Linalool- and α-terpineol-induced programmed cell death in Chlamydomonas reinhardtii

Cyanobacterial VOCs β-ionone and β-cyclocitral poisoning Lemna turionifera by triggering programmed cell death

β-Ionone and β-cyclocitral are two typical components in cyanobacterial volatiles, which can poison aquatic plants and even cause death. To reveal the toxic mechanisms of the two compounds on aquatic plants through programmed cell death (PCD), the photosynthetic capacities, caspase-3-like activity, DNA fragmentation and ladders, as well as expression of the genes associated with PCD in Lemna turionifera were investigated in exposure to β-ionone (0.2 mM) and β-cyclocitral (0.4 mM) at lethal concentration. With prolonging the treatment time, L. turionifera fronds gradually died, and photosynthetic capacities gradually reduced and even disappeared at the 96th h. This demonstrated that the death process might be a PCD rather than a necrosis, due to the gradual loss of physiological activities. When L. turionifera underwent the death, caspase-3-like was activated after 3 h, and reached to the strongest activity at the 24th h. TUNEL-positive nuclei were detected after 12 h, and appeared in large numbers at the 48th h. The DNA was cleaved by Ca2+-dependent endonucleases and showed obviously ladders. In addition, the expression of 5 genes (TSPO, ERN1, CTSB, CYC, and ATR) positively related with PCD initiation was up-regulated, while the expression of 2 genes (RRM2 and TUBA) negatively related with PCD initiation was down-regulated. Therefore, β-ionone and β-cyclocitral can poison L. turionifera by adjusting related gene expression to trigger PCD.

Identification of algicidal monoterpenoids from four chemotypes of Cinnamomum camphora and their algicidal mechanisms on Microcystis aeruginosa

Cyanobacterial blooms cause serious environmental issues, and plant secondary metabolites are considered as new algaecide for controlling them. Cinnamomum camphora produces a wide spectrum of terpenoids and has 4 main chemotypes, including linalool, camphor, eucalyptol and borneol chemotype. To develop the new cyanobacterial algaecide by using suitable chemotype of Cinnamomum camphora and the main terpenoids, we analyzed the terpenoid composition in the 4 chemotype extracts, evaluated the algicidal effects of the extracts and their typical monoterpenoids on Microcystis aeruginosa, and investigated the algicidal mechanism of the stronger algicidal agents. Among the 4 chemotypes, eucalyptol and borneol chemotype extracts exhibited stronger algicidal effects. In the 4 chemotype extracts, monoterpenoids were the main compounds, of which linalool, camphor, eucalyptol and borneol were the typical components. Among the 4 typical monoterpenoids, eucalyptol and borneol showed stronger algicidal effects, which killed 78.8% and 100% M. aeruginosa cells, respectively, at 1.2 mM after 48 h. In 1.2 mM eucalyptol and borneol treatments, the reactive oxygen species levels markedly increased, and the caspase-3-like activity also raised. With prolonging the treatment time, M. aeruginosa cells gradually shrank and wrinkled, and the cell TUNEL fluorescence intensity and DNA degradation gradually enhanced, indicating that the lethal mechanism is causing apoptosis-like programmed cell death (PCD). Therefore, eucalyptol and borneol chemotype extracts and their typical monoterpenoids have the potential for developing as algaecides to control cyanobacteria through triggering apoptosis-like PCD.

Transcriptomic hallmarks of in vitro TiO2 nanotubes toxicity in Chlamydomonas reinhardtii

Recently, more accessible transcriptomic approaches have provided a new and deeper understanding of environmental toxicity. The present study focuses on the transcriptomic profiles of green microalgae Chlamydomonas reinhardtii exposed to new industrially promising material, TiO₂ nanotubes (NTs), as an example of a widely used one-dimensional nanomaterial. The first algal in vitro assay included 2.5 and 7.5 mg/L TiO₂ NTs, resulting in a dose-dependent negative effect on biological endpoints. At a working concentration of 7.5 mg/L, RNA-sequencing showed a mainly negative effect on the cells. In summary, the results indicated metabolic disruption, ^{such as ATP loss, damage to mitochondria and chloroplasts, loss of solutes due to permeated membranes,} and cell wall damage. Moreover, apoptosis-induced transcripts were detected. Interestingly, reactivation of transposons was observed. In signalling and transcription pathways, including chromatin remodelling and locking, the annotated genes were downregulated.

Phytotoxicity of Chemical Compounds from Cinnamomum camphora Pruning Waste in Germination and Plant Cultivation

Much previous research has indicated most composts of pruning waste are characterized by potential phytotoxicity, it is highly correlated with the chemical compounds of raw materials. Cinnamomum camphora, a common kind of pruning waste in Southeast Asia and East Asia, is characterized by intense bioactivities due to complex chemical components. This study investigated the potential phytotoxicity of C. camphora pruning waste in light of germination and higher plant growth. C. camphora extracted from leaves completely inhibited seed germination and still showed suppression of root elongation at an extremely low dosage. C. camphora extract also displayed significant inhibition of nutrient absorption in tomato seedlings, including moisture, available nutrients (N, P and K) and key microelements (Fe, Mn, Zn and S). The gene expression of aquaporins and transporters of nitrate and phosphate was significantly up-regulated in roots. This could be regarded as a positive response to C. camphora extract for enhancing nutrient absorption. Moreover, the severe damage to the plasma membrane in roots caused by C. camphora extract might seriously affect nutrient absorption. Camphor is the main component of the C. camphora extract that may induce the phytotoxicity of plasma membrane damage, resulting in the inhibition of nutrient absorption and low biomass accumulation. This study provided a new understanding of the ecotoxicological effects of C. camphora pruning waste, indicating that the harmless disposal of pruning waste requires much attention and exploration in the future.

Programmed cell death process in freshwater Microcystis aeruginosa and marine Phaeocystis globosa induced by a plant derived allelochemical

Harmful algal blooms (HAB) are a serious problem worldwide. Allelochemicals from natural plants were recently thought to be promising anti-algaecide in controlling harmful algae. However, the programmed cell death (PCD) process of algae under allelopathic pressure induced by 5,4'-dihydroxyflavone (5,4'-DHF) was poorly understood. In this study, two common and worldwide distributed microalgae, Microcystis aeruginosa and Phaeocystis globosa were selected as target algae, and the PCD processes induced by 5,4'-DHF were cross-compared between the two species. Both algae species were inhibited significantly by 5,4'-DHF with the relative sensitivity of 0.11. To uncover the PCD progress systematically, signals for PCD triggering, antioxidant enzyme activity, photosynthetic ability variation, caspase-like activities and typical indicators were investigated. In both species, typical indicators of PCD - phosphatidylserine externalization and chromatin condensation - were detected. The intracellular reactive oxygen species (ROS), nitric oxide (NO) and H₂O₂ were the potential signal molecules to stimulate PCD, and caspase-like activities were activated with an elevation of cytochrome c indicating the initiation of PCD in both species. However, P. globosa responded to 5,4'-DHF immediately after 3 h with the elevation of ROS and not in M. aeruginosa. Antioxidant enzyme activities of superoxide dismutase (SOD) and catalase (CAT) in M. aeruginosa and P. globosa also showed different patterns on day 3. Specifically, SOD activity in M. aeruginosa increased significantly while it decreased significantly in P. globosa, CAT activity in M. aeruginosa decreased significantly while it increased significantly in P. globosa (p < 0.05). Malondialdehyde (MDA) content in P. globosa increased significantly (p < 0.001) while it showed no variation in M. aeruginosa. Overall, this study is one of the earliest studies to explore the inhibition and action mechanism of plant derived flavonoids on harmful algae from the perspective of PCD, and provide new insights into the antialgal mechanism of allelochemicals.

The effects of secondary bacterial metabolites on photosynthesis in microalgae cells

Secondary metabolites of bacteria are regulatory molecules that act as "info-chemicals" that control some metabolic processes in the cells of microorganisms. These molecules provide the function of bacteria communication in microbial communities. As primary producers of organic matter in the biosphere, microalgae play a central ecological role in various ecosystems. Photosynthesis is a central process in microalgae cells, and it is exposed to various biotic and abiotic factors. Various secondary metabolites of bacteria confer a noticeable regulatory effect on photosynthesis in microalgae cells. The main purpose of this review is to highlight recent experimental results that demonstrate the impact of several types of common bacterial metabolites (volatile organic compounds, non-protein amino acids, and peptides) on photosynthetic activity in cells of microalgae. The use of these molecules as herbicides can be of great importance both for practical applications and for basic research.

Effects of allelochemical artemisinin in Artemisia annua on Microcystis aeruginosa: growth, death mode, and microcystin-LR changes

To investigate the effects of an allelochemical artemisinin extracted from Artemisia annua (A. annua) on cell growth, death mode, and microcystin-LR (MC-LR) changes of Microcystis aeruginosa (M. aeruginosa), a series of morphological and biochemical characteristics were studied. The results showed that artemisinin could inhibit the growth of M. aeruginosa and reduce the content of phycobiliprotein. Under the allelopathy of artemisinin, algae cells deformed due to swelling, which caused cell membranes to rupture and cell contents to leak. FDA/PI double-staining results showed that 15.10-94.90% of algae cells experienced the death mode of necrosis-like. Moreover, there were 8.35-14.50% of algae cells undergoing programmed cell death, but their caspase-3-like protease activity remained unchanged, which may mean that algae cells were not experiencing caspase-dependent apoptosis under artemisinin stress. Attacked by artemisinin directly, both intracellular and extracellular MC-LR increased sharply with the upregulation of mcyB, mcyD, and mcyH. The upregulation multiple of mcyH suggested that M. aeruginosa could accelerate transportation of algal toxin under adverse conditions of artemisinin. Artemisinin not only can inhibit the growth of M. aeruginosa but it also causes the accelerated release and increase of microcystin-LR. These imply that the application of artemisinin should be reconsidered in practical water bodies.

Programmed cell death of Chlamydomonas reinhardtii induced by three cyanobacterial volatiles β-ionone, limonene and longifolene

β-Ionone, limonene and longifolene are 3 main components in cyanobacterial volatile organic compounds, which are formed through different pathways and can poison and even kill other algae. To uncover their toxic mechanism from programmed cell death (PCD), the photosynthetic pigments, chlorophyll fluorescence, caspase-like activities, cell size, nuclear variations and DNA ladders were investigated in Chlamydomonas reinhardtii treated with β-ionone (0.2 mM), limonene (0.2 mM) and longifolene (0.4 mM) at lethal concentration during 24 h. In the treatments with the 3 compounds, the photosynthetic pigments in C. reinhardtii cells gradually degraded, and Fv/Fm gradually decreased and disappeared at 24 h, suggesting that the cell death might be a PCD, due to the physiological activities gradually disappearing. During the cell death, the activities of caspase-9-like and caspase-3-like significantly increased, with the highest at 1 h. With prolonging the treatment time, C. reinhardtii cells gradually shrank, and the nuclei concentrated firstly following by a broken process, with moving to the cell edge. For DNA, obvious ladders were detected at 1 h, and then they gradually degraded to fragments of 100-250 bp at 24 h. These hallmarks suggested that β-ionone, limonene and longifolene may poison other algae by inducing PCD.

A review on control of harmful algal blooms by plant-derived allelochemicals

Harmful algal blooms (HABs) have several negative impacts on aquatic ecosystem, and even harm to humans. Utilization of allelochemicals to inhibit microalgal overgrowth is an environment-friendly approach for controlling HABs. This paper demonstrated the development of allelochemicals with algicidal effects, including the development history of allelopathy, the application methods, the reported allelopathic plants and their derived allelochemicals. Allelopathy is a promising strategy to control HABs as the effectiveness of allelochemicals on inhibiting microalgae cells has been discovered and confirmed for many years. The proposed allelopathic mechanisms and species-selective properties were expounded as well. Moreover, this paper further proposed suggestions for the further research and development of allelopathy strategy for HABs control.

Interaction of Drug Candidates with Various SARS-CoV-2 Receptors: An in Silico Study to Combat COVID-19

The world is currently facing the COVID-19 pandemic caused by the SARS-CoV-2 virus. The pandemic is causing the death of people around the world, and public and social health measures to slow or prevent the spread of COVID-19 are being implemented with the involvement of all members of society. Research institutions are accelerating the discovery of vaccines and therapies for COVID-19. In this work, molecular docking was used to study (in silico) the interaction of 24 ligands, divided into four groups, with four SARS-CoV-2 receptors, Nsp9 replicase, main protease (Mpro), NSP15 endoribonuclease, and spike protein (S-protein) interacting with human ACE2. The results showed that the antimalarial drug Metaquine and anti-HIV antiretroviral Saquinavir interacted with all the studied receptors, indicating that they are potential candidates for multitarget drugs for COVID-19.

Synergistic effects of amorphous OSA-modified starch, unsaturated lipid-carrier, and sonocavitation treatment in fabricating of Lavandula angustifolia essential oil nanoparticles

This investigation aims to evaluate the synergistic effects of amorphous OSA-modified starch, unsaturated lipid-carrier (RBD-SFO), and high-energy microfluidization in synergy with the ultrasonic techniques in fabricating of Lavandula angustifolia essential oil (LAF-EO) nanoparticle. GC-MS and SEM techniques were employed to investigate the LAF-EO isolation method used. DLS analysis was employed along with CLSM and TEM techniques to investigate the physicochemical properties of nanoemulsion formulation (NE) matrices. The NE achieved the optimal spherical and size distributions of droplets (125.7 nm), Poly Dispersity Index (PdI) (0.183), and ζ-potential (-40.3 mV) when the contents of the formulation matrix were as follows: OSA-MS (2%), LAF-EO (1%), RBD-SFO (1%), and Tween-80 (1%). The findings of this work provide a new concept about the synergistic effects of amorphous OSA-modified starch and unsaturated lipid carrier as safe-grade macromolecules in the fabricating of LAF-EO nanoparticles. Besides, the application of the ultrasound cavitation phenomenon has been shown to have effective effect in reducing the droplet hydrodynamic diameter along with enhancing the distribution (PdI) and electrokinetic potential of the LAF-EO nanoparticles.

Toxic mechanism of eucalyptol and β-cyclocitral on Chlamydomonas reinhardtii by inducing programmed cell death

Eucalyptol and β-cyclocitral are 2 main compounds in cyanobacterial volatile organic compounds and can poison other algae. To uncover the toxic mechanism of the 2 compounds, the cell growth, photosynthetic abilities, H₂O₂ production, caspase-like activities, nuclear variation and DNA laddering were investigated in Chlamydomonas reinhardtii treated with eucalyptol and β-cyclocitral. Eucalyptol at ≥ 0.1 mM and β-cyclocitral at ≥ 0.05 mM showed toxic effects on C. reinhardtii cells, and 1.2 mM eucalyptol and 0.4 mM β-cyclocitral killed the whole of the cells during 24 h. During the death process, the photosynthetic pigment gradually degraded, and Fv/Fm gradually declined, indicating that the death is not a necrosis due to the gradual disappearance of the physiological process. In the treatments with 1.2 mM eucalyptol and 0.4 mM β-cyclocitral, H₂O₂ content burst at 10 min and 30 min, respectively. Caspase-9-like and caspase-3-like were activated, and cell nucleuses concentrated firstly and then broke with prolonging the treatment time. Meanwhile, DNA showed laddering after 1 h, and was gradually cleaved by Ca²⁺-dependent endonucleases to mainly about 100-250 bp fragments. These hallmarks indicated that eucalyptol and β-cyclocitral may poison other algal cells by inducing programmed cell death triggered by the increased H₂O₂.

Effects of high light and temperature on Microcystis aeruginosa cell growth and β-cyclocitral emission

Cyanobacteria always massively grow and even occur blooms in summer, with releasing amount of β-cyclocitral. To uncover the effects of summer high irradiance and temperature on cyanobacterial growth and β-cyclocitral emission, the cell growth, reactive oxygen species (ROS) levels, photosynthetic pigment content, chlorophyll fluorescence and β-cyclocitral emission were investigated in Microcystis aeruginosa under high light and temperature. Compared to the control under 50 μmol m^-2·s^-1, the cell growth was promoted under 100 μmol m^-2·s^-1, but inhibited under 500 and 1000 μmol m^-2·s^-1. The inhibition was also detected under high temperature at 30 and 35 °C in contrast to the control at 25 °C. Under high light and high temperature, M. aeruginosa increased ROS levels and reduced photosynthetic pigment content and photosystem II (PSII) efficiency, which resulted in the inhibition on cell growth. With increasing the light intensity and temperature, ¹O₂ levels gradually increased, while β-carotene content gradually decreased by quenching ¹O₂, with increasing β-cyclocitral emission. In summer, high irradiance and temperature not benefited the growth of cyanobacteria, but the emission of β-cyclocitral derived from β-carotene quenching ¹O₂ may offset the disadvantages by poisoning other algae.

Terpenoids, Cannabimimetic Ligands, beyond the Cannabis Plant

Medicinal use of Cannabis sativa L. has an extensive history and it was essential in the discovery of phytocannabinoids, including the Cannabis major psychoactive compound—Δ9-tetrahydrocannabinol (Δ9-THC)—as well as the G-protein-coupled cannabinoid receptors (CBR), named cannabinoid receptor type-1 (CB1R) and cannabinoid receptor type-2 (CB2R), both part of the now known endocannabinoid system (ECS). Cannabinoids is a vast term that defines several compounds that have been characterized in three categories: (i) endogenous, (ii) synthetic, and (iii) phytocannabinoids, and are able to modulate the CBR and ECS. Particularly, phytocannabinoids are natural terpenoids or phenolic compounds derived from Cannabis sativa. However, these terpenoids and phenolic compounds can also be derived from other plants (non-cannabinoids) and still induce cannabinoid-like properties. Cannabimimetic ligands, beyond the Cannabis plant, can act as CBR agonists or antagonists, or ECS enzyme inhibitors, besides being able of playing a role in immune-mediated inflammatory and infectious diseases, neuroinflammatory, neurological, and neurodegenerative diseases, as well as in cancer, and autoimmunity by itself. In this review, we summarize and critically highlight past, present, and future progress on the understanding of the role of cannabinoid-like molecules, mainly terpenes, as prospective therapeutics for different pathological conditions.

Why Algae Release Volatile Organic Compounds-The Emission and Roles

A wide spectrum of volatile organic compounds (VOCs) are released from algae in aquatic ecosystems. Environmental factors such as light, temperature, nutrition conditions and abiotic stresses affect their emission. These VOCs can enhance the resistance to abiotic stresses, transfer information between algae, play allelopathic roles, and protect against predators. For homogeneous algae, the VOCs released from algal cells under stress conditions transfer stress information to other cells, and induce the acceptors to make a preparation for the upcoming stresses. For heterogeneous algae and aquatic macrophytes, the VOCs show allelopathic effects on the heterogeneous neighbors, which benefit to the emitter growth and competing for nutrients. In cyanobacterial VOCs, some compounds such as limonene, eucalyptol, β-cyclocitral, α-ionone, β-ionone and geranylacetone have been detected as the allelopathic agents. In addition, VOCs can protect the emitters from predation by predators. It can be speculated that the emission of VOCs is critical for algae coping with the complicated and changeable aquatic ecosystems.