Required for acclimation to reactive oxygen species (ROS) responses downstream of beta-cyclocitral, including singlet oxygen 1O(2) detoxification reactions, especially upon light-mediated photooxidative stress, and leading to programmed cell death (By similarity). Prevents leaf senescence (PubMed:24151292). Moves from homogeneous distribution in the cytosol to discrete spots (e.g. stress granules (SGs) and processing bodies (PBs)) in response to singlet oxygen 1O(2) exposure. Accumulates during senescence. Plants lacking both MBS1 and MBS2 exhibit premature leaf senescence.