A quantitative physicochemical approach to ion relations of biological
solutions is presented, which applied fundamental laws of physical
chemistry to these systems and allows analysis of dependent variables
([H+], [OH-] and the
dissociation state of partially dissociated ('weak') ions including
carbonate species) in relation to independent variables (concentrations of
strong and weak ions, dissociation constants and CO2 partial pressure).
Within this concept the influence of strong (fully dissociated) ions is
confined to their net unbalanced positive charge which is referred to as
SID (strong ion difference). The SID concept is then applied to membrane
transport processes and ion relations of xylem and phloem sap: simple
transmembrane transport of protons between compartments cannot affect pH on
either side of the membrane, because rather small deviations from
electrical neutrality results in substantial changes of the membrane
potential under natural conditions. Thus the membrane ATPases as
electrogenic pumps cannot control the pH of adjacent compartments, but they
energize secondary active transmembrane ion transport that results in pH
changes. The SID approach is shown to be valid by matching pH values
calculated from analysis of xylem and phloem saps with actual measured
values. Sensitivity analysis based on the SID approach allows (1) to detect
inconsistency in determination of composition in the analysed solutions and
(2) quantitatively to analyse the influence of ion export or import and
variations of pCO2 on pH and dissociation state of
weak acids of complex biological solutions. The SID concept thus allows the
evaluation of the contribution of a proposed pH-regulating or pH-affecting
mechanism on a quantitative physicochemical basis.Key
words: Electrical neutrality, membrane potential, pH regulation,
phloem sap, SID, xylem sap.
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Methods
Experiments were conducted during 30 d of flooding (waterlogging or submergence) with or without shading and subsequent recovery of 20 d under growth conditions. Changes in dry mass, number of branches/tillers, and length of the longest internodes and main stems were recorded to characterize growth responses. Photosynthetic parameters (photosystem II efficiency and non-photochemical quenching) were determined in mature leaves based on chlorophyll a fluorescence measurements.
Key Results
In both species growth and photosynthesis recovered after the end of the submergence treatment, with recovery of photosynthesis (starting shortly after de-submergence) preceding recovery of growth (pronounced on days 40–50). The effective quantum yield of photosystem II and non-photochemical quenching were diminished during submergence but rapidly increased upon de-submergence. Similar changes were found in all shaded plants, with or without flooding. Submerged plants did not suffer from photoinhibition throughout the recovery period although their growth recovery was retarded.
Conclusions
After sudden de-submergence the C3 plant A. philoxeroides and the C4 plant H. altissima were both able to maintain the functionality of the photosynthetic apparatus through rapid acclimation to changing O2 and light conditions. The ability for photosynthetic acclimation may be essential for adaptation to wetland habitats in which water levels fluctuate.Key words: Aerenchyma, Alternanthera philoxeroides, flooding, growth, Hemarthria altissima, low light, photosynthesis, shade, submergence, waterlogging, wetland plant相似文献
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