed to evaluate if the increase of P levels in the soil and associated with ectomycorrhizal fungi and its effects on morphological parameters, nutritional status, biochemistry, and physiology of P. taeda. The experiment was conducted in a greenhouse, with Pinus taeda inoculated (With) and non-inoculated (Without) with Pisolithus microcarpus, under three soil P levels: Low P – without P addition; Medium P (30 mg P kg−1); and High P (60 mg P kg−1). Morphological parameters of the shoot and root system, nutritional status, chlorophyll a fluorescence, photosynthetic variables, photosynthetic pigments, oxidative stress indicators and antioxidant enzymes were evaluated. The addition of P to the soil increased the values of aerial and root growth parameters, P status in the plant, and photosynthetic efficiency of P. taeda. The increase of P in soil provided an increase in P uptake and development of surface area, volume, and length roots, enhanced by inoculation with P. microcarpus. The increase of P within the plant increased the values of variables related to the physiological apparatus such as A, Gs, WUE, A/Ci, and Ci and the fluorescence efficiency (i.e., ETR, Fv/Fm and Y(II)). This increased C assimilation in leaf tissues and thus increased needles and stem dry matter production, and development in height and stem diameter of P. taeda.

Resistance but not recovery is related to the role of specialist taxa in river communities submitted to hydric stress

One of the main effects of global change is the human interference in the global water cycle, which alters river hydrological dynamics and submits their biological communities to hydric stress. Hydric stress is a pulse disturbance with potential multiple effects on biodiversity and functions in river ecosystems. The presence of habitat specialists may support the response of biological communities to pulse disturbances, maintaining ecological functions more consistently than other communities only having generalists. We tested this general hypothesis in stream communities submitted to increasing hydric stress (normal conditions vs humidity vs desiccation). We used communities with variable proportion of specialist algal and cyanobacterial taxa and tested their resistance to hydric stress by analyzing potential changes on their number of species, biovolume, proportion of intact cells, and photosynthetic variables (basal fluorescence, photosynthetic yield). We also evaluated the recovery of ecological functions (net community primary production, community respiration, phosphorus uptake) once hydric stress conditions ended. Hydric stress caused a slight decrease in the number of species and biovolume of assemblages, but the proportion of intact cells did not significantly change because of the disturbance. Basal fluorescence and photosynthetic yield under hydric stress decreased more markedly in communities without specialist taxa, while communities with habitat specialists resisted better. Metabolism did not remarkably decrease under moderate hydric stress, but dropped by half under desiccation in all communities, having or not specialist taxa. Overall, specialist taxa did provide higher resistance to stress but did not support a distinct recovery of ecological functions. We suggest that this characteristic response is related to the high plasticity of biofilm structures.

Rhizobium induced modulation of growth and photosynthetic efficiency of Lens culinaris Medik. grown on fly ash amended soil by antioxidants regulation.

Rhizobium leguminosarum is a rhizospheres' nitrogen fixing microbe that improves plant growth and productivity by releasing sufficient nutrient sources from the root, by biological nitrogen fixation, solubilization of phosphorous, acquisition of iron, and enhancement of antioxidant activity in plants. On this account, a greenhouse experiment was carried out to assess the feasibility of growing lentil (Lens culinaris Medik.) on fly ash (FA) amended soil (0%, 10%, 20%, and 30%) in combination with R. leguminosarum inoculation. The data was recorded at 45day after sowing to evaluate the plant growth characteristics, photosynthetic variables (total chlorophyll and carotenoid pigments, carbonic anhydrase activity, nitrate reductase activity), damage markers (ROS, MDA, and cell viability), and defensive factors (proline and antioxidants). Among the FA-proportions tested, 20% proved most favorable in all the mentioned attributes while 30% concentration had negative repercussions on all the variables. Rhizobium inoculation had synergistic effect on all the concentrations being maximum on 20% FA. Thus, Rhizobium and 20% FA caused a significant increase on growth characteristics, photosynthetic pigments; stomatal behavior (aperture shape, size, and frequency of stomata); and activity of CA and NR, and cell viability. Application of Rhizobium on 20% FA was corroborated with decline in MDA and ROS contents and a coordinated enhancement of the activity of SOD, CAT, and POX. Therefore, 20% FA with flyash-tolerant strain of Rhizobium in Lens culinaris may be utilized as an integrated approach towards sustainable agriculture and an impulse of management of fly-ash.

Silicon as an attenuator of the toxic effects of aluminum in Schinus terebinthifolius plants.

Aluminum (Al) is highly toxic to plants, since it causes stress and inhibits plant growth. Silicon (Si) is known to mitigate the stress caused by Al in several plant species. Thus, the current study aims to investigate the soothing effects of Si on morphophysiological and photosynthetic variables, and the attributes associated with oxidative stress in Schinus terebinthifolius plants exposed to Al. Treatments have followed a completely randomized design, with three repetitions based on the following Al/Si combinations (in mM): Treatment 1: 0 Al + 0 Si; Treatment 2: 0 Al + 2.5 Si; Treatment 3: 1.85 Al + 0 Si; Treatment 4: 1.85 Al + 2.5 Si; Treatment 5: 3.71 Al + 0 Si; Treatment 6: 3.71 Al + 2.5 Si. Each sampling unit consisted of a tray with 15 plants, totaling forty-five per treatment. Shoot and root morphological variables, photosynthetic variables, photosynthetic pigments, hydrogen peroxide concentration, lipid peroxidation (MDA), guaiacol peroxidase (POD) and superoxide dismutase (SOD) enzymes, and non-enzymatic antioxidant such as Ascorbic acid (AsA) and non-protein thiol (NPSH) concentration were assessed. Root growth inhibition followed by changes in root morphological variables have negatively affected root and shoot biomass production in plants only subjected to Al. However, adding 2.5 mM Si to the treatment has mitigated the toxic effects caused by 1.85 mM of aluminum on S. terebinthifolius plants.

Mecanismos morfofisiológicos e bioquímicos de tolerância ao cobre em plantas de Handroanthus heptaphyllus

ABSTRACT Copper (Cu)-contaminated soils are becoming more common, and phytoremediation is an effective strategy for reducing the negative effects of Cu on soils. Tree species are commonly used for this technique because they act as a barrier to this type of contamination. It is necessary to evaluate Cu tolerance and toxicity thresholds together with the harm this metal causes to plants. The objective of the current study was to investigate the tolerance of Handroanthus heptaphyllus plants to Cu through morpho-physiological, biochemical, and tissue Cu concentration analyses. H. heptaphyllus seedlings were subjected to nutrient solutions with varying concentrations of copper: 0, 5, 32, 64, 96, and 128 µM Cu in a hydroponic system. We conducted a morpho-physiological trait analysis on shoot height, root length, dry weight, morphological variables of the root system, leaf area, and photosynthetic variables. In addition, we also looked into photosynthetic pigments, antioxidant enzymes, lipid peroxidation, hydrogen peroxide concentration, and Cu accumulation in tissues. The values obtained for variables such as dry weight and pigments did not show significant differences, regardless of Cu concentration. Moreover, photosynthetic and transpiration rates were negatively affected only at the highest Cu concentration (128 µM). Overall, excess Cu had no effect on Handroanthus heptaphyllus below 128 µM. Cu accumulated mainly in the roots without a decrease in biomass, which could indicate the tolerance of the species to this metal as well as its great potential in the phytostabilization of Cu in contaminated soils.

Desenvolvimento de cultivares de mangueiras israelenses no semiárido brasileiro

Abstract The objective of this work was to evaluate the initial adaptive performance of Israeli mango tree cultivars grown in the submedian region of the São Francisco Valley, Brazil. The experiment was carried out from January 2019 to July 2020 using seedlings of the Omer and Shelly cultivars, at six months after transplanting, at a 3×6 m spacing. The experimental design was randomized complete blocks in a 2×3 factorial arrangement, corresponding to the two Israeli mango tree cultivars and the number of branches after formative pruning (three, four, and five branches), with four replicates. Biometric, biochemical, and photosynthetic variables were analyzed, differing between the evaluation times after pruning. The Omer cultivar is more vigorous than Shelly, and formative pruning with three, four, and five branches is recommended for both mango cultivars under the cultivation conditions of the São Francisco Valley.

Understanding drought response mechanisms in wheat and multi-trait selection.

Wheat crop is very sensitive to osmotic stress conditions. As an abiotic stress, drought may exert a considerable effect on the levels of specialized metabolites in plants. These metabolites may exert beneficial biological activities in the prevention or treatment of disorders linked to oxidative stress in plants and humans. Furthermore, osmoprotector accumulation helps wheat to increase the maintenance of osmotic balance. Therefore, identifying wheat genotypes with better drought tolerance is extremely important. In this sense, this research aimed to understand agronomic, physiological and biochemical responses of spring wheat strains and cultivars to drought stress, under field conditions, and jointly select strains via multi-trait index. We evaluated agronomic, physiological and biochemical variables in 18 genotypes under field condition. The results demonstrated that all variables were affected by the drought. Most genotypes were significantly reduced in grain yield, except VI_14774, VI_14668, VI_9007 and TBIO_ATON. The variables related to photosynthesis were also affected. An increase above 800% was observed in proline contents in genotypes under drought. Sodium and potassium also increased, mainly for VI_131313 (Na), while VI_130758 and VI_14774 presented increased K. We evaluated the antioxidant potential of the different strains and the total content of phenolic compounds. The most drought-responsive genotypes were BRS_264, VI_14050 and VI_14426. Reduced grain yield and photosynthetic variables, and increased specialized metabolism compounds are due to plant defense mechanisms against drought conditions. Furthermore, variation in genotypes can be explained by the fact that each plant presents a different defense and tolerance mechanism, which may also occur between genotypes of the same species. Four strains were selected by the multivariate index: VI_14055, VI_14001, VI_14426 and VI_1466. Such results allow us to predict which genotype(s) performed best in semi-arid environments and under climatic fluctuations.

Can species Cedrela fissilis Vell. be used in sites contaminated with toxic aluminum and cadmium metals?

Toxic metals are among the main pollutants contributing to environmental degradation. Cadmium (Cd) and aluminum (Al) stand out among these metals as extremely toxic elements. The use of native species in reforestation programs can compensate for degradation and re-establish the ecological conditions of the affected environments. Cedrela fissilis Vell., popularly known as cedar, may be used as an alternative in phytoremediation, since it is a fast-growing native woody species widely distributed in tropical America. In this study we investigated the possibility of using C. fissilis in sites contaminated with Al and Cd by evaluating morphological, physiological, and biochemical variables of seedlings grown in hydroponic system. C. fissilis seedlings were subdivided into two experiments with a completely randomized design. The first experiment evaluated the effect of four Al concentrations, namely: 0 (complete nutrient solution without phosphorus), 25, 50 and 100 mg l-1. The second experiment evaluated four Cd concentrations, namely: 0 (complete nutrient solution), 25, 50 and 100 μM. Each sample unit consisted in a pot with four plants. Morphological, physiological and biochemical variables of seedlings were evaluated after 15-day exposure to different treatments in the hydroponic system. Aluminum concentration of 100 mg l-1 caused oxidative stress in C. fissilis seedlings, reduced shoot and root dry weight, and increased hydrogen peroxide contents, which led to lipid peroxidation. Cadmium concentration of 100 µM also damaged C. fissilis seedlings by significantly reducing root dry weight and involving the most severe effects on photosynthetic variables. Cadmium presence in the nutrient solution negatively affected morphophysiological and biochemical variables of Cedrela fissilis seedlings, and it was also harmful to their growth. Based on our results, the investigated species shows a sensitive behavior upon exposure to cadmium. On the other hand, C. fissilis tolerates high Al concentrations (up to 50 mg l-1), which suggests a moderate tolerance to this metal.

Carbon allocation strategies and water uptake in young grafted and own-rooted hazelnut (Corylus avellana L.) cultivars

In this study, grafted and own-rooted young hazelnut plants of three high-quality cultivars were cultivated in Central Italy to investigate possible differences in growth, fruit and flower production, and physiological processes encompassing water uptake, photosynthetic variables and non-structural carbohydrate allocation. Stable isotopes and photosynthetic measurements were used to study carbon and water fluxes in plants. For the first time, an ecophysiological study was carried out to understand the seasonal growth dynamics of grafted plants in comparison with own-rooted plants. The own-rooted hazelnuts showed rapid above-ground development with large canopy volume, high amount of sprouts and earlier yield. The grafted plants showed greater below-ground development with lower canopy volumes and lower yield. However, later, the higher growth rates of the canopy led these plants to achieve the same size as that of the own-rooted hazelnuts and to enter the fruit production phase. Different seasonal behaviour in root water uptake and leaf photosynthesis-related variables was detected between the two types of plants. The grafted plants showed root development that allowed deeper water uptake than that of the own-rooted hazelnuts. Moreover, the grafted plants were characterized by a higher accumulation of carbohydrate reserves in their root tissues and by higher stomatal reactivity, determining significant plasticity in response to seasonal thermal variations.

Green and brown stream trophic food chains show specific responses to constant or hump-shaped inputs of copper

The brown food chain (based on decomposers) co-exists in streams with the green food chain (based on primary producers). The two trophic chains perform specific ecosystem functions which may be altered by the effect of contaminants. Copper is a common contaminant with recognized effects on several compartments of the two trophic chains. We applied it in two separate mesocosm experiments, in which we tested the effects of copper after contrasting patterns of contaminant exposure (constant vs hump-shaped). The constant input simulated a chronic contamination (average of 20 μg/L Cu), while the hump-shaped simulated the steady arrival of copper, the occurrence of a peak (reaching ca. 60 μg/L Cu), and its progressive decrease (down to 10–15 μg/L Cu). In the green trophic food chain, copper exposure decreased the total chlorophyll-a as well as the basal fluorescence and the photosynthetic yield. The treatment receiving hump-shaped inputs caused the highest mortality of the green food chain consumer, the snail Radix balthica. In the chronic copper exposure, mortality achieved a maximum of 80% by the end of the experiment but occurred later than that in the hump-shaped treatment. Effects on the brown food chain were not so pronounced; the microbial decomposition rate of leaflitter decreased nearly ca. 50% after 14 days of copper exposure. Effects on decomposition translated into the ingestion performance of detritivores, which decreased in the two copper treatments. Our results provide evidence that copper affected the two trophic food chains. The hump-shaped arrival included a peak of high concentration, which caused lethal effects on the consumers, but also a decreasing limb, which allowed a partial recovery of the algal photosynthetic variables. Our results suggest the need to consider the different compartments and functions performed within the stream trophic web when evaluating the effects of a contaminant in a river ecosystem.

Different strategies lead to a common outcome: different water-deficit scenarios highlight physiological and biochemical strategies of water-deficit tolerance in diploid versus tetraploid Volkamer lemon.

Water scarcity restricts citrus growth and productivity worldwide. In pot conditions, tetraploid plants tolerate water deficit more than their corresponding diploids. However, their tolerance mechanisms remain elusive. In this study, we focused on which mechanisms (i.e., hydraulic, osmotic or antioxidative) confer water-deficit tolerance to tetraploids. We exposed diploid and tetraploid Volkamer lemon rootstock (Citrus volkameriana Tan. and Pasq.) to quickly (fast) and slowly (slow) developing water-deficit conditions. We evaluated their physiological, antioxidative defense and osmotic adjustment responses, and mineral distribution to leaves and roots. Water-deficit conditions decreased the photosynthetic variables of both diploid and tetraploid plants. Moreover, the corresponding decrease was greater in diploids than tetraploids. Higher concentrations of antioxidant enzymes, osmoprotectants and antioxidant capacity were found in the leaves and roots of tetraploids than diploids under water deficit. Diploid plants showed fast response in slow water-deficit condition, but that response did not persist as the deficit intensified. Meanwhile, tetraploids had lower water loss, which slowed the onset of slow water deficit relative to diploids. This response allowed stronger photosynthesis, while antioxidant and osmoprotectant production allowed for further tolerance once desiccation began. Overall, our results concluded that Volkamer lemon tetraploid plants tolerate rapid and slow water deficit by maintaining their photosynthesis due to low conductance (stem or roots), which helps to avoid desiccation, and stronger biochemical defense machinery than their corresponding diploids.

Volkamer Lemon Tetraploid Rootstock Transmits the Salt Tolerance When Grafted with Diploid Kinnow Mandarin by Strong Antioxidant Defense Mechanism and Efficient Osmotic Adjustment

Salinity restricts plant growth and production by specific ions toxicity to particular plants. Cl ion is exceptionally toxic to citrus. Citrus rootstock and scion has a significant effect on each other under unfavourable conditions. Nevertheless, their specific response can be different depending on the way to translocate and compartment the toxic ions, or to induce antioxidant systems. In this paper, we studied the behaviour of diploid (2x) and tetraploid (4x) Volkamer lemon rootstocks grafted with commercial cultivar Kinnow mandarin (KM/VM2x and KM/VM4x, respectively) when exposed to moderate (75 mM) and high salt stress (150 mM). Both genotypes showed a decrease in their photosynthetic variables (Pn, gs, E, Fv/Fm, Fv′/Fm′, NPQ), and the decline was more significant in KM/VM2x plants as compared to KM/VM4x. The highest increase in the concentration of stress indicators (MDA and H2O2) was observed in leaves and roots of KM/VM2x at 75 and 150 mM of salt stress. The KM/VM4× showed the maximum increase in antioxidative enzymes (SOD, CAT, POD, APx, GR) and osmolytes (PRO, GB) in leaves and roots at 75 and 150 mM. Minerals (Cl ion, Na, K, P, N, Ca) accumulation was also significantly affected in leaves and roots of KM/VM2x and KM/VM4x under moderate and high NaCl stress. Overall, our results showed that Cl ion accumulation presents a robust correlation with stress indicators and their scavenging enzymes in leaves and roots. Moreover, 2x scion significantly mitigated by the 4x rootstock and showed more tolerance as compared to grafted on 2x rootstock.

Physiological and biochemical responses of Kinnow mandarin grafted on diploid and tetraploid Volkamer lemon rootstocks under different water-deficit regimes.

Water shortage is among the major abiotic stresses that restrict growth and productivity of citrus. The existing literature indicates that tetraploid rootstocks had better water-deficit tolerance than corresponding diploids. However, the associated tolerance mechanisms such as antioxidant defence and nutrient uptake are less explored. Therefore, we evaluated physiological and biochemical responses (antioxidant defence, osmotic adjustments and nutrient uptake) of diploid (2x) and tetraploid (4x) volkamer lemon (VM) rootstocks grafted with kinnow mandarin (KM) under two water-deficit regimes. The KM/4xVM (VM4) and KM/2xVM (VM2) observed decrease in photosynthetic variables, i.e., photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E), leaf greenness (SPAD), dark adopted chlorophyll fluorescence (Fv/Fm), dark adopted chlorophyll fluorescence (Fv´/Fm´), relative water contents (RWC) and leaf surface area (LSA), and increase in non-photochemical quenching (NPQ) under both water-deficit regimes. Moreover, oxidative stress indicators, i.e., malondialdehyde (MDA) and hydrogen peroxide, and activities of antioxidant enzymes, i.e., superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APx), glutathione reductase (GR) were increased under both water-deficit regimes. Nonetheless, increase was noted in osmoprotectants such as proline (PRO) and glycine betaine (GB) and other biochemical compounds, including antioxidant capacity (AC), total phenolic content (TPC) and total soluble protein (TSP) in VM2 and VM4 under both water-deficit regimes. Dry biomass (DB) of both rootstocks was decreased under each water-deficit condition. Interestingly, VM4 showed higher and significant increase in antioxidant enzymes, osmoprotectants and other biochemical compounds, while VM2 exhibited higher values for oxidative stress indicators. Overall, results indicated that VM4 better tolerated water-deficit stress by maintaining photosynthetic variables associated with strong antioxidant defence machinery as compared to VM2. However, nutrient uptake was not differed among tested water-deficit conditions and rootstocks. The results conclude that VM4 can better tolerate water-deficit than VM2. Therefore, VM4 can be used as rootstock in areas of high-water deficiency for better citrus productivity.

Silicon nanoparticles elicit an increase in lemongrass (Cymbopogon flexuosus (Steud.) Wats) agronomic parameters with a higher essential oil yield

Lemongrass (Cymbopogon flexuosus (Steud.) Wats) is an aromatic grass with great industrial potential. It is cultivated for its essential oil (EO) which has great economical value due to its numerous medicinal, cosmetic and culinary applications. The present study was conducted on silicon nanoparticles (SiNPs) application to lemongrass with the objective of overall agronomic enhancements. Graded concentrations (50–200 mg L-1) of SiNPs were exogenously applied to lemongrass leaves. The physiological and biochemical analyses revealed that 150 mg L-1 SiNPs is the optimum concentration for lemongrass plants. This concentration triggered photosynthetic variables, gas exchange modules and activities of enzymes involved in EO (geraniol dehydrogenase) and nitrogen (nitrate reductase) metabolism as well as in the antioxidant system (catalase, peroxidase and superoxide dismutase). These SiNPs-induced metabolic changes altogether significantly (p ≤ 0.05) enhanced overall plant growth and yield. Moreover, SiNPs treatments assisted in palliating lipid peroxidation and H2O2 content in lemongrass leaves which added further advantage to plant metabolism. Overall, data indicates SiNPs elicit beneficial effects on lemongrass growth and yield through inducing various physiological and biochemical responses. This renders high possibility that similar objectives could be achieved with SiNPs biotechnological application on further related agronomic crops as well as in diverse industries.