Reduction In Phenoloxidase Activity Research Articles

Regulation of melanization in aphids by parasitoid wasp venom proteins enhances mummification.

Interactions between parasitic insects and their hosts demonstrate the complexity of evolutionary processes. Specifically, the parasitoid wasp Aphidius ervi manipulates its host, the pea aphid Acyrthosiphon pisum, through strategic venom injection to enhance mummification. This study explores how this venom affects the aphid's immune system, particularly targeting the activity of the phenoloxidase (PO) enzyme. Following the injection of venom from A. ervi, significant changes were observed in the expression of immune-related genes in A. pisum, especially notable expression changes of ApPPOs and a reduction of PO activity. Multi-omics sequencing identified 74 potential venom proteins in the venom gland of A. ervi, including serine protease homolog 1 (AeSPH1) and serine protease inhibitor (AeSPN1), hypothesized to regulate PO activity. The injection of recombinant protein AeSPH1 and AeSPN1 into the A. pisum hemocoel selectively reduced the expression of ApPPO1, without affecting ApPPO2, and effectively suppressed melanization. Moreover, RNAi targeting AeSPH1 significantly reduced the mummification rate in A. pisum population parasitized by A. ervi. Our findings clarify the complex biochemical mechanisms underlying host-wasp interactions and highlight potential avenues for developing targeted biological control strategies. © 2024 Society of Chemical Industry.

Immune and nutritional responses of Podisus nigrispinus (Hemiptera: Pentatomidae) nymphs sprayed with azadirachtin

AbstractAzadirachtin is an efficient biopesticide, and it is considered safe for natural enemies because its mode of action is mainly by ingestion. The predator, Podisus nigrispinus Dallas, is found in various agroecosystems as a potential tool for biological control. However, there is much debate on the safety of this stinkbug if azadirachtin is used. Thus, we evaluated the cellular and humoral responses as well as biochemical parameters of the fifth‐instar nymphs of P. nigrispinus treated with azadirachtin. The insects were divided into three treatment groups and sprayed with azadirachtin (Azamax®), deltamethrin (Decis®), and water (control). After 24 h, total and differential hemocyte counts were performed. The analysis of phenoloxidase activity and quantification of nitric oxide, lipids, sugar, glycogen, and protein were performed after an interval of 24 and 72 h. Azadirachtin was found to affect the immune system of this stinkbug and decrease the number of hemocytes, especially pro‐hemocytes and oenocytoids, and it may have caused a reduction in phenoloxidase activity and nitric oxide level. In addition, the decrease in protein levels indicated the interference of azadirachtin in protein synthesis. We conclude that damage caused by the botanical insecticide has been less harmful than that caused by the synthetic insecticide, but use of azadirachtin may still interfere with biological control due to undesirable immune system damage reducing predator efficiency.

Winter soil freeze-thaw cycles lead to reductions in soil microbial biomass and activity not compensated for by soil warming

Air temperatures are rising and the winter snowpack is getting thinner in many high-latitude and high-elevation ecosystems around the globe. Past studies show that soil warming accelerates microbial metabolism and stimulates soil carbon (C) and nitrogen (N) cycling. Conversely, winter snow removal to simulate loss of snow cover leads to increased soil freezing and reductions in soil microbial biomass, exoenzyme activity, and N cycling. The Climate Change Across Seasons Experiment (CCASE), located at Hubbard Brook Experimental Forest, NH (USA) is designed to evaluate the combined effects of growing season soil warming and an increased frequency of winter soil freeze-thaw cycles on a northern forest ecosystem. Soils were collected from CCASE over two years (2014 and 2015) and extractable C and N pool sizes, as well as microbial biomass, exoenzymes, and potential net N mineralization and microbial respiration were measured. Soil warming alone did not stimulate microbial activity at any sampling time. Extractable amino acid N and organic C, proteolytic and acid phosphatase activity, and microbial respiration were reduced by the combination of warming in the growing season and winter soil freeze-thaw cycles during the period following snowmelt through tree leaf out in spring. The declines in microbial activity also coincided with an 85% decline in microbial biomass N at that time. Growing season warming and winter soil freeze-thaw cycles also resulted in a two-fold reduction in phenol oxidase activity and a 20% reduction in peroxidase activity and these declines persisted throughout the snow-free time of the year. The results from this study suggest that positive feedbacks between warming and rates of soil C and N cycling over the next 100 years will be partially mitigated by an increased frequency of winter soil freeze-thaw cycles, which decrease microbial biomass and rates of soil microbial activity.

Cellular and humoral responses of Pieris brassicae to infection by Steinernema feltiae, its symbiont bacteria, and their metabolites

This study describes the mortality effects of the culture broth ofXenorhabdus bovieniiand its aqueous and organic extracts onPieris brassicaelarvae. All the treatments had insecticidal activities when injected into the haemocoel. The culture broth of bacteria and its aqueous extracts exhibited more insecticidal activity. The results showed the immune response ofP. brassicaeexposed toSteinernema feltiae, its symbiont bacteria,X. bovienii, and aqueous and organic extracts of bacteria. Both cellular and humoral responses were investigated. After infection of the larvae ofP. brassicaewithS. feltiae, the total number of haemocytes quickly increased. A reduction in the number of haemocytes was observed over post-injection time. In addition, plasmatocytes and granulocytes showed increased frequency and significant changes when compared to other haemocytes in responding to entomopathogenic nematode injection.Steinernema feltiaeincreased phenoloxidase activity but 3 h post-injection the concentration gradually decreased. However, a reduction in phenoloxidase activity was observed when the larvae were infected with bacteria or their aqueous and organic extracts. This study showed that both living and heat-killed bacteria have suppression effects on phenoloxidase activity. The lysozyme concentration increased inP. brassicaelarvae when they were exposed to living and heat-killedX. bovienii. No suppression effect of the bacteria was detected on lysozyme.

Parasitism by Cotesia flavipes alters the haemocyte population and phenoloxidase activity of the sugarcane borer, Diatraea saccharalis

AbstractParasitism of Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae) larvae by Cotesia flavipes Cameron (Hymenoptera: Braconidae) or injection of C. flavipes polydnavirus causes numerous alterations in host physiology including developmental arrest, abrogation of host immunity, and biochemical changes in proteins, carbohydrates, glycogen, and lipids. This study focused on changes in haemocyte composition occurring in the cellular immune system of parasitised D. saccharalis larvae. We also analysed the effects of parasitisation by C. flavipes on humoral immunity in terms of phenoloxidase (PO) activity in the host. In nonparasitised D. saccharalis larvae, granular cells represented the main haemocyte type (39%) and plasmatocytes were also present at around 35% among the total haemocytes. The percentages of these two major haemocytes decreased significantly in parasitised larvae after 6 days of parasitoid oviposition and the total haemocyte counts exhibited a significant reduction in parasitised larvae 3 and 6 days following parasitisation. The parasitised larvae also showed a significant decrease in humoral immune capacity as evidenced by reduction of PO activity. Moreover, the plasma had more PO activity than the haemocytes and the parasitised larvae showed less PO activity than the control larvae. This research demonstrates that the parasitism of C. flavipes adversely affects the total haemocyte populations and PO activity of D. saccharalis larvae, which would contribute to host immunosuppression.

Cellular immune reactions of the sunn pest, Eurygaster integriceps, to the entomopathogenic fungus, Beauveria bassiana and its secondary metabolites.

In this study, five morphological types of circulating hemocytes were recognized in the hemolymph of the adult sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae), namely prohemocytes, plasmatocytes, granulocytes, adipohemocytes, and oenocytoids. The effects of the secondary metabolites of the entomopathogenic fungus Beauveria bassiana on cellular immune defenses of Eurygaster integriceps were investigated. The results showed that the fungal secondary metabolites inhibited phagocytic activity of E. integriceps hemocytes and hampered nodule formation. A reduction of phenoloxidase activity was also observed. The data suggest that B. bassiana produce secondary metabolites that disable several immune mechanisms allowing the fungus to overcome and then kill its host. This characteristic makes B. bassiana a promising model for biological control of insect pests such as E. integriceps.

Immune effects of HFO on European sea bass, Dicentrarchus labrax, and Pacific oyster, Crassostrea gigas

The European sea bass, Dicentrarchus labrax, and the Pacific oyster, Crassostrea gigas, were exposed to a soluble fraction of heavy fuel oil for 5 and 9 days, respectively. The organisms were then transferred to non-contaminated seawater for 1 month. The bioaccumulation and elimination of PAHs in contaminated tissues were dissimilar between species. In fish, acenaphthene and naphthalene were detected and naphthalene was still detectable 30 days after the beginning of the recovery period. In oysters, on the other hand, pyrene and phenanthrene were bioaccumulated and 14 days after exposure no more PAHs were detected. Concerning innate immune parameters, the increase of haemolytic activity of the alternative complement pathway in fish and the reduction of phenoloxidase activity in oysters endured, respectively, 1 and 2 weeks in contaminated organisms. This indicates that these two enzymatic cascades could be quite useful for monitoring pollution by oil.

Detection of phenoloxidase activity in early stages of the Pacific oyster Crassostrea gigas (Thunberg)

The presence of phenoloxidase (PO) activity was detected in different developmental stages of the Pacific oyster, Crassostrea gigas. A significant reduction in PO activity was observed from the 6 h embryo stage to the day 11 larvae by spectrophotometry. A progressive increase was also observed from the day 13 larvae right through to the juvenile stage. The microscopy studies with ‘6 h embryo’ and adult samples confirmed the presence of PO activity. Various modulators of PO activity were used to study the triggering of pro-phenoloxidase (proPO) activating system of C. gigas but also to confirm the exact nature of the monitored activity. The enzyme activation mechanisms appear to differ with the developmental stage: bacterial lipopolysaccharides constitute an early elicitor of the proPO–PO system, whereas a purified trypsin triggers proPO–PO system in C. gigas spat. Phenoloxidase activity was totally suppressed by PO-specific inhibitors such as β-2-mercaptoethanol, sodium diethyldithiocarbonate and tropolone. This study demonstrated the selective response of PO-like activity by different elicitors and suggested that proPO–PO activating system, which is supposed to play an important function in non-self recognition and host immune reactions in oyster, is expressed early in the Pacific oyster, C. gigas.

RNA interference of Hemolin causes depletion of phenoloxidase activity in Hyalophora cecropia

Melanization is regulated by the prophenoloxidase cascade and functions as a response to intruding microorganisms in invertebrates. When injecting dsRNA of the lepidopteran immune protein hemolin in pupae of Hyalophora cecropia (Lepidoptera: Saturniidae), we observed a significant reduction in phenoloxidase activity after 24 h, but not after 72 h. The link between hemolin and the prophenoloxidase system suggests that hemolin is a pattern recognition protein important for the triggering of the prophenoloxidase cascade in the defence against bacterial infections.

ATMOSPHERIC NITRATE DEPOSITION AND ENHANCED DISSOLVED ORGANIC CARBON LEACHING

Atmospheric NO3− deposition has the potential to disrupt litter decomposition in temperate forests by suppressing enzymes responsible for lignin degradation. A reduction in phenol oxidase activity could potentially trigger an increase in soluble phenolic compounds, which in turn are known to decrease the activity of cellulolytic enzymes like β‐glucosidase. Our study investigated whether the inhibition of lignin degradation by experimental NO3− deposition could increase soluble phenolics in soil, suppress β‐glucosidase activity, and potentially explain a greater export of dissolved organic C (DOC) from northern hardwood ecosystems. We found no evidence that the suppression of phenol oxidase by NO3− additions increased soluble phenolics in mineral soil, nor did we find a strong inverse relationship between soluble phenolics and β‐glucosidase activity. It appears that reductions in mineral soil lignolytic activity induced by experimental deposition are not responsible for greater DOC export from soil.

Radiation-Induced Changes in Melanization and Phenoloxidase in Caribbean Fruit Fly Larvae (Diptera: Tephritidae) as the Basis for a Simple Test of Irradiation

First instars of the Caribbean fruit fly, Anastrepha suspensa (Loew), were irradiated with 0, 5, 10, 20, 50, 75, 100, and 150 Gy doses from a Cs-137 source, and observed for whole body melanization as late third instars. Control larvae rapidly melanized, whereas larvae irradiated at {ge}20 Gy failed to show typical melanization after freezing and thawing. Assays of phenoloxidase in control and irradiated larvae showed greatly decreased enzyme activity at {ge}20 Gy and substantial reduction at lower doses. Larvae were also irradiated on the 1st d of each instar, and phenoloxidase activity was determined when they became late third instars. Larvae irradiated on the 1st d of the first instar and on 1st d of the second instar has {approx}90% or greater reduction in phenoloxidase activity as late third instars. Larvae irradiated on the 1st d of the instar had {approx}50% reduction in phenoloxidase activity at the time they became late third instars leaving the food to pupate. A simple spot test for phenoloxidase was developed that produced a red color with a crushed control larvae and no color with a larva irradiated at {ge}25 Gy. The radiation induced changes in melanization and phenoloxidase activity, and a simple spotmore » test may serve as tests for irradiation treatment of Caribbean fruit fly larvae. 10 refs., 2 figs., 2 tabs.« less

Activation of prophenoloxidase and inhibition of melanization in the haemolymph of immune Galleria mellonella larvae

After immunization of Galleria larvae with bacterial lipopolysaccharide, inhibition of haemolymph melanization developed parallel with antibacterial immunity. Failure of melanization was correlated with significantly decreased amounts of active cell-associated phenoloxidase (PO). In normal, nonimmune haemolymph, cellular PO originated from plasma proPO activated by, and largely attached to, the haemocytes; activation was maximal by 150 min. With immune haemolymph, such cellular activation of plasma proPO did not occur. Immune plasma proPO was activated by homogenization, but not by freeze-thawing. Normal plasma proPO was activated by freeze-thawing, but only to a very slight extent by homogenization. Mixing immune plasma with the freeze-thaw activated PO in normal plasma (1:2, v:v) caused a 37%, average reduction in PO activity. The results suggest that inhibition of melanization in immune Galleria haemolymph is caused by plasma factor(s) inhibiting the activation of plasma proPO by haemocytes.