| Co-Investigator(Kenkyū-buntansha) |
KONNO Haruyoshi Research Institute for Bioresources, Okayama University, Associate Professor, 資源生物科学研究所, 助教授 (10108178)
MAEDA Takanori Nihon University, College of Bioresource Sciences, Professor, 生物資源学部, 教授 (10038309)
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| Research Abstract |
Low temperature tolerance or cold hardiness refers to the capacity of an organism to survive exposure to low temperatures. The tolerance is divided into two classes, freeze susceptible and freeze tolerant. Since freeze susceptible insects cannot survive ice formation in their bodies, they enhance their supercooling capacity in winter to decrease the probability of freezing. They accumulated polyols and sugars, and excrete or inactivate ice nuclei. In contract, freeze tolerant insects can survive the extracellular freezing, but not intracellular freezing. They accumulate polyols and sugars as cryoprotectants, and produce ice nuclei to avoid intracellular freezing. This research results are as follows; Diapause of Helicoverpa armigera was mainly induced by low temperatures. Diapausing pupae supercooled below -20℃ and were freezing intolerant, 2) Aphids were freezing intolerant. However, they could not survive at -10℃, even though their supercooling points were below -23℃, 3)Diapusing larvae of Chilo suppressalis were freezing tolerant. The endogenous ice nucleus production in larvae was activated by JH, which induced diapause, and was inhibited by ecdysone, which terminated diapause, 4) the ice nuclei were present on the outside of the cell membranes of the muscle and epidermis and induced the freezing of the haemolymph to prevent intracellular freezing. In cultured fat body cells of Mamestra brassicae, nonfreezing injury might be induced by the damage of Na^- and Ca^-channels rather than K^-channel, 5) In diapause-specific genes in C. suppressalis, the partial DNA clone having a length of ca 900bp was expressed only in diapausing larvae. The function of the gene has been studied, 6) Ice nucleus protein produced by Fusarium moniliforme var. subglutinans isolated from the gut of larvae of C. suppressalis was purified. Amino acids of the protein are being sequenced.
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