Hypoxic induction of anoxia tolerance in Avena coleoptiles

Seedlings of Avena sativa were subjected to 24 h anoxic stress after 24 h hypoxic-pretreatment (H-PT). The H-PT increased 4.5-fold the survivability of the anoxia in coleoptiles of the seedlings compared to that of non-pretreated (N-PT) seedlings. During pretreatment periods, alcohol dehydrogenase (ADH, EC 1.1.1.1) and pyruvate decarboxylase (PDC, EC 4.1.1.1) activities in the coleoptiles became 4.1- and 3.9-fold greater respectively than those of N-PT seedlings. After the onset of anoxic stress, ADH and PDC activities in all coleoptiles increased, but their activities in the H-PT coleoptiles remained much greater than those in the N-PT coleoptiles, and the average production rate of ethanol for the initial 6 h was 3.1 and 1.4 μmol g−1 fresh weight h−1 for the H-PT and N-PT coleoptiles, respectively. Coleoptiles of the seedlings lost ATP rapidly under anoxic stress; however, the decrease in ATP was much slower in the H-PT coleoptiles than in the N-PT coleoptiles. These results suggest that the H-PT may improve the subsequent tolerance of anoxia in Avena coleoptiles due to maintenance of ATP levels with rapid induction of ethanolic fermentation. The present results are consistent with the results that were found in roots of several plants, suggesting that the mechanism in hypoxic acclimation to anoxia implicated in their roots may act in Avena coleoptiles.