酸素同位体分別を利用したイネ葉身におけるシアン耐性呼吸の測定

A reduction in the dark respiration of rice may improve dry-matter production and yield. To explore the possibility of controlling cyanide-resistant alternative respiration, of which energy production efficiency is low, we constructed a measuring system for cyanide-resistant respiration in leaf blades of rice with the use of oxgen isotope discrimination. Dark respiration was lowest at 10mM KCN, the inhibitor of cytochrome pathway, and it was lowest at 30mM salicylhydroxamic acid (SHAM), the inhibitor of the alternative pathway. Oxygen isotope discrimination was highest when leaf blade had HCN applied for 1 hour after being soaked in 10mM KCM for 3 minutes, and it was lowest when lowest when leaf blade was soaked in 30mM SHAM regardless of the soaking method. The discrimination factors of the alternative oxidase and the cytochrome oxidase of leaf blade were estimination factors of the alternative oxidase and the cytochrome oxidase of leaf blade were estimated as 20.3‰ and 13.9‰, respectively, and the ratio of cyanide-resistant respiration to dark respiration of leaf blade was 38%.

イネの暗呼吸の抑制は乾物生産や収量の増大に貢献すると考えられている．エネルギー生産効率の低いシアン耐性呼吸の抑制の可能性を検討するため，酸素同位体分別を利用したシアン耐性呼吸の測定装置を製作し，イネ葉身の測定法を検討した．その結果，葉身の暗呼吸速度はシトクロム経路の阻害剤であるKCN溶液の濃度が10mMのときに，また，シアン耐性呼吸経路の阻害剤であるSHAM溶液の濃度が30mMのときに低下が最大であった．分別係数は３分間10mM KCN溶液に浸漬後HCNに１時間さらした場合に最も高い20.3‰が得られた．いっぽう，SHAM処理では30mMの溶液であれば浸漬法にかかわらず，13.9‰であった．これらから，イネ葉身のオルターティブ酸化酵素とシトクロム酸化酵素の分別係数はそれぞれ20.3‰と13.9‰であると推定され，このときのシアン耐性呼吸の割合は38%であった。