Flood‐induced leaf elongation in Rumex species: effects of water depth and water movements

Abstract

S U M M A R YSeveral species from the genus Rumex are found in Dutch river forelands. Species such as R. palustris Sm. from the low, frequently flooded areas are well adapted to wet conditions, Rumex species from higher and less frequently flooded sites are poorly adapted and therefore sensitive to flooding. One of the adaptations to flooding is enhanced shoot elongation upon connpiete submergence, enabling plants to restore leaf-air contact, provided that the water is not too deep. This paper demonstrates the strong variation in the absolute extent of flood-induced leaf elongation among species of the genus Rumex. The effects of flooding on shoot dr>' and fresh weight and internal gas \'olunies of an elongating and a non-elongating species, R. palustris and R. acetosetla L,, were compared. Net water uptake in response to complete submergence was observed in the shoots of both species. Based on results presented here, we conclude that in plants of R. palustris water enters the cells and is used for cell expansion leading to petiole elongation, whereas in plants of R. acetosella at least part of the water taken up fills the intercelfular gas spaces. Elongation of complete))* submerged Rumex plants does not vary with different depths of submergence, Tbis was concluded from the observation that there is little effect of either hydrostatic pressure or irradiance on leaf elongation during complete submergence. Howe\ er, when R. palustris plants were subjected to a changing water depth, i.e, alternate periods of complete submergence and waterlogging, they elongated less strongly than under permanent complete submergence. Water movements did not affect leaf elongation induced by submergence.

Ethylene Biosynthesis and Accumulation under Drained and Submerged Conditions (A Comparative Study of Two Rumex Species)

“…2B) and a decline of the internal ethylene concentration is observed from the 4th d of submergence onward. However, in flooding-sensitive R. acetosella plants, high ethylene levels do not cause a shoot elongation response (Banga et al, 1995). Moreover, the rate of ACC formation remains high in this species.…”

“…In flooding-resistant R. palustris plants, this causes a more vertical orientation of leaves and a greatly enhanced petiole elongation (Voesenek and Blom, 1989;Banga et al, 1995). Furthermore, after 8 h of submergence, high ethylene concentrations negatively regulate ACC synthase in R. palustris plants.…”

“…Using this relationship, we calculated the amount of entrapped ethylene, which escaped from plants after removal from submergence, from the height of the peak in ethylene release that was measured. Thereafter, the internal gas volume of the same plant(s) was determined by means of a modified pycnometer method (Jensen et al, 1969;Banga et al, 1995). By dividing the amount of entrapped ethylene (nL) by the internal gas volume (mL), we calculated the ethylene concentration (juL L" 1 ) in the intercellular gas spaces of a plant just before removal from submergence.…”

“…is a well-adapted floodingresistant species from frequently flooded field sites, whereas R. acetosella L. grows on dry, sandy soils that are never flooded under natural conditions. This floodingsensitive species does not elongate its petioles upon submergence (Banga et al, 1995). The seeds were germinated on moist filter paper in Petri dishes under a 12-h day/ 12-h night regime at 25/ 10°C for 7 d (R. palustris) or 27/10"C for 10 d (R. acetosella) and a PPFD of 25 pmol m-' s-' (over the waveband 400-700 nm; Philips TL 8W / 33).…”

Sensitivity to ethylene: the key factor in submergence‐induced shoot elongation of Rumex

“…In vegetative rosettes of flooding-resis tant R. palustris, submergence stimulates shoot elongation. This response is stronger in younger leaves, particularly the petioles (Voesenek & Blom I989a,b;Banga, Blom & Voesenek 1995). In rosettes of flooding-intolerant R. ace tosella, which are never flooded under natural conditions, leaf elongation is neither stimulated nor inhibited when plants are submerged in the laboratory ( Banga et al 1995).…”