Plant Selenium Metabolism: Genetic Manipulation, Phytotechnological Applications, and Ecological Implications - Environmental Contamination: Health Risks and Ecological Restoration - page 306

The. Se-tolerant. moth. accumulated. Se. in. the. ingested. form,. methyl-SeCys,.
which.is.not.incorporated.into.proteins,.while.a.Se-sensitive.population.of.
diamondback.moths.from.a.nonseleniferous.habitat.converted.the.ingested.
methyl-SeCys.to.SeCys.(Freeman.et.al..2006b).
Herbivores.may.avoid.Se-rich.plant.tissue.as.another.strategy.to.minimize.
Se.toxicity..Se.is.not.distributed.evenly.throughout.Se-hyperaccumulating.
plants,.and.Se.levels.luctuate.over.the.growing.season..Se.concentrations.
in.leaves.peak.in.early.spring,.and.young.leaves.and.reproductive.tissues.
contain.much.higher.Se.levels.than.older.leaves.(Galeas.et.al..2007)..Also,.
lowers. of. hyperaccumulators. have. higher. Se. levels. than. leaves. or. roots,.
and.within.the.lowers.of. S. pinnata ,.the.stamens.and.pistils.have.a.higher.
Se.concentration.than.the.petals.and.sepals.(Quinn.et.al..2011b)..As.men-
tioned.earlier,.hyperaccumulators.allocate.Se.to.the.periphery.of.the.leaf..In.
S. pinnata ,.Se.is.stored.primarily.in.specialized.cells.in.the.epidermis,.and.
in. A. bisulcatus ,.Se.is.stored.primarily.in.leaf.hairs.(Freeman.et.al..2006b)..
Therefore,. it. appears. that. hyperaccumulators. preferentially. allocate. Se. to.
areas. that. irst. come. into. contact. with. attackers,. and. predominantly. in.
their. most. valuable. tissues,. for. maximal. protection. from. herbivores. and.
pathogens..Sequestration.in.the.epidermis.may.also.contribute.to.Se.toler-
ance,. since. it. keeps. the. Se. away. from. metabolically. sensitive. processes..
Depending. on. herbivore. feeding. mode,. Se. hyperaccumulation. may. be.
more.or.less.effective.against.different.herbivores..In.view.of.the.particu-
larly.high.Se.levels.in.the.lowers,.Se.may.also.have.an.effect.on.pollination.
ecology..This.will.be.an.interesting.area.of.further.research..Recent.studies.
(Quinn. et. al.. 2011b). indicate. that. insect. pollinators. in. seleniferous. areas.
can.accumulate.substantial.Se.levels.and.that.high-Se.plants.are.visited.at.
similar.rates.as.low-Se.plants..It.will.be.interesting.to.study.whether.this.Se.
has.any.toxic.effects.on.the.pollinators.
As. already. discussed. earlier,. plant-associated. microbes. may. affect. plant.
Se. metabolism.. Conversely,. the. elevated. Se. levels. in. and. around. (hyper)
accumulator. plants. also. appear. to. affect. local. microbial. communities.. Soil.
around.Se-hyperaccumulating.plants.has.a.∼10-fold.higher.Se.concentration.
than. the. surrounding. bulk. soil. (El. Mehdawi. et. al.. 2011a),.and.there. is. evi-
dence.that.rhizospheric.and.saprophytic.fungi.from.seleniferous.areas.have.
evolved.enhanced.Se.tolerance.(Wangeline.et.al..2011,.Quinn.et.al..2011b).
Another. class. of. ecological.interaction.that.may. be. affected. by.Se. is. that.
between.hyperaccumulators.and.their.plant.neighbors..As.mentioned.earlier,.
Se.levels.around.hyperaccumulators.tend.to.be.higher.compared.to.other.soil.
in.the.area..Recent.data.(El.Mehdawi.et.al..2011b).indicate.that.neighbors.of.
these.high-Se.plants.have.signiicantly.higher.Se.levels.when.growing.next.
to.hyperaccumulators..Depending.on.whether.the.neighbors.are.Se.tolerant.
or.sensitive,.this.increased.Se.concentration.may.have.a.positive.or.negative.
effect..If.they.are.tolerant,.they.may.beneit.from.the.Se.in.a.similar.way.to.
the.hyperaccumulators.themselves,.enjoying.less.herbivory..If.they.are.sensi-
tive,.on.the.other.hand,.they.may.suffer.reduced.germination.and.growth.