Abstract:

This study investigated the response to low temperature stress of the ascorbic acid-glutathione （AsA-GSH） cycle in radicle mitochondria of alfalfa（Medicago sativa） seeds. Alfalfa seeds were germinated at two temperatures （10 or 20 ℃） and during imbibition antioxidant mechanisms， including hydrogen peroxide content， AsA-GSH cycle enzyme activity and antioxidant content were measured in radicle mitochondria imbibed for different times （6， 12 and 24 h）. It was found that the H₂O₂ content of radicle mitochondria under low temperature （10 ℃） was higher than that under normal temperature （20 ℃） after 12 and 24 hours imbibition. The glutathione reductase （GR） activity of radicle mitochondria at 10 ℃ was lower than that at 20 ℃ after imbibition for 6， 12 and 24 h. After 12 and 24 h imbibition， the ascorbic acid （AsA） content of radicle mitochondria at 10 ℃ was lower than that at 20 ℃. After 24 h imbibition under low temperature stress， the glutathione （GSH） content of radicle mitochondria decreased significantly （P<0.05） compared with seeds imbibed at normal temperature. During imbibition under low temperature， the normal process of seed germination was inhibited by oxidative damage， mainly through decrease in the activities of GR， monodehydroascorbate reductase， and peroxidase and decreased levels of AsA and GSH in the AsA-GSH cycle， which led to the accumulation of H₂O₂ in the radicle mitochondria.

Key words: alfalfa, low temperature stress, mitochondria, antioxidant enzyme, antioxidant, AsA-GSH cycle