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. 2018 Apr 19;13(4):e0195349.
doi: 10.1371/journal.pone.0195349. eCollection 2018.

Stress pre-conditioning with temperature, UV and gamma radiation induces tolerance against phosphine toxicity

Saad M Alzahrani  1   2 , Paul R Ebert  1   3
Affiliations

Stress pre-conditioning with temperature, UV and gamma radiation induces tolerance against phosphine toxicity

Saad M Alzahrani et al. PLoS One. .

Abstract

Phosphine is the only general use fumigant for the protection of stored grain, though its long-term utility is threatened by the emergence of highly phosphine-resistant pests. Given this precarious situation, it is essential to identify factors, such as stress preconditioning, that interfere with the efficacy of phosphine fumigation. We used Caenorhabditis elegans as a model organism to test the effect of pre-exposure to heat and cold shock, UV and gamma irradiation on phosphine potency. Heat shock significantly increased tolerance to phosphine by 3-fold in wild-type nematodes, a process that was dependent on the master regulator of the heat shock response, HSF-1. Heat shock did not, however, increase the resistance of a strain carrying the phosphine resistance mutation, dld-1(wr4), and cold shock did not alter the response to phosphine of either strain. Pretreatment with the LD50 of UV (18 J cm-2) did not alter phosphine tolerance in wild-type nematodes, but the LD50 (33 J cm-2) of the phosphine resistant strain (dld-1(wr4)) doubled the level of resistance. In addition, exposure to a mild dose of gamma radiation (200 Gy) elevated the phosphine tolerance by ~2-fold in both strains.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Heat shock preconditioning against phosphine-induced mortality of C. elegans in wild-type, phosphine-resistant and heat shock response mutants.
A four-hour heat shock at 30◦C was followed by a 4 hour recovery period, after which the nematodes were subjected to 24 hour exposure to phosphine. Mortality was scored after a further 48 hour recovery period, either without or with heat shock preconditioning. Wild-type (N2), phosphine-resistant (dld-1(wr4)). (A) PS3551 (hsf-1) (B) RB791 (hsp-16.48) (C) RB1104 (hsp-3).
Fig 2
Fig 2. Analysis of LC50 value for heat shock preconditioning against phosphine-induced mortality of C. elegans.
(A) Comparison of the wild-type and the phosphine-resistant mutant and (B) heat shock mutants either without or with heat or cold preconditioning. A four-hour heat shock at 30◦C was followed by a 4 hour recovery period, after which the nematodes were subjected to phosphine exposure for 24 hours. Mortality was scored after a further 48 hour recovery period. The LC50 value for each strain is shown, either without or with heat shock preconditioning. Error bars represent the 95% confidence intervals for each LC50 data point. One-way ANOVA followed by Dunnett’s multiple comparisons for the LC50 values, ****p < 0.0001. Wild-type (N2), phosphine-resistant (dld-1(wr4)). Unpaired t-test was used to compare the LC50 values of each heat shock mutant strain, ****p < 0.0001, ***p < 0.001. RB791 (hsp-16.48), RB1104 (hsp-3) and PS3551 (hsf-1).
Fig 3
Fig 3. Effect of cold shock on phosphine-induced mortality of wild-type C. elegans and the phosphine-resistant dld-1 mutant.
A four-hour cold shock at 10◦C was followed by a 4 hour recovery period, after which the nematodes were subjected to 24 hour exposure to phosphine. Mortality was scored after a further 48 hour recovery period. Wild-type (N2), phosphine-resistant (dld-1(wr4)).
Fig 4
Fig 4. Effect of UV light on phosphine-induced mortality of wild-type C. elegans and the phosphine-resistant dld-1 mutant.
C. elegans were exposed to 18 and 33 J cm-2 UV radiation 24 hours, after which the nematodes were subjected to 24 hour phosphine exposure. Mortality was scored after a further 48 hour recovery period. Wild-type (N2), phosphine-resistant (dld-1(wr4)).
Fig 5
Fig 5. Effect of UV and gamma radiation on phosphine-induced mortality of C. elegans in wild-type and the phosphine-resistant dld-1 mutant.
Nematodes were exposed to a range of dosages of either UV light or gamma radiation at the L1 stage. Mortality was assessed 48hrs after exposure as lack of movement in response to a bright light stimulus. LC50 values are shown and the error bars represent the 95% confidence intervals for each LC50 data point. Wild-type (N2), phosphine-resistant (dld-1(wr4)). One-way ANOVA followed by Dunnett’s multiple comparison test for the LC50 values, **p < 0.01.
Fig 6
Fig 6. Exposure to gamma radiation induces tolerance to phosphine exposure in the wild-type and the phosphine-resistant worms. C. elegans were exposed to 200 Gy gamma radiation 24 hours, after which the nematodes were subjected to 24 hour exposure to phosphine.
Mortality was scored after a further 48 hour recovery period. Wild-type (N2), phosphine-resistant (dld-1(wr4)).
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