| Heavy metal pollution has been one of the environmental pollution problems.Heavy metals are easily transferred and enriched in food chain.The effects of heavy metal stress on the growth and reproduction of Spodoptera.exigua and its mechanism have not been systematically studied.The accumulation of heavy metals in four hosts of S.exigua and the accumulation and distribution of heavy metals in S.exigua with different cadmium concentrations(0,0.2,3.2,51.2 mg/kg)were systematically studied in this paper.Some indexes of growth and development were determined and the related differentially expressed genes were selected for analysis.The main results are as follows:1 Determination of heavy metal content in hosts of S.exiguaBecause heavy metals enter the body mainly through food intake,which affects the growth and reproduction of S.exigua.Therefore,five heavy metals(copper,lead,cadmium,chromium and mercury)in the main vegetable hosts of S.exigua(pakchoi,scallion,cabbage and asparagus)were determined.The results showed that mercury was not detected in four hosts,and lead and cadmium content exceeded the standard.It was found that pakchoi and cabbage had high accumulation ability of lead,the content of cadmium in scallion and asparagus was higher,the content of lead in cabbage was the highest,and the content of lead and cadminm in asparagus was the highest.Compared with host,the content of copper and lead in pakchoi,scallion and cabbage was the highest,the content of cadmium in asparagus was the highest,and the content of chromium in cabbage was the highest.2 Distribution of cadmium in tissues of S.exiguaThe cadmium contents in different tissues of S.exigua under cadmium stress were studied.The differences of cadmium contents in different tissues between larvae and adults under cadmium stress at different concentrations(0.2,3.2,51.2 mg/kg)and between males and females were investigated.(1)The cumulative concentration in the midgut of the 5th instar larvae was the highest,significantly higher than that in the fat body,and significantly higher than that in the epidermis and hemolymph.(2)For cadmium content in adult tissues,there were similar pattern between male and female adults at different concentrations,and the cumulative concentration of cadmium in abdomen was significantly higher than that in head,thorax,legs and wings.For males and females,the cadmium content in head,thorax and wings of females was significantly higher than that of males at the same concentration,while there was no significant difference between males and females in the cadmium content in abdomen and legs.(3)The accumulative concentration of cadmium In fat body of males was significantly higher than that in midgut,hemolymph and testis.3 Effect of cadmium stress on reproduction of S.exiguaThe effects of heavy metals on the growth and development of S.exigua and its offspring were studied.The reproductive effects of different concentrations of heavy metals(CK,0.2,3.2,51.2 mg/kg)on two generations of S.exigua were studied.(1)The survival rates of F1 and F2 generations with CK,0.2 and 3.2 mg/kg concentrations were not significantly different.The survival rates were 0.2>CK>3.2 mg/kg.Only 51.2 mg/kg survival rate was significantly lower than those of the other three treatments and the F2 generation was significantly lower than the F1 generation.(2)The pupation rate of F1 and F2 generations decreased with the increase of cadmium concentration.The pupation rate of F2 generation of 0.2 and 3.2 mg/kg was higher than that of F1 generation.The pupation rate of F2 generation of CK and 51.2 mg/kg was lower than that of F1 generation,and the pupation rate of F2 generation of 3.2 and 51.2 mg/kg was significantly different from that of F1 generation.(3)The emergence rate of CK and 0.2 mg/kg in F2 generation was slightly higher than that of F1 generation,while that of 3.2 and 51.2 mg/kg in F1 generation was lower than that of F2 generation,and there was no significant difference between CK,0.2 and 3.2 mg/kg in F1 generation and F2 generation.The emergence rate of 51.2 mg/kg in F1 generation was significantly different from that of F2 generation.(4)The number of eggs laid in F1 and F2 generations decreased with the increase of cadmium concentration.The number of eggs laid in F1 generation of CK and 0.2 mg/kg was slightly higher than that in F2 generation,and the number of eggs laid in F2 generation of 3.2 and 51.2 mg/kg was significantly lower than that in F1 generation.In order to understand the difference of reproductive effects between males and females,adults under different concentrations of cadmium stress were paired and found that:comparing the number of spawning after pairing on 0.2 mg/kg:only female was under stress>only male was under stress;on 3.2 mg/kg:only females were under stress<only males were under stress;on 51.2 mg/kg:only females were under stress<only males were under stress;In general,maternal females are more affected by cadmium stress than males by cadmium stress,which has a greater impact on oviposition.Subsequently,the continuous stress on female F2 generation showed that the survival rate,pupation rate,emergence rate and oviposition rate of F2 generation declined with the increase of the concentration,and the other concentration indexes were less than those of non-stressed F2 generation except 0.2 mg/kg concentration.4 Analysis of ovarian gene expression under cadmium stress and determination of related gene expressionDifferent cadmium stress had significant effects on the number of eggs laid by single female,and affected the morphology and ultrastructure of ovaries during development.The mechanism of cadmium stress could be understood by exploring the expression of ovarian genes.The transcriptional sequencing technique is to measure the sequence of the transcript by high throughput sequencing technology,so as to study the function and structure of the gene based on the whole level.In this experiment,the ovarian genomes of S.exigua under four different cadmium stresses were sequenced by transcriptional sequencing technique,and the mechanism of cadmium stress was explored from the gene level,and fatty acid synthesis was carried out from the point of view of gene level.The genes in Amino Acid Synthesis and hormone synthesis pathway were screened.The expression level was verified by Real time PCR.The results showed that the expression of two related genes of fatty acid synthesis increased with the increase of concentration,and the expression of two related genes of acetylcoenzyme A Carboxylase decreased with the increase of concentration.The expression of fatty acid synthase decreased with the decrease of concentration at low concentration of 0.2mg/kg.With the increase of concentration,the expression of tyrosine protein kinase and aspartate transaminase related genes increased,while the expression of polyphenol oxidase decreased with the increase of concentration.With the increase of concentration,the expression of apolipoproteins and estrogen thiosyltransferase increased with the increase of concentration. |
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