How Does Epinasty (the Epinastic Affect) Help a Plant During Flooding?

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socrtwo@gmail.com - 29 Jun 2005 03:36 GMT

Suggestion: Epinasty during flooding is adaptive because the downward
directed leaves act as sails in the wind, and the wind action on the
leaf acts on the plant and leaf stems like somebody working a lever
water pump.

That is there is a physical mechanism within the stem similar to a
lever water pump which is activated by the up and down movements of
Epinastic leaves blown in the wind. There therefore should be
structures in the stem analogous to the piston, valves etc.

The idea is that a flooded plant needs to pump water out of space
surrounding the roots as quickly as possible. Epinasty then does this
through ramped up transpiration induced by a higher water pressure from

a lever pump action. (Maybe downward directed leaves also transpire
more quickly in the wind even without pump action because when they
become perpendicular to it -to the wind- or when the plant makes sure
to
epinastically grow perpendicular to the most common prevailing wind -
this makes transpiration faster than if the leaves are parallel to the
wind as the are on the most part during normal conditions.)

Teachers might have students dissect plants looking for the possible
mechanism, which they could display in science projects.

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David R. Hershey - 29 Jun 2005 19:36 GMT

The hypothesis that leaf movement would increase transpiration due to a
"lever water pump" is not viable because there are no structures in a
"stem analogous to the piston, valves etc." of a pump.

The hypothesis that leaves becoming "perpendicular to the most common
prevailing wind" would increase transpiration and lower flood waters is
not viable because the stomata are closed (Jackson 2002). Closed
stomata means transpiration is close to zero.

Higher ethylene concentrations due to flooding may be adaptive in at
least two ways. Ethylene may cause more rapid shoot elongation,
allowing shoots to rise above the water surface and act as snorkels
(Voesenek et al. 1993). Atmospheric oxygen can flow into shoots above
the water line and move to roots internally via intercellular spaces.

In some species, ethylene causes cell wall breakdown in adventitious
roots (Bragina et al. 2003). Tissue with larger internal air spaces
(aerenchyma) may allow for more efficent movement of gas between shoots
above the water level and submerged parts.

Epinasty may just be a symptom of flooding with no adaptive value.
Voesenek et al. (2003) found the flooding response involved several
hormones and resulted in a hyponastic leaf response (upward bending of
leaves) due to rapid petiole elongation. Hyponasty could be adaptive
because leaves might rise above the flood water and allow roots to
receive oxygen.

References

Bragina, T.V., Rodionova, N.A.,and Grinieva, G.M. 2003. Ethylene
Production and Activation of Hydrolytic Enzymes during Acclimation of
Maize Seedlings to Partial Flooding. Russian Journal of Plant
Physiology, 50: 794-798.
http://www.ingentaconnect.com/content/maik/rupp/2003/00000050/00000006/00479064

Jackson, M. B. 2002. Long-distance signalling from roots to shoots
assessed: the flooding story
Journal of Experimental Botany. 53: 175-181.
http://jxb.oxfordjournals.org/cgi/content/full/53/367/175

Voesenek, L.A.C.J., M. Banga, R.H. Thier, C.M. Mudde, F.J.M. Harren,
G.W.M. Barendse and C.W.P.M. Blom
1993. Submergence-Induced Ethylene Synthesis, Entrapment, and Growth in
Two Plant Species with Contrasting Flooding Resistances. PLANT
PHYSIOLOGY , 103, 783-791.
http://www.plantphysiol.org/cgi/reprint/103/3/783

VOESENEK, L.A.C.J., J.J. BENSCHOP, J. BOU, M.C.H. COX, H.W. GROENEVELD,
F.F. MILLENAAR, R.A.M. VREEBURG and A.J.M. PEETERS. 2003. Interactions
Between Plant Hormones Regulate Submergence-induced Shoot Elongation in
the Flooding-tolerant Dicot Rumex palustris. Annals of Botany 91:
205-211.
http://aob.oxfordjournals.org/cgi/content/full/91/2/205

David R. Hershey

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Natural Science Forum / Biology / Botany / June 2005

How Does Epinasty (the Epinastic Affect) Help a Plant During Flooding?