継代培養にチアミンを要求しないイネカルスの系統を2品種のイネから得ることができた. ここでは品種,愛知旭から生じたチアミン要求性および非要求性カルスについて検討した. 抗チアミン物質を用いた実験から,このカルスはチアミンを自己生産するために,外部からのチアミン供給を必要としないことが示唆された. 肉眼あるいは光学顕微鏡または走査電子顕微鏡などによる観察結果から,これらのカルスでは茎葉と不定根の分化の決定因子としてチアミンが重要な役割をもつことが示唆された. また,カイネチンによるイネカルスの分化制御にチアミンが関与することが示された.

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Experiment I. The author investigated the influence of the alternate cutting of the primary rachis-branch on the protein content in the brown rice and some agronomic traits using the japonica and the improved semi-dwarf, high-yielding indica varieties. The results are as follows; 1. In all varieties, "the product of the percentage of ripened grains and the weight of 1000 grains" increased by this treatment. In this occasion, the increasing rate was much higher in the improved indica varieties than in the japonica variety. 2. In all varieties, the protein content in brown rice increased by this treatment. Experiment 2. The author compared some agronomic traits between cv. Koganemochi and its mutant whose greatest characteristic was partial sterility. It was very convenient to use this for this research. 1. There was no significant difference in the heading date, the number of panicles per hill, the number of spikelets per panicle, and the culm length between the two. 2. 1000 grains weight of the mutant and the original variety was 23.9 g and 22.0 g, respectively. The percentage of ripened grains was 94.5% in the original variety and 26.8% in the mutant. 3. Grain weight and the ammount of protein content in a grain increased more rapidly after flowering in the mutant than in the original variety. 4. The percentage of the protein content in the brown rice was always higher in the mutant than in the original variety during the ripening period. The percentages of the protein content of the mutant and the original varicty at the time of maturity were 10.56% and 7.33%, respectively. From the results of these experimcnts, it was assumed that the percentage of the protein content in brown rice became higher by the limitting of the number of the ripening grains per panicle under no restriction of dry matter production in rice plant.

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Nitrogenous nutrient is one of the major element to regulate plant growth, however little is known on the plant hormones relationships in the mechanisms of growth regulation with nitrogenous nutrient. Present experiment was conducted to study ethylene relationships in the regulatory mechanism of nitrogenous nutrient in the growth of rice plant. Growth rate, nitrogen content and ethylene evolution in leaves under different nitrogen levels were examined. The results obtained were as follows. 1. The higher the content of nitrogen in leaves and the greater the plant growth, the less was the ethylene evolution in rice leaves. 2. Very clear positive correlation was found between the nitrogen content in the leaves and the growth rate, while high negative correlation was detected between nitrogen content in leaves and ethylene evolution from leaves. 3. Therefore, a fairly close negative correlations were observed between the ethylene evolution from leaves and the rate of growth. Based on those results, it seems probable that the reduced ethylene evolution from leaves under high nitrogen condition may play an important role to explain growth promotion by nitrogen supply in plant.

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トウモロコシの第1雌穂より上部の葉をその登熟期間に直立させ,その影響が,異なる気象条件(特に日照条件)でいかに変化するかを,1974,75,76年の3年間の結果から検討した. 品種は3年間アズマイエローを供試し,76年にはこれにホクユウを加えた. 栽培密度は,74年には,3000,6000,9000,75年には,4000,6000,8000,10000,76年には,6000,9000,12000本/10aであった. 栄養生長期間の日射量には3ヵ年ともほとんど差がみられなかったが,登熟期間には差が大きく,1970～76年の平均値に対して,74年は88.8%,75年は111.8%,76年は77.2%であった. 子実収量は登熟期間の日射量に大きく左右され,75年に最高で,76年には最低,74年は両年の中間であった. 葉身直立姿勢の子実収量への影響は低収年に大きく,多収年にはほとんどみられず,中間年には密植区でのみ見られた. 葉身直立姿勢の子実:茎葉重比への影響は,その値の低い場合,すなわち,トウモロコシが光条件に恵まれずその子実生産能力を十分に発揮できないような条件で,大きく現われていた. 単位面積当りの粒数をみると,葉身直立姿勢の影響の見られなかった75年にはかなり多く,その影響のみられた76年にはかなり少なかった. 葉身直立姿勢は粒数を増大させており,これが同化産物の子実への転流の向上に寄与したものと考えられた. 葉身直立姿勢の処理直後に測定したLAIの値には,各年次とも葉身姿勢処理間で差が認められず,栄養生長量には差がなかったものと考えられた. したがって,葉身直立姿勢による粒数の増大は,光合成産物の不足による雌穂不稔の発生の危険の大きい絹糸抽出期後の約3週間に,受光態勢が改善されたことで光合成産物の不足が抑えられたことによると判断された. 葉身直立姿勢の効果に年次間差のあったことから,その効果の発現には日射量が関係し,少照年次には比較的低栽植密度でも現われるが,多照年次にはかなり密植条件でなければ現われないものと考えられた. 以上から,トウモロコシにおいては,葉身が直立していることは,夏期に日照の不足しやすい地域での収量安定,あるいは密植条件での収量向上にとって,重要な形質であると推察された.

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Distribution of P, K and Mg on the ventral and dorsal side of the rice kernels was investigated at 8, 16 and 30 days after flowering. The obtained results are as follows; 1. 8 days after flowering 0n the dorsal side: Mg and P were distributed markeeily in the aluerone layer. They were distributed more concentratedly in the pericarp (especially in the vascular bundle) than in the starch cell layer. K was distributed throughout the pericarp, aluerone layer, and vascular bundle and was less concentrated in the starch cell layer than in the pericarp, aluerone layer, and vascular bundle. On the ventral side: The results were almost the same with that on the ventral side. But K was distributed more concentratedly in alueronelayer than that on the dorsal side. 2.16 days after flowering 0n the dorsal side: Mg and P were distributed markcdly in the aluerone layer. Mg in starch cell layer was distributed more conccntratedly than that of 8 days after flowering and was distributed in pericarp, too. P was not almost distributed in pericarp. K was distributed throughout the rice kernel including the starch cell layer. On the ventral side: The results were almost the same with that on the dorsal side. But Mg, P, K, in aluerone layer were distributed more concentratedly than in dorsal-aluerone layer. This tendency was very peculiar in K. 3. 30 days after flowering Both on the two side: P, Mg and K were concentrated in aluerone layer. K (markedly) and Mg were distributed in preicarp, but P was not almost distributed in pericarp.

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In order to obtain basic data on the effective application of artificiallights and colored transparent shelters to plant cultivation, effects of composite lights with a dominant energy in the blue (B), green (G), red (R) and blue and red (BR) on photosynthesis of the following crop plants were investigated: tomato (Lycopersicum esculentum Mill.), sweet pepper (Capsicum annuum L.), strawberry (Fragaria grandiflora Ehrh.), cucumber (Cucumis sativus L.) and squash (Cucurbita moschata Duch.) as vegetable species; and peach (Prunus persica Sieb. et Zucc.), grape (Vitis aestivalis Micahux) and satsuma mandarin (Citrus unshiu Mark.) as fruit tree species. At an irradiance 50 W m^-2 in the waveband 400-700 nm, which gives a rate of about 1/3 of the maximum photosynthesis, the photosynthetic rate relative to white (W) light was generally higher in R, slightly lower in BR and B and clearly lower in G for both species of vegetables and fruit trees. This difference among the light qualities was negligible at irradiances close to the light-saturation point, but extended with decreasing the irradiance. Photosynthetic efficiency, which was expressed in terms of photosynthetic rate at the original slope of light-response curve, was raised with increasing the energy in the red region when the efficiency was shown for unit energy incident (400-700 nm), while the efficiency for unit quanta incident (400-700 nm) was not much different among the light qualities. A possibility of the prcsence of enhancement effect for photosynthesis was found in most of the composite lights, assuming that no enhancement effect is present in G light. The enhanced part, however, did not exceed more than 10 percent even in W light in the average of the species. From the data of the present study and the literature, it was concluded that red light energy is the most important to photosynthesis and that the relative effectiveness of composite lights on photosynthesis can be roughly estimated by means of the sum of the products of the averagc action spectrum by the energy distribution of each light, or by the quantum flux density incident in the waveband 400-700 nm of each light.

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The ultrastructure of small vascular bundles of the 8th leaf blades in rice seedlings was examined with the electron microscope. 1. In the parenchyma sheath cells the chloroplasts have a centrifugal position, whereas the mitochondria have a centripetal position. The phloem is bounded by a single layer of thick-walled parenchyma cells, which differentiate into the mestome sheath cells in the upper leaves. The thick-walled parenchyma cells have the plastids with starch granules, mitochondria and dictyosomes. The suberized lamellae are not detected in the walls of these sheath cells. 2. The protophloem sieve elements and companion cells locatcd abaxially within the vascular bundles show an apparent degeneration in the expanded leaf, but the degeneraion is not observed in the elongating zone of the folded leaf. Thus, the protophloem may degencrate during the leaf emergence and ceases to function after leaf expansion. 3. Late-formcd metaphloem sieve elements are narrow and thickwalled, but the associated companion cells are wider than the sieve elements. The metaphloem sieve elements have the P-type plastids and a small amount of mitochondria and endoplasmic reticulum. The rnetaphloem companion cells contain many mitochondria and endoplasmic reticulum, and often contain osmiophilic globules. Ultrastructural features of the metaphloem parenchyma cells are the same as the companion cells. 4. The distribution of plasmodesmata in transections of the small vascular bundles has been determined. The plasmodesmata occur in the outer and inner tangential walls of the parenchyma sheath cells. The late-formed metaphloem companion cells are connected by numerous plasmodesmata with adjacent parenchyma cells of the metaphloem and metaxylem, and also with the thick-walled parenchyma cells respectively. The companion cell and the sieve element are connected by plasmodcsmata which are branched on the companion cell side. The data support the view that photosynthate moves through a symplastic pathway from mesophyll to the metaphloem sievc elements. The following pathways are suggested.[table]

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Structure of protein bodies in the seeds of 16 species (rice, buckwheat, wheat, Japanese black pine, sesame, Brazil nut, sunflower, water melon, soybean, pea, almond, cashew nut, peanut, hazelnut, walnut and pecan) was studied with semithin sections of aldehyde fixed and GMA embedded tissues. The occurrence of globoid was significantly different among tissues of different species. Globoid size and frequency (number per unit area of section) were estimated to clarify their relationships with total phosphorus content in these tissues. The size and frequency of globoid seems to associated with the difference in phosphorus content. The difference in the appearance of globoid, which is found among various tissues in the seeds or various regions in the tissues suggested the unequal distribution of phosphorus within the seed. In comparison with the seeds of rice, cotton and castor bean in structure of the protein bodies, it was indicated that the difference in protein content in the protein bodies corresponded with the mass of the proteinous regions, that is, protein matrix and crystalloid.

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最近北海道中央部長沼地力に発生した粗皮塊茎の生理的発生要因について検討を加えた. バレイショ,メークイン種の塊茎は周皮がラセット状の粗皮を形成し,褐色のウロコ状となり品質低下を来すことがある. 生育中の塊茎が高温(30℃前後)に遭遇すると二次生長を起し,その結果塊茎の内圧が局在し,厚化した周皮に割れ目を生ずる. これが周皮全体に網目状に発達し,こまかく割れた周皮の残片が塊茎表面に付着し,褐変してラセット状の粗皮となる. これらの周皮細胞はペクチン,ヘミセルローズなどの含量が高く,これが周皮片の剥離を阻害し,ラセット形成の一因となる. このような二次生長にともなうラセット形成は器官培養法によってつくられたin vitroの塊茎においても確められた. また二次生長の発生の少ない男爵薯ではラセットの形成が少ないことも確められた.

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水稲根系を構成する発根節位の異る根群間の生理機能の特徴を比較するために,地上部の遮光処理がそれらの根群の呼吸とアンモニア吸収活性に及ばす影響を調べた. 葉と根の出現・伸長の規則性を利用してあらかじめ分級した第1節以下,第2・3節,第4・5節および第6節から出現・伸長した1次根(節根)をもつ第9葉期の水稲を用いた. 遮光は最上位節根(第6節根)の出現・伸長を遅延させ,遮光解除はそれらを促進した. また,これらの処理は,上位節根(第4・5節根,第6節根)の乾物重・窒素含有量に対しても同様の影響を与えた. 酸素吸収力と窒素吸収力の両者はともに,最上位節根でもっとも高く,下位の節根になるにしたがって低かった. 遮光によるこれらの活性低下は最上位節根でもっとも小さく,中位の節根(第2・3節根,第4・5節根)でもっとも大きかった. 最下位節根の窒素吸収力の低下は酸素吸収力の低下に比して顕著であった. 各節根の酸素吸収力と窒素吸収力との間に高い正の相関が認められた. その回帰係数は,より上位の節根(第4・5節根,第6節根)とより下位の節根(第1節以下の節根,第2・3節根)とで異り,後者で大きかった. 酸素吸収力に対する窒素吸収力の比(窒素吸収効率)は最下位節根でもっとも大きく,上位の節根になるに従って小さくなった. 窒素吸収効率に対する遮光と遮光解除の影響は,上位の節根(第4・5節根,第6節根)に比較して下位の節根(第1節以下の節根,第2・3節根)でより大きくあらわれた. これらの結果にもとづき,水稲の生長における根系の役割について若干の考察を行った.

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Investigations have been carried out to determine the lipid content and the fatty acid composition of lowland non-glutinous rice kernel of one line for Sake brewing and three varieties at intervals of 10 days from dough ripening (20 to 25 days before full ripening) to over ripening (35 to 45 days after full ripening). From dough ripening to full ripening, the lipid content and the fatty acid composition varied widely. The lipid content decreased especially until 10 or 15 days before full ripening on dry basis and decreased after increasing until 3 or 15 days before full ripening in 1000 kernels. As to the fatty acid composition, the myristic acid, olelic acid, and linolenic acid content increased and the palmitic acid, stearic acid, and linoleic acid content decreased. After full ripening, the lipid content had a tendency to decrease slightly on dry basis and in 1000 kernels. However, the fatty acid composition was little varied. With respect to each of one line and three varieties, the lipid content on dry basis showed significantly positive correlations with the palmitic acid and linoleic acid content and negative correlation with the oleic acid content. The oleic acid content showed significantly negative correlations with the palmitic acid and linoleic acid content.

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Our primary objectives in this study are to make clear the histological process of transformation of lemma and leafy-organ in proliferated spikelets to the foliage leaf in rice. For this purpose, an X-ray mutant of rice, which was selected from plants two generations after 20 kR X-ray irradiation of dry seed of Japonica cultivar, 'Reimei', was used. In this mutant spikelets are proliferative, changing from Spikelet-type (S-type) to Pistil-type (P-type) to Leafy shoot-type (L-type) as seasons change. Lemmas of S-type proliferation and P-type proliferation were the same on their shapes as normal lemma, but leaf-like organ in the leafy-shoot of L-type proliferation was almost the same as the first leaf on its shape. Leafy-organ above the fifth from the base in the leafy-shoot of L-type proliferation differentiated to blade and sheath. The number of longitudinal veins in this mutant lemmas and leafy-organ was more than that in normal lemma; the number in S-type proliferation was about seven, that in P-type proliferation was seven to nine, and that in L-type proliferation was nine to eleven. Transverse veins were frequently observed in P-type proliferation and L-type proliferation. In the outer surface of S-type lemma, tubercle formation was poorly expressed, and, wart-shaped protuberances and many papillae differentiated in place of the poorlydeveloped tubercles, and, comb-shaped undulations of tangential cell wall in the outer epidermis also was poorly expressed, changing to wave-shaped one as that of the tangential cell wall in the first foliage leaf epidermis. In P-type and L-type proliferations, rows of long-cell and short-cell system differentiated instead of tubercles in their lemma surfaces. In contrast with normal lemma, lemmas and leafy-organs in all of proliferations have cork-silica cell pairs, and those of P-type and L-type proliferations have stomata in their outer surfaces respectively. Leafy-organ of L-type proliferation has lysigenous aerenchyma in its inner tissue. Thus, lemmas of S-type and P-type proliferations, and leafy-organ of L-type one have one of the characters expressed only in foliage leaves. In this study, light microscopic observation on the surface of lemma and leafy-organ of S-type, P-type, and L-type proliferation showed that the epidermal system thereon was transformed to one closely resembling to that of rice leaf surface.

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An investigation was made concerning the influence of nitrogen top-dressing at a later stage of growth on the leaf photosynthetic activity in some newly improved rice varieties of Korea obtained by indica-japonica crossing. The results are as follows: 1. Considerable varietal differences were observed in the apparent photosynthetic activity on leaf area basis determined by oxygen evolution. The Milyang lineage and the Iri lineage showed the highest activity, the other varieties being in the order of Suweon lineage, the japonica (Somewake), and the indica (T-136). The early-maturing varieties showed a tendency to have somewhat higher photosynthetic activity than the later-maturing varieties. 2. Nitrogen content on leaf area basis was lower in the indica-japonica hybrid varieties than in the japonica variety. 3. The nitrogen top-dressing promoted photosynthetic activity in all the varieties, but the degree of response differed from variety to variety. 4. Photosynthetic activity on leaf nitrogen basis also showed varietal differences, regardless of the nitrogen top-dressing. 5. Furthermore, the photosynthesis-promoting effect of increased leaf nitrogen content duc to top-dressing was generally higher in the indica-japonica hybrid varieties than in the Japonica or the indica. 6. By nitrogen top-dressing both NAR and leaf area development were enhanced, leading to increased CGR. This trend was especially clear in the indica-japonica hybrid varicties.

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In order to reconfirm the influence of the producing places especially meteorological conditions upon the chemical components and the disposition structures of starch-cells in the cross section of rice kernels, chemical analyses and observations were made on specimens of the "Koshihikari" variety (the "nanshitsu-mai" type), lowland rice plants cultivated on a standard basis at a lowland rice field attached to the Fukui University as well as those supplied from the lowland rice crop situation experiment stations, Ministry of Agriculture, Forestry and Fisheries of Mito, Chiba, Mie, Miyazaki and Nagaoka for the 4 years between 1975 and l978. It was shown from the above inquiry that some difference in the producing places especially in meteorological conditions serves to produce a difference in the chemical components and the disposition structures of starch-cells in the cross section of rice kernels even on the same variety, that a line of demarcations is to be drawn in this respect, namely in the difference of (P) (Protein-N/Crude starch (each in dry basis %) × 100) and (T) (Soluble-N+Total Sugar (each in dry basis %)), between specimens from soft and hard-textured rice producing areas, that meteorological conditions, especially amount of solar radiation, sunshine hours and air temperature, during each 5 half decades before and after heading stage, exert considerable influences, and that meteorological conditions, especially the sames as above, during 2 or 3 half decades after heading stage, exert great influences upon the disposition structures, while originally it forms the essential characteristic of a rice variety. It was revealed that meteorological conditions have a serious effect-too serious to be ignored after all. Our finding served to point to the identical trend as our reports so far made on other varieties, thus reaffirming the truth of our reports hitherto made.

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The formation of lateral roots in rice plants was examined in relation to the diameter of the crown roots on which they developed. The crown roots were classified into the followilng three types according to their acropetally decreasing rate of diameter; i.e. the crown roots of the low-(A-type), the intermetdiate- (B-type) and the high-(C-type) decreasing rates, respectively. At the lower shoot-units, the A-type roots were mostly common, while towards the upper shoot-units, the proportion of the number of each type roots varied, changing abruptly at about the IX-th shoot-unit, and above it the B-type roots and especially the C-type roots predominated. The time of crown root cmergence on the IX-th shoot-unit coincided with the panicle differentiation stage of the plant. The number oflaterals formed per unit crown root length was more in the C-type roots, decreasing successively in the B- and A-type roots. On the contrary, the length of the laterals showed a reverse tendency, being longer in the A-type roots and decreasing in the order of the B- and C-type roots, respectively. From the result mentioned above, the numerical density of laterals as well as their elongation appeared to be closely related to the changes in diameter of the crown roots ton which they were formed.

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Rice plants develop the fibrous root system which consists of several sets of numerous primary roots initiating from each stem node. There is a definite correlation between leaves and roots in their emergence and development; when the (n) th leaf of a stem is developing, a set of primary roots emerges from the (n-3) th node of the same stem. By using this rooting habit, relations between the growth of roots initiating from the different nodes were investigated with special reference to the nitrogcn movement from shoots to roots. Roots developing during the period of the 9th leaf development were designated as the roots from the 6th node (6th nodal roots) and they were separated from those emerging from the other nodes by tying up into a loose bundle with a fine string of nylon just before the emergence of the 10th leaf. Similarlyr, the roots emerging during the development of the 8th and 10th leaves were separated and designated as the 5th and 7th nodal roots, respectively. For more than 2 weeks prior to the start of experiment, plants were kept in the Kasugai's culture solution containing ¹⁵NH₄⁺ as a tracer. At the beginning of growth of the 6th nodal roots (Day 0 of experiment), plants were transplanted into a culture solution without tracer (CS-plant) or into tap water (W-plant), and the process of growth of the 5th, 6th, and 7th nodal roots was examined for 15 days thereafter. The number of the 6th nodal roots increased 2ts the 9th leaf blade elongated and expanded, then reached maximum at Day 7 when the 7th nodal roots began to emerge. Total length of the 6th nodal roots increased throughout the experimental period. The root length of W-plant exceeded that of CS-plant. The maximum increasing rates of number and of total length of the 6th nodal roots were found during the period from Day 2 to Day 4 and from Day 4 to Day 9, respectively. In a set of the 6th nodal roots, the variation range of root length expanded markedly during the period from Day 4 to Day 7, and the percentage of the primary roots having branches also increased eminently. Dry weight of the 6th nodal roots increased progressively during experimental period in both CS- and W-plant. On the other hand, total nitrogen and ¹⁵N content of the 6th nodal roots increased up to Day 9, then decreased. Absorption of nitrogen from nutrient solution continued for the first 7 days of the experimental period, therefore, the total amount of nitrogen fixed in the CS-plant increased during this period, while the amount was kept constant throughout the experimental period in W-plant. In both CS- and W-plant, however, total nitrogen and ¹⁵N content of the 5th nodal roots ceased to increase on Day 4 when those in the 6th nodal roots began to increase. Similar relation between 6th and 7th nodal roots was found on Day 9 in CS-plant and on Day 11 in W-plant. From these results it is likely to be considered that nitrogen supply from shoot to growing roots terminated at the onset of development of the new set of roots emerging from the nearest upper node. It is conceivable that the growth of nodal roots largely depends upon the nitrogen supplied from shoot rather than upon the nitrogen absorbed from culture solution.

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落花・落莢は冷害時における大豆の収量減をもたらす最も重要な現象の一つであり,開花前の低温に最も敏感である. 本試験は低温下における落花・落莢に対する抵抗性を高める物質を見出すために行った. 種々の化学物質を供試してその結莢におよばす効果を検討した結果,B-995は低温下での結莢を高める効果のあることを見出した. B-995について,さらに低温処理の時期と散布時期・散布濃度・散布回数を組合せて効果を検討した. 開花前の低温処理下においてはB-995散布が莢数を増加させ,その効果は低温に敏感な花芽の発達のステージで顕著であった. 結莢を高める最も効果的なB-995の投与は1000ppmの水溶液を低温処理開始時前後に5日間隔で2回葉面散布する様式であった. 開花後の低温処理ではB-995の結莢性促進効果が認められない. 適温下の場合は散布時期・散布濃度・散布回数にかかわらず結莢におよぼす効果は認められなかった. 矮化と結莢の関係から,開花前の低温処理下では茎長の抑制と莢数の増加が対応した関係がみられたが,適温下では茎長が短縮されても莢数の増加はみられない. これらの結果から,B-995が低温下では栄養生長と生殖生長に関与しているホルモンないしホルモン代謝に関与している物質の調節に何がしかの役割をはたし,結果的に生殖生長を優位に保ち,莢数増加をもたらしたものと考えられる.

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Photosynthetic activity measured by O₂ evolution and other physiological characteristics such as content of total nitrogen, soluble protein, fraction I protein and chlorophyll (a+b) were investigated in the developing 9th leaf of rice grown under conditions different in air-temperature, light intensity or nitrogen supply. The results obtained are as follows: 1. When the leaf blade emerges out from the preceding leaf sheath, the quantity of fraction I protein increases most rapidly as compared with other leaf constituents. 2. High temperature given during leaf expansion increases photosynthetic activity as well as the content of soluble protein, of fraction I protein and of chlorophyll (a+b). However, high temperature gives no effect on these physiological characteristics after the leaf has attained its final size. 3. Both photosynthetic activity and the content of various leaf constituents increase with increasing nitrogen supplied. Under the same level of nitrogen supply, fraction I protein synthesis is subject to the greatest influence of light intensity, and the transformation from absorbed nitrogen being inhibited by low light intensity. 4. Although considerable amount of total nitrogen and soluble protein are accumulated in the non-emerged part of leaf blade, little amount of fraction I protein is contained with a very low photosynthetic activity. 5. Variation in the photosynthetic activity of a rice leaf during its development (0-12 days after leaf emergence), inducing the effect of environmental conditions, shows the closest curvilinear correlationship with the content of fraction I protein in the leaf, among various leaf constituents. Thus, the content of fraction I protein which is most rapidly synthesized during the leaf development, seems to be the most important limiting factor for the photosynthetic activity of a leaf.

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水田はイネ,雑草,ソウ類,土壌生物,土壌,田面水より構成された1つの生態系と考えることができる. 著者らは,この系の動態,これに及ばす環境要因,圃場管理の影響を,炭素の循環の面から明らかにすることを目的として本研究を開始した. 本報告では田面とそれに接する気層との間のCO₂交換の日変化,その季節的推移,ならびにそれらに影響する要因について検討した. 主要な結果は次の通りである. 1. 湛水期間を通し,夜間には田面水から大気に向けてのCO₂の放出がおこる. 日の出後時刻のすすみに伴い,CO₂放出量は減少し,イネの生育初・中期においては,やがて大気から田面水へのCO₂の吸収がみられるようになる. CO₂の吸収速度は午後最大値に達した後下降し,夜間には再び田面水から大気へのCO₂の放出がおこる. このようなCO₂交換速度の日変化は日射強度の日変化と密接な関係を示す. しかし前者の推移は後者のそれに比べかなり遅れ,日没後もしばらく田面水によるCO₂の吸収がつづく. 稲の生育がすすむと,日中における大気から田面水へのCO₂の吸収はみられなくなり,1日を通じてCO₂の放出がおこるが,放出速度は日中小さく,夜間大きい. CO₂交換速度の日変化の幅は,イネ生育初期に大きく,その後次第に小さくなる. 2. 田面水中の全炭酸濃度(DIC)は夜間増加し,日中低下する. 田面水のpHは夜間低下し日中上昇する. DIC,pHから計算により求めた遊離CO₂分圧(pCO₂)の時刻的推移はDICのものと似ているが,日変化の幅はいっそう大きい. DIC,pH,pCO₂の日変化の幅はイネの生育の初期に大きく,群落が繁茂し,その葉層の光透過率が減少するにつれて小さくなる. 以上のようなDIC,pH,pCO₂の動きは,ソウ類の光合成によるCO₂の取り込み,ソウ類,土壌および田面水中の生物,イネ地下部などの呼吸によるCO₂の発生によりひきおこされるものと考えられる. 3. 田面水のpCO₂と大気・田面水間のCO₂交換速度との関係を検討し,両者の間に一定の量的関係が存在することを認めた. このことから前記の関係を基礎に,DICおよびpHから求めたpCO₂によりCO₂交換速度を求めることが可能であることが示唆された. 4. 非作付け期間には供試水田は落水状態に保たれたが,この時期には昼夜を通じ,土壌から大気へのCO₂の放出がおこった. その速度は夜間小さく,日中に大きく,日変化は地温の日変化と密接な関係を示した. しかし同一温度下で比較した場合,昇温過程では降温過程よりもCO₂の放出速度が大きかった. 日平均地温と日平均CO₂放出速度の対数との間に,高い正の相関が認められた.

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水田生態系においてソウ類は,イネ,雑草とともに一次生産者として光合成を行ない,生産物を消費者や分解者に供給している. 本報告は,ソウ類の現存量・光合成量の季節的推移を調べ,併せてその変動の要因について検討を行なったもので,得られた結果は次の通りである. 1. ソウ類の現存量は,イネ作付期間中の初期に小さく,季節のすすみに伴い増加した. 特に稲生育中期以降の増加が顕著であった. クロロフィル量であらわした現存量は30～183mg/m²で中栄養湖ないしは富栄養湖のそれに相当した. 2. ソウ類は主に土壌表面に付着するものとミドロ類で,浮遊性のものは極めて少なかった. 初期には付着性ソウ類が,後期にはミドロ類が優占した. このような優占種の交替は水温の低下によりもたらされるものと推察された. 3. ソウ類の光合成速度の日中における経過は日射強度のそれとほぼ並行した. 両者の日変化から求めた光-光合成曲線には,光飽和の傾向が認められなかった. 光合成速度をクロロフィル当りでみた時,光-光合成曲線の勾配は水稲の初期に緩く,季節のすすみに伴い大きくなった. この変化は,付着性ソウ類からミドロ類への優占種の変化と対応するものと考えられた. 4. 1日当りの総生産量は,初期881mgC/m²であったが次第に低下し,後期には300～400mgC/m²となった. 5. 水稲の葉層を通過し田面に到達した光合成有効放射の総生産への利用効率は初期には0.24～0.42%と低く,その後次第に増加し,最大値は4.78%と極めて高い値を示した. 6. ソウ類のターンオーバーレートは初期には大きい(0.3回/日)が後期にはその10%程度(0.04回/日)に低下した. このことが季節のすすみに伴い田面に到達する光の強度が低下し,光合成量が減少するにもかかわらず,現存量が増加した要因と考えられた. 7. 測定期間中(5月27日より10月17日までの144日間) の総生産量は71gC/m²,1日当り0.49gC/m²で,この値は富栄養湖における一次生産量に匹敵する.

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