CHARACTERIZATION OF THE EARLY STAGES OF GENETIC SALT-STRESS RESPONSESIN SALT-TOLERANT LOPHOPYRUM-ELONGATUM, SALT-SENSITIVE WHEAT, AND THEIR AMPHIPLOID

Eleven unique cDNA clones corresponding to genes showing enhanced mRNA accumulation in the early stages of salt stress (early salt stress in duced, ESI) were previously isolated. The accumulation of these mRNAs in Lophopyrum elongatum (Host) A. Love, salt-sensitive wheat (Triticum aestivum L.), and their amphiploid is compared. The accumulation of E SI mRNAs was much greater in the L. elongatum roots than in the shoots . Additionally, mRNA accumulation in the roots of the three genotypes showed a biphasic response. The first phase occurred within a few hour s after the onset of stress and had a large osmotic shock component, a s indicated by induction of the accumulation of these mRNAs by a nonsa line osmoticum. The ion-specific component, however, also played a rol e. External Ca2+ reduced this response. The second phase was character ized by either constantly elevated mRNA levels or gradually increasing mRNA levels. The same biphasic response was elicited by exogenous abs cisic acid (ABA). The response of all mRNAs to ABA closely approximate d the response to 250 mm NaCl treatment in all three genotypes. The di fferences among the three genotypes in response to NaCl and ABA treatm ents were largely confined to the first phase of the response, in whic h mRNA levels were highest in L. elongatum and lowest in wheat. The le vels of ESI mRNAs in the amphiploid closely approximated levels calcul ated on the basis of the doses of wheat and L. elongatum genomes in th e amphiploid, which indicated an additive contribution of the genomes to early salt stress response in the amphiploid. The inducer of the ES I mRNA accumulation in response to NaCl and other osmotica is produced in the stressed roots and shows only minor, if any, translocation. A putative candidate for this inducer is root ABA.