ROS Signaling Pathways in Chilling Stress.

It was known that application of glycine betaine (GB) to plants could improve tolerance to stress caused by chilling, frost, salt, drought and high light intensities, and that this effect was accompanied by gene expression changes, but whether the gene expression changes were implicated in GB's effect and which genes were involved has been unclear. In the fourth issue of Physiologia Plantarum, we identified genes upregulated by GB that are involved in reactive oxygen species (ROS) metabolism and membrane trafficking processes. Direct evidence was provided for a role for a membrane trafficking protein (RabA4c) in GB's effect on ROS accumulation during chilling. In this Addendum, we discuss our findings that chilling stress is so closely linked with ROS accumulation. Chilling elevates ROS levels and results in inhibited root growth upon transfer of plants back to normal growing conditions. During the 2-4 day recovery period, ROS levels decline in root tips and in leaves. If ROS accumulation in response to chilling is blocked by pretreatment with GB, optimal root growth begins as soon as plants are transferred back to normal growing conditions without a recovery period, suggesting that chilling stress involves a ROS signaling pathway.