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Plasma phenoloxidase of the larval tobacco budworm, Heliothis virescens, is virucidal.

Shelby KS, Popham HJ - J. Insect Sci. (2006)

Bottom Line: Preliminary results indicated that phenoloxidase is primarily responsible for this virucidal effect.Addition of the enzyme superoxide dismutase to plasma did not affect virucidal activity; however addition of catalase had an inhibitory effect.Inhibitors of nitric oxide synthase activity did not affect virucidal activity.

View Article: PubMed Central - PubMed

Affiliation: USDA, Agricultural Research Service, Biological Control of Insects Research Laboratory, Columbia, MO 65203, USA. shelbyk@missouri.edu

ABSTRACT
Heliothis virescens larval plasma contains high levels of an antiviral activity against the budded form of the Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) in vitro. Preliminary results indicated that phenoloxidase is primarily responsible for this virucidal effect. However it is known that other enzymes that generate antimicrobial reactive oxygen intermediates and reactive nitrogen intermediates are present in hemolymph that could contribute to the observed virucidal activity. To elucidate the contributions of phenoloxidase and other candidate activities to plasma innate immune response against baculovirus infection specific metabolic inhibitors were used. In vitro the general inhibitors of melanization (N-acetyl cysteine, ascorbate and glutathione), and specific inhibitors of phenoloxidase (phenylthiourea and Kojic acid), completely blocked virucidal activity up to the level seen in controls. Addition of the enzyme superoxide dismutase to plasma did not affect virucidal activity; however addition of catalase had an inhibitory effect. Inhibitors of nitric oxide synthase activity did not affect virucidal activity. Our results confirm that phenoloxidase is the predominate activity in larval plasma accounting for inactivation of HzSNPV in vitro, and that phenoloxidase-dependent H(2)O(2) production may contribute to this virucidal activity.

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Elevated levels of dietary ascorbic acid resulted in delayed pupation and adult emergence times of Heliothis virescens larvae compared to those reared on basal diet. Diets were supplemented with 12.0, 24.0, and 48.0 mg/ml ascorbic acid (5 to 20 times the basal level (2.4 mg/ml) of ascorbic acid. Larvae were placed on the diets as neonates (n = 75).
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i1536-2442-6-13-1-f401: Elevated levels of dietary ascorbic acid resulted in delayed pupation and adult emergence times of Heliothis virescens larvae compared to those reared on basal diet. Diets were supplemented with 12.0, 24.0, and 48.0 mg/ml ascorbic acid (5 to 20 times the basal level (2.4 mg/ml) of ascorbic acid. Larvae were placed on the diets as neonates (n = 75).

Mentions: In separate experiments we had observed that inclusion of excess dietary ascorbic acid inhibited the melanization activity of larval H. virescens plasma. High plasma levels of ascorbic acid might then be expected to alter the melanization-dependent virucidal activity. Larvae were reared on artificial diet supplemented with increasing amounts of ascorbic acid, and pupation, adult emergence and mortality data were collected. The time required for larvae to progress to pupation and adult emergence increased with the concentration of added dietary ascorbic acid (Fig. 4A). Larvae fed basal diet (2.4 mg/ml) attained 50% pupation after 12.8 ± 0.1 days and 50% had emerged as adults by 24.8 ± 0.2 days. When dietary ascorbic acid levels were raised to 12.0 to 48.0 mg/ml (5 to 20 times the basal level) pupation was delayed until 13.2 ± 0.2, 14.8 ± 0.2, and 17.6 ± 0.4 days, while emergence was delayed until 25.3 ± 0.3, 27.3 ± 0.3, and 29.5 ± 0.5 days, with highest mortality at the highest concentration of ascorbic acid (Fig. 4A). Pupal weights did not differ significantly between those reared on diets containing from basal to 24.0 mg/ml ascorbate (246.5 ± 26.5, 247.8 ± 33.4, and 250.7 ± 26.6 mg/pupa) (Fig. 4B). However, the pupal weight attained by larvae reared on diet containing 48.0 mg/ml ascorbic acid was significantly lower than the other groups (220.8 ± 28.2 mg, n = 30, p < 0.018, Dunn’s pairwise multiple comparison test; Fig. 4B) which correlated with the very high mortality of this group (62%).


Plasma phenoloxidase of the larval tobacco budworm, Heliothis virescens, is virucidal.

Shelby KS, Popham HJ - J. Insect Sci. (2006)

Elevated levels of dietary ascorbic acid resulted in delayed pupation and adult emergence times of Heliothis virescens larvae compared to those reared on basal diet. Diets were supplemented with 12.0, 24.0, and 48.0 mg/ml ascorbic acid (5 to 20 times the basal level (2.4 mg/ml) of ascorbic acid. Larvae were placed on the diets as neonates (n = 75).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2990302&req=5

i1536-2442-6-13-1-f401: Elevated levels of dietary ascorbic acid resulted in delayed pupation and adult emergence times of Heliothis virescens larvae compared to those reared on basal diet. Diets were supplemented with 12.0, 24.0, and 48.0 mg/ml ascorbic acid (5 to 20 times the basal level (2.4 mg/ml) of ascorbic acid. Larvae were placed on the diets as neonates (n = 75).
Mentions: In separate experiments we had observed that inclusion of excess dietary ascorbic acid inhibited the melanization activity of larval H. virescens plasma. High plasma levels of ascorbic acid might then be expected to alter the melanization-dependent virucidal activity. Larvae were reared on artificial diet supplemented with increasing amounts of ascorbic acid, and pupation, adult emergence and mortality data were collected. The time required for larvae to progress to pupation and adult emergence increased with the concentration of added dietary ascorbic acid (Fig. 4A). Larvae fed basal diet (2.4 mg/ml) attained 50% pupation after 12.8 ± 0.1 days and 50% had emerged as adults by 24.8 ± 0.2 days. When dietary ascorbic acid levels were raised to 12.0 to 48.0 mg/ml (5 to 20 times the basal level) pupation was delayed until 13.2 ± 0.2, 14.8 ± 0.2, and 17.6 ± 0.4 days, while emergence was delayed until 25.3 ± 0.3, 27.3 ± 0.3, and 29.5 ± 0.5 days, with highest mortality at the highest concentration of ascorbic acid (Fig. 4A). Pupal weights did not differ significantly between those reared on diets containing from basal to 24.0 mg/ml ascorbate (246.5 ± 26.5, 247.8 ± 33.4, and 250.7 ± 26.6 mg/pupa) (Fig. 4B). However, the pupal weight attained by larvae reared on diet containing 48.0 mg/ml ascorbic acid was significantly lower than the other groups (220.8 ± 28.2 mg, n = 30, p < 0.018, Dunn’s pairwise multiple comparison test; Fig. 4B) which correlated with the very high mortality of this group (62%).

Bottom Line: Preliminary results indicated that phenoloxidase is primarily responsible for this virucidal effect.Addition of the enzyme superoxide dismutase to plasma did not affect virucidal activity; however addition of catalase had an inhibitory effect.Inhibitors of nitric oxide synthase activity did not affect virucidal activity.

View Article: PubMed Central - PubMed

Affiliation: USDA, Agricultural Research Service, Biological Control of Insects Research Laboratory, Columbia, MO 65203, USA. shelbyk@missouri.edu

ABSTRACT
Heliothis virescens larval plasma contains high levels of an antiviral activity against the budded form of the Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) in vitro. Preliminary results indicated that phenoloxidase is primarily responsible for this virucidal effect. However it is known that other enzymes that generate antimicrobial reactive oxygen intermediates and reactive nitrogen intermediates are present in hemolymph that could contribute to the observed virucidal activity. To elucidate the contributions of phenoloxidase and other candidate activities to plasma innate immune response against baculovirus infection specific metabolic inhibitors were used. In vitro the general inhibitors of melanization (N-acetyl cysteine, ascorbate and glutathione), and specific inhibitors of phenoloxidase (phenylthiourea and Kojic acid), completely blocked virucidal activity up to the level seen in controls. Addition of the enzyme superoxide dismutase to plasma did not affect virucidal activity; however addition of catalase had an inhibitory effect. Inhibitors of nitric oxide synthase activity did not affect virucidal activity. Our results confirm that phenoloxidase is the predominate activity in larval plasma accounting for inactivation of HzSNPV in vitro, and that phenoloxidase-dependent H(2)O(2) production may contribute to this virucidal activity.

Show MeSH
Related in: MedlinePlus