Cryoprotective role of polyols independent of the increase in supercooling capacity in diapausing adults of Pyrrhocoris apterus (Heteroptera: Insecta)

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology 2001-10, Vol.130 (3), p.365-374
• Main Authors: Košt’ál, Vladimı́r, Šlachta, Martin, Šimek, Petr
• Format: Article
• Language: English
• Subjects: Acclimation; Adaptation, Physiological - drug effects; Aging - physiology; Animals; Cold hardiness; Cold Temperature; Cryoprotection; Cryoprotective Agents - metabolism; Cryoprotective Agents - pharmacology; Diapause; Gas Chromatography-Mass Spectrometry; Hemolymph - drug effects; Hemolymph - metabolism; Heteroptera - drug effects; Heteroptera - growth & development; Heteroptera - metabolism; Linear Models; Organ Specificity; Overwintering; Polymers - metabolism; Polymers - pharmacology; polyols; Preferential exclusion of solutes; Pyrrhocoridae; Pyrrhocoris apterus; Ribitol - pharmacology; Sorbitol - pharmacology; Supercooling; Survival Rate; Time Factors
• ISSN: 1096-4959; 1879-1107
• DOI: 10.1016/S1096-4959(01)00441-9

Diapausing cold-acclimated adults of the bug Pyrrhocoris apterus accumulate four ‘winter’ polyols, ribitol, sorbitol, mannitol and arabinitol, in total concentrations of up to 100 mM. The accumulation started only when the temperatures dropped below a threshold of +5°C in laboratory acclimated insects. The supercooling capacity ( SCP) was not affected by polyol accumulation and remained constant at approximately −17°C. Cold hardiness, measured as survival time ( Lt50) at −15°C, increased from approximately 1 day to approximately 1 week in parallel with polyol accumulation. There was a tight correlation ( r=0.98) between the concentration of ‘winter’ polyols in haemolymph and Lt50 −15. When a mixture of ribitol and sorbitol was injected into the haemolymph of the bugs acclimated to +5°C, the concentration of polyols increased from 2.5 to 83.1 mM in haemolymph, or from 0.07 to 6.61 μg/mg of fresh weight in the whole body, the SCP remained unchanged and survival after exposure to −14°C for 3 days increased approximately three-fold in comparison to untreated controls. Such results were interpreted as evidence for the cryoprotective role of accumulated polyols independent of the depression of SCP. Acclimation protocol using thermoperiod, mimicking daily temperature oscillations, resulted in moderately lower SCP, higher sum of polyols accumulated and significantly longer Lt50 −15 than at acclimation protocol with constant temperatures.