SURVIVAL OF ZIZANIA EMBRYOS IN RELATION TO WATER-CONTENT, TEMPERATUREAND MATURITY STATUS

The interactions between water content and temperature on freezing and desiccation damage were examined for Zlzania (wild rice) embryos at s everal stages of maturity. The water content of excised embryos was ma nipulated by flash drying at 35 degrees C or room temperature to betwe en 2.5 g H2O/g dw and 0.05 g/g. Embryos were then exposed to temperatu res ranging from 5 to -50 degrees C. Viability following the drying an d cooling treatments was assayed by leakage of electrolytes and germin ation in culture. viability of embryos decreased when embryos were dri ed below a critical water content. The critical water content was grea test for the least mature embryos. Critical water contents were also t emperature dependent and increased with decreasing temperature. Even t hough the critical water content varied with developmental status and temperature, the water activity corresponding to the critical water co ntent appeared to be constant at 0.90. The most mature embryos survive d temperatures as low as -50 degrees C while the least mature embryos survived only to -18 degrees C. These trends were predicted by 'phase diagrams' based on the physical properties of water in embryos at diff erent stages of maturity (Vertucci et al., 1994a). Our results confirm the earlier prediction that long term preservation of Zizania grains is possible at -20 degrees C and the degree of success will be related to the maturity status of the embryos.