Photosynthetic Performance of the Imidazolinone Resistant Sunflower Exposed to Single and Combined Treatment by the Herbicide Imazamox and an Amino Acid Extract

Phenotypic Characteristics and Occurrence Basis of Leaf Necrotic Spots in Response of Weedy Rice to Imazethapyr

Weedy rice is the most challenging weed species to remove in rice production. We found a novel phenotype of seedling leaves which rapidly generates necrotic spots in response to imidazolinone herbicides in weedy rice, but its influencing factors and formation basis are still unknown. In this study, we used the leaf necrotic spot-producing type of weedy rice as the material. First, leaf necrotic spots were defined as physiological and vacuole-mediated cell necrosis by microscopic examination. The imazethapyr concentration was positively correlated with the degree of necrotic spots occurring, while the action site was in accordance with necrosis using herbicide stability tests combined with fluorescence parameters. Furthermore, transcriptome analysis revealed significant differences in the gene expression of endoplasmic reticulum stress and the lipid metabolism membrane structure damage pathway during necrosis, as confirmed by transmission electron microscopy. The light-temperature test also showed that high temperature and intense light could promote the appearance of necrotic spots. These experimental results are helpful in clarifying the process and basis of imazethapyr in inducing the rapid generation of necrotic spots in rice leaves and providing new insight into understanding the mechanism of response to imidazolinone herbicides and the control of weedy rice.

Research on phytotoxicity assessment and photosynthetic characteristics of nicosulfuron residues on Beta vulgaris L

Nicosulfuron is a common herbicide used to control weeds in maize fields. In northeast China, sugar beet is often grown as a subsequent crop after maize, and its frequently suffers from soil nicosulfuron residue damage, but the related toxicity evaluation and photosynthetic physiological mechanisms are not clear. Therefore, we experimented to evaluate the impacts of nicosulfuron residues on beet growth, photochemical properties, and antioxidant defense system. The results showed that when the nicosulfuron residue content reached 0.3 μg kg-1, it inhibited the growth of sugar beet. When it reached 36 μg kg-1 (GR50), the growth stagnated. Compared to the control group, a nicosulfuron residue of 36 μg kg-1 significantly decreased beet plant height (70.93 %), leaf area (91.85 %), dry weights of shoot (70.34 %) and root (32.70 %). It also notably reduced the potential photochemical activity (Fv/Fo) by 12.41 %, the light energy absorption performance index (PIabs) by 46.09 %, and light energy absorption (ABS/CSm) by 6.56 %. It decreased the capture (TRo/CSm) by 9.30 % and transferred energy (ETo/CSm) by 16.13 % per unit leaf cross-section while increasing the energy flux of heat dissipation (DIo/CSm) by 22.85 %. This ultimately impaired the photochemical capabilities of PSI and PSII, leading to a reduction in photosynthetic performance. Furthermore, nicosulfuron increased malondialdehyde (MDA) content while decreasing superoxide dismutase (SOD) and catalase (CAT) activities. In conclusion, this research clarified the toxicity risk level, lethal dose, and harm mechanism of the herbicide nicosulfuron residue. It provides a theoretical foundation for the rational use of herbicides in agricultural production and sugar beet planting management.

Effect of herbicide stress on synchronization of carbon and nitrogen metabolism in lentil (Lens culinaris Medik.)

Weed invasion causes significant yield losses in lentil. Imazethapyr (IM), a broad-spectrum herbicide inhibits the biosynthesis of branched chain amino acids necessary for plant growth. Plant growth depends upon translocation of photo-assimilates and their partitioning regulated by carbon and nitrogen metabolism. This study aimed to investigate the impact of imazethapyr spray on carbon and nitrogen metabolism in tolerant (LL1397 and LL1612) and susceptible (FLIP2004-7L and PL07) lentil genotypes during vegetative and reproductive development. Significantly higher activities of invertases and sucrose synthase (cleavage) in leaves and in podwall and seeds during early phase of development in tolerant genotypes were observed as compared to susceptible genotypes under herbicide stress that might be responsible for providing hexoses required for their growth. Activities of sucrose synthesizing enzymes, sucrose phosphate synthase and sucrose synthase (synthesis) increased significantly in podwalls and seeds of LL1397 and LL1612 genotypes during later phase of development towards maturity while the activities decreased in FLIP2004-7L and PL07 genotypes under herbicide stress. Activities of nitrate and nitrite reductase, glutamine 2-oxoglutarate aminotransferase, glutamine synthetase and glutamate dehydrogenase were increased in leaves, podwalls and seeds of LL1397 and LL1612 under herbicide stress. A proper synchronization of carbon and nitrogen metabolism in tolerant lentil genotypes during vegetative and reproductive phase might be one of the mechanisms for their recovery from herbicide stress. This first ever comprehensive information will provide a basis for future studies on the molecular mechanism of source sink relationship in lentil under herbicide stress and will be utilized in breeding programmes.

Application of an Enzymatic Hydrolysed L-α-Amino Acid Based Biostimulant to Improve Sunflower Tolerance to Imazamox

Herbicides, commonly used in agriculture to control weeds, often cause negative effects on crops. Safeners are applied to reduce the damage to crops without affecting the effectiveness of herbicides against weeds. Plant biostimulants have the potential to increase tolerance to a series of abiotic stresses, but very limited information exists about their effects on herbicide-stressed plants. This study aims to verify whether the application of a potential safener such as Terra-Sorb®, an L-α-amino acid-based biostimulant, reduces the phytotoxicity of an Imazamox-based herbicide and to elucidate which tolerance mechanisms are induced. Sunflower plants were treated with Pulsar® 40 (4% Imazamox) both alone and in combination with Terra-Sorb®. Plants treated with the herbicide in combination with Terra-Sorb® showed higher growth, increased acetolactate synthase (ALS) activity, and amino acid concentration with respect to the plants treated with Imazamox alone. Moreover, the biostimulant protected photosynthetic activity and reduced oxidative stress. This protective effect could be due to the glutathione S-transferase (GST) induction and antioxidant systems dependent on glutathione (GSH). However, no effect of the biostimulant application was observed regarding phenolic compound phenylalanine ammonium-lyase (PAL) activity. Therefore, this study opens the perspective of using Terra-Sorb® in protecting sunflower plants against an imazamox-based herbicide effect.

Use of Biostimulants as a New Approach for the Improvement of Phytoremediation Performance—A Review

Environmental pollution is one of the most pressing global issues, and it requires priority attention. Environmental remediation techniques have been developed over the years and can be applied to polluted sites, but they can have limited effectiveness and high energy consumption and costs. Bioremediation techniques, on the other hand, represent a promising alternative. Among them, phytoremediation is attracting particular attention, a green methodology that relies on the use of plant species to remediate contaminated sites or prevent the dispersion of xenobiotics into the environment. In this review, after a brief introduction focused on pollution and phytoremediation, the use of plant biostimulants (PBs) in the improvement of the remediation effectiveness is proposed. PBs are substances widely used in agriculture to raise crop production and resistance to various types of stress. Recent studies have also documented their ability to counteract the deleterious effects of pollutants on plants, thus increasing the phytoremediation efficiency of some species. The works published to date, reviewed and discussed in the present work, reveal promising prospects in the remediation of polluted environments, especially for heavy metals, when PBs derived from humic substances, protein and amino acid hydrolysate, inorganic salts, microbes, seaweed, plant extracts, and fungi are employed.

Dynamics of Phosphorus and Biostimulants on Agro-Morphology, Yield, and Essential Oil Profile of German Chamomile (Matricaria chamomilla L.) Under Acidic Soil Conditions of the Western Himalaya

German chamomile (Matricaria chamomilla L.) is a promising and easy to cultivate crop under suitable nutrient supply conditions, but acidic soils of Indian western Himalayas limit the availability of phosphorus to the plant and reduce flower production. Thus, a field experiment was conducted for two consecutive seasons (2018-2019 and 2019-2020) to study the effect of phosphorus dynamics and biostimulant application on the agro-morphological traits, essential oil (EO) yield, and chemical constituents of German chamomile in the mid hills of the western Himalayan region. The experiment consisted of 12 treatments, four phosphorus fertilizer levels (0, 30, 60 and 90 kg ha^-1) and three biostimulants levels (control, amino acid at 5 mL L^-1, and humic acid at 10 mL L^-1). The experiment was replicated three times in a factorial complete randomized block design (FRBD). Agro-morphological and yield characteristics were significantly higher in phosphorus at 90 kg ha^-1 and humic acid application compared to the control. Dry flower and EO yield was 17.87 and 26.76% higher with the 90 kg ha^-1 phosphorus application while 2.45 and 5.79% higher in humic acid at 10 mL L^-1 compared to the control. The EO constituents viz., chamazulene was 12.04 and 8.85% higher in phosphorus at 90 kg ha^-1 and humic acid at 10 mL L^-1 application compared to the control. On the other hand, α-bisabolol oxide B and α-bisabolol oxide A were decreased with increase in phosphorus application. This study presents novel facts, elucidation, and explanation for farmers and industrialists to produce German chamomile in acidic soils by integrating biostimulants with phosphorus fertilization and getting maximum yield and quality EO.

The Impact of Cameraria ohridella (Lepidoptera, Gracillariidae) on the State of Aesculus hippocastanum Photosynthetic Apparatus in the Urban Environment

The paper presents the results on resistance of Aesculus hippocastanum Linnaeus, 1753 trees to Cameraria ohridella Deschka & Dimić, 1986 (Lepidoptera, Gracillariidae) impact under conditions of a modern urban environment on the example of Dnipro city as the largest industrial city in Ukraine. Field experiments were conducted in all park areas of the city, which allowed covering the full gradient of the existing urban environment and considered the different degrees of the tree settlement by the invasive insect species. The research of the impact of C. ohridella caterpillars’ vital activity on the photosynthetic apparatus state was carried out by applying a chlorophyll fluorescence induction technique. Diagnosis of photosynthetic dysfunction of fresh Ae. hippocastanum leaves was conducted using a portable “Floratest” fluorometer manufactured in Ukraine. Interpretation of the obtained Kautsky curves showed that significant changes in their critical parameters associated with the degree of leaf damage by C. ohridella caterpillars were not detected. The influence of tree growth site conditions on the following 4 main indicators of chlorophyll fluorescence induction was established: the initial value of fluorescence induction after irradiation; the value of “plateau” fluorescence induction; the maximum value of fluorescence induction; the stationary value of fluorescence induction after light adaptation of the plant leaf. It was found that the efficiency coefficients of photochemical processes in Ae. hippocastanum trees growing in low terrain levels differed significantly, which can probably be interpreted as their response to the specific characteristics of the urban environment.

Phytotoxicity response of sugar beet (Beta vulgaris L.) seedlings to herbicide fomesafen in soil

Fomesafen is the most widely used herbicide in the soybean field. However, there are urgent practical challenges with the long-term persistence of fomesafen in soil and its effects on the subsequent crops in agricultural production. Therefore, pot experiments were conducted to study the effects of fomesafen residues (0-0.05 mg kg^-1) on growth, photosynthetic characteristics, and the antioxidant defense system of sugar beet seedlings. The results showed that with the increase of fomesafen residues, the phytotoxicity index increased, while the plant height, leaf area, root length, root volume, and dry weight of sugar beet decreased. Photosynthetic pigment content, net photosynthetic rate (Pn), maximum photosynthetic efficiency (Fv/Fm), and actual photosynthetic efficiency (Y(II)) declined with a dose-dependent manner of fomesafen, but the intercellular CO₂ concentration (Ci) and non-photochemical quenching coefficient (NPQ) increased under fomesafen. On the other hand, the residues of fomesafen increased the content of malondialdehyde (MDA) and membrane permeability by aggravating oxidative stress and triggering the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO). In addition, sugar beet seedlings were significantly sensitive to fomesafen as the concentration of fomesafen in the soil was up to 0.025 mg kg^-1. In conclusion, the present study showed that fomesafen residues in the soil could affect the morphophysiology and photosynthetic performance of sugar beet. This study is beneficial for understanding the effects of the herbicide fomesafen residues on non-target crops.

Methylglyoxal detoxification pathway - Explored first time for imazethapyr tolerance in lentil (Lens culinaris L.)

Lentil is an important pulses crop but it's short stature and slow growth rate make it vulnerable to weed competition, limiting crop productivity. There is need to identify herbicide tolerant genotypes and their tolerance mechanism. The present investigation was conducted to understand the effect of imazethapyr (IM) treatment on accumulation of methylglyoxal (MG) and its detoxification mechanism in IM-tolerant (LL1397 and LL1612) susceptible (FLIP2004-7L and PL07) genotypes sown under control (weed free), weedy check (weeds were growing with crop) and sprayed with imazethapyr. The enzymes of glyoxalase pathway (glyoxalase I, II and III) and non glyoxalase pathway (methylglyoxal reductase), lactate dehydrogenase (LDH), glutathione content, gamma-glutamyl-cysteine synthetase (γ-GCS) were estimated in lentil genotypes at different days after spray. Higher activities of glyoxalase I, II and III and MGR along with the increased glutathione content (GSH) content in LL1397 and LL1612 under IM treatment as compared to FLIP2004-7L and PL07 might be responsible for lowering MG accumulation and increasing lactate content, which is end product of these pathways. Enhanced LDH activity in LL1397 and LL1612 might be responsible for energy production via TCA cycle that might be responsible for growth and recovery of tolerant genotypes after IM treatment. Higher γ-GCS activity in tolerant genotypes led to increased glutathione content required for glyoxalase pathway. However, decreased activities of glyoxalase enzymes and MGR in susceptible genotypes result in MG accumulation which limit plant growth. This is the first ever study elucidating the role of MG detoxification pathway conferring IM tolerance in lentil.

High-Level Expression of Nitrile Hydratase in Escherichia coli for 2-Amino-2,3-Dimethylbutyramide Synthesis

In the synthesis of imidazolinone herbicides, 2-Amino-2,3-dimethylbutyramide (ADBA) is an important intermedium. In this study, the recombinant production of nitrile hydratase (NHase) in Escherichia coli for ADBA synthesis was explored. A local library containing recombinant NHases from various sources was screened using a colorimetric method. NHase from Pseudonocardia thermophila JCM3095 was selected, fused with a His-tag and one-step purified. The enzymatic properties of recombinant NHase were studied and indicated robust thermal stability and inhibition of cyanide ions due to substrate degradation. After systematic optimization of fermentation conditions, the OD600 (optical density at 600 nm), enzyme activity and specific activity of recombinant strain E. coli BL21(DE3)/pET-28a+NHase reached 19.4, 3.72 U/mL and 1.04 U/mg protein at 42 h, representing 5.86-, 26.6- and 4-fold increases, respectively. These results offered an efficient recombinant whole-cell biocatalyst for ADBA synthesis.

Synthesis of Tyrosol 1,2,3-Triazole Derivatives and Their Phytotoxic Activity against Euphorbia heterophylla

The synthesis and phytotoxic activity of a series of tyrosol 1,2,3-triazole derivatives are reported herein. Target compounds were synthesized through the copper(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC), known as click reaction, and these were tested for phytotoxic activity on leaves of wild poinsettia (Euphorbia heterophylla), fleabane (Conyza sumatrensis), and tropical spiderwort (Commelina benghalensis). These are three highly noxious agricultural weeds that challenge available weed control methods, including the use of chemical herbicides. Twenty-five compounds were synthesized and tested. None of the compounds showed phytotoxic activity against C. benghalensis and C. sumatrensis, but almost all of them produced yellowing, bleaching, and necrosis on leaves of E. heterophylla. Two of the tyrosol 1,2,3-triazole derivatives produced more extensive lesions than those produced by the commercial herbicide diquat, used as a positive control (p ≤ 0.05). When applied on leaves of E. heterophylla, these compounds interfered with the stomatal conductance, net photosynthesis, internal carbon concentration, transpiration rate, water-use efficiency, and chlorophyll A and B contents. The interference of such compounds on such photosynthesis-related variables indicates that tyrosol 1,2,3-triazole derivatives may be capable of lowering the competitiveness of E. heterophylla and acting as additional tools for managing this competitive weed in agricultural lands.

Selectivity of metsulfuron applied to soybean before sowing in different intervals and soils

This work aimed to evaluate the selectivity of the herbicide metsulfuron applied at different times on the development of soybeans grown in soils with different characteristics. The experiment was conducted in a randomized block design, in a factorial scheme (4 x 4), with four replicates. Factor A was application time (0, 15, 30, and 45 days before sowing, DBS) and factor B was soil type (Erechim, Itaqui, Piratini, and Santa Maria). Soybean plants cultivated in the Erechim soil showed moderate phytotoxicity, with greater damage to the leaf area and plant dry matter, mainly after application at 30 DBS. Those cultivated in Itaqui soil showed gradual phytotoxicity between 14 and 28 days after emergence (DAE). Soybean plants grown in the Piratini and Santa Maria soils showed the highest phytotoxicity and photosynthetic reduction, mainly at 15 and 0 DBS. Metsulfuron application at 45 DBS caused reduced plant growth by up to 40%, and reduced shoot development (30%) in soybean plants grown in Piratini and Santa Maria soils, respectively. There were gradual changes in phytotoxicity and the morphophysiological traits of soybean plants exposed to the residual effect of metsulfuron in different soils, which indicates that soybeans should be sown more than 45 days after the application of metsulfuron, regardless of soil characteristics.