Transgenic Vegetables - Transgenic Horticultural Crops: Challenges and Opportunities - page 46

Various.monoterpenes.that.contribute.to.fruity.and.loral.scents.were.found.to.accu-
mulate.in.the.transgenic.tomatoes,.which.eventually.enhanced.the.lavor.and.aroma.
of.the.lesh. 91
Inulins. are. beneicial. for. human. health. and. are. produced. naturally. in. some.
plants.as.storage.carbohydrates..They.serve.as.replacements.for.high.caloric.fats.and.
sugars,.since.inulins.have.a.sweet.taste.and.are.not.absorbed.through.the.digestive.
tract.. Transgenic. lettuce. lines. expressing. the. asparagine synthetase A . gene. from.
Escherichia coli . accumulated. lowered. amounts. of. sucrose,. glucose,. and. fructose,.
whereas.inulin.content.increased.up.to.30.times.in.transgenic.leaves. 92 .These.lettuce.
genotypes.with.high.content.of.foliar.inulin.represent.useful.materials.for.breeding.
strategies.and.a.potential.source.for.low-molecular-weight.inulin.useful.for.dietary.
supplements,.in.addition.to.the.potential.for.enhanced.taste.
e nhanced a ntIoxIdant a ctIvItIeS
Enhancement. of. antioxidant. content. is. an. important. trait. in. the. light. of. potential.
health. beneits. imparted. by. these. chemicals. in. plants. and. animals.. α-Tocopherol.
is. the. most. biologically. active. form. of. vitamin. E,. which. is. implicated. in. decreas-
ing. the. risk. of. several. types. of. cancers,. coronary. heart. disease,. and. a. number. of.
.degenerative. human. conditions.. Manipulating. the. tocopherol. biosynthetic. path-
way. in. plants. to. convert. tocopherols. into. more. active. α-tocopherol. form. could.
have. signiicant. health. beneits. 93 . An. Arabidopsis . γ -tocopherol methyltransferase .
(γ -TMT ).gene.was.overexpressed.in.lettuce.to.improve.the.tocopherol.composition..
This.resulted.in.higher.TMT.activity.and.the.conversion.of.the.γ-tocopherol.pool.to.
α-tocopherol.in.transgenic.plants. 93 .In.another.attempt,.in.order.to.increase.tocoph-
erol.content.by.increasing.total.lux.to.the.tocopherol.biosynthetic.pathway,.two.dif-
ferent. Arabidopsis .genes.were.constitutively.expressed.in.lettuce..Transgenic.plants.
expressing.either.of.these.genes.had.total.tocopherol.content.increased.by.more.than.
twofold.mainly.due.to.an.increase.in.γ-tocopherol. 94
Increased.isoprenoid.levels,.the.precursors.to.many.important.nutrients,.can.be.
achieved. in. tomato. through. genetic. manipulation. of. mevalonic. acid. (MVA). and.
methylerythritol-4-phosphate. (MEP). pathways,. leading. to. the. formation. of. iso-
pentenyl. diphosphate. (IPP),. using. 3-hydroxymethylglutaryl . CoA. ( hmgr-1 ). and.
1-deoxy-d-xylulose-5-phosphate synthase .( dxs ).genes,.respectively..Transgenic.toma-
toes. expressing. the. Arabidopsis . hmgr-1 . gene. had. double. the. phytosterol. levels. 95 .
Additionally,. tomatoes. expressing. a. bacterial. dxs . gene. targeted. to. the. plastids.
resulted. in. signiicantly. increased. carotenoid. content,. which. was. attributed. to.
enhanced. levels. of. phytoene. and. β-carotene. 95 . In. order. to. increase. the. carotenoid.
and.lavonoid.content.in.tomato.fruits,.an.endogenous.phytomorphogenesis.regula-
tory.gene.( DET1 ).was.suppressed.by.RNAi.in.a.fruit-speciic.manner. 96 .The.resulting.
transgenic.fruits.accumulated.higher.levels.of.carotenoids.and.lavonoids.compared.
to.the.controls. 96 .Plastid.expression.of.a.bacterial.lycopene-β-cyclase.gene.in.tomato.
resulted.in.the.conversion.of.the.main.storage.carotenoid-lycopene,.to.β-carotene,.
leading.to.a.fourfold.increase.in.provitamin.A.content.of.the.fruits. 97
Although. β-carotene. (provitamin. A),. α-carotene,. and. lutein. are. widely. preva-
lent. in. many. fruits. and. vegetables,. ketocarotenoids,. such. as. canthaxanthin. and.