Growing the rice plants under various conditions of some possible combinations of daytime air-temperatures (A_D : 26, 20 and 14°C), the daytime water-temperatures (W_D : 26, 20 and 14°C), the nocturnal air-temperatures (A_N : 20, 14 and 8°C), the nocturnal water-temperatures (W_N : 20, 14 and 8°C) and the number of days of treatment (P : 3, 6 and 9 days), the authors examined their main effects and interactions on the heading date. The rice variety "Eiko" was used. The daytime was settled for eight hours from 9.00 a.m. to 5.00 p.m. and the night-time was settled for sixteen hours from 5.00 p.m. to 9.00 a.m. of the next day. The water was kept four cm. in depth above the soil surface in pots. The experimental design was 3⁵ factorial in 81 units (1/3 replicate) with one block and defining contrasts 1=A_DW_DA_NW_N<SUP2>P. The results were summarized as follows; 1. At the fourth leaf stage (T₁; the transplanting time), the main effects of W_D, W_N and P were significant at 0.1% level and all the other were not significant (table 2). And regardless of the difference of W_N, it was inferred that W_D of 21°C hastened the heading date (fig. 1-T₁(P₃)). 2. At the seventh leaf stage (T₂; about ten days before the differentiating stage of first bract primordia), the main effects of A_D, W_D, A_N and W_N and the two-factor interactions of A_D × P, A_N × W_N and A_N × P were significant. The contour lines of each date of heading based on W_D and W_N were almost straight and parallel with the line of mean water-temperature for nine days treatment (fig. 1-T₂ (P₃)). On the other hand, the contour lines of each date of heading based on A_D and A_N were curved. And regardless of the difference of A_N, it was inferred that A_D of 20°C hastened the heading date (fig. 2-T₂ (P₃)). Moreover, T₂ was considered to be the most sensitive stage to temperature, because the heading date and the total leaf number on the main stem were most variable by both air- and water-temperature among all the treatment stages. 3. At the stages of nine leaves (T₃; the differentiating stage of first bract primordia) and ten leaves (T₄; the middle differentiating stage of primary branch primordia), the main effects of each factor and their interactions were similar to those of T₂, but the strengths were weaker than those of T₂ (table 2, 3 and 4). 4. At the thirteenth leaf (flgg leaf) stage (T₅; the stage of reduction division of pollen mother cells), the main effects of A_D, A_N and P and the two-factor interaction of A_N × P were significant greatly (table 2). The contour lines of each date of heading based on A_D and A_N were almost straight and parallel with the line of mean air-temperature (fig. 2-T₅ (P₃)).

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For the purpose of finding the effect of culture condition on the activity of roots and the growth of aerial parts, tobacco plants of MC variety were water cultured using a specially devised hydroponic bed and tank. Dry matter production, amount of absorbed elements, respiratory rate and activity of roots were investigated with reference to the depth and velocity of the stream. The results obtained were as follows: 1. Dry matter production and physiological functions of roots such as the respiratory rate and activity were highest when the tobacco plants were grown on the solution 4 cm in depth. 2. When the speed of the culture solution was within 10.7 cm a minute, dry matter production and respiratory rate and activity of roots decreased proportionally with the decrease of stream velocity. Tobacco plants grown under low stream velocity showed lower absorption of elements than those grown on the high stream velocity. 3. In case of the velocity more than 10 cm a minute, dry weight was not proportional to the increase of stream velocity. Respiratory rate and activity of roots grown under high stream velocity was higher than that grown under low stream velocity. Amount of absorbed element was about the same level over the velocities more than 5 cm a minute. 4. There seemed to exist positive correlations between stream velocity and respiratory activity. The auther concludes from the experiment described above that the optimum depth of the solution is 4 cm and the optimum stream velocity is 10 cm a minute when the hydroponic bed 8 cm in height is used.

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水稲と大豆の各品種を用いて, これらの葉の生長および老衰に伴つてサイトカイニン含量およびアブサイシン酸様活性がどのように変化するか調査した. ガスクロマトグラフィーで定量された3種のゼアチン化合物のうちで, 水稲葉ではゼアチン含量は分けつ初期に最高に達し, その後登熟期における老衰に伴つて著しく減少している. しかし, ゼアチンリボサイドと結合型ゼアチン(ゼアチングルコサイド+ゼアチンリボチド)はゼアチン程顕著に減少していない. これらに対して, アブサイシン酸様活性ほ幼穂形成期にかなり上昇するが, 分けつ初期と老衰の起る登熟期との間では大きな変化はみられない. さらに, 作物各品種間におけるサイトカイニンおよびアブサイシン酸様活性の差異についてみると, 水稲ではサイトカイニンレベルは老衰の早い品種では老衰の遅い品種に比べてより急速に低下する. しかし, アブサイシン酸活性はこれらの品種間において大きな差異はみられない. いつぽう, 大豆ではサイトカイニンレベルの低下と対応してアブサイシン酸活性が著しく増加しており, また落葉の早い品種では落葉の遅い品種に比べて, サイトカイニンレベルがより急速に低下し, かわつてアブサイシン酸活性がより上昇している.

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本実験は10種のC₃, C₄型植物を用いて高炭酸ガス濃度下における単葉の光合成と蒸発の種間差を検討すると同時に, さらに31種のC₃, C₄型植物について夏季に大型同化箱のなかで栽培し, 炭酸ガス濃度の0.03%(対照区) 0.10%(中濃度区)および 0,20あるいは0.25%(高濃度区)の3区を設けて実験を反復し, 炭酸ガスの富化が乾物生産に及ぼす影響の種間差を解明しようとした. 得られた主な結果は次の如くである. 1) C₄型植物の光合成はC₃型植物より比較的低い炭酸ガス濃度において飽和に達した. また炭酸ガス濃度を大気濃度より高めてゆくと, 気孔は漸時次閉鎖し, 蒸散は低下してゆくが, その際, C₄型植物はC₃型植物より気孔の閉鎖による蒸散の低下が著しかつた. 2) C₃型植物では炭酸ガス富化による乾物生産の増加は著しく, 対照区に比して1.50～4.70倍の増加を示した. これに対してC₄型植物では炭酸ガスの富化による乾物生産の増加がほとんどなく, C₃型植物と著しい対照を示した. このような炭酸ガス富化の効果の種間差は炭酸ガス光合成関係に見られる差, 気孔開度に対する炭酸ガス影響の差などによつてもたらされたと思われる. なお, C₃型植物のなかで炭酸ガス富化の効果が著しかつたものの大部分は冬作物に属していた. 本実験から, 炭酸ガス富化の効果は光合成系を異にするC₃型植物とC₄型植物によつて異なることが明確にされた. このことは大気中の炭酸ガス濃度の変化が光合成系の進化過程と密接な関係をもつであろうことの可能性を示すと同時に, 実用的な面から炭酸ガス施肥における種の選択に対して一つの示唆を与えると考えられる.

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It has been known that the mesocotyl of the japonica type of rice does not elongate more than 1 cm even in darkness. In the previous paper, however, it was shown that the mesocotyl of some seedlings of a japonica rice elongated more than 1 cm, whereas the mean mesocotyl length of total seedlings was less than 3 mm. Assuming that this variation of mesocotyl length may be caused by some physiological differences in the seeds, the following experiments were conducted. Rice seeds, Oryza sativa L. cv. Sasanishiki, belonging to the japonica type were used as materials. After harvesting, the panicles were dried 45 days under the room conditions in 1972. Seventy-two panicles with each 8 primary branches (Fig. 1) were selected for the experimental use. Terminal (I), middle (V) and lowest (VIII) branches were cut off at their bases. They were sterilized, washed and placed on a sheet of wet cotton wool, being incubated in darkness at 30°C for 11 days. The almost all seedlings of the terminal and the middle branches had short mesocotyls, whereas the some seedlings of the lowest (VIII) branches, especially located at 2' and 3' positions on secondary branches, produced long mesocotyls (Fig. 1, 2 and Table 1, 2). When the seeds located at 1, 2, 3, and 4 positions of the upper primary branches (&xotime;), and those located at 2', 3' and 4' positions of the lower secondary branches (●) were sampled (Fig. 1), and incubated separately in darkness at 30°C for 10 days, 4 % of the former and 50% of the latter plants produced long mesocotyls (more than 6 mm), respectively. The growth pattern of these plants with long mesocotyls was very similar to that of the plants treated with abscisic acid (ABA) as shown in the previous study (Fig. 2). The seeds harvested in the falls of 1970, 71 and 72, i.e. 2.1, 1.1 year and 1.5 month after harvest, respectively, were sterilized, and placed on a sheet of wet cotton wool in Petri dishes, being applied with or without 10 ppm of gibberellic acid (GA₃), and were incubated in darkness at 30°C for 10 days. As shown in Fig. 3, a half of the 2.1 year seeds did not germinate, whereas almost all seeds germinated in both 1.1 year and 1.5 month seeds. In 2.1 year old seeds, the frequency of longer mesocotyls increased (Fig. 3). This mesocotyl, elongation was promoted by GA₃ treatment, i.e. about one thirds of mesocotyls elongated to 15-36 mm in 2.1 year old seeds, while no mesocotyl reached over 15 mm in both current and 1.1 year old seeds. In this case too, the growth pattern of seedings with long mesocotyls was vas very similar to the plants treated with ABA (Fig. 4). From above results, it may be suggested that the variation in mesocotyl growth reflects the difference of some internal factors which are affected by the location of seed in a panicle or the time after the seed harvest.

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The shortage of leaf area restrains improvement of corn yield under the routine method. In the present paper, as a basic research for the study of increment of dry matter production, the growth of corn seedlings under extremely dense population (plots consist of 5cm and 7.5 cm of planting interval) was investigated on experimental scale. Large seed variety of Koh No. 7 was planted five times throughout growing season, and each experiment was started from five-leaf stage until lodging. Results are as follows. 1. The total amount of five final standing crops attained 3349.2 g/m² and 2651.4 g/m² at 5 cm plot and 7.5 cm plot, respectively. 2. Mean CGR throughout the growing season were 20.2 g/m²·day and 17.3 g/m²·day and which efficiency for sunlight utilization were 2.11% and 1.80% at 5 cm plot and 7.5 cm plot, respectively. 3. Maximum LAI 18.7 and maximum CGR 54.7g/m²·day for one-week period were obtained at higher population density. The outline of the discussion about the mechanism of ascent of CGR under extremely high LAI can be expressed as follows. With the increment of LAI, adaptation to low light intensity such as decline in light extinction coefficient K and ascent of specific leaf area was occurred. As the effect of these two factors, efficiency for sunlight utilization ascended and respiration rate descended under low light intensity. Therefore, high CGR was attained.

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The characterization and varietal differences of α-amylase isozymes in rice callus tissues were studied by disc electrophoresis and gel electricfocusing on polyacrylamide gel electrophoresis (isoelectricfocusing). (1) Amylase in callus tissues grown on a Maeda's chemical defined medium containing 10^-5M 2, 4-D was resolved into six isozymes by disc electrophoresis and ten by isoelectricfocusing. From the investigations on heat (70°C, 15 min.) stability, Ca²⁺ -requirement and EDTA (5 × 10^-3M)resistancy of ten isozymes by isoelectricfocusing, we found that all of these isozymes were α-amylase, and only one isozyme (band a), which was fastest-migrating and most acidic, was a new rice o'-amylase that was not required Ca²⁺ and not inactivated by EDTA. (2) Some biochemical changes in Aichi asahi callus tissues grown in the 10^-5M 2, 4-D medium containing various carbon sourses (glucose, fructose, maltose, lactose, xylose, galactose, arabinose and soluble starch) which were added in place of sucrose, were investigated. The growth, α-amylase isozyme patterns and protein content in callus tissues grown in soluble starch were not different from sucrose medium. In all sugars, as only arabinose did not allow the callus growth, it was suggested that this sugar was inappropriate as carbon sourse. The banding patterns of α-amylase isozymes in arabinose medium were different from other sugars, that is, amylase "g" was strongly inhibited. (3) α-Amylase isozyme banding patterns in callus tissues of three normal varieties (Ginbozu, Aichi asahi, Te-Tep) and three dwarf varieties (Tan ginbozu, Waisei shinriki, Kotake tamanishiki), which were studied by isoelectricfocusing, were different from each others and these isozyme activities were changed in compliance with total α-amylase activity. α-Amylase activity in Tan ginbozu callus tissus was lowest in six varieties, but this callus tissus contains ten isozymes. Hence, this dwarfism is not elucidated by changes in isozyme banding patterns. (4) Changes in α-amylase activity and its isozymes in rice variety, Fujiminori and its four strains (Reimei, 71, 71L, and 71S) derived by ⁶⁰Co-irradiation were studied. The callus tissue of strain "71", which showed the low plant height and was thus dwarf mutant, represented poor growth, low protein content and low enzyme activity. Beside, each activity of ten α-amylase isozymes were relatively low. The callus tissue of strain "71S", which showed the lowest plant height, represented the same biochemical changes as ones of Fujiminori.

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Using the callus tissues of Tan ginbozu (dwarf) and Aichi asahi (normal), sequential changes in the growth patterns and the activities of some enzymes during aseptic culture were studied. (1) The control tissue of Aichi asahi began rapid growth after one week of calls culture, and this growth rate continued during the culture periods. In Tan ginbozu callus tissues, the sluggish growth rate continued during the culture periods. But GA₃-response in Tan ginbozu became significant after 15 to 20 days of callus culture. The growth patterns of Tan ginbozu which displayed the GA₃-response looked like that of control tissue of Aichi asahi. Protein content increased gradually after innnoculation of callus tissue, and reached its maximum values at 15 day in Tan ginbozu and 25 day in Aichi asahi. (2) In control tissue of Tan ginbozu and Aichi asahi, the activities of α-amylase, RNase, and acid phosphatase were minimum at 15 day and 8 day, respectively. However, it was observed that the minimum stages of α-amylase and RNase specific activity in Tan, ginbozu callus tissue responding to GA₃ coincided with the patterns of enzyme activities in control tissue of Aichi asahi.

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Transport of newly absorbed ¹⁵N and previously accumulated ¹⁴N in young soybean plants was examined following the application of nitrate- ¹⁵N to the root medium. During a 12-hour absorption period the roots exported both ¹⁵N and ¹⁴N to the shoots in the ratio of 51 : 49 for Experiment 1 and 82 : 18 for Experiment 2. A higher ¹⁵N ratio found in the Experiment 2 may be attributed to the aerated condition of the root medium, while in the Experiment 1 this condition was omitted. The proportion of ¹⁵N and ¹⁴N in the nitrogen transported to apical growing region of the stem showed a marked difference from that of the nitrogen exported from the roots with a considerably lesser ¹⁵N ratio to ¹⁴N such as 16 : 84 for Experiment 1 and 30 : 70 for Experiment 2. The total amount of nitrogen entering leaves during the experiment was estimated from the leaves with the "ringing" treatment to their petioles. It was found that the nitrogen transported into leaves also consisted of ¹⁵N and ¹⁴N components, and their ratios were intermediate between those of the roots and those of the apical growing regions. When comparison was made among the leaves of different ages, the percentage of ¹⁴N increased as the age decreased. Thus, it may be said that the relative content of ¹⁴N in the translocating nitrogen increased as the nitrogen moved through the stem toward the apex.

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Structure of the leaf blades at adaxial and abaxial surfaces was observed by scanning electron microscope in the second leaves of chlorophyll mutants of rice plants, Norin 8 Oryza sativa. Photomicrographs show stomata, wart-like protuberances, unicellular trichomes and bicellular protuberances. Stomata are about 18 μm in length. Surface structure was also investigated on longitudinal rows above a vein and on lamina joints. No essential difference was observed between green and albino plants in the surface structure of leaf blades.

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Canopy structure (geometrical structure) that plays an important role in light interception and air mixing was measured with two rice cultivars: Manryo and IR-8: cultivated at rectangular spacing of 30 and 17.4 cm. The silhouette method was used for obtaining phytomeirical data of rice canopies. The phytometrical measurements were repeated at intervals of about two weeks during the rice growing season from JuIy to Sept.28 in 1971. Results can besummarized as follows: 1. Fig.2 shows that there is no pronounced difference in the profile of leaf area density between the two cultivars, despite the difference in absolute value of leaf area density. The leaf area density profties for these cultivars were found to be a grass type with its maximum in middle layer of the canopy. The height at which the maximum in leaf area density is observed moved gradually upward with the development of rice canopy. The such movement was somewhat marked in Manryo canopy comparing with IR-8 canopy, this was due mainly to the differenc in light penetration between these two canopies. 2. The spatial distributions of leaf area density around the hill are shown in Fig. 3. The leaf area density decreased drastically with increasing the distance from the center of hill, implying that the almost all of leaf area was within the confines of cylinder with the diameter.of 20cm. In order to characterize the dispersion of spatial distribution of leaf area density, the values of kurtosis were calculated as a measure of disprsion. During the whole growing season of rice crops, the values of kurtosis obtained were larger than 3.0 for normal distribution curve. The values of kurtosis reached the maximum at the stage with largest leaf area index and were 3.48 and 4.31 for Manryo and IR-8 canopies, respectively. 3. Although the leaf area distribution of the two cultivars was non preferential as to azimuth angle throughout the growing season (see Fig. 5), the leaf area distribution with respect to inclination angle was manifest to be far from the uniform distribution and to be a distribution in which vertical leaves are most frequent. The leaf area inclination index, X_L, calculated from Eq. 9 is shown in Table 1. The values of X_L were less than 0 throughout the growing period, indicating that the leaf distribution is preferential in the large inclination angle. Except the early stage of rice growth, IR-8 canopy consisted of strongly vertical leaves comparing with Manryo canopy. Manryo - canopy shifted clearly from the Vertical distribution type to the near spherical distribution type at the heading stage, whereas IR-8 canopy was consistently most frequent in vertical leaves. Fig. 7 shows that such a difference in canopy structure is due mainly to varying leaf angle with depth in the Manryo canopy. Before the heading time, Manryo canopy had upper strate composed of vertical leaves and becoming more horizontal in display with increasing depth and might be more efficient in light utilization. Manryo canopy, after the heading time, however, showed the quite inverse leaf arrangement. Such clear change in leaf arrangement should give very strong influences on light utilization in photosynthesis. 4. Comparison of the leaf area inclination index with the kurtosis of spatial distribution of leaf area density revealed that there exists negative correlation between them (Fig. 8).The "gathering type" arrangement with kurtosis larger than 3.0 composes more strongly vertical leaves and operates to make light distribution in the canopy uniform. This result agrees well with that obtained by Tsunoda. It is concluded from the results described here that the studied two rice cultivars, particulary IR-8 have advantage of rice cultivars with "dispersing type" arrangement in canopy structure.

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年間を通じて稲の栽培が可能な熱帯において, 栽植季節によつて, 生育がちがうかどうか, 気象要因の変化にどう反応するかを研究した. すなわち, タイ国バンコク近郊のバンケン稲作試験場において, 感光性のない, あるいはごく僅かな品種, RD 1, BKN 17-3, C4-63 および IR 8 を供試し, 1969年5月より1年間, 毎月1日に播種し, 移植栽培によつて生育相をしらべた. N・P₂O₅・K₂Oを各75kg/ha施用した. その結果, 季節によつて, 生育にかなりのちがいが認められ, 気象要因のうち, 温度が大きな影響をもつようにみられた. まず, 12月, 1月頃の低温期には, 苗代, 本田において, 草丈の伸長が顕著に低下することが明らかに認められた. このような場合には, 植物体重の増加や葉面の展開も抑制される. また, 品種の成熟時の草丈とみられる, 出穂期近くの草丈と, その時期までの1ヵ月間の平均気温との間には, 年間を通じて高い正の相関があつた. 一方茎数・穂数に対する温度の影響は, やや不明瞭であつた. しかし, 分けつ盛期から節間伸長期にかけて低温にあうと, 分けつが多く, かつ有効茎歩合が高く, 穂数が多いという特徴がみられた. 試験地点は熱帯低地で, 気温は年間を通じて高い. 実験期間中の日平均気温の月平均値は25.1～29.8℃であり, その差はわずか5℃にすぎなかつた. このような条件下で, 熱帯稲の生育が温度の影響を強くうけていることは注目される.

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第1報の実験に続いて, タイ国バンケン稲作試験場において, 1970年5月より1年間, RD I および IR 8 を毎月作付して, 収量および収量構成要素の季節的変化と, 環境条件との関係をしらべた. N, P₂O₅, K₂O を各 75 kg/ha 施用した. 収量は作付時期によつてかなりの変化を示したが, そのちがいは, 登熟の良否に強く左右された. すなわち, 登熟歩合・干粒重は収量に対して, 形態的要因よりも高い正の相関を示した. そして, 日射の多い乾期で, しかも低温の時期に登熟した場合最高の収量をえた. 気象要因のうち, 登熟期の日射は, 当然のことながら収量に対してプラスの作用をしているものとみられた. これに対して, 登熟期の気温はマイナスの方向に影響した. 12回の収穫において, 登熟および収量は登熟期の温度が低いほど良好な傾向にあつた. 実験期間中の気温は, 日平均気温の月平均にして, 24.8～29.8℃, その差はわずか5℃であつた. このような条件に適応していると想像される熱帯稲においても, 熱帯低地での高温は, 登熟には不利なのである. そしてこの結果から, 実用的には, 高収量をうるためには, 日射の多い乾期で, しかも低温期の12月, 1月頃に登熟させるのがよいということになる.

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According to the authors previous studies, it was estimated that the effects of nitrogen depletion treatment at the middle stage of growth (70-90 in leaf number index) on the growth control varied with the amount of dry matter at the starting time of that treatment and with the length of treatment period. Therefore, raising rice plants with different amount of dry matter at the starting time of that treatment and varying the length of treatment period under gravel culture, the authors tried to clarify the above mentioned effects. The following are the results obtined in this study. 1. The plant with larger amount of dry matter at the starting time of that treatment gave less effect on the growth control than the plant with smaller amount of dry matter, even though the nitrogen depletion treatment was practised at the same growth stage for the same period. If the amount of dry matter at the starting time of that treatment was the same, the effect of 4 week-treatment was severer than that of 3 week-treatment. 2. When the dry matter of rice plants was lower than 100g/m² at the starting time of that treatment and the treatment was carried out for 4 weeks, the retardation of the plant growth by that treatment could not be recovered in spite of the nitrogen being fully supplied after that treatment, and the rice plant suffered from root-rot and then died away. However, in the case of the amount of dry matter being more than 300g/m² at the starting time of treatment, only little control effect on the plant growth was observed, even if 4 week-treatment was conducted. 3. It was supposed that there exsisted an optimum growth amount at the starting time of nitrogen restriction treatment and its corresponding optimum length of treatment period; so far as the present experiment was concerned, for example, the optimum growth amount at the starting time of the treatment appeared to be 200-300g/m² in the dry matter of rice plants (800-1000 in the number of tillers per square meter and 6-9 g/m² in the absorbed amount of nitrogen) and its corresponding optimum length of treatment period seemed to be 4 weeks. 4. From the results above mentioned, it will be deduced that the effect of nitrogen depletion treatment on growth control was difinitely governed by both the growth amount at the starting time of that treatment (which was mainly proportional to the amount of nitrogen absorbed by that time) and the length of treatment period.

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Varietal differences were investigated on the occurrence of white-belly kernel with reference to weight and size of kernel and a panicle character. Occurrence of white-belly ranged from small to large degree depending upon varieties. But no essential difference was recognized in the occurrence among japonica and indica varieties. White-belly abundantly occrred in upland and late-lowland varieties of japonica type and Chinese Sen type of indica variety. Percentage of white-belly kernel considerably differed with cropping year, except for varieties of two extremes on white-belly occurrence. External type of white-belly occured more frequently in japonica lowland varieties. External and internal white-belly was abundantly found in varieties of high white-belly percent. A close relationship between the length·width/thickness and the occurrence of white-belly was observed. But no correlation was found between length-width ratio and white-belly occurrence. Relation between kernel weight and white-belly occurence was possitive and highly significant. Density of spikelet born on panicle and white-belly occurrence were negatively correlated. From these results, it could be said that white-belly may occur more frequently in the well-developed but slightly flat kernel. And furthermore, it can be assumed that vigorous growth of kernel in early stage and declining accumulation of carbohydrates in later stage may lead to the occurrence of opaque tissue in the outer-ventral part of kernel which might be very susceptible to ill ripening.

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大豆の同化速度の品種間差異をもたらす機作を解明するため, クロロプラストの2・3の形質を調べ, 品種同化速度との相関々係を検討した. 供試品種の同化速度品種間順位は, Harosoy>ワセコガネ>しなのめじろ>シロメユタカ>農林1号であつた. 単位葉面積中に存在するクロロプラストの総容積には品種間差が認められなかつたが, 同化速度の大きい品種は概して小型のクロロプラストを数多く持つ傾向があることが認められた. クロロフィル濃度と同化速度との関係は, クロロフィル濃度の低い段階では正の相関が認められたが, 高い段階では認められなかつた. 単位葉面積中に存在するクロロプラストのHill活性と同化速度との間にはきわめて密接な正の相関が認められた. これらの結果は, クロロプラストには形態学的形質と光化学活性に品種間差異があり, 同化速度の品種間差異をもたらす要因はクロロプラストの側にも存在することを示唆した.

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貧養状態で育てた水稲の出穂期にある主稈から, 止葉の直下の節と葉鞘の一部をつけた長さ6 cmの茎切片を切取り, 暗黒下で直立にした基部から, DL-tryptophane-¹⁴Cの水溶液を3時間半吸収させた. 水洗後, 切片の基部を湿つた脱脂綿に包んで管びん中に封じ, 暗黒下で切片が水平または直立になるようにして, 3～24時間保つた. 採取した材料から組織抽出液をつくり, 薄層クロマトグラフィーにより分離したIAA-¹⁴Cの比放射能を測定比較した. 水平茎の節間基部では, IAA-¹⁴Cが, インキュベーション開始後12時間目まで上下両半側にほぼ 40 : 60の比に分布したが, その後この非対称性は減退した. しかし, 水平茎の節間頂部では, 直立茎の節間基部および頂部と同様, 終始この非対称性を認めにくかつた. 切片全体について求めたIAA-¹⁴Cの比放射能は, 実験期間を通じて水平茎が直立茎より12～23%高く, 前者は後者よりオーキシンの生合成能において優れていることが示された. このことと筆者の過去の実験結果とを総合すると, 水平に置かれた水稲にみられる発根および節間伸長の促進は, それらが行なわれる部位における, オーキシンの生合成能が増大することに基づくところが大きいと示唆された.

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