Negative effects on the water status of plants is one of the most common and deleterious stresses experienced by wild and cultivated plants throughout the world. Sunflower is the second most important edible oil crop on a worldwide production basis. In the middle-east, insufficient water or irrigation of sunflower using salt-contaminated water from rivers or reservoirs is a major problem for field establishment and final crop production. Our project is designed to identify, clone and characterize gene sequences regulated in response to water stress (e.g., drought and/or salinity). We employed the differential-display reverse transcriptase polymerase chain reaction (DD-RT-PCR) methodology to accomplish our objectives. To date five drought-regulated and ten salinity-regulated gene sequences have been cloned. These represent genes that are either induced de novo, up-regulated or down-regulated in response to water stress, and preliminary evidence shows that individual transcripts may be present in all tissues/organs or expressed specifically in roots, shoots or leaves. Sequence analysis has tentatively identified genes for at least five clones: guanylate kinase (Cap1-1U), an enzyme important in second messenger signaling pathways; selenium binding protein (GAp1-D), also implicated in ABA-response; activator-encoded transposase (CAp2-U), an essential factor for the mobility of Ac-like elements; polyprotein (RSG10-U), a retrotransposon-associated reverse transcriptase-like sequence; and LytB (VC2-D), a pneumococcal murein hydrolase important in cell-division. Current efforts focus on acquiring full-length cDNA and genomic clones, identifying and characterizing their cis-acting regulatory elements and trans-acting factors, precisely defining expression patterns on a tissue and temporal basis, and determining the in vivo biochemical/physiological function of the proteins encoded by each gene clone.

Key words: differential display, drought stress, osmotic stress, salt stress, sunflower