André Läuchli

Salinity : environment - plants - molecules

Acknowledgements. Introduction. A: Environment. 1. Global impact of salinity and agricultural ecosystems M.G. Pitman, A. Lauchli. 2. Salinity in the soil environment K.K. Tanji. 3. Salinity, halophytes and salt affected natural ecosystems S.-W. Breckle. B: Organisms. 4. Adaptation of halophilic Archaea to life at high salt concentrations A. Oren. 5. Adaptation of the haloterant alga Dunaliella to high salinity U. Pick. 6. Mangroves U. Luttge. C: Mechanisms. 7. Ultrastructural effects of salinity in higher plants H.-W. Koyro. 8. Intra- and inter-cellular compartmentation of ions - a study in specificity and plasticity G. Wyn Jones, J. Gorham. 9. Salinity, osmolytes and compatible solutes D. Rhodes, et al. 10. Sodium-calcium interactions under salinity stress G.R. Cramer. 11. Salinity and nitrogen nutrition W.R. Ullrich. 12. Pressure probe measurements of the driving forces for water transport in intact higher plants: effects of transpiration and salinity U. Zimmermann, et al. 13. Salinity, growth and phytohormones R. Munns. 14. The adaptive potential of plant development: evidence from the response to salinity G.N. Amzallag. D: Photosynthesis. 15. Influence of salinity on photosynthesis of halophytes C.E. Lovelock, M.C. Ball. 16. Performance of plants with C4-carboxylation modes of photosynthesis under salinity U. Luttge. 17. Induction of Crassulacean acid metabolism by salinity -- molecular aspects H.J. Bohnert.E: Molecules. 18. Function of membrane transport systems under salinity: plasma membrane L. Reinhold, M. Guy. 19. Function of membrane transport systems under salinity: tonoplast M. Binzel, R. Ratajczak. 20. Genetics of salinity responses and plant breeding J. Gorham, G.Wyn Jones. 21. Halotolerance genes in yeast R. Serrano. 22. The long and winding road to haloterance genes A. Maggio, et al. Index.

Potassium transport in salt-stressed barley roots

Salinization of the medium inhibits both K+ uptake by excised barley (Hordeum vulgare L.) roots and K+ release from their stele, as measured by short-term 86Rb uptake and xylem exudation, respectively. Although inhibition was not specific to chloride, mannitol caused a different response from that of inorganic sodium salts, indicating that inhibition was at least partly the result of an ion effect. In roots previously exposed to low levels of NaCl, NaCl stress directly affected stelar K+ release, whereas in low-sodium roots stelar K+ release was much less salt-sensitive than K+ uptake.

Kinematics and Dynamics of Sorghum (Sorghum bicolor L.) Leaf Development at Various Na/Ca Salinities (I. Elongation Growth)

In many salt-sensitive species, elevated concentrations of Ca in the root growth media ameliorate part of the shoot growth reduction caused by NaCl stress. The physiological mechanisms by which Ca exerts protective effects on leaf growth are still not understood. Understanding growth inhibition caused by a stress necessitates locating the leaf expansion region and quantifying the profile of the growth reduction. This will enable comparisons and correlations with spatial gradients of probable physiologically inhibiting factors. In this work we applied the methods of growth kinematics to analyze the effects of elevated Ca concentrations on the spatial and temporal distributions of growth within the intercalary expanding region of salinized sorghum (Sorghum bicolor [L.] Moench, cv NK 265) leaves. NaCl (100 mM) caused a decrease in leaf elongation rate by shortening the leaf growing zone by 20%, as well as reducing the peak value of the longitudinal relative elemental growth rate (REG rate). Increasing the Ca concentrations from 1 to 10 mM restored the length of the growing zone of both emerged and unemerged salinized leaves and increased the peak value of the REG rate. The beneficial effects of supplemental Ca were, however, more pronounced in leaves after their appearance above the whorl of encircling older leaf sheaths. Elevated Ca then resulted in a peak value of REG rate higher than in the salinized leaves. The peak value of unemerged leaves was not increased, although it was maintained over a longer distance. The duration of elongation growth associated with a cell during its displacement from the leaf base was longer in salinized than control leaves, despite the fact that the elongation zone was shorter in salinity. Although partially restoring the length of the elongation region, supplemental Ca had no effect on the age of cessation of growth. Elongation of a tissue element, therefore, ceased when a cellular element reached a certain age and not a specific distance from the leaf base.

Radioassay for β-emitters in biological materials using cerenkov radiation

Abstract An investigation was conducted on the detection of β-emitting radionuclides in plant roots by means of Cerenkov radiation. The samples were directly radioassayed in polyethylene vials with an aqueous solution of the wavelenght shifter 7-amino-1,3-naphthalene-disulfonic acid. High efficiencies are obtained for hard β-emitters, e.g. about 60% for 86 Rbuin 1 g tissue. The relatively weak β-emitter 36 Cl can still be determined with an efficiency of 13 per cent in plant roots. The maximum β-energy of a nuclide must be at least 0.5 MeV for radioassay by Cerenkov radiation in biological material. Self-absorption of weak β-emitters in tissues has to be considered. The procedure described here should be applicable to other plant tissues and to animal materials. The method was tested in experiments on the kinetics of ion absorption by plant roots and earlier work in which radioactivity was determined with a gas-flow counter was confirmed.

Growth and development of sorghum leaves under conditions of NaCl stress: possible role of some mineral elements in growth inhibition

Elongating leaf tissue, which in monocotyledonous species is a small region located near the leaf base, requires a continuous supply of nutrients to maintain cell expansion and is, therefore, highly susceptible to nutrient disturbances. The objective of this work was to investigate the effects of salinity on the availability of nutrient elements within the elongating region of sorghum (Sorghum bicolor [L.] Moench, cv. ‘NK 265’) leaves, in order to assess their possible role in salt-induced growth inhibition. Plants grown in complete nutrient solution were exposed to 1 or 100 mol·m−3 NaCl salinity. Spatial distributions of biomass and bulk tissue K, Na, Ca, and Mg were determined on a millimeter scale in the growth zone of leaf 6, while it was growing rapidly just after emergence from the encircling whorl of older leaf sheaths. Spatial patterns of net rates of element deposition were also calculated. Potassium, Ca, Mg, and Na exhibit along the leaf growing zone, distinct spatial concentration patterns which are changed by exposure to saline stress. Salinity induces a decrease in K concentration and deposition rate throughout the elongation zone. The inhibition of K deposition rate due to salinity increases with distance from the leaf base, as did the inhibition of growth. Salinity induces a dramatic decrease in Ca that could also be responsible for leaf growth inhibition. The concentration of Mg is lower under salt stress in the basal part of the growing region, where Na is preferentially accumulated. Since the base of the growth zone is where growth is least affected by salinity, high levels of Na are not the cause of growth inhibition in this salt-affected leaf tissue.

Effect of salt stress on growth and cation compartmentation in leaves of two plant species differing in salt tolerance

Summary Salinity can cause toxic symptoms, especially in mature leaves after long-term exposure. Thus, Na + accumulation in leaves could be responsible for salt toxicity. The infiltration-centrifugation technique was employed for the isolation of apoplastic washing fluids (AWF) from leaves and the detection of Na + , K + and Ca 2+ was carried out by ion chromatography. The Na + concentrations in the leaf apoplast of salt-sensitive corn and salt-tolerant cotton plants significantly increased with higher Na + supply. Nevertheless, the apoplastic Na + concentration did not exceed 10 and 30 mmol/L, respectively, after salt exposure up to 150 mmol/L in the medium in short- and long-term salt treatments. Higher Na + concentrations were found in the leaf apoplast of salt-tolerant cotton in comparison to those of salt-sensitive corn, particularly in fully expanded leaves. No bound Na + was found in the leaf apoplast. The Na + concentration in the leaf apoplast did not reach high enough concentrations to be responsible for the decline in leaf growth under salinity. Supplemental Ca 2+ did not affect Na + concentration in the leaf apoplast under salinity. Apoplastic Ca 2+ concentration remained constant, while K + concentrations increased in the leaf apoplast under salinity. Our results do not support the hypothesis by Oertli (1968) who proposed that salt accumulation in the leaf apoplast could be responsible for the death of leaves in plants exposed to salinity.

Growth and development of sorghum leaves under conditions of NaCl stress

Elevated concentrations of NaCl in plant growth media cause a reduction in leaf growth. In grasses, where the leaf growth zone is a small part of the entire leaf, it is important to locate the expanding region and spatially quantify the extent of growth reduction under stress. This will allow comparisons and correlations with possible physiologically important factors. We studied the spatial distribution of growth within the intercalary growth zone of sorghum (Sorghum bicolor [L.] Moench, cv. NK 265) leaves. Salinity (100 mM NaCl) shortened the length of the growth zone from 30 mm in the controls to about 24 mm, and reduced the maximal relative elemental growth rate (REG rate). The extent of growth inhibition varied with spatial location along the elongation region. The growth in the basal 3–9 mm of salinized plants was not affected. Young leaves, while still enclosed in the protected whorl of older sheaths and elongating rapidly, were affected more severely by the stress than emerged leaves. The distribution of growth along the leaf growth zone was not steady throughout the elongation period. The length of the elongation region of young nonemerged leaves increased with leaf age and reached a maximum of about 30 mm at leaf emergence. Toward the end of the elongation period, the growth zone shortened for both the control and salinized leaves, and was confined to more basal regions. The maximal REG rate increased after leaf emergence, the increase being larger in control than salinized leaves. Toward the end of the elongation period, when growth was no longer linear with respect to time, the maximum REG rate decreased and its position shifted closer to the leaf base. Growth profiles of leaves 8, 9 and 10 were similar in both control and salinized plants. This suggests that within that time frame of plant development, successive leaves are similarly affected by the stress, and that the length of time the plant was exposed to a steady level of salinity plays no role in specific leaf inhibition.

Electron Probe Analysis

Progress in modern plant physiology has been largely dependent upon the development of new analytical methods. Each increase in analytical sensitivity has been accompanied by a wave of discoveries which were not observable before the new method was devised. To gain a deeper insight into the secrets of the plant’s life, microanalytical methods are being employed through which the complex physiological and biochemical processes may be studied at the molecular level. In simple terms — what one really wants is to learn more and more about less and less. That the use of radioisotopes in autoradiography at the light and electron microscope level did contribute effectively to such progress has been demonstrated in the preceding chapters of this book.

Cell-specific localization of Na(+) in roots of durum wheat and possible control points for salt exclusion

Sodium exclusion from leaves is an important mechanism for salt tolerance in durum wheat. To characterize possible control points for Na(+) exclusion, quantitative cryo-analytical scanning electron microscopy was used to determine cell-specific ion profiles across roots of two durum wheat genotypes with contrasting rates of Na(+) transport from root to shoot grown in 50 mm NaCl. The Na(+) concentration in Line 149 (low transport genotype) declined across the cortex, being highest in the epidermal and sub-epidermal cells (48 mm) and lowest in the inner cortical cells (22 mm). Na(+) was high in the pericycle (85 mm) and low in the xylem parenchyma (34 mm). The Na(+) profile in Tamaroi (high transport genotype) had a similar trend but with a high concentration (130 mm) in the xylem parenchyma. The K(+) profiles were generally inverse to those of Na(+). Chloride was only detected in the epidermis. These data suggest that the epidermal and cortical cells removed most of the Na(+) and Cl(-) from the transpiration stream before it reached the endodermis, and that the endodermis is not the control point for salt uptake by the plant. The pericycle as well as the xylem parenchyma may be important in the control of net Na(+) loading of the xylem.

Interaction of NaCl and Cd stress on compartmentation pattern of cations, antioxidant enzymes and proteins in leaves of two wheat genotypes differing in salt tolerance

Physiological mechanisms of salinity–Cd interactions were investigated in inter- and intracellular leaf compartments of salt-tolerant wheat × Lophopyrum elongatum (Host) A. Löve (syn. Agropyron elongatum) amphiploid and its salt-sensitive wheat parent (Triticum aestivum L. cv Chinese Spring). In comparison with the intracellular fluid, only very low Na+ concentrations (up to about 4 mM) were found in the intercellular leaf compartment of wheat after a 75 mM supply of NaCl. NaCl salinity led to a higher Cd concentration in leaves of the salt-sensitive genotype. Cd in the intercellular leaf compartment was not detectable. Higher K+ concentrations in the intercellular leaf compartment of the salt-sensitive genotype suggest a higher plasma membrane permeability caused by NaCl + Cd stress. Ascorbate peroxidase (APX) activity was increased in leaves of the salt-sensitive genotype under the combined NaCl and Cd stress. The highest non-specific peroxidase activities were detected under the combined stresses. It is suggested that NaCl and Cd stress in combination enhance the production of oxygen radicals and H2O2, especially in leaves of the salt-sensitive genotype. As a consequence, disturbed membrane function may cause elevated Cd concentrations in the intracellular leaf compartment under salinity. Cd did not change protein concentration and pattern in leaves. The protein content in inter-and intracellular leaf compartments of both genotypes was increased under salinity. A different protein pattern was obtained in inter- and intracellular leaf compartments. Thus, several physiological interactions between NaCl stress and Cd were found in the two wheat genotypes.