Spot assay for stress resistance. Cultured cells were harvested, exposed to stress factors, and 5 μL aliquots were spotted onto a BG11 plate (see details in Materials and methods). The cells were incubated for 6 days to observe stress resistance. (A) Samples were spotted onto the plate immediately after the stress treatments. (B) Samples were spotted onto the plate 24 h after the stress treatments. UV, ultraviolet irradiation; HD, heat dry; FD, freeze dry.