Desiccation tolerance of alfalfa ( Medicago sativa L.) somatic embroys. Influence of abscisic acid, stress pretreatments and drying rates

Abstract

Desiccation tolerance was induced in alfalfa ( Medicago sativa L.) somatic embryos by exogenous application of abscisic acid (ABA). Subsequently, embroys were dried to 10–15% moisture and stored for at least 3 weeks in the dry state. To estimate embryo survival, dried somatic embryos were imhibed on moist paper with no moist filter paper with no added nutrients. Under the appropriate treatment conditions, 65% of the somatic embryos survived and germinated in a manner analagous to true seed. The rate of drying affected the survival of the somatic embryos under some but not all treatment conditions. A slow drying rate of 1.2 g H 2O · g −1 · day −1 over 6 days, generally gave higher and more consistent embryo survival, compared to fast (6.9 g H 2 g H 2O · g −1 · day −1) drying over 1 day. Tolerance of desiccation was also induced in these somatic embryos by exposure to sub-lethal levels of low temperature, water, nutrient or heat stress prior to desiccation. However, some of these stress pretreatments had other deleterious effects on embryo maturation and seedling vigor after imbibition. Treatment of embryos with the triazole, uniconazole, also induced desiccation tolerance in these somatic embryos, but other undesirable side effects on seedling growth were observed. The only stress pretreatment that was comparable to exogenous application of ABA, as a means of inducing desiccation tolerance without detrimental effects on other characteristics, was heat shock.