Accumulation Of Toxic Ions Research Articles

Solute accumulation and distribution during shoot and leaf development in two sorghum genotypes under salt stress

Seedlings of two forage sorghum genotypes ( Sorghum bicolor (L.) Moench) differing in salt tolerance were subjected to 0 and 100 mM NaCl and shoot development, leaf elongation, and organic and inorganic solutes contents in leaves were measured. Salt stress reduced both shoot development and leaf elongation and enhanced leaf senescence and injury. It also led to accumulation of toxic ions (Na + and Cl −), organic solutes (carbohydrates, amino acids and proline), and reduction of K + content in leaf blades. Toxic ion accumulation was higher in the basal zone of the leaf blade and occurred during the period of intense leaf growth while organic solutes accumulation, mainly proline, was higher in the apical zone and occurred when the leaves practically had reached their final size . All these changes were more conspicuous in the sensitive than in the tolerant genotype. The latter also retained more toxic ions in leaf sheath tissue than the former. It is suggested that the reduction in shoot development and leaf elongation were related to toxic ion accumulation and depletion of K + ions in the leaf blades. The accumulation of organic solutes in leaves did not appear to be related to salt tolerance. Proline accumulation appears to be a reaction to salt stress damage and not a plant response associated with salt tolerance.

Salt Tolerance of Cotton: Some New Advances

Referee: Dr. Lin Wu, Department of Environmental Horticulture, University of California, Davis, Davis, CA 95616Cotton is a dual-purpose crop, widely used for fiber and oil purposes throughout the world. It is placed in the moderately salt-tolerant group of plant species with a salinity threshold level 7.7 dS m−1, its growth and seed yield being severely reduced at high salinity levels and different salts affect the cotton growth to a variable extent. However, inter- and intraspecific variation for cotton salt tolerance in cotton is considerable and thus can be exploited through specific selection and breeding for enhancing salt tolerance of the crop. There are contrasting reports regarding the crop response to salinity at different plant growth stages, but in most of them it is evident that the crop maintains its degree of salt tolerance consistently throughout its entire developmental phases. In the latter case an effective selection for salt tolerance is possible to be made at any growth stage of the crop. The pattern of uptake and accumulation of toxic ions (Na+ and/or Cl−) in tissues of plants subjected to saline conditions appears to be due mostly to the mechanism of partial ion exclusion (exclusion of Na+ and/or Cl−) in cotton. Maintenance of high tissue K/Na and Ca/Na ratios is suggested to be an important selection criterion for salt tolerance in cotton. While judging the appropriate mechanism of ion transport across the membranes in view of existing literature, it was evident that the PM-ATPase responds to increasing supply of Na+ in the growth medium, but the activity of the transport proteins on the plasma membrane alone were insufficient to regulate intracellular Na+ levels. Vacuolar-ATPase is also not responsive to increased external Na+. The inability of V-ATPase to respond to Na+ gave indication of the lack of effective driving force for compartmentalization of Na+ in cotton. However, in view of some latest studies concenrning the role of some antioxidants in salt tolerance of cotton it was suggested that high levels of antioxidants and an active ascorbate-glutathione cycle are associated with salt tolerance in cotton. Genetic studies with cotton in relation to salinity tolerance exhibited that most of growth, yield, and fiber characteristics are genetically based and most being QTL controlled and variable. The high additive component of variation can be exploited for breeding to produce further improvement in the salt tolerance of cotton.

Chromosomally encoded arsenical resistance of the moderately thermophilic acidophile Acidithiobacillus caldus.

Arsenical resistance is important to bioleaching microorganisms because these organisms release arsenic from minerals such as arsenopyrite during bioleaching. The acidophile Acidithiobacillus caldus KU was found to be resistant to the arsenical ions arsenate, arsenite, and antimony via an inducible, chromosomally encoded resistance mechanism. Because no apparent alteration of the toxic ions was observed, Acidithiobacillus (At.) caldus was tested to determine if it was resistant as a result of decreased accumulation of toxic ions. Reduced accumulation of arsenate and arsenite by induced At. caldus cells supported this hypothesis. It was also found that, with the addition of an energy source, induced At. caldus could transport arsenate and arsenite out of the cell against a concentration gradient. The lack of efflux in the absence of an added energy source and in the presence of inhibitors suggested that efflux was energy dependent. Induced At. caldus also expressed arsenate reductase activity, indicating that At. caldus has an arsenical resistance mechanism that is analogous to previously described systems from other Bacteria. Southern hybridization analysis showed that At. caldus and other gram-negative acidophiles carry an Escherichia coli arsB homologue on the chromosome.

Salt and oxidative stress: similar and specific responses and their relation to salt tolerance in citrus.

Salt damage to plants has been attributed to a combination of several factors including mainly osmotic stress and the accumulation of toxic ions. Recent findings in our laboratory showed that phospholipid hydroperoxide glutathione peroxidase (PHGPX), an enzyme active in the cellular antioxidant system, was induced by salt in citrus cells and mainly in roots of plants. Following this observation we studied the two most important enzymes active in elimination of reactive oxygen species, namely, superoxide dismutase (SOD) and ascorbate peroxidase (APX), to determine whether a general oxidative stress is induced by salt. While Cu/Zn-SOD activity and cytosolic APX protein level were similarly induced by salt and methyl viologen, the response of PHGPX and other APX isozymes was either specific to salt or methyl viologen, respectively. Unlike PHGPX, cytosolic APX and Cu/Zn-SOD were not induced by exogenously added abscisic acid. Salt induced a significant increase in SOD activity which was not matched by the subsequent enzyme APX. We suggest that the excess of H2O2 interacts with lipids to form hydroperoxides which in turn induce and are removed by PHGPX. Ascorbate peroxidase seems to be a key enzyme in determining salt tolerance in citrus as its constitutive activity in salt-sensitive callus is far below the activity observed in salt-tolerant callus, while the activities of other enzymes involved in the defence against oxidative stress, namely SOD, glutathione reductase and PHGPX, are essentially similar.

Simplified Model of Integrated Water and Solute Uptake by Salts‐ and Selenium‐Accumulating Plants

AbstractThe rate of soil salinization and the accumulation of toxic ions in soils are affected by evapotranspiration and the uptake of ions by plant roots. These are two counteracting processes and the interrelationship between them can be quantified by a mathematical model. The objectives of this study were to: (i) formulate an analytical model describing soil salinization and accumulation of toxic ions and (ii) suggest a criterion for irrigation water quality (C*0) and demonstrate its behavior under varying transpiration rates. The processes by which the soil becomes saline were simulated with an analytical solution to the convection‐diffusion equation. The model was based on ion and water uptake by plant roots. The calculations indicated that crops classified as salinity tolerant remove more salt from the soil than salinity‐sensitive crops. The rates of ion removal are 5, 15, and 40 × 10−3 dS m−1 d−1 for salinity‐sensitive, semisensitive, and tolerant crops, respectively. Therefore the ratio between the uptake rates of ions and water per unit soil volume is presented here as a criterion for the upper limit of allowable salinity in irrigation water. This ratio is inversely related to transpiration rate (evaporation neglected). Theoretically, the maximum allowable salinity of salt‐tolerant crops, C*0, decreases from 20 to 4 dS m−1 when the transpiration rate increases from 2 to 10 × 10−3 m d−1. For the same transpiration rate increase, C*0 of sensitive crops decreases from 3 to 0.5 dS m−1; thus, a lower quality of water can be permitted for irrigation in a moderate or cool climate than in an arid climate. The model applies also for Se‐accumulating crops. Theoretically, at a transpiration rate of 5 × 10−3 m d−1, Se can be removed from a soil solution containing a high concentration (C*0 = 1 mg kg−1) when the uptake rate of the growing crop is 25.8 × 10−3 mg kg−1 d−1.

Function of roots in NaCl-stressed bean plants

Higher plants have adopted two physiological strategies in response to saline environments; either the uptake of toxic ions is reduced (E.G. Na +, CI− and others), or accumulation of toxic ions in the aerial part may be prevented by their retention in the roots (or stem) and in consequence — reduction of their transport to the youngest, developing part of shoot [2].

SOLINIZATION INFLUENCE ON STRUCTURE YIELD ELEMENTS OF DURUM WHEAT VARIETIES (T. DURUM DESF.) IN TERMS OF PLANT DEVELOPMENT STAGE

The studies were carried out at the Dagestan Experimental Station of VIR. The most salt-tolerant varieties of durum wheat of different ecological and geographical origin served as the material for the study. Plants were exposed to salinity in different phases of vegetation. In all phases (germination, tillering, budding, heading), the number of grains from the main ear is most susceptible to salinity (58.0%, 73.5, 75.1, 77.0% of control, respectively). Indicators of other traits: plant height - 68.0%, 83.0, 86.2, 86.6; the number of spikelets in an ear – 72.5, 84.4, 87.3, 93.0; ear length - 74.0, 82.8, 84.0, 88.3%, respectively. In the early stages of development (germination, tillering), durum wheat varieties show poor resistance to salinity. Salt tolerance growing to heading is a manifestation of the body's adaptation to the accumulation of toxic ions under conditions of increasing salinity due to water evaporation and the pulling of salts into the root layer during the growing season.