INDUCTION OF DESICCATION TOLERANCE IN MICROSPORE-DERIVED EMBRYOS OF BRASSICA-NAPUS L BY THERMAL-STRESS

The use of dry microspore derived embryos as cloning materials greatly facilitates long term storage and transportability. The effects of heat and cold pretreatments on microspore-derived embryos of Brassica napus L. were investigated in an attempt to induce desiccation tolerance in these embryos before drying to about 12% moisture. Heat treatment was optimal between 30 and 33-degrees-C for shoot survival and plant regeneration from dry embryos. Induction of desiccation tolerance also was achieved with 2 day exposure to 2-degrees-C; however, its effectiveness was relatively less than heat shock treatment. Cold stratification at 4-degrees-C for 10 days enhances germination of embryos whether they were previously dried or not. Following desiccation, plant regeneration frequencies varied considerably among 4 winter lines tested, which may have been associated with genotype factors that influence synchronized embryo development and maturation. The results presented here demonstrate that thermal stress is capable of expressing an enhanced desiccation tolerance in microspore derived embryos of Brassica napus L. and this response is related to genotype, stress temperature, age of the embryos and stratification.