The Key Role of Plant Hormone Signaling Transduction and Flavonoid Biosynthesis Pathways in the Response of Chinese Pine (Pinus tabuliformis) to Feeding Stimulation by Pine Caterpillar (Dendrolimus tabulaeformis).

In nature, plants have developed a series of resistance mechanisms to face various external stresses. As understanding of the molecular mechanisms underlying plant resistance continues to deepen, exploring endogenous resistance in plants has become a hot topic in this field. Despite the multitude of studies on plant-induced resistance, how plants respond to stress under natural conditions remains relatively unclear. To address this gap, we investigated Chinese pine (Pinus tabuliformis) using pine caterpillar (Dendrolimus tabulaeformis) under natural conditions. Healthy Chinese pine trees, approximately 10 years old, were selected for studying induced resistance in Huangtuliangzi Forestry, Pingquan City, Chengde City, Hebei Province, China. Pine needles were collected at 2 h and 8 h after feeding stimulation (FS) via 10 pine caterpillars and leaf clipping control (LCC), to simulate mechanical damage caused by insect chewing for the quantification of plant hormones and transcriptome and metabolome assays. The results show that the different modes of treatments significantly influence the contents of JA and SA in time following treatment. Three types of differentially accumulated metabolites (DAMs) were found to be involved in the initial response, namely phenolic acids, lipids, and flavonoids. Weighted gene co-expression network analysis indicated that 722 differentially expressed genes (DEGs) are positively related to feeding stimulation and the specific enriched pathways are plant hormone signal transduction and flavonoid biosynthesis, among others. Two TIFY transcription factors (PtTIFY54 and PtTIFY22) and a MYB transcription factor (PtMYB26) were found to be involved in the interaction between plant hormones, mainly in the context of JA signal transduction and flavonoid biosynthesis. The results of this study provide an insight into how JA activates, serving as a reference for understanding the molecular mechanisms of resistance formation in conifers responding to mandibulate insects.

Metabolites and Plant Hormones Related to the Resistance Response to Feeding Stimulation and Leaf Clipping Control in Chinese Pine (Pinus tabuliformis Carr.).

This experiment was conducted to define changes in metabolic pathways in response to mandibulate insect feeding and to provide a reference for further investigation of the molecular mechanisms underlying the development of conifer resistance. Chinese pine (Pinus tabuliformis Carr.) in good growth status in natural condition was chosen for stimulation by 10 pine caterpillars (Dendrolimus tabulaefomis Tsai et Liu) as feeding stimulation (FS), leaf clipping control (LCC) as mechanical damage, and CK group (with no treatment) (recorded as 0 h). The metabolome and total flavonoid content were measured in the needles at 0, 2, and 8 h after treatment. Plant hormones were measured with needles at 0, 0.5, 1, 1.5, 2, 4, 6, and 8 h after different treatments. The results show that a total of 30.8% flavonoids are identified by metabolomics analysis. Compared with leaf clipping control, feeding stimulation of Chinese pine caterpillars significantly induced the upregulation of metabolites in the flavonoid pathway in Chinese pine, and the plant hormones JA and IAA showed expression trends consistent with those of the metabolome. According to the biological processes of the four plant hormones involved, JA and SA are mostly involved in resistance formation, and in this study, both of them also have fluctuating expressions influenced by feeding stimulation, while the expressions of the growth-related hormones IAA and ABA have no significant changes at other time points except for 1 h after treatment. Thus, the flavonoid pathway is one of the main pathways involved in resistance formation in conifers, and JA and IAA are involved in the formation of resistance.

Stochastic Collision-Attachment-Based Monte Carlo Simulation of Colloidal Fouling: Transition from Foulant-Clean-Membrane Interaction to Foulant-Fouled-Membrane Interaction.

The initial behavior of colloidal fouling is governed by foulant-clean-membrane interaction (F-M), and its long-term behavior is determined by foulant-fouled-membrane interaction (F-F). Nevertheless, the transitional fouling behavior from F-M to F-F has not been fully understood. This study reports a novel collision attachment (CA)-Monte Carlo (MC) approach, with the stochastic colloid-membrane collision events modeled by MC and the probability of colloidal attachment to the membrane determined by the interplay of flux and the energy barrier arising from colloid-membrane interaction (Em for F-M and Ef for F-F). The long-term membrane flux remains stable for large Ef, whereas severe fouling occurs when both Em and Ef are small. Our study reveals the existence of a metastable flux behavior for the combination of large Em but small Ef. The time evolution of flux behavior and colloidal deposition patterns shows a nearly constant flux for an extended period, with the high energy barrier Em retarding initial colloidal deposition. However, accidental random deposition of a colloidal particle could reduce the local energy barrier (toward the smaller Ef), seeding for further colloidal deposition in its vicinity. This initiates an uneven patch-wise fouling and eventually leads to a complete transition to F-F-dominated behavior. The metastable period can be effectively extended by increasing the energy barrier (Em or Ef) or lowering flux, which provides important implications to membrane design and operation.

Modeling Dynamics of Colloidal Fouling of RO/NF Membranes with A Novel Collision-Attachment Approach.

We report a novel collision-attachment approach for modeling the dynamics of colloidal fouling. The model treats fouling as a two-step process: colloidal particles colliding with a membrane surface followed by their attachment onto the surface. An attachment coefficient is adopted to describe the probability of successful foulant attachment for any given collision event, the value of which can be determined by the classical Boltzmann distribution. Our model shows excellent agreement with experimental data in terms of both the kinetics of flux decline and foulant mass deposition. Modeling results reveal the critical roles of water flux and energy barrier in governing colloidal fouling. Greater water flux or lower energy barrier can lead to a collision-controlled condition, where severe fouling occurs and nearly all collision events lead to successful foulant attachment. On the contrary, fouling is increasingly controlled by the probability of successful attachment at lower water flux and/or greater energy barrier. Our model provides deep insights into the various mechanisms governing the dynamics of colloidal fouling (i.e., concentration polarization, collision, and attachment) and the self-limiting fouling behavior under constant-pressure mode.

Collision-attachment simulation of membrane fouling by oppositely and similarly charged colloids.

The fouling propensity of oppositely charged colloids (OCC) and similarly charged colloids (SCC) on reverse osmosis (RO) and nanofiltration (NF) membranes are systematically investigated using a developed collision-attachment approach. The probability of successful colloidal attachment (i.e., attachment efficiency) is modelled by Boltzmann energy distribution, which captures the critical roles of colloid-colloid/membrane interaction and permeate drag. Our simulations highlight the important effects of ionic strength Is, colloidal size dp and initial flux J0 on combined fouling. In a moderate condition (e.g., Is =10 mM, dp=50 nm and J0= 100 L/m2h), OCC mixtures shows more severe fouling compared to the respective single foulant owing to electrostatic neutralization. In contrast, the flux loss of SCC species falls between those of the two single foulants but more closely resembles that of the single low-charged colloids due to its weak electrostatic repulsion. Increased ionic strength Is leads to less severe fouling for OCC but more severe fouling for SCC, as a result of the suppressed electrostatic attraction/repulsion. At a high Is (e.g., 3-5 M), all the single and mixed systems show the identical pseudo-stable flux Js. Small colloidal size leads to the drag-controlled condition, where severe fouling occurs for both single and mixed foulants. On the contrary, better flux stability appears at greater dp for both individual and mixed species, thanks to the increasingly dominated role of energy barrier and thus lowered attachment efficiency. Furthermore, higher J0 above limiting flux exerts greater permeate drag, leading to elevated attachment efficiency, and thus more flux losses for both OCC and SCC. Our modelling gains deep insights into the role of energy barrier, permeate drag, and attachment efficiency in governing combined fouling, which provides crucial guidelines for fouling reduction in practical engineering.

Relating critical and limiting fluxes to metastable and long-term stable fluxes in colloidal membrane filtration through collision-attachment theory.

In membrane technology for water/wastewater treatment, the concepts of critical flux (JC) and limiting flux (JL) suggest the existence of a threshold flux below which no fouling occurs. However, their important roles on stable flux duration have not been sufficiently understood. This work adopts a collision-attachment approach to clarify the relationship of JC, JL to metastable (i.e., short-term stable) and long-term stable fluxes based on their dependence on initial flux (J0), foulant-clean-membrane energy barrier (Ef-m), and foulant-fouled-membrane energy barrier (Ef-f). When J0 is below JL, water flux remains stable over a long time even for the case of J0 over JC, thanks to the strongly repulsive Ef-f. At J0 > JL and J0 > JC, the water flux is unstable at the beginning of filtration, and the flux ultimately decreases to JL as the long-term stable flux. Under the condition of JL < J0 ≤ JC, an initial metastable flux appears owing to the high Ef-m, with longer metastable period observed at lower J0 and for more hydrophilic/charged membrane or colloids. Nevertheless, rapid flux decline occurs subsequently due to the energy barrier shifting to weak Ef-f, and the water flux eventually degenerates to JL in long-term fouling duration. Our results provide significant guidelines for fouling control strategies with respect to membrane design, feedwater pretreatment, and operational optimization.

Insights into the roles of membrane pore size and feed foulant concentration in ultrafiltration membrane fouling based on collision-attachment theory.

Membrane property and feed characteristics play critical roles in membrane fouling. This paper aims to clarify the roles of membrane pore size (φ) and feed foulant concentration (Cb ) in ultrafiltration fouling induced by polysaccharides. The fouling behaviors were expounded by collision-attachment theory, where the rate of membrane fouling is mainly determined by collision frequency (JCb ) and attachment efficiency (γ). At the initial fouling stage, rapid flux decline was observed at large φ or high Cb due to the great JCb and/or γ. At the later fouling stage, there existed a nearly identical maximum stable flux attributing to the same JCb and γ, which was independent of φ and Cb . Moreover, the smaller φ can lead to less foulants passed through the membrane and thus more foulants attaching on the membrane, while the higher Cb can give rise to more foulants on both the membrane surface and in the permeate. The results presented in current study provide fundamental basis in understanding membrane fouling. PRACTITIONER POINTS: Collision-attachment theory was employed to expound the UF fouling behavior. Rapid flux decline occurred at large membrane pore size or high feed foulant concentration in the initial fouling stage. Membranes with different pore size or feed foulant concentration had an identical flux at the latter fouling stage. Lowering membrane pore size or increasing feed foulant concentration can lead to more foulants attaching on the membrane surface.

Analysis of organic foulants in the coagulation-microfiltration process for the treatment of Taihu Lake.

This paper analysed organic foulants in the coagulation-microfiltration process for Taihu Lake treatment. High-performance size-exclusion chromatography (HPSEC) and fluorescence excitation-emission matrices (EEM) were applied to elucidate the influence of characteristics of organics on microfiltration (MF) membrane fouling. Results showed that coagulation pretreatment could extend the operation duration of MF based on the fact that pretreatment could effectively remove macromolecular substances as well as a portion of small molecular weight (MW) organics. The analysis of foulants indicated that organics of strong hydrophobic acids (SHA) and neutral hydrophilic (Neut) fractions (based on hydrophobicity) and medium and small MW components (based on MW distribution) contributed greatly to irreversible fouling. EEM fluorescence analysis of chemical solutions exhibited that aromatic proteins and soluble microbial products were mainly a response to irreversible fouling.

PEGylated Perylenemonoimide-Dithienylethene for Super-Resolution Imaging of Liposomes.

We have designed and synthesized an amphiphilic photoswitchable fluorophore, PEGylated perylenemonoimide-dithienylethene (PEG-PMI-DTE), which exhibits evident bistable photochromism, fluorescence switching, and fatigue resistance. The fine nanostructures of liposomes can be observed directly under super-resolution fluorescent microscopy by aid of the amphiphilic photoswitchable fluorophore as a staining agent, with an optical resolution of 30 nm.