一篇阅读理解题.Haveyoueverwonderedwhystems(茎)gro一篇阅读理解题.Haveyoueverwonderedwhystems(茎)growupwardsandrootsdownwards?Whydoplantsalwaysseemtoturntowardsthelightandclimbingplantsrunupratherthandown?

　　一篇阅读理解题.Haveyoueverwonderedwhystems(茎)gro

　　一篇阅读理解题.

　　Haveyoueverwonderedwhystems(茎)growupwardsandrootsdownwards?Whydoplantsalwaysseemtoturntowardsthelightandclimbingplantsrunupratherthandown?Theanswerissimple:auxin(生长素),achemicalsubstancethatcontrolsgrowthinplants.

　　Auxingivesawayitssecrets

　　Auxinisaplanthormone(激素).Darwinwasalreadyinterestedinitinthe19thcentury.Onlyinrecentyears,however,hasthehormonestartedtogiveawayitssecrets,thankstointensivemolecularresearch.Auxinisproducedintheyoung,growingpartsofplantsandthentransportedthroughouttheplant—toalow­lyingstemforexample.Thestemneedstostraightenoutassoonaspossibletobeabletoabsorbthetopside,resultingintheundersidegrowingfasterandthestemstraighteningout.Forthesamereason,plantsinfrontofwindowswillalwaysturntothelight.Thisactiveregulationofauxintransportallowsplantstotakeidealadvantageoflocalandchangingconditions.

　　Anewmeansoftransportforauxin

　　Thetransportofauxinthroughtheplantplaysavitalrole.And,fromallappearances,itisnotasimplematter.Theresearchersidentifiedanimportantnewlinkandmeansoftransportforauxin:PILSproteins(蛋白质).PILSproteinsarevitalforauxin­dependentplantgrowthandadjusttheintracellular(细胞内的)storageofthehormone.Itisexactlythiscompartmentalizing(分类)ofauxinthatseemsfunctionallyimportantforthevariousdevelopmentalprocesses.

　　Growingcropsmor