Jinya Yazaki

Family-dependent cadmium accumulation characteristics in higher plants

SummaryThirty four plant species belonging to 9 families were grown on a sand soil with various levels of added Cd. The Cd content of aerial parts of the plants (tc) was correlated to the soil Cd level (sc) in a double-logarithmic relationship: log (tc)=α+β log (sc). The regression coefficients α and β statistically differed among plant families. Plant families were classified into 3 groups based on the α values; (1) low accumulation, Leguminosae; (2) moderate accumulation, Gramineae, Liliaceae, Cucurbitaceae and Umbelliferae; and (3) high accumulation, Chenopodiaceae, Cruciferae, Solanaceae and Compositae. Values of β also enabled to discriminate the families into (1) Umbelliferae, Cucurbitaceae and Cruciferae in which Cd accumulation was promoted at higher soil Cd levels, and. (2) the other families which were of the excluder type.

Genetic improvement of heavy metal tolerance in plants by transfer of the yeast metallothionein gene (CUP1)

Cauliflower (Brassica oleracea var. botrytis) tolerates treatment with 25 µM CdCl2 for eight days, but is killed by that with a 50 µM concentration. However, even 15 µM CdCl2 is toxic in the presence of 1 mM L-buthionine sulfoximine (BSO), suggesting the presence of a Cd-inducible phytochelatin and its involvement in Cd-tolerance in cauliflower. To develop heavy metal-tolerant transgenic plants, we ligated the structural gene of yeast metallothionein gene (CUP1) downstream of CaMV35S promoter and introduced the fused gene into cauliflower. A Cd-tolerant transgenic cauliflower was selected, which grew well in the presence of 400 µM or less Cd, whereas the non-transformed cauliflower tolerated only up to 25 µM Cd. The transgenic cauliflower accumulated more Cd, especially in the upper leaves, than the non-transformed plant.In conclusion, by transfer of the yeast metallothionein gene into cauliflower increased Cd-tolerance and Cd-accumulating ability can be conferred to the plant.

Variation of natural 15N abundance of crops and soils in Japan with special reference to the effect of soil conditions and fertilizer application.

Abstract The natural 15N abundance (δ15N) of the crops subjected to long-term fertilizer treatments under paddy and upland conditions in the different experimental stations throughout Japan were analyzed. The δ15N values of the grains of paddy rice which were +6.3‰ on the average in the fields without application of chemical fertilizers decreased by the treatment with chemical fertilizers. The average δ15N values of the upland crops were lower than those of paddy rice without application of N fertilizers. The δ15N values of upland crops decreased with the dose of chemical fertilizer N, but increased with the application of composts containing animal feces. The pot experiments using three soils showed that the δ15N values of paddy rice were higher than those of upland rice and sorghum and that these values were comparable to the δ15N values of ammonium and nitrate produced in the incubated soils, respectively. The δ15N values of fertilizer N absorbed by paddy rice were higher than those of fertilizer N, wh...

RELATIONSHIP BETWEEN TOLERANCE AND ACCUMULATION CHARACTERISTICS OF CADMIUM IN HIGHER PLANTS

Ten plant species belonging to 5 families,i.e., Cruciferae, Cucurbitaceae, Gramineae, Leguminosae, and Solanaceae, were grown in a sand soil at two pH levels. The soil was subjected to an application of CdCl2 at rates of 0 to 700 mgCd·kg−1 soil. The relationship between Cd concentration in the shoots (tc) and soil (sc; NH4NO3 extractable) was expressed by the equation: log (tc)=α+βlog (sc). The coefficients α and β were estimated for each species at each level of soil pH. Plottings of the scores on α and β axes showed that the Cd accumulation characteristics in the plants appeared to depend on the families irrespective of soil pH. Based on theupper critical concentration of Cd in the tops (Ct), the Cruciferae and Leguminosae species were found to be the most and the least tolerant to Cd, respectively. The Ct values correlated exceedingly well with the values of α.

Nitrite utilization in the roots of higher plants

Abstract Nitrite utilization by the roots of kidney bean, corn, and sunflower plants was investigated using 15N-labeled nitrite, and the following were concluded. (1) The primary roots of the corn plant assimilate nitrite to amino acids by a combination of nitrite reductase, glutamine synthetase and glutamate synthase. The reduction rate is rapid in the apical zone compared to the rates in the more mature zones. (2) Nitrite reduction to amino level occurs rapidly in the roots of 20-day-old seedlings of the three plants at similar rates in the daytime and in the night. This reduction seems to be more rapid than the reduction of nitrate to amino level. (3) The nitrogen derived from fed nitrogen was transferred from the root to the leaf more actively in the daytime than in the night. This trend was true for both the nitrite-fed and nitrate-fed plants. However, nitrite does not seem to be transferred to the leaf, but some nitrate may be transferred in an unchanged form.

Use of xylem sap to determine differences in the availability of mineral elements in soils

Changes of concentration of mineral elements (P, K, Ca, Mg, Mn, Zn and Cu) in xylem sap obtained from cut hypocotyls of plants reflected the differences in the behaviour of elements in soil. A high correlation coefficient was obtained between concentrations of the elements in plant tops and those in xylem sap. Therefore, “xylem sap method” was proposed as a new method in evaluating the difference in availability of elements in soils, instead of the usual “extraction method”.

Characterization of iron deficiency response system with riboflavin secretion in some dicotyledonous plants

Plants secreting riboflavin in response to iron deficiency possess an unusual iron-acquriring mechanism. The ferric-reducing capacity was particularly high at the root apex and the concentration of both riboflavin and ascorbic acid was also high in that region. This phenomenon was not observed in plant roots that did not secrete riboflavin even under iron deficiency. The response to H+-ATPase inhibitors, indicated that the ferric-reducing capacity which increased with riboflavin secretion during iron deficiency is different from that in the iron-sufficient roots, and is specifically induced by iron deficiency.

Heavy-metal tolerant transgenic plants — Expression of the yeast metallothionein gene CUP1 in plants and evaluation of heavy-metal tolerance in transgenic plants at the stage of callus

We are trying to improve heavy-metal-tolerance plants by introducing genes involved in heavy-metal-tolerance to plants with high biomass. In this study, we overexpressed the yeast CUP1 gene to increase metallothionein synthesis in sunflower calli, tried to evaluate heavy-metal-tolerance at the stage of callus by TTC-reducing activity, and to select tolerant clones. The transgenic calli of several strains showed high TTC-reducing activity even after a treatment with Cd for 10 days. In the transgenic calli of a few strains, which showed low TTC-reducing activity, the quantity of metallothionein was lower than that in the other transgenic strains. These results suggest that the transformation of sunflower with the CUP1 gene increased the ability to synthesize metallothioneins and made the calli tolerant to Cd. These findings also showed that the measurement of cell viability by TTC reduction is a useful method for the evaluation of Cd tolerance at the stage of callus.

Physiological characterisation of root cell Cd2+ absorption and translocation to shoots in Brassica

In nutrient solutions containing Cd in the presence of heavy metals differing in electro-negativity, Cd absorption by cauliflower roots was decreased in the presence of Cu and Pt but slightly increased in the presence of Mn. Copper absorption by cauliflower roots was decreased in presence of Pt. Cadmium treatment also inhibited Ca absorption by cauliflower roots. The inhibitors of the calcium pump were inhibited by Cd absorption as was also the case for Cu pretreatment. Furthermore, Cd absorption by protoplast cells prepared from cauliflower root was increased by treatment of a Ca2+-ionophore These results suggest that on Cd absorption by root cells Cd entered into the root symplast through the calcium pump.

Possibility of copper deficiency and impediment in ripening in rice from application of crop residues in submerged soil

Pot experiments were conducted to determine the cause of impediment in ripening in rice (Oryza sauva L.) grown under submerged soil conditions with addition of crop residues. Cu content in rice decreased considerably when compared to other elements when crop residues were added under submerged condition. Plants that showed severe unfilled spikelets had lower Cu content at panicle formation. We hypothesize that the impediment in ripening is caused by Cu deficiency brought about by a reduction in available Cu caused by decomposition of crop residues under submerged conditions.