Yoshiyuki Maeda

Characteristics of Na+ and K+ absorption in Suaeda salsa (L.) Pall.

Suaeda salsa can grow well in saline soils with high sodium (Na)-low potassium (K) concentrations. While high Na accumulation in plant tissues plays an important role in osmoregulation and maintenance of water absorption for normal growth of Suaeda salsa, characteristics of Na and K absorption in S. salsa grown in such saline soils have not been elucidated. We thus examined Na and K absorption characteristics of S. salsa grown in nutrient solutions of graded sodium chloride (NaCl) with 1 mmol L−1 K or of graded potassium chloride (KCl) with 1 mmol L−1 Na. The K accumulation capacity in S. salsa plant tissues was greater than the Na accumulation capacity. Although Na showed no competitive effects on K absorption, K application suppressed Na absorption drastically. Selectivity for K over Na in the absorption system became higher than that for Na over K concomitantly with increased Na or K concentration in the medium, indicating that Suaeda salsa is able to absorb K effectively with absorption of a large amount of Na. Sodium absorption was significantly decreased by tetra-ethylammonium (typical K channel inhibitor). Calcium (Ca) application increased not Na absorption but K absorption, resulting in enhancement of selectivity for K over Na. We speculate Na absorption pathways in S. salsa are partly mediated by AKT1 (Arabidopsis K transporter 1) type K channel and LCT (a low-affinity cation transporter) and NSCCs (non-selective cation channels) are not the major Na absorption pathway. These results may provide an explanation for the fact that S. salsa can grow well under saline soils with high Na-low K concentrations.

Variations in salt tolerance of reed canarygrass (Phalaris arundinacea L.) plants grown at sites with different degrees of cattle urine contamination

Abstract Variations in the salt tolerance of reed canarygrass (RCG) plants grown at sites with different degrees of cattle urine contamination were investigated. Cattle urine overflowed the urine reservoir and invaded the grassland. Soils and RCG plants were collected from sampling spots selected along the urine flowing line from 0 (contaminated site beside the urine reservoir) to 100 m. With increasing distance from the reservoir, the contents of K, Na, Ca, Mg and NO3-N in the soil and Na, K and NO3-N in the collected RCG plants decreased. The RCG plants were grown in a standard solution to obtain a large number of clones and seeds for the next generation. After the RCG clones and their next generation were subjected to water culture to the fifth leaf stage, NaCl was applied to the solution to investigate their salt tolerance. The salt tolerance, which was the highest in the RCG clones and their next generation for the plants collected from the site beside the reservoir, decreased with increasing distance from the reservoir. Under saline water culture conditions, Na and free-proline contents in shoots, K content in shoots and roots, water potential of leaves and plasmalemma ATPase activity of roots increased in the RCG clones and their next generation along with a higher salt tolerance. In conclusion, responses to saline conditions were similar between the RCG clones and the next generation that were cross-pollinated. It was considered that, even within a confined range of the grassland, salt-tolerant RCG plants that had adapted to the urine-contaminated soils were selected, and that high salt tolerance was genetically controlled. It appears likely that the maintenance of the water potential and K-absorbing function under NaCl stress contributed to the high salt tolerance.

Comparison of Ca Effect on the Salt Tolerance of Suspension Cells and Intact Plants of Tobacco (Nicotiana tabacum L., cv. Bright Yellow-2)

Salt tolerance and the effect of Ca application on the salt tolerance were compared between suspension culture cells and intact plants of tobacco (Nicotiana tabacum L., cv. Bright Yellow-2). The suspension culture cells and intact plants of tobacco were grown in a culture medium without NaCl and with 100 mM NaCl containing 0.3 or 10 mM CaCl2. At 7 d after the treatment, the dry weight of the cells and intact plants grown in the medium containing 100 mM NaCl with 0.3 mM CaCl2 decreased and the decreasing rate of the weight was much higher in the intact plants. In the medium containing 100 mM NaCl with 10 mM CaCl2, the growth of the cells and intact plants was improved, and the improvement of the growth by Ca application was much more significant in the cultured cells. Sodium content in the intact plants markedly increased with the increase of the NaCl concentration, compared to that in the cells. Calcium application decreased the Na content both in the cells and intact plants and the decreasing rate was higher in the cells than in the intact plants. Thus, it was suggested that the growth inhibition and the increase of the Na content under 100 mM NaCl conditions were more pronounced in intact plants, and that the alleviatory effect of Ca on the growth inhibition was much more conspicuous in the cells. Although the contents of total Ca and pectic acid-binding Ca in the cells and plant roots decreased with the increase of the NaCl concentration, they increased by Ca application. The activity of plasmalemma ATPase of the cells and plant roots decreased in the medium containing 100 mM NaCl with 0.3 mM CaCl2, but increased by Ca application, regardless of the NaCl concentration. In summary, Ca application to the culture medium containing 100 mM NaCl alleviated the growth inhibition, and the difference in the growth inhibition induced by 100 mM NaCl between the suspension culture cells and intact plants was closely related to that in the Na content. It appears that the alleviatory effect of Ca on the growth inhibition might be caused mainly by the enhancement of the Na-excluding function. The high content of pectic acid-binding Ca on the cell wall also contributed moderately to the alleviatory effect of Ca through the decrease of apoplasmic Na translocation.

Effect of exogenous application of sugars on the salt tolerance of perennial ryegrass protoplasts

Various sugars were introduced by electroporation into perennial ryegrass protoplasts, and the involvement of intracellular functional groups of the sugars in salt tolerance was investigated. The protoplasts were prepared from the young leaves of perennial ryegrass, and those into which sugars were introduced were treated with NaCl solution (250 mM, pH 7.0) for 6 h at 10°C. The survival rate of the protoplasts increased when xylitol, cellobiose, 1-kestose, maltose, maltotriose, raffinose and trehalose were introduced, while no changes occurred when fructose, fucose, galactose, glucose, inositol, mannitol, mannose, rhamnose, sorbitol, sorbose, fructobiose, lactose and sucrose were introduced. Cellobiose, 1-kestose, maltose, maltotriose, raffinose and trehalose possess a number of equatorial OH (e-OH) groups that promote the structuration of H2O. Xylitol, however, structures H2O even though it does not possess the e-OH groups. Hence, it is suggested that under conditions of NaCl stress, structured H2O protects the structure of cell membranes and the activity of enzymes, and that e-OH groups are involved in enhancing salt tolerance.

Effect of organic matter removal treatments and addition of aluminum-containing substances on incidence of Fusarium wilt of lettuce

Abstract In order to determine the mechanism of lettuce root rot suppression in topsoil of andosols we investigated the effect of removing humus from a topsoil of andosol and adding aluminum substances to a disease-conducive subsoil of andosol on the incidence of lettuce root rot. Both topsoil of andosols heated at 250°C and treatment with hydrogen peroxide sustained disease suppressive effect, and exhibited similar levels of disease suppression as the untreated topsoil of andosol. The disease suppressive effect was lost by heating topsoil of andosol at 400°C. Next, both subsoil of andosol amendment with aluminum-containing humic acid (Al-humic acid) and aluminum hydroxide gel (Al(OH)3) added the disease suppressive effect, but not with humic acid or crystalline structure aluminum hydroxide [crystalline Al(OH)3]. The addition of Al-humic acid and Al(OH)3 to potato dextrose agar medium significantly inhibited growth of the causal agent of lettuce root rot, Fusarium oxysporum f. sp. lactucae, compared with the control. Based on the above results, we speculate that noncrystalline aluminum hydroxide, which forms complexes with humus, inhibits growth of pathogenic fungus and thereby suppresses incidence of lettuce root rot.

Enhancement of nitrate reduction by chlorine application in Suaeda salsa (L.) Pall

Abstract We have previously reported that one of the mechanisms of growth stimulation of the halophyte Suaeda salsa (L.) Pall by NaCl is partly attributed to increased activity of photosystem II by Cl application. In the present study, the effect of Na and/or Cl application on the reduction and assimilation of nitrate in S. salsa was examined by growing plants in nutrient solutions with the following four treatments: –Na·–Cl, +Na·–Cl, –Na·+Cl and +Na·+Cl at 5 mol m−3. Growth was stimulated by the application of Cl, but not Na. The total amount of nitrogen absorbed did not differ among treatments. However, nitrate accumulation in the plant, particularly in the stem, was much higher in the –Na·–Cl and +Na·–Cl treatments than in the –Na·+Cl and +Na·+Cl treatments. In contrast, the accumulation of crude protein in all plant tissues and of amino acids in the leaves was higher in the –Na·+Cl and +Na·+Cl treatments than in the –Na·–Cl and +Na·–Cl treatments. Thus, nitrate reduction and assimilation were stimulated by Cl application, irrespective of Na application. Increased nitrate reduction was considered to be the main cause of the increased nitrate assimilation induced by Cl. Mechanisms of stimulation of nitrate reduction and assimilation are discussed.

Salt tolerance of reed canarygrass (Phalaris arundinacea L.) grown on soil perfused with urine

The differences in salt tolerance between reed canarygrass (Phalaris arundinacea L., RCG) grown on soil perfused with urine (U-RCG) and on soil not-perfused (C-RCG) were discussed. The seedlings grown on each soil were cultured in standard solution for 10 days, then NaCl was applied to the solution to adjust its concentration to 0 and 100 mM. Ten days after NaCl application, the plants were harvested to measure the weights, leaf water potential and cation contents. When the growth rates for 10 days of U-RCG and C-RCG in standard solution were expressed as 100, the rate of U-RCG was higher than that of C-RCG at 100 mM NaCl (86 and 64). Leaf water and osmotic potentials of both RCGs at 100 mM were lower than those at 0 mM. After NaCl application, the decline rate of water potential in C-RCG showed higher than that in U-RCG (95 and 24%), whereas the rate of osmotic potential was lower in C-RCG than that in U-RCG (10 and 70%). After NaCl application, the contents and plant top/root ratios in Na, K, Mg and Ca were higher in U-RCG.