Differential antioxidant responses to cold stress in cell suspension cultures of two subspecies of rice

Crops often encounter oxidative stresses due to changes of environmental conditions. Cold damage is one of the serious problems to agricultural production. In this study, cell suspension cultures of two subspecies of rice (Oryza sativa L.), Japonica cv. Nipponbare and indica cv. 9311, were developed to investigate their antioxidant responses to cold stress. The inherent morphology and surface features of cultured cells were examined by use of Cryo-scanning electron microscopy technique. The transcript of OsDREB2B, a cold-inducible transcription factor encoding gene, was strongly induced by cold stress in both cell lines. A significant accumulation of malondialdehyde, a product of lipid peroxidation, in cv. 9311 cells exposed to low temperature after 24 h demonstrated that they had higher levels of membrane damage compared with cv. Nipponbare under cold stress. In addition, responses of the antioxidant system to cold stress were genotype dependent. Compared to cv. 9311, cell suspension cultures of cv. Nipponbare exhibited elevated levels/contents of glutathione peroxidase, higher catalase, glutathione reductase, and glutathione. These would serve to protect cells against oxidative injury during the first few hours of chilling stress.