Leaf Tissue Concentrations Research Articles

Some special features of the water regime and the photosynthetic apparatus activity in Feijoa sellowiana (O. Berg) O. Berg plants under the water stress

When assessing the drought tolerance of Feijoa sellowiana cultivars and forms, the total water content in leaf tissues and their waterretaining and regenerative capacity were determined, and the parameters of chlorophyll fluorescence induction were measured at different water content in leaves. Current-year leaves were characterized by a higher sensitivity to drought. According to the complex of water regime parameters and characteristics of the chlorophyll fluorescence induction (CFI), it was found that the cultivar Aromatnaya Fantazia and the form 3/1 are characterized by a relatively high drought tolerance. It has been demonstrated that the common method for assessing plant tolerance by the index of their water-retaining forces, in relation to Feijoa sellowiana genotypes, does not allow determining the critical level of water deficit. It has been found that in the cultivars and forms with low water stress tolerance, with the water loss of 20-25% from the leaf tissues complete hydration, irreversible irregularities in the PS II structures occurred. The most sensitive to the lack of water in the leaves were such parameters as variable fluorescence, rate constants of the photochemical and non-photochemical deactivation of the excitation, as well as the processes of Qa reduction in the reaction centers of PS II.

Economical nitrogen dose for production of irrigated naturally colored cotton in the semi-arid region

ABSTRACT Determining the economical dose of nitrogen (N) for colored cotton can increase yield and income of farmers. The experiment was carried out under field conditions at the Experimental Farm of the Universidade Federal Rural do Semi-Árido, in the years 2016 and 2017. The objective was to determine the economical N dose for four colored cotton cultivars. The experimental design was in randomized blocks, with split plots and four repetitions. Five N doses (0, 50, 100, 150 and 200 kg ha-1) were randomized in the main plots and four colored cotton cultivars (BRS Safira, BRS Rubi, BRS Topázio and BRS Verde) were randomized in the subplots. The characteristics evaluated were seed cotton yield, cotton fiber yield, N concentration in leaf tissue, technical dose and economical dose of N. Higher yield of naturally colored cotton can be obtained using the economical doses of 140 kg ha-1 N for cultivars BRS Rubi and BRS Verde, 150 kg ha-1 N for BRS Topázio and 160 kg ha-1 N for BRS Safira. Highest yield was achieved with the cultivar BRS Topázio and lowest with the cultivar BRS Verde.

Leaf and root attributes as growth and phosphorus uptake determinants in two grass species from South America’s natural grasslands

AbstractPhosphorus uptake by grass species from natural South American grasslands can change depending on root and leaf attributes capable of determining higher, or lower, relative growth rate. The aim of the current study is to investigate whether leaf and root attributes capable of determining leaf and root area production in native C4 grass species Axonopus affinis and Andropogon lateralis are related to higher relative growth rate (RGR), P uptake capacity (maximum P influx; Imax) and concentration. Species grown in 2-litre pots with added nutrition solution were subjected to two treatments, namely 5 μM P l−1 and 30 μM P l−1. Solution aliquots (10 ml) were collected for 30 hours at the end of the study to determine P concentrations. RGR was 3.6 and 2.8 times higher in A. affinis than in A. lateralis in treatments with 5 μM P and 30 μM P. Axonopus affinis recorded the highest P concentration in leaf tissue. This outcome was associated with Imax 85% higher in A. affinis. High RGR was associated with larger leaf and root surface area per dry mass unit, as well as with high P influx capacity and with higher affinity transporters. These species often prevail in areas accounting for greater natural fertility and are more responsive to phosphate fertilization.

Evaluation of Systemic Imidacloprid and Herbicide Treatments on Flatheaded Borer (Coleoptera: Buprestidae) Management in Field Nursery Production.

The flatheaded appletree borer, Chrysobothris femorata (Olivier) (Coleoptera: Buprestidae), and related species are deciduous tree pests. Female beetles prefer to oviposit at tree bases, and larvae tunnel beneath the bark, which weakens or kills young or newly transplanted trees. In the first objective of this study, Discus N/G (2.94% imidacloprid + 0.7% cyfluthrin) applied at six lower-than-labeled rates (0.0, 0.98, 1.97, 3.94, 5.91, and 7.87 ml/cm of average trunk dia.) was evaluated for protection of field-grown maples. A second objective evaluated imidacloprid with and without herbicides to assess the impact of weed competition at the tree base on insecticide effectiveness. A third objective determined relative imidacloprid concentrations in leaf tissue samples with ELISA and related to insecticide rates, herbicide treatments, and the level of flatheaded borer protection. In two trials, higher rates of insecticide were more effective at protecting trees, with rates ≥3.94 ml product/cm trunk diameter performing equivalently. Weed-free trees had more borer attacks and grew faster than trees in weedy plots. Imidacloprid content in leaf tissues had a trend for higher concentrations in smaller, weedy trees in the first season, but that pattern disappeared in subsequent years. Based on fewer attacks in weedy versus weed-free trees (60−90% reduction), it was concluded that weed presence can reduce borer attack success in nurseries independent of insecticide treatment, but tree growth was reduced by weed presence. In addition, Discus applied at rates >3.94 ml/cm did not confer added borer damage protection in weedy plots.

Carbon and nitrogen metabolism in young Tachigali vulgaris plants subjected to water deficit

Plants’ biochemical responses to water deficit are associated with their ability to synthesize accumulate osmolytes compatible to regulatory properties of water potential. The aim of the current study is to evaluate carbon and nitrogen metabolism in Tachigali vulgaris plants subjected to three water suspension periods. The experiment was carried out in greenhouse and followed a completely randomized design, at 3 x 2 factorial arrangement (three times: zero, five and ten water suspension days; and two water conditions: control and water deficit), with 4 repetitions; results were subjected to analysis of variance and means were compared through t-test at 5% probability level, in statistical package (Assistat 7.7 beta). The following variables recorded decreased values: relative water content RWC in leaf tissue (by 32.14%); nitrate ion in leaves (by 18.67%) and in roots (by 14.40%); nitrate reductase enzyme activity in leaves (by 17.06%) and roots (by 15.77%); starch concentration in leaf tissue (by 44.98%) and roots (by 21.07%). On the other hand, the following variables recorded increased values: free ammonium concentration in leaves (by 64.83%) and roots (by 1.61%); total soluble amino acids in leaf tissue (by 28.03%) and roots (by 8.42%); total soluble carbohydrates in leaves (by 3.12%) and roots (by 11.05%); sucrose in leaves (by 4.77%) and roots (by 24.77%); proline in leaves (by 193.58%) and roots (by 57.26%). Biochemical processes observed in T. vulgaris plants were affected by water deficit, which indicated that this species is capable of adopting mechanisms and strategies in order to survive under stressful conditions.

Rapid uptake and retention of neonicotinoids in nursery citrus trees as a safeguard against Asian citrus psyllid (Diaphorina citri) infestation

There are specific regulations in the USA for the inter-state shipment of containerized citrus from production nurseries located within Diaphorina citri Kuwayama (Asian citrus psyllid; ACP) quarantine zones. To ensure trees are protected from the insect, nurseries must treat trees with an approved systemic neonicotinoid at least 30 days, and not more than 90 days, before trees can be shipped. The objective of this study was to reevaluate the necessity for a 30-day pre-shipment restriction by providing regulators with further data on the uptake of imidacloprid, thiamethoxam and dinotefuran, during the days immediately following treatments. In previous studies, ACP-effective thresholds were determined for 1-year old containerized citrus trees by correlating residue concentrations in leaf tissue with ACP efficacy. In this study, we used target concentrations to compare the uptake and retention of these neonicotinoids in 4 cultivars of 1-year old containerized citrus trees. ACP-effective thresholds were achieved within 3 days of treatment with the current lowest label rate (6.43 g AI/m3 soil) of generic formulations of imidacloprid, and within 1 day of treatment with the maximum label rate (97 g AI/m3 soil) of the name brand formulation Admire Pro®. The establishment of dinotefuran at ACP-effective thresholds was erratic in citrus cultivars, and residues of both dinotefuran and thiamethoxam had largely dissipated before the 30-day pre-shipment period had expired. The uptake and retention of all three neonicotinoids were significantly compromised under excessive watering (400% ET), although ACP-effective thresholds were still achieved with all imidacloprid treatment rates and thiamethoxam within 3 days. Overall, our results strongly support shortening the 30-day pre-shipment restriction to at most 3 days for trees treated with either imidacloprid or thiamethoxam. And, dinotefuran should be removed from the list of systemic insecticides approved for quarantine treatments.

Differential response of Trichloris ecotypes from different habitats to drought and salt stress

Native plant genetic resources have evolved from long processes of natural selection and adaptation to specific environments, and have developed tolerance to various stresses prevailing in their natural habitats via adaptive morphophysiological features. The associations between environmental stress conditions (aridity degree and salinity) prevailing in the original habitat of Argentine native Trichloris species (T. crinita and T. pluriflora) and various biometric and physiological traits were evaluated. Trials were carried out in hydroponics in a growth chamber. Components of initial plant growth, oxidative stress expression and antioxidant activity under drought and salt stress were measured in ecotypes of both species, as well as Na+ and K+ leaf tissue concentration and excretion rates under salinity. Ecotypes from arid and semiarid origin of both species had higher drought tolerance. Regarding salt stress, T. crinita ecotype from alkali soil showed stimulated growth under salinity and an ecotype from saline soil kept high root and shoot biomass production. Although the ecotypes of T. pluriflora were not significantly salt-sensitive, none stood out. Many active salt glands on the abaxial leaf surface, high Na/K excretion ratio and high leaf tissue concentration of sodium were found for salt-tolerant ecotypes. This study identified ecotypes with tolerance to prevailing stressful conditions of natural habitat of native forage species to be introduced to plant breeding programmes for restorations purposes. Trichloris pluriflora is an unexplored genetic resource for semiarid rangeland, thus this study is the first report of drought tolerant ecotypes.

Establishment of Leaf Tissue Nutrient Sufficiency Ranges of Two Perovskia Selections by Chronological Age

The objective of this study was to determine optimum fertilizer concentrations, identify leaf tissue nutrient sufficiency ranges by chronological age, and establish leaf tissue nutrient standards of containerized Russian sage (Perovskia sp.). Common Russian sage (P. atriplicifolia Benth.) and ‘Crazy Blue’ Russian sage were greenhouse-grown in a soilless substrate under one of six constant liquid fertilizer concentrations [50, 75, 100, 200, 300, or 400 mg·L−1 nitrogen (N)] with a constant level of a water-soluble micronutrient blend. Fertilizer concentrations sufficient for optimal plant growth and development were determined by analyzing plant height, diameter, growth index, primary shoot caliper, axillary shoot number, and total dry mass; they were found to be 100 to 200 mg·L−1 N after a 6-week crop cycle. Recently, mature leaf tissue samples were collected from plants fertilized with 100 to 200 mg·L−1 N and analyzed for elemental contents of 11 nutrients at 2, 4, and 6 weeks after transplant (WAT). An overall trend of increasing foliar nutrient concentrations over time was observed for all elemental nutrients. For instance, at 2 WAT, the total N concentrations of common Russian sage and ‘Crazy Blue’ Russian sage ranged between 3.68% and 5.10% and between 3.92% and 5.12%, respectively, and increased to ranges of 5.94% to 5.98% and 5.20% to 5.86% at 6 WAT, respectively. Before this study, no leaf tissue concentration standards have been reported; therefore, this study established leaf tissue concentration sufficiency ranges for the trialed Perovskia selections.

Drought-induced stress in leaves of Coix lacryma-jobi L. under exogenous application of proline and GABA amino acids

Coix lacryma-jobi L. is an Asian plant widely used in traditional medicine. Drought conditions can lead to an impairment of photosynthesis which can be softened by the exogenous application of proline and γ-aminobutyric acid (GABA) to maintain the electron transport chain (ETC) and avoid reactive oxygen species-induced oxidative damage by inducing antioxidative enzymes. The aim of this study was to evaluate the effects of water deficit on C. lacryma-jobi leaves under the application of proline and GABA. Chlorophyll (Chl) a fluorescence emission, antioxidative enzyme activity (catalase, superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase) and proline and GABA contents in leaf tissues were performed in plants subjected to 12 days of drought. Chl a fluorescence indicated impairments on photosynthetic apparatus due to water deficit that resulted into increased activity of antioxidant enzymes. The application of proline but not GABA was more efficient in alleviating the effects of water deficit, as evidenced by the maintenance of the dynamic dissipation of the photosynthetic energy, besides the greater accumulation of proline under these conditions. Water deficit induces alterations in the ETC, which is softened by the application of proline to cope with the deleterious effects of drought in C. lacryma-jobi plant leaves.

Conventional inoculants and biological protector, co-inoculation and nitrogen fertilization in soybean

There is little information that supports the new technology of inoculants with biological protectors and indecates the results in soybean crop. In order to evaluate the morphophysiological responses of soybean crop to conventional inoculants, inoculants with protectors, co-inculation with Azospirillum brasilense and at increasing doses of N. The treatments consisted of: Control; Bradyrhizobium elkanii + biological protector; Bradhyrizobium elkanii + Bradhyrizobium japonicum + biological protector; Bradyrhizobium elkanii; Bradyrhizobium elkanii + co-inoculation with Azospirillum brasilense; Bradyrhizobium elkanii + biological protector + co-inoculation with Azospirillum brasilense; Bradyrhizobium elkanii + Bacillus amyloliquefaciens + biological protector; Dose 20 kg ha-1 of N; Dose N 40 kg ha-1 and Dose N 60 kg ha-1 of N. Nodulation, chlorophyll a, b and total content, nitrogen content in leaf tissue and grains were evaluated thousand grain mass and productivity were evaluated. The biological agents tested in the experiment provided an increase in the number of nodules and an increase in the mass of 1,000 grains when compared nitrogen fertilization. The treatments with nitrogen fertilization, compared to the treatments with inoculation, were higher for chlorophyll a, b and total contents. Long-life inoculants, in the absence and presence of coinoculation in seed treatment, demonstrated efficiency in number of nodules and in the supply of N in soybean crop, with superior responses on the non-inoculated control, even in soil with initial concentration 1,510 10-4 bacteria cells per gram of soil. Long-life inoculants offer greater practicality to the rural producer and demonstrated efficiency in the supply of N to soybean crop.

Arbuscular mycorrhizal fungi as mitigating agents of salt stress in Formosa papaya seedlings

The objective of the present study was to evaluate the effect of mycorrhization on the nutritional, hydric and biochemical components of papaya seedlings, Carica papaia L., from the Formosa Group, Hybrid Tainung Nº 1, submitted to irrigation with saline water. The research was conducted at the Federal Institute of Paraíba, Sousa Campus, from March to December 2018. The experimental design used completely randomized blocks, with treatments arranged in a 4 x 5 factorial scheme, referring to the fungi species: Gigaspora candida, Acaulospora scrobiculata, Dentiscutata heterogama and without mycorrhizae, and the five salt concentrations in irrigation water: 0.0; 10.0; 20.0; 30.0 and 40.0 mmolc L-1 in four repetitions. The characteristics evaluated were: relative water content, water saturation deficit, membrane damage, photosynthetic pigments, concentration and accumulation of nitrogen, phosphorus, potassium, sodium and the relationship between potassium and sodium concentrations in leaf tissue. The species D. heterogama and G. candida presented the highest rates of leaf hydration and the lowest damage to biomembranes at all saline levels. Mycorrhizae increased the absorption of N and P, especially from 30 mmolc L-1 of salt. A greater relationship between potassium and sodium concentrations was evidenced in seedlings mycorrhized with D. heterogama.

Physiological and Biochemical Aspects of Frost Resistance in Оlea europaea L.

The results of studies on the frost resistance of Olea europaea L. varieties and its subspecies O. europaea subsp. cuspidata (Wall. and G. Don) Cif. under the conditions of the Southern Coast of Crimea (SCC), as well as the influence of temperature close to the absolute minimum value (–15°С) on the state of the photosynthetic apparatus, catalase activity, polyphenol oxidase, and the content of proline and phenolic compounds, are shown. It was established that a relatively high frost resistance is characteristic of the Nikitskaya variety under the conditions of the SCC. Varieties Ascoliano, Coregiolo, and Razzo turned out to be slightly frost-resistant. Minimum resistance was detected in the subspecies O. europaea subsp. cuspidata. The temperature of –15°C led to irreversible disruptions in the photosynthetic apparatus of weak varieties Razzo, Coregiolo and O. europaea subsp. cuspidata, which manifested in a significant decrease in photosynthetic activity immediately after the end of low-temperature exposure (by 80.19, 50.0, and 89.78%, respectively) as well as a fluorescence decay coefficient below the vital norm. After 24 h, a slowdown in the decrease in the parameters of chlorophyll fluorescence induction (CFI) was noted in the Ascoliano and Nikitskaya varieties. It was revealed that negative temperatures contribute to a decrease in the activity of catalase in weakly resistant O. europaea genotypes (by 40–60% on average) in contrast to the frost-resistant variety Nikitskaya, in which the activity of this enzyme remained almost unchanged. The change in polyphenol oxidase activity was multidirectional. In the Razzo and Coregiolo varieties, an increase in polyphenol oxidase activity was noted (19 and 24%, respectively). A decrease (by 8 and 37%, respectively) was noted in the subspecies O. europaea subsp. cuspidata and Nikitskaya variety. It was shown that, under the influence of negative temperatures, representatives of O. europaea decrease proline concentration in leaf tissues (by 17–55%). The most significant changes were detected in the variety Coregiolo (by 45.09%). The total content of phenolic compounds decreased in all weakly frost-resistant varieties and O. europaea subsp. cuspidata by 7–42% and remained unchanged in the frost-resistant variety Nikitskaya. It has been established that negative temperatures cause irreversible changes in the photosynthetic apparatus in weakly resistant representatives of O. europaea. The correlation of the degree of frost resistance of the studied genotypes with the activity of catalase and with the content of proline and phenolic compounds in leaf tissues was revealed.

Do soil test levels and fertilization with phosphorus and potassium impact field crop tissue concentrations?

AbstractSoil testing and plant tissue nutrient concentrations form the basis for fertilizer recommendations in Ohio. The response of crop phosphorus (P) and potassium (K) nutrient concentrations to soil test levels and fertilizer applications influences fertilizer recommendations but have not been rigorously evaluated in this region. The objective of our study was to determine the effects of (a) soil test P and K levels and (b) P and K fertilization on mid‐season leaf and grain P and K concentrations of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.). From 2014–2018, we conducted 186 on‐farm trials (99 P, 87 K trials) over a diversity of soil types, crop genetics, and management histories in 39 counties throughout Ohio. Soil test P and K levels, mid‐season leaf P and K concentrations, and grain P and K concentrations were measured on randomized and replicated plots. Both leaf and grain nutrient concentrations generally increased with the soil test levels, but the relationships were weak in all three crops. Fertilization of P and K marginally but consistently increased leaf tissue concentrations in all crops but had a lesser effect on grain P and K concentrations. Our data suggest that current sufficiency ranges for corn, soybean, and wheat are too high and need revision. Collectively, our results show that crop P and K tissue concentrations are positively, but weakly related to soil test levels and fertilization, and this information has important implications for future development of nutrient management frameworks in Ohio.

Responses of Autumn Phenology to Climate Change and the Correlations of Plant Hormone Regulation

Current understanding of autumn phenological responses to climate change in deciduous tree species remains limited, mainly due to the difficulties in defining autumn events and the lack of knowledge about its mechanism. Here we applied a method based on measuring chlorophyll A (Chla) content in leaf tissue during the entire autumn senescence processes to appropriately quantify autumn phenological processes. Beginning of leaf coloring could be defined as when about 50% of the Chl was lost. End of leaf coloring could be defined as when about 95% of the Chl was lost. Then the mechanism behind the timing of autumn senescence responses to climate change through hormone regulation was studied for the first time. Four dominate deciduous tree species with representative senescence type (Salix babylonica, Ginkgo biloba, Acer mono, Cotinus coggygria) were chosen as the subject of study. Variations in climate factors (temperature, day length, precipitation, humidity) were recorded and nine major endogenous hormones (IAA, IPA, ZR, DHZR, GA3, GA4, ABA, MeJA, BR) in leaf tissues were monitored during the entire autumn senescence processes. The experimental results verified temperature and day length are the major climate factors affecting autumn phenology. Low temperature and short day length could result in the decrease of ZR level and the increase of ABA level in leaf tissue, which directly trigger/promote senescence. Meanwhile, low temperature and short day length could cause the decrease of MeJA level and the increase of GA3 and GA4 level, which regulate the timing of autumn senescence indirectly through ZR, ABA, and IAA. Our study improves the understanding of autumn phenological response to climate change in deciduous trees.

Towards oilcane: Engineering hyperaccumulation of triacylglycerol into sugarcane stems

AbstractMetabolic engineering to divert carbon flux from sucrose to oil in high biomass crop like sugarcane is an emerging strategy to boost lipid yields per hectare for biodiesel production. Sugarcane stems comprise more than 70% of the crops' biomass and can accumulate sucrose in excess of 20% of their extracted juice. The energy content of oils in the form of triacylglycerol (TAG) is more than twofold that of carbohydrates. Here, we report a step change in TAG accumulation in sugarcane stem tissues achieving an average of 4.3% of their dry weight (DW) in replicated greenhouse experiments by multigene engineering. The metabolic engineering included constitutive co‐expression of wrinkled1; diacylglycerol acyltransferase1‐2; cysteine‐oleosin; and ribonucleic acid interference‐suppression of sugar‐dependent1. The TAG content in leaf tissue was also elevated by more than 400‐fold compared to non‐engineered sugarcane to an average of 8.0% of the DW and the amount of total fatty acids reached about 13% of the DW. With increasing TAG accumulation an increase of 18:1 unsaturated fatty acids was observed at the expense of 16:0 and 18:0 saturated fatty acids. Total biomass accumulation, soluble lignin, Brix and juice content were significantly reduced in the TAG hyperaccumulating sugarcane lines. Overcoming this yield drag by engineering lipid accumulation into late stem development will be critical to exceed lipid yields of current oilseed crops.

Relationship of Nitrogen Deficiency-Induced Leaf Senescence with ROS Generation and ABA Concentration in Rice Flag Leaves

Nitrogen (N) deficiency is one of the critical environmental factors that induce leaf senescence, and its occurrence may cause the shorten leaf photosynthetic period and markedly lowered grain yield. However, the physiological metabolism underlying N deficiency-induced leaf senescence and its relationship with the abscisic acid (ABA) concentration and reactive oxygen species (ROS) burst in leaf tissues are not well understood. In this paper, the effect of N supply on several senescence-related physiological parameters and its relation to the temporal patterns of ABA concentration and ROS accumulation during leaf senescence were investigated using the premature senescence of flag leaf mutant rice (psf) and its wild type under three N treatments. The results showed that N deficiency hastened the initiation and progression of leaf senescence, and this occurrence was closely associated with the upregulated expression of 9-cis-epoxycarotenoiddioxygenase genes (NCEDs) and with the downregulated expression of two ABA 8′-hydroxylase isoform genes (ABA8ox2 and ABA8ox3) under LN treatment. Contrarily, HN supply delayed the initiation and progression of leaf senescence, concurrently with the suppressed ABA biosynthesis and relatively lower level of ABA concentration in leaf tissues. Exogenous ABA incubation enhanced ROS generation and MDA accumulation in a dose-dependent manner, but it decreased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in detached leaf. These results suggested that the participation of ABA in the regulation of ROS generation and N assimilating/remobilizing metabolism in rice leaves was strongly responsible for induction of leaf senescence by N deficiency.

Two Festuca Species-F. arundinacea and F. glaucescens-Differ in the Molecular Response to Drought, While Their Physiological Response Is Similar.

Impact of photosynthetic and antioxidant capacities on drought tolerance of two closely related forage grasses, Festuca arundinacea and Festuca glaucescens, was deciphered. Within each species, two genotypes distinct in drought tolerance were subjected to a short-term drought, followed by a subsequent re-watering. The studies were focused on: (i) analysis of plant physiological performance, including: water uptake, abscisic acid (ABA) content, membrane integrity, gas exchange, and relative water content in leaf tissue; (ii) analysis of plant photosynthetic capacity (chlorophyll fluorescence; gene expression, protein accumulation, and activity of selected enzymes of the Calvin cycle); and (iii) analysis of plant antioxidant capacity (reactive oxygen species (ROS) generation; gene expression, protein accumulation and activity of selected enzymes). Though, F. arundinacea and F. glaucescens revealed different strategies in water uptake, and partially also in ABA signaling, their physiological reactions to drought and further re-watering, were similar. On the other hand, performance of the Calvin cycle and antioxidant system differed between the analyzed species under drought and re-watering periods. A stable efficiency of the Calvin cycle in F. arundinacea was crucial to maintain a balanced network of ROS/redox signaling, and consequently drought tolerance. The antioxidant capacity influenced mostly tolerance to stress in F. glaucescens.

Identification and functional analysis of soybean stearoyl-ACP Δ⁹ desaturase (GmSAD) gene family

Stearoyl-ACP Δ⁹ desaturase (SAD) catalyzes the synthesis of monounsaturated oleic acid or palmitoleic acid in plastids. SAD is the key enzyme to control the ratio of saturated fatty acids to unsaturated fatty acids in plant cells. In order to analyze the regulation mechanism of soybean oleic acid synthesis, soybean (Glycine max) GmSAD family members were genome-wide identified, and their conserved functional domains and physicochemical properties were also analyzed by bioinformatics tools. The spatiotemporal expression profile of each member of GmSADs was detected by qRT-PCR. The expression vectors of GmSAD5 were constructed. The enzyme activity and biological function of GmSAD5 were examined by Agrobacterium-mediated transient expression in Nicotiana tabacum leaves and genetic transformation of oleic acid-deficient yeast (Saccharomyces cerevisiae) mutant BY4389. Results show that the soybean genome contains five GmSAD family members, all encoding an enzyme protein with diiron center and two conservative histidine enrichment motifs (EENRHG and DEKRHE) specific to SAD enzymes. The active enzyme protein was predicted as a homodimer. Phylogenetic analysis indicated that five GmSADs were divided into two subgroups, which were closely related to AtSSI2 and AtSAD6, respectively. The expression profiles of GmSAD members were significantly different in soybean roots, stems, leaves, flowers, and seeds at different developmental stages. Among them, GmSAD5 expressed highly in the middle and late stages of developmental seeds, which coincided with the oil accumulation period. Transient expression of GmSAD5 in tobacco leaves increased the oleic acid and total oil content in leaf tissue by 5.56% and 2.73%, respectively, while stearic acid content was reduced by 2.46%. Functional complementation assay in defective yeast strain BY4389 demonstrated that overexpression of GmSAD5 was able to restore the synthesis of monounsaturated oleic acid, resulting in high oil accumulation. Taken together, soybean GmSAD5 has strong selectivity to stearic acid substrates and can efficiently catalyze the biosynthesis of monounsaturated oleic acid. It lays the foundation for the study of soybean seed oleic acid and total oil accumulation mechanism, providing an excellent target for genetic improvement of oil quality in soybean.

Titanium dioxide nanoparticles provoke transient increase in photosynthetic performance and differential response in antioxidant system in Raphanus sativus L.

Titanium dioxide nanoparticles (TiO2NPs) generally have positive effects on growth and physiological parameters in plants, but their impacts on photosynthesis and antioxidant system are poorly understood. This work aimed to assess the effects of TiO2 NPs on photosynthetic performance and antioxidant system in Raphanus sativus L. plants. Treatments consisted of TiO2 NPs and microparticles (μPs) applied foliarly by increasing doses from 10 to 1500 mg L−1, using deionized water as a control. As expected, Ti concentration in leaf tissue increased concomitant with the applied dose, being higher in μPs than NPs. A transient increase in net photosynthetic rate (by about 50 %) and stomatal conductance were observed from 12 to 60 h after the beginning of NPs and μPs treatments compared to the control. These increments were independent of doses and particles size. The photochemical parameters were more influenced by the time than the doses, being electron transport rate (ETR) increased, and non photochemical quenching (NPQ) decreased. The instantaneous water use efficiency (WUEins) was 2-fold higher, and intrinsic water use efficiency (WUEint) was 70 % lower in the treated plants respect to the control. Total phenols concentration increased with increasing doses of NPs and μPs. It is suggested that TiO2 NPs and μPs had a transient positive impact on photosynthesis likely by diffusive effects, increasing the WUEins, and a slight activation of secondary metabolism.

Differences in growth and physiological and metabolic responses among Canadian native and hybrid willows (Salix spp.) under salinity stress.

Globally, soil salinization is becoming increasingly prevalent, due to local hydrogeologic phenomena, climate change and anthropogenic activities. This has significantly curtailed current world food production and limits future production potential. In the prairie region of North America, sulfate salts, rather than sodium chloride, are often the predominant cause of soil degradation. In order to amend soil quality, revegetate salt-affected sites and recover economic loss associated with soil salinization, the establishment of short-rotation coppice plantations with willows (Salix spp.) has been suggested as a possible solution. To screen for the best candidates for such an application, 20 hybrid and 16 native willow genotypes were treated with three different salt conditions for 3 months. The treatments were designed to reflect the salt composition and concentrations on North American prairies. Under moderate salinity treatment (7dSm-1), hybrid willows had better growth, as they established quickly while managing salt transport and mineral nutrition balance. However, native willows showed higher potential for long-term survival under severe salinity treatment (14dSm-1), showing a lower sodium:potassium ratio in roots and better photosynthetic performance. Two native willow genotypes with high osmotic and salinity tolerance indices, specifically LAR-10 and MJW-9, are expected to show superior potential for remediating salt-affected sites. In addition, we observed significantly higher sulfate/sulfur concentrations in both leaf and root tissues in response to the severe salinity treatment, shedding light on the effect of sulfate salinity on sulfate uptake, and potentially sulfur metabolism in plants.