ALLOCATION OF CYSTEINE FOR GLUTATHIONE PRODUCTION IN CATERPILLARS WITH DIFFERENT ANTIOXIDANT DEFENSE STRATEGIES: A COMPARISON OF Lymantria dispar AND Malacosoma disstria

Abstract

Sulfur amino acids [cysteine (Cys) and methionine (Met)] play two major roles during animal development: protein synthesis for growth and glutathione synthesis for defense. For caterpillars, the levels of sulfur amino acids found in foliar protein can be especially low relative to their nutritional needs. Previous work has measured concentrations of glutathione (GSH; containing Cys) in specific animal tissues, but has not examined whole-body levels to ascertain the costliness of this defense in terms of Cys allocation. This study examined whether the production of GSH varies between species and within individuals in accordance with an insect's need for antioxidant defense. Secondly, we quantified the allocation of total Cys (peptide-bound plus free Cys) to GSH in caterpillars as an estimate of its cost. Two contrasting species were compared: Lymantria dispar (Lymantriidae), a species that is highly defended, and Malacosoma disstria (Lasiocampidae), a species that is less defended. As expected, GSH levels were significantly higher in L. dispar than in M. disstria. Consistent with the function of the midgut as a first line of defense against ingested toxins, GSH levels were significantly higher in these tissues than in the whole bodies of both species. A major finding in this study was that a large fraction of total Cys is used to produce GSH: GSH in the midguts of L. dispar and M. disstria contained 23 and 21%, respectively, of the total Cys in these tissues, and the GSH in their remaining body tissues contained 19 and 17% of the total Cys in these tissues. Levels of total Cys in caterpillar tissues followed the same pattern of distribution as did GSH, producing a strong association between GSH and total Cys (R(2) = 0.794). We conclude that GSH is a costly defense, especially in generalist tree-feeding species such as L. dispar. These results further suggest that the large allocation of Cys to GSH in highly defended species might produce a tradeoff by limiting the amount of Cys available for rapid growth.

Reconfiguration of the immune system network during food limitation in the caterpillarManduca sexta

“…Unfortunately, this strategy will also increase the risk of damage to the host, and probably helps explain why absent-nutrition caterpillars were more sensitive to paraquat, a chemical that generates oxidative stress (Halliwell and Gutteridge, 2007). GSH requires the sulphur-containing amino acid cysteine, and this amino acid is not abundant in the diet of leaf-eating caterpillars (Barbehenn et al, 2013); therefore, a reduction in GSH with food limitation may be unavoidable. Network reconfiguration also led to changes that may mitigate costs.…”

Predator stress-induced immunosuppression: trade-off, immune redistribution or immune reconfiguration?

“…GSH represents a substantial pool of scarce amino acids such as cysteine (Barbehenn et al, 2013) that may be required elsewhere to augment anti-predator behaviour. The two explanations are not mutually exclusive, and both may contribute to selection to reduce GSH during chronic predator stress.…”

INSECTICIDAL AND OXIDATIVE EFFECTS OF AZADIRACHTIN ON THE MODEL ORGANISM Galleria mellonella L. (LEPIDOPTERA: PYRALIDAE)

“…GST is a phase II detoxifying enzyme and catalyzes the conjugation of GSH with electrophilic metabolites during oxidative stress involving in the cellular detoxification for overcoming environmental pollutants (Masella et al., ; Büyükgüzel et al., ; Barbehenn et al., ). GST activity has been correlated with the toxicity of insecticides and allelochemicals on insects including lepidopteran species (Büyükgüzel et al., ; War et al., ).…”