[APD] epicuticular wax adaptations

["Steve Pushak" <teban at powersonic_bc.ca>]

There is quite a lot of references to epicuticular wax or cuticular wax
on plants. I agree totally with Stephan that this is an adaptation of
terrestrial plants which prevents desiccation. I believe that it is also
well understood that submerse plant leaves lack this coating & that the
coating on emerse leaves prevents them from respiring CO2 underwater.
This was the reason advanced to explain why emerse grown Alternanthera
do not survive underwater.

I don't think we know if the ability to grow a thin or absent cuticle is
an adaptation to grow underwater. I submit that plants which adapt to
seasonal flooding need to have this ability, whereas obligate
terrestrial plants lack this ability. I suggest that controlling
epicuticular wax is an important physiological adaptation for seasonally
flooded plants.

There are other more important adaptations that fast growing plants need
to make; they need lots of nutrients so they need their roots in the
mud; this requires them to have large aerenchyma to conduct O2 into the
root zone to prevent damage to the roots by ammonia or sulphides. Slow
growing underwater plants may not send their roots as deep as in the
case of Anubias but certainly Crypts are well adapted to anaerobic
substrates. They have thick white roots & I suspect the aerenchyma are
developed as well. Control of epicuticular wax is not the most important
adaptation.

Here are some literature citations that I cannot follow up:
<http://www.hort.purdue.edu/hort/people/faculty/jenks.shtml>

Here is a discussion of the importance of thin cuticle to facilitate gas
exchange:
<http://www.botgard.ucla.edu/html/botanytextbooks/lifeforms/aquaticplant
s/fulltextonly.html>

I could not discover a term for areas that experience seasonal flooding
except perhaps "unconsolidated shores". Other terms for contrast:
Lacustrine - lake
Palustrine - swamp
Riverine - river

There is a massive amount of research & web information available about
epicuticular wax adaptations. Its referred to as a micro-morphological
adaptation however the control mechanisms must exist at cellular process
level.

OK, get off your duffs & dig all you folks who complain of a lack of
interesting cogent discussion on the APD! Some should take the pro side
of this argument & others the con. Heck switch sides for fun!

Steve P

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