Comparative transcriptome analyses of barley and rice under salt stress.

Although barley and rice belong to the same family Poaceae, they differ in their ability to tolerate salt stress. In an attempt to understand the molecular bases of such differences, we compared changes in transcriptome between barley and rice in response to salt stress using barley cDNA microarrays. At 1 and 24 h after salt stress, many genes were up-regulated in barley, but not in rice. Leaf water potential declined in the first 10 h of stress in both species, but recovered in the period 24-48 h only in barley. In addition, we found that barley partitioned Na+ to the roots and away from the shoots more efficiently than rice. These differences in physiological responses were correlated with the differences in the steady-state abundance of transcripts for the genes related to adaptive functions. Transcripts for plasma membrane protein 3 and inorganic pyrophosphatase were up-regulated in both species, but only transiently in rice. This indicates that adaptive mechanisms for regulating ion homeostasis are partly conserved in the two species, but it seems that rice cannot sustain cellular ion homeostasis for a long time like barley. These results imply that genetic modification of regulatory controls of early salt-responsive genes might lead to development of the salt tolerance trait in rice.