Likepeople，plantsexperiencestress．Andalso，likepeople，theresponsetothatstresscandeterminesuccess．Badenvironmentalconditions，suchasdrought，flood，heatandotherstresses，affectyields（产量）morethancroppestsan

　　Likepeople，plantsexperiencestress．Andalso，likepeople，theresponsetothatstresscandeterminesuccess．

　　Badenvironmentalconditions，suchasdrought，flood，heatandotherstresses，affectyields（产量） morethancroppestsanddiseases．Wearetryingtofindawaytoequipplantswiththeabilitytotolerateenvironmentalstressandmaintainhighyields，saidStephenHowell，aprofessorofgeneticsandcellbiology．

　　Plantcellsproduceproteins （蛋白质） andshipthemtodifferentpartsofthecell．Undernormalconditions，theseproteinsarefoldedintotheirnormal，healthystructuresastheyareproduced．Whenaplantisunderstress，itscellsproducepoorlyfoldedorunfoldedproteins．Thenabuilt-insystemsensesthisand"setsoffanalarminthecell，"saidHowell．

　　Inresponsetothealarm，anotherprotein （IRE1）startsworkingandcreatesadifferentprocesswhichactivates （激活） thestressresponsegeneswhoseproductsbringaboutdefensivemeasuresthathelptheplantsurvive．

　　"Asitturnsout，responsesthatareactivatedunderstressconditionsactually inhibit thegrowthofplants，"saidHowell．"Thisallowsthemtopreservetheirenergytosurvivethestressconditions．"

　　Forplantsinthewild，thisresponseisahelpforsurvival，hesaid．Inproductionofagriculturecrops，however，thisresponsereducesyields．

　　"Youdon'twantcropplantstostopgrowing，"Howellsaid．"Youwantthemtocontinuetogrowandproduceeventhoughtheyareunderstress．"

　　Withthenewunderstandingofthisstressresponse，thenextstepmaybetosilencethealarmsystem，saidHowell．"Whatmaybeimportantistodisablesomeofthesestressresponses．Thatmaymaketheplantmoreproductiveunderstressconditions．"

　　28．Accordingtothetext，analarmintheplantcellsiscausedby___．

　　A．thefoldedproteins

　　B．thechangedproteins

　　C．thedefensivemeasures

　　D．thestressresponsegenes

　　29．Theenergypreservedintheplantsunderstressconditions___．

　　A．helpstheplantstosurvive

　　B．helpstomaintainhighyields

　　C．keepstheplantsgrowing

　　D．helpstoproducep