The seeds having cracked seedcoats (the cracked seeds) are not only regarded as an inferior quality in an exterior view but also tended to cause lower seedling emergence. However, since the cracked seeds seem generally to occur among bigger seeds, it is suggested the possibility to bring the better seedling emergence by elaborating the cultural methods. Soybean seed, cultivar Enrei, was used in a series of experiments. The experiments related with seedling emergence were carried out on the field nursery beds in natural conditions or on beds in glasshouse, and ones related with germination were done on filter paper folded up in V-shape. The results obtained are summarized as follows : (1) The seeds having uncracked seedcoats (the uncracked seeds) emerged, but the cracked seeds did not (Table 1) under natural conditions in much rainy days (Fig. 1, Oct.9-25). (2) Significance (p=0.05) in percentages of seedling emergence by sowing uncracked seeds, cracked seeds, and germinated seeds developed from cracked and uncracked seeds, under adequate sprinkling water in glasshouse, was not recognized. But 92% seedling emergence by sowing germinated seeds developed from cracked seeds was a slightly higher than the other treatments (Table 2). (3) Percentages of seedling emergence by sowing germinated seeds developed from uncracked seeds and from cracked seeds were about 90%, but ones by sowing ungerminated seeds were very low (Table 3) under natural conditions in continuous much rainy days (Fig. 1, Oct. 31-Nov. 14). (4) Percentage of germination by seeding the cracked seeds was a little higher than that by seeding the uncracked ones. That was progressed to be higher by pasting Himosab (one of the granular rosins which is able to absorb water rapidly) with starch paste on a part of hilum (Fig. 3). (5) Elongation of each part in the seed was measured by changing the seeding directions. The longest elongation in length was found in case of seeding the cracked seeds and the second one in case of submerging hilum and micropyle of seed in water (Fig. 4). Supposing from the above results, the following cultural methods are persuaded to bring the better seedling emergence in case of using the cracked seeds. 1) The cracked seeds are sown at adequate soil moisture in the field. 2) Germinated seeds developed from the cracked seeds are used. 3) Transplanting seedlings which are developed from cracked seeds under adequate sprinkling water on the beds in glasshouse are used.

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[in Japanese]

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Elongation of crown roots in rice plant was studied in relation to the growth stage of the top. Cultivars used were Ginmasari and Toyonishiki, of medium type with respect to the number of leaves on the main stem (15 and 16, respectively). They were grown in submerged pots. Four types of elongation were recognized as follows. The first type was slow elongation, with the final length being not so long. The second type was rapid elongation in the early course, followed by gradually reducing rate, with the final length and the elongating duration being both long. The third type was elongation in which crown roots elongated with approximately constant rate during the entire course, with the final length being as long as that of the second type. The last type was elongation with constant rate, terminating in comparatively shorter length. As to the lower roots of the shoot unit in the main stem, each of these four types was found in the crown roots of the following shoot units or growth stage. The first type was observed only in the crown roots of two or three shoot units which developed just after germination or transplanting. Therefore, it was designated here as the early growth-stage type of crown roots elongation (abbreviated to E G type elongation). The second type was seen in the crown roots which appeared in a few shoot units after E G type elongation. As those shoot units were situated in relatively lower position, this type was referred as the elongation type of the crown roots from the lower shoot unit (L U type elongation). The crown roots which appeared from the couple of shoot units upper than those lower ones showed the third type of elongation. Those shoot units occupied relatively higher position and so this type was called the elongation type of the crown roots from the higher shoot units (H U type elongation). The fourth type was found in the uppermost-positioned crown roots of one or two shoot units (U P type elongation). In general trend, the higher the position of the shoot unit from which crown roots developed became, the greater the elongation rate of its crown roots was, until reaching the maximum in the crown roots of higher-positioned shoot units out of the ones of H U type elongation. In a tiller, a similar transition of elongation types to that in the main stem was observed in advancing sequence of shoot units, except that E G type elongation was not found. But the tiller which appeared from the higher shoot unit of the main stem had less number of shoot units whose crown roots showed L U type elongation. As to the upper roots, the final length was much shorter than that of the lower roots within the same shoot unit. Besides this, several inferiorities were observed in regard to the elongating rate and/or the final length in the upper roots from the upper shoot units in the main stem and tillers or from the higher-positioned tiller. The panicle differentiation stage was around the transition from the appearance of crown roots of L U type elongation to that of H U type, or was the early time of crown roots appearance of H U type elongation. Crown roots of E G type and those of L U type elongation of lower shoot units finished elongation slightly before the panicle differentiation stage and the later the crown roots appeared, the later their elongation terminated. All the crown roots ceased elongation around the heading stage.

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Rice plants, cv. Nipponbare were grown under three temperature conditions with day/night temperature(°C) of 33/27(H), 29/23(M) and 25/19(L) during the young panicle development (from the initiation to the full heading). Using the main stems of plants, the effects of temperature on growth of panicle, leaf blade, leaf sheath and internode at each position of the main stem were examined. The results are summarized as follows : 1. Effects of temperature on growth of plant parts varied depending on the ontogenic stage of development. At the early stage of development, elongation was strongly accelerated with increase in temperature. However, after rapid growth had started, temperature had no strong accelerative effect on elongation (Figs. 1-3). In the case of panicle, the difference between L and H in the period from the initiation to 1 cm-stage was 8 days while from the 1 cm-stage to the full length, it was only 1 day (Fig. 4). Thus, it seemed that the growth of plant organs or their parts is sensitive to temperature at the early stage of development but becomes less sensitive at later stages. 2. Since temperature affects growth of every organ or its part evenly, synchronous relations in elongating processes among definite combinations of plant parts were maintained irrespective of temperature conditions. For example, panicle, leaf sheath of the flag leaf and the third internode (counted from the top) grew synchronously (Fig. 6). 3. The effect of temperature on final length of plant parts was different depending on the kind of organ and the position of the part. Leaf blade of the uppermost three leaves was longer under higher temperature (Fig. 7). With rise in temperature, the uppermost internode was lengthened while the penultimate, the third and the fourth internode were shortened (Fig. 8). Thus, culm length was almost constant in the temperature range applied. Similarly, panicle length was little affected by temperature (Fig. 9).

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Variation of grain shedding among rice varieties may be attributed to the morphological and physiological characteristics of abscission region formed between pedicel and rachilla, i.e. no abscission layer, uncracking abscission layer or cracking abscission layer. In the present study, to clarify the varietal difference in the formation and development of abscssion layer during boot stage, change of histological peculialities in the tissue between pedicel and rachilla was observed. Varieties used were two Japonica-Indica hybrids bred in Korea (Yushin and Milyang 23) with cracking abscission layer, two Korean local varieties with uncracking abscission layer (Jojeongjo and Nengjo), and a Japanese paddy rice variety without abscission layer (Akibare). The results obtained were summarized as follows. 1. Rapid growth of panicle and spikelet were observed from 16 to 4 days before heading (Fig. 1). At 16 days before heading, when the panicle length was 20 to 30 mm and spikelet length was 2 mm, abscission layer could be observed by elongation of cells in the pedicel and rachilla (Fig. 2-D and E). 2. At 12 days before heading, when panicle length was 50 to 80 mm and spikelet length was 3 to 4 mm, abscission layer was clearly distinguished from the sclerenchymatous cells in the pedicel with thickened cell wall. Further, the cracking abscission layer of Japonica-Indica hybrid was composed by two layers of parenchymatous cell, while that of uncracking abscission layer of Korean local rice by one layer (Fig. 2-G, H). 3. At six days before heading, when panicle length was 120 to 190 mm and spikelet length was 7 to 8 mm, cell division was observed in the abscission layer of Japonica-Indica hybrid but not in the layer of Korean local rice. In both rice plants with abscission layer, cell walls of all the sclerenchymatous cells were lignified (Fig. 2-J, K). 4. In the rice plants with abscission layer, diameter of the parenchymatous cell composing abscission layer varied from 6 to 8 μm at heading time. This result seemed to show that little elongation of the cell occured after cell division. In another variety without abscission layer, on the other hand, cell was about 16 μm in length and cell wall was lignified at heading time (Figs. 2-O and 3). 5. At the heading time, length of sclerenchymatous cells in the protrusion at the top of pedicel was 70 to 110 μm. This result showed that remarkable elongation of scleren-chymatous cell has occured during boot stage as compared with parenchymatous cell in the abscission layer or with sclerenchymatous cell in the abscission region (Fig. 4). 6. From the above results, no clear differences in the formation and development of abscission layer and its around tissue was observed between the both rice plants with cracking and uncracking abscission layers. At harvest time, however, the former had one or two layers of parenchymatous cell and the latter had one layer of parenchymatous cell in the abscission layer. Further, activity of cell division seems to be higher in rice plant with cracking abscission layer than that with uncracking one. On the other hand, in a Japanese paddy rice cultivar, no abscission layer was observed during boot stage (Fig. 2-M, N, O).

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It was suggested in the previous paper that the increase of photosynthetic rate owing to higher nitrogen content appears remarkably in case with little water stress, and that the decrease of photosynthetic rate due to the decrease of water absorption appears remarkably under the condition which brings on intense transpiration. The present study was conducted to ascertain the suggestion by investigating the effects of humidity or leaf-air vapour pressure deficit (LAVPD) on the photosynthetic rate of leaves in rice plants under different conditions. Transpiration rate increased with the increase of LAVPD and was practically constant under the condition of more than 11 mmHg LAVPD, while photosynthetic rate, diffusive conductance and photosynthetic rate/transpiration rate ratio (water use efficiency) decreased with the increase of LAVPD (Fig. 3). Photosynthetic rate of leaves with higher nitrogen was much higher in smaller LAVPD, but it was not so much different due to nitrogen content in larger LAVPD because the depression rate of photosynthetic rate was higher in leaves with higher nitrogen content (Figs. 1 and 4). Leaf nitrogen content was more effective for increasing photosynthetic rate in smaller LAVPD (Fig. 7). In rice plants with low root activity induced by application of soluble starch with additional ammonium sulfate to soil, and with low root-top ratio induced by shading and high humidity, the photosynthetic rate decreased severely with the increase of LAVPD (Figs. 5 and 6). From these results it can be considered that the increase of leaf nitrogen content is not sufficient for increasing photosynthetic rate in a day, and that in addition to the increase of leaf nitrogen content the increase of root activity and the promotion of root system development by improving soil condition of root zone are essential for increasing the daily total of photosynthesis (Fig. 8).

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[in Japanese]

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Three levels of shading (70, 50 and 25% of natural light condition) were used in the field-grown spring wheat (cv. Haruyutaka) during three weeks before and after heading time in order to determine the difference in effects for time of shading on dry matter production, partitioning, and yield. Effect of shading during three weeks before heading. Dry weights of each part (ears, leaves, culms including leaf sheath and roots) decreased with decreases in light intensity (Fig. 1). As shading increasing, however, distribution ratio of dry matter increased in leaves and ears, but decreased in roots (Table 3), resulted in greater reduction in root dry weight. Total dry weights were 75, 52 and 40% of that of unshaded (light intensity=100%) in 70, 50 and 25% light plots, respectively. Leaf area and surface area of ears and culms were also decreased by shading (Fig. 1). The decreasing percentages of leaf and culm area, however, were lower compared with those of dry weights, because of increasing in area per unit dry weight (cm²/g) as shading increasing (Table 3). After shading treatments were stopped, crop growth rates (CGR) of shade imposed increased more than that of unshaded, mainly due to increasing in net assimilation rates (NAR) (Table 4). This was also accompanied with drastic increasing in dry weights of culms and roots, and NAR was closely correlated with their dry weights (r=0.998). Grain yields were reduced 15% significantly only by 75% shade (25% light plot) (Table 6). Effect of shading during 22 days after heading. Green area indices were not different except that of 25% light plot, but dry weights of ears, culms and roots decreased with decreases in light intensity (Fig. 2). The restricting light during the post-heading stage resulted in greater yield reduction than for the pre-heading stage. Yields were 88, 78 and 51% of that of unshaded in 70, 50 and 25% light plots, respectively (Table 6). CGRs and NARs during both shading periods decreased in parallel (r≥998) with decreases in light intensity in accordance with sigmoid curves. The saturation point of NAR was lower for the post-heading stage (at about 15 MJ/m²/day) (Fig. 3). It is interesting that root growth was very flexible in response to light intensity regardless of stages of plant development.

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The images of whole root system with regard to the growth direction of individual primary roots and their relationships to yield were examined using the improved cylinder sampling method. There was a proportional increase in the percentage of horizontally-growing primary roots with increase in yield up to about 500 g/m². However, with further increase in yield, the proportion of vertically-growing primary roots and the diameter of primary roots became larger. From above-mentioned results, it is suggested that the vertically-growing primary roots with large diameter are important for higher yield.

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In this paper, the relations between the seedling characters and the dry matter production were analyzed using 31 different seedlings. The results obtained were summarized as follows ; 1. The seedling age in leaf number and the ratio of dry matter weight to plant height were the useful parameters to estimate the character of seedling. The seedling character index (SCI) was calculated using following equation : (the seedling age in leaf number) × (the ratio of dry matter weight to plant height). The dry matter weight at each stage of growing and the heading date were significantly correlated with SCI (Fig. 2, Table 1). 2. The grain yield indicated positive correlation with the percentage of ripened grains, but negative correlation with the number of grains (Fig. 3). 3. The number of grains increased with the amounts of nitrogen in rice plant at the heading time and reached to 4.4 × 10⁴/m² in high nitrogen level. SCI indicated positive correlation with the dry matter weight but negative correlation with the nitrogen percentage content at the heading time. Therefore, the correlation between the number of grains and SCI was not significant (Fig. 4, Fig. 5). 4. The percentage of fully ripened grains to fertilized grains was determined by the ratio of the amounts of dry matter production to the number of grains and the dry matter partitioning ratio to the ear. The amount of dry matter production after the heading time and the dry matter partitioning ratio to the ear were correlated with the accumulated temperature for 40 days after the heading date (Fig. 6). 5. From these results, it may be concluded that the percentage of ripened grains was affected considerably, but the number of grains was not affected very much, by the character of seedling (Fig. 7).

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This experiment was conducted to clarify the relation between the process of root regeneration and changes in some chemical components in root-pruned teaplants (Camellia sinensis (L.) O. Kuntze cv. Yabukita). The growth of top and roots, and TAC (total available carbohydrate), total amino acid and nitrogen contents were investigated over about six-month period after the root pruning. About a half of root of one-year old plants were pruned in early September 1983 (Fig. 1). The top growth was prominently retarded by the pruning. The weight of top (including the mother stem) in the pruned plants was reduced to nearly 75% of that in the intact plants (Table 1). In contrast, the root growth was activated after the pruning. The weight of roots was markedly increased. especially in wite roots. At the 36th day after the pruning. the root of the pruned plants rather exceeded in weight that of the intact plants. The remarkable increase in the white roots on the mother stem was recognized within 36 days succeeding the pruning, while that on lignified roots required one month after the pruning. The percentage of the white roots in the treated plants was around 10% higher than that in the intact plants. Although the T/R ratio of the treated plants had been considerably raised due to the pruning, it returned to approximately the same level as that of the intact plants at the 26th day (Table 2). The pruning not only raised the TAC content, but the partition of the TAC to the mother stem and roots greatly increased (Figs. 3, 4). Furthermore, the pruning increased the partition of nitrogen to the mother stem and roots, in spite of a deterioration in content (Figs. 5, 6). The amino acid content in the treated plants showed a lower level as compared with that in the intact plants. The amino acid content of lignified roots greatly decreased following vigorous regeneration of roots (Fig. 7). The distribution of the TAC and nitrogen in the treated plants, however, approximately accorded with these in the intact plants after 187 days. The above results suggest that the root regeneration after the pruning in tea plants rapidly proceeds through active growth of white roots exceeding the growth in the intact plants. The translocation of some chemical components to under-ground parts and the accumulation there that were induced by the root pruning were considered to closely concern with the root regeneration. The retardent of the top growth following the root pruning was estimated to be induced by the translocation of substances to roots and vigorous regeneration of roots. To promote the root regeneration after the root pruning, treatments that maintain a proper level of hormons and relieve the deficit of photosynthate and nitrogen are necessary.

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