Characterization of the Early Stages of Genetic Salt-Stress Responses in 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 induced, 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 ESI 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 hours after the onset of stress and had a large osmotic shock component, as indicated by induction of the accumulation of these mRNAs by a nonsaline osmoticum. The ion-specific component, however, also played a role. External Ca2+ reduced this response. The second phase was characterized by either constantly elevated mRNA levels or gradually increasing mRNA levels. The same biphasic response was elicited by exogenous abscisic acid (ABA). The response of all mRNAs to ABA closely approximated the response to 250 mM NaCl treatment in all three genotypes. The differences among the three genotypes in response to NaCl and ABA treatments were largely confined to the first phase of the response, in which mRNA levels were highest in L. elongatum and lowest in wheat. The levels of ESI mRNAs in the amphiploid closely approximated levels calculated on the basis of the doses of wheat and L. elongatum genomes in the amphiploid, which indicated an additive contribution of the genomes to early salt stress response in the amphiploid. The inducer of the ESI 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.