Environmental and hormonal regulation of barley late‐embryogenesis‐abundant (Lea) mRNAs is via different signal transduction pathways

Late‐embryogenesis‐abundant ( Lea ) genes are induced in immature embryos by ABA and osmotic stress. Using the ABA‐biosynthesis inhibitor norflurazon in combination with ionic and non‐ionic stress, the expression of three distinct groups of Lea transcripts in immature barley embryos was investigated, these groups being embryoand aleurone‐specific B15C mRNAs, embryo‐specific B19 inRNAs, and rab /dehydrin mRNAs, which encode stress‐related proteins that are also expressed in vegetative tissues. The expression of B15C and rab /dehydrins in response to mannitol was not affected by the addition of norflurazon, which decreased the endogenous ABA levels by 89%; this observation is consistent with an ABA‐independent pathway. The expression of B19 was only slightly dependent on ABA. In contrast, induction of the Lea genes by salt (NaCI) required at least 25ümol m −3 endogenous ABA. Together, these results are evidence for different signal transduction pathways linking ionic and non‐ionic osmotic stress to Lea mRNA accumulation in barley embryos.