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Supercooling capacity in relation to the contents of water and biochemical substances in eggs of Bryodemella tuberculatum dilutum( Orthoptera:Oedipodidae)
Pages: 745-753
Year: Issue:  7
Journal: Acta Entomologica Sinica

Keyword:  Bryodemella tuberculatum dilutumcold resistancesupercooling pointfatamino acidlow molecular sugar and polyol;
Abstract: 【Aim】Low temperature is one of the key factors affecting the growth,development and survival of insects. In order to clarify the cold hardiness of Bryodemella tuberculatum dilutum eggs and its mechanisms,we investigated the relationship between supercooling capacity and the contents of water and biochemical substances related to cold resistance in eggs in the laboratory. 【Methods】The supercooling points( SCPs) were measured by thermocouple method,and the contents of water,fat,amino acids,low molecular sugars and polyols were determined by oven-drying method,residue method,automatic amino acid analyzer and high performance liquid chromatograph( HPLC),respectively. 【Results】Soil water contents significantly influenced the SCPs,and water and fat contents in the pre-diapause eggs( P <0. 01). Water content in eggs increased from 45. 12% to 55. 25% and fat content( fresh weight)decreased from 10. 39% to 9. 39%,whereas the SCP rose from-30. 11℃ to-25. 69℃ with the increase of soil water content from 4% to 13%. The SCPs and the contents of water,fat,amino acids,low molecular sugars and polyols in eggs had extremely significant differences among different developmental stages( P < 0. 01). From 1 to 120 d after oviposition,the SCP decreased from-26. 78℃to-30. 18℃,water content declined from 51. 93% to 46. 69%,whereas fat content increased from9. 99%( fresh weight) and 17. 37%( dry weight) to 13. 92%( fresh weight) and 25. 29%( dry weight),respectively. The SCPs of diapause eggs were significantly lower than those of pre-diapause eggs. Seventeen amino acids were detected in eggs,five of which were significantly correlative with the SCPs( P < 0. 05). The SCPs declined with the increase of glycin and proline contents whereas increased with the increase of cystine,leucine and aspartic acid contents. With the egg development,the contents of trehalose,glycerol,myo-inositol and sorbitol increased,whereas the contents of glucose and fructose decreased. The contents of trehalose and glycerol were much higher than those of the other low molecular sugars and polyols in the developmental process of eggs. There were significant correlations between the SCPs and contents of six low molecular sugars and polyols,among which trehalose and glucose contents were the most correlative with the SCPs. The SCPs decreased with the increase of trehalose,glycerol,myo-inositol and sorbitol contents whereas increased with the increase of glucose and fructose contents.【Conclusion】In the developmental progress of B. tuberculatum dilutum eggs,the supercooling capacity is enhanced by the reduction of water content and the accumulation of cryoprotectants such as fat,glycin,praline,trehalose,glycerol,myo-inositol and sorbitol.
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