The differentiation of visual pigments in metamorphosing larvae of Rana catesbeiana
[摘要] Therehavebeenseveralreportsinthelastfifteenyearsthatthevisualpigmentsofamphibiantadpoleschangeduringmetamorphosis.ThisphenomenonhasbeenexaminedindetailintadpolesofRanacatesbeiana.Ithasbeenshownthattheretinasofbullfrogtadpolescontain70–85%porphyropsinand15–30%rhodopsinpriortometamorphosis.Duringthyroxine-inducedmetamorphosisintheabsenceoffeeding,thehormonestimulatesphotopigmentconversion;asaresulttheretinasofpostmetamorphicanimalscontainsolelyrhodopsin.Atthesametimecellsofthepigmentedepitheliumdisplaymorphologicalevidenceofincreasedsyntheticactivity.Possiblemechanismsoperativeinthisconversionhavebeenexamined.Experimentsutilizingthyroxine-inducedmetamorphosisprovethatdietarychangescannotexplaintheconversion.Nordochangesinthesubstratespecificitiesofretinalalcoholdehydrogenase,isomerase,oropsinoccur.Severalexperimentswerecarriedoutinordertodeterminethetissuespecificityofthyroxineinthissystem.Unilaterallocalimplantationofthyroxine-agarintotheeyeisunusuallyeffectiveinhasteningphotopigmentconversion,butnoreproducibledifferencesbetweenthecontrolandexperimentaleyeswerefound.Noqualitativechangesinthecarotenoidcontentofeyesandliveroccurduringmetamorphosis.ThevitaminA2moleculeisanorgan-specificvitamin,beingrestrictedtotheeye.Argumentsarepresentedwhichsuggestbutdonotprovethattheactionofthyroxineisspecificallyontheeye,changingthecourseofvitaminAmetabolismthere.
[发布日期] [发布机构]
[效力级别] [学科分类] 生物科学（综合）
[关键词] [时效性]
