Investigations have been carried out to determine the influence of soil moisture, i. e. pF: 0, 1.5, 2.2 and 2.7, after young panicle formation stage on the phosphorus, potassium, magnesium, manganese and iron contents in lowland brown rice of two varieties. The results indicated that all the components were influenced by the soil moisture conditions. The phosphorus, potassium, magnesium and manganese contents on dry matter basis decreased with decreasing the soil moisture. In regard to the composition in ash with decreasing the soil moisture, the phosphorus and manganese contents decreased and the iron content increased, whereas the magnesium content decreased after increasing. The most affected component was manganese both on dry matter basis and in ash. The second was potassium on dry matter basis and was iron in ash.

View full abstract

Investigations have been carried out to determine the effect of nitrogen dressings, i.e. basal dressing (N: 5, 10 and 20 g/m²), topdressing at panicle formation stage (N: 4 g/m²) and topdressing at full heading stage (N: 4 g/m²), on the protein, fat, ash, phosphorus, potassium and magnesium contents of lowland brown rice. The results indicated that the ash, phosphorus, potassium and magnesium contents on dry matter basis decreased and the phosphorus, potassium and magnesium contents in ash increased with increasing the amount of basal dressing. With respect to the application of topdressing at panicle formation stage, it was shown that the fat content increased and the ash, phosphorus and magnesium contents decreased on dry matter basis and the phosphorus and potassium contents increased in ash. The application of topdressing at full heading stage gave the increase of the protein content and the decrease of the fat, ash and potassium contents on dry matter basis.

View full abstract

Although shoot differentiation in rice callus culture has been reported by several workers, details of gross morphology on the differentiation process are obscure. In this work, two methods (Saka and Maeda's and Nishi et al's) for shoot differentiation were compared and the gross morphological variation connected with shoot differentiation were investigated in rice callus culture. 1. Two different processes of shoot formation with relation to the change in region showing morphological variation were observed in the Saka and Maeda's medium. There is a developmental process which shows a series of changes from 'Dry' region to 'Protuberances' or 'Green', to 'Green protuberances', and finally to 'Green leaves'. And there is another process which shows a series of changes from 'White' region to 'White and green', and finally to 'Green leaves'. Two processes were compared in the time of appearance of the each region. 2. Similar variation was also observed in the rice callus in the Nishi et al's medium for shooting. However, few leaves but many roots were appeared in their medium. In many cases, the appearance of 'Green' region was related to the initiated roots. 3. The two methods were compared in time of appearance and number of regions representing leafy structure. As a result, it was ascertained that Saka and Maeda's method is available to our following histological and physiological investigations. 4. From the investigation with the effect of growth hormones on the variation in the Saka and Maeda's medium, it was revealed that the high level of kinetin is required mainly for the appearance of 'Dry' and 'Protuberances' regions, and the low level of 2, 4-D for 'White' and 'Green' regions. 5. Friable and compact callus tissues were inoculated separately into the Saka and Maeda's medium for shooting. The number of regions representing the variation was compared between both callus tissues. The appearance of 'Dry' region was poor in the friable callus tissues. 6. The region representing the variation was observed with stereomicroscope. Moreover fresh hand sections of a part of the region were made and observed histologically with ordinary microscope. As a result, it was, shown that (a) tiny protuberances and trichomes are accompanied with 'Dry' and 'Green' regions, respectively, and (b) green cells are always observed near to tracheary elements.

View full abstract

Raising the rice plant under the conditions of the different amount of basal nitrogen or nitrogen top-dressing and of the restricted nitrogen supply during the middle growth stage (70-90 in leaf number index), the authors tried to make a right evaluation of the nitrogen restriction treatment during the same stage. The grade of leaf color observed in the field, the percentage of stained length of leaf sheath by iodine solution as an index of starch accumulation and the nitrogen content in leaf blades in upper three leaves at the end of the treatment were checked. The following are the obtained results in this experiment. 1. A positive correlation was obtained between the leaf color grade and the nitrogen content in the upper three leaves as shown in the previous reports. On the other hand, the percentage of stained length of leaf sheath showed negative correlation with the nitrogen content in leaf blades and the leaf color grade. Consequently, the ratio of the leaf color grade to the percentage of stained length of leaf sheath showed a high positive correlation with the nitrogen content in leaf blades. 2. The grade of leaf color observed in the field, the percentage of stained length of leaf sheath and the ratio of them played an important role in the evaluation of the nitrogen restriction effect on the growth of rice. 3. According to these characteristics, tested materials were classified into 4 groups. For example, it seemed that the effect of nitrogen restriction was accomplished very well when the following conditions were satisfied at the same time; 1) when the leaf color was less than 2.5 in color plate index, 2) when the percentage of leaf sheath was about 50-60%, 3) when the ratio of 1) to 2) was less than about 0.05 and 4) moreover when the percentage of stained length of the third 1eaf sheath was nearly equal to that of the second one.

View full abstract

In order to obtain some informations whether the nitrogen restriction treatment was adequately carried out or not, the leaf color grade in field conditions, the growth amounts such as the dry weight, the number of tillers and the length of lower internodes (especially the fifth internode from the uppermost one) were individually checked at the late stage of spikelets initiation (90 in leaf number index). The effects of above mentioned factors on the lodging, 'the percentage of ripened grains and the grain yield, as far as var. Manryo was concerned, were summarized as follows: 1. As to the combined effects of nitrogen content in leaf blades and the top weight of the plant on the grain yield, two optimal combinations of the former and the latter, i.e., (2.2∼2.6%)×(500-600 g/m²) and (2.6∼3.0%)×(400∼500 g/m²), brought the highest yield. However, in case of the nitrogen content and the top weight being larger or smaller than the optimal values indicated above, the grain yield decreased. 2. Even if the nitrogen content in leaf blades was substituted by the ratio of the leaf color grade to the percentage of stained length of leaf sheath, and the dry weight of the top was replaced with the number of tillers, the similar relations mentioned above were recognized. For instance, the combination of 0.05∼0.08 in the ratio of the leaf color grade to the percentage of stained length of leaf sheath and 500∼700 tillers per square meter brought forth the maximum grain yield. 3. When the nitrogen content in leaf blades or the dry weight of the top exceeded their optimum, the decrease of the grain yield was brought about by the decrease of the percentage of ripened grains. This decrease of percentage was caused mainly through lodging which was attributed to the length of the fifth internode. 4. Judging from the factors mentioned above, the following conditions seemed to be desirable for raising of the grain yield. That is, a) 0.05∼0.08 in the ratio of the leaf color grade to the percentage of stained length of leaf sheath (or 2.2∼2.6% in nitrogen content of leaf blades), b) 500∼700 tillers per square meter (or 500∼600 g/m² in dry weight of the top) and c) less than 4cm in length of the fifth internode.

View full abstract

In some cases of direct sowing culture (direct sowing of paddy rice under upland condition) in the Kanto district, there is observed a year by year decrease in yield. The purpose of this experiment is to clarify the reasons for this decrease. In preceding papers, we have reported about the causes of this problem from two points of view, i.e. the movement of inorganic nitrogen in the soil and phosphorus nutrition. In this paper, the cause is described in relation to the fall of nitrogen supplying potentiality of soil. The experiments consist of chemical analysis of the soil (contents of total-N, total-C, ammonification of organic nitrogen in the soil) and yield analysis under the fertilizing condition of basal application but no top- dressing. The results are presented as follows: 1. Chemical analysis of the soil. Both the contents of total nitrogen and total carbon in the soil decreased according to the succeeding year under the continual direct sowing culture. There was a decreasing tendency in the ammonification of organic nitrogen in the soil (temperature-raising effect and pre-drying effect in ammonification), by the continuance of direct sowing culture. From above facts it is recognized that the further continuation of direct sowing culture decreases the amout of easy composable organic matter in the soil, and that it results in the fall of nitrogen supplying potentiality of soil. 2. Growth and yield of rice. There was observed a tendency of rice yield decrease by the continuance of direct sowing culture accompanied with the fall of nitrogen supplying potentiality of soil. 3. From the above facts it could be concluded that the fall of nitrogen supplying potentiality of soil must be one of the causes of the yield decrease in the continuous direct sowing culture. This yield decrease could be lightened to some extent by increasing the ammout of nitrogen application or more frequent top-dressing of nitrogenous fertilizer. However, the supply of such organic substances as compost should be necessary to inhibit the decrease of rice yield in the continual direct sowing culture.

View full abstract

The structure of radiation environment within the canopies of two rice cultivars of Manryo and IR-8 was studied using the phytometrical data reported in a previous paper. The data of Aug. 25 and Sept. 14 which were before and after heading were used in the calculations. In the calculations, special interest was mainly directed toward clarifying the diffuse radiation fluxes due to scattering of solar radiation by plant elements, and the radiation energy partition between leaves. the distribution functions of leaf area with respect to the angle between leaf normal γ_L and the direction of solar γ₀ presented in Table 1 were used as the original data for studying the structure of radiation environment within rice canopies. Adopting reasonable assumptions concerning the scattering of radiation fluxes by plant elements, the upward flux U(j) and downward flux D(i) of complementary diffuse radiation due to light scattering by plant elements through reflection and transmission can be approximated by U(j)=B(j)+U(j-1)exp.[-τ(_{s, j}f_{L, i}], D(i)=C(i)+D(i-1)exp[-τ(_{s, j}f_{L, i}], where B(j) is the diffuse radiation flux emanated upward from the upper boundary of the j-th layer due to first scattering of radiation flux in this layer, C(i) the diffuse radiation flux emanated downward from the bottom boundary of the i-th layer due to first scattering of radiation in this layer, τ=1-T the term for considering the effect of the second scattering of radiation flux on light distribution approximately, and T leaf ransmissibility assumed to be 0.3. When the scattering of direct solar radiation by plant elements is considered, B(j) and C(i) are given by B(j)=Q₀(h_o)a(j, h_o)f_{L, i}·RΣ^^(10)__(j=1)P(j, l)N(l), C(i)=Q₀(h_o)a(j, h_o)f_{L, i}·TΣ^^(10)__(i=1)P(i, l)N(l), where Q₀(h_o) is the direct solar radiation intensity on surface normal to sun's ray at sun altitude of h_o, a(j, h_o) and a(i, h_o) are the sunlit area in j- and i-th layers at sun altitude of h_o, P(j, l) and P(i, l) the leaf area distribution functions with respect to |cos <γ_Lγ_o>^^^^^| of j- and i-th layers, N(l) is the mean value of |cos <γ_Lγ_o>^^^^^| for class l, and R is the albedo of leaf surfaces to total short-wave radiation and assumed to be 0.30. For the sake of simplicity, R is assumed to be equal to T and independent of the incident angle of light. The rice canopies were divided into twenty layers with the 5cm depth (i=j=20). The intiger i is counted downward from the canopy top and the integer j upward from the canopy bottom. Important results obtained can be summarized as follows: 1. With increasing sun altitude, the extinction coefficient of direct solar radiation decreased drastically from 2-3 at sun altitude of 10° to 0.4-0.6 at sun altitude of 60°. Although the sun altitude dependence of k_d changed somewhat during the growing stage of rice plants, two rice canopies were found to behave to direct solar radiation like a plant canopy forming from leaves with inclination angle between 60 and 75°. IR-8 canopy with more erected leaves indicates somewhat larger extinction coefficient at low sun altitude and smaller extinction coefficient at high sun altitude than those of manryo canopy (see Fig. 2). 2. A simple tool for measuring the sunlit area (measurement rod of sunlit area) was used to determine the penetration of direct solar radiation into the rice canopy. The data obtained from measurement of sunlit area using the rod were analyzed by E_q. (8) to yield the effective leaf area projection G_L(h_o), and the extinction coefficient of direct solar radiation k_d. [the rest omitted]

View full abstract

The data of the variation in radiation environment from leaf to leaf have been used in order to study the microstructure of canopy photosynthesis of rice plants. The gross photosynthesis Φ(i) of the whole leaf area of the layer i can be given by Φ(i)=ΣΔF(i)F(i, S)Φ(S), where ΔF is the partial leaf area of the layer i, F(i, S) the probability density function of the leaf area of the i-th layer which is radiated by a given value of irradiance S, and Φ(S) the irradiance-photosynthesis function of the leaf. Therefore, the gross photosynthesis Φ_t of the whole leaf area of the rice canopy is the sum of the Φ(i) as follows: Φ_t=Σ^^n__(i=1)Φ(i), where n is the total number of the canopy layers. The main results from the calculations made by using the data of the partition function of solar energy between the leaves can be summarized as follows: 1. The layer's mean of the gross photosynthesis of shaded leaves decreased with the leaf area depth, mainly because of attenuation of the intensity of diffuse radiation flux on leaf surfaces. The gross photosynthesis intensity of the shaded leaves in an upper layer goes up with increasing the total diffuse radiation flux I_T which consists of sky diffuse radiation flux and complementary diffuse radiation fluxes (upward and downward) due to the scattering of radiation by plant elements. On the other hand, the layer's mean of the gross photosynthesis of the sunlit leaves was approximately constant reagardless of sun altitude and the canopy depth. The above results were compared with those obtained by Ross and Bikhele (1968, 69) in good agreement. 2. The contribution of leaves which are irradiated by a certain irradiance S=Q₀(γ_o)|cos <γ_oγ_L>^^^^^|+I_T to the gross photosynthesis of the layer i or the canopy was determined by Φ(S)=ΔF·F(S)Φ(s)/Φ. As can be seen in Figs. 2 and 3, when sun altitude is relatively low, the contribution function Φ(S) is characterized by three peaks at low (0∼0.2ly/min), medium (0.4∼0.6ly/min) and high (0.9∼1.1ly/min) irradiance intensities. The peak in low irradiance region is due mainly to the contribution of the shaded leaves and the peak in high irradiance range is because of the sunlit leaves with relatively small value of the angle between the sun's ray and the leaf normal. The characteristics of Φ(S) function as described here was more manifest for canopies with more erected leaves (Manryo, Aug. 25 : IR-8, Sept. 14) than for a canopy with somewhat lax leaves (Manryo, Sept. 14). With increasing sun altitude, the peak observed in the high irradiance range became gradually indistinct due chiefly to the decrease of the angle <γ_oγ_L>^^^^^. When sun altitude is high, the function Φ(S) shows pronounced asymmetry, indicating the broader skirts in the higher irradiance range than in the lower irradiance range. 3. Fig. 4 shows the gross photosynthesis of sunlit leaves and shaded leaves is zero at the canopy top, increases with the depth, to reach its maximum and decreases again. Although the peak of gross photosynthesis was approximately the same between sunlit and shaded leaves when sun altitude was low, the peak intensity of gross photosynthesis of the sunlit leaves increased more rapidly with increasing sun altitude than the shaded leaves did. It was about two times as large as the peak intensity of the shaded leaves at the time of southing. The canopy level at which the gross photosynthesis of the sunlit leaves became maximal was higher than that of the shaded leaves. The canopy level with the maximal photosynthesis moved gradually downward with increasing sun altitude. Fig. [the rest omitted]

View full abstract

Developmental processes of shoot formation in rice callus tissues of var. Aichi asahi and Te-Tep grown in the organ forming medium were investigated in detail. At the same time, the changes in various hydrolytic enzyme activities (α-amylase, RNase; catalase, acid phosphatase) and α-amylase isozyme patterns in these processes were studied and compared with the some biochemical changes in rice seedlings. For this purposes, the callus tissues with green or white shoot protuberances were divided into organ-forming regions and non-organ-forming callus parts. (1) The clear cut results on organogenesis in callus tissues were obtained by adding the casein hydrolysate (4 g/1) and 5×10^-5 M kinetin to Maeda's medium containing 10^-7 M 2, 4-D and by using the 3 passage callus tissues, in light (3, 000 lux) conditions of 25°C instead of 30°C. Such conditions as above mentioned inhibited early growth of callus parts showing organogenesis. The callus tissue in these conditions was designated as K-callus tissues. (2) In K-callus tissue, organ-forming regions and shoot primordia were observed after 6 days of callus innoculation. Also, various hydrolytic enzyme activities during these periods were rather inhibited in comparison with control callus tissue in the 10^-5 M 2, 4-D medium without kinetin (C-callus). (3) Shoot formation began to start gradually after a week and became vigorous from 10 to 14 days in culture. But root formation was slight at this stage. As the shoots were formed, RNase and α-amylase activities in shooting regions increased rapidly. α-Amylase activity was maximum at 10 day-old. At the 10th day, RNase and (α-amylase activities were about 7- and 10-times as much as that of C-callus tissue, respectively (fig. 12, table 2). These data suggest that histological and biochemical "lag phase" in organogenesis present about one week after callus innoculation. (4) In the callus tissue grown in the GA₃-treated (5×10<-5> M) organ-forming medium (KG_callus tissue), organogenesis and its related enzyme activities were strikingly decreased (fig. 13). (5) In the organ forming medium containing yeast extract (5 g/1), the shoot or root primordia of Te-Tep callus tissue were observed after about two week. The shoot primordia were initiated exogenously and root ones endogenously, and both primordia were formed independently to each other. The shoot primordia were circularly surrounded by a large number of vascular bundles, but the root ones were not. Their singularities were discussed. (6) From the observations on α-amylase banding patterns, the results were obtained that the activities of α-amylase "g" and "e" conspicuously increased and a new isozyme "1" was induced with organ developments in K-callus tissue and in the organ forming regions of KG-callus tissue. (7) Several hydrolytic enzyme activities in rice Seedlings of 2 to 4 day-old were studied to compare the changes in developmental processes in redifferentiation of shoot. Enzyme activities were lower than those of C-callus (10 day-old) or shoot-initiating regions of K-callus tissue except catalase. Only one isozyme of α-amylase which was considered to correspond with amylase "a" in callus tissue was isolated from rice seedlings. From the results mentioned above, the intimate relations between histological and gross morphological aspects and some biochemical changes in redifferentiation processes of rice callus tissues were suggested. The role of hydrolytic enzymes and vascular systems surrounding circularly shoot primordia in these processes were discussed.

View full abstract

In Japan, rice is harvested at the relatively early stage of ripening to prevent the occurence of the checked grains caused by rainfall, consequently, a difference of about 10% in moisture content is recognized between early and late ripened grains at the harvest-time. This unbalance in moisture content is more conspicuous in late or large-panicle variety than in early or small-panicle variety. It is indispensable to make uniform the moisture contents in process of the drying treatment of rough rice grains in order to preserve the good quality.

View full abstract

[in Japanese]

View full abstract

This study consists of two experiments. The first experiment was performed in the growth cabinet illuminated by YOKO lamps (Toshiba D-400) with a day length of 12 hours and with relative humidity of 70%. The mean air temperatures were maintained at 20°C (day and night temperature ; 25°C and 15°C), 25°C (30°C and 20°C) and 30°C (35°C and 25°C), using three varieties of peanut plants, namely Chiba-handachi(large seed, semi-erect type), Java no. 13 (small seed, erect type) and Chiba no. 43 (large seed, runner type) as materials. In the second experiment, the effective heat summations required for the first flowering were calculated from the data on flowering of the plants sowed at the different times. 1. As air temperature became higher, the days required for the first flowering became shorter and the increasing rate of the dry matter and the leaf emergence rate on the main stem were promoted more remarkably. But the promoting rate of temperature on flowering in the case that air temperature was raised from 25°C to 30°C was less as compared with that in the case from 20°C to 25°C. 2. Regardless of air temperature, a turning point of the leaf emergence rate on the main stem was found at the time of the fourth leaf emergence, including the three varieties used. 3. The number of the leaves on the main stem and the dry matter weight at the time of the first flowering of plants grown at air temperature of 30°C were more than those of plants grown at 20°C or 25°C. 4. The number of the leaves on the main stem, the dry matter at the first flowering time and the days required for the flowering after sowing of Java no. 13 were less than those of Chiba-handachi and Chiba no. 43. 5. It is assumed that the flower bud of peanut plants is formed at earlier stage after germination when cultured at higher air temperature. So it seems quite reasonable to assume that air temperature has a direct effect on flowering. 6. The effective heat summation required for the flrst flowering which was obtained by integrating a daily mean temperature over 12°C, was 417.3±12.8°C and showed the least variation among the peanut plants sowed at the different times.

View full abstract

The authors examined the effect of air temperature on pod development after peg penetration and the influence of air temperature on the yield of peanut plants after the first flowering. The experiments were carried out in pot and field, using a variety of peanut plants, Chiba-handachi (large seed, semi-erect type). The results obtained were as follows. 1. Pod development of peanut plants was suppressed according to the retardation of the time of peg penetration into the soil, regardless of the difference in sowing time. 2. The effect of air temperature on the pod development was very remarkable at the stage of pod enlargement from 21 to 40 days after peg penetrating. 3. When the effective heat summation accumulated by a daily mean temperature over 15°C in the pod stage was higher than 450°C, the pod development was affected chiefly by inner factors of plant, while when this value was lower than 450°C, the pod development was influenced mainly by air temperature. 4. The shoot weight of peanut plants usually increased rapidly and reached its maximal value at about 60 or 70 days after the first flowering time. While the starting time of increase in pod weight was a little later that of the shoot weight, namely at about 30 days and reached its maximal weight at about 90 or 100 days after the first flowering time. 5. The influence of air temperature on the yield of peanut plants was striking beween 31 and 60 days after the first flowering time.

View full abstract

To examine the effects of soil temperature and soil moisture in the podding zone on the pod development of a peanut variety, Chiba-handachi (large seed, semi-erect type), three experiments were carried out under the condition separating the podding zone from that in which the roots were grown. In experiment-I in 1969, the mean soil temperatures in the podding zone were 38.6°C, 30.6°C, 22.9°C and 15.3°C. Experiment-II was performed under four soil moisture conditions, namely 57.3, 40.3, 21.5 and 7.8 percent to the total soil volume. In experiment-III, the effects of the treatments combining high soil temperature (37-39°C) and low soil moisture (6-8 percent) in the podding zone in every 10 days after the peg penetration upon the pod development were exermined. The results obtained were as follows. 1. The beginning time and the rate. of the pod development were affected remarkably by soil temperature in the podding zone. The following relations were observed between the pod development and soil temperature in the podding zone. Optimum soil temperature ; 31 to 33°C Minimum soil temperature; 15 to 17°C Maximum soil temperature; 37 to 39°C 2. It was recognized that the optimum soil moisture content in the podding zone was about 40% to the total soil volume, regardless of the soil moisture content in the rooting zone. When the soil moisture content was lower than 40%, the podding percentage and the thickening growth of the pod were reduced, and when it was higher than 40%, only the thickening growth of the pod was reduced. 3. Considering the rsults obtained in experiment-III, the most critical period in the pod stage was the first 30 days, especially between 20 to 30 days after the peg penetrated into the soil.

View full abstract

This experiment was carried out to compare the proliferations in the spikelets of a mutant strain induced by the treatment of ethylene imine with that induced by X-ray irradiation which had been reported previously, and to make clear the common structural tendencies between both proliferations. External morphological phenomena observed in this experiment were as follows; 1) initiation of adventitious roots at the basal portion of spikelets, 2) remarkable elongation and multi-venation of empty glumes, 3) successive initiation of foliage leaves forming a vegetative plantlet, 4) decrease of stamens in number, 5) increase of spikelets in number, etc. Almost of those phenomena mentioned above were the same as the result s induced by X-ray irradiation, and a seedling-like plantlet observed in this experiment were agreed with a "leafy shoot", reported previously, on the point that it was composed of many leafy glumes like a primary leaf of the seedling, arranging 1/2 alternate phy11otaxis. It was made, therefore, clear that those proliferations which have been observed in this experiment were the same phenomena as those of X-ray irradiation in the point of indicating a kind of re-vegetative growth in the tendency of the degenration of reproductive organs. Judging from that the gradual morphological changes of leaves which composed a seedling-like plantlet followed almost the same tendency as seen in the seedling plant, it could be said for certain that the proliferation initiated on the spike in this experiment assumed to follow the same morphogenetic process as in the seedling developed from the the germination of seed. Therefore, the development of the proliferation was considered to be a kind of the transformation from reproductive growth stage (or phase) to vegetative one in the spikelet primordium, showing the capacity to develop into the individual plantlet by means of the initiation of adventitious roots. On the physiological background of the initiation of the proliferation, it was suggested that some changes of the endogenous gibberellin might be participated with the initiation of the proliferation judging from the fact that the number of spikelets in a proliferated panicle revealed the same tendency of increase as in a panicle treated with gibberellic acid.

View full abstract

Capacities of photosynthesis and respiration of rape plant population were investigated at various stages of development. The rape plants, var. Norin No. 16, were grown under ordinary cultivating condition. CO₂ exchange of the population was observed under field conditions at two weeks intervals during the period from early stage of growth to full maturation. After the beginning of flowering, CO₂ exchange of the defoliated plants was also observed in order to estimate the extent of contribution of pods and stems to total CO₂ exchange in this period. Dry weight of each part of plant and surface area of leaves and pods were also measured at each occasion of measurment of CO₂ exchange. The results obtained were as follows: 1. Dry weight of whole plant increased very slowly till the beginning of bolting and rapidly thereafter. The rapid increase of dry weight of whole plant was continued also in ripening period in spite of marked defoliation due to senescence. 2. Leaf area (per unit area of land) was small and almost constant during the winter season because the withering due to severe cold offset the leaf formation. Leaf area started to increase gradually after the end of February which is just before the beginning of bolting and then rapidly at the beginning of flowering. Leaf area attained to its maximum value (LAI 3.31) 30 days after the beginning of flowering and decreased thereafer because of withering and defoliation. Surface area of pods increased markedly after the middle period of flowering. 3. During the winter season apparent photosytnhetic rate of the plant population increased gradually whereas leaf area was unchanged. The photosynthetic rate increased rapidly after the end of February and attained to its maximum value (5.26 g CO₂/m²/h) 44 days after the beginning of flowering, and then it decreased. 4. The respiration rate of plant population increased with growth and attained to its maximum value (0.67 g CO₂/m²/h) 44 days after the beginning of flowering, and then it decreased slightly. Depression of respiration in later period of ripening was less than of photosynthesis, consequently respiration/photosynthesis ratio increased as the maturation Proceeded. 5. The proportion of gross Photosynthesis performed by pods+stems to total gross photosynthesis (gross photosynthesis performed by undefoliated plant population) began to increase at the middle period of flowering and reached a value of 76% at the middle period of ripening. Thereafter, the proportion continued to increase further till the end of ripening. In ripening period, the pods possess relatively high photosynthetic activity and extensive surface area. Moreover, the pods were located at upper level in space of the population receiving plentiful sunlight. Therefore, most of the photosynthesis of pods+stems might be constituted by that of pods. From the above-mentioned reasons, it was concluded that pods contributed considerably to matter production in the ripening period.

View full abstract

The present study was conducted to clarify the effects of oxygen concentration under various leaf temperatures on the growth of wheat and rice plants (C₃-plants). Seedlings of both species were growth for 7 days in specially devised growth chamber equiped with water culture facilities, under 2.5% O₂, 0.03% CO₂ and 21% O₂, 0.03% CO₂, and at light intensity 45 Klx (at 20. 25 and 30°C leaf temperature) or 25 Klx (at 5 and 10°C) under a regime of 12hr light and 12hr darkness. The growth paramenters of the plants were investigated at the start and the end of each experiment. The results obtained are summarized as follows: 1. The dry matter production (ΔW_T and RGR) was enhanced in both species under overall leaf temperatures, and plant height and leaf emergence were somewhat inhibited except at 30°C in wheat and 20°C in rice plant with low oxygen ooncentration. 2. NAR of both species enlarged extremely at low oxygen concentration under overall leaf temperatures. According to these results, it can be deduced that acceleration of the apparent photosynthetic rate at low oxygen concentration, due to suppression of the photorespiration et al., persists for a long time. 3. NAR and RGR were enhanced under low leaf temperature (5 and 10°C) at low oxygen concentration, therefore these results suggest that the function of photorespiratory mechanism still may continue under low leaf temperature. 4. It has been shown that the apparent photosynthetic rate increases at low oxygen concentration with leaf temperature increases, and it reaches maximum rate at 30∼35°C. However, RGR of both species at low oxygen concentration in this experiment was greatest at 20°C and it decreased with falling or rising temperature. It is considered that at low oxygen concentration the optimum temperature for the apparent photosynthetic rate as momentary value does not fit the maximum growth of plants. On the other hand, difference between RGR at low oxygen concentration and RGR at normal air was greater under higher temperature, hence it can be explained that the effect of suppression of the photrespiration et al., on the dry matter production is greater under higher temperature. 5. RLGR was reduced under low oxygen concentration, and subsequently decreasing of LAR came out. In spite of decrease of LAR, RGR was increased through greater increase of NAR under low oxygen concentration. 6. The surplus dry matter in plants under low oxygen concentration (ΔW at 2.5%O₂-ΔW at 21% O₂) was allotted to leaf blades and roots in wheat, and leaf sheaths+stems and roots in rice plant, respectively. It may be considered that above difference was based on the characteristics of species.

View full abstract

The results of the investigation showed that 3-hydroxy-5-methylisoxazole (HMI) accelerated the geotropic response of rice seedlings. In general, the horizontally placed rice seedlings gradually revert to a nearly vertical positon. This response to gravity is referred to as the geotropic curvature of rice seedlings. The extent of this response by rice seedlings is important in determining their physiological status which influences future growth and development. The HMI-treated seedlings had a high geotropic curvature response. The effect of HMI on the geotropic curvature could also be observed when untreated control seedlings were soaked in HMI solution. The rate of geotropic curvature response of rice seedlings increased with increasing HMI dosage. HMI showed no auxin activity in the rice lamina joint test. However, the auxin activity of indoleacetic acid was increased in the presence of HMI. Therefore, the increased geotropic curvature response of rice seedlings caused by HMI may be due to a synergistic effect of HMI on endogenoud auxin.

View full abstract

1) Variety Koh No. 7 of corn plant with 3 different planting densities (5, 10 and 20 cm intervals) was grown in green house to study the status of light extinction in the canpy. Light extinction coefficient K in Monsi and Saeki's formula can be divided into following two components according to Monteith's model (1965). One is light transmission rate through d single leaf (τ_λ) and another is a parameter S representing the average arrangement and orientation of the leaves. S is the fraction of incident radiation that passes through a layer without being intercepted by any leaf or stem. 2) Stratified clip method was adopted at regular intervals to estimate light extinction coefficient K. Light intensity under the canopy was mesured with sillicon blue cell (SBC) covered with infrared absorbing filter. 3) Light transmission rate through single leaf (τ_λ) was measured with a spectro-photometer (Hitachi EPS-3T type) using jointly the integrating sphere and an opal glass in order to apply to Monteith's model. 4) According with the increase of planting density and the advance of growth stage, light extinction coefficient K declined and light transmission rate (τ_λ) through single leaf were enhanced. However, being on Monteith's model, it became clear that the light transmission rate (τ_λ) scarcely affected light extinction coefficient K, whereras the parameter S played an important role in K.

View full abstract