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
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.
Jackson, M. B. 2002. Long-distance signalling from roots to shoots
assessed: the flooding story
Journal of Experimental Botany. 53: 175-181.
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.
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:
David R. Hershey