Genome-Wide Identification and Expression Analysis of TGA Family Genes Associated with Abiotic Stress in Sunflowers (Helianthus annuus L.)

Sunflower (Helianthus annuus L.) is an important, substantial global oil crop with robust resilience to drought and salt stresses. The TGA (TGACG motif-binding factor) transcription factors, belonging to the basic region leucine zipper (bZIP) family, have been implicated in orchestrating multiple biological processes. Despite their functional significance, a comprehensive investigation of the TGA family's abiotic stress tolerance in sunflowers remains elusive. In the present study, we identified 14 TGA proteins in the sunflower genome, which were unequally distributed across 17 chromosomes. Employing phylogenetic analysis encompassing 149 TGA members among 13 distinct species, we revealed the evolutionary conservation of TGA proteins across the plant kingdom. Collinearity analysis suggested that both HaTGA01 and HaTGA03 were generated due to HaTGA08 gene duplication. Notably, qRT-PCR analysis demonstrated that HaTGA04, HaTGA05, and HaTGA14 genes were remarkably upregulated under ABA, MeJA, and salt treatments, whereas HaTGA03, HaTGA06, and HaTGA07 were significantly repressed. This study contributes valuable perspectives on the potential roles of the HaTGA gene family under various stress conditions in sunflowers, thereby enhancing our understanding of TGA gene family dynamics and function within this agriculturally significant species.

HSF and Hsp Gene Families in sunflower: a comprehensive genome-wide determination survey and expression patterns under abiotic stress conditions

Sunflowers belong to the Asteraceae family, which comprises nutrimental and economic oilseed plants. Heat shock proteins (Hsps) are protein families vital for all organisms' growth and survival. Besides the ordinary conditions, the expression of these proteins ascends during abiotic stress factors such as high temperature, salinity, and drought. Using bioinformatics approaches, the current study identified and analyzed HSF and Hsp gene family members in the sunflower (Helianthus annuus L.) plant. HSF, sHsp, Hsp40, Hsp60, Hsp70, Hsp90, and Hsp100 domains were analyzed in the sunflower genome, and 88, 72, 192, 52, 85, 49, and 148 genes were identified, respectively. The motif structures of the proteins in the same phylogenetic tree were similar, and the α-helical form was dominant in all the protein families except for sHsp. The estimated three-dimensional structure of 28 sHsp proteins was determined as β-sheets. Considering protein-protein interactions, the Hsp60-09 protein (38 interactions) was found to be the most interacting protein. The most orthologous gene pairs (58 genes) were identified between Hsp70 genes and Arabidopsis genes. The expression analysis of selected genes was performed under high temperature, drought, and high temperature-drought combined stress conditions in two sunflower cultivars. In stress conditions, gene expressions were upregulated for almost all genes in the first half and first hours at large. The expressions of HanHSF-45 and HanHsp70-29 genes were raised in two cultivars under high temperature and high temperature-drought combined stress conditions. This study presents a blueprint for subsequent research and delivers comprehensive knowledge of this vital protein domain.

Biochar Decreases Cr Toxicity and Accumulation in Sunflower Grown in Cr(VI)-Polluted Soil

Biochar is preferentially recommended for the remediation of heavy metal-polluted soils. Sunflower is an important high-biomass oil crop with a promising potential for phytoremediation of Cr(VI)-polluted soil. However, how biochar affects sunflower growth and Cr accumulation in Cr(VI)-polluted soil needs to be elucidated. Here, a pot culture experiment was conducted to study whether soil amendment with biochar (0, 0.1%, 1%, and 5%, w/w) can mitigate Cr toxicity and accumulation in sunflower seedlings grown in soils artificially polluted with different levels of Cr(VI) (0, 50, and 250 mg Cr(VI)/kg soil). The addition of Cr(VI) exhibited significant phytotoxicity, as evidenced by inhibited plant growth and even the death of seedlings at 250 mg/kg Cr(VI). Overall, biochar amendment showed positive effects on plant growth and Cr immobilization, dependent on both the biochar dose and Cr addition level. When 50 mg/kg Cr(VI) was added, 1% biochar showed positive effects similar to 5% biochar on improving plant growth and mineral nutrition (particularly K), reducing Cr content in shoots and roots, and decreasing Cr availability and Cr(VI) content in the soil. In comparison with non-amendment, 1% and 5% biochar caused 85% and 100% increase in shoot dry weights, and 75% and 86% reduction in shoot Cr concentrations, respectively. When 250 mg/kg Cr(VI) was added, a 5% dose produced much better benefits than 1%, while a 0.1% dose did not help plants to survive. Overall, an appropriate dose of biochar enhanced Cr(VI) immobilization and subsequently decreased its toxicity and accumulation in sunflower seedlings. Our findings confirm that biochar can be used as an efficient amendment for the remediation of Cr(VI)-polluted soils and cleaner production of sunflower oil and biomass.

Sunflower and Palm Kernel Meal Present Bioaccessible Compounds after Digestion with Antioxidant Activity

Sunflower (Helianthus annuus L.) and African palm kernel (Elaeis guineensis Jacq.) are among the most cultivated in the world regarding oil extraction. The oil industry generates a large amount of meal as a by-product, which can be a source of nutrients and bioactive compounds. However, the physiological effects of bioactive compounds in such matrices are only valid if they remain bioavailable and bioactive after simulated gastrointestinal digestion. This study evaluated the chemical composition and antioxidant and prebiotic potential of de-oiled sunflower (DS) and de-oiled palm kernel (DP) meal after in vitro digestion. The DS sample had the highest protein content and the best chemical score, in which lysine was the limiting amino acid. Digested samples showed increased antioxidant activity, measured by in vitro methods. The digested DS sample showed a better antioxidant effect compared to DP. Moreover, both samples managed to preserve DNA supercoiling in the presence of the oxidizing agent. The insoluble fractions after digestion stimulated the growth of prebiotic bacterium, similar to inulin. In conclusion, simulated gastrointestinal digestion promoted in both matrices an increase in protein bioaccessibility and antioxidant capacity, pointing to a metabolic modulation favorable to the organism.

Seven undescribed compounds from the flower heads of Helianthus annuus L

Seven undescribed compounds, namely, 4-hydroxy-3-(2'-hydroxy-3'-methyl-1'-butenyl) acetophenone-1'-O-β-D-glucopyranoside (1), 4-hydroxy-3-((Z)-3'-hydroxy-3'-methyl-1'-butenyl) acetophenone-8-O-β-D-glucopyranoside (2), 4,6-hydroxy-3-((Z)-3'-hydroxy-3'-methyl-1'-butenyl) acetophenone-8-O-β-D-glucopyranoside (3), 4-hydroxy-3-((Z)-3'-hydroxy-3'-methyl-1'-butenyl) acetophenone-6-O-β-D-glucopyranoside (4), 2-hydroxymethylimino-3,4-dimethyl-7-hydroxy-6-methyl ketone-2H-chromon (5), annuolide A-15-O-β-D-glucopyranoside (6) and heliannuoside A (7), together with eighteen known compounds, were obtained from water extract of the flower heads of Helianthus annuus L. (Asteraceae). The structures of these compounds were elucidated based on spectroscopic analyses. Upon evaluation of the anti-inflammatory activity of compounds 1-9, 15-18, 21 and 24-25 by their effects on the release of NO in MH-S cells, compound 6 showed significant inhibition of NO secretion at 12.5 μM (P < 0.05) and 25 μM (P < 0.01) in a dose-dependent manner, and compound 18 showed inhibition of NO secretion at 25 μM (P < 0.05).

5-Aminolevulinic acid mitigates the chromium-induced changes in Helianthus annuus L. as revealed by plant defense system enhancement

Chromium (Cr) in the soil is one of the major pollutants for agricultural production. This study examined the efficiency of sunflower plants to remediate Cr-contaminated soils using a plant growth regulator, 5-aminolevolinic acid (ALA). At six leaf stage, sunflower plants were exposed to soil-applied Cr (0.15 g kg^-1), manganese (Mn, 0.3 g kg^-1) and trisodium (S,S)-ethylenediamine-N,N'-disuccinic acid (EDDS, 2.5 mmol kg^-1), ALA (10 mg L^-1) was sprayed. After ALA treatment, the plants were harvested for further biochemical analyses. Results showed that EDDS and Mn improved the Cr accumulation but restrained plant growth. Conversely, ALA improved the growth of Cr-stressed plants by promoting chlorophyll concentration in the top fully expanded leaves. The bioaccumulation quantity and removal efficiency of sunflowers treated by Cr + EDDS + ALA was improved by 47.92% and 47.94%, respectively, as compared to the Cr treatment. This was further supported by qRT-PCR analysis, where the expression of heavy metal transport genes such as ZIP6 and NRAMP6 and subsequently Cr accumulation in sunflower tissues increased by EDDS, Mn, and ALA application. However, compared with other treatments, ALA ameliorated cellular injury from Cr-stress by uptake or movement of Cr prevention, modulation of antioxidant enzymes, and elimination of reactive oxygen species. Our study suggested that ALA as an ideal option for the phytoremediation of Cr-contaminated soils.

Molecular Sieve, Halloysite, Sepiolite and Expanded Clay as a Tool in Reducing the Content of Trace Elements in Helianthus annuus L. on Copper-Contaminated Soil

The aim of this study was to determine the effect of copper soil contamination on the trace element content of sunflower aerial parts and in roots. Another aim was to assess whether the introduction of selected neutralizing substances (molecular sieve, halloysite, sepiolite and expanded clay) into the soil could reduce the impact of copper on the chemical composition of sunflower plants. Copper soil contamination with 150 mg Cu²⁺ kg^-1 of soil and 10 g of each adsorbent per kg of soil were used. Soil contamination with copper caused a significant increase in the content of this element in the aerial parts (by 37%) and roots (by 144%) of sunflower. Enriching the soil with the mineral substances reduced the amount of copper in the aerial parts of sunflower. Halloysite had the greatest effect (35%), while expanded clay had the smallest effect (10%). An opposite relationship was found in the roots of this plant. In copper-contaminated objects, a decrease in the content of cadmium and iron and an increase in the concentrations of nickel, lead and cobalt in the aerial parts and roots of sunflower were observed. The applied materials reduced the content of the remaining trace elements more strongly in the aerial organs than in the roots of sunflower. Molecular sieve had the greatest reducing effect on the content of trace elements in sunflower aerial organs, followed by sepiolite, while expanded clay had the least impact. The molecular sieve also reduced the content of iron, nickel, cadmium, chromium, zinc and, especially, manganese, whereas sepiolite reduced the content of zinc, iron, cobalt, manganese and chromium in sunflower aerial parts. Molecular sieve contributed to a slight increase in the content of cobalt, while sepiolite had the same effect on the content of nickel, lead and cadmium in the aerial parts of sunflower. All materials decreased the content of chromium in sunflower roots, molecular sieve-zinc, halloysite-manganese, and sepiolite-manganese and nickel. The materials used in the experiment, especially the molecular sieve and to a lesser extent sepiolite, can be used effectively to reduce the content of copper and some other trace elements, particularly in the aerial parts of sunflower.

Genome-Wide Identification and Expression Analysis of UBiA Family Genes Associated with Abiotic Stress in Sunflowers (Helianthus annuus L.)

The UBiA genes encode a large class of isopentenyltransferases, which are involved in the synthesis of secondary metabolites such as chlorophyll and vitamin E. They performed important functions in the whole plant's growth and development. Current studies on UBiA genes were not comprehensive enough, especially for sunflower UBiA genes. In this study, 10 HaUBiAs were identified by domain analysis these HaUBiAs had five major conserved domains and were unevenly distributed on six chromosomes. By constructing phylogenetic trees, 119 UBiA genes were found in 12 species with different evolutionary levels and divided into five major groups, which contained seven conserved motifs and eight UBiA subsuper family domains. Tissue expression analysis showed that HaUBiAs were highly expressed in the roots, leaves, and seeds. By using promoter analysis, the cis-elements of UBiA genes were mainly in hormone signaling and stress responses. The qRT-PCR results showed that HaUBiA1 and HaUBiA5 responded strongly to abiotic stresses. Under ABA and MeJA treatments, HaUBiA1 significantly upregulated, while HaUBiA5 significantly decreased. Under cold stress, the expression of UBiA1 was significantly upregulated in the roots and stems, while UBiA5 expression was increased only in the leaves. Under anaerobic induction, UBiA1 and UBiA5 were both upregulated in the roots, stems and leaves. In summary, this study systematically classified the UBiA family and identified two abiotic stress candidate genes in the sunflower. It expands the understanding of the UBiA family and provides a theoretical basis for future abiotic stress studies in sunflowers.

Genome-wide analysis of the WSD family in sunflower and functional identification of HaWSD9 involvement in wax ester biosynthesis and osmotic stress

The wax esters are important cuticular wax composition that cover the outer surface of plant organs and play a critical role in protection and energy metabolism. Wax ester synthesis in plant is catalyzed by a bifunctional wax ester synthase/acyl-CoA: diacylglycerol acyltransferase (WSD). Sunflower (Helianthus annuus L.) is an important oil crop in the world; however, little is known about WSD in sunflower. In this study, we identified and performed a functional analysis of twelve HaWSD genes from sunflower genome. Tissue-specific expression revealed that 12 HaWSD genes were differentially expressed in various organs and tissues of sunflower, except seeds. HaWSD genes were highly induced by salinity, drought, cold, and abscisic acid (ABA) in sunflower. To ascertain their function, HaWSD9, with highly expressed levels in stems and leaves, was cloned and expressed in a yeast mutant defective in triacylglycerol (TAG) biosynthesis. HaWSD9 complemented the phenotype by producing wax ester but not TAG in vivo, indicating that it functions as a wax ester synthase. Subcellular localization analysis indicated that HaWSD9 was located in the endoplasmic reticulum (ER). Heterologous introduction of HaWSD9 into Arabidopsis wsd1 mutant exhibited increased epicuticular wax crystals and cuticular wax contents on the stems. As compared with the wsd1 mutant, HaWSD9 overexpressing transgenic Arabidopsis showed less cuticle permeability, chlorophyll leaching and water loss rate. Further analysis showed that the HaWSD9 transgenics enhanced tolerance to ABA, mannitol, drought and salinity, and maintained higher leaf relative water content (RWC) than the wsd1 mutant under drought stress, suggesting that HaWSD9 play an important physiological role in stress response as well as wax synthase. These results contribute to understanding the function of HaWSD genes in wax ester synthesis and stress tolerance in sunflower.

Evaluation of the Usefulness of Sorbents in the Remediation of Soil Exposed to the Pressure of Cadmium and Cobalt

An undesirable side effect of economic progress is increasingly severe pollution with heavy metals, responsible for the degradation of ecosystems, including soil resources. Hence, this research focused on examining six adsorbents in order to distinguish a reactive mineral with the highest capacity to remediate soils contaminated with heavy metals. To this end, the soil was polluted with Co²⁺ and Cd²⁺ by applying the metals in concentrations of 100 mg kg^-1 d.m. The extent of soil equilibrium disturbances was assessed by evaluating the response of the soil microbiome, activity of seven soil enzymes, and the yields of Helianthus annuus L. Six sorbents were evaluated: a molecular sieve, expanded clay (ExClay), halloysite, zeolite, sepiolite and biochar. Co²⁺ and Cd²⁺ proved to be significant inhibitors of the soil's microbiological and biochemical parameters. Organotrophic bacteria among the analysed groups of microorganisms and dehydrogenases among the soil enzymes were most sensitive to the effects of the metals. Both metals significantly distorted the growth and development of sunflower, with Co²⁺ having a stronger adverse impact on the synthesis of chlorophyll. The molecular sieve and biochar were the sorbents that stimulated the multiplication of microorganisms and enzymatic activity in the contaminated soil. The activity of enzymes was also stimulated significantly by zeolite and sepiolite, while the growth of Helianthus annuus L. biomass was stimulated by the molecular sieve, which can all be considered the most useful reactive materials in the remediation of soils exposed to Co²⁺ and Cd²⁺.

Micro/trace/toxic elements and insecticide residues level in monofloral bee-collected sunflower pollen- health risk assessment

The aim of the current research was to determine the content of (potentially) toxic elements and insecticide residues in monofloral sunflower bee-collected pollen. For micro- and trace elements determination Inductively Coupled Plasma Optical Emission (ICP-OES) analytical method was used while insecticide residue content was monitored by applying Liquid Chromatography-Mass Spectrometry (LC-MS/MS) technique. In total, seventeen micro/trace elements were quantified. None of the twenty four examined insecticides were detected above the limit of detection (LOD) which makes studied sunflower bee-collected pollen eco-friendly both to bees and humans. Based on presence of several toxic as well as potentially toxic elements calculations for estimated weekly intakes (EWI), and oral intakes (OI) were made and used for health risk assessment based on the computation of two different health risk quotients (HQ)- acute (HQ_A) and long-term (HQ_L). The obtained results proved that all HQ values for adults were negligible or low except in case of HQ_L value for arsenic (0.32) which can be characterized as medium. However, in case of children much more precaution is needed due to significant HQ_L risk for arsenic (1.511). The attained data can help to make additional linkage between bee-collected pollen as food ingredients and potential benefits/risks for human health.

Comparative assessment of chromate bioremediation potential of Pantoea conspicua and Aspergillus niger

The recent work aims at the use of Pantoea conspicua (MT5) and Aspergillus niger (CRS3) to assess their bioremediation potential and growth restoration of Helianthus annuus L. under chromate (Cr⁺⁶) stress. The growth of the P. conspicua and A. niger was tested in Cr⁺⁶ supplemented media. The strains can withstand up to 1200 and 900 ppm respectively in the media and effectively bio-transform it to nontoxic form. Supplemented metal's levels significantly decreased the growth attribute of H. annuus (p< 0.05). On the other hand, P. conspicua and A. niger rescued the host plant by establishing higher colonization frequency with the host roots. Moreover, MT5 bio-transformed the toxic Cr⁺⁶ to non-toxic Cr⁺³ form in the rhizosphere. It also enhanced the host plant growth by producing phytohormones and ceasing Cr uptake and accumulation. Contrarily, CRS3 tends to accumulate and bio-transform metal in their hyphae. Nonetheless, both of the microbes tend to modulate phytohormones production and strengthening antioxidant system of the host. Improvement in the antioxidant system enabled the host plant to produce higher phenolics and flavonoids, and lower peroxidase. The associated plant species also exhibited higher ROS scavenging and lower ROS accumulation. Besides, the strains were able to produce higher amounts of phytohormones, including IAA, GA, and SA. Such activities rendered them as excellent phytostimulants, that can be used as biofertilizers in chromium polluted soils.

The combined effect of water deficit stress and TiO2 nanoparticles on cell membrane and antioxidant enzymes in Helianthus annuus L

Nanotechnology has become one of the several approaches attempting to ameliorate the severe effect of drought on plant's production and to increase the plants tolerance against water deficit for the water economy. In this research, the effect of foliar application of TiO₂, nanoparticles or ordinary TiO₂, on Helianthus annuus subjected to different levels of water deficit was studied. Cell membrane injury increased by increasing the level of water deficit and TiO₂ concentration, and both types of TiO₂ affected the leaves in analogous manner. Ord-TiO₂ increased H₂O₂ generation by 67-240% and lipid peroxidation by 4-67% in leaves. These increases were more than that induced by Nano-TiO₂ and the effect was concentration dependent. Proline significantly increased in leaves by water deficit stress, reaching at 25% field capacity (FC) to more than fivefold compared to that in plants grown on full FC. Spraying plants with water significantly decreased the activities of enzymes in the water deficit stressed roots. The water deficit stress exerted the highest magnitude of effect on the changes of cell membrane injury, MDA, proline content, and activities of CAT and GPX. Nano-TiO₂ was having the highest effect on contents of H₂O₂ and GPX activity. In roots, the level of water deficit causes highest effect on enzyme activities, but TiO₂ influenced more on the changes of MDA and H₂O₂ contents. GPX activity increased by 283% in leaves of plants treated with 50 and 150 ppm Nano-TiO₂, while increased by 170% in those treated with Ord-TiO₂, but APX and CAT activities increased by 17-197%, in average, with Ord-TiO₂. This study concluded that Nano-TiO₂ didn't ameliorate the effects of drought stress on H. annuus but additively increased the stress, so its use in nano-phytotechnology mustn't be expanded without extensive studies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-022-01153-z.

Evaluation of some in vitro bioactivities of sunflower phenolic compounds

Phenolic compounds in crude extracts were obtained from defatted sunflower seed flour using sodium bisulfite and ethanol solutions as extracting agents. The antioxidant, antimicrobial, anti-proliferative, and DNA protective activities of the phenolic compounds in crude extract were analyzed. The phenolic compound contents were determined as chlorogenic acid (CGA) equivalent, presenting 11.57 and 15.44 g CGA eq/100g regarding the sodium bisulfite extract and ethanolic extract, respectively. The ORAC, DPPH, and ABTS methods were used to evaluate antioxidant activity. Both extracts presented antioxidant properties, considering that the ethanolic extract demonstrated higher values (EC₅₀ 0.36 g extract/g DPPH•). The antimicrobial action was analyzed as to the minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) of 4 kinds of bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis). The ethanolic extract was effective against all of these microorganisms, out of which E. coli was the most sensitive, with a MIC of 11.6 mg CGA/mL. The ethanolic extract presented DNA protective activity without cytotoxic activity concerning in vitro anti-proliferative assay. These findings can be considered as initial evidence of the potential use of phenolic compounds obtained from sunflower seed flour as natural additives in the food industry.

•

Sunflower flour processing provides a phenolic extract as a byproduct.

•

Sunflower phenolic extract exhibited antioxidant and antibacterial activity.

•

Ethanolic sunflower phenolic extract exhibited DNA protection.

•

Phenolic compounds extracts from sunflower has a potential as a food additive.

Photosynthesis, lipid peroxidation, and antioxidative responses of Helianthus annuus L. against chromium (VI) accumulation

The present study was performed to address how Cr(VI) posed its toxicities on photosynthesis, lipid peroxidation, and its retaliation by antioxidative system of Helianthus annuus L. during Cr(VI) accumulation. For this, a pot experiment was performed wherein three different concentrations viz, 15, 30, and 60 mg Cr(VI) kg-1 soil were applied to Helianthus annuus L. at the time of seeds sowing. The results revealed that Cr(VI) accumulation was two to three folds higher in roots than in shoots which suggests that root is the major site for Cr(VI) accumulation. It was observed that with increasing doses of Cr(VI), growth indices hampered significantly, along with closure of stomata and damaged guard and epidermal cells. Photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids), leaf gaseous exchange parameters (A, E, GH2O), and PSII efficiency (Fv/Fm) worsened under Cr(VI) toxicity in dose dependent manner. Cr(VI) accumulation intensified the lipid peroxidation, too by triggering the MDA and H2O2 production, however, the plant responded well against the lipid peroxidation by enhancing the coordinated action of enzymatic (SOD, APX, GR) and non-enzymatic (GSH, AsA) antioxidants. In a nutshell, Helianthus annuus L. could be used as a potential Cr(VI) accumulator because of its good tolerance strategies against Cr(VI) toxicities.NOVELTY STATEMENT The results revealed that Cr(VI) accumulation was two to three folds higher in roots than in shoots which suggests that root is the major site for Cr(VI) accumulation. Photosynthetic pigments, leaf gaseous exchange parameters, and Fv/Fm worsened under Cr(VI) toxicity. Cr(VI) accumulation intensified lipid peroxidation by triggering MDA and H2O2 production, however, the plant responded well against the lipid peroxidation by enhancing the coordinated action of enzymatic and non-enzymatic antioxidants. In a nutshell, Helianthus annuus L. could be used as a potential Cr(VI) accumulator because of its good tolerance strategies against Cr(VI) toxicities.

Strategies for applying gray water effluent on ornamental sunflower crops

In a context of scarcity of good quality water, reuse is a mandatory practice to increase water availability, thus allowing the exploitation of more cropland. Although several studies have evaluated the hydric potential of domestic gray water to promote the economic and environmental sustainability of agriculture, the focus of this study was to evaluate the application of this effluent on an ornamental plant, the sunflower. The experiment was conducted in a protected environment using a completely randomized block design with split plots and four replicates. Irrigation solutions containing different mixtures of treated gray water effluent (TGW) and drinking water (DW) (100% DW, 25% TGW + 75% DW, 50% TGW + 50% DW, 75% TGW + 25% DW, and 100% TGW) were arranged in the plots, while the ornamental sunflower cultivars (Bonito de Outono Sortido and Sol Vermelho) were arranged in the split plots. Irrigation with treated gray water did not affect the growth of the plants and the quality of the flowers until the dilution of 55% in drinking water. The cultivar Sol Vermelho showed better plant growth and flower quality when fertigated with dilutions of treated gray water. The principle of mixing fresh with gray water, applied to the production of ornamental sunflowers, allows obtaining flowers of good quality while saving drinking water and decreasing the deposition of effluents in the environment.

Salt-tolerance induced by leaf spraying with H2O2 in sunflower is related to the ion homeostasis balance and reduction of oxidative damage

Salinity is still one of the main factors that limit the growth and production of crops. However, currently, hydrogen peroxide (H₂O₂) priming has become a promising technique to alleviate the deleterious effects caused by salt. Therefore, this study aimed to test different leaf spraying strategies with H₂O₂ for acclimation of sunflower plants to salt stress, identifying the main physiological and biochemical changes involved in this process. The experiment was conducted in a completely randomized design, with four replications. Initially, four concentrations of H₂O₂ were tested (0.1; 1; 10 and 100 mM) associated with different applications: 1AP - one application (48 h before exposure to NaCl); 2AP - two applications (1AP + one application 7 days after exposure to NaCl) and 3AP - three applications (2AP + one application 14 days after exposure to NaCl), besides this two reference treatments were also added: control (absence of NaCl and absence of H₂O₂) and salt control (presence of 100 mM of NaCl and absence of H₂O₂). The experiment was conducted in hydroponic system containing Furlani's nutrient solution. Salt stress reduced the growth of sunflower plants, however, the H₂O₂ priming through leaf spraying was able to reduce the deleterious effects caused by salt, especially in the 1 mM H₂O₂ treatment with one application. H₂O₂ acts as a metabolic signal assisting in the maintenance of ionic and redox homeostasis, and consequently increasing the tolerance of plants to salt stress.

CYP71BL9, the missing link in costunolide synthesis of sunflower

Despite intensive research in recent years, the biosynthetic route to costunolide in sunflower so far remained obscured. Additional P450 sequences from public sunflower transcriptomic database were screened to search for candidate enzymes which are able to introduce the 6α-hydroxy-group required for the esterification with the carboxy group of germacarane A acid, the final step in costunolide formation. CYP71BL9, a new P450 enzyme from sunflower was shown to catalyze this hydroxylation, hence being identified as HaCOS. Phylogentically, HaCOS is closer related to HaG8H than to any other known costunolide synthase in Asteraceae.The enzyme was successfully employed to reconstruct the sunflower biosynthesis of costunolide in transformed tobacco. Contrary, in yeast, only minor amounts of sesquiterpene lactone was produced, while 5-hydroxyfarnesylic acid was formed instead. HaCOS in combination with HaG8H produced 8β-hydroxycostunolide (eupatolide) in transformed plants, thus indicating that sunflower possesses two independent modes of eupatolide synthesis via HaCOS and via HaES. The lack of HaCOS expression and of costunolide in trichomes suggests that the enzyme triggers the costunolied synthesis of the inner tissues of sunflower and might be linked to growth regulation processes.

Influence of hydro- and osmo-priming on sunflower seeds to break dormancy and improve crop performance under water stress

This study explored the effects of two hydro- and osmo-priming durations (8 and 16 h) on growth and yield components of sunflowers (Helianthus annuus L.) under water stress. The pot experiment, performed under a rain shelter, consisted of 9 treatments replicated five times: unprimed seeds as control (C), hydro-primed seeds (T0), osmo-primed seeds in 10, 20, and 30% PEG-6000 (T1, T2, and T3, respectively). Severe water stress was applied for 12 days to all treatments at the beginning of the flowering stage. Statistical analysis revealed a very highly significant positive effect (p < 0.01) by all treatments on sunflower seed germination compared with the control. Moreover, primed seeds improved significantly for all growth parameters and yield components, but no significant differences were observed according to either priming technique or duration. The highest value of germination capacity, for fresh and dry biomasses, was obtained with PEG-primed seeds at 10% for 16 h. The grain number per anthodium and grain yield per plant from primed seeds were higher than those in the control (1.9- to 2.5-fold and 2.8- to 3.3-fold respectively). Under conditions of water stress, the proline content in primed plants was significantly higher than that in unprimed ones, with the exception of T3 treatment primed for 8 h. Soluble sugars and chlorophyll contents increased significantly with all applied treatments compared with the control. The study showed that the applied priming treatments improved germination characteristics in particular and increased growth and yield components for sunflowers under drought stress conditions.

Seed and floret size parameters of sunflower are determined by partially overlapping sets of quantitative trait loci with epistatic interactions

KEY MESSAGE

Floret and seed traits are moderately correlated phenotypically in modern sunflower cultivars, but the underlying genetics are mostly independent. Seed traits in particular are governed in part by epistatic effects among quantitative trait loci. Seed size is an important quality component in marketing commercial sunflower (Helianthus annuus L.), particularly for the in-shell confectionery market, where long and broad seed types are preferred as a directly consumed snack food globally. Floret size is also important because corolla tube length was previously shown to be inversely correlated with pollinator visitation, impacting bee foraging potential and pollinator services to the plant. Commercial sunflower production benefits from pollinator visits, despite being self-compatible, and bees are required in hybrid seed production, where "female" and "male" inbred lines are crossed at field scale. Issues with pollination of long-seed confectionery sunflower suggest that there may be an unfavorable correlation between seed and floret traits; thus, our objective was to determine the strength of the correlation between seed and floret traits, and confirm any co-localization of seed and floret trait loci using genome-wide association analysis in the SAM diversity panel of sunflower. Our results indicate that phenotypic correlations between seed and floret traits are generally low to moderate, regardless of market class, a component of population substructure. Association mapping results mirror the correlations: while a few loci overlap, many loci for the two traits are not overlapping or even adjacent. The genetics of these traits, while modestly quantitative and influenced by epistatic effects, are not a barrier to simultaneous improvement of seed length and pollinator-friendly floret traits. We conclude that breeding for large seed size, which is required for the confectionery seed market, is possible without producing florets too long for efficient use by pollinators, which promotes bee foraging and associated pollination services.

Construction of a high-density genetic linkage map and QTL mapping of oleic acid content and three agronomic traits in sunflower (Helianthus annuus L.) using specific-locus amplified fragment sequencing (SLAF-seq)

High-density genetic linkage maps are particularly important for quantitative trait loci (QTL) mapping, genome assembly, and marker-assisted selection (MAS) in plants. In this study, a high-density genetic linkage map of sunflower (Helianthus annuus L.) was constructed using an F₂ population generated from a cross between Helianthus annuus L. '86-1' and 'L-1-OL-1' via specific-locus amplified fragment sequencing (SLAF-seq). After sequence preprocessing, 530.50 M reads (105.60 Gb) were obtained that contained a total of 343,197 SLAFs, of which 39,589 were polymorphic. Of the polymorphic SLAFs, 6,136 were organized into a linkage map consisting of 17 linkage groups (LGs) spanning 2,221.86 cM, with an average genetic distance of 0.36 cM between SLAFs. Based on this high-density genetic map, QTL analysis was performed that focused on four sunflower phenotypic traits: oleic acid content (OAC), plant height (PH), head diameter (HD), and stem diameter (SD). Subsequently, for these four traits eight QTLs were detected that will likely be useful for increasing our understanding of genetic factors underlying these traits and for use in marker-assisted selection (MAS) for future sunflower breeding.

The effect of fly ash on sunflower growth and human health

One of the challenges brought by the circular economy requires a reconsideration of waste, which may under certain circumstances turn into genuine resources. By extension, soil pollution with heavy metal is a major concern since it directly affects the health of the population. The goal of the present research work is to analyze the impact of the use of waste from other technological processes in agriculture: fly ash (resulting ash from thermal power plants), zeolite bush (resulting from the processing of rock from zeolite quarries), and manure (garbage from zoo technical farms). In this respect, complex treatments based on inorganic substances (fly ash and volcanic indigenous tuff with 70% clinoptilolite) were applied to less-favored agricultural soils in the absence and in the presence of an organic fertilizer (manure), respectively. After cultivating sunflower (Helianthus annuus L.), a semi-early hybrid grown in the type of soil on which fly ash has been applied, there have been obtained seed crops 15.8% higher than the seed crops grown in the soil on which no fertilizer has been applied. The results obtained when combining fly ash and manure tend to amount to those obtained when combining manure with indigenous volcanic tuff with 70% clinoptilolite. The quality of the seed crops, obtained in the case of the three types of soil on which amendments were added in the absence/presence of the fertilizer, corresponds to the requirements of the national rules and allows their food processing.

Antifungal Polyamides of Hydroxycinnamic Acids from Sunflower Bee Pollen

The aim of the bioassay-guided fractionation was the selection of the most potent group of compounds responsible for the protection of sunflower bee pollen grains. Synthesis of prospective antifungal polyamides of hydroxycinnamic acids was based on previous structural elucidation of ethanol soluble fraction by ¹H,¹H-PFG-COSY, ¹H,¹³C-HSQC, FT-IR, FT-Raman, and LC-MS experiments. The main compounds found were tri- p-coumaroylspermidines accompanied by other HCAA of spermidine and putrescine. Several model HCAA derivatives were prepared to test their antifungal activity against widespread spoilage fungi ( A. niger 42 CCM 8189, F. culmorum DMF 0103, and P. verrucosum DMF 0023). A. niger CCM 8189 and F. culmorum DMF 0103 exhibited higher resistance to the antifungal effects of hydroxycinnamic acid amides, whereas P. verrucosum DMF 0023 was the most sensitive strain. It has been discovered the effect of HCAA polarity on the role of secondary metabolites in the microbial protection of pollen grains. The combination of bioassay-guided fractionation, structural elucidation, selection of prospective compounds, and their synthesis to determine their antifungal properties could be considered as an original approach.

SSR Markers Suitable for Marker Assisted Selection in Sunflower for Downy Mildew Resistance

The effectiveness of Pl genes is known to be resistant to downy mildew (DM) disease affected by fungus Plasmopara halstedii in sunflower. In this study phenotypic analysis was performed using inoculation tests and genotypic analysis were carried out with three DM resistance genes Plarg, Pl13 and Pl8. A total of 69 simple sequence repeat markers and 241 F₂ individuals derived from a cross of RHA-419 (R) x P6LC (S), RHA-419 (R) x CL (S), RHA-419 (R) x OL (S), RHA419 (R) x 9758R (S), HA-R5 (R) x P6LC (S) and HA89 (R) x P6LC (S) parental lines were used to identify resistant hybrids in sunflower. Results of SSR analysis using markers linked with downy mildew resistance genes (Plarg, Pl8 and Pl13) and downy mildew inoculation tests were evaluated together and ORS716 (for Plarg and Pl13), HA4011 (for Pl8) markers showed positive correlation with their phenotypic results. These results suggest that these markers are associated with DM resistance and they can be used successfully in marker-assisted selection for sunflower breeding programs specific for downy mildew resistance.

Sewage sludge used as organic manure in Moroccan sunflower culture: Effects on certain soil properties, growth and yield components

The wastewater treatment and sludge production sectors in Morocco are recent. Considered as waste, no management strategy for sewage sludge (SS) has been implemented. Thus, its disposal definitely represents a major environmental problem since sludge is either incinerated, used as landfill or simply deposited near wastewater treatment plants. The objective of this study was to determine the effects of dehydrated SS on certain soil properties (pH, electrical conductivity (EC), Mineral nitrogen, available phosphate P₂O₅, and soluble potassium K₂O), and also on growth and yield components of the sunflower (Helianthus annuus L.). An experiment was conducted using six treatment rates (0; 0 + NPK; 15; 30; 60 and 120 t ha^-1). The results showed that soil pH was significantly affected by SS, becoming less alkaline compared to the control, while electrical conductivity increased significantly when the applied doses were above 30 t ha^-1. Also, a significant enrichment in mineral N and available phosphorus was detected in amended soil. However, no differences were found between pots having received the mineral fertilization and the SS at 15 t ha^-1. Stem height growth of the sunflower seedlings receiving SS increased significantly compared to the two controls. For both the aerial and root parts, significant increases in dry biomass accumulation were observed compared to the unamended plants. Net CO₂ assimilation (A_n) increased, while stomatal conductance (g_sw) and transpiration rates (T_r) decreased with increasing SS rates. SS application at 15 t ha^-1 presented similar values of the yield components compared to plants fertilized chemically. However, grain yield (in quintals ha^-1) was noted to be 2.4, 5 and 8 times higher in treatments receiving SS respectively at the rate of 30, 60 and 120 t ha^-1.

Morphological and functional responses of a metal-tolerant sunflower mutant line to a copper-contaminated soil series

The potential use of a metal-tolerant sunflower mutant line for biomonitoring Cu phytoavailability, Cu-induced soil phytotoxicity, and Cu phytoextraction was assessed on a Cu-contaminated soil series (13-1020 mg Cu kg^-1) obtained by fading a sandy topsoil from a wood preservation site with a similar uncontaminated soil. Morphological and functional plant responses as well as shoot, leaf, and root ionomes were measured after a 1-month pot experiment. Hypocotyl length, shoot and root dry weight (DW) yields, and leaf area gradually decreased as soil Cu exposure rose. Their dose-response curves (DRC) plotted against indicators of Cu exposure were generally well fitted by sigmoidal curves. The half-maximal effective concentration (EC₅₀) of morphological parameters ranged between 203 and 333 mg Cu kg^-1 soil, corresponding to 290-430 μg Cu L^-1 in the soil pore water, and 20 ± 5 mg Cu kg^-1 DW in the shoots. The EC₁₀ for shoot Cu concentration (13-15 mg Cu kg^-1 DW) coincided to 166 mg Cu kg^-1 soil. Total chlorophyll content and total antioxidant capacity (TAC) were early biomarkers (EC₁₀: 23 and 51 mg Cu kg^-1 soil). Their DRC displayed a biphasic response. Photosynthetic pigment contents, e.g., carotenoids, correlated with TAC. Ionome was changed in Cu-stressed roots, shoots, and leaves. Shoot Cu removal peaked roughly at 280 μg Cu L^-1 in the soil pore water.

Potential impacts of climate change and adaptation strategies for sunflower in Pakistan

Growth, development, and economic yield of agricultural crops rely on moisture, temperature, light, and carbon dioxide concentration. However, the amount of these parameters is varying with time due to climate change. Climate change is factual and ongoing so, first principle of agronomy should be to identify climate change potential impacts and adaptation measures to manage the susceptibilities of agricultural sector. Crop models have ability to predict the crop's yield under changing climatic conditions. We used OILCROP-SUN model to simulate the influence of elevated temperature and CO₂ on crop growth duration, maximum leaf area index (LAI), total dry matter (TDM), and achene yield of sunflower under semi-arid conditions of Pakistan (Faisalabad, Punjab). The model was calibrated and validated with the experimental data of 2012 and 2013, respectively. The simulation results showed that phenological events of sunflower were not changed at higher concentration of CO₂ (430 and 550 ppm). However LAI, achene yield, and TDM increased by 0.24, 2.41, and 4.67% at 430 ppm and by 0.48, 3.09, and 9.87% at 550 ppm, respectively. Increased temperature (1 and 2 °C) reduced the sunflower duration to remain green that finally led to less LAI, achene yield, and TDM as compared to present conditions. However, the drastic effects of increased temperature on sunflower were reduced to some extent at 550 ppm CO₂ concentration. Evaluation of different adaptation options revealed that 21 days earlier (as compared to current sowing date) planting of sunflower crop with increased plant population (83,333 plants ha^-1) could reduce the yield losses due to climate change. Flowering is the most critical stage of sunflower to water scarcity. We recommended skipping second irrigation or 10% (337.5 mm) less irrigation water application to conserve moisture under possible water scarce conditions of 2025 and 2050.

Genetic Architecture of Capitate Glandular Trichome Density in Florets of Domesticated Sunflower (Helianthus annuus L.)

Capitate glandular trichomes (CGT), one type of glandular trichomes, are most common in Asteraceae species. CGT can produce various secondary metabolites such as sesquiterpene lactones (STLs) and provide durable resistance to insect pests. In sunflower, CGT-based host resistance is effective to combat the specialist pest, sunflower moth. However, the genetic basis of CGT density is not well understood in sunflower. In this study, we identified two major QTL controlling CGT density in sunflower florets by using a F₄ mapping population derived from the cross HA 300 × RHA 464 with a genetic linkage map constructed from genotyping-by-sequencing data and composed of 2121 SNP markers. One major QTL is located on chromosome 5, which explained 11.61% of the observed phenotypic variation, and the second QTL is located on chromosome 6, which explained 14.06% of the observed phenotypic variation. The QTL effects and the association between CGT density and QTL support interval were confirmed in a validation population which included 39 sunflower inbred lines with diverse genetic backgrounds. We also identified two strong candidate genes in the QTL support intervals, and the functions of their orthologs in other plant species suggested their potential roles in regulating capitate glandular trichome density in sunflower. Our results provide valuable information to sunflower breeding community for developing host resistance to sunflower insect pests.

Drought-induced embolism in stems of sunflower: A comparison of in vivo micro-CT observations and destructive hydraulic measurements

Vulnerability curves (VCs) are a useful tool to investigate the susceptibility of plants to drought-induced hydraulic failure, and several experimental techniques have been used for their measurement. The validity of the bench dehydration method coupled to hydraulic measurements, considered as a 'golden standard', has been recently questioned calling for its validation with non-destructive methods. We compared the VCs of a herbaceous crop plant (Helianthus annuus) obtained during whole-plant dehydration followed by i) hydraulic flow measurements in stem segments (classical destructive method) or by ii) in vivo micro-CT observations of stem xylem conduits in intact plants. The interpolated P₅₀ values (xylem water potential inducing 50% loss of hydraulic conductance) were -1.74 MPa and -0.87 MPa for the hydraulic and the micro-CT VC, respectively. Interpolated P₂₀ values were similar, while P₅₀ and P₈₀ were significantly different, as evidenced by non-overlapping 95% confidence intervals. Our results did not support the tension-cutting artefact, as no overestimation of vulnerability was observed when comparing the hydraulic VC to that obtained with in vivo imaging. After one scan, 25% of plants showed signs of x-ray induced damage, while three successive scans caused the formation of a circular brownish scar in all tested plants. Our results support the validity of hydraulic measurements of samples excised under tension provided standard sampling and handling protocols are followed, but also show that caution is needed when investigating vital plant processes with x-ray imaging.

Effects of supplement with sanitary landfill leachate in gas exchange of sunflower (Helianthus annuus L.) seedlings under drought stress

Sanitary landfill leachate is one of the major problems arising from disposal of urban waste. Sanitary landfill leachate may, however, have use in agriculture. This study, therefore, aimed to analyze initial plant growth and gas exchange in sunflower seedlings supplemented with sanitary landfill leachate and subjected to drought stress through variables of root fresh mass (RFM), shoot fresh mass (SFM), total fresh mass (TFM), relative chlorophyll content (CL), stomatal conductance (g _s ), transpiration rate (E), net photosynthetic rate (A), ratio of internal to external CO₂ concentration (Ci/Ca),water use efficiency (EUA), instantaneous carboxylation efficiency (A/Ci), and electron transport rate (ETR). The experimental design was a completely randomized 2 (irrigated and non-irrigated) × 4 (sand, sand + 100 kg N ha^-1 organic fertilizer, sand + 100 kg N ha^-1 sanitary landfill leachate, and sand + 150 kg N ha^-1 sanitary landfill leachate) factorial with five replicates. Under drought stress conditions, leachate treatment supplemented with 100 kg N ha^-1 exhibited higher plant fresh weights than those of the treatment containing 150 kg N ha^-1. Increases in fresh mass in plant treatments supplemented with 100 and 150 kg N ha^-1 sanitary landfill leachate were related to higher photosynthetic rates.

The effectiveness and efficiency of phytoremediation of a multicontaminated industrial site: Porto Marghera (Venice Lagoon, Italy)

The Venice Lagoon is worldwide considered as a typical example of the human impact on the surrounding ecosystem. The development of the industrial zone of Porto Marghera begun in 1917 as an extension of the Venice Port, in order to sustain activities related to oil and coal, as well as to exploit the railway system. Despite the recent decrease in the number of employees, Porto Marghera is still one of the most important chemical districts in Italy. This study reports early results from the ongoing in-situ phytoextraction of potentially toxic elements (Cd, Hg, Zn) within the industrial area of Porto Marghera. Two agronomic plant species with high annual biomass yield (Helianthus annuus L., Brassica juncea (L.) Czern.) were used. This paper also reports the microcosms and mesocosms tests to evaluate the efficacy of the treatments to be applied to the in-situ phytoextraction process of the polluted site. The combined use of EDTA and Ammonium Thiosulfate during phytoextraction increases the efficiency of Cd, Hg, Zn removal from contaminated soil.

Integration of transcriptomic and metabolic data reveals hub transcription factors involved in drought stress response in sunflower (Helianthus annuus L.)

By integration of transcriptional and metabolic profiles we identified pathways and hubs transcription factors regulated during drought conditions in sunflower, useful for applications in molecular and/or biotechnological breeding. Drought is one of the most important environmental stresses that effects crop productivity in many agricultural regions. Sunflower is tolerant to drought conditions but the mechanisms involved in this tolerance remain unclear at the molecular level. The aim of this study was to characterize and integrate transcriptional and metabolic pathways related to drought stress in sunflower plants, by using a system biology approach. Our results showed a delay in plant senescence with an increase in the expression level of photosynthesis related genes as well as higher levels of sugars, osmoprotectant amino acids and ionic nutrients under drought conditions. In addition, we identified transcription factors that were upregulated during drought conditions and that may act as hubs in the transcriptional network. Many of these transcription factors belong to families implicated in the drought response in model species. The integration of transcriptomic and metabolomic data in this study, together with physiological measurements, has improved our understanding of the biological responses during droughts and contributes to elucidate the molecular mechanisms involved under this environmental condition. These findings will provide useful biotechnological tools to improve stress tolerance while maintaining crop yield under restricted water availability.

Use of Blue-Green Fluorescence and Thermal Imaging in the Early Detection of Sunflower Infection by the Root Parasitic Weed Orobanche cumana Wallr

Although the impact of Orobanche cumana Wallr. on sunflower (Helianthus annuus L.) becomes evident with emergence of broomrape shoots aboveground, infection occurs early after sowing, the host physiology being altered during underground parasite stages. Genetic resistance is the most effective control method and one of the main goals of sunflower breeding programmes. Blue-green fluorescence (BGF) and thermal imaging allow non-destructive monitoring of plant diseases, since they are sensitive to physiological disorders in plants. We analyzed the BGF emission by leaves of healthy sunflower plantlets, and we implemented BGF and thermal imaging in the detection of the infection by O. cumana during underground parasite development. Increases in BGF emission were observed in leaf pairs of healthy sunflowers during their development. Lower BGF was consistently detected in parasitized plants throughout leaf expansion and low pigment concentration was detected at final time, supporting the interpretation of a decrease in secondary metabolites upon infection. Parasite-induced stomatal closure and transpiration reduction were suggested by warmer leaves of inoculated sunflowers throughout the experiment. BGF imaging and thermography could be implemented for fast screening of sunflower breeding material. Both techniques are valuable approaches to assess the processes by which O. cumana alters physiology (secondary metabolism and photosynthesis) of sunflower.

Regulation of reserve mobilisation in sunflower during late seedling establishment in continuous darkness

Reserve mobilisation, metabolite partitioning and reserve-degrading enzyme activity were studied in sunflower seedlings cultivated in vitro under a 12-h photoperiod or in the dark to investigate the involvement of source-sink relation and carbon starvation in the regulation of reserve mobilisation under continuous darkness. Reserves, metabolites and enzyme activity were determined with standard spectrophotometric methods. At the first 24 h of treatment (acclimation phase), darkness did not affect growth, but restricted carbon and nitrogen use, as indicated by sugar and amino acid accumulation in the different seedling parts. After 5 days of treatment (survival phase), extended darkness limited growth and retarded storage lipid mobilisation due to carbon starvation, as evidenced by the depletion of carbohydrates in cotyledons and hypocotyl, as well as the consumption of amino acids in hypocotyls and roots. Alterations in the source-sink relationship might have been a response to prolonged darkness, instead of a mechanism used to regulate reserve mobilisation, as these alterations cannot be associated with negative feedback mediated by metabolite accumulation. Storage lipid degradation depends, at least in part, on mechanisms that co-ordinately regulate the activities of lipases and isocitrate lyase. Taking these results together, it is possible that reserve mobilisation in sunflower seedlings cultivated in the dark might be regulated by mechanisms that perceive the absence of light and predict carbon starvation, adjusting reserve use according to future energy demands to allow, at least in the short term, seedling survival.

In vitro mutagenicity assay (Ames test) and phytochemical characterization of seeds oil of Helianthus annuus Linné (sunflower)

The objective of this research was to investigate the genotoxic potential of the oil of H. annuus L. (sunflower) seeds via the Ames test as well as its oxidative properties and lipid composition. The pre-incubation method, system metabolic activation (S9 fraction) and five S. typhimurium strains (TA97, TA98, TA100, TA1535 and TA102) were employed for the Ames test. The oxidative stability and fatty acid composition were analyzed by standard methods and gas chromatography. A revertant analysis showed no significant differences between the treatment doses (10–200 μl/plate) and the negative controls, regardless of S9⁺ and S9⁻, and included all of the S. typhimurium strains. Chromatographic analysis showed high levels of polyunsaturated fatty acids, followed by monounsaturated, saturated and total trans-isomers. Among the polyunsaturated, monounsaturated and saturated fatty acids, linoleic, oleic and palmitic acids predominated. The results suggest that the sunflower oil is not genotoxic as indicated by frameshift mutations and base pair substitutions regardless of the treatment dose, but shows dose-dependent toxicity. The oxidative properties of the sunflower oil were consistent with the requirements of national and international standards. However, its composition could also indicate phytotherapeutic properties.

Identification and characterization of contrasting sunflower genotypes to early leaf senescence process combining molecular and physiological studies (Helianthus annuus L.)

Leaf senescence is a complex mechanism ruled by multiple genetic and environmental variables that affect crop yields. It is the last stage in leaf development, is characterized by an active decline in photosynthetic rate, nutrients recycling and cell death. The aim of this work was to identify contrasting sunflower inbred lines differing in leaf senescence and to deepen the study of this process in sunflower. Ten sunflower genotypes, previously selected by physiological analysis from 150 inbred genotypes, were evaluated under field conditions through physiological, cytological and molecular analysis. The physiological measurement allowed the identification of two contrasting senescence inbred lines, R453 and B481-6, with an increase in yield in the senescence delayed genotype. These findings were confirmed by cytological and molecular analysis using TUNEL, genomic DNA gel electrophoresis, flow sorting and gene expression analysis by qPCR. These results allowed the selection of the two most promising contrasting genotypes, which enables future studies and the identification of new biomarkers associated to early senescence in sunflower. In addition, they allowed the tuning of cytological techniques for a non-model species and its integration with molecular variables.

Differential hormonal and gene expression dynamics in two inbred sunflower lines with contrasting dormancy level

Seed germination and dormancy are tightly regulated by hormone metabolism and signaling pathway. We investigated the endogenous content of abscisic acid (ABA), its catabolites, and gibberellins (GAs), as well as the expression level of certain ABA and GAs metabolic and signaling genes in embryo of dry and imbibed cypselas of inbred sunflower (Helianthus annuus L., Asteraceae) lines: B123 (dormant) and B91 (non-dormant). Under our experimental conditions, the expression of RGL2 gene might be related to the ABA peak in B123 line at 3 h of imbibition. Indeed, RGL2 transcripts are absent in dry and early embedded cypselas of the non-dormant line B91. ABA increase was accompanied by a significant ABA-Glucosyl ester (ABA-GE) and phaseic acid (PA) (two ABA catabolites) decrease in B123 line (3 h) which indicates that ABA metabolism seems to be more active in this line, and that it would be involved in the imposition and maintenance of sunflower seed dormancy, as it has been reported for many species. Finally, an increase of bioactive GAs (GA1 and GA3) occurs at 12 h of imbibition in both lines after a decrease in ABA content. This study shows the first report about the RGL2 tissue-specific gene expression in sunflower inbred lines with contrasting dormancy level. Furthermore, our results provide evidence that ABA and GAs content and differential expression of metabolism and signaling genes would be interacting in seed dormancy regulation through a mechanism of action related to embryo itself.

Fluorescence Imaging in the Red and Far-Red Region during Growth of Sunflower Plantlets. Diagnosis of the Early Infection by the Parasite Orobanche cumana

Broomrape, caused by the root holoparasite Orobanche cumana, is the main biotic constraint to sunflower oil production worldwide. By the time broomrape emerges, most of the metabolic imbalance has been produced by O. cumana to sunflower plants. UV-induced multicolor fluorescence imaging (MCFI) provides information on the fluorescence emitted by chlorophyll (Chl) a of plants in the spectral bands with peaks near 680 nm (red, F680) and 740 nm (far-red, F740). In this work MCFI was extensively applied to sunflowers, either healthy or parasitized plants, for the first time. The distribution of red and far-red fluorescence was analyzed in healthy sunflower grown in pots under greenhouse conditions. Fluorescence patterns were analyzed across the leaf surface and throughout the plant by comparing the first four leaf pairs (LPs) between the second and fifth week of growth. Similar fluorescence patterns, with a delay of 3 or 4 days between them, were obtained for LPs of healthy sunflower, showing that red and far-red fluorescence varied with the developmental stage of the leaf. The use of F680 and F740 as indicators of sunflower infection by O. cumana during underground development stages of the parasite was also evaluated under similar experimental conditions. Early increases in F680 and F740 as well as decreases in F680/F740 were detected upon infection by O. cumana. Significant differences between inoculated and control plants depended on the LP that was considered at any time. Measurements of Chl contents and final total Chl content supported the results of MCFI, but they were less sensitive in differentiating healthy from inoculated plants. Sunflower infection was confirmed by the presence of broomrape nodules in the roots at the end of the experiment. The potential of MCFI in the red and far-red region for an early detection of O. cumana infection in sunflower was revealed. This technique might have a particular interest for early phenotyping in sunflower breeding programs. To our knowledge, this is the first work where the effect of a parasitic plant in its host is analyzed by means of fluorescence imaging in the red and far-red spectral regions.

Exogenous malic and acetic acids reduce cadmium phytotoxicity and enhance cadmium accumulation in roots of sunflower plants

There is increasing evidence showing that low molecular weight organic acids (LMWOA) are involved in heavy metal resistance mechanisms in plants. The aim of this study was to investigate the effects of exogenous malic (MA) or acetic (AA) acids on the toxicity and accumulation of cadmium (Cd) in sunflower (Helianthus annuus L.). For this purpose, plants were grown in hydroponics under controlled conditions. Single Cd stress (5 μM Cd for 14 days) induced strong phytotoxic effects, as indicated by a decrease in all growth parameters, concentration of photosynthetic pigments, and root activity, as well as a high level of hydrogen peroxide (H2O2) accumulation. Exogenous MA or AA (250 or 500 μM) applied to the Cd-containing medium enhanced the accumulation of Cd by the roots and limited Cd translocation to the shoots. Moreover, the MA or AA applied more or less reduced Cd phytotoxicity by increasing the growth parameters, photosynthetic pigment concentrations, decreasing accumulation of H2O2, and improving the root activity. Of the studied organic acids, MA was much more efficient in mitigation of Cd toxicity than AA, probably by its antioxidant effects, which were stronger than those of AA. Plant response to Cd involved decreased production of endogenous LMWOA, probably as a consequence of severe Cd toxicity. The addition of MA or AA to the medium increased endogenous accumulation of LMWOA, especially in the roots, which could be beneficial for plant metabolism. These results imply that especially MA may be involved in the processes of Cd uptake, translocation, and tolerance in plants.

Isolation of Bioactive Compounds from Sunflower Leaves (Helianthus annuus L.) Extracted with Supercritical Carbon Dioxide

The work described herein is a continuation of our initial studies on the supercritical fluid extraction (SFE) with CO2 of bioactive substances from Helianthus annuus L. var. Arianna. The selected SFE extract showed high activity in the wheat coleoptile bioassay, in Petri dish phytotoxicity bioassays, and in the hydroponic culture of tomato seeds. Chromatographic fractionations of the extracts and a spectroscopic analysis of the isolated compounds showed 52 substances belonging to 10 different chemical classes, which were mainly sesquiterpene lactones, diterpenes, and flavonoids. Heliannuol M (31), helivypolides K and L (36, 37), and helieudesmanolide B (38) are described for the first time in the literature. Metabolites have been tested in the etiolated wheat coleoptile bioassay with good results in a noteworthy effect on germination. The most active compounds were also tested on tomato seeds, heliannuol A (30) and leptocarpin (45) being the most active, with values similar to those of the commercial herbicide.

Plasticity in sunflower leaf and cell growth under high salinity

A group of sunflower lines that exhibit a range of leaf Na(+) concentrations under high salinity was used to explore whether the responses to the osmotic and ionic components of salinity can be distinguished in leaf expansion kinetics analysis. It was expected that at the initial stages of the salt treatment, leaf expansion kinetics changes would be dominated by responses to the osmotic component of salinity, and that later on, ion inclusion would impose further kinetics changes. It was also expected that differential leaf Na(+) accumulation would be reflected in specific changes in cell division and expansion rates. Plants of four sunflower lines were gradually treated with a relatively high (130 mm NaCl) salt treatment. Leaf expansion kinetics curves were compared in leaves that were formed before, during and after the initiation of the salt treatment. Leaf areas were smaller in salt-treated plants, but the analysis of growth curves did not reveal differences that could be attributed to differential Na(+) accumulation, since similar changes in leaf expansion kinetics were observed in lines with different magnitudes of salt accumulation. Nevertheless, in a high leaf Na(+) -including line, cell divisions were affected earlier, resulting in leaves with proportionally fewer cells than in a Na(+) -excluding line. A distinct change in leaf epidermal pavement shape caused by salinity is reported for the first time. Mature pavement cells in leaves of control plants exhibited typical lobed, jigsaw-puzzle shape, whereas in treated plants, they tended to retain closer-to-circular shapes and a lower number of lobes.

Precision phenotyping of imidazolinone-induced chlorosis in sunflower

Chlorosis level is a useful parameter to assess imidazolinone resistance in sunflower (Helianthus annuus L.). The aim of this study was to quantify chlorosis through two different methods in sunflower plantlets treated with imazapyr. The genotypes used in this study were two inbred lines reported to be different in their resistance to imidazolinones. Chlorosis was evaluated by spectrophotometrical quantification of photosynthetic leaf pigments and by a bioinformatics-based color analysis. A protocol for pigment extraction was presented which improved pigment stability. Chlorophyll amount decreased significantly when both genotypes were treated with 10 μM of imazapyr. Leaf color was characterized using Tomato Analyzer(®) color test software. A significant positive correlation between color reduction and chlorophyll concentration was found. It suggests that leaf color measurement could be an accurate method to estimate chlorosis and infer chlorophyll levels in sunflower plants. These results highlight a strong relationship between imidazolinone-induced chlorosis and variations in leaf color and in chlorophyll concentration. Both methods are quantitative, rapid, simple, and reproducible. Thus, they could be useful tools for phenotyping and screening large number of plants when breeding for imidazolinone resistance in this species.

Acetohydroxyacid synthase activity and transcripts profiling reveal tissue-specific regulation of ahas genes in sunflower

Acetohydroxyacid synthase (AHAS) is the target site of several herbicides and catalyses the first step in the biosynthesis of branched chain amino acid. Three genes coding for AHAS catalytic subunit (ahas1, ahas2 and ahas3) have been reported for sunflower. The aim of this work was to study the expression pattern of ahas genes family and AHAS activity in sunflower (Helianthus annuus L.). Different organs (leaves, hypocotyls, roots, flowers and embryos) were evaluated at several developmental stages. The transcriptional profile was studied through RT-qPCR. The highest expression for ahas1 was shown in leaves, where all the induced and natural gene mutations conferring herbicide resistance were found. The maximal expression of ahas2 and ahas3 occurred in immature flowers and embryos. The highest AHAS activity was found in leaves and immature embryos. Correlation analysis among ahas gene expression and AHAS activity was discussed. Our results show that differences in ahas genes expression are tissue-specific and temporally regulated. Moreover, the conservation of multiple AHAS isoforms in sunflower seems to result from different expression requirements controlled by tissue-specific regulatory mechanisms at different developmental stages.

A biomarker based on gene expression indicates plant water status in controlled and natural environments

Plant or soil water status is required in many scientific fields to understand plant responses to drought. Because the transcriptomic response to abiotic conditions, such as water deficit, reflects plant water status, genomic tools could be used to develop a new type of molecular biomarker. Using the sunflower (Helianthus annuus L.) as a model species to study the transcriptomic response to water deficit both in greenhouse and field conditions, we specifically identified three genes that showed an expression pattern highly correlated to plant water status as estimated by the pre-dawn leaf water potential, fraction of transpirable soil water, soil water content or fraction of total soil water in controlled conditions. We developed a generalized linear model to estimate these classical water status indicators from the expression levels of the three selected genes under controlled conditions. This estimation was independent of the four tested genotypes and the stage (pre- or post-flowering) of the plant. We further validated this gene expression biomarker under field conditions for four genotypes in three different trials, over a large range of water status, and we were able to correct their expression values for a large diurnal sampling period.

Proteolytic system in sunflower (Helianthus annuus L.) leaves under cadmium stress

The effect of oxidative stress induced by cadmium on growth parameters and on the balance between protein synthesis and degradation was studied in sunflower (Helianthus annuus L.) leaves. Plants were germinated for 10 days and then transferred to hydroponic medium devoid (control) or containing 100, 200 and 300μM CdCl2. Analyses were performed between days 0 and 4 of Cd-treatment. All Cd(2+) concentrations significantly reduced leaf area and, fresh and dry weight, but leaf relative water content only decreased with 200 and 300μM Cd(2+). Control and treated plants had similar soluble protein content and showed the same rate of soluble protein labeling under the assay conditions. Although protease activity increased with cadmium treatment, proteasome activity was significantly inhibited. Expression of 20S proteasome remained similar to controls in cadmium treated plants. Cadmium caused an increase in ubiquitin-conjugated proteins and carbonyl groups content of treated plants, compared to control values. Cadmium induced an increase in protease specific activity; nevertheless, this increase was not relevant enough to avoid accumulation of oxidized proteins. Oxidation of proteins is one of the most important effects of cadmium treatment. The results presented here provide evidence for the role of the proteolytic system in sunflower plants subjected to cadmium stress.

Shade-Induced Action Potentials in Helianthus annuus L. Originate Primarily from the Epicotyl

Repeated observations that shading (a drastic reduction in illumination rate) increased the generation of spikes (rapidly reversed depolarizations) in leaves and stems of many cucumber and sunflower plants suggests a phenomenon widespread among plant organs and species. Although shaded leaves occasionally generate spikes and have been suggested to trigger systemic action potentials (APs) in sunflower stems, we never found leaf-generated spikes to propagate out of the leaf and into the stem. On the contrary, our data consistently implicate the epicotyl as the location where most spikes and APs (propagating spikes) originate. Microelectrode studies of light and shading responses in mesophyll cells of leaf strips and in epidermis/cortex cells of epicotyl segments confirm this conclusion and show that spike induction is not confined to intact plants. 90% of the epicotyl-generated APs undergo basipetal propagation to the lower epicotyl, hypocotyl and root. They propagate with an average rate of 2 +/- 0.3 mm s(-1) and always undergo a large decrement from the hypocotyl to the root. The few epicotyl-derived APs that can be tracked to leaf blades (< 10%) undergo either a large decrement or fail to be transmitted at all. Occasionally (5% of the observations) spikes were be generated in hypocotyl and lower epicotyl that moved towards the upper epicotyl unaltered, decremented, or amplified. This study confirms that plant APs arise to natural, nontraumatic changes. In simultaneous recordings with epicotyl growth, AP generation was found to parallel the acceleration of stem growth under shade. The possible relatedness of both processes must be further investigated.