Toshiaki Tadano

Interactive Effects of Sodium Chloride and Nitrogen on Growth and Ion Accumulation of a Halophyte

Abstract A sand culture experiment was conducted with a total of 20 treatments including 5 sodium chloride (NaCl) levels (0, 50, 100, 200, and 500 mM) and 4 nitrogen (N) levels (0, 3, 7.5, and 15 mM) to evaluate the interactive effects of NaCl and N on the growth and ion accumulation of the halophyte Suaeda salsa. Under 0 mM N condition, NaCl did not affect plant height significantly, while it increased branch number and root dry weight. Addition of N increased plant growth significantly; this increase was greatest at moderate level and further increase of N concentration did not increase growth significantly. Sodium chloride concentration 50 mM stimulated plant growth in moderate levels of N. Plant growth was significantly inhibited by 500 mM NaCl. Sodium uptake increased with increases of NaCl concentrations, while uptake of potassium (K), calcium (Ca), and magnesium (Mg) decreased. Addition of N increased Na uptake, and decreased K, Ca, and Mg uptake compared with no N treatment. Potassium/Na ratio in plants decreased with addition of 3 mM N, but was unaffected by further increasing N concentration. Ca/Mg ratio in plants increased by addition of moderate N and then decreased by further addition.

Comparison of Iron Availability in Leaves of Barley and Rice

Iron (Fe) is an essential trace element in all eukaryotes. In higher plants, Fe deficiency causes interveinal chlorosis in young leaves. However, in barley and rice, both of which are “Strategy II” plants, the degree and the pattern of Fe-deficiency symptoms differ. In the present study, barley and rice plants were grown in the same container, i.e., by “coculturing,” to compensate for the amount of mugineic acids in rice in the nutrient solution. We examined the differential availability of Fe for distribution and retranslocation in shoots between barley and rice without considering the difference in the iron acquisition ability, which is affected by the differential mugineic acid secretion between barley and rice. Although the Fe concentration of young barley leaves had decreased under the coculture conditions, the SPAD value was similar to that in monocultured barley. In contrast, although there was an increase in the Fe concentration of the young leaves of cocultured rice, the SPAD value decreased, as in the case of monocultured rice. Rice accumulated Fe in old leaves, whereas in barley Fe was efficiently distributed to young leaves. Therefore, the SPAD value of the second leaf in rice remained constantly high. The Fe concentration of the second leaf in barley decreased under Fe-deficient coculture conditions, the SPAD value decreased and the senescence of the second leaf become accelerated. 59Fe pulse-labeling experiments suggested that in barley Fe was more efficiently retranslocated from old leaves to young leaves than that in rice. As a result, the level of Fe present in the fraction with a molecular weight lower than the 10,000/water-soluble Fe ratio was higher in the old leaves of barley than in the old leaves of rice under Fe-deficient conditions. Based on the results obtained, we suggest that the distribution and retranslocation characteristics of internal Fe in barley may be well adapted to Fe deficiency.

Difference in the distribution and speciation of cellular nickel between nickel‐tolerant and non‐tolerant Nicotiana tabacum L. cv. BY‐2 cells

To evaluate Ni dynamics at the subcellular level, the distribution and speciation of Ni were determined in wild-type (WT) and Ni-tolerant (NIT) tobacco BY-2 cell lines. When exposed to low but toxic levels of Ni, NIT cells were found to contain 2.5-fold more Ni (14% of whole-cell Ni values) in their cell walls than WT cells (6% of whole-cell Ni values). In addition to higher levels of Ni in the apoplast, a higher proportion (94%) of symplastic Ni was localized in the vacuoles of NIT cells than in the vacuoles of WT cells (81%). The concentration of cytosolic Ni in the NIT cells was significantly lower (18 nmol g(-1) FW) than that in the WT cells (85 nmol g(-1) FW). In silico simulation showed that 95% of vacuolar Ni was in the form of Ni-citrate complexes, and that free Ni(2+) was virtually absent in the NIT cells. On the other hand, the amount of free metal ions was markedly increased in WT cells because free citrate was depleted by chelation of Ni. A protoplast viability assay using BCECF-AM further demonstrated that the main mechanism that confers strong Ni tolerance was present in the symplast as opposed to the cell wall.

Comparative effect of NaCl and seawater on seed germination of Suaeda salsa and Atriplex centralasiatica

Seed germination in annual halophytes usually occurs when soil salinity levels are low and soil moisture is relatively high [1]. Optimum germination of halophyte seeds is often obtained under freshwater and inhibited by increasing salinity concentrations [2–4], but the ability to germinate at higher salinities is varied with species, for example Salicornia herbacea germinated at 1,700 mM NaCl [5], Arthrocnemum macrostachyum can germinate at 1,000 mM NaCl solution with 10% germination percentage [6]. Some secreting halophytes could also germinate above seawater salinity [7–11]. Most secreting halophytes show germination at NaCl concentrations ranging from 0.34–0.52 M NaCl. Few of them have low salt tolerance during germination [12–14].

A Comparative Study On Responses Of Growth And Solute Composition In Halophytes Suaeda Salsa And Limonium Bicolor To Salinity

Suaeda salsa (leaf succulence) and Limonium bicolor (secreting) are common halophytic species grown in coastal saline soil area in China. They possess different physiological adaptations which help them to avoid salt stress. Their mechanism of salt tolerance is varied and not properly understood. Therefore, the proposed plan to grow them in highly saline conditions could be hampered. The present study was designed to study the effect of salinity on growth and various solute compositions. Growth of S. salsa showed a 94% and 48% increases in comparison to control in 50 and 100 mM NaCl respectively in both shoot and root while at high salinity (400 mM NaCl) shoot and root dry weight were not significantly different from control. However, in L. bicolor root showed little promotion of shoot growth at 150 and 100 mM NaCl respectively and growth was substantially inhibited at 400 mM NaCl. Suaeda salsa accumulated more Na + and Cl - ions in comparison to L. bicolor. These ions accumulated more in shoots of S. salsa whereas distributions of ions were similar in both shoots and roots of L. bicolor. Shoot soluble sugar decreased and proline increased with increase of external salinities of both species but shoots of L. bicolor contained relatively higher amount of sugar and proline at high salinity levels.

Iron deficiency causes zinc excess in Zea mays.

Abstract Iron deficiency stress causes a severe reduction in plant growth. Although Fe deficiency causes an imbalance in divalent heavy metal nutrients, the mechanisms underlying the growth reduction caused by this imbalance remain unclear. We investigated Zn uptake and accumulation in maize under Fe-deficient conditions. Under Fe-deficient conditions, Zn uptake was 15-fold higher and Zn accumulation was 16-fold higher than that under normal nutrient conditions. The Zn content of maize leaves under Fe-deficient conditions was >0.4 mg g−1 dry weight, which was higher than the content of plants grown in a nutrient solution containing 50 µM ZnCl2. Plant growth under conditions of both Fe and Zn deficiency was significantly higher than that under only Fe-deficient conditions. Moreover, Fe deficiency increased the thiol content of the plant. These results indicate that Fe deficiency causes excess uptake and accumulation of Zn, and that the stress resulting from the Zn overload accelerates growth reduction in maize.

Interactive Effect of Moisture Levels and Salinity Levels of Soil on the Growth and Ion Relations of Halophyte

Abstract A pot culture experiment with four levels of soil moisture (40, 55, 70, and 85% of field capacity) and five levels of sodium chloride (NaCl) concentration (0, 50, 100, 150, and 200 mM) in soil was conducted to examine the interactive effect of soil moisture and NaCl on the growth of halophyte Suaeda salsa. Results showed that growth was largest at 55% of field capacity, in the range of 50–100 mM NaCl. However, at 85% of field capacity, it can grow better at higher salinity levels; and at 40% of field capacity, the growth of S. salsa was increased greatly by moderate salinity. Contents of sodium (Na) and chloride (Cl) in plant tissues increased with the decrease of moisture levels of soil. Potassium (K) concentrations were also increased at low soil moisture. Drought tolerance was increased by moderate NaCl concentrations. It is thus considered that some amounts of Na and Cl are required to absorb water in this plant.

Medicinal plants for suppressing soil-borne plant diseases: II. Suppressive effect of Geranium pratense L. on common scab of potato and identification of the active compound

Abstract Most plants exhibit inhibitory and stimulatory biochemical interactions with other plants and microorganisms, referred to as “allelopathy.” Especially, through root exudates, higher plants are able to affect the microfiora in the rhizosphere. Production of biological active substances by higher plants that prevent phytopathogens (bacteria, fungi, and nema-todes) from infecting crops has been reported (Yoshihara et al. 1988; Schenk et al. 1991). In addition, many species of plants which have been widely used for medicinal purpose also exert an allelopathic effect (Fujii et al. 1991).

Growth response of Suaeda salsa (L.) Pall to graded NaCl concentrations and the role of chlorine in growth stimulation

Abstract Growth response of a halophyte species, Suaeda salsa (L.) Pall, to graded NaCl concentrations was examined under water culture conditions. Growth increased with increasing NaCl concentration from 2 to 200 mol m−3, but decreased at NaCl concentrations above 200 mol m−3. Maximum growth was attained at 50 to 200 mol m−3. The role of Na and Cl in the growth stimulation by NaCl was examined by growing S. salsa in nutrient solutions with or without Na and Cl separately at 5 and 50 mol m−3. The growth stimulation induced by Cl was greater than that induced by Na, and Na did not significantly induce growth stimulation. The effect of Na or Cl on O2 evolution from leaves was examined under 5 and 50 mol m−3 concentrations using an oxygen electrode. Oxygen evolution from leaves in –Cl treatments was smaller than that in +Cl treatments both at 5 and 50 mol m−3. The O2 evolution in Na treatments with Cl was similar to that at NaCl. These results indicated that the mechanism of growth stimulation induced by Cl was mainly an increased photosystem II of photosynthesis in leaves. The contribution of Na on the growth stimulation of S. salsa by NaCl was smaller than Cl.

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.