Environmental Engineering Reference
In-Depth Information
available.to.the.plant..In.addition.to.bacteria,.unicellular,.polymorphic,.and.
ilamentous.fungi.have.the.ability.to.reduce.selenite.to.elemental.Se.(Gharieb.
et.al..1995);.volatilization.of.Se.has.also.been.reported.in.fungi.(Fleming.and.
Alexander.1972,.Thompson-Eagle.et.al..1989).
In.several.studies,.bacteria.have.shown.to.contribute.to.plant.Se.uptake.and.
volatilization..In.broccoli.(
B. oleracea
),.95%.of.Se.root.volatilization.was.inhib-
ited.when.roots.were.treated.with.bacterial.antibiotics.(Zayed.and.Terry.1994)..
Also,.Indian.mustard.(
B. juncea
).treated.with.antibiotics.volatilized.30%.less.Se.
and.accumulated.70%.less.Se.than.untreated.plants..In.addition,.Indian.mus-
tard. plants. grown. from. surface-sterilized. seeds. that. were. inoculated. with.
rhizospheric.bacteria.accumulated.ivefold. more. Se.and.volatilized. fourfold.
more.Se.than.control.plants.from.seeds.that.were.not.inoculated.with.bacteria..
The.mechanism.for.the.stimulatory.effect.by.the.bacteria.appeared.to.be.both.
stimulation.of.root.growth.and.stimulation.of.plant.S/Se.uptake.and.assimila-
tion.. When. inoculated. with. rhizospheric. bacteria,. the. plants. had. increased.
root.surface.area,.and.the.culture.media.contained.ninefold.higher.serine.lev-
els.than.control.plants..OAS.is.known.to.stimulate.sulfate.uptake.and.assimi-
lation.(de.Souza.et.al..1999)..In.another.study,.Di.Gregorio.et.al..(2006).using.
B. juncea
. grown. in. soil. spiked. with. selenite. and. selenate. also. showed. that.
rhizobacteria. stimulated.
B. juncea
. Se. uptake. and. volatilization. and. that. the.
bacteria.contributed.to.the.reduction.of.these.oxyanions.in.the.soil.
As.for.the.effects.of.plant-associated.fungi.on.plant.Se.uptake.and.volatil-
ization,.much.less.is.known..In.one.study,.ryegrass.(
Lolium
.spp.).accumulated.
less.Se.when.treated.with.the.mycorrhizal.fungus.
Glomus mosseae
.compared.
to.controls.lacking.this.fungus.(Munier-Lamy.et.al..2007)..There.is.also.vir-
tually.nothing.known.about.the.role.endophytic.microbes.play.in.plant.Se.
uptake,.metabolism,.and.volatilization.
Effects of Plant Se on Ecological Partners
The.high.Se.levels.in.hyperaccumulators.likely.play.an.important.role.in.the.
ecology.of.these.plants,.and.even.Se.accumulated.in.crop.plants.may.have.
ecological. effects. (Figure. 14.3).. The. best-known. effects. of. plant. Se. hyper-
accumulation.on. other.species. are.the.toxic.effects.of.plant. Se. on.livestock.
herbivores.. Se. ingestion. of. hyperaccumulator. plants. has. been. reported. to.
be. responsible. for. poisoning. and. death. of. cattle,. sheep,. and. horses. to. the.
extent.of.hundreds.of.millions.of.U.S..dollars.annually.in.the.United.States.
alone.(Wilber.1980)..Thus,.hyperaccumulators.may.sequester.Se.as.a.defense.
against.herbivory..In.support.of.this.elemental.defense.hypothesis.(irst.pro-
posed.by.Boyd.and.Martens.1992),.laboratory.and.ield.studies.showed.that.
Se. accumulation. can. protect. plants. from. a. range. of. herbivores. and. patho-
gens,.from.prairie.dogs.to.a.variety.of.arthropods.and.fungi.(Hanson.et.al..
2003,.2004,.Freeman.et.al..2006a,.2007,.2009,.Quinn.et.al..2008,.2011a)..Se.pro-
tected.the.plants.both.through.deterrence.of.herbivores.and.toxicity..Also.in.
support.of.the.elemental.defense.hypothesis,.Se-hyperaccumulating.species.
Search WWH ::
Custom Search