HeatstressnGaannTTCnnGAAnDNAHeatshockelementHSP70HeatshockproteinmRNAHeat-shockfactor(HSF)HeatshockproteinsFigure 13-6(HSP)FIGURE25.11Theheatshockfactor(HSF)cycleactivatesleadingtothetranslationof HSPsamongwhichareHSP70thesynthesisofheatshockproteinmRNAs.Innonstressed(4).TheHSFtrimers associated withtheHSE arephospho-cells,HSFnormallyexistsinamonomericstate(1)associ-rylated(5)facilitatingthebindingofHSP70tothephos-ated withHSP70proteins.Upontheonsetofanepisodeofphorylated trimers (6).TheHSP70trimer complex(7)disso-heatstress,HSP70dissociatesfromHSFwhichsubseciatesfromtheHSEanddisassemblesanddephosphoryquently trimerizes (2).Activetrimersbind to heat shocklatesintoHSFmonomers(8),whichsubsequentlybindHSPelements(HSE)inthepromoterofheatshockprotein(HSP)reformingtherestingHSP7o/HSFcomplex.(AfterBrayetgenes (3),andactivatethe transcription ofHSPmRNAsal.2000.)
Figure 13-6
(A)(B)EnEPFIGURE25.18Scanningelectronmicrographsoftransversenentgas-filledspaces(gs)inthecortex(cx),formedbysections through roots ofmaize,showing changes in strucdegeneration of cells.Thestele(all cells interior to theturewithoxygensupply.(150x)(A)Controlroot,suppliedendodermis,En)andtheepidermis(Ep)remainintact.Xwithair,withintactcorticalcells.(B)Oxygen-deficientrootxylem.(CourtesyofJ.L.BasqandM.C.Drew.)growing in a nonaerated nutrient solution.Note the promi-Figure 13-7
Figure 13-7
OUTSIDEOFCELLPathogenElicitor(productofanavrgene)CellwallReactiveoxygen02Cell wallcross-linkingspeciesNADPHoxidasePlasmamembraneReceptor(RgeneActivationofgenesfor:lonfluxes,product)changeinHypersensitiveresponsemembrane？PhytoalexinbiosynthesispotentialLigninbiosynthesisSystemicSalicylicacidbiosynthesisacquiredBiosynthesisofhydrolyticresistanceenzymesCYTOPLASMFigure 13-9FIGURE13.25Manymodesof antipathogendefenseare inducedbyinfection.Fragments of pathogen molecules called elicitors initiate a complex signaling pathwayleading to the activation of defensive responses.Some bacterial protein elici-tors areinjected directlyinto the cell, wheretheyinteract with Rgeneproducts
Figure 13-9
F1gure13-1oOxidesof sulfuremitted from fossil fuel power plants and other industries,andoxides of nitrogen from automobile exhaust,are converted inthe moist atmosphere intoacidsthat become dispersed overwide areas.Unlike unpolluted rain (average pH 5.6),the pH ofacid rain has been measured at 4.2 and evenlower. Plants,suchas these trees photographed in the Black Forest of Germany,may be damaged when the resulting increase in soil aciditycausescertain minerals,particularly calcium ions,to leach outofthesoil.(HansReinhard/BruceColeman)
Figure 13-10