The effect of ABA analogs on callus viability and gene expression in Craterostigma plantagineum

We have used callus tissue of the desiccation-tolerant plant Craterostigma plantagineum Hochst. to probe the stereochemical requirements of ABA in the desiccation tolerance response, using ABA analogs. Callus was treated with (S)-(+)-ABA and (R)-(-)-ABA and two pure isomer derivatives of each, and Viability after a drying treatment and the expression of four desiccation-induced late embryogenesis abundant (LEA)-type transcripts and sucrose synthase from Craterostigma were measured. Both stereoisomers alone caused transcript expression and highest viability. The two derivatives of (R)-(-)-ABA gave poor or no transcript expression and no viability, suggesting that alteration of a ring double bond to a single bond in this series of compounds is significant in ABA perception for both responses. One (S)-(+)-ABA derivative was effective in inducing all transcripts and causing callus viability. The other analog derivative induced all protein transcripts without concomitant tissue viability after drying. This suggests that some other ABA-inducible factor(s) are vital for desiccation tolerance of callus.