Signaling mechanisms and biochemical pathways regulating pollen-stigma interaction, seed development and seedling growth in sunflower under salt stress.

Sunflower (Helianthus annuus L.) is one of the major oilseed crops cultivated world over for its high-quality oil rich in linoleic acid. It also has established applications in pharmaceutical and biotechnological industries, mainly through recombinant production of unique oil body (OB) membrane proteins-oleosins, which are used for producing a wide variety of vaccines, food products, cosmetics and nutraceuticals. The present review provides a critical analysis of the progress made in advancing our knowledge in sunflower biology, ranging from mechanisms of pollen-stigma interaction, seed development, physiology of seed germination and seedling growth under salt stress, and finally understanding the signaling routes associated with various biochemical pathways regulating seedling growth. Role of nitric oxide (NO) triggered post-translational modifications (PTMs), discovered in the recent past, have paved way for future research directions leading to further understanding of sunflower developmental physiology. Novel protocols recently developed to monitor temporal and spatial distributions of various biochemicals involved in above-stated developmental events in sunflower, will go a long way for similar applications in plant biology in future.

Exogenous plant growth regulator alleviate the adverse effects of U and Cd stress in sunflower (Helianthus annuus L.) and improve the efficacy of U and Cd remediation.

Plant growth regulators (PGRs) are widely used in agricultural activities and have the potential to improve plant growth and plant tolerance against metal stress. PGR-assisted phytoextraction is now an effective and inexpensive method for enhancing the plant removal of toxic metals from soil. In this study, we conducted experiments to determine the effects of PGR treatments on soil uranium (U) and cadmium (Cd) removal by sunflowers as well as their stress response to U and Cd contamination. We found that the plant growth was inhibited by combined U and Cd stress in sunflowers compared with that of the control; however, the application of exogenous PGR had reduced the combined U and Cd stress by stimulating photosynthesis, decreasing the levels of active oxygen and lipid peroxidation, and enhancing the activity of the antioxidant defence systems. Exogenous PGR also increased the uptake of U and Cd by sunflowers and therefore, improved their U and Cd remediation efficiency. Moreover, indoleacetic acid (IAA) was the most effective PGR at removing U and Cd in the soil; the U and Cd removal efficiency was 484.21% and 238.85% higher in the 500 mg L-1 IAA application compared with that of the control without PGR application, respectively. Furthermore, none of the PGR treatments significantly influenced the available U and Cd contents in soil. Our results, therefore, may provide some detailed understanding on the technologies for the sustainable remediation of U and Cd contaminated soil by the combination of PGR treatments and phytoextraction.

Activated sludge treatment for promoting the reuse of a synthetic produced water in irrigation.

Large volumes of produced water are generated as a byproduct in activities of oil and gas exploitation, which can be reused in agriculture after a treatment process. Activated sludge treatment has been successfully used to remove oil from wastewater, but systematic studies on the toxicity of this effluent using this treatment are scarce in the literature. In this study, it was investigated the performance of an activated sludge system in the treatment of a synthetic produced water under different initial conditions in terms of salinity and oil and grease concentration. Furthermore, it was evaluated this effluent phytotoxicity in the germination, and seedling and plant growths of sunflower and corn seeds using untreated and treated synthetic produced water. Results revealed the activated sludge effectiveness in oil and grease and salinity removal from produced water, viz. high removal efficiency of 99.01 ± 0.28 and 91.07 ± 0.39%., respectively. Untreated produced water showed considerable toxic effects on the germination (74.67 ± 2.31% and 82.67 ± 2.31 for sunflower and corn seeds, respectively) and growth stages of sunflower and corn seed plants. The germination percentage was approximately 100% for both types of seed. The seedling and plant growth of the two seeds irrigated with treated produced water had similar performance when used tap water. These results highlighted the potential reuse as an unconventional water resource for plant irrigation of the synthetic produced water treated by an activated sludge process, which technology has showed high removal performance of salinity and oil.

Mapping of the New Fertility Restorer Gene Rf-PET2 Close to Rf1 on Linkage Group 13 in Sunflower (Helianthus annuus L.).

The PET2-cytoplasm represents a well characterized new source of cytoplasmic male sterility (CMS) in sunflower. It is distinct from the PET1-cytoplasm, used worldwide for commercial hybrid breeding, although it was, as PET1, derived from an interspecific cross between Helianthus. petiolaris and H. annuus. Fertility restoration is essential for the use of CMS PET2 in sunflower hybrid breeding. Markers closely linked to the fertility restorer gene are needed to build up a pool of restorer lines. Fertility-restored F1-hybrids RHA 265(PET2) × IH-51 showed pollen viability of 98.2% ± 1.2, indicating a sporophytic mode of fertility restoration. Segregation analyses in the F2-population of the cross RHA 265(PET2) × IH-51 revealed that this cross segregated for one major restorer gene Rf-PET2. Bulked-segregant analyses investigating 256 amplified fragment length polymorphism (AFLP) primer combinations revealed a high degree of polymorphism in this cross. Using a subset of 24 AFLP markers, three sequence-tagged site (STS) markers and three microsatellite markers, Rf-PET2 could be mapped to the distal region of linkage group 13 between ORS1030 and ORS630. Three AFLP markers linked to Rf-PET2 were cloned and sequenced. Homology search against the sunflower genome sequence of HanXRQ v1r1 confirmed the physical location of Rf-PET2 close to the restorer gene Rf1 for CMS PET1. STS markers were mapped that can now be used for marker-assisted selection.

Green synthesis of sulfur nanoparticles using Ocimum basilicum leaves and its prospective effect on manganese-stressed Helianthus annuus (L.) seedlings.

A novel green approach was utilized to fabricate sulfur nanoparticles (SNPs) with the aid of Ocimum basilicum leaves extract. The effective formation of the synthesized SNPs was examined and approved using UV-visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The average particle size was 23 nm with spherical shape and crystalline in nature. In the pot experiment, the synthesized SNPs were applied with different concentrations (12.5, 25, 50, 100 and 200 µM) as pre-soaking to Helianthus annuus seeds and irrigated with 100 mM MnSO4. As a result of manganese (Mn) exposure, the harvested 14-day sunflower seedlings showed a significant decline in the growth parameters (shoot length, leaf area and the relative water content of both shoot and root), photosynthetic pigments, mineral content (N, P, K, Ca, and Mg), and protein content compared to the control. The root length, electrolyte leakage, Na and Mn levels, metabolites content (amino acids, protein, glycine betaine, proline, and cysteine) were greatly raised as affected by Mn stress. Mn toxicity reduction using SNPs was demonstrated, as the medium doses enhanced seedlings growth, photosynthetic pigments, and mineral nutrients. Application of SNPs decreased Mn uptake and enhanced S metabolism through increasing cysteine level. Likewise, SNPs elevated seedlings water content and eliminated physiological drought via increasing osmolytes such as amino acids and proline. It can be concluded that green-synthesized SNPs had the potential to limit the deleterious effects of Mn stress.

Identification of high cadmium-accumulating oilseed sunflower (Helianthus annuus) cultivars for phytoremediation of an Oxisol and an Inceptisol.

Forty oilseed sunflower cultivars were screened in two soil types for phytoremediation of Cd coupled with maximum biomass yield and oil production. Several cultivars exhibited a significant difference in biomass and yield with enhanced uptake in shoots and low accumulation in roots from two Cd-contaminated soil types, an Oxisol and an Iceptisol. The Transfer Factor of Cd was >1 in several cultivars in both soil types, where as a significant difference in phytoextraction of Cd was observed in the Oxisol (acidic soil), greater than in the Inceptisol (alkaline soil). The results revealed that of the 40 cultivars, S9178, Huanong 667in the Oxisol and cvs. DW 667, HN 667, Huanong 667 and 668F1 in the Inceptisol showed a high biomass, better yield and enhanced accumulation of Cd in the shoots but a lesser accumulation in oil. The screened cultivar S 9178 produced the greatest amount of oil (55.6%) with 77% oleic acid, which makes it suitable for human consumption. Cultivar Huanong 667 was found to be the highest accumulating cultivar in both soil types. It is therefore suggested that some sunflower cultivars do exhibit phytoremediation potential together with agro-production potential.

Evaluation of in vitro genotoxic effects induced by in vitro anther culture conditions in sunflower.

Sunflower is a globally important oilseed, food, and ornamental crop. This study seeks to investigate the genotoxic effects of tissue culture parameters in sunflower calli tissues belongs to two genotypes obtained via anther culture. Anthers were pretreated with cold for 24 hours at 4°C and heat for 2 days at 35°C in the dark and plated onto media supplemented with different concentrations and combinations of 6-benzylaminopurine, 2,4-dichlorophenoxyacetic acid, α-naphthalene acetic acid and indole-3-acetic acid. Obtaining calli tissues were used to detect the DNA damage levels by Comet assay, evaluating changes on superoxide dismutase and guaiacol peroxidase activities derived from in vitro culture factors. 0.5 mg/L 2,4-dichlorophenoxyacetic acid and 2 mg/L α-naphthalene acetic acid from plant growth regulators showed acute genotoxic effect while 0.5 mg/L indole-3-acetic acid and 0.5 mg/L α-naphthalene acetic acid showed no genotoxic effect. Total protein content analysis of antioxidant enzymes revealed that although superoxide dismutase activity did not increase, Guaiacol peroxidase (GPOX) activity decreased in comparison to control. The obtained results have indicated that in vitro culture factors apparently lead to genotoxicity and oxidative stress.

Treatment of Common Sunflower (Helianthus annus L.) Seeds with Radio-frequency Electromagnetic Field and Cold Plasma Induces Changes in Seed Phytohormone Balance, Seedling Development and Leaf Protein Expression.

Treatment of plant seeds with electromagnetic fields or non-thermal plasmas aims to take advantage of plant functional plasticity towards stimulation of plant agricultural performance. In this study, the effects of pre-sowing seed treatment using 200 Pa vacuum (7 min), 5.28 MHz radio-frequency cold plasma (CP -2, 5, and 7 min) and electromagnetic field (EMF -5, 10, 15 min) on seed germination kinetics, content of phytohormones, morphometric parameters of seedlings and leaf proteome were assessed. CP 7 min and EMF 15 min treatments caused 19-24% faster germination in vitro; germination in the substrate was accelerated by vacuum (9%) and EMF 15 min (17%). The stressors did not change the seed germination percentage, with exception of EMF 5 min treatment that caused a decrease by 7.5%. Meanwhile both CP 7 min and EMF 15 min treatments stimulated germination, but the EMF treatment resulted in higher weight of leaves. Stressor-specific changes in phytohormone balance were detected in seeds: vacuum treatment decreased zeatin amount by 39%; CP treatments substantially increased gibberellin content, but other effects strongly varied with the treatment duration; the abscisic acid content was reduced by 55-60% after the EMF treatment. Analysis of the proteome showed that short exposure of seeds to the EMF or CP induced a similar long-term effect on gene expression in leaves, mostly stimulating expression of proteins involved in photosynthetic processes and their regulation.

Enterobacter sp. strain Fs-11 adapted to diverse ecological conditions and promoted sunflower achene yield, nutrient uptake, and oil contents.

Plant growth-promoting rhizobacteria are under extensive investigation to supplement the chemical fertilizers due to cost-effective and eco-friendly nature. However, their consistency in heterogeneous soil and diverse ecological settings is unclear. The current study presents in vitro and field evaluation of pre-characterized PGPR strain Enterobacter sp. Fs-11 (GenBank accession # GQ179978) in terms of its potential to enhance sunflower yield and oil contents under diverse environmental conditions. Under in vitro conditions, strain Fs-11 showed optimal growth at a range of temperature (15 to 40 °C) and pH values (6.5 to 8.5). Extracellular and intracellular localizations of the strain Fs-11 in sunflower root cortical cells through transmission electron microscopy confirmed its epiphytic and endophytic colonization patterns, respectively. In field experiments, conducted at three different agro-climatic locations, inoculation of strain Fs-11 at 50% reduced NP fertilizer resulted in a significant increase in growth, achene yield, nutrient uptake, and oil contents. Inoculation also responded significantly in terms of increase in mono- and polyunsaturated fatty acids (oleic and linoleic acids, respectively) without rising saturated fatty acid (palmitic and stearic acids) contents. We concluded that Enterobacter sp. Fs-11 is a potential candidate for biofertilizer formulations to supplement chemical fertilizer requirements of sunflower crop under diverse climatic conditions.

Role of supplemental UV-B in changing the level of ozone toxicity in two cultivars of sunflower: growth, seed yield and oil quality.

Ultraviolet-B radiation (UV-B) is inherent part of solar spectrum and tropospheric ozone (O3) is a potent secondary air pollutant. Therefore the present study was conducted to evaluate the responses of Helianthus annuus L. cvs DRSF 108 and Sungold (sunflower) to supplemental UV-B (sUV-B; ambient + 7.2 kJ m-2 d-1) and elevated ozone (O3; ambient + 10 ppb), given singly and in combination under field conditions using open-top chambers. The individual and interactive effects of O3 and sUV-B induced varying changes in both the cultivars of sunflower ranging from ultrastructural variations to growth, biomass, yield and oil composition. Reduction in leaf area of Sungold acted as a protective feature which minimized the perception of sUV-B as well as uptake of O3 thus led to lesser carbon loss compared to DRSF 108. Number- and weight of heads plant-1 decreased although more in Sungold with decline of oil content. Both the stresses when given singly and combination induced rancidification of oil and thus made the oil less suitable for human consumption.

A Reduced Phosphorus Application Rate Using a Mycorrhizal Plant as the Preceding Crop Maintains Soybean Seeds' Nutritional Quality.

We tested whether introducing an arbuscular mycorrhizal fungi (AMF)-host plant with a reduced P application rate could maintain soybean seeds' nutrient quality. The dynamic variation of 14 nutrients was analyzed in source and sink organs during the seed-filling stage. The AMF-host and non-AMF-host plants, sunflower and mustard, were grown as preceding crops (PCs). Soybeans, the succeeding crops, were planted with three different phosphorus levels, namely, 0, 50, and 150 kg P2O5 ha-1. The results showed that the AMF-host PC with a reduced P application rate maintained the seed's yield and nutrients quality. During the seed-filling stage, the AMF-host PC with a reduced P application rate increased the uptake of most nutrients compared to the non-AMF-host PC, and improved the remobilization efficiency of all nutrients except Mn, Fe, and Se, compared to the optimal P application rate. These results could help improve the utilization efficiency of P fertilizers and protect soybeans' nutritional value.

Aqueous plant extracts in the control of Bidens pilosa L / Extratos aquosos vegetais no controle de Bidens pilosa L

Secondary compounds have allelopathic action on germination and growth, and initial development of seedlings and beggar tick can have its germination and growth affected by the action of allelopathic extracts. Thus, this work aimed to evaluate the allelopathic potential of Brachiaria (Brachiaria brizantha), sunflower (Helianthus annuus) and sorghum extracts (Sorghum bicolor) on germination and initial growth of beggar ticks (Bidens pilosa). For this, an experiment was conducted in a completely randomized design with four treatments and six replicates and brachiaria, sunflower and sorghum extracts and control (distilled water) treatments. Extracts were obtained using 200 g of plant material and 1,000 mL of distilled water. Seeds were distributed in gerbox containing two sheets of germitest paper moistened with treatments and taken to germination chamber. Germination was daily monitored, and ten days after, initial growth was evaluated. Extracts did not reduce germination. However, they caused increase in germination time, mainly by brachiaria extract. Seedlings submitted to brachiaria and sorghum extracts showed lower growth. Brachiaria and sorghum extracts showed no action on germination, but controlled the initial growth of beggar tick, being potential natural herbicides.(AU)

Compostos secundários têm ação alelopática sobre a germinação, crescimento e desenvolvimento inicial de plântulas, e a Bidens pilosa pode ter sua germinação e crescimento afetados pela ação dos extratos alelopáticos. Nesse sentido, objetivou-se avaliar o potencial alelopático de extratos de braquiária (Brachiaria brizantha), girassol (Helianthus annus) e sorgo (Sorghum bicolor) na germinabilidade e no crescimento inicial de picão-preto (Bidens pilosa). Para isso foi instalado um experimento no delineamento inteiramente casualizado, com quatro tratamentos e seis repetições, sendo eles extrato de braquiária, girassol, sorgo e o controle (água destilada). Os extratos foram obtidos utilizando 200 g de material vegetal fresco para 1.000 mL de água destilada. As sementes foram distribuídas em caixa gerbox contendo duas folhas de papel germitest umedecidas com os tratamentos e levadas para a câmara de germinação. Foi acompanhada diariamente a germinação e, após 10 dias, foi avaliado o crescimento inicial. Os extratos não causaram prejuízos à germinação, porém, provocaram demora em seu tempo de eclosão, sendo o extrato de braquiária o mais prejudicial. As plântulas submetidas aos extratos de braquiária e sorgo apresentaram menor crescimento. Os extratos de braquiária e sorgo não apresentaram ação sobre a porcentagem de germinação das sementes de picão-preto, mas controlaram o crescimento inicial das plântulas e podem ser indicados para possíveis herbicidas naturais.(AU)

Pseudomonas sp. AF-54 containing multiple plant beneficial traits acts as growth enhancer of Helianthus annuus L. under reduced fertilizer input.

Plant growth promoting rhizobacteria (PGPR) are capable to increase the growth and yield of crops in eco-friendly and sustainable manner. To evaluate the response of sunflower towards inoculation with PGPR, a sunflower root associated bacterium AF-54 isolated from Diyar Gali Himalayan Mountain region, Azad Jammu and Kashmir (AJK), identified as Pseudomonas sp. by 16S rRNA sequence analysis and was characterized using polyphasic approach. The bacterium produced 23.9 µgmL-1 indole-3-acetic acid in tryptophan-supplemented medium, showed 44.28 nmoles mg-1 protein h-1 nitrogenase activity through acetylene reduction assay and released 48.80 µg mL-1 insoluble phosphorus in Pikovskaya's broth. During P-solubilization, the pH of the Pikovskaya's medium decreased from 7 to 3.04 due to the production of acetic acid, malic acid and gluconic acid. Pseudomonas sp. AF-54 showed metabolic versatility by utilizing 79 carbon sources from BIOLOG GN2 plates and resistance to many antibiotics. Furthermore, it inhibited the growth of Fusarium oxysporum in dual culture assay. To evaluate the plant-inoculation response, series of experiments conducted in hydroponic, sterilized soil and fields at AJK, and Faisalabad where inoculated plants with reduced fertilizer showed a significant increase in growth, yield, oil contents and achene NP uptake as compared to non-inoculated control. AF-54 showed extensive root colonization in sterilized and non-sterile conditions documented through yfp-labeling and fluorescent in situ hybridization coupled with confocal laser scanning microscopy. This study concludes that the Pseudomonas sp. strain AF-54 containing multiple plant growth promoting traits can be a potential candidate for biofertilizer production to enhance sunflower crop yield with reduced application of chemical (NP) fertilizers.

Aflatoxins in sunflower seeds and unrefined sunflower oils from Singida, Tanzania.

A total of 61 samples comprising sunflower seeds (40) and unrefined sunflower oils (21) samples collected randomly from Singida, Tanzania were analysed by Reverse Phase-high performance liquid chromatography (RP-HPLC). 15% (6/40) of the seed samples were contaminated with aflatoxin B1 ranging from limit of detection (LOD) to 218 ng g-1 with three of them exceeding the European Commission/European Union (EC/EU) and Tanzania Bureau of Standards (TBS)/Tanzania Food and Drug Authority (TFDA) maximum limits of 2 ng g-1 for AFB1 in oilseeds. The levels of total aflatoxins (AFT) in seeds ranged from LOD to 243 ng g-1. Other aflatoxins, except AFG2, were also detected. For the unrefined sunflower oils, the levels of AFB1 ranged from LOD to 2.56 ng mL-1. About 80.9% (17/21) of the analysed oil samples contained AFB1 of which 17.65% (3/17) exceeded the EC/EU and TBS/TFDA maximum limits of 2 ng mL-1. Other aflatoxins were also detected in the oils. The measured levels indicate there is a need for food quality education among food processors.

Light response of sunflower and canola as affected by plant density, plant genotype and N fertilization.

Crop response to light is an important parameter determining crop growth. Three field (split plots) experiments were conducted to investigate the effects of plant density, plant genotype and N fertilization on the light absorption and light extinction of sunflower (Helianthus annuus L.) and canola (Brassica napus L.). A detailed set of plant growth, light absorption and crop yield and oil related parameters were determined. Light was measured at noon during the sunny days with clear sky. In experiment I, although the plant density (PD) of 14 resulted in the highest rate of sunflower light absorption (31.37%) and light extinction (0.756), the highest rate of grain yield and grain oil yield was resulted at PD12 at 3639 and 1457.9kg/ha, respectively; as well as by genotype SUP.A. In experiment II (canola), PD80 resulted in the highest rate of light absorption (13.13%), light extinction (0.63), grain yield (2189.4kg/ha) and grain oil yield (556.54kg/ha). This was also the case for Genotype H. In experiment III (canola), although N150 resulted in the highest rate of light absorption (10.74%) and light extinction (0.48), the highest rate of grain yield (3413.6kg/ha) and grain oil yield (891.86kg/ha) was resulted at N100 as well as by Genotype H401. Results indicate how light properties, crop growth and yield of sunflower and canola can be affected by plant and environmental parameters, which are also of practical use by farmers.

Triploid Production from Interspecific Crosses of Two Diploid Perennial Helianthus with Diploid Cultivated Sunflower (Helianthus annuus L.).

Wild Helianthus species are a valuable genetic resource for the improvement of cultivated sunflower. We report the discovery and characterization of a unique high frequency production of triploids when cultivated sunflower was pollinated by specific accessions of diploid Helianthus nuttallii T. & G. and H. maximiliani Schr. Genomic in situ hybridization (GISH) analyses indicated that the triploid F1s had two genomes from the wild pollen sources and one from the cultivated line. Mitotic chromosome analyses indicated that the frequency of triploid progenies from the crosses of cultivated lines × H. nuttallii accession 102 (N102) was significantly higher than those of unexpected polyploid progenies from the crosses of wild perennial species × N102, and no unexpected polyploids were obtained from the reverse crosses. Pollen stainability analysis suggested the existence of a low percentage of unreduced (2n) male gametes in some accessions, especially N102 and H. maximiliani accession 1113 (M1113), which were generated at the telophase II and tetrad stages of meiosis. The triploid F1s could be the results of preferred fertilization of the low frequency of 2n male gametes with the female gametes of the cultivated sunflower, due to the dosage factors related to recognition and rejection of foreign pollen during fertilization. The triploids have been used to produce amphiploids and aneuploids. Future studies of the male gametes' fate from pollination through fertilization will further uncover the mechanism of this whole genome transmission. Studies of the genetic control of this trait will facilitate research on sunflower polyploidy speciation and evolution, and the utilization of this trait in sunflower breeding.

ePro-ClearSee: a simple immunohistochemical method that does not require sectioning of plant samples.

Investigations into the epigenetic status of individual cells within tissues can produce both epigenetic data for different cell types and positional information of the cells. Thus, these investigations are important for understanding the intra- and inter-cellular control systems of developmental and environmental responses in plants. However, a simple method to detect epigenetic modifications of individual cells in plant tissues is not yet available because detection of the modifications requires immunohistochemistry using specific antibodies. In this study, we developed a simple immunohistochemical method that does not require sectioning to investigate epigenetic modifications. This method uses a clearing system to detect methylated histones, acetylated histones, methylated DNA and/or centromeric histone H3 variants. Analyses of four dicots and five monocots indicated that this method provides a universal technique to investigate epigenetic modifications in diverse plant species.

Temperature effect on triacylglycerol species in seed oil from high stearic sunflower lines with different genetic backgrounds.

BACKGROUND: This study characterized the influence of temperature during grain filling on the saturated fatty acid distribution in triacylglycerol molecules from high stearic sunflower lines with different genetic backgrounds. Two growth chamber experiments were conducted with day/night temperatures of 16/16, 26/16, 26/26 and 32/26 °C. RESULTS: In all genotypes, independently of the genetic background, higher temperatures increased palmitic and oleic acid and reduced linoleic acid concentrations. Increasing night temperature produced an increase in saturated-unsaturated-saturated species, indicating a more symmetrical distribution of saturated fatty acids. The solid fat index was more affected by temperature during grain filling in lines with high linoleic than high oleic background. Higher variations in symmetry among night temperatures were observed in lines with high oleic background, which are more stable in fatty acid composition. CONCLUSION: The effect of temperature on triacylglycerol composition is not completely explained by its effect on fatty acid composition. Thus night temperature affects oil properties via its effects on fatty acid synthesis and on the distribution of fatty acids in the triacylglycerol molecules. © 2016 Society of Chemical Industry.

Life form-specific gradients in compound-specific hydrogen isotope ratios of modern leaf waxes along a North American Monsoonal transect.

The use of hydrogen isotope ratios (δ(2)H) of sedimentary n-alkanes from leaf waxes has become an important tool for reconstructing paleoenvironmental and ancient hydrologic conditions. Studies of modern plant waxes can elucidate driving ecological mechanisms behind geologic deposits. Here, we used a transect across the North American Monsoon region of the western USA from Tucson, Arizona to Salt Lake City, Utah to study variations in leaf wax δ(2)H among co-occurring plants. Three co-occurring life forms were selected: perennial shrub (rabbit brush, Chrysothamnus nauseosus; sagebrush, Artemisia tridentata); tree (Gambel's oak tree, Quercus gambelii); and annual (sunflower, Helianthus annuus). Our results showed that the distributions and abundances of n-alkanes in perennial plants were similar across all sites and generally did not vary with environmental conditions (e.g., precipitation and temperature). In contrast, variations in n-alkane δ(2)H were significantly correlated with the fraction of the annual precipitation coming during the summer monsoon period. We use a modified Craig-Gordon model to speculate on the possible drivers of the δ(2)H values of leaf wax n-alkanes of plants across the region. The model results suggest that the most likely explanation for variation in wax δ(2)H values was a combination of seasonal source water usage and subsequent environmental conditions.

Effect of phosphogypsum on growth, physiology, and the antioxidative defense system in sunflower seedlings.

Phosphogypsum (PG) is the solid waste product of phosphate fertilizer production and is characterized by high concentrations of salts, heavy metals, and certain natural radionuclides. The work reported in this paper examined the influence of PG amendment on soil physicochemical proprieties, along with its potential impact on several physiological traits of sunflower seedlings grown under controlled conditions. Sunflower seedlings were grown on agricultural soil substrates amended with PG at rates of 0, 2.5, and 5 %. The pH of the soil decreased but electrical conductivity and organic matter, calcium, phosphorus, sodium, and heavy metal contents increased in proportion to PG concentration. In contrast, no variations were observed in magnesium content and small increases were recorded in potassium content. The effects of PG on sunflower growth, leaf chlorophyll content, nutritional status, osmotic regulator content, heavy metal accumulation, and antioxidative enzymes were investigated. Concentrations of trace elements in sunflower seedlings grown in PG-amended soil were considerably lower than ranges considered phytotoxic for vascular plants. The 5 % PG dose inhibited shoot extension and accumulation of biomass and caused a decline in total protein content. However, chlorophyll, lipid peroxidation, proline and sugar contents, and activities of antioxidant enzymes such as superoxide dismutase and catalase increased. Collectively, these results strongly support the hypothesis that enzymatic antioxidation capacity is an important mechanism in tolerance of PG salinity in sunflower seedlings.