03263nam a2200361 a 450000100080000000500110000800800410001910000220006024500700008226000410015230000100019350000170020352023230022065000110254365000230255465000220257765000100259965000130260965000260262265000150264865000240266365000140268765000230270165000110272465000270273565000240276265000110278665300230279765300140282065300220283465300250285665300200288115596642000-02-23       1998    bl uuuu  m   00u1 u    #d1 aNEPOMUCENO, A. L.  aPhysiological and molecular responses of plants to water deficit.  a[S.l.]: University of Arkansasc1998  a269p.  aPhD. Thesis.  aTolerance to drought in plants results from networks of mechanisms working isolated or in combination. Genotypes that differ in tolerance to water-deficit stress should have qualitative and/or quantitative differences in gene expression. Therefore, to identify and isolate genes, which may differ among four cotton genotypes with diverse responses to water deprivaton, Differential Display (DDRT-PCR) was used. These genotypes were first physiologically characterized in growth chamber and greenhouse experiments. Water and osmotic potential of roots and leaves, photosynthetic rate and relative water content were some of the physiological parameters used to measure plant responses during and after the water defficit applied. Cultivar Siokra L-23 and the wild type T-1521, two drought tolerant genotypes, showed a significant ability of osmotic adjust during water deficit. Photosynthetic rate and relative water content were maintained near control values in the two tolerant genotypes. However, cultivar CS 50 and Stoneville 506, showed significant sensitivity to the water deficit applied, confirming previous observations. These results guided subsequent work with DDRT-PCR using mRNA samples colected during these experiments. Fifty-two cDNA fragments differentially expressed during water deficit were identified using DD. The differentially displayed fragments were isolated from the polyacrylamide gels and cloned in pGEM-T vectors. After cloning they were sequenced using thermocycling dideoxynucleotide chain termination protocols. Search of gene banks revealed 17 clones with high homology to known genes, and 20 clones with low homology, while 15 clones had no homologous entries. Among the sequences that showed high homology was a heat shock protein that binds to calmodulin. This gene was expressed only in the water-deficit tolerant genotypes (Siokra L-23 and T-1521) during the stress.  Another gene identified by homology was trehalose-6-phosphate synthase. This enzyme is part of the metabolic pathway for production of trehalose, a sugar known to osmoprotect cell membranes during desiccation. The differentially expressed gene sequences could have use in screening germplasm banks for similar genotypes, in plant physiology studies, and in molecular mapping of plant responses to water deficit.  acotton  amolecular genetics  awater deprivation  aÁgua  aAlgodão  aDeficiência Hídrica  aFisiologia  aGenética Molecular  aGenótipo  aGossypium Hirsutum  aPlanta  aRelação Água-Planta  aResistência a Seca  aStress  aDrought resistance  aGenotypes  aPlant pohysiology  aPlant water relation  aPlante response