How plants cope with complete submergence

L A C J Voesenek,F F Millenaar,A J M Peeters,R Pierik,T D Colmer

doi:10.1111/j.1469-8137.2006.01692.x

L A C J Voesenek, F F Millenaar + Show 3 more

Open Access

https://doi.org/10.1111/j.1469-8137.2006.01692.x

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Abstract

Flooding is a widespread phenomenon that drastically reduces the growth and survival of terrestrial plants. The dramatic decrease of gas diffusion in water compared with in air is a major problem for terrestrial plants and limits the entry of CO(2) for photosynthesis and of O(2) for respiration. Responses to avoid the adverse effects of submergence are the central theme in this review. These include underwater photosynthesis, aerenchyma formation and enhanced shoot elongation. Aerenchyma facilitates gas diffusion inside plants so that shoot-derived O(2) can diffuse to O(2)-deprived plant parts, such as the roots. The underwater gas-exchange capacity of leaves can be greatly enhanced by a thinner cuticle, reorientation of the chloroplasts towards the epidermis and increased specific leaf area (i.e. thinner leaves). At the same time, plants can outgrow the water through increased shoot elongation, which in some species is preceded by an adjustment of leaf angle to a more vertical position. The molecular regulatory networks involved in these responses, including the putative signals to sense submergence, are discussed and suggestions made on how to unravel the mechanistic basis of the induced expression of various adaptations that alleviate O(2) shortage underwater.

Highlights

In emergent wetland plants, atmospheric O2 enters the shoot and moves, via aerenchyma, to the tips of the roots
Light reaching the leaves of submerged plants is attenuated by water, dissolved organic matter, particles and/or phytoplankton suspended in the water column (Bach et al, 1998; Vervuren et al, 2003)
The enhanced capacity for underwater gas exchange by new leaves of R. palustris produced following submergence was evidenced by higher internal O2 concentrations in petioles of these leaves during periods in light, when compared with O2 concentrations in plants grown in air prior to submergence (Mommer et al, 2004)

Summary

Sensing of submergence

In order to react appropriately to the flooded environment, plants have to sense the changes that take place. Decreases of O2, ranging from low concentrations (hypoxia) to complete absence (anoxia), in plants have been associated with changes in the expression of genes related to carbohydrate and lipid metabolism, glycolysis, fermentation pathways, ethylene synthesis, auxin-mediated processes, and calcium- and ROS-mediated signal transduction pathways (Klok et al, 2002; Paul et al, 2003; Branco-Price et al, 2005; Liu et al, 2005; Loreti et al, 2005) Morphological responses, such as aerenchyma and adventitious root formation, and cell and organ elongation of shoots, are induced in some species. A stimulating contribution of low blue light intensities can occur as this light signal is attenuated in water under turbid field conditions

Summary of possible submergence signals

Internal aeration and underwater photosynthesis

Stimulated shoot elongation

Findings

Perspectives