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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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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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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[in Japanese]

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