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 embryo s by ABA and osmotic stress, Using the ABA-biosynthesis inhibitor norf lurazon in combination with ionic and non-ionic stress, the expression of three distinct groups of Lea transcripts in immature barley embryo s was investigated, these groups being embryo- and aleurone-specific B 15C mRNAs, embryo-specific B19 mRNAs, and rab/dehydrin mRNAs, which en code stress-related proteins that are also expressed in vegetative tis sues, 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 A BA-independent pathway, The expression of B19 was only slightly depend ent on ABA, In contrast, induction of the Lea genes by salt (NaCl) req uired 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 embry os.