Virus-Resistant Transgenic Horticultural Crops: Safety Issues and Lessons from Risk Assessment Studies - Transgenic Horticultural Crops: Challenges and Opportunities - page 269

nontarget. organisms. can. be. dificult. to. evaluate,. and. even. when. an. effect. is. seen,.
it. can. be. dificult. to. assess. the. signiicance. of. this. observation.. With. respect. to.
virus-resistant.transgenic.crops,.it.is.not.easy.to.identify.a.mechanism.which.might.
result.in.an.effect.on.nontargets,.because.the.titer.of.the.transgene.protein.product.
is. likely. manyfold. lower. than. the. amount. of. the. corresponding. viral. protein. in. a.
non-transgenic.virus-infected.plant. 46,47 .In.addition,.given.the.fact.that.the.resistance.
mechanism.is.likely.to.be.RNA.silencing,.in.many.cases.little.to.no.protein.is.likely.
produced.at.all,.especially.in.the.case.of.untranslatable.transgenes..Furthermore,.crop.
plants.derived.through.traditional.breeding.practices.have.been.shown.to.produce.a.
wide.range.of.allergens.and.toxins.with.clear.effects.on.animals,.plants,.insects,.and.
nematodes.that.may.come.into.contact.with.these.plants.during.their.lifetime. 48
a llerGenIcIty and h uman h ealth e ffectS
Another.area.of.concern.regarding.transgenic.horticultural.crops.is.the.possibility.
of.the.introduction.of.allergenic.proteins.into.the.food.supply.and.the.introduction.
or. increase. in. the. production. of. toxic. compounds. 48-52 . Although. this. concern. also.
applies.to.crop.varieties.developed.using.conventional.breeding.methods,.transgenic.
products.have.received.strict.scrutiny.presumably.because.of.the.nature.of.the.trans-
gene.proteins..The.underlying.concept.of.safety.evaluations.of.genetically.modiied.
foods.was.proposed.in.the.early.1990s 53 .and.is.based.on.comparative.analyses.of.the.
transgenic.crop.with.the.conventionally.bred.parent.that.has.a.history.of.safe.use.(i.e.,.
substantial.equivalence). 54 .Additionally,.safety.testing.of.whole.foods.in.animals.is.
used.to.determine.toxicity.and.allergenicity.of.genetically.modiied.foods.as.well.as.
toxicity.testing.of.individual.proteins..The.latter.tests,.in.combination.with.nutritional.
analysis,.are.regarded.as.more.sensitive.and.accurate. 55,56 .While.postmarket.monitor-
ing.of.transgenic.food.crops.provides.data.on.patterns.of.human.nutritional.exposure.
and.may.be.useful.in.conirming.premarket.risk.assessment.and.the.detection.of.rare.
unintended.effects.on.health,.the.evaluation.is.not.regarded.as.a.component.of.risk.
assessment.and.is.not.a.substitute.for.thorough.premarket.risk.assessment. 57
Based.on. this.approach,.a.number.of.transgenic. crops.expressing.protein.prod-
ucts,. such. as. those. derived. from. Bt -derived. toxins. ( cry ). and. marker. transgenes.
( npt II,. uid A),.have.been.found.to.present.little.to.no.risk.to.food.or.feed.safety. 2,58-62 .
Further,.analysis.of.potential.pleiotropic.effects.on.inherent.plant.toxins.and.antinu-
trients.of.transgenic.plants.and.their.progenitor.cultivars.(e.g.,.maize,.rape,.tomato,.
potato,. and. soybean). has. shown. minor. to. perceptible. variations,. albeit. within. the.
ranges. documented. in. literature,. in. the. contents. of. these. compounds. 63 . Natural.
biological.variation,.including.nutrient.variation,.of.individual.plants.grown.under.
the.same.conditions.is.expected,.given.the.inluences.of.differences.in.plant.devel-
opment,. metabolism,. and. biotic. factors. 63,64 . However,. the. differences. between. the.
transgenic. and. the. progenitor. cultivar. can. also. be. attributed. to. somaclonal. varia-
tion,. given. that. the. transformation. of. many. crops,. including. papaya,. involves. an.
adventitious. regeneration. protocol,. and. in. some. cases,. 2,4-dichlorophenoxyacetic.
acid, 65-68 . a. plant. growth. regulator. known. to. introduce. genetic. mutations,. is. used..
Nonetheless,.backcrossing.to.the.original.parental.variety.(and.selecting.progeny.with.
appropriate.traits).effectively.eliminates.composition.alterations.caused.by.tissue.