Tolerance to drought in plants is not a simple trait, but a complex of mechanisms working in combination to avoid or to resist water deficit. Genotypes that differ in tolerance to water deficit may show qualitative and quantitative differences in gene expression when submitted to drought periods. Four cotton (Gossypium hirsutum L.) genotypes (Siokra L-23, Stoneville 506, CS 50 and T-1521) with contrasting responses to water deficit stress were studied using the Differential Display (DD)

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... e to identify and isolate genes which may differ among them. Fifty-two cDNA fragments differentially expressed during water deficit were isolated, cloned and sequenced. Search of gene bank databases showed that two cDNA clones, A12B15-6 and A12B13-1, have high homology with a heat shock protein that binds to calmodulin found in Nicotiana tabacum (2.9e-32 P(N)) and with an Arabidopsis thaliana trehalose-6-phosphate synthase enzyme (9.0e-37 P(N)), respectively. One of the presumed functions of heat shock proteins is related to prevention of protein denaturation during cellular dehydration. Trehalose-6-phosphate synthase is involved in the production of trehalose, a disaccharide known to osmotically protect cell membranes during dehydration. The HSP homologue was found to be differentially expressed during the drought period in two drought tolerant genotypes but not in drought-sensitive genotypes. The trehalose-6-phosphate synthase homologue was also up-regulated during water deficit stress, however, all four genotypes were induced to express this homologue. Ribonuclease protection assays confirmed these results. This is an important finding since there are only few reports of trehalose presence in higher plants and none in cotton.