Hill Reaction Research Articles

Arbuscular Mycorrhiza Improves Photosynthesis and Restores Alteration in Sugar Metabolism in Triticum aestivum L. Grown in Arsenic Contaminated Soil.

Contamination of agricultural soil by arsenic (As) is a serious menace to environmental safety and global food security. Symbiotic plant–microbe interaction, such as arbuscular mycorrhiza (AM), is a promising approach to minimize hazards of As contamination in agricultural soil. Even though the potential of AM fungi (AMF) in redeeming As tolerance and improving growth is well recognized, the detailed metabolic and physiological mechanisms behind such beneficial effects are far from being completely unraveled. The present study investigated the ability of an AM fungus, Rhizophagus intraradices, in mitigating As-mediated negative effects on photosynthesis and sugar metabolism in wheat (Triticum aestivum) subjected to three levels of As, viz., 0, 25, and 50 mg As kg–1 of soil, supplied as sodium arsenate. As exposure caused significant decrease in photosynthetic pigments, Hill reaction activity, and gas exchange parameters such as net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration. In addition, As exposure also altered the activities of starch-hydrolyzing, sucrose-synthesizing, and sucrose-degrading enzymes in leaves. Colonization by R. intraradices not only promoted plant growth but also restored As-mediated impairments in plant physiology. The symbiosis augmented the concentration of photosynthetic pigments, enhanced Hill reaction activity, and improved leaf gas exchange parameters and water use efficiency of T. aestivum even at high dose of 50 mg As kg–1 of soil. Furthermore, inoculation with R. intraradices also restored As-mediated alteration in sugar metabolism by modulating the activities of starch phosphorylase, α-amylase, β-amylase, acid invertase, sucrose synthase, and sucrose-phosphate synthase in leaves. This ensured improved sugar and starch levels in mycorrhizal plants. Overall, the study advocates the potential of R. intraradices in bio-amelioration of As-induced physiological disturbances in wheat plant.

The toxicological mechanism of two typical imidazole ionic liquids in textile industry on Isatis tinctoria

Ionic liquids (ILs1) which are called “green solvents”, are used widely in the textile industry as adjuvants due to their many advantages. However, their persistent residues may cause ecotoxicity. The aim of the study is to explore the toxicity of different anions on imidazole ILs and their toxicological mechanism. For the experiments 1-butyl-3-methylimidazole tetrafloroborate ([C4mim]BF4) and 1- butyl -3-methylimidazolium chloride ([C4mim]Cl) were selected to study their toxic effects on Isatis tinctoria. ILs may affect the germination rate. Fresh weight, dry weight and Hill reaction activity decreased continuously with increasing of IL concentrations, showing an effect-dose relationship. Transmission electron microscopy (TEM) revealed that cell walls were fuzzy, starch granules had accumulated and the chloroplast structure was damaged. These changes will affected the function and electron transport efficiency of photosystemⅡ. Superoxide anion accumulation stimulated the activity of antioxidant enzymes (SOD, POD, CAT) and caused lipid peroxidation as well as an increased malondialdehyde content. ILs also reduced indirubin and total flavonoids contents, which reduced the pharmacological efficacy of Isatis tinctoria. This is demonstrated by three-dimensional fluorescence chromatogram. [C4mim]Cl was more toxic than [C4mim]BF4. ILs caused toxic effects to Isatis tinctoria. The ecological toxicity of ILs should be considered when using them as additives in the textile industry.

Effects of Acetogenins from Annona coriacea on the in Vitro Reactions of Photosynthesis.

Our search for candidates for photosynthesis inhibitors is allowing us to report the effect of two acetogenins identified in Annona coriacea Mart. leaves, ACG-A and ACG-B, a non-adjacent bis-THF and a mono-THF types, respectively. This is an important class of natural products which presents biological properties such as anticancer, neurotoxic, larvicidal and insecticidal. However, this is only the second report associated to its herbicidal activity. Their mechanisms of action on the light reactions of the photosynthesis were elucidated by polarographic techniques. Compounds inhibited the noncyclic electron transport on basal, phosphorylating, and uncoupled conditions from H2 O to methyl viologen (MV); therefore, they act as Hill reaction inhibitors. Studies on fluorescence of chlorophyll a (ChL a) indicated that they inhibited the acceptor side of PSII between P680 and PQ-pool, exactly as the commercial herbicide DCMU does.

Analog Electronic Circuits to Model Cooperativity in Hill Process

In the field of computational biology, electronic modeling of bio-cellular processes is in vogue for about a couple of decades. Fast, efficient and scalable electronic mimetics of recurrently found bio-chemical reactions are expected to provide better electronic circuit simulators that can also be used as bio-sensors or implantable biodevices at cellular levels. This paper presents some possible electronic circuit equivalents to model dynamics of one such bio-chemical reaction commonly involved in many bio-cellular processes, specifically pathways in living cells, known as the Hill process. The distinguishing feature of this process is cooperativity which has been modeled in silicon substrate using a pair of transistors, one transistor driving current in the other the same way ligand binding to one receptor site controls the binding affinity of the other receptor sites. Two possible circuits have been proposed and compared to electronically model cooperativity of a Hill reaction. The main idea is to exploit the natural analogies found between structures and processes of a bio-cell and electronic transistor mechanics, to efficiently model fundamental bio-chemical reactions found recurring in bio-processes. These circuits can then be combined and rearranged quickly to form larger, more complex bio-networks, thus mitigating the intricacies involved in modeling of such systems.

The Functional State of the Photosynthetic Apparatus of Potato Plants upon Destruction of the Tubulin Cytoskeleton

We have investigated the effect of colchicine, a disrupting agent of the tubulin cytoskeleton, on chlorophyll fluorescence parameters, the Hill reaction, noncyclic photophosphorylation, and the lipid peroxidation reaction in Solanum tuberosum grown in soil in a greenhouse environment. The destruction of microtubules caused an increase in the content of lipid fatty acid hydroperoxides, the primary product of lipid peroxidation, and led to changes in fluorescence parameters: F0 increased, Fm and the maximum quantum efficiency of PSII (Fv/Fm) decreased, and the dissipation of electronic excitation energy as heat increased. Simultaneously, it was found that the Hill reaction rate and the intensity of the process of noncyclic photophosphorylation decreased. The results obtained in this work are discussed in view of the destruction of the integrity of the chloroplast membrane and changes in chlorophyll fluorescence parameters due to colchicine application, as well as in light of our previously obtained data on the change in the content of phytohormones and their concentration ratios in potato leaves when microtubules are destroyed.

Insight into the interaction between Fe-based nanomaterials and maize (Zea mays) plants at metabolic level

Properly understanding the fundamental interactions between engineered nanoparticles (NPs) and plants is crucial for nano-enabled agriculture. In this study, Fe and Fe3O4 (magnetite), which are naturally occurred nanosized crystals and minerals, were foliar applied to 4-week-old maize plants for 10 days to evaluate their impact on plant photosynthesis and growth. Hill reaction of isolated maize leaf chloroplasts was carried out to determine the performance of two Fe-based NPs on photosynthetic activities at cell level. Meanwhile, gas chromatography–mass spectrometry (GC–MS) based metabolomics was used to explore the deep insight into the interaction between Fe-based NPs and maize plants. Results showed that maize leaf net photosynthesis rate and chlorophyll content were significantly increased by Fe NPs for 19.9% and 19.3%; and Fe3O4 NPs for 27.5% and 26.1%, respectively. Accordingly, plant biomass has been significantly increased by Fe and Fe3O4 NPs by 31.8% and 34.6%, respectively. Metabolomics revealed that both Fe-based NPs induced metabolic reprogramming in maize leaves. The biosynthesis of some compatible solutes and antioxidant compounds were inhibited. In addition, exposure to Fe-based NPs tentatively shut down some energy consuming pathways, such as photorespiration, alanine metabolism, branch chain amino acid biosynthesis. The trade-off of energy consuming pathways might be alternative explanation for the enhanced photosynthesis. The results of this study exhibited the promising potential for Fe-based NPs to be used in nano-enabled agriculture to promote plant growth.

Nitrogen alleviates NaCl toxicity in maize seedlings by regulating photosynthetic activity and ROS homeostasis

Seven-day-old maize seedlings were subjected to NaCl (150 mM) without or with the presence of equimolar concentrations of urea, potassium nitrate or ammonium sulfate (at 60 kg N ha−1) for the subsequent 15 days. The results show that NaCl significantly decreased photosynthetic activity parameters (Hill reaction, Pn, Ci and Gs), shoot fresh and dry weights, chlorophylls, protein, GSH and AsA. The activities of ALA-D, Rubisco, PEP-C, MDH, PPDK, SOD, CAT and APX were significantly inhibited. On the contrary, NaCl significantly elevated MDA, O 2 ∙− , H2O2, soluble sugars and proline. The application of the nitrogenous sources mostly ameliorated the photosynthetic activity synchronous with counterbalancing the decreases in growth, protein and pigments. The activities of ALA-D, Rubisco, PEP-C, MDH and PPDK enhanced remarkably with N applied under salinity. Furthermore, enhancements were detected in GSH and AsA contents and SOD, CAT and APX activities, which decreased free radicals, soluble sugars and proline. These effects reveal that maize was vulnerable to NaCl stress; however, N overcame the stress status and ameliorated the plant tolerance to salinity concomitant with repairing photosynthetic activity and maintaining higher antioxidants and ROS homeostasis; urea seemed to be the most efficient. Taken together, these findings conclude that N enhanced the capability of maize to tolerate NaCl via protecting photosynthetic apparatus for normal photochemical functioning and improving antioxidants and ROS homeostasis as effective salt tolerance mechanisms.

Tuzluluk Stresi altında Lathyrus sativus L.'nin Çimlenme ve Büyümesini İyileştirmede, Salisilik Asit ile Tohum Priming Uygulaması

Increasing the ability of crops to maintain growth and productivity under saline conditions is of paramount importance. The effect of salicylic acid (SA) priming on germination and physiological traits of Lathyrus sativus under salinity stress was studied in a factorial experiment based on a completely randomized design. The experimental treatments composed of SA at three levels (0, 0.1, and 0.2 mM) and NaCl salinity at three levels (0, 50, and 100 mM). The effect of salinity level and SA priming was significant on all recorded factors, except from final germination percentage. As salinity level increased, all germination and physiological traits declined compared with control, whereas the mean germination time and percentage of cell death were increased. Moreover, as salinity was intensified, the Hill reaction was decreased significantly. Salinity exhibited the strongest effects at NaCl rate of 100 mM. Seed priming with SA increased germination speed index, reduced mean germination time, and increased leaf relative water content, seedling fresh and dry weight compared with plants from non-primed seeds. Seedling vigor index was increased by 23.4% in primed seeds with 0.2 mM SA. SA priming especially at 0.2 mM rate increased the Hill reaction rate and reduced percentage of cell death. SA priming could be regarded as a practical approach to improve germination traits, seedling growth, and physiological traits of Lathyrus sativus L. under salinity stress conditions.

Photochemical activity of chloroplasts of isogenic lines (E genes) of soybean (Glycine max (L.) Merr.) under different periods of red-light irradiation

The effect of different periods of red-light (RL, 660 nm) irradiation of plants on the biomass, leaf area, chlorophyll content, level of the Hill reaction and photophosphorylation in short-day (SD) and photoperiodical neutral (PhPN) lines of soybean have been studied in vegetation experiments. The objects of study were the isogenic lines (E genes) of soybean (Glycine max (L.) Merr.), Clark variety. The SD (E1E2E3) and PhPN lines (e1e2e3) were used. The plants were grown in a vegetation chamber in the soil culture (black soil). Plants of SD and PhPN lines were grown in 9 vessels of three liters volume. 10–12 plants were grown in each vessel. The constant growing conditions were provided during the experiment: temperature – 20–24/17–20°С (day/night), soil moisture – 60–70 % of the total soil moisture content, intensity of illumination – 20 klx, photoperiod duration – 10 hours. After 4–5 weeks of vegetation (after the second true leaf formation), plants of each line in three vessels were irradiated for 30 minutes with low intensity red light at the beginning (experiment 1) or in the middle of the dark period (experiment 2). The light diodes emitting in the region of 630±10 nm were used for plant irradiation. Other plants in three vessels of each line, which were not illuminated by the red light, were used as a control group. It was shown that under the short day the SD line in the control group passed to flowering 43±1.8 days after germination and PhPN line – 44±2.2 days after germination. The red-light irradiation, both before the beginning and in the middle of night, caused a delay of the transition to flowering in the SD line by 5±1 and 7±2.2 days, respectively. In the PhPN line, changing flowering period due to RL was not established. In the SD line, activation of the phytochromes by RL before the dark period caused an increase of the biomass, leaf area, total chlorophyll content, reduction of potassium ferrocyanide and photophosphorylation by isolated chloroplasts per chlorophyll of one leaf. While interruption of the night by RL caused decrease of these parameters and Hill reaction intensity per 1 mg of chlorophyll. The effect of RL on the studied parameters in the PhPN soybean line has not been detected.

Exploring high zinc efficiency physiological traits in rice(Oryza sativa L.) seedlings

The present investigation was undertaken to unfold the physiological traits associated with zinc efficiency in rice. Twelve rice genotypes with diverse inherent zinc content were selected for the study during two consecutive years (2016–2017). Thirty-five days old rice seedlings were examined for the associated physiological attributes. The genotypes PR 113 and PR 121 recorded high dry weight, chlorophyll content, Hill reaction activity, superoxide dismutase activity, total soluble sugars, starch, total soluble proteins, free amino acids which were significantly and positively correlated with zinc uptake. However, genotypes PAU2K10-23-451-21-81-5-0-0 (RYT 3403) and RRHZ1H-7 (RYT Biofort 1) exhibited least of these parameters as compared to the other genotypes. Based upon the study, PR113 and PR121 genotypes were characterized as zinc efficient and PAU2K10-23-451-21-81-5-0-0 and RRHZ1H-7 genotypes as zinc inefficient.

Фотосинтетичні індикатори стану забруднення атмосферного повітря Покутсько-Буковинських Карпат

Досліджено взаємозв'язок стану атмосферного повітря та показників фотосинтетичного апарату представників дендрофлори Покутсько-Буковинських Карпат бука звичайного (Fagus silvatica L.) та тополі пірамідальної (Topulus pyramidalis Moenoh.), що вегетують в умовах різного антропогенного навантаження. Зразки листків відбирали із чотирьох екотопів, що відрізняються рівнем функціонального призначення та забруднення атмосферного повітря. Вивчено вміст хлорофілів та їх співвідношення, а також інтенсивність процесів світлової фази фотосинтезу. Встановлено, що зменшення відносного вмісту хлорофілу "b" в умовах забруднення атмосферного повітря тісно корелює із швидкістю переносу електронів по електрон-транспортному ланцюгу (реакція Хілла). У порівняно чистих, за показниками атмосферного повітря, територіях (заповідній зоні та зоні стаціонарної рекреації національного природного парку) існує тісна позитивна кореляція між вмістом легких негативних аероіонів, нагромадженням зелених пігментів та активністю фотофізичних процесів. Побудовано кореляційну матрицю взаємозалежності показників активності фотосинтетичного апарату рослин та стану атмосферного повітря досліджених територій. Обґрунтовано доцільність використання фотосинтетичних показників дендрофлори заповідної зони об'єктів природоохоронних територій як індикаторів стану екологічної безпеки атмосферного повітря. Результати досліджень опрацьовано статистично.

Synthesis of new tetronamides displaying inhibitory activity against bloom-forming cyanobacteria.

The increasing frequency and intensity of cyanobacterial blooms pose a serious threat to aquatic ecosystems. These blooms produce potent toxins that can contaminate drinking water and endanger the life of wild and domestic animals as well as humans. Consequently, the development of effective methods for their control is a matter of high priority. We have previously shown that some γ-benzylidenebutenolides, related to the rubrolide family of natural products, are capable of inhibiting the photosynthetic electron transport chain (Hill reaction), a target of commercial herbicides. Here we report the synthesis and biological properties of a new class of rubrolide-inspired molecules featuring a tetronamide motif. A total of 47N-aryl tetronamides, including 38 aldol adducts, were prepared bearing phenyl, biphenyl, naphthyl, aliphatic and heteroaromatic groups. Some of the aldol adducts were dehydrated to the corresponding γ-benzylidenetetronamides, although satisfactory yields were obtained in only three cases (52-97%). None of the synthesized compounds were capable of blocking the Hill reaction. This notwithstanding, several aldol adducts equipped with a biphenyl substituent displayed excellent inhibitory activity against Synechococcus elongatus and other cyanobacterial strains (IC50 = 1-5μM). Further, these tetronamides were found to be essentially inactive against eukaryotic microorganisms. Several newly synthesized biphenyl-containing tetronamides were shown to display potent and selective inhibitory activity against cyanobacteria. These compounds appear to exert their biological effects without interfering with the Hill reaction. As such, they represent novel leads in the search of environmentally benign agents for controlling cyanobacterial blooms. © 2019 Society of Chemical Industry.

Effect of the red light on the photosynthesis and phenolic accumulation in leaves of Hedyotis corymbosa (L.) Lam

Hedyotis corymbosa (L.) Lam a native herbaceous species containing many phenolic compounds is used in traditional medicine and medicinal technology. Phenolic acid, as well as many other secondary metabolites are photosynthetic-derived products. In this research, red LEDs (660 nm) and white fluorescent light were used to investigate the effects of different light sources on the photosynthesis and leaf phenolic compound accumulation of in vitro and ex vitro plants. Red LED (50 umol/m2/sec) promoted the stem elongation without changing plant biomass of in vitro plants. Increasing red LED intensities (from 50 to 100 or 150 umol/m2/sec) decrease maximum photochemical quantum yield of PS II (Fv/Fm) and coefficient of photochemical fluorescence quenching (qP), but stabilized electron transfer (ETR) and coefficient of non-photochemical fluorescence quenching (qN) of in vitro leaves. Under 100 umol/m2/sec of red LED, ex vitro leaf area, carotenoid contents, isolated chloroplast. Hill reaction and total sugar content were significantly reduced in comparison to those parameters from control plants under white light. Ex vitro plants' total carbohydrate contents were not statistically different the total leaf phenolic content of ex vitro plants under red LED light exposure was much higher than that the of control.

Impact of short-term exposure to elevated temperatures on physiology of Thai rice (cv. Riceberry)

High temperature is an important limiting factor for the growth and development of rice cultivation worldwide. The current research aimed to investigate the efficiency of PSII system, photosynthetic changes in photosynthetic pigments and membrane stability in Thai seedlings of Thai rice cv. Riceberry after exposure to different temperatures viz., 25, 30, 35, 40, 45, 50 and 55°C for 30 min. The experiment was designed in CRD with four replications. The results showed that the highest Fv/Fm was realized when seedlings were exposed to 30°C and 35°C and decreased when exposed to 40°C for 30 min. The content of photosynthetic pigments such as total chlorophyll (TC) and chlorophyll a (Chl a) were the highest after short-term exposure to a temperature of 25°C. However, the contents of all photosynthetic pigment such as TC, Chl a, Chl b and carotenoids were the lowest when exposed to 55°C for 30 min. The membrane stability of Riceberry seedlings affected on short-term exposure to temperatures of 50°C and 55°C. Thus, Fv/Fm and Hill reaction were the first mechanisms to be significantly affected by the short-term exposure to a temperature of 40°C followed by membrane stability and contents of photosynthetic pigments which were affected by short-term exposure to temperature of 50°C -55°C and 55°C, respectively.

Effects of Some Hill Reaction-Inhibiting Herbicides on Nitrous Oxide Emission from Nitrogen-Input Farming Soil

Nitrous oxide (N2O) emission-suppressing activity of some electron-transport inhibitors of the Hill reaction system was investigated. The Hill reaction inhibitors—paraquat, isouron, bromacil, diquat, and simazine—all of which have been or are currently being used as herbicides in farming activity are expected to inhibit the electron-transporting pathways of nitrate respiration in denitrifying bacteria. Using N2O-emitting soil bed (5.0 g of fresh weight) from a continuously manured Andisol corn farmland in Hokkaido, Japan, which was autoclaved and further supplemented with an active N2O-emitter, Pseudomonas sp. 5CFM15-6D, and 1 mL of 100 mM NH4NO3 or (NH4)2SO4 solution as the sole nitrogen source (final concentration, 0.2 mM) in a 30 mL gas-chromatography vial, the effects of the five herbicides on N2O emission were examined. Paraquat and isouron (each at 50 µM) showed a statistically significant suppression of N2O emission in both the nitrification and the denitrification processes after a 7-day-incubation, whereas diquat at the same concentration accelerated N2O emission in the presence of NO3−. These results suggest that paraquat and isouron inhibited both the nitrification and the denitrification processes for N2O generation, or its upstream stages, whereas diquat specifically inhibited N2O reductase, an enzyme that catalyzes the reduction of N2O to N2 gas. Incomplete denitrifiers are the key players in the potent emission of N2O from Andisol corn farmland soil because of the missing nosZ gene. The electron relay system-inhibiting herbicides—paraquat and isouron—possibly contribute to the prevention of denitrification-induced nitrogen loss from the farming soil.

Interactive Effects of Salinity and ZnO Nanoparticles on Physiological and Molecular Parameters of Rapeseed (Brassica napus L.)

ABSTRACTSalinity is considered as the main factor limiting the yield of crops in arid and semi-arid regions. There are still many uncertainties about the nanotechnology and its potential applications, as well as doubts about its efficacy and safety in the long term. The aim of this study was to examine the alleviative effects of ZnO NPs (nanoparticles) (0, 20 and 80 mgL−1) on toxicity damage caused by NaCl (0, 50 and 100 mM) at physiological and molecular parameters in Rapeseed. Rapeseed plants were treated at the rosette stage by different levels of salinity and ZnO NPs based on a completely randomized design (CRD) with three replications. At the physiological level, salinity stress significantly increased root ion leakage and decreased relative water content (RWC), stomata density and Hill reaction while application of ZnO NPs improved Hill reaction, and reduced ion leakage. At the molecular level, salinity stress significantly reduced the expression of ARP, MYC and SKRD2 genes compared to non-stressed plants while MPK4 gene expression increased under a high level of NaCl imposition. Foliar spraying of ZnO NPs considerably decreased the expression of MYC, MPK4, and SKRD2 genes and increased the expression of the ARP gene. It can be concluded that ZnO NPs had the ability to reduce the toxicity created under salinity stress at the optimal concentration (20 mgL−1) in rapeseed and could play an important role in increasing the resistance of rapeseed plants to salinity stress.

Diclofenac as an environmental threat: Impact on the photosynthetic processes of Lemna minor chloroplasts

Mechanisms of pharmaceuticals action on biochemical and physiological processes in plants that determine plant growth and development are still mostly unknown. This study deals with the effects of non-steroidal anti-inflammatory drug diclofenac (DCF) on photosynthesis as an essential anabolic process. Changes in primary and secondary photosynthetic processes were assessed in chloroplasts isolated from Lemna minor exposed to 1, 10, 100, and 1000 μM DCF. Decreases in the potential and effective quantum yields of photosystem II (FV/FM by 21%, ΦII by 44% compared to control), changes in non-photochemical fluorescence quenching (NPQ), and a substantial drop in Hill reaction activity (by 73%), especially under 1000 μM DCF, were found. Limitation of electron transport through photosystem II was confirmed by increased fluorescence signals in steps J and I (by 50% and 23%, respectively, under 1000 μM DCF) in OJIP fluorescence transient. Photosystem I exhibited changes only in the redox state of P700 reaction centres (decrease in Pm by 10%, increase in reduced P700 by 5% under 1000 μM DCF). Similarly, RuBisCO activity was only lowered by 30% under 1000 μM DCF. In contrast, a significant increase in reactive oxygen and nitrogen species (by 116% and 157%, respectively) was observed under 10 μM DCF, and lipid peroxidation increased even at 1 μM DCF (by nearly seven times compared to the control). Results demonstrate the ability of environmentally relevant DCF concentrations to induce oxidative stress in isolated duckweed chloroplasts; however, photosynthetic processes were affected considerably only by the highest DCF treatments.

Increased ZnO nanoparticle toxicity to wheat upon co-exposure to phenanthrene

Polycyclic aromatic hydrocarbons and zinc oxide nanoparticles are ubiquitous pollutants in the environment. However, little information is available about their toxicity interaction in food crops. In this study, seed germination and hydroponic experiments were conducted to assess the impact of ZnO (NPs and bulk at 250, 500 and 1000 mg L−1) individual and combined with phenanthrene (1 mg L−1) on wheat growth for 15 days. Under ZnO (NPs and bulk) alone and combined with phenanthrene exposure, dose-dependent toxicity in some indexes (germination rate, biomass, shoot height, root length) was observed. Both ZnO NPs and bulk inhibited plant growth at high concentrations, but no significant difference was observed between them (P > 0.05). The chlorophyll concentration of wheat leaves decreased by 0.43–0.60 fold when the levels of ZnO NPs and bulk treated were elevated. There was a negative correlation between ZnO (NPs and bulk) and total chlorophyll. Hill reaction activity also exhibited the same tendency. Through transmission electron microscopy, ZnO NPs were found in wheat seedling root apoplast and symplasm at 1000 mg L−1 with or without phenanthrene. High doses (500 and 1000 mg L−1) of ZnO (NPs and bulk) caused more DNA damage to wheat seedling root cells, and ZnO NPs induced stronger genotoxicity than bulk ones to wheat root cells. Superoxide dismutase (SOD) and catalase (CAT) activities of wheat seedling roots decreased at 1000 mg L−1 ZnO (NPs and bulk), especially in the co-exposure treatments. Hence, ZnO (NPs and bulk) combined with phenanthrene cause more damage to wheat seedling roots, and even destroy the antioxidant system. Our findings are helpful for not only assessing the individual and combined toxicity between phenanthrene and ZnO (NPs and bulk), but also for understanding the different response of plants to individual and combined pollution.

Phytotoxic Potential of Zanthoxylum affine and Its Major Compound Linarin as a Possible Natural Herbicide.

Four compounds, the flavone linarin (1), the triterpene lupenone (2), the tocopherol (vitamin E, 3), and the new natural alkaloid 1,2,3,4-tetrahydro-1,1-dimethyl-6,7-isoquinolindiol (affineine, 4), were the major natural products isolated from Zanthoxylum affine (syn. Zanthoxylum fagara, Rutaceae). Compound 1 is highly abundant in this plant and was isolated as a white precipitate obtained from the acetone and methanol extracts. The structure of these four compounds was established by 1D and 2D NMR spectroscopy including 1H, 13C, DEPT, COSY, HSQC, and HMBC experiments. The hexane, acetone, and methanol extracts, as well as 1, were evaluated for their potential phytotoxic effects in pre- and post-emergent assays, as well as to identify their mechanisms of action. As pre-emergent phytotoxic agents, the hexane, acetone, and methanol extracts inhibited germination and residual growth (root and stem elongation) of Lactuca sativa (lettuce) and Lolium perenne (perennial ryegrass). As post-emergent agents, they inhibited dry biomass. Compound 1 acts as a pre-emergent herbicide, by inhibiting germination, seed respiration, residual seedling growth and, notably, root hair development. Furthermore, 1 inhibited the synthesis of ATP and the electron transport chain of isolated spinach chloroplasts; in this way, it behaves as a Hill reaction inhibitor. The site of inhibition was located at the donor site of PSII from the oxygen evolving complex to QA, thus acting as a multisite compound. These results suggest that compound 1 can be used as a lead for a potential green herbicide with different targets.

Improved salt tolerance in a wheat stay-green mutant tasg1

Salt stress inhibited the growth of both tasg1 and wild-type (WT) wheat seedlings, but the inhibition in tasg1 plants was relatively weaker than that of WT. Compared to the WT, the chlorophyll content, thylakoid membrane polypeptides, Hill reaction activity, actual photochemical efficiency of PSII (ΦPSII), and Mg2+- and Ca2+-ATPase activities were higher in tasg1 under salt stress. At the same time, the photosynthetic activity of the tasg1 was significantly higher than that of WT. In addition, tasg1 plants displayed relatively less accumulation of reactive oxygen species and oxidative damage accompanied by higher activity of some antioxidant enzymes, and the up-regulation of antioxidant genes further demonstrated the improvement of antioxidant activity in tasg1 under salt stress. Furthermore, tasg1 plants also showed relatively weaker Na+ fluorescence and lower Na+ content, but relatively higher content of K+ in their roots and shoots, and then, the roots of tasg1 plants enhanced net outward Na+ flux and a correspondingly increased net inward K+ flux during salt stress. This might be associated with the relatively higher activity of H+-ATPase in tasg1 plants. These results suggest that the improved antioxidant competence and Na+/K+ ion homeostasis play an important role in the enhanced salinity tolerance of tasg1 plants.