Pot cultured wheat plants, cv. Asakaze-komugi, were grown under sufficient soil water till ripening period. They were then grouped into two soil moisture treatments, 75% (control) and 40% (water stressed) of field capacity, respectively. Photosynthesis and transpiration of various plant parts i.e. ear, top internode, leaf sheath of flag leaf, leaf blades of two or three uppermost leaves were measured using a small chamber and the effects of water stress on these physiological processes were examined. The results obtained are summarized as follows : 1. Photosynthesis and transpiration of each plant part were strongly depressed by the water deficit treatment. The extent of depression in photosynthesis and transpiration was largest immediately after the start of the water deflcit treatment. However, as the water deficit condition was prolonged, the effect diminished (Figs. 1-3). 2. The extent of depression in photosynthesis by water deficit was larger in the leaf blades than in the ear, leaf sheath and the stem. Comparing leaf blades at different positions, depression was larger in the lower leaf blades than in the upper ones. Thus, it was concluded that photosynthetic sensitivity to water deficit varied among plant parts (Figs. 4-7). 3. The sensitivity of plant parts to water deficit in photosynthesis was closely correlated with that of transpiration. This suggested that the photosynthesis sensitivity of a certain plant part to water deflcit is related to the sensitivity of the stomatal behavior of that part.

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In the previous paper, it was pointed out that the extent of depression in photosynthesis by soil water deficit treatment was different from part to part of the wheat plant. The objective of the present study was to find out the physiological basis for this phenomenon from the viewpoint of water potential and CO₂ diffusion resistances, i.e. leaf resistance (r₁) and mesophyll resistance (r_m) using the same materials as those for the previous paper. The results are summarized as follows : 1. Water potential of each plant part was decreased by water deficit treatment. The extent of decrease in water potential was the same in every plant part. It was concluded form this finding that the difference in photosynthetic sensitivity among plant parts is not be attributable to the difference in the extent of decrease in water potential of plant parts (Figs. 1, 2). 2. Both r₁ and r_m were increased by the water deficit treatment. The extent of increase in r₁ and r_m was largest just after the start of the water deficit treatment. However, when the water deficit condition was prolonged, r₁ and r_m tended to decrease and come close to those of unstressed plants (Figs. 6-9). 3. Both r₁ and r_m increased to a larger extent in lower leaves than in upper ones by the water deficit treatment (Figs. 3-4). The extent of increase in r₁ and r_m resulted from water deficit was always larger in lower leaves than in upper ones (Figs. 5-9). Since there was no difference in the extent of decreasse in water potential by the water deficit treatment between lower and upper leaves, both stomata and the photosynthetic mechanism of lower leaves seemed to have greater sensitivity to decrease of water potential than those of upper leaves.

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The rice plants, cultivated in paddy field, were cut in 6 periods (I-VI), on every 7 days during the maximum tiller number stage (July 17, 1981 : I) to the first heading stage (Aug. 21 : VI). The cutting was conducted at 15cm (H) or 7.5cm (L) in height above the ground. Regrowth plants from the stubbles were investigated on 2 and 5 weeks after cutting, and their yield components were examined after harvest (Oct. 23). 1. The stems which had been grown after cutting and attained to heading were classified into two types as follows : (1) SS (survived stem) : stems which survived in spite of the cutting and attained to heading, and (2) NS (new stem) : tillers newly developed from axillary buds of the cut stems. 2. Regrowth in I-III plots accomplished by development of SS, and V and VI plots are by NS (Table 2). In IV-H plot, shoot apices (young panicles) were cut off in only 5.5% of the whole stems (Table 1), and the regrowth was carried out by both of NS and SS. On the other hand, shoot apices of 65.4% stems were not cut off in IV-L plot, but they did not grow up after cutting, consequently their regrowth were consisted of only NS. 3. After cutting, number of stems per stubble reduced in I-III and IV-L plots, because of death of non-productive tillers (Fig. 3). In V-H and VI-H plots, number of stems increased after cutting because some of the cut stems bore two or three NS. 4. Number of fully ripened grains per panicle was fewer according to delaying the cutting time, and it was lesser in L than H plot (Table 3). And no grain yield was obtained from the panicles of NS in V-L and VI plots. The yield of brown rice became inferior through delaying the cutting time and lower cuttings (Table 4).

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The objective of the present study was to obtain fundamental knowledge to monitor remotely the physiological and ecological status of crops in fields. In this paper the relationships between photosynthetic rate (Pn), transpiration rate (Tr), vapor pressure deficit (VPD), and other meteorological data such as photosynthetically active radiation (PAR) were investigated under field conditions. A model relating Pn and Tr was presented. The influence of chlorophyll concentration (Chl) of leaves on Pn was also examined. 1. A theoretical model to interrelate Pn and Tr was presented, which was based on the biophysical processes for gas and vapor transfer via stomata and boundary layer (Eq.1-6). P_n = a[C_a-C_i][Tr/VPD₁] (6) where, a is a physical constant, C_a, C_i are ambient and substomatal CO₂ concentration, respectively. The Pn is a product of the difference of those two CO₂ concentrations and Tr/VPD as indicated in the eq. (6). 2. Close positive correlations between Pn and Tr/VPD were obtained for both corn and soybean as the results of experiments under field conditions. The correlation coefficients were around 0.9 and consistently higher than those coefficients between Pn and Tr in all cases. This relationship held under a wide range of environmental and crop conditions such as air temperature, PAR, VPD, soil water content, crop variety, chloropyll concentration of leaves, developmental stage, leaf position, rolling or wilting of leaves and time of measurements (Tables 1, 2). 3. Linear regression equations were obtained on the above relationships for both corn and soybean. According to those equations the difference of ambient and substomatal CO₂ concentrations remains constant, because Pn is proportional to Tr/VPD. The difference of external and internal CO₂ concentration was estimated as 159ppm for corn and 51ppm for soybean from the regression coefficients of those equations (Figs. 1∼2). Since the possibility of remote estimation of transpiration rate Tr had been already shown by INOUE¹⁰⁾, the photosynthetic activity could also be estimated remotely by means of combination of remotely sensed data and meteorological data connecting above relationships. 4. As a result of the regression analysis the chlorophyll concentration (Chl) of a leaf had as large positive influence as PAR on Pn under water stress free conditions. The partial regression coefficients for Chl were around 0.7. On the other hand the effect of VPD on Pn increased negatively under water stress conditions. The partial regression coefficients were around -0.5 (Table 3).

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The varietal difference of stomatal aperture in rice seedlings was studied in the phytotron, in relation to the cool temperature susceptibility of Tongil group (an indica-japonica hybrid group) varieties. Eight varieties including 4 japonica and 4 Tongil group were used. They were Sangpungbyeo (cool temperature tolerant), Daecheongbyeo (medium), Odaebyeo (medium) and Hwasongbyeo (medium) as japonica type, and Suwon 339 (moderately susceptible), Iri 377 (moderately susceptible), Samgangbyeo (susceptible) and Yongmunbyeo (susceptible) as Tongil group. The seedlings were grown in a natural light room of the phytotron upto the early hardening stage. The temperature treatments were started at the middle hardening stage (approximately 2-leaf stage) in the artificially lit room, under about 30, 000 lux illumination (0700-1900 hours) and at about 60 percent relative humidity. The set temperatures were (1) 20°C, (2) 16°C, (3)20°C → 16°C from the 6th day, (4) 20°C → l2°C from the 8th day and (5) 16°C → 12°C from the 8th day. Several fAactors affecting the estimation of stomatal aperture of rice seedlings in the artificially lit room were examined (Tables 1-4, Figs. 1 and 2). The following results were obtained in relation to the varietal difference of stomatal aperture in rice seedlings : (1) Stomatal aperture was larger in the Tongil group varieties than in the japonica type, and varietal difference was observed also within the japonica type or the Tongil group varieties (Tables 1-6 and Figs. 3-6). (2) More tolerant varieties of cool temperature generally showed smaller stomatal aperture, except Daecheongbyeo which showed particularly small aperture (Figs. 3-6). (3) Stomatal aperture decreased at lower temperature, and the degree of decrease was smaller in the Tongil group varieties (Figs. 3 and 4). Accordingly, the varietal diffecrence was larger at lower temperature. (4) Preliminary experiments showed that reactions in the stomatal aperture to the temperature shift from 20°C to 16°C, 20°C to 12°C and 16°C to 12°C were all different (Figs. 5 and 6). (5) Stomatal aperture showed a diurnal change, higher in the afternoon, in the experimental condition in the artificially lit room (Figs. 3 and 4). These results implies that stomatal aperture has a high reciprocal correlation with the cool temperature tolerance of rice seedlings, and that thus the estimation of stomatal aperture would contribute to the elucidation of physiological mechanism of cool temperature tolerance in rice seedlings.

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The objective of this study was to investigate the effects of planting density on the dry-matter (DM) production and yield of maize for whole-plant silage in the north-marginal area in Japan (where accumulated temperature from June to September is 1946°C). Experiments were conducted for 5 years from 1978 to 1982, based on the same design. Wase-homare (early hybrid) was grown at four planting densities from 40, 000 to 100, 000 plants/ha in 1978∼1980 and from 58, 000 to 103, 000 plants/ha in 1981 and 1982 (Table 1). DM weights in each organ and leaf area were measured at the 4th-, 7th-, 11th-leaf fully developed stages, silking stage, and, 3 and 6 weeks after silking. DM yields and percentage of barren plants were measured at harvesting date. The results obtained were as follows : I. As planting desity increased, top growth rates (TGR) during the vegetative growth period were increased. Contrarily, TGR during the ear-filling period were decreased rapidly, resulted in the minimum at the highest planting density of about 100, 000 plants/ha during the latter half of the ear-filling period (Fig. 1). It was due to rapid decrease of net assimilation rates (NAR) during the ear-filling period in high planting density causing increase of mutual shading and specific leaf area (SLA) (Table 2). 2. The optimum leaf area index (LAI), under which maximum TGR obtained, during the ear-filling period, was about 3.0 in all the years (Fig. 5). The planting density which gave the optimum LAI of about 3.0 during the ear-filling period was obtained at the planting density of 73, 000 plants/ha (Fig. 1). 3. The maximum ear growth rates (EGR) during the latter half of the ear-filling period were obtained at 60, 000∼80, 000 plants/ha, and EGR decreased at the higher planting density than the above. Furthermore, the declines of EGR at the higher planting density were promoted in the cold years of 1980 and 1981 (Fig.2). 4. The incidence of barren plant was obviously increased with increasing planting density (Table 2). It reached above 20% as NAR during the latter half of the ear-filling period decreased below 2.0g/m²/day (Fig. 4). 5. Although the highest ear DM yields were obtained at the medium planting density as 60, 000∼80, 000 plants/ha, stover DM yields and total DM yields increased with increasing planting density. Percentage of dry-matter in whole-plant did not differ significantly among planting densities in most years. Ear/Total ratio was decreased and maturity was delayed with increasing planting density (Table 3). 6. It was concluded that the optimum planting desity was about 70, 000∼75, 000 plants/ha for high yield and high quality of maize for whole-plant silage in the north-marginal area.

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Using seven parent varieties of Japonica-Indica hybrid bred in Korea, 16 aman, 17 aus, 10 boro, 15 bulu and 15 tjereh rice varieties, excised seminal roots (root-tips) were cultured in modified White's medium containing 0% or 0.2% casamino acids. The excised roots were cultured at 28°C in the dark for two weeks. The results obtained were as follows. 1. In Japonica type parents, the excised seminal root growth was better in the 0.2% casamino acids lot than in the 0% lot. In Indica type parents, on the other hand, main root length was almost same between the two lots of casamino acids concentration in each of three varieties, while the length was shorter in the 0.2% casamino acids lot than in the 0% lot in two varieties. But, dry root weight was larger in the former than in the latter in every variety (Table 1). 2. In all the varieties belonging to aman and tjcreh ecotypes, main root length was shorter in the 0.2% casamino acids lot than in the 0% lot. In each ot aus, boro and bulu ecotypes, the length in the above half of varieties was shorter in the 0.2% casamino acids lot than in the 0% lot and it was opposite in the rest. Dry root weight, on the other hand, was larger in the 0.2% casamino acids lot than in the 0% lot in all the varieties in every ecotype (Table 2).

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The changes in the distribution of phytin-containing particles (phytin particles) were microscopically studied in rice ovary tissues during the development of embryo and endosperm. Similarity in the phytate nature of these particles was confirmed by histochemical and ultrastructural procedures^{7, 25)}. Phytin particles appeared within the aleurone layer and scutellar parenchyma 5 or 6 days after anthesis. This is followed by an increase in number and also by the formation of relatively large particles (3 to 7 μm in diameter). In addition to their presence in these storage tissues, phytin particles were also temporarily found in different parts of ovary tissues after anthesis, as follows : (1) the peripheral regions of pericarp, for a period of 10 days, (2) parenchymatous cells in dorsal vascular bundles for about 20 days, (3) nucellar epidermis and nucellar projection and the modified aleurone cells abutting the embryo or the suspensor cells for about 10 days, (4) the outer layer of starchy endosperm from day 8 to day 20, and (5) scutellar epithelium until about 25 days. With regards to the route of flowing materials into the developing endosperm, the presence of two suggested transport pathways from dorsal vascular bundles into endosperm, i. e. 'the dorsal pathway' and the nucellar epidermal pathway'^{6, 8, 9, 23)}, was confirmed by our observations with the distribution changes of phytin particles in close association with the ovary histogenesis. The observations also suggests the routes into the developing embryo, namely, (1) from nucellar tissue and modified aleurone layer to suspensor, (2) from the modified aleurone layer and starchy endosperm to the embryo surface, and (3) from endosperm to scutellar epithelium. These processes seem to operate within 10 days after anthesis, while the scutellar epithelial process mainly play a role later. Phytin particles frequently occurred in the epidermal or peripheral regions of tissues, such as pericarp and endosperm etc., in contrast to starch grains, which appeared rather in the inner parts of tissues. Accumulation of mineral elements in aleurone cells being a peripheral zone, could not only be a result of deposition of large amounts of mirlerals, supplied from source organs through the supposed transport pathways via the nucellar projection and nucellar epidermis extending around the aleurone layer, but could also be influenced by probable interactions in deposition processes of minerals and carbohydrates. Furthermore, the sink activity of young embryos appeared superior in terms of tissue development based on higher accumulation of mineral elements when compared to the modified aleurone layer which was adjacent to the embryo. The depleted layer in endosperm near the epithelial surface of the scutellum was formed due to the disappearence of starch grains and degradation of endosperm cells during embryo development. These phenomena could be explained in terms of the 'pulling' function of embryo, based on its hypothetically young developmental age, high metabolic activities in protein synthesis, ion absorption and accumulation.

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Japonica typc cv. Kinmaze and Indica type cv. IR8 were grown on water culture. Seasonal changes in photosynthesis and root respiration of the both cultivars were measured by assimilation chamber method and Warburg manometric method, respectively. At the time of maximum tillering, the roots were submerged in a solution on nine different of enzyme inhibitors at three concentrations (10^-2, 10^-3, 10^-4M) and in a reductive solution of -300mV, prepared by addition of soluble starch in water culture solution in order to inhibit root respiration. Photosynthetic rate was measured prior to treatment as well as for a period during treatment. Cultivarietal differences grown under the same nutrient condition revealed that IR8 had high quantity of roots, much more leaf area per plant and lower activity in photosynthetic rate per leaf area throughout its whole growing stages (Figs. 1, 2). The roots of cv. Kinmaze showed higher per-cent in nitrogen and carbohydrate (starch + total sugar) compared with cv. IR8. Further it also showed higher rate of root respiration than that that of IR8 at ripenning period (Tables 1, 2). The degree of inhibition of root respiration by treatments of enzyme inhibitors, reductive solution and 70°C hot water almost coincided with the degree of decline in photosynthesis of the treated plant (Fig. 5). The influence of As₂O₃, NaN₃ and DNP in 10^-2M on the drop in root respiration was remarkable (Table 5). Submerging of root in the reductive solution resulted in a sharp decline in photosynthetic rate at the time of maximum tillers, however significant influence at mid-period of ripenning was not recognized in the same treatment. Degree of inhibition of root respiration by the reductive solution was different according to the stage of growth and root age, i.e., aged roots showed lower rate in respiration and a slight drop compared with vigorous roots at ripenning period (Fig. 6). Transmittance of β-ray through the leaf blade suggested that rapid decline of the photosynthesis by the root submerged in the inhibitor solution was caused by leaf water deficit due to decrease of root activity for water absorption (Fig. 7).

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The objectives of this series of papers are to elucidate the differences in the root morphology among rice varieties which belong to different ecotypes. and thus to contribute to analyse the morphological and functional relations between roots and aerial parts of rice plant. This paper reports the results of estimations on several morphological characters of crown roots for 53 rice varieties belonging to different ecotypes (Table 2). Examinations were carried in the experimental field (clay loam) located in Konosu city, Saitama prefecture. 1. The morphological characters were estimated in portion of 1∼5cm from the base of crown root. The third node counted from the highest rooting node was selected for the estimation, according to results of preliminary experiments. 2. The depth of tillage, the amount of applied fertilyzers or the climate of cultivation year did not affect greatly the morphological characters of crown roots (Tables 1 and 2), and accordingly the varietal orders in the characters were very close among the data obtained from experiments of different cultivation conditions or under different climatic conditions (Fig. 2). 3. The varieties used were divided into two groups, according to the thickness of crown root stele : the one group had a smaller transectional area of crown root steles (Group A in Fig. 3), and the other a larger one (Group B in Fig. 3). The former group included japonica, indica, Chincse indica, and some javanica lowland varieties. The latter included some javanica, American long grain lowland varieties and upland varieties (Fig. 3). 4. Japanese lowland varieties had thinner crown roots and thinner crown root steles, except that Hokkaido varieties and Tanginbozu had comparatively thicker ones in Group A (Fig. 3). 5. The transectional area of stele was highly correlated to the total transectional area of metaxylem II in the stele of a crown root among different varieties (Fig. 4). They were highly correlated also to number of metaxylem I (Fig. 5) and metaxylem II (Fig. 6) in the stele of a crown root. Varieties which had a comparatively small transectional area of crown root stele such as japonica or indica lowland generally had smaller and fewer vascular bundles in the crown root (Figs. 4 to 6). Some javanica varieties, however, had a thinner stele, but a larger number of vascular bundles (Figs. 5 and 6). 6. Varieties with thicker stele (Group B in Fig. 3) showed larger transectional area of metaxylem II per hill (that is, the product of the transectiolal area of metaxylem II per crown root and the number of crown root per hill). In varieties with thinn steles (Group B in Fig. 3), japonica lowland varieties showed smaller transectional area of metaxylem II per hill than indica lowland (Table 3). The ratio of the transectional area of metaxylem II to leaf area per hill, which is an index of the balance of water conductibility and transpiration, showed a similar order among varieties to total transectional area of metaxylem II per hill (Table 3). This order coincides with the order in transpiration ability reported by previous literature. These results stated above implies that the morphological analyses of rice roots in relation to the varieties will contribute to understand not only morphological characters of roots but also physiological or functional relations between aerial parts and roots, and ecotypical differences of them in rice plants.

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Relationships between the growth direction of primarer roots (Fig. 1) and shoot growth were studied by treating the shoot in various ways for controlling the amount of assimilates translocated from shoot to root system (Table 1). Experiment 1 : With shading and defoliation, the growth of shoot was suppressed and the percentage of horizontally growing primary roots was higher than the control. The removal of tillers, on the other hand, let the growth of the main stem more vigorous and the percentage of primary roots growing obliquely or vertically was higher than the control (Figs. 2 and 3). Experiment 2 : Under high planting density, the growth of shoot was suppressed and the percentage of horizontally growing primary roots was higher than the control. Meanwhile under low planting density, the growth of shoot was more vigorous and the percentage of obliquely or vertically growing primary roots was higher than the control (Table 2, Fig. 4). The growth direction of primary roots is strongly influenced by the shoot growth in each case mentioned above ; i.e. the better growth of shoot increases the proportion of obliquely or vertically growing primary roots, and on the contrary the poor growth of shoot increases the proportion of horizontally growing primary roots. These facts seem to support our assumption that the amount of assimilates translocated from shoot to root system might control the growth direction of primary roots in rice plants.

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Two cultivars of potted rice plants were given various treatments, such as, 10 cm depth inundation, high water parcolation (30 mm/day) and excision of lower leaves below top three leaves, in order to change the respiratoy rate of roots. Photosynthesis and dark respiration were measured by the assimilation chamber method under the given conditions of temperature range from 20°C to 40°C during 4 hours at the time of young panicle formation, heading and mid-period of ripening. Immediately after this measurement, the roots were sampled with thoroughly washing out soil and the root respiration in normal air was measured by chamber method. At the time of young panicle formation, the respiratory rate of younger roots from upper three nodes at the base of stem showed much higher activity than that of older roots on lower nodes, however, such diflbrences were not noticed during the period after heading. The ratio of gross photosynthesis of 30°C to 40°C showed a high positive correlation to the respiratory rate of root ; the plants with lower rate of respiration exhibited strongly depressed photosynthesis at high temperature of 40°C perhaps due to thermoactivc closure of stomata. The depression observed at high temperature appears to be caused by water deficit in leaves due to inferior water absorption, since the transpiration efticiency at 30°C was quite dependent on the respiratory rate of roots. Multiple regression analysis of root respiration, nitrogen and sugar content in root revealed that the respiratory rate of root had high positive correlation with the nitrogen as well as the sugar content of the roots. The nitrogen content in root was swayed by nitrogen concentration at the top whereas the sugar content was parallel to net photosynthetic, activity of the plant which in turn is capable of expressing by nitrogen content in leaves of the plant.

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Present experiment was conducted to clarify the effect of natural daylength on the floral induction of rice plants, using four Japanese cultivars : Sasanishiki (less sensitive to photoperiod), Tosan No.38 (moderately sensitive to photoperiod), Hatsushimo (photoperiod-sensitive) and Zuiho (photoperiod-sensitive). The plants sown on two different dates were treated by natural day length or short day 1 or 10 days at 10 days intervals (Table 1, Fig. 1). The dates of young panicle initiation and heading were compared with those of the plants grown under long day condition. In Sasanishiki sown on 1 May, short day effect was obtained by the natural daylength treatment for 10 days started from 2O June when astronomical daylength is the longest in ycar. In Tosan No. 38 sown on 1 May, the time of earliest natural daylength treatment showing short day effect was not claified. The earliest natural daylength treatment showing short day effect started on 30 June in Sasanishiki sown on 22 May, on 10 July in Tosan No. 38 sown on 31 May, on 20 July in Hatsushimo sown on 1 May and sown on 10 June, on 30 July in Zuiho sown on 1 May and on 9 August in Zuiho sown on 10 June, respectively (Figs. 2, 3, 4 and 5). From these results, the dates when rice cultivars begin short day response to natural daylength in Osaka can be estimated as fellows : 28 June in Sasanishiki sown on 22 May, 15 July in Tosan No. 38 sown on 31 May, 20 July in Hatsushimo sown on 1 May, 25 July in Hatsushimo sown on 10 June, 28 July in Zuiho sown on 1 May and 7 August in Zuiho sown on 10 Junc (Table 3). It is discussed that critical daylength is the daylength controlling heading date of Japanese rice cultivars.

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It is recognized in various species that triacontanol (TRIA) increases the growth of seedlings at very low concentrations. However, very fcw reports so far have actually shown increases in dry weight or yield in grain crops under field conditions. A field experiment was, therefore, carried out in 1983 and 1984 at the University Farm of Tokyo Univcrsity of Agriculture, Atsugi, Kanagawa Pref., using two cultivars of rice, with the aim to clarify the cffect of foliar-applied TRIA in colloidal dispersion at concentrations between 0.1 and 10 ppb. Main results obtained are as follows : 1. In 9 out of 16 TRIA-treated plots, increases of 5% to 14% (significant at 5% level in the latter) over control were found in the yield of hulled rice, i.e., brown rice (Tables 7 and 8). 2. As for the effect of TRIA on yield componcnts, increases in the number of ears and 1000-grain weight of hulled rice were often observed (Table 7). 3. The effective concentration of}TRIA for increasing the yield was found to be 0.2-10ppb and the most effective tilnc of application was at the early tillering stage or the end of nursery stage (Tables 7 and 8). 4. Plant length, total leaf area and total dry weight in early growth stages showed a tcndency to be slightly inhibited by TRIA-treatment at concentrations 0.2 to 10ppb (Tables 3 and 4). 5. At the activc ripening stage, however, not only the totalleaf area but also the total root mass were found to be larger in the TRIA-treated plants than in the non-treated control (Tables 4 and 5). It is highly possible that these characters have contributed heavily to increasing the yield through promoting the dry matter accumulation after heading (ΔW) in the TRIA-treated plants (Fi9. 1) . 6. It was found that ΔW was positively correlated with NAR (Fig.2) and that the latter in turn was negatively correlated with SLA (Fig. 3). These may be interpreted to suggest that photosynthetic rate during the active ripcning period was accelerated in the TRIA-treated plants, thus leading to arl increased yield.

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In order to examinc the varietal differences in photosynthetic rate, transpiration rate and leaf conductance for leaves of rice plants, rates of photosysthesis and transpiration of fifty cultivars as shown in Table 1 were simultaneously measured under the controlled conditions : 1800 μmol·m^-2·s^-1 light intensity, 30.4°C leaf temperature, 14.5 mbar vapour pressure difference and 340 μl·l^-1 CO₂ concentration. The measurements were performed three times during the period from maximum tiller number stage to panicle heading stage. We designate these as periods I, II, and III with period I being the maximum tiller number stage, period II being midway between periods I and III, and period III being the heading stage. From the data obtained in this experiment, water use elficiency, leaf conductance, mesophyll conductance and intercellular CO₂concentration (Ci) were calculated. In addition, chlorophyll content, nitrogen content and specific leaf area (SLA) were measured. Using these parameters, the causes of differences in photosynthesis for the different rice cultivars w'ere analyzed in relation to the diffusion pathway of carbon dioxide from the atmosphere to the chloroplasts and to its biochemical activity. The results obtained were as follows : 1. The maximum rate of photosynthesis was 51 mgCO₂·dm^-2·hr^-1 in 'Century Patna 231' and the minimum rate was 22 mgCO₂·dm^-2·hr^-1 in 'Senbon asahi' rice cultivars. The mean value for fifty rice cultivars was 39.8, 36.2 and 33.1 mgCO₂·dm^-2·hr^-1 for periods I, II and III, respectively. The coefficients of variation for each of these periods was 12.1, 11.1 and 13.4%, respectively (Table 1). 2. The transpiration rates lbr the cultivars ranged from 2.21 to 4.88 with an average of 3.70, 3.59 and 3.40 gH₂O·dm^-2·hr^-1 for periods I, II and III, respectively. The cocfficients of variation for each period were 12.6, 15.5 and 16.4%, respectively (Table 1). 3. From the linear regression analysis, there were close correlations between photosynthetic rate and leaf or mesophyll conductance. There were loose correlations, however, between photosynthetic rate and chlorophyll content, nitrogen content, or SLA. Intercellular CO₂ concen-tration, which is considered to be onc of the parameters strongly regulating the photosynthetic rate, was not associated with photosynthetic rate in the rice cultivars (Table 2). 4. Using the least squares method, we tried to obtain some information on the relationships between photosynthetic rate and leaf or mesophyll conductance in the rice cultivars. Both of the relationships were approximated by a fburth order polynomial. It appeared from the former relationship that the photosynthetic rate has an optimum leaf conductance ; that is, for values up to 1 cm·s^-1 of leLlf conductance, photosynthetic rate increased with increasing in leaf conductance. Beyond tlle value, photosynthetic rate decreased (Fig. 1-A). On the other hand, photosynthetic rate was linealy correlated with mesophyll conductance (Fig. 1-B). Consequently, it is clear that differences in photosynthetic rate among the rice cultivars examined was due to the differences in mesophyll conductance.

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Isoprothiolane (diisopropyl-1, 3-dithiolan-2-ylidenemalonate, IPT) is a compound originally developed as a systemic fungicide to control rice blast disease. VVe investigated the growth regulating effect of IPT on rice seedling, especially on root growth. The results obtained are summarized as follows : 1. When the germinated rice (cv. Nipponbare) seeds were induced on agar medium containing various concentrations of IPT at 25°C, it remarkably promoted the growth of seminal root dependent on the conc(tntration from 10^-6 to 10^-4M. IPT also promoted notably the growth of crown root, too, at 10^-5 and 10^-4M. On the other hand, the plant hcight and second leaiA sheath were inhibited by IPT at high concentrations above 10^-4M (Fig.2). 2. The promoting effct of seminal root growth by IPT shit-ted low concentration sides by reducing the incubation temperature in steps (20, 18 and 16°C). That is, 10^-6 and 10^-5M IPT promoted the seminal root growth without eflbctiveness for plant height at 16°C. We also observed that this compoLlnd hastened the elongation of crown roots (Figs. 3, 4). 3. The in vitro root-tip (1cm long) culture in modified Kawatas' liquid medium exhibited that IPT also promoted the elongation of excised seminalroot at 10^-6 and 10^-5M, and inhibited its clongation and secondary root development at high concentration above 10^-4M (Figs. 5, 6). The original part ofinoculated root-tip tissue cultured in the medium containing IPT remained to be white color with brown in control even after three weeks. This excised root part which was immersed in hydrochloric acid-phloroglucinol mixture fbr the detection of lignification faded rose color compared with control one ( Figs. 6, 7). From these results, it is clear that IPT is directly associated with root metabolism and promotes its growth. IPT may take part in maintenance and buildup of root activity under low temperature in rice seedlings.

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レンゲの窒素固定活性(アセチレン還元活性)におよぼす環境要因の影響を調べ, 圃場条件下で固定される窒素量を推定した. アセチレン還元活性は湛水によって著しく抑制され通常の10%以上に減少した. 湛水状態から通常の状態にもどすと, 活性はすみやかに回復した. またアセチセン還元活性は酸素分圧の減少につれて低下し, 窒素ガス中ではまったく認められなかった. これらのことより湛水による活性の低下は主として酸素欠乏によって引き起こされるものと考えられた. 20～30℃の温度範囲では活性に変化はなかった. 圃場条件下での活性は植物1個体当り, 日中で平均10μモル/時間, 夜間で5μモル/時間であった. 以上の結果より植物1個体によって同定される窒素量は1.26mg/日となり, レンゲの旺盛な生育期間中に固定される窒素量は栽植密度を考慮に入れ約40 kg/haと推定された. この値は水稲作に施用される窒素量の約40%に相当するものであった.

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異なった来歴をもつ水稲(Oryza sativa L., 日本晴, IR30) と陸稲(同, タチミノリ, IRAT13), 各2品種ずつについて幼苗期における乾燥下生存能力を比較した. そして, これら品種間に生存能力の差があるのか, また生存能力と浸透調節能力とには関係があるのかどうかを明らかにしようとした. 播種後15日目から18日間, 植物体を自然光人工気象室で様々な段階に土壌水分状態を設定したポットで育てた. その結果, 土壌への給水量が少ない(第1図)はど処理18日目の夜明け前の葉身水ポテンシャルは低かった(第1表). そして, この時の葉身を膨潤させて求めた浸透ポテンシャル値も, ほぼ土壌乾燥の程度に応じて低下した(第2図). さらにこの低下の程度を湿潤区との差から浸透調節量として比べると, 陸稲に比べ水稲のほうが大きかった. 一方, 葉身の枯死率はこの夜明け前の葉身水ポテンシャルと密接な関係があり, 水ポテンシャルが低下するにつれて枯死率は増加した(第3図). そして, 葉身水ポテンシャルの低下にともなう枯死率の増大程度は水稲よりし陸稲で著しく(第4図), 乾物生産速度の低下も水稲に比べ陸稲の方がやや大きいという同様の傾向があった(第5図). しかし, 夜明け前の葉身の水ポテンシャルと浸透ポテンシャルとの関係を見ると, この関係には水稲と陸稲間で明確な差は認められなかった(第6図). すなわち, 水稲品種が陸稲品種よりも浸透調節が大きかったのは, 水稲品種が単に低い水ポテンシャルにさらされたためであり, 本質的な浸透調節能力の差にもとずくものではなかった. 以上のことから, 葉身の枯死率と乾物生産かろみた乾燥下における幼植物の生存能力は, 陸稲品種に比べ水稲品種の方が高いとみなされるにもかかわらず, 浸透調節能力には違いが認められないことから, 浸透調節は幼苗期のイネの干ばつ下生存能力の差には関与していないものと判断される.

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間作ダイズ(品種:中鉄砲)の生育・収量に及ぼす栽植様式(1列交互作区, 3列交互作区) と組合せ作物(トウモロコシ・・・品種ハニーバンタム, サトイモ・・・品種岐阜早生)の影響を1983年に岐阜大学内研究圃場においてポット栽培により検討した. 栽植様式の違いによる光環境の差異とダイズ収景との関係を明確化するためダイズ開花始期にダイズボッ卜の一部を組合せ作物毎に栽植様式区間で相互に移動(1列交互作区=3列交互作区) した(第1図). 実験結果は以上のとおりであった. 生育:ダイズ主茎長(草高)はダイズ生育初期～開花期前の生育段階ではトウモロコシとの1列交互作区で徒長したのに対し, サトイモとの間作ではいずれの栽植様式区においても伸長程度は小さかった. ダイズ開花始期以降の主茎長の伸長率はいずれの組合せ作物区においてもポット移動による有意な差異を示さなかった(第2表, 第2図). 節間長は全般的に7節～13節の間で最も伸長率が高かった(第3図). 分枝数はサトイモとの組台せの方がトウモロコシとの組合せよりも多い傾向にあっだ(第2表). ダイズ草冠部上の群落内照度は生育初期～開花始期前の生育段階で組合せ作物の影響を最も強く受け, トウモロコシの1列交互作区で最も遮光程度が高く, 最低値を示した. これに対し, サトイモとの間作では遮光程度は栽植様式に関わらず低かった. これらの両作物種間の生育速度の違いがダイズ群落の受光態勢に大きく影響した(第2図). 開花始期にはトウモロコシとの間作ではトウモロコシ葉の枯れ上がりのため1列区, 3列区ともダイズ草冠部上の照度は高まった. サトイモとの間作ではサトイモ葉の拡大により, 照度は逆に両区とも低下した. 成熟期ではいずれの作物種との組合せにおいてもダイズ草高の高まりと各組合せ作物葉の顕著な枯れ上がりのためダイズ群落の光環境は大きく改善された(第6図). 収量 : ダイズ収量は栽植様式に関わらずサトイモとの間作の方がトウモロコシとの間作よりも高かった. 栽植様式とポット移動処理による収量への影響については 3列区≒3列→1列区>1列区≒1列→3列区 の傾向があった. ダイズ開花始期以前のダイズ群落における低照度は完全芙数及び完全粒数の減少を末し, これが最終的には低収量と結びついた(第4, 5図)が, 開花始期以降の光条件は収量に殆ど影響を与えなかった. 収量構成要素に関しては卜ウモロコシとの間作で不完全英数が多く, このことが組合せ作物間の収量差の直接的な原因となった(第5表). なお, トウモロコシとサトイモの生育・収量については栽植様式の違いに関わらず, 各作物区間ともいずれも有意差は認められなかった(第1, 3, 4表).

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根系における保守的形質と可塑的形質を区別する試みとして, 播種後38日間, 3つの異なる土壌水分条件に設定された根箱中で, 生育したダイズ品種・奥原1号枝豆の全根系を定量的に調査した. 対照区 (C)は, 週1回最大容水量(42.6%)の水が与えられた. 上層濯水区(S)と下層濯水区(B)の根箱は, 毎週秤後, 減量分に相当する水がS区は表層から, B区は下層から与えられ, 最大容水量の36.2%の水分に維持された. C区の根系は, 根箱全体にほぼ均等に発達した. それとは対照的に, B区の根系発達は, 根箱の上層部に密に, 下層部で疎であった. S区の根系発達は, B区と逆のバターンであった(第1図). どの区でも高次の側根を出す, 長くて, 太い1次側根(L型)を直根基部から発根した. 30cm以上の長さのこれらの側根数を比較すると, B区は14本, S区は12本, C区は5本であった. 植物体軸の下方への延長線とそれらの側根の基部がなす角度(走向角)は, 明らかにC区よリS・B両区で小さかった(第1図). どの区でも, 側根は全根長のみならず全根系表面積の98%以上を占めた. またどの区でも側根の分枝次数は4次までであった. C区では全側根数の約65%をL型1次側根と分枝をしない(S型)2次側根が占めた. S・B両区では, 全側根数の約66%をL型2次側根とS型3次側根が占めた. これらの側根は, 全根長と全根系表面積の拡大に大きく寄与した(第2表). 根径は直根を除き, C区に比べてS・B両区で太くなる傾向を示した(第2表). 土壌水分条件が変わっても, 根粒の70%以上はL型1次側根に着生し, その着生が認められたのは2次側根までであった(第2図). 根粒の着生分布は, C区では根系の全体にわたったが, S区では根系の上半部に, B区で上半部に集中した(第3図). 土壌水分変動の測定結果(第3表) とS・B両区の根系像(第1図)から判断して, 側根の分枝能は土壌水分が比較的低くても, 安定している土層で高まると推察された. 根系の諸形質の内, 異なる土壌水分条件でも変化しなかったものを保守的形質, 変化したものを可塑的形質として, それらを整理すると, 保守的形質は, (1)4次までの分枝能, (2)2次側根までの根粒の着生および, L型1次側根へい集中的着生, 可塑的形質は, (1)長く, 太いL型1次側根数, その長さおよび走向角, (2)側根の根径, (3) 4次分枝の範囲内での分枝能, であった.

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先報¹³⁾で得られた結果より, “集中型"根系をもつ作物群から陸稲を, "分散型"根系をもつ作物群からトウモロコシを対象としてとりあげた(第1図). とくにL型側根とS型側根の役割分化に注目しつつ, これらの作物の根系の構造を明らかにする目的で, それぞれの播種後1か月の根系について, 直接法によって根系構成要素の定量を行なった. 陸稲は29本の節根上に計42,394本の側根(高次の側根を含む)を発生させ, 根系全休の表面積は58,048mm²に達した. それに対し, トウモロコシでは, 17本の節根上に計11,628本の側根(高次の側根を含む)が発生し, 根系全体の表面積は122,697mm²に及んだ(第1表). 側根が全根系表面積に占める割合は, 陸稲で77%, トウモロコシで88%であった(第1表). 全側根の中でその構成をみると, 両種は似かよっていた. 第1次S型側根は数, 長さ, 表面積で全体の20%から25%の割合を占めた. 一方, 数では全体の5～6%を占めるにすぎない第1次L型側根は, そこから発生する高次のS型およびL型側根も含めると, 表面積で全体の約76%を占めた(第1表). 側根の分枝次元を比較すると, 陸稲は第3次側根, トウモロコシは第4次側根まで分枝していた. そして, 表面積において両種を比較すると, 高次側根(2次以上)の全根系および全側根に占める割合は, いずれもトウモロコシの方が高かった(第1表). 両種ともに, これら側根の1本の節根上における数, 長さ, 表面積の分布は極めて不均一であり, その中で第1次L型側根が大きな位置を占めていた(第2, 3図). 根系の土層別の分布を見ると, あらゆる土層で第1次L型側根はその上に分枝している側根も含めて, 根系の全表面積に対して, 極めて高い割合を維持していた. 根系全表面積の分布パターンを見ると, 陸稲では地表下約20cmにピークをもつ単純なカーブを描いた. それに対して, トウモロコシは表層から増減を繰り返して, 深層へと発達した. 全体的に見ると両種とも, 根系が一部に偏在することはなかった(第4, 5図). 以上の結果より, 陸稲の根系は, 相対的に節根に依存する程度が高く, 一方, トウモロコシでは側根に依存する程度が高い特徴を示した. 両種の根系の特徴をまとめると次のようであった. 陸稲では, 節根の走向角が小さく, 節根が密に分布しでいる結果生じた比較的狭い空間において, 第1次S型側根, L型側根が, ともにそれぞれ長さは短いが, 圧倒的に数が多いことによって根系拡大に貢献していた. また, トウモロコシにおいては, 側根は, 数では陸稲の約1/3あるいはそれ以下であった. しかし, 長さでは, 第1次S型側根は陸稲のそれとほとんど同じであったが, L型側根は変異が極めて大きく, 極端に短いものから, 長く, 高次側根を旺盛に分枝しているものまでが発生していた. これらが, 節根の走向角が大きく, さらに節根が疎に分布している結果生じた比較的大きな空間において, それぞれ根系拡大に寄与していた(第2表). これらのことより, 両型の根系拡大戦略が基本的に異なることが明確に示された.

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改良根箱法を用いて, 13種のイネ科作物について(第1表), 根系構造を比較した(第1図・第2図). 節根(種子根を含む, 以下同じ) の走向角と(第3図), 側根の発達程度にもとづいて, それらの根系を次の4つのグループに大別した. 第1グループ:節根の走向角は比較的小さく, その多くは上壌を縦走した。節根数は4つのグループの中で最も多い傾向があった. 第1次側根は細く, 短く, 分枝に乏しかった. 水稲, 陸稲, シコクビエ, ヒエが含まれた. 第2グループ:数本の節根は株直下へ縦走するが, 他の多くの節根は, 走向角が大きく土壌中を斜走した. アワ, キビが含まれた. 第3ブループ:節根の走向角は大きく, 土壌中を斜走した. 第1次側根は長く, 太く, 分枝が盛んであった. トウジンビエ, モロコシ, 卜ウモロコシ, オオムギ, コムギ, ライムギ, エンバクが含まれた. 第4グループ:節根が斜走し, それらの発達は偏在して進んだ. 側根の発達は旺盛であった. ハ卜ムギが含まれた. これらの作物の根系構造上の特徴より, 第1グループおよび第3グループに属する作物の根系をそれぞれ "集中型", "分散型"と呼んだ. また, 第2グループの根系はそれらの中間型, ハトムギの根系は仲自な型を形戊すると考えた. この2つの型の根系間の重要な差異は, "集中型"では, 節根が, 比較的狭い土壌空間に高い密度で分布したのに対し, "分散型"では, 節根は比較的広い土壌空間に疎に分布したことであった. また, 種子根上の側根で比較した場合(第3表, 第4図, 第5図), 前者ではS型(短く, 比較的根径が小さく, 高次の側根を分枝しない)1次側根の発生数および単位種子根長当りの密度が高く, 根系構成要素に占める割介が比較白勺高かった. それに対し, 後者においてはS型1次側根は発生密度も低く, 根系要素中に占める割介が極めで小さかったが, L型(長く, 比較的根径が大きく, 高次の側根を分枝する)1次側根の割台が高く, 長さでみると根系のほとんどを占めていた. また, ハトムギの根系の側根発達の様相は, "集中型"根系のものに類似していた. この根系によるイネ科作物の分類と, 耐湿性・耐早性程度による分類^10,21)とは比較的よく一致した.

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イネの色素体の初期発達に及ぼす低温の影響を, 低温抵抗性の異なる3品種を用いて, 特に "弱光プロラメラボディ(w-PLB)"の形成に注目して研究した. イネの色素体が発達する間に, 低温抵抗性と密接に関連した3つの顕著な変化が認められた. すなわち, プロラメラボディ (PLBs)を含めた色素体の膜系の変化, プラス卜顆粒の増加, および, デンプン粒の急速な消失である. 1. IR8を20℃, 光強度5.5w/m²の条件下で培養するとき, PLBsは色素体の発達初期に消失し, その後, PLBsが再形成されることはなかった. しかるに, ホウネジワセの色素体では, 色素体の発達と共にw-PLBsの数が増加した. 坊主では, w-PLBsを含む色素体が観察した色素体の 96%に達した. しかし, IR 8を26℃, 5.5 w/m²で培養すると, 20℃, w/m²で培養したホウネンワセと同程度の w-PLBs を形成した. 20℃, 5.5w/m²の条件下では, 低温抵抗性が大きいほど, wr-PLBsの形成が容易であった. したがって, w-PLBsの形成が低温抵抗性のレベルを判定する1つの指標として用いられるかもしれない. 2. IR8の色素体内のデンブン粒は, 色素体の発達後期まで保持された. しかし, ホウネンワセと坊主では, 発達初期にデンブン粒は消失した. これは, 可溶性糖の低温障害に対する保護を示唆している. 3. IR 8の色素体では, 他の2品種と比較すると, より多くのプラス卜顆粒が蓄積された. これはPLBs からチラコイド膜への発達が, 低温によって阻害された結果を示している.

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コムギ葉の先端部において, 水孔下の細胞間隙が直接, 導管節と接していることが観察された. 水孔には濃縮された溶質によると思われる硬質の沈着物が見られた. 表皮細胞の外側細胞壁は, 電子密度の高い顆粒を含む多層構造からなる. これらの構造を, 水通導系及びクチクラ蒸散との関係から論議し, 水の移動を容易にするものであることを示した.

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栽植様式の違い(長方形植え, 正方形植え, 正三角形植え)が, ダイズの子実収量に及ぼす影響を標準密度区(800株/a ; 1株2本立で)と高密度区(1200株/a)で検討した. 試験は, トヨスズとスズヒメの2品種を供試し, 1986年, 帯広畜産大学作物試験圃場(褐色乾性火山灰土)で行った. 単位面積当たりの子実収量は, 標準密度区で正方形植えと正三角形植えが, 長方形植えに比べ品種平均でそれぞれ 14.9%, 12.7%増となった. 高密度区でも正方形植えと正二角形植えが上回ったが, 正三角形植えの方が高収となったため, 密度と様式の間に相互作用が認められた. 正方形植えおよび正三角形植えによる収量増加は, 主茎の子実収景に比べ分枝の子実収量(分枝数)の増加によるところが大であった. 栽植様式の違いによる子実収量の変動を, 個体当たりの利用可能な生育面積との関連で考察した. 利用可能な生育面積として, 正方形植えと正三角形植えでは, 憐り合った株との距離の1/2を半径とする円の面積を想定した. 長方形植えでは圃場でのLA1最大期の観察をもとに, 畦間の40%の長さを長径とし, 株間の1/2の長さを短径とする楕円の面積を想定した. その結果, 両品種とも個体当たりの子実収量の変動は, これら面積の対数変換値に対する2次回帰で説明できた. 以上より, 栽植様式の違いによる子実収量の変動は, 与えられた生育面積の違いに対する分枝の反応に強く依存するものと推察された.

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前報¹⁴⁾において水稲の花成を誘導する暗期の計時反応機構の開始には光量のある程度までの低下とともに光質, とりわけ遠赤光が特異的に関与している可能性が示唆された. 本実験では主として感光性の高い水稲品種農林18号を用い, 暗期直前の遠赤光照射が花成反応におよぼす影響について検討した. 1) 暗期前の遠赤光照射の影響は暗期の長さによって異なり, 12時間以下の比較的短い暗期では花成を促進し, 14時間をこえる長い暗期のときは抑制した. 2) 遠赤光による花成の促進または抑制は, 遠赤光照射時間に相当する時間だけ暗期を延長したときの花成反応を凌駕し, さらに促進または抑制の程度は遠赤光により増強された. 3) 10時間暗期直前の遠赤光は2時間まで照射時間の増大にともない花成を促進したが, とくに0.5時間以下の短時間照射の効果が著しかった. 4) 限界暗期より短い9時間以下の暗期でも, その直前に0.5時間以下の遠赤光照射を行うと花成は誘導され, 限界暗期は1時間前後短縮した. 5) 10時間暗期による花成誘導が最少10回の処理周期を必要としたとき, 毎暗期直前に1時間の遠赤光照射を行うと, 僅か3回で花成は誘導され, 必要最少誘導周期数の著しい減少がみられた. 6) 遠赤光の暗期前照射による花成促進は感光性の高い「農林18号」や「瑞豊」ばかりでなく, 感光性程度は低いとされている「こしにしき」, 「トドロキワセ」, 「コシヒカリ」および「ニホンマサリ」など早生品種においてもみられた.

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開花期のイネをファイトトロン自然光室で12℃, 2～8日間冷温処理し, 花粉内でんぶん糖化異常の顕微鏡観察と杓の生理的活性の測定を行った. 正常な花粉の発育過程では, でんぷん粒が花粉の中心から端に充満したのち, 発芽孔の反対側ででんぷんが一部消失(糖化)する(第1図). このでんぷん糖化は開頴直前の3～4時間の間に急速におこり, 正常な条件では開頴開始時において70%以上が糖化型花粉であった(第2, 3図). 冷温処理された花粉のでんぶん糖化は花粉壁内側の周辺全体からおこり, 正常な糖化とは明らかに異なる(第1図). この糖化異常は処理中にも一部おこるが, 処理終了後開頴開始までの間に急速に進んだ(第3図). 約当りのでんぶん含量は処理日数の増加に伴って減少し, 可溶性糖含量は一時的に増加した(第6図). これは処理中の花粉でんぶん糖化の顕微鏡観察の結果とよく符号した. ATP含量は冷温処理によって低下しなかった(第9図). これらの事実は, 冷温処理によっても呼吸と炭水化物代謝に関する機能は保持されていることを示し, 処理中に呼吸基質としてでんぷんが一部消費されること, また処理終了後の急速な糖化現象を支持している. しかし, 糖化が正常型と異なって何故異常となるかは, この結果からは説明できなかった. 処理日数の増加による稔実歩合の低下と糖化異常花粉歩合との正の相関関係が認められ(第3, 4図), 冷温処理による糖化異常が花粉の発芽能力の低下の原因と考えられた.

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品種農林2号を用いて2つのポット実験を行った. 実験1では葉の組織中の内生ABAの濃度と土壌水分条件との関係を検討した. 実験2では葉へのABA溶液の散布が葉の物理的な伸長性と生長速度に与える影響を検討した. そして, これら2つの実験の結果から, 土壌水分の葉面生長への影響におけるABAの役割につき論じた. 1) ポットへの水供給を停止すると, 土壌水分含量の低下にともない葉中のABA濃度が急速に上昇した. その後, 土壌水分含量を低しルベルで一定に保ったところ, 葉のABA濃度は, 実験終了時までこの高いレベルを維持した. 2) 中央小葉に1日2回6日間にわたって種々の濃度のABA 溶液を十分に散布したところ, 葉の物理的伸長性と生長速度が明らかに低下した. 低下の程度はABAの濃度が高い程大きかった. 3) 上記2実験, ならびに既報の結果から, 低土壌水分による葉面生長の低下は, 主として次のような一連の変化を通じて起きるものと考えられた. すなわち, 葉内ABAレベルの顕著な上昇 : 葉の物理的伸長性の顕著な低下 : 葉面生長の減退

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品種農林2号を用いてポット試験を行ない, 葉における浸透濃度の調節をカリウムおよび糖の濃度から解析した. 1) 葉組織を圧搾してえた汁液の浸透濃度とカリウム濃度は, ともに土壌水分含量の低下に対応して上昇した. これら二つの濃度の上昇程度は葉位により異なり, 上位葉では下位葉におけるよりも大であった. 2) 浸透濃度とカリウム濃度との間には密接な相関がみられた. 両者の間の相関係数は葉位の上昇にともない規則正しく増加した. 3) 糖も浸透濃度の調節に貢献した. カリウムと糖の浸透濃度調節に対する貢献度は葉位により異なり, 上位葉ではカリウムが糖に比べてはるかに大きい貞献度を示した. 下位葉ではカリウム糖の貢献度は同程度であった. 4) 浸透濃度に対するカリウムの貢献度がもっとも人きい最上位の展開中の葉(浸透濃度とカリウム濃度との間の相関係数が 0.921)においてさえ, カリウムが溶質として浸透濃度に直接貢献する程度は, 約30%にすぎなかった. この事実は, 浸透濃度調節のうえでカリウムが溶質として直接的に貞献するほかに, 何らかの間接的な貢献を行っていることを示唆する.

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