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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トウモロコシ自殖4系統およびそれらの間の雑種第一代4組合せを材料とし, 生育時期にともなって, 単位葉面積あたりの光合成速度がどのように変動するかについて検討した. 材料は1974年6月上旬ポットに播種し, 葉色が退色しないよう適宜追肥を行ない野外にて生育させた. 光合成速度, 蒸散量の測定は生育時期を追って播種後ほぼ1ケ月ごとに6月末, 7月末(絹糸抽出直前), 8月末に着生したままの活動中心葉について同化箱法により行なった. 測定は温度30℃, 光強度0.45cal/cm²/min (PAR), 大気中CO²濃度下で行ない, 光合成速度はCO₂濃度0.03%における値で示した. その結果, 生育時期が早い時の測定においては, 4組合せのF₁すべてにおいてその光合成速度は, better parentの値よりも明らかに高く, vigorの程度も大きかった. しかし, 生育が進むにつれて近縁同志のF₁では光合成速度にvigorがあらわれない場合が多く, 遠縁間のF₁には一時vigorが消失するがそれ以後再びvigorがみられた(第1表). 一方, 蒸散量についても光合成速度の場合とほぼ同じ傾向が認められた(第2表). しかし, 窒素含量と光合成速度の間には1, 2, の特定の場合を除いて相関がみられなかった. また, 光合成速度と蒸散量の間には各測定時期ごとに強い相関がみられた. これらの結果は, トウモロコシの光合成速度にみられるF₁ vigorは生育時期および組合せにより変動し, それらの変動をもたらす主要な要因は気孔の拡散低抗の変動にあると考えられた.

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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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小型で可搬型のスペクトロフォトメータをマイクロコンピュータに接続し, 原動機付油圧クレーン車と組み合わせて野外用移動分光計測システムを製作した. フォトメータは回折格子方式で400～1,200nmを連続走査し, 光電子増倍管とシリコン光電池で光電変換する. 50mm対物レンズで集光し, ファィンダで対象と視野範囲(1.1°×9.4°)を確認できる. 測定出力は対数増幅器を経て, 12ビットA/D変換器でデジタル化され, デスクトップ型マイクロコンピュータに読み込まれる. 測定部およびコンピュータの写真とブロック図を各々第1図と第2図に示す. また, 光学系と電気系の主な諸元を第1表に掲げた. このフォトメータを圃場上空数メートルの位置で下向きに保持するための補助装置(Platform)として, 第3図に示したような小型クレーン車を製作した. ブームの最大長5.8メートルで油圧で昇降・起伏する. ブームの先端には起伏角に拘らずフォトメータが真下を向くようなセンサ基台が取り付けられている. また, 高所からのフォトメータの較正用に, 1メートル四方の大型標準白板(第4図)を用意した. このシステムにより測定した水稲10品種の個体群からの反射スペクトルを第5図に示した. 野外でのテストの結果400nm～1,000nmの波長範囲では安定した測定ができるが, 1,000nm以上では光検知器の感度が落ちるためデータの信頼性がやや低下することが明らかになった. しかし, このシステムを使用することにより, 作物個体群の反射スペクトルを迅速に(走査時間約50秒), しかも圃場内に踏み込むことなく取得できる見通しを得た.

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可搬型で野外で容易に扱える分光反射係数計測システム(既報)を用いて, 最高分けつ期から登熟期における水稲個体群の反射スペクトルを波長域400～1,200nmで測定した. 小型クレーン車を利用することにより, 圃場での垂直下向き観測を実施した. 供試した材料は, 日本型, インド型及び日印交雑種を含む14の水稲品種である(第1表). 分光反射係数の測定後, 葉緑素計(富士フィルム)により各区の葉身クロロフィル含量(CHL:mg/dm²)を測り(較正図を第1図に示す), また, 抜き取りによって葉面積指数(LAI)を推定した. クロロフィルインデックス(CI:g/m²土地面積べース)はCHL及びLAIの積として求めた. スペクトルデータから緑(G:560nm), 赤(R:680nm)並びに近赤外(NIR:800～900nm)の各反射率を上記の三種の作物情報との相関関係を調ベ, 次の結果を得た(第2, 3表). 1. CHLと単独で最も相関の高かったのはG反射係数で, 相関関係(r)は-0.714であった(第2図). 2. NIR/R (バイバンド)比とCIとの相関関係は, NIR/R比とLAIとの相関関係よりも強い傾向を示した. 3. CIと最も高い相関係数を示したのは, NIR/G (バイバンド)比であった(r=0.816) (第3図). 以上の結果から, 野外の分光反射係数, 特に可視～近赤外域の情報では, LAIないしCHLを推定するよりも両者の積のCI(単位土地面積当たりクロロフィル量)を推定する方が, 精度が良くなることが示唆された. また, CIを推定するパラメータとしてはNIR/G及びNIR/Rが良好だったが、NIR/Gの方が若干有利であると思われた.

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可搬型スペクトロフォトメータ(既報)を用いて水稲14品種の個体群分光反射特性を測定した(前報). 本報告では, このとき得られた波長400～980nmのスペクトルデータと, 葉身・茎・穂の乾燥粉砕物をN-Cアナライザによって分折した窒素含有率データとをつき合わせて相関分折を施すことにより, 水稲窒素量を野外分光測定によって推定することの可能性を検討した. 1. 葉身窒素含有率(LNC), 地上部窒素含有率(TNC), 単位土地面積当たり地上部窒素量(TNA), 同葉身窒素量(LNA), およびLNAの自然対数値の各々について400nmから980nmまで20nm間隔30波長反射係数との相関係数を計算した(第1表). 2. LNAおよびIn(LNA)と赤色～遠赤域反射係数が比較的大きな負の相関関係を示した. LNCとLNAとを較べると, 後者の方が可視域反射係数との相関係数が高く, またTNC, TNAは各波長反射係数との相関係数は極めて低かった. 3. 2ないし3波長反射係数を用いて, ln(LNA)を推定する重回帰モデルを設定し, 30個の波長を総当たり式に調べ, 重相関係数の高かった組み合わせを第2表に示した. 2変数では620nmと760nmが, そして3変数では400nm, 620nm, 880nmの組み合わせで最高の重相関係数(0.855および0.868)が得られた(N=140). データを2分して一方から重回帰モデルの各係数を推定し, この式を残りのデータに適用した. この時の重回帰分折の結果を第3, 4表に各々示す. 実測されたln(LNA)に対する推定値をプロットした図が, 第1, 2図である. 第1図は620nmと720nmを用いた場合で, 第2図は400nm, 620nm, 880nmの3波長を用いた場合を示した. 実測値と推定値間の相関係数は, 各々0.874および0.894で多くの品種の異なる生育時期をこみにした結果としては, かなり精度の高い推定が行われた. 第3図は第1, 2図と同様だが, 重回帰モデルの従属変数として対数をとらないLNAを用いた場合の結果を示した. 高い窒素レベルで推定誤差が大きくなり, 両者の関係が直線的ではないことが判る. 4. 以上の結果より, 赤・紫および近赤外域の波長帯を利用することにより, 野外分光反射係数から水稲葉身の窒素量を非接触計測することが実現の可能性をもつと推察された.

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16品種の水稲およびソルガム幼植物個体群について低光エネルギー下における光-光合成関係の光エネルギー転換効率(E)および暗呼吸速度を比較し, 以下の結果を得た.1. 水稲幼植物個体群の光-光合成関係においてKok効果は必ずしも認められなかった. 2. 標肥下で育て, 十分な葉面積をもった水稲幼植物個体群の大気中30℃におけるEの値には, 有意と思われる品種間差は認められなかった. また, 低酸素濃度下における水稲幼植物個体群のEは, 大気中のEに比べ明らかに高く, ソルガムのそれよりも高かった.

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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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主要生育段階を基準にして, 栄養器官と生殖器官の分化と生長の動的なパターンによるトウモロコシの生育相の概念モデルを提案した. 主要生育段階は品種ならびに播種期を異にしても変わることがなく, 基準として利用できる. モデルの骨格は, 第1図に示すように, 葉原基分化過程における同伸葉・同伸分げつ関係により形成される主茎ならびに一次分枝と7主要生育段階とからなる. その結果, トウモロコシの全生育期間は4生育相に分けられる. 第一相は出芽期から雄穂分化期までの期間で, 葉原基の分化によって特徴づけられる. 第二相は雄穂分化期から絹糸抽出期までの期間であり, 葉原基の生長と穎花原基の分化という質的に異なる過程が並行して進む. この相はさらに3つの期間に細分することができる. 第一期は雄穂分化期から雌穂分化期までの期間であり, 最上位側枝が花芽誘導に至るまでの準備期間とみなしうる. 第二期は雌穂分化期から絹糸の伸長開始期までの期間であり, 穎花原基の形成期間である. 第三期は絹糸の伸長開始期から絹糸抽出期までで, 上位の節間伸長と絹糸の突出とにより特徴づけられる. 第三相は絹糸抽出期から澱粉蓄積始期までの期間で, 葉原基の生長と穎花の原基の生長とが競合する. この期間は品種とか播種期を異にしても変異はほとんど見られない. 第四相は澱粉蓄積始期から生理的成熟期までの期間で, 穎花の生長により特徴づけられる.

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前報告のトウモロコシの生育相の概念モデルから提示された形態的・生理的な構成要素のうちから, 生育各相を特徴づける形質を検出し, それらの品種間差異を明らかにしようとした. 1. 生育各相の期間の長さを有効積算気温で評価して解析すると, 全生育期間の長短は, 出芽期から雄穂分化期までの第1相(X₁), 雌穂分化期から絹糸伸長姶期までの第2相・第2期(X₂), ならびに澱粉蓄積始期から生理的成熟期までの第4相(X₃)の3変数によって次式で予測できる. Y(degree-days)=465.9+1.21X₁+0.77X₂+1.12X₃(R²=0.827) 2. 第1相の有効積算気温は, 雄穂分化期の展開葉数別にみると, 葉展開速度と直線的関係にあり, また葉展開速度は葉原基分化速度に密接に関係する(第1, 2図). 葉原基分化速度には品種間差異が認められ, 15.3-20.0(degree-days/leaf primordium)の変異を示す. 3. 第2相・第2期の有効積算気温は穎花原基分化速度と直接的関係を示す(第3図). 穎花分化速度には, P3422の0.13(degree-days/floret primordium)からムツミドリの0.31(degree-days/floret primordium)までの品種間変異が認められる(第2表). 4. 第4相の有効積算気温は, 導入品種では粒の生長速度とほぼ直接的関係を示したが, 日本品種ではその関係は明瞭ではない(第5図). 粒の生長速度は粒重と相関関係をもち, XL1214の0.640(mg/degree-day)からムツミドリの0.944(mg/degree-day)までの品種間差異を示す(第2表). 5. 以上の結果から, 葉数, 穎花数, 粒重などの形態的形質から算出される葉原基分化速度, 穎花原基分化速度, ならびに粒の生長速度はトウモロコシの生育期間を決定する生理的形質とみなされる.

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栽植密度を異にしたときのダイズの子実収量とその構成要素に及ぼす正方形植えの効果をみるために, 6品種を供試し, 1984, 85年の2年間試験を行った. 両年とも栽植様式と栽植密度の間に相互作用が認められ, 標準密度区と疎植区では正方形植えが増収となり, 密植区では長方形植えが増収となった. 標準密度区での6品種の平均値でみると, 正方形植えは1984年が30.7kg/a(8.4%増), 1985年が32.7kg/a (11.4%増)となったが, 増収程度は品種間で大きく異なった. 子実収量の栽植様式と栽植密度に対する反応は, 一莢内粒数や100粒重に比べ, 個体当り莢数, 特に分枝莢数の反応に強く依存していた. 個体当り分枝莢数を分枝数と一分枝莢数に分割したとき, 標準密度区と疎植区では正方形植えで分枝数が増加し, 密植区では長方形植えで一分枝莢数が増加したことがわかった. このように, 栽植密度によって正方形植えの効果が植物体の器官で異なることは, 与えられた生育空間に対する分枝の反応能力と関連があるものと推察された. これらの形質では, 品種と栽植様式, 栽植密度の間に相互作用があり, 生育空間に対する反応は遺伝的に異なることがわかった.

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チャ越冬葉の低温による光合成阻害部位を解析するために, a)ポッット植えの1年生苗を温度制御できるチャンバーに入れ, 冬季間, 昼/夜温;5/10℃(自然光)で育て, ほ場で生育した茶樹と光合成能を比較し(第1図, 2図), b)また, 明下(12klx), 12℃の低温処理が光合成能に与≠える影響を検討した(第3～5図, 第1表). 2つの温度処理実験の結果, 光-光合成曲線の初期勾配と光飽和のヒル反応活性は光合成速度と対応して変化したが, 可溶性タンパク質とフラクション-1タンパク質量, リブロース-1, 5-ジリン酸カルボキシラーゼ活性およびCO₂-光合成曲線の初期勾配は光合成速度の変化とは対応しなかった. つぎに, 低温処理した葉から葉緑体(タイプC)を単離してその光化学反応を測定した. 系I活性(Asc/DPIP→MV)は対照の90%の活性を保持していたが, 系II活性(H₂O→PD→MV)は約70%に低下した(第2表). 以上の結果から, 光合成の低温阻害は光合成明反応, とくに系IIの抑制によることが示唆された.

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チャ葉の光合成阻害における光と低温の相互作用について検討した. 他の葉で遮断されている越冬葉の光合成速度は遮蔽されていない葉よりも高く(第1表), 低温阻害に光強度が関係することが予想された. そこで, 葉ディスクまたは個葉を用いて明下(12klx), 12℃の低温処理を2日間行なうと, 光合成速度と光飽和のヒル反応活性はともに対照(20℃)の60%に低下した. そのとき, 光強度を25%遮光すると, これらの低下の程度は小さかった(第2図). また, ほ場で生育している茶樹を冬季間, 寒冷紗で遮光しても, 光合成速度は高い値で推移した(第4図). これらの結果から, チャ越冬葉の光合成低温阻害は光障害により起きることが示唆された. 以上の結果は人為的な遮光処理によりチャ越冬葉の光合成低温阻害を軽減できることを示唆している. 実際, 寒冷紗による遮光で越冬葉の光合成は遮光期間中も除去した後も高く保たれ, 一番茶の収量の増加も認められた(第5～7図).

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イネ分離種子根を, 二培地法により無菌的に培養した. 蔗糖と植物ホルモンを胚盤から与え, 根をMSの無機塩培地に入れた. 12.5%の蔗糖濃度が, 根の生長に好適であった. IAAとフィガロンほ, 低位または中位の濃度で根の生長を促進したが, 高濃度でほ阻害した. フィガロンの阻害作用は, IAAより顕著であった. カイネチンとベンジルアデニンは, 高濃度で特に著しく根の生長を抑制した. しかし, わずかな促進効果は, 非常に低い濃度(10^-10M)で得られた. GA₃とGA₄でも, 比較的低い濃度で, 生体重・一次根長・全根長・側根数において促進効果が得られた. この場合でも, 高濃度では根の生長を抑制した. 得られた結果は, イネ分離根における植物ホルモンの制御作用を研究するために, 二培地法が好適であることを示している. 特にこの方法は, 植物体において, 茎葉から移動する植物ホルモンの根の生長制御に対する役割を明らかにするために有効である. これらの研究成果は, 関係文献に見られる実験結果とともに論議された.

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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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