Some aspects of the extreme anoxia tolerance of the sweet flag,Acorus calamus L.Weber, Michel; Brändle, Roland
doi: 10.1007/BF02803992pmid: N/A
Acorus calamus L. is a neophyte in Europe with remarkable properties. Among other things, it is the most anoxial tolerant species and a competitive invader at eutrophic sites. The following overview presents the most recent work on these subjects. Carbohydrates of the rhizomes sustain anaerobic ATP production for very long periods. Ethanolic fermentation naturally occurs in winter and produces rather low, but sufficient amounts of ATP for survival, as shown by adenylate energy charge and total adenylate content. Fermentation energy is mainly used for the synthesis and preservation of essential macromolecules, such as proteins and membrane lipids. The extent of these processes is unique. Moreover, ammonia and sulphide uptake is maintained during the cold season. Both ions are detoxified to alanine and thiols which are translocated into the rhizome, where the nitrogen of alanine is used to form arginine. Overwintering leaves contain asparagine instead of arginine. Recycled nitrogen compounds from the rapidly degrading summer leaves return into the rhizomes. Therefore, the nitrogen nutrition consists of an external and internal cycle. The abundance of carbohydrates and nitrogen compounds allows spring shoot growth earlier than other species. These strategies could contribute markedly to the competitive power ofA. calamus at its natural site.
The effect of post-hypoxia on roots inSenecio andMyosotis species related to the glutathione systemBiemelt, Sophia; Albrecht, Gerd; Wiedenroth, Ernst-Manfred
doi: 10.1007/BF02803995pmid: N/A
This paper shows the effect of re-aeration following hypoxic pretreatment on the glutathione system in plants with different flooding tolerance. Re-aeration of hypoxically pretreated roots led to an increase of TBA-rm content indicating an accelerated lipid peroxidation (post-anoxic injury). Re-admission of oxygen resulted in a clear increase in the content of total glutathione in both flooding-intolerant speciesMyosotis arvensis andSenecio jacobaea. Simultaneously, the high ratio between reduced (GSH) and oxidized (GSSG) glutathione decreased in these species upon the onset of re-aeration, while the tolerantMyosotis palustris andSenecio aquaticus showed only little changes in contents of GSH and GSSG. An imbalance in GSH/GSSG ratio reflects oxidative stress. The glutathione reductase (GR) reacted very differently in the investigated genera. The metabolic response to varying oxygen pressure is much stronger in the flooding-intolerant species compared to species naturally growing in wetlands. The present results suggest that glutathione system is an important component in overcoming oxidative stress.
Pressurised aeration in wetland macrophytes: Some theoretical aspects of humidity-induced convection and thermal transpirationArmstrong, William; Armstrong, Jean; Beckett, Peter
doi: 10.1007/BF02803991pmid: N/A
The pressurised gas-flows, humidity-induced convection (HIC) and thermal transpiration (TT), which are important for aeration and for greenhouse gas emissions in some wetland macrophytes, are described and discussed. Results obtained from simple mathematical modelling of the processes are presented to illustrate some of their more relevant features. It is emphasised that both processes require the presence of a micro-porous partition having a significantly greater resistance to pressure flow than to diffusion. In particular it is shown that whilst the potential to pressurise by these processes is inversely related to the pore diameters of the partition, the maximum gas flows are generated where pore diameters range from 0.1 to 0.2 μm. Where partitions are a surface feature (e.g. emergent macrophytes) a dominant role for HIC is predicted; where partitions are an embedded feature (e.g. water-lilies) it is deduced that HIC will still play a significant role, but the contribution of TT could be greater.
Whole plant adaptations to fluctuating water tablesCrawford, Robert
doi: 10.1007/BF02803990pmid: N/A
Why some plants are damaged by flooding and others are not, is not a question that can be answered by citing any one particular mechanism or sequence of events. Flood-tolerant plants like obligate aquatic species can survive inundation but differ in that they are also adapted to withstand the consequences of becoming unflooded. Flooding implies a transitory state so that when water tables drop, adapted species have to be able to survive being deprived of the physical support of flood-water as well as re-exposure to a normal air supply. A review of flooding tolerance mechanisms reveals that tolerant species combine a range of adaptations which, depending on the life strategy of the species, can play different roles in enabling intact plants to adjust to both rising and falling water levels. Flooding is also a seasonal stress with many temperate plant communities being subjected to high water tables in winter. The mechanisms that confer tolerance of winter flooding also differ from those that allow plants to grow when flooded during the growing season. This review argues therefore, that reductionist investigations, which examine isolated organs or individual processes, may not be the most suitable method to apply to understanding the complexity of reactions that are needed to survive flooding. Instead, a holistic approach is advocated which examines the reactions of whole plants to changing water levels at different seasons of the year.
Hormone sensitivity and plant adaptations to floodingVoesenek, Laurentius; Banga, Minke; Rijnders, Jan; Visser, Eric; Blom, Cornelis
doi: 10.1007/BF02803993pmid: N/A
Plant hormones play a key role as mediators between environmental signals and adaptive plant responses. Auxin, ethylene and gibberellins are involved in the initiation of adaptive plant responses such as the development of adventitious roots and stimulated shoot elongation upon flooded conditions. These adaptive plastic responses in plants are frequently linked to changes in the concentrations of the hormones involved, but only rarely to shifts in sensitivity. Examples from ecophysiological research performed with species from the genusRumex demonstrate the importance of the hormone sensitivity concept in plant adaptations to flooding: (a)Rumex species can be grouped into three response categories according to the ethylene sensitivity of the youngest petioles: positive, negative and indifferent; (b) Sub-ambient oxygen concentrations sensitize petioles of wetlandRumex species to ethylene; (c) Enhanced ethylene levels sensitize petioles of wetlandRumex species to gibberellin; (d) Auxin is the primary plant hormone responsible for the initiation of adventitious roots in wetlandRumex species. However, a factor related to waterlogging, possibly ethylene, is required to sensitize the root-shoot junction to endogenous auxin.
Factors associated with reed decline in a eutrophic fishpond, Rožmberk (South Bohemia, Czech Republic)Čížková, Hana; Strand, John; Lukavská, Jaroslava
doi: 10.1007/BF02803996pmid: N/A
Characteristics of the growth and performance ofPhragmites australis as well as sediment characteristics were investigated along the western shore of Rožmberk fishpond. The reed performance decreased toward the southern end of the shore, proximate to outlets of wastewater effluent and untreated sewage. While the reed stand was closed and looked healthy at the northern end, gaps occurred within the flooded part of the reed belt further southwards; reed was absent in water along the southernmost part of the shore, though dead shoot stubble indicated its presence in earlier times. In the latter site, the surface layer of sediment consisted of fine mud with a high organic matter content and a high oxygen demand. To a smaller extent, patches of partly decomposed reed litter inside the gaps showed the same properties. It is suggested that organic matter accumulating within the flooded part of the reed belt may have reduced plant performance which ultimately lead to the formation of gaps. At a later stage, the lakeside fringe of the reed belt collapsed, thus completing the retreat of reed from water. A protective effect of calcium against the adverse effects of organic matter is suggested.