Biomedical Engineering Reference
In-Depth Information
These.data.also.show.not.only.that.the.structure.of.the.diatom.has.a.strong.diffracting.
effect,.but.also.that.the.eficiency.of.transmission.of.light.depends.strongly.on.the.wave-
length..Calculations.were.performed.to.evaluate.the.absolute.diffracted.intensity.in.each.
peak.in.each.diffracted.order.by.integrating.over.the.area.under.the.curve..These.values.
were.then.compared.with.the.initial.incident.light.intensity.in.order.to.obtain.the.absolute.
values..For.wavelengths.in.the.blue.and.green,.the.transmission.is.relatively.low,.with.mean.
absolute.totals.(measured.using.valves.from.ive.separate.diatoms).of.22.(±1).%.for.472.nm.
incident. light. and. 29. (±1). %. for. 543. nm. incident. light.. However,. consistently. and. signii-
cantly.higher.absolute.transmission,.78.(±2).%,.was.measured.for.red.light.(632.nm).
The.strong.diffraction.exhibited.by.light.passing.through.the.diatom.valve,.identiied.in.
these.experiments,.is.a.mechanism.by.which.the.available.light.intensity.is.more.evenly.
spatially.distributed.over.the.internal.volume.of.
C. wailesii
.(Figure 25.16)..It.has.a.signiicant.
effect:.it.facilitates.diffraction-assisted.diffusion.of.the.radiant.energy.throughout.a.larger.
proportion.of.the.diatom's.internal.volume..Not.only.would.this.minimize.the.likelihood.
of.photobleaching-related.damage.due.to.high.incident.intensity.in.any.one.unit.volume.of.
the.diatom,.but.in.environments.where.the.available.light.intensity.is.much.lower,.but.still.
nonetheless. exceeds. the. photosynthetic. activity. threshold,. such. diffraction. would. assist.
with.the.distribution.of.light.throughout.the.internal.diatom.volume,.thereby.increasing.
the.number.of.chloroplasts.within.the.diatom.that.have.suficient.incident.energy.to.pho-
tosynthesize..Furthermore,.if.the.diatom.itself.is.not.optimally.oriented,.the.diffraction.of.
the.incident.light.redirects.a.proportion.of.the.light.energy.such.that.the.irst-.and.second-
order.diffraction.peaks.will.pass.through.the.central.volume.of.the.diatom.
These.combined.effects.would.therefore.likely.cause.the.chloroplasts.within.the.valve.to.
be.subjected.to.net.elevated.light.intensities.that.would.trigger.or.enhance.photosynthetic.
productivity.despite.their.inferior.intradiatom.location,.thereby.increasing.the.eficiency.
of.the.diatom.and.offering.a.distinct.advantage.in.the.wide.ranges.of.lighting.conditions.
that.are.associated.both.with.weather-related.variable.sunlight.and.with.the.variation.in.
their.water.depth.due.to.turbulent.mixing.and.bloom.cycles.
55
Furthermore,.the.measurement.presented.here.of.preferential.transmission.of.red.and.
far-red. wavelengths. through. the. valve. ultrastructure. of.
C. wailesii
. (Figures 25.14.b. and.
25.16). appears. to. conirm. experimentally. several. indings. from. a. previous. theoretical.
study.of.a.very.closely.related.centric.diatom,.
C. granii
.
This.diatom.has.an.ultrastructure.entirely.analogous.to.that.observed.in.
C. wailesii
..In.
their.paper,.Fuhrmann.et.al.
56
.calculated.the.band.structure.and.thereby.showed.that.the.
optical.properties.of.the.
C. granii
.shell.strongly.inluenced.incoming.light.by.coupling.it.
into.distinct.waveguide.modes.
For. a. variety. of. these. modes,. the. waveguide-coupled. light. is. distinctly. blue-green.
and.is.absent.of.red,.implying.that.red.light.is.preferentially.transmitted..The.experi-
mental. measurement. in. this. investigation. into.
C. wailesii
—that. there. is. as. much. as. a.
fourfold.increase.in.the.transmission.of.red.compared.to.blue.light.into.the.diatom—
highlights.the.extent.of.the.interaction.of.incident.light.with.the.centric.diatom.form.
of.ultrastructure.
56
This.phenomenon.also.appears.congruous.with.separate.and.detailed.biological.evidence.
that. suggests. the. importance. of. red. and. far-red. wavelengths. in. some. marine. environ-
ments.has.been.grossly.underestimated..By.studying.diatom.responses.to.informational.
light.signals,.Falciatore.and.Bowler.identiied.extraordinary.sensitivity.to.red.and.far-red.
wavelengths,
57
.a.phenomenon.that.infers.the.existence.of.a.phytochrome-type.photorecep-
tor.in.marine.diatoms..The.evolved.ultrastructure.of.
C. wailesii
.therefore.appears.particu-
larly.well.designed.to.enhance.the.intravalve.delivery.of.speciically.appropriate.radiant.
