変化する塩ストレス条件下における湛水の電気伝導度とイネの乾物生産低下の関係

　Knowledge about the relationships between the intensity of salinity of rooting medium and dry matter production may contribute to the improvement of rice yield under saline conditions. A rice cultivar Koshihikari was grown in pots with soils under submerged soil conditions. The stagnant water was salinized with NaCl from 31, 45 and 59 days after sowing, and for each of those, the level of salinity was increased every 6 days to maturity at three different rates of increase. Electrical conductivity (EC) of stagnant water was measured. Final dry weight of above ground parts and panicles decreased as initiation of salinization took place earlier and the rate of increase of EC was higher. Reduction in panicle dry weight was correlated with the occurrence of white heads. The values of EC at which plants died increased with the plant development and the rate of increase of EC, while these depended mainly on the rate of increase of EC but not on the time of salinization. In the plants which survived after heading, the final dry weight decreased in proportion to accumulated EC (sum of EC values for each day until harvest). Therefore, except for strong salinity where plants may die before heading, accumulated EC should be abe to predict dry matter production under salinity as an integrated indicator of level and duration of salinity.塩性環境における稲作改善のために，イネの乾物生産と根域の塩性程度との関係を知ることは重要である．水稲品種コシヒカリを用い，土壌を詰めたポットで湛水栽培し，湛水に塩化ナトリウム（塩）を添加することによって塩ストレスを与えた．塩添加は播種後31，45および59日目から開始され，それぞれ６日ごとに３段階の異なる速度で塩を添加するとともに，湛水の電気伝導度（EC）を測定した．地上部および穂の最終的な乾物重は，塩添加開始が早いほど，EC の増加速度が大であるほど低下した．そして，穂の乾物重は白穂の発生率が高いほど低下した．植物体が枯死したときの EC 値もまた，塩添加の開始時期が早いほど速度が大であるほど大きかったが，この EC 値は主にEC 増加速度に依存しており，塩添加開始時期の影響は小さかった．一方，出穂した植物で乾物重は積算 EC 値（毎日の EC の値を植物体採取日まで足した値）に対して直線的に低下した．以上より，出穂する前に枯死するような強い塩性環境を除けば，積算 EC 値は塩ストレスの強さと期間を総合した指標で，イネの最終的な乾物生産をよく予測すると考えられた

Changes of Rice Sodium Content due to Sodium Exclusion and Transpiration under Salinity

The relationship between sodium contents of tops and transpiration rates was studied in two rice varieties with different sodium exclusion rates in roots; Kala-Rata1-24(KR1;low exclusion rate) and IR28 (high exclusion rate). Seedlings at 7th leaf stage grown in culture solution were subjected to saline water(100mM sodium chloride) and transpired for 12 hours. Various transpiration rates were obtained under different humidity, light intensity and temperature conditions. Transpiration stream concentration factor of Na+ (TSCFNa+), which denotes the sodium exclusion rate in the root, decreased with increase in the transpiration rate under different humidity and light intensity conditions. On the other hand, TSCFNa+ was lower in KR1 than in IR28 under different temperature conditions. There were no different in the sodium exclusion rates at high transpiration rates. Sodium contents of tops initially increased with the transpiration rates but afterwards decreased with the transpiration rates. Sodium contents of tops were higher in KR1 than in IR28 at low transpiration rates under high humidity and low light intensity conditions, but it was higher in IR28 under low temperature conditions. There were no varietal differences in the sodium contents of tops at high transpiration rates. These results indicated that the varietal differences in sodium exclusion rates were detectable at low transpiration rates and affected the sodium contents of tops, but there were no differences in the sodium contents of tops at high transpiration rates.イネでは、ナトリウム（Na)含有率が高いほど光合成速度、苗の生存率および相対生長速度が低下することから、塩ストレス下における体内Na含有率の品種間差異に着目した研究が進められてきた。しかし、塩ストレスに対する体内Na含有率の品種による反応は、研究によって異なる。Makiharaらは、幼苗期にNa含有率が異なるとされる品種を成熟まで栽培したところ、Na含有率に大きな差異を見出さなかった。また、Makiharaらの研究でNa含有率が低かった品種が、森田らの研究では高かった。イネは、根においてナトリウムイオン（Na+）を分離排除する能力をもし、その程度は品種によって異なる。この能力は体内に入り込む水のNa+濃度に影響を与えるのが、体内に取り込まれるNa+の質は、流れる水の総量に影響される。すなわち、イネのNa含有率は、蒸散量と蒸散流に含まれるNa+濃度によって決まり、後者は根におけるNa+排除率によって変わる。蒸散と排除率はいずれも環境条件によって変わると考えられ、それによって体内Na含有率も変わるであろう。したがって、研究によってNa含有率の反応が異なるのは、両者の相互作用によると考えられえる。しかし、蒸散量とNa+排除率の変化が体内Na含有率にどのように影響を与えるのかは知られていないので、本研究で調べた

Analysis of Physiological Dynamics in Plant Growth

In order to realeze a high-efficient growth control for higher yielding, it is important to clarify the relationships between the physiolofical dynamics and the growth of a particular crop. Therefore, an assimilation chamber for simultaneous measurement of photosynthesis, shoot and root respiration,transpiration and ion uptake of a whole plant was developed. The relationship between plant growth and constructive respiration coefficient which was calculated by using McCree's equation, was investigated. The coefficient increased with the ratio of the assimilation of nitrogen and carbohydrate(⊿N/⊿C) during measurement. The higher ratio of ⊿N/⊿C is closely related to an increase in dry-matter partitioning of the leaf blade.In this measurement,light intensity was daily lowered to estimate the constructive respiration coefficient and plant gowth might be influenced under these conditions. Then measurements at condtant daylight intensity were done under different humidity and nutrient conditions, using several varieties. Consequently,shoot respiration rate was estimated by relative shoot growth rate and leaf blade/sheath ratio of dry matter increase.Respiratory enegy costs for organogenesis differed among the plant parts, and that of the leaf blade was higher than that of the leaf sheath. Root respiration rate was explained by the combination of relative root growth rate and nitrogen uptake rate. The respiratory energy cost for nitrogn uptake did not change with the transpiration rate, the nitrogen concentration in the culture solution nor with other varieties. Dry matter partitioning rate to shoot was found to have two main componets,i.e.initial nitrogen content of shoot and ratio of assimilated nitrogen and carbon in the first day. Dry-matter increase and dry matter partitioning of intact plants could be discovered by measuring CO2 exchange, nitrogen uptake and shoot nitrogen content.光強度を日毎に低下させながら個体のCO2収支を測定することによって、光合成産物と窒素増加量の比を知り得ることが明らかになり、その比は乾物分配に密接に関与するものと考えられた。そして、光強度を一定にした場合、異なる湿度および培養液濃度条件下において、あるいは、非構造性炭水化物含有率の異なるイネ個体を対象にした場合でも、個体のCO2収支、養分吸収および窒素含有率を測定することによって、乾物増加量の推定のみならず、茎葉部への乾物分配率の推定が可能なことが明らかになった。このことから、さらに他の環境条件、例えば、光強度、CO2濃度、温度などが異なる条件においても同様の結果が得られるか検討を行なうとともに、実際に、CO2収支、養分吸収および窒素含有率を測定し、乾物分配率を予測する重回帰式に当てはめることで、乾物分配率が推定できることを実証するための実験を行なう必要があるものと考えられた。また、同時に、個体の表面電位の測定による生理状態の検出方法についての研究を進めることで、植物の新たな生育診断法の確立に役立つものと考えられた

Growth and Sodium Accumulation in the Tillers which Appear on the Upper Nodes in Rice (Oryza sativca L.) Under Saline Conditions

The mechanism of late-grown tillers which come out of the upper culm nodes in rice (Oryza sativa L.) under saline conditions was examined. A rice cultivar, Akihikari was grown in pots under flooding conditions. The panicles were excised below the neck node of the panicle at the heading stage. Salinity treatment consisted of adding 100mM sodium chloride to water of pot at the excision of panicle (Na0), and 14 days after the excision (Na2). Tillers on the upper clum nodes grew in NaO and Na2. Dry weight of tillers increased with decrease of dry weight of stock shoots that produced the tillers. So the sum of dry weights of the stock shoots and tillers did not change, indicating that tiller growth apparently depended on reserve of carbohydrate in the stock shotts. Sodium was accumulated gradually in the plant, while sodium content of internode and tiller were kept lower than those of leaa blade and leaf sheath. In the leaf blade and leaf sheath, the upper organs accumulated less sodium than the lower organs. The tillers on the upper nodes grow faster and had low sodium content in the early stages of tiller development in NaO. Therefore, it was concluded that tillers which come out of the upper culm nodes could grow under saline conditions because the sodium content of tiller, internode and the upper leaf sheath were kept at a relatively low level.塩条件下において高節位分げつが成長する要因を調べた．水稲品種アキヒカリをポットに移植し湛水条件で栽培し，出穂期に穂を穂首節真下より切除した．ポットの水にNaCl濃度100mMとなるようにNaClを添加する処理を穂切除直後（Na０区）と14日後（Na２区）に行った．Na０とNa２区ともに高節位分げつが成長，乾物重が増加するとともに分げつを発生させた茎（母茎）の乾物重は低下した．分げつと母茎の乾物重の和は変化がなく，分げつの成長は母茎の貯蔵炭水化物によっていた．節間と分げつのNa含有率は葉身と葉より低く保たれ，葉身，葉鞘でも下位節に比べ上位節のNa含有率が低かった．またNa０区の分げつ成長初期では茎上部の分げつほど成長が早く，Na含有率が低かった．以上のことから塩条件下で高節位分げつが成長するのは分げつと乾物供給源である節間と上位葉のNa含有率が比較的低く抑えられるためであると考えられた

The Effect of Prevention of Root Injury on Growth, Development and Dry Weight in Rice (Oryza sativa L.) Transplanted to Saline Soil

Rice root has an important role in water absorption and exclusion of sodium ion in saline soil. However, it is injured during transplanting to paddy field. The objective of this study was to examine whether prevention of such root injury reduces salinity damage in rice. Extremely early rice cultivar "Akihikari" that is not salt tolerant was grown in plastic bags filled with soil. Roots of seedlings were clipped leaving 5mm~10mm, then transplanted to 5L pots filled with soil applied with 0g, 7g and 10g of sodium chloride (NaCl). The growth and dry weight at the mature stage was compared to those of plants transplanted with intact roots. Time of transplanting was 12, 19, 26 and 33 days after sowing. Increase of number of stems was suppressed due to root clipping and salinity, but there was no interaction between the two factors. Dry weight of total above ground part and panicle decreased due to salinity though root clipping did not change them. The reduction of panicle dry weight was caused by the reduction of mean number of spikelets per panicle, thus mean panicle dry weight, as number of panicles and mean spikelet dry weight showed no changes. It was concluded that prevention of the root injury may not effectively alleviate salinity damage in less salt tolerant rice cultivars.イネの根は吸水するとともにナトリウムイオンを排除する役割を持っている．水田移植栽培において根の損傷を防ぐことが効果的に塩害を軽減するかどうかを検討した．耐塩性の弱いイネ極早生品種アキヒカリを用い，土壌を詰めたビニール袋で育苗した．苗の根を5 ㎜～10 ㎜ 残し切除して，塩化ナトリウム（NaCl）0ｇ，7ｇ，10ｇを土壌に添加したポットに移植し，根を傷つけないように移植した植物と生育と成熟期の乾物重を比較した．移植は播種後12日，19日，26日，33日の4回行った．茎数の増加は根の切除および塩添加によって抑制されたが，二要因の交互作用はなかった．成熟期の地上部と穂の乾物重は塩添加によって減少したが，根切除の影響はなかった．穂の乾物重の減少は穂数と平均1籾重が変わらなかったため，平均1穂籾数の低下による平均1穂重の低下によっていた．以上の結果から耐塩性が小さい日本の品種において移植時の根の損傷を防ぐことは，塩害軽減に効果的でないと考えられた

Superconductivity in Ternary Scandium Telluride Sc6MTe2 with 3d, 4d, and 5d Transition Metals

We report the discovery of bulk superconductivity in Sc6MTe2 with seven kinds of transition-metal elements M. The critical temperatures for M = 3d elements are higher than those for 4d and 5d elements and increase in the order of M = Ni, Co, and Fe with the highest Tc of 4.7 K in Sc6FeTe2. First principles calculations indicate the presence of significant contribution of Fe 3d orbitals at the Fermi energy, which most likely enhance the Tc of Sc6FeTe2. The upper critical field for M = Os is considerably enhanced by the strong spin-orbit coupling. These results show Sc6MTe2 to constitute a unique family of d-electron superconductors, in which d electrons of 3d and 5d M atoms strongly influence the superconducting properties.Comment: 8 pages, 10 figure

Large Magnetic-Field-Induced Strains in Sintered Chromium Tellurides

Sintered samples of Cr3Te4 and Cr2Te3 are found to show large strains accompanied by large volume changes under a magnetic field. In Cr3Te4, volume increases of deltaV/V = 500-1170 ppm by applying a magnetic field of 9 T are observed over the entire temperature range below 350 K. At room temperature, the deltaV/V value exceeds 1000 ppm, which is considerably larger than the maximum values reported for Cr-based magnets thus far and is comparable to the room-temperature value of forced-volume magnetostriction in invar alloys. Cr2Te3 show a large deltaV/V of 680 ppm when applying a magnetic field of 9 T at 200 K. Both samples display particularly large volume increases around the Curie temperature, where they also show negative thermal expansion due to microstructural effects, suggesting that the cooperation between anisotropic lattice deformation associated with the magnetic ordering and microstructural effects is essential for the manifestation of the large magnetic-field-induced volume changes.Comment: 6 pages, 6 figure