Response to temperature stress of reactive oxygen species scavenging enzymes in the cross-tolerance of barley seed germination

A number of studies have shown the existence of cross-tolerance in plants,but the physiological mechanism is poorly understood.In this study,we used the germination of barley seeds as a system to investigate the cross-tolerance of low-temperature pretreatment to high-temperature stress and the possible involvement of reactive oxygen species (ROS) scavenging enzymes in the cross-tolerance.After pretreatment at 0 °C for different periods of time,barley seeds were germinated at 35 °C,and the content of malondialdehyde (MDA) and the activities of ROS scavenging enzymes were measured by a spectrophotometer analysis.The results showed that barley seed germinated very poorly at 35 °C,and this inhibitive effect could be overcome by pretreatment at 0 °C.The MDA content varied,depending on the temperature at which seeds germinated,while barley seeds pretreated at 0 °C did not change the MDA content.Compared with seeds germinated directly at 35 °C,the seeds pretreated first at 0 °C and then germinated at 35 °C had markedly increased activities of superoxide dismutase (SOD),ascorbate peroxidase (APX),catalase (CAT),and glutathione reductase (GR).The SOD and APX activities of seeds germinated at 35 °C after 0 °C-pretreatment were even substantially higher than those at 25 °C,and GR activity was similar to that at 25 °C,at which the highest germination performance of barley seeds was achieved.These results indicate that low-temperature pretreatment can markedly increase the tolerance of barley seed to high temperature during germination,this being related to the increase in ROS scavenging enzyme activity.This may provide a new method for increasing seed germination under stress environments,and may be an excellent model system for the study of cross-tolerance.