ENVIRONMENTAL AND HORMONAL-REGULATION OF BARLEY LATE-EMBRYOGENESIS-ABUNDANT (LEA) MESSENGER-RNAS 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 embryo- and aleurone-specific B15C mRNAs, embryo-specific B19 mRNAs, 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 (NaCl) required at least 25 mu mol 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.