Insights into the toxicity mechanism of and cell response to the herbicide 2,4-D in plants

Although structurally similar to the natural plant hormone indol-3- acetic acid, auxin herbicides were developed for purposes other than growth, and have been successfully used in agriculture for the last 60 years. Concerted efforts are being made to understand and decipher the precise mechanism of action of IAA and synthetic auxins. Innumerable results need to be interconnected to resolve the puzzle of auxin biology and action mode of auxin herbicides. To date, different breakthroughs are providing more insights into the process of plant-herbicide interactions. Here we highlight some of the latest findings on how the 2,4-dichlorophenoxyacetic acid damages susceptible broadleaf plants, emphasizing the role of ROS as a downstream component of the auxin signal transduction under herbicide treatment.     

Thermographic visualization of cell death in tobacco and Arabidopsis

Pending cell death was visualized by thermographic imaging in bacterio‐opsin transgenic tobacco plants. Cell death in these plants was characterized by a complex lesion phenotype. Isolated cell death lesions were preceded by a colocalized thermal effect, as previously observed at sites infected by tobacco mosaic virus (TMV) ( Chaerle et al. 1999 Nature Biotechnology 17, 813–816). However, in most cases, a coherent front of higher temperature, trailed by cell death, initiated at the leaf base and expanded over the leaf lamina. In contrast to the homogenous thermal front, cell death was first visible close to the veins, and subsequently appeared as discrete spots on the interveinal tissue, as cell death spread along the veins. Regions with visible cell death had a lower temperature because of water evaporation from damaged cells. In analogy with previous observations on the localized tobacco–TMV interaction ( Chaerle et al. 1999 ), the kinetics of thermographic and continuous gas exchange measurements indicated that stomatal closure preceded tissue collapse. Localized spontaneous cell death could also be presymptomatically visualized in the Arabidopsis lsd2 mutant.     

Assessment of plant secondary metabolites in oil palm seedlings after being treated with calcium,copper ions and salicylic acid

The effect of calcium, copper ions and salicylic acid (SA) amendment on the incidence of basal stem rot and activity of secondary metabolites in oil palm seedlings were investigated in glasshouse study. Disease incidence (DI) in positive control (T8) was 75% at nine months after inoculation (9 MAI). However, weekly pre-immunisation with Ca^2+?+^?Cu^2+?+^?SA prior to inoculation significantly suppressed DI and delayed disease onset as noted in T7. In the present study, the lowest %DI was observed in T7 (15%) followed by T1, T5, T6, T3, T4 and T2. The Ca²⁺, Cu²⁺ and SA amendments were resulted in earlier and higher accumulation of plant secondary metabolites as noted in leaves, stems and root tissues in response to invasion by Ganoderma boninense. High total phenolic content concentration was detected in T7 (leaf: 233.38 ± 0.12 mg/g; stem: 132.78 ± 0.04 mg/g and root: 86.98 ± 0.28 mg/g). Similar trend was obtained in peroxidase activity, total lignin content and hydrogen peroxide scavenging activity. These results suggested that it could be due to the accumulation of phenolics, peroxidase activities, lignin content and hydrogen peroxide scavenging activities in oil palm seedling tissues which might have collectively contributed to induce resistance against G. boninense.     

Overexpression of a small GTP-binding protein Ran1 in Arabidopsis leads to promoted elongation growth and enhanced disease resistance against P. syringae DC3000

Plants resist infection through an innate immune response, which is usually associated with slowing of growth. The molecular mechanisms underlying the trade-off between plant growth and defense remain unclear. The present study reveals that growth/defense trade-offs mediated by gibberellin (GA) and salicylic acid (SA) signaling pathways are uncoupled during constitutive overexpression of transgenic AtRAN1 and AtRAN1_Q72L (active, GTP-locked form) Arabidopsis plants. It is well known that the small GTP-binding protein Ran (a Ras-related nuclear protein) functions in the nucleus–cytoplasmic transport of proteins. Although there is considerable evidence indicating that nuclear–cytoplasmic partitioning of specific proteins can participate in hormone signaling, the role of Ran-dependent nuclear transport in hormone signaling is not yet fully understood. In this report, we used a combination of genetic and molecular methods to reveal whether AtRAN1 is involved in both GA and SA signaling pathways. Constitutively overexpressed AtRAN1 promoted both elongation growth and the disease resistance response, whereas overexpression of AtRAN1_Q72L in the atran2atran3 double mutant background clearly inhibited elongation growth and the defense response. Furthermore, we found that AtRAN1 coordinated plant growth and defense by promoting the stability of the DELLA protein RGA in the nucleus and by modulating NPR1 nuclear localization. Interestingly, genetically modified rice (Oryza sativa) overexpressing AtRAN1 exhibited increased plant height and yield per plant. Altogether, the ability to achieve growth/defense trade-offs through AtRAN1 overexpression provides an approach to maximizing crop yield to meet rising global food demands.     

Zosteric acid and salicylic acid bound to a low density polyethylene surface successfully control bacterial biofilm formation

The active moieties of the anti-biofilm natural compounds zosteric (ZA) and salicylic (SA) acids have been covalently immobilized on a low density polyethylene (LDPE) surface. The grafting procedure provided new non-toxic eco-friendly materials (LDPE-CA and LDPE-SA) with anti-biofilm properties superior to the conventional biocide-based approaches and with features suitable for applications in challenging fields where the use of antimicrobial agents is limited. Microbiological investigation proved that LDPE-CA and LDPE-SA: (1) reduced Escherichia coli biofilm biomass by up to 61% with a mechanism that did not affect bacterial viability; (2) significantly affected biofilm morphology, decreasing biofilm thickness, roughness, substratum coverage, cell and matrix polysaccharide bio-volumes by >80% and increasing the surface to bio-volume ratio; (3) made the biofilm more susceptible to ampicillin and ethanol. Since no molecules were leached from the surface, they remained constantly effective and below the lethal level; therefore, the risk of inducing resistance was minimized.     

Bioactive Phytochemicals and Antioxidant Capacity of Wheatgrass Treated with Salicylic Acid under Organic Soil Cultivation

This study was undertaken to determine the influence of salicylic acid (SA) on the bioactive phytochemicals and antioxidant capacity of wheatgrass extract in the organic growing medium. Wheatgrass was cultivated in SA-enriched organic growing medium, obtained from acetylsalicylic acid (aspirin) of various concentrations (0 [control], 0.25, 0.50, 1.00, and 2.00 mM) in a plant growth chamber by controlling atmosphere (20/15 °C, day/night), light (14/10 h, light/dark; light intensity 150 μmol m⁻² s⁻¹, using quantum dot light-emitting diodes), and atmospheric moisture (60 %) for 10 d. The 0.25 mM SA-treatment showed the highest impact on germination rate, wheatgrass length, weight, yield, and chlorophyll content. Levels of bioactive phytochemicals, mainly phenolic compounds, flavonoids, β-carotene, and vitamin C, were the highest in the 1.00 mM SA-treated wheatgrass extract. The DPPH radical and nitrite-scavenging capacities were the highest in the 1.00 mM SA-treated wheatgrass extract. The 0.50 mM SA-treated wheatgrass extract showed the highest superoxide dismutase-like capacity, whereas the 2.00 mM SA-treated wheatgrass extract showed the highest anthocyanin content and ABTS radical-scavenging capacity. Therefore, it might be suggested that the appropriate levels of SA-treatment were between 0.5 and 1.0 mM to enhance the bioactive phytochemicals and antioxidant capacity of wheatgrass.     

HPLC study on Fenton-reaction initiated oxidation of salicylic acid. Biological relevance of the reaction in intestinal biotransformation of salicylic acid

Abstract

Fenton-reaction initiated in vitro oxidation and in vivo oxidative biotransformation of salicylic acid was investigated by HPLC-UV-Vis method. By means of the developed high performance liquid chromatography (HPLC) method salicylic acid, catechol, and all the possible monohydroxylated derivatives of salicylic acid can be separated. Fenton oxidations were performed in acidic medium (pH 3.0) with two reagent molar ratios: (1) salicylic acid: iron: hydrogen peroxide 1:3:1 and (2) 1:0.3:1. The incubation samples were analysed at different time points of the reactions. The biological effect of elevated reactive oxygen species concentration on the intestinal metabolism of salicylic acid was investigated by an experimental diabetic rat model. HPLC-MS analysis of the in vitro samples revealed presence of 2,3- and 2,5-dihydroxybenzoic acids. The results give evidence for nonenzyme catalysed intestinal hydroxylation of xenobiotics.     

水杨酸调控盐胁迫下羽衣甘蓝种子萌发的机理

盐胁迫是植物种子萌发与植株生长的重要限制因子。以羽衣甘蓝(Brassica oleracea var.acephala)名古屋为材料,研究不同盐分对其种子萌发的影响,探索水杨酸(SA)及其合成抑制剂氨基茚磷酸(AIP)处理对羽衣甘蓝种子萌发的调控效应。实验结果表明,150与200 mmol·L^–1 NaCl处理后的羽衣甘蓝种子活力显著降低。盐胁迫显著降低种子的吸水速率、种子活力与幼苗质量,降低苯丙氨酸裂解酶活性与内源SA含量,提高过氧化氢(H2O2)与超氧阴离子(O2^–.)含量。SA可以缓解盐胁迫对羽衣甘蓝种子活力的抑制作用,通过促进内源SA合成,从而提高种子吸水率与种子活力,促进种子对K^+、Mg^2+的吸收,降低Na+含量。此外,外源施加SA能够显著增强超氧化物歧化酶和过氧化物酶活性,降低H2O2与O2^–.的积累。相反,氨基茚磷酸(AIP)处理能够增强盐胁迫对种子萌发的抑制作用,推测这与AIP处理能够显著降低种子内源SA含量密切相关。研究表明外源SA主要通过提高保护酶活性、降低活性氧积累和维持体内离子平衡来增强羽衣甘蓝的耐盐性。     

外源水杨酸对光抑制条件下小麦叶片光合作用的影响

以浓度为50、100、200 mg·kg-1的水杨酸(SA)预先处理灌浆期的小麦叶片,可有效防护强光所致的氧化损伤,维持较高的超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性,减轻丙二醛(MDA)积累.叶片在光抑制条件下,可维持较高的通过PSⅡ电子传递速率(Fm/Fo)、PSⅡ原初光化学效率(Fv/Fm)、PSⅡ量子效率(ΦPSⅡ)、光化学猝灭系数(qP)、净光合速率(Pn)和较低的非光化学猝灭系数(qNP).其中,以较低浓度SA(50 mg·kg-1)的效果较好.     

The effect of salicylic acid on barley response to water deficit

The effect of a moderate (PEG −0.75 MPa) and severe (PEG −1.5 MPa) water deficit on SA content in leaves and roots as well as the effect of pre-treatment with SA on reaction to water stress were evaluated in two barley genotypes — the modern cv. Maresi and a wild form of Hordeum spontaneum. Water deficit increased SA content in roots, whereas SA content in leaves did not change. The level of SA in the roots of control plants was about twofold higher in ‘Maresi’ than in H. spontaneum. After 6 hours of a moderate stress the level of SA increased about twofold in H. spontaneum and about two and a half-fold in ‘Maresi’. Under severe stress conditions the level of SA increased about twofold in the both genotypes, but not before 24 hrs of the stress. Plant treatment with SA before stress reduced a damaging action of water deficit on cell membrane in leaves. A protective effect was more noticeable in H. spontaneum than in ‘Maresi’. SA treatment increased ABA content in the leaves of the studied genotypes. An increase of proline level was observed only in H. spontaneum. The obtained results suggest that ABA and proline can contribute to the development of antistress reactions induced by SA.