Transgenic Vegetables - Transgenic Horticultural Crops: Challenges and Opportunities - page 47

astaxanthin,.are.rarely.present.in.plants..Ketocarotenoids.are.strong.antioxidants.and.
are.chemically.synthesized.and.used.as.dietary.supplements.and.as.pigments.in.the.
aquaculture.and.neutraceutical.industries..Ketocarotenoid.biosynthetic.pathway.was.
engineered.in.carrot.tissues.by.introducing.a.β -carotene ketolase .gene.isolated.from.
the.red.alga. Haematococcus pluvialis . 98 .In.the.transgenic.carrot.taproots,.up.to.70%.
of.total.carotenoids.were.converted.to.novel.ketocarotenoids,.with.accumulation.up.
to.2.4.mg/g.root.dry.weight..Astaxanthin,.adonirubin,.and.canthaxanthin.were.most.
prevalent,.followed.by.echinenone,.adonixanthin,.and.β-cryptoxanthin,.and.all.these.
ketocarotenoids.have.neutraceutical.importance. 98
Glucosinolates.are.an.important.group.of.secondary.metabolites.found.in.almost.
all.the.members.of.the.family. Brassicaceae ..Although.glucosinolates.are.well.known.
for.their.toxic.effects.in.both.humans.and.animals.at.high.doses,.at.subtoxic.doses,.
their.hydrolytic.and.metabolic.products.act.as.chemoprotective.agents.against.chemi-
cally.induced.carcinogens.and.thereby.block.initiation.of.a.variety.of.tumors.in.addition.
to.having.a.wide.range.of.bioactivities. 99 .Sulforaphane,.a.metabolite.of.methionine-
derived.4-methylsulinylbutyl.glucosinolate.(glucoraphanin),.has.attracted.attention.
because. of. its. potential. anticarcinogenic. activity. 100 . Glucoraphanin. is. an. aliphatic.
glucosinolate.abundant.in.broccoli.and. Arabidopsis .ecotype.Columbia,.but.nonexis-
tent.in.Chinese.cabbage..Three. Arabidopsis .genes,.required.for.aliphatic.glucosino-
late.biosynthesis,.were.introduced.into.Chinese.cabbage. 101 .The.resulting.transgenic.
lines.accumulated.signiicantly.higher.levels.of.the.aliphatic.glucosinolates,.gluco-
napin,.and.glucobrassicanapin. 101,102
f ruIt r IpenInG
Although.ripening.is.a.process,.which.renders.the.fruits.to.become.more.edible,.the.
ripening-phenomenon. itself. can. be. either. beneicial. or. detrimental. to. both. fresh-
ness. and. processing. quality. of. fruits. and. vegetables.. For. instance,. during. ripen-
ing. of. tomato,. cell. wall. disassembly. is. closely. associated. with. loss. of. fresh. fruit.
irmness.and.subsequently.with.a.loss.of.viscosity.in.the.processed.products..In.
tomato,.PG and.expansin.(Exp).are.among.the.cell.wall.proteins.that.cooperatively.
participate.in.ripening-associated.cell.wall.disassembly..Transgenic.suppression.of.
either. LePG .or. LeExp1 .expression.alone.resulted.in.altered.softening.and.shelf-life.
characteristics. of. fruits. 103 . Suppression. of. LeExp1 . or. LePG . alone. did. not. signii-
cantly.increase.fruit.irmness..However,.fruits.suppressed.for.both. LePG .and. LeExp1 .
expression. were. signiicantly. irmer. throughout. the. ripening. phase. and. were. less.
susceptible.to.deterioration.during.long-term.storage..The.viscosity.of.juice.prepared.
from. the. transgenic. tomato. fruit. with. reduced. LePG . and. LeExp1 . expression. was.
higher.than.that.of.controls. 103
DISCUSSION
Although. genetically. engineered. tomato. (Flavr. Savr). with. enhanced. fruit-quality.
characteristics.was.the.irst.example.of.a.transgenic.vegetable.crop.to.be.marketed.
in.the.United.States.and. United.Kingdom.in.the.1990s,.most. transgenic.vegetable.
crop.species.have.not.reached.the.market.as.rapidly.as,.for.example,.transgenic.ield.