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アマランサスやキノアについて地下水位が生育や収量へ及ぼす影響を明らかにした. 供試したアマランサスはA. caudatus L., A. cruentus L., A. hypochondriacus L.の3種でキノアの供試品種はBaer2とNL-6である. 地下水位は水を入れた深さの異なる容器にポットを浸して調整した. A. hypochondriacus L.はA. caudatus L.やA. cruentus L.に比べ, より高い地下水位でも出芽率や生育・収量の低下が少なかった. また, A. hypochondriacus L.は地下水位3 cmでも播種後70日目の枯死率が対照区と変わらなかった. このことから, 供試した3種のアマランサスの中でA. hypochondriacus L.は高地下水位における生育量の低下が他の2種に比べ少ないと考えられた. 一方, キノアはアマランサスのA. hypochondriacus L.より地下水位の上昇による生育量の低下が生じやすく高地下水位に対する耐性はA. caudatus L.やA. cruentus L.と同程度であると考えられた. さらに, これらを栽培するにあたってはダイズを栽培する時以上に地下水位を低下させる必要があると考えられた.

本研究は, 酸性硫酸塩土壌を有するタイ南部ナラチワ県を研究対象地とし, 酸性土壌地域でのイネ収量を向上させることを目的として行ったものである. 第1報として, まず, 人工的に作った強酸性土壌にイネ (Oryza sativa L.) 48品種を移植し, 4週間後の個体の生存率によって14品種を選抜した. なお, 参考として, 酸性土壌に強いとされるアフリカイネ (Oryza glaberrima Steud.) 29品種もイネと同様に栽培し, 耐酸性を調べた. その結果, イネ14品種とアフリカイネ10品種が選抜された. 選抜されたイネ品種14のうち, 強酸性土壌で最も高い生長速度を示した4品種と, タイ南部ですでに耐酸性があるとされている2品種, それに本研究で耐酸性がないとされた3品種を比較することによって, イネの耐酸性機構を生理学的側面から検討した. 対照区に対する酸性土壌区の相対根長は, 耐性品種で大きく, 非耐性品種で小さかった. 葉面積においても根長と同様な傾向が見られた. さらに, 酸性土壌条件下での作物生長の阻害は, アルミニウム (Al) に起因することから, 酸性土壌条件下で栽培された植物体の葉身Al濃度を調べた. その結果, 葉身Al濃度は耐性品種よりも非耐性品種の方で高くなっていた. そこで, 葉身の光合成速度を測定したところ, 葉身の光合成速度は耐性品種の方が非耐性品種よりも有意に高い値を示した. これらのことから, Alが葉身にまで移行しにくく, その結果高い光合成能力が維持されていることが, 酸性土壌耐性の大きな原因の一つと考えられた.

本研究はフェーン現象下の気象を風洞装置を用いて再現し, 高温乾燥風に対する耐性イネ品種と感受性品種との水分状態とクロロフィル含量の差を調べたものである. 耐性品種として韓国農村振興庁嶺南農業試験場の盈徳出張所で選抜した日本型Naepung-byeo (NP), 感受性品種として同定されたオーストラリア原産の日本型Ilabong (IB) を供試し, それぞれ水田土壌をつめた1/1250aポットに移植し, 屋外自然条件下の湛水状態で生育させた. 3時間の高温乾燥風処理は出穂後4日目に行った. 穂の水ポテンシャルの変化は処理終了直後から顕著に現れ, NPでは処理開始前の-0.25 MPaに比べ, -0.75 MPaと大きく低下した. 一方, IBではさらに著しく, 処理開始前の-0.34 MPaから-1.53 MPaに大きく低下した. NPの穂の水ポテンシャルは, 処理終了後2時間目までは低下したが, 処理終了後6時間目には回復する傾向を示した. 葉身における水ポテンシャルは低下する傾向があったものの, 高温乾燥風処理による差は小さく, 品種間で有意な差は認められなかった. また, 穂の相対水分含量は水ポテンシャルと同様, NPでは高温乾燥風処理による低下はほとんど見られず, 処理終了後6時間目には回復する傾向を示した. しかし, IBでは処理終了直後の相対水分含量は処理開始前に比べて大きく低下し, 処理終了後6時間目では22%と極めて低かった. 穂のクロロフィル含量もNPで高く維持され, IBでは顕著に低下し, 処理終了後6時間目にはほとんどが白穂となった. このことから, 耐性品種であるNPは高温乾燥風に対し, 頴花で水分損失を防ぐ何らかの防御機構を有し, 時間の経過とともに回復したと考えられた.

It was reported that a supernodulating soybean mutant, En6500 derived from the variety of Enrei, could produce many root nodules, but the growth rate of the plant was not necessarily high. The purpose of this paper, therefore, is to examine the characteristics of nodulation and also of plant growth in En6500 for elucidation of the mechanism of its low growth rate. The relative growth rate was low in En6500 compared with Enrei. The dry weight of the nodules per unit root mass was greater in En6500 than in Enrei, suggesting that the root of En6500 is supporting too many or an excess of nodules, which presumably leads to a reduction of plant growth rate. Reduced growth rate was associated with low net assimilation rate and further with low leaf photosynthesis. Moreover, the reduced leaf photosynthesis was associated with low partitioning of nitrogen to the leaves in En6500. Much allocation of nitrogen to the plant organs besides the leaves resulted in low photosynthesis, and also in the reduced nitrogen-use efficiency for dry matter production, which might be a potential mechanism for the low growth rate of En6500, a supernodulating soybean mutant.

The influence of potassium (K) deficiency on leaf water and osmotic potentials, and concentrations of major solutes was determined to assess their contributions to the leaf growth of soybean plants grown in solution cultures containing 5.0 and 0.2 mM KCl. A deficient supply of K restricted leaf growth due to decreased mesophyll cell numbers and cell enlargement, though water content, water and osmotic potentials of the expanding leaves were not affected by the treatment. The osmolarity of the expanding leaves showed very similar values in both treatments, though the K+ concentration in the K-deficient plants was remarkably lower than that of the control. In response to the K-deficiency, some cations, anions, sugars and amino acids accumulated in the expanding leaf, compensating the decrease in K concentration approximately 92%. These findings suggest that the leaf growth depression observed in the K-deficient plant occurred when the water relations of the K-deficient leaves are maintained close to that of the control.

We found in a previous study that Brazilian tall cultivars of spring wheat (Triticum aestivum L.) were more resistant to drought in respect of photosynthesis as compared to Mexican and Japanese semidwarf cultivars. In this study, a yield trial was performed with the same 20 cultivars to elucidate the yield and yield component responses to the soil water conditions in Cerrados, a semiarid region of Brazil. Under dry conditions, the dry matter yield of the Brazilian cultivars was significantly higher than the yields of the Mexican and Japanese cultivars. The grain yield of the Brazilian cultivars was also 34-46% greater than those of the Mexican and Japanese cultivars. Under fully-irrigated conditions, however, the Mexican and Japanese cultivars showed higher harvest indices and 18-21% greater grain yield than the Brazilian cultivars, although no practical difference was found among the cultivar groups in terms of dry matter yield. An analysis of yield components showed that the Brazilian cultivars had a larger 1000 kernel weight than the Mexican and Japanese cultivars under dry conditions, while the Mexican and Japanese cultivars had a higher kernel number than the Brazilian cultivars under fully-irrigated conditions. The reverse rotation of yield ranking among the cultivars under non-irrigated and fully-irrigated conditions is due to the fact that the Mexican and Japanese cultivars are more sensitive to soil moisture than the Brazilian cultivars.

Although many studies have shown cultivar differences in photosynthetic response to water deficit, the understanding of detailed mechanisms is not sufficient. We examined the mechanisms of water stress-resistance in terms of photosynthetic performance under low soil water potential (Ψsoil) with sixteen cultivars of wheat (Triticum aestivum L.) from different habitats, which had shown different drought resistance on a grain yield basis. Cultivar differences in photosynthetic maintenance in response to decrease of Ψsoil (water stress resistance), were found at ail seedling, booting, and grain filling stages. Cultivars with high drought resistance based on grain yield also showed high water stress resistance in photosynthetic performance. Water stress resistance (Rws) was caused more by tolerance (Tws, maintenance ability of photosynthesis in response to decrease of leaf water potential, ΨL)in some cultivars, which maintained relatively high photosynthesis (PN) in spite of decreases in ΨL, while it was caused more by water stress avoidance (Aws, maintenance ability of ΨL in response to decreases in Ψsoil) in other cultivars, which showed a relatively high PN by maintaining a relatively high ΨL under the same low Ψsoil. However, there was a positive correlation between Rws and Tws or between Rws and Aws. It is suggested that avoidance and tolerance usually occur simultaneously in adaptation to low Ψsoil, although water stress resistant cultivars varied in the water stress resistance mechanism.

The mechanism of cultivar difference in salt tolerance was investigated with Korean rice cultivars, paying special attention to the relationship between sodium (Na) and potassium (K) ions in various organs. Three tolerant and three sensitive cultivars, with Nipponbare and IR8 as the reference cultivars, were cultured in solutions containing different concentrations of NaCl. The Na ion concentration in the leaf blade, leaf sheath and root increased with increasing NaCl in the culture solution in all cultivars. Furthermore, with increasing Na ion, the K ion concentration decreased in the root and leaf sheath. Conversely, in the leaf blade, the K ion concentration increased with increasing Na ion. No relationship between thc extent of accumulation of Na and K ion in the leaf blade and salt tolerance was observed, hence, these findings do not support the hypothesis that salt tolerance is related with the exclusion of K ion by absorbed Na ion in the leaf blade. However, exclusion of K ion by Na ion in the root was round in all the cultivars tested, and extent of the K exclusion might be related to the salt tolerance in rice plants.

Reduction of relative growth rate (RGR) due to the NaCl treatment was examined in the seedlings of six Korean rice cultivars which had been reported to be different in salt tolerance on the level of grain yield. On the level of RGR, three of the cultivars were identified as salt tolerant, and the remaining three were identified as the sensitive cultivars. Further analysis of RGR indicated that the reduction of RGR by NaCl treatment was attributed in large part to the reduction of the net assimilation rate (NAR) rather than to that of the leaf area ratio (LAR). Leaf photosynthesis which is closely related with NAR, was also reduced by NaCl treatment in salt sensitive cultivars to a greater extent than tolerant cultivars. Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) content was determined in a tolerant cultivar, Han-Kang-Chal, and a sensitive one, Dong-Hae. Han-Kang-Chal showed a smaller decrease of Rubisco content per absorbed Na in the NaCl-treated leaves. This indicates that degradation of Rubisco by absorbed Na is slower in tolerant cultivars than in sensitive cultivars. Moreover, Han-Kang-Chal showed a larger decrease in osmotic potential in the NaCl treated leaves, suggesting that osmotic adjustment was developed under salt stress conditions in a tolerant cultivar.

Cultivar differences in leaf photosynthesis (LPS) and grain yield of wheat [Triticum aestivum L.] were examined under irrigated and non irrigated conditions in Cerrados, a semi-arid region in Brazil. Twelve Brazilian, five Mexican and two Japanese cultivars were used in this project. The plants were grown under low planting density to elucidate the relationship between LPS and the potential yield of an individual plant. Brazilian cultivars ranked high in LPS, followed by Mexican and Japanese cultivars under non-irrigated conditions, although there were practically no differences in LPS among these three groups of cultivars in irrigated conditions. The LPS showed a significant positive correlation with grain yield (r=0.63) and dry matter yield (r=0.73) per plant in non-irrigated conditions. However, LPS showed neither correlation with grain yield nor dry matter yield per plant in irrigated conditions. The present results suggests that PLS could be a breeding criteria to increase the yield per plant under soil water deficit conditions.

This research was conducted to elucidate the mechanisms in water stress tolerance of Oryza glaberrima Steud. with special reference to stomatal conductance. Leaf photosynthesis (LPS) of O. glaberrima Steud. with developing soil water deficiency, was still maintained above zero when the leaf water potential decreased to as low as -2.0 MPa, while in O. sativa L. LPS became zero at -1.6 MPa. Stomatal conductances also changed in parallel with LPS in both species, suggesting that the different response of LPS to reduced leaf water potential is due to the different stomatal response between two species. In the relationship between the stomatal conductance and abscisic acid (ABA) content in the leaves, Saka, a line of O. glaberrima Steud., showed a slower decrease of stomatal conductance with increase of ABA than Nipponbare, a cultivar of O. sativa L. This attenuated response of stomatal conductance to leaf ABA content in O. glaberrima Steud. was supposed to be the cause of maintenance of higher LPS than in O. sativa L. under low leaf water potential conditions. The Rubisco content showed no significant difference in the response to developing low leaf water potential between the two species.

Effects of soil water deficit, low air humidity and in combination were examined at the milky stage under controlled conditions. Low air humidity which plants experienced prior to measurement affected leaf photosynthesis in a manner different from effects of soil water deficit, in regard of the order of depression extent among leaves, i.e., photosynthetic depression by soil water deficit was in the order of flag leaf 2nd leaf < 3rd leaf. Stomatal (gs) and mesophyll (gm) conductances for CO2 diffusion, and Rubisco content varied in parallel with photosynthesis, though there was one exception. It was suggested that the above-mentioned responses of photosynthesis were caused by the corresponding depression in stomatal aperture and photosynthetic activity of mesophyll. Among the three leaves examined, little difference was observed in decrease of leaf water potential (ψ) caused by soil water deficit, while the decrease in ψ by precedent low air humidity was especially large in the flag leaf. The lower the leaf position, the larger the sensitivity of gs, gm, and Ribisco content to decrease in ψ was. Thus, difference in the extent of photosynthetic depression by soil water deficit among the uppermost three leaves was attributed mainly to different sensitivity to decrease in ψ, while that by dry air was attributed to the difference in the extent of decrease of ψ in addition to sensitivity differences. The effect of low soil water and low air humidity on photosynthesis seemed to be additive when combined.

As a physiological basis for the difference among parts of a wheat plant in photosynthetic depression by soil water deficit, the stomatal response to abscisic acid (ABA) was examined in an ABA-sprayed plant. An additional experiment was also conducted in order to confirm whether there is a direct inhibitory effect of ABA on non-stomatal mediated photosynthesis. About 1 hour after ABA was sprayed, photosynthesis (PS) and transpiration (Tr) in the leaf blades, the stem and the flag leaf sheath decreased to as low level as less than 10% of the initial rates. But, in the ear, the decreases of PS and Tr were not as much as in such parts as above-mentioned. This means that the stomata in the ear are less sensitive to ABA, which accumulates in water stress condition, than those in other plant parts. Non-stomatal photosynthesis was not inhibited by ABA addition to the reaction mixture in any part of a plant. It was suggested that photosynthetic depression by soil water deficit was not caused by the direct inhibition of photosynthetic mechanism by ABA, but by stomatal sensitivity to accumulated ABA.

In order to explore the physiological basis of the difference in photosynthetic depression by soil water deficit, the non-stomatal mediated photosynthesis (NSP) and ribulose-1, 5-bisphosphate carboxylase (RuBPCase) content were compared among different parts of a wheat plant grown under soil water deficit condition. The depression of NSP due to water stress was larger in the lower leaf blades than in the upper ones, and in leaf blades than in ear, sheath and stem. The content of RuBPCase was decreased by soil water deficit to a larger extent in the lower leaf blades than in the upper ones, and in leaf blades than in stem and leaf sheath. But, in the ear, the extent of RuBPCase decrease was relatively large, compared with that of photosynthetic depression. The results here suggest a possibility that the difference among plant parts in photosynthetic depression by soil water deficit is partly attributed to the different sensitivity of photosynthetic apparatus to water stress.

The mechanism of different water relations in each part of a wheat plant was examined to elucidate the physiological basis for the difference among plant parts in photosynthetic drought resistance. As the soil water deficit developed, the upper leaf blades maintained the higher turgor potential (TP) and relative water content (RWC) compared with the lower ones. The stem and the leaf sheath also maintained the similar level of Tp and RWC to the flag leaf. The ear, however, showed the highest RWC with a low TP. The mechanism for osmotic/adjustment was analyzed by separating the osmotic potential (OP) decrease into two components, the concentration effect and the solute accumulation effect. It was found that the solute accumulation effect was the highest in the ear, followed by the stem, the leaf sheath, the upper leaf blades and the lower ones in the last, and that the concentration effect showed the reverse order of the plant parts as above mentioned. In order to know the reason for this peculiar watch relations in the ear, the water relations were investigated in the glumes and the grain separately. It was found that the glumes showed a similar water relations to the flag leaf, whereas the grain maintained a extremely higher water content with much lower TP than any other plant part, even under severe soil water deficit condition. The strong maintaining ability of RWC seemed to be the main cause of the higher drought resistance in the ear.

Effects of brassinolide (BR) on growth and developmental processes were examined in wheat plants applying the solution at various growth stages and at various concentrations. The results are summarized as follows: 1. Elongation of root, stem and leaf was not promoted by the treatment but rather a little inhibited at higher concentratiens (Fig. 1). 2. Formation of primary roots of seedling, tillers and spikelets was promoted by the BR-treatments. The number of productive tillers decreased, though that of total tillers increased by the treatments (Figs. 1∼5). 3. Heading was delayed by the BR-treatments (Fig. 4). 4. The effects of BR on ear-and grain yield were quite different depending on the growth stages at which the treatments were given. The BR-treatments before anthesis resulted in reduction of yield mainly due to decrease in productive tillers. On the other hand, the treatment during the ripening period (from anthesis to full maturity) considerably increased ear-and grain yield (in ear weight per plant, 15%) as a result of improvement in set and filling of grains, especially in inferior ones (Figs. 6, 7). 5. Photosynthesis was promoted a little by the leaf treatment of BR. However, the frequent application extending to later stages of leaf ontogeny brought about reduction of photosynthetic rates of leaves due to acceleration of senescence (Figs. 8∼10). 6. The BR-treatment scarecely affected total dry matter production (Table 2).

The time course of respiration in soybean plants was examined under different physiological conditions to elucidate the mechanism of the determination of respiration rate. Respiratory CO2 evolution per unit dry weight (RPW) decreased after the onset of the dark period and showed a temporary acceleration around midnight, called the midnight rise of respiration (MRR) in this paper, reaching a constant level at about 48 hours after the initiation of the dark. Throughout this time course, RPW was high in younger and nitrogen-supplied plants, and low in the aged or nitrogen-depleted plants. Furthermore, MRR disappeared in the aged or nitrogen-depleted plants. From the results obtained, it was hypothesized that the time course of RPW, especially the existence of MRR, was determined by the demand for the energy and metabolic products which could be derived from respiration.

The purpose of this study is to determine if there is an interaction of nitrogen nutrition and water stress on apparent photosynthesis (APS), transpiration (Tr), and water-use efficiency in rice (Oryza sativa L.). The potted plants, which were cultured in high and low nitrogen levels, were exposed to the water stress condition, and the gas exchange rates were measured. A significant interaction of nitrogen supply and soil water stress on APS and Tr occurred, with high nitrogen plants being more affected by water stress, in respects of APS and Tr, compared with low nitrogen plants. This high responsiveness of APS and Tr in high nitrogen plants was due to stomatal sensitivity to water stress. In addition, high nitrogen plants maintained better photosynthetic machinery under water stress condition. As the results, it was found that the characteristics of greater stomatal sensitivity and better photosynthetic machinery in high nitrogen plants, led to their higher water-use efficiency.

The time course of respiration in the continuous dark was examined with soybean plants having experienced various preceding light conditions, aiming to elucidate the determination mechanism of changes with time in respiration rate. The initial value of respiration rate per unit dry weight (RPW) observed immediately after the onset of dark period was dependent on the light intensity in the preceding light period, and it was not affected by the length of light period. However, the bottom level of RPW observed after the initial decrease was affected by the length, with the lower levels in the plants exposed to the shorter light period. Furthermore, the magnitude of midnight rise of respiration, the temporal rise in the dark period, was affected by both light intensity and length of light period. It showed the linear relationship against cumulative light intensity which was obtained from light intensity multiplied by length of light period. RPW in nitrogen-depleted plants did not respond to length of light period. In this experiment, it was found that the time course of respiration consisted of two different phases. One was in the initial part of the dark period and dependent on light intensity. The other was in the following part and dependent on cumulative light intensity in the preceding light period. From this observation, it was considered that respiration in the dark period was regulated by two different physiological processes.

Time course challges of respiration rate in a leaf and roots were examined in attached and detached conditions to obtain information of the internal factors determining the time course change of respiration in different organs. In the attached condition, an expanding leaf showed a rapid increase of respiration around midnight (Midnight rise of respiration, MRR), while, an expanded leaf showed a steady state of respiration around midnight, followed by a rapid decrease, resulting in a vague MRR. The attached roots showed a clear MRR. In the detached condition the changes in leaf respiration rate were almost the same as in attached condition; whereas in roots, MRR completely disappeared. The results suggested that the respiration of a leaf is not affcted by other organs, whereas that of roots was strongly dependent on the existence of a shoot. The results also suggested that the internal factors causing MRR existed in a leaf, especially in an expanding leaf.

In order to examine the effect of nonunifomity of seedling number per hill on the growth, yield and yield components, seven kinds of rice populations were set; A)uniform populations which consist of the hills of the same number of seedlings, 1. all one seedling hills (1-1), 2.all three seedlings hills (3-3), 3. all six seedlings hills (6-6), B) nonuniform populations which consist of the hills of the different number of seedlings, 4. one and three seedlings hills alternately (1-3), 5. three and six seedlings hills alternately (3-6), 6. one and six seedlings hills alternately (1-6), 7. one, three and six seedlings hills alternately (l-3-6). The results of the study were as follows. 1. Differences in tiller number and top fresh and dry weight were observed among treated populations at the beginning of growing period, however, ultimately significant differences could not be observed. 2. In nonuniform population, each hill showed interaction and mutual compensation among one another. For an example, in the nonuniform population, 1-6, six seedlings hill depressed the growth of one seedling hill and reversely one seedling hill promoted the growth of six seedlings hill, compared to those in uniform one or six seedlings population, 1-1, or 6-6. These mutual effect was almost equal, so the growth of the nonuniform population, 1-6, as a whole, was almost same as the average of the growth of two uniform populations, 1-1 and 6-6. Accordingly the growth decrease caused by nonuniformity could not be observed over the growing period. 3. The growth variabilities among each hill in the nonuniform populations remained to.be greater than those in the uniforrn populations over the growing period. 4. These tendencies found in growth refLected to yield, so, yield decrease by nonuniformity could not be observed.

Growth compensation between neighbouring hills consisting of different number of seedlings was studied in relation to degree of nonuniformity and planting density. According to the result obtained, the rate of growtht compensation increases with increase of density and degree of nonuniformity. Growth compensation is thought to be caused by interaction or competition between neighbouring hills or among individual plants. So, in order to express quantity of competition, competition index was tried. In this trial, total competition among individual plants is sum of competition within hill (intra-hill competition) and between neighbouring hills (inter-hill competition). The method of calculation of competition index is as follows. log+/+ = 1o9 7#+/77+1o9- +/Q/-here I(n) is dry weight of the isolated hill whose number of seedlings is n, P(n) is dry weight of the hill whose number of seedlings is n in population. According to this equation, competition index was calculated about populations which had different planting densities. The intra-hill competition index increases with increase of the number of seedlings of a hill. The inter-hill competition index increases with increase of plant density. In the distance between hills below 24 cm, inter-hill competition index exceeds intra-hill competition index. Reversely, in the distance between hills above 36 cm, intra-hill competition index exceeds inter-hill competition index. So, the converting point of intra- and inter-hill competition is in the distance between 24 cm and 36 cm.