Different Survival Strategies Amongst Plants to Cope with Underwater Conditions
Many plants experience flooding at some point during their life cycle. The underwater environment creates a carbon and energy crisis for the plant, for which two successful strategies have been identified, quiescence and escape. During quiescence, growth
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Abstract Many plants experience flooding at some point during their life cycle. The underwater environment creates a carbon and energy crisis for the plant, for which two successful strategies have been identified, quiescence and escape. During quiescence, growth is actively reduced until the water levels recede, whereas escape encompasses rapid upward shoot elongation to establish air contact. An inherent cost is associated with flood-induced elongation, which is also reflected by the difference in managing energy production and expenditure compared to plants adopting a quiescence strategy. The underwater elongation, via a combination of cell elongation and division, is mainly driven by changes in the internal gaseous composition of ethylene, carbon dioxide, and oxygen. Interestingly, the same internal and environmental cues induce contrasting growth responses, depending on the species. The underlying hormonal network and molecular components constituting these differences amongst wetland species are further discussed.
1 Growth Strategies Determine Plant Survival and the Occupied Niche Terrestrial plant species face many challenges in an underwater environment. Primarily, the severely reduced gas exchange in the aqueous surroundings, ~10.000 times slower compared to air, can lead to a dramatic oxygen (O2) shortage in the belowground tissue. In the above ground tissue photosynthesis is severely reduced due to the poor exchange of carbon dioxide (CO2) with the environment (Mommer and Visser 2005). In the absence of O2 mitochondrial respiration is
H. van Veen (*) • D. Vashisht • L.A.C.J. Voesenek • R. Sasidharan Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands e-mail: [email protected] J.T. van Dongen and F. Licausi (eds.), Low-Oxygen Stress in Plants, Plant Cell Monographs 21, DOI 10.1007/978-3-7091-1254-0_17, © Springer-Verlag Wien 2014
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arrested. Therefore, plants have to solely rely on glycolysis for energy production, leading to a mere two to four ATP molecules produced per molecule hexose. It is essential that fermentation pathways are activated to regenerate NAD+ to sustain the energy production through glycolysis. Interestingly, a large range of species experience partial to complete submergence during some stage of their life cycle. Indeed, a shift from an exclusive terrestrial to an amphibious lifestyle is estimated to have occurred more than 200 times throughout the diversification of angiosperms (Cook 1999). A common response to submergence is the formation of new “aquatic” leaves, which have an increased specific leaf area (SLA), thinner epidermal cell walls, and increased chloroplast orientation towards the leaf surface. These traits minimize the diffusion distance and thus resistance between the chloroplast and environment and thereby improve gas exchange underwater. This leaf plasticity is a widespread response that somewhat alleviates adverse underwater conditions (Mommer et al. 2005, 2007; Sand-J
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