Enhanced Protoplast Division in Rice ( Oryza sativa L.) following Heat Shock Treatment

The effect of a heat shock pre-treatment (45 °C for 5 min) on the survival and division of rice ( Oryza sativa cv. Taipei 309) cell suspension culture protoplasts was investigated. Heat shock treated protoplasts exhibited an effective doubling in both the frequency of plated protoplasts dividing after 10-14 days (45 %) and in sustained division (plating efficiency 1.1 % after 30 days) compared with untreated protoplasts. The optimum plating density for sustained division was 3.0 × 10 5/ml. Colonies were obtained only from protoplasts subjected to the heat shock when cultured at a reduced density of 1.0 × 10 5/ml. This is the first report of enhanced protoplast division following an elevated temperature pretreatment. The implications of these findings and some possible explanations for the observations are discussed.