To understand the gene expression that enables the survival of barley under high salt conditions, we have performed differential display RT-PCR (DDRT-PCR) with the mRNAs expressed in leaves of barley plants subjected to high salt in a stepwise manner. The expression profile of genes often tells us eloquently about what is taking place in a particular cell under a particular situation. We expected that the mRNAs expressed in such salt-stressed leaves include the genes whose products are important in conferring salt tolerance to the plant. DDRT-PCR using various single primers actually enabled us to obtain several DNA fragments, which were amplified preferentially from mRNA expressed in the salt-stressed leaves (Table 21.1). Subsequent Northern blot analysis, using them as probes, confirmed that most of the obtained fragments derived from genes actually expressed in the stressed leaves specifically or preferentially. One of the PCR fragments appeared to encode ascorbate peroxidase, according to the partial sequence. Ascorbate peroxidase is a hydrogen peroxide-scavenging enzyme in plant cells.1 It was reported that the expression and activity of ascorbate peroxidase is increased during drought stress. Environmental stress, such as drought, salt, high light and low temperature, causes the evolution of toxic active-oxygen species in chloroplasts, which is called oxida-tive stress. Therefore, this result validates our approach to isolate salt-induced genes by differential display, in order to unveil mechanisms of salt tolerance.

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