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Acid sulfate soil (ASS) has an extremely low pH (3.0) and a high capacity to fix phosphate; symptoms of phosphate deficiency are commonly observed in many crop plants. Arbuscular mycorrhizal (AM) fungi form mutualistic relationships with plant roots, and improve uptake of phosphate from soil. However, there is little information on the actual situation of AM fungi in ASS in Thailand. The purpose of the present study is to determine the indigenous AM fungal density and species in ASS in Thailand. AM fungal spores were retrieved and identified by molecular approaches from ASS field at the central plain of Thailand. This study showed that AM fungal spore density in ASS was 0.232 spores per g dry soil. Among the plant species growing in the natural ASS, there was no AM fungal colonization in the roots of four plant species, i.e. Digitaria sp., Fimbristylis sp., Mimosa pudica L., and Sesbania sp.; however, AM colonization was found in Wedelia roots. Using phylogenetic analysis, four operational taxonomic units (OTUs), i.e., one Glomus, one Entrophospora, one Paraglomus and one unknown species were identified from the AM fungal spores. Five OTUs, i.e., two Glomus, one Acaulospora, one Entrophospora and one unknown Glomeromycota were indentified from Wedelia roots. To our knowledge, this is the first report of the actual situation of AM fungi in ASS in Thailand determined by using molecular approaches.

Aluminum (Al) is a major phytotoxic mineral in the soil at low pH conditions (Jones and Kochian, 1996). Pellet et al. (1995) reported that Al would damage the roots by making the plants more sensitive to other abiotic stresses such as defi ciency of water and nutrients, and eventually reduce the crop yield. One of the Al-tolerance mechanisms in plants would be Al exclusion from the root apices. In several upland plants, Al tolerance is closely associated with an increased ability of roots to release organic acids, such as citrate (de la Fuente et al., 1997; Ma et al., 1997a; Pineros et al., 2002), malate (Osawa and Matsumoto, 2001; Tesfaye et al., 2001), and oxalate (Ma et al., 1997b; Wenzl et al., 2001), which may prevent Al uptake by chelating Al. Rice, a lowland plant, has been identifi ed as a high Al-excluder at root apex (Osaki et al., 1997), but the mechanism of Al exclusion in rice plants has not been fully elucidated. The purpose of the present study is to confi rm that the varietal difference of the Al tolerance in rice is associated with organic acid formation in the intact root apices when Al was added to the low pH nutrient solution, and furthermore, to identify the sort of organic acid formed in the root exposed to Al.

本研究は, 酸性硫酸塩土壌を有するタイ南部ナラチワ県を研究対象地とし, 酸性土壌地域でのイネ収量を向上させることを目的として行ったものである. 第1報として, まず, 人工的に作った強酸性土壌にイネ (Oryza sativa L.) 48品種を移植し, 4週間後の個体の生存率によって14品種を選抜した. なお, 参考として, 酸性土壌に強いとされるアフリカイネ (Oryza glaberrima Steud.) 29品種もイネと同様に栽培し, 耐酸性を調べた. その結果, イネ14品種とアフリカイネ10品種が選抜された. 選抜されたイネ品種14のうち, 強酸性土壌で最も高い生長速度を示した4品種と, タイ南部ですでに耐酸性があるとされている2品種, それに本研究で耐酸性がないとされた3品種を比較することによって, イネの耐酸性機構を生理学的側面から検討した. 対照区に対する酸性土壌区の相対根長は, 耐性品種で大きく, 非耐性品種で小さかった. 葉面積においても根長と同様な傾向が見られた. さらに, 酸性土壌条件下での作物生長の阻害は, アルミニウム (Al) に起因することから, 酸性土壌条件下で栽培された植物体の葉身Al濃度を調べた. その結果, 葉身Al濃度は耐性品種よりも非耐性品種の方で高くなっていた. そこで, 葉身の光合成速度を測定したところ, 葉身の光合成速度は耐性品種の方が非耐性品種よりも有意に高い値を示した. これらのことから, Alが葉身にまで移行しにくく, その結果高い光合成能力が維持されていることが, 酸性土壌耐性の大きな原因の一つと考えられた.

本研究はフェーン現象下の気象を風洞装置を用いて再現し, 高温乾燥風に対する耐性イネ品種と感受性品種との水分状態とクロロフィル含量の差を調べたものである. 耐性品種として韓国農村振興庁嶺南農業試験場の盈徳出張所で選抜した日本型Naepung-byeo (NP), 感受性品種として同定されたオーストラリア原産の日本型Ilabong (IB) を供試し, それぞれ水田土壌をつめた1/1250aポットに移植し, 屋外自然条件下の湛水状態で生育させた. 3時間の高温乾燥風処理は出穂後4日目に行った. 穂の水ポテンシャルの変化は処理終了直後から顕著に現れ, NPでは処理開始前の-0.25 MPaに比べ, -0.75 MPaと大きく低下した. 一方, IBではさらに著しく, 処理開始前の-0.34 MPaから-1.53 MPaに大きく低下した. NPの穂の水ポテンシャルは, 処理終了後2時間目までは低下したが, 処理終了後6時間目には回復する傾向を示した. 葉身における水ポテンシャルは低下する傾向があったものの, 高温乾燥風処理による差は小さく, 品種間で有意な差は認められなかった. また, 穂の相対水分含量は水ポテンシャルと同様, NPでは高温乾燥風処理による低下はほとんど見られず, 処理終了後6時間目には回復する傾向を示した. しかし, IBでは処理終了直後の相対水分含量は処理開始前に比べて大きく低下し, 処理終了後6時間目では22%と極めて低かった. 穂のクロロフィル含量もNPで高く維持され, IBでは顕著に低下し, 処理終了後6時間目にはほとんどが白穂となった. このことから, 耐性品種であるNPは高温乾燥風に対し, 頴花で水分損失を防ぐ何らかの防御機構を有し, 時間の経過とともに回復したと考えられた.

The influence of potassium (K) deficiency on leaf water and osmotic potentials, and concentrations of major solutes was determined to assess their contributions to the leaf growth of soybean plants grown in solution cultures containing 5.0 and 0.2 mM KCl. A deficient supply of K restricted leaf growth due to decreased mesophyll cell numbers and cell enlargement, though water content, water and osmotic potentials of the expanding leaves were not affected by the treatment. The osmolarity of the expanding leaves showed very similar values in both treatments, though the K+ concentration in the K-deficient plants was remarkably lower than that of the control. In response to the K-deficiency, some cations, anions, sugars and amino acids accumulated in the expanding leaf, compensating the decrease in K concentration approximately 92%. These findings suggest that the leaf growth depression observed in the K-deficient plant occurred when the water relations of the K-deficient leaves are maintained close to that of the control.

Our previous paper showed that cultivar difference of flag leaf photosynthesis (LPS) in rice (Oryza sativa L.) was attributed to the difference in mesophyll resistance (rm). In this paper, we tried to divide rm into CO2 transfer resistance (rr) and CO2 fixation resistance (rc) for further analysis of rm by means of 3C determination of photosyntheti c products. In the heading time, rr, and rc occupied 14, and 58% in the total resistance, respectively, in average through 31 cultivars. This suggests that cultivar difference of LPS is mainly caused by the difference of r c. The percentage ratios of each resistance to the total one were maintained comparatively constant through the senescing process of the flag leaves. Moreover, the CO2 concentration in CO 2 fixating site showed almost the same values in different cultivars in a whole life span of a flag leaf. The rc showed a close correlation with ribulose-l,5-bisphosphate carboxylase/oxygenase (RubisCO) content. Carbonic anhydrase (CA) activity showed no correlation with rr, but showed positive correlation with rc. It was suggested that a mutual regulation system between CA activity and RubisCO activity could exist.

Intergeneric hybrid plants were obtained by the sexual crossing of Diplotaxis muralis DC, a C3 species, and Moricandia arvensis (L.) DC, a C3-C4 intermediate species. The morphological characteristics and chromosome numbers showed that these plants were true hybrids. The hybrid had a CO2 compensation point of 27 μl/ L, nearly as low as that of M. arvensis (20 μl/L). A C3-like value of 45 μl/L for this point was found in somatic hybrids produced in our laboratory by protoplast fusion between red cabbage (Brassica oleracea L. var. capitata) or cauliflower (Brassica oleracea L. var. botrytis) and M. arvensis. However, significant differences were not found among the sexual and the somatic hybrids in the concentration or total activity of ribulose-l,5-bisphosphate carboxylase/oxygenase. The results showed that the expression, of a C3-C4 intermediate character of photosynthesis from M. arvensis appears to depend on the combination of other characters of the parental species.

This research was conducted to elucidate the mechanisms in water stress tolerance of Oryza glaberrima Steud. with special reference to stomatal conductance. Leaf photosynthesis (LPS) of O. glaberrima Steud. with developing soil water deficiency, was still maintained above zero when the leaf water potential decreased to as low as -2.0 MPa, while in O. sativa L. LPS became zero at -1.6 MPa. Stomatal conductances also changed in parallel with LPS in both species, suggesting that the different response of LPS to reduced leaf water potential is due to the different stomatal response between two species. In the relationship between the stomatal conductance and abscisic acid (ABA) content in the leaves, Saka, a line of O. glaberrima Steud., showed a slower decrease of stomatal conductance with increase of ABA than Nipponbare, a cultivar of O. sativa L. This attenuated response of stomatal conductance to leaf ABA content in O. glaberrima Steud. was supposed to be the cause of maintenance of higher LPS than in O. sativa L. under low leaf water potential conditions. The Rubisco content showed no significant difference in the response to developing low leaf water potential between the two species.

As a physiological basis for the difference among parts of a wheat plant in photosynthetic depression by soil water deficit, the stomatal response to abscisic acid (ABA) was examined in an ABA-sprayed plant. An additional experiment was also conducted in order to confirm whether there is a direct inhibitory effect of ABA on non-stomatal mediated photosynthesis. About 1 hour after ABA was sprayed, photosynthesis (PS) and transpiration (Tr) in the leaf blades, the stem and the flag leaf sheath decreased to as low level as less than 10% of the initial rates. But, in the ear, the decreases of PS and Tr were not as much as in such parts as above-mentioned. This means that the stomata in the ear are less sensitive to ABA, which accumulates in water stress condition, than those in other plant parts. Non-stomatal photosynthesis was not inhibited by ABA addition to the reaction mixture in any part of a plant. It was suggested that photosynthetic depression by soil water deficit was not caused by the direct inhibition of photosynthetic mechanism by ABA, but by stomatal sensitivity to accumulated ABA.

Photosynthetic plants convert light energy into ATP and NADPH in photosynthetic electron transfer and photophosphorylation, and synthesize mainly carbohydrates in the Calvin–Benson cycle. Here we report the enhancement of photosynthesis and growth of plants by introducing the gene of an algal cytochrome c6, which has been evolutionarily eliminated from higher plant chloroplasts, into the model plant Arabidopsis thaliana. At 60 d after planting, the plant height, leaf length and root length of the transformants were 1.3-, 1.1- and 1.3-fold those in the wild-type plants, respectively. At the same time, in the transgenic plants, the amounts of chlorophyll, protein, ATP, NADPH and starch were 1.2-, 1.1-, 1.9-, 1.4- and 1.2-fold those in the wild-type plants, respectively. The CO2 assimilation capacity of the transgenic plants was 1.3-fold that of the wild type. Moreover, in transgenic Arabidopsis expressing algal cytochrome c6, the 1 � qP, which reflects the reduced state of the plastoquinone pool, is 30% decreased compared with the wild type. These results show that the electron transfer of photosynthesis of Arabidopsis would be accelerated by the expression of algal cytochrome c6. Our results demonstrate that the growth and photosynthesis of Arabidopsis plants could be enhanced by the expression of the algal cytochrome c6 gene.

Community structure of arbuscular mycorrhizal fungi (AMF), evaluated as spore samples and mycorrhizal roots of four herbaceous plant species, was investigated at different altitudes in a primary successional volcanic desert on Mount Fuji using molecular methods (fragment and sequence analysis of the large ribosomal subunit RNA gene). In total, 17 different AMF clades were identified, and most were members of the Glomaceae, Acaulosporaceae, and Gigasporaceae. The AMF community structures detected by spore sampling were inconsistent with those from plant roots. Of all AMF clades, six (35.3%) were detected only on the basis of spores, six (35.3%) only in roots, and five corresponded to both spores and roots (29.4%). Although an Acaulospora species was the most dominant among spores (67.1%), it accounted for only 6.8% in root samples. A species analysis of AMF communities at different altitudes demonstrated that AMF species diversity increased as altitude decreased and that the species enrichment at lower altitudes resulted from the addition of new species rather than species replacement. The inconsistencies in the species composition of spore communities with those in roots and the change in species diversity with altitude are discussed.

Arbuscular mycorrhizal (AM) colonization was observed on four plant species in primary successional volcanic deserts on the Southeast slope of Mount Fuji. The AM colonization of the dominant species, Polygonum cuspidatum, contradicts the conclusion that Polygonaceae are often regarded as being non-mycorrhizal species. The secondary dominant species, Polygonum weyrichii var. alpinum, formed no mycorrhizas. The roots of Cirsium purpuratum, Clematis stans and Campanula punctata ssp. hondoensis, showed a higher percentage of AM colonization than P. cuspidatum. AM colonization and spore density in the rhizosphere soil of P. cuspidatum significantly decreased as elevation increased. AM colonization in roots of Cirsium purpuratum and Clematis stans also tended to decrease with increased altitudes. Cirsium purpuratum and Campanula punctata ssp. hondoensis formed single structural types of Arum- and Paris-type, respectively, whereas P. cuspidatum and Clematis stans formed both Arum- and Paris-type morphologies.

The starch stored temporarily in the leaf sheath of rice plants is translocated to the grain, contributing to the grain yield. In this paper, the relationship between starch accumulation and the activities of enzymes involved in the starch biosynthetic pathway in the leaf sheaths of rice plants was examined to elucidate the regulation mechanism of starch accumulation in the temporary sink organ. When the starch content was compared between different leaf sheath positions on the main stem, the 14th leaf sheath counted from the bottom, which elongated just before anthesis, showed about a four-fold higher value than the 10th leaf sheath. Among the enzymes involved in carbohydrate metabolism, the activity of starch branching enzyme (BE, EC2.4.1.18) was greatly higher in the 14th leaf sheath than in the 10th leaf sheath, while that of ADPglucose pyrophosphorylase (EC2.7.7.27) was similar between the two leaf sheaths. The starch content increased rapidly in the period around anthesis in the 12th and 14th leaf sheaths, but did not in the 10th and 11th leaf sheath. In the higher leaf sheath position, the activity of BE changed with noticeably similar trend to the starch content. Soluble starch synthase (SSS, EC2.4.1.21), granule-bound starch synthase (GBSS, EC2.4.1.21) and plastidial fructose- 1,6-bisphosphatase (FBPase, EC3.1.3.11) were also significantly correlated with the starch content. These results suggest that BE is involved in regulation of starch metabolism, possibly in collaboration with other enzymes such as SSS, GBSS and plastidial FBPase in temporary sink organs like the leaf sheath.

The time course of respiration in soybean plants was examined under different physiological conditions to elucidate the mechanism of the determination of respiration rate. Respiratory CO2 evolution per unit dry weight (RPW) decreased after the onset of the dark period and showed a temporary acceleration around midnight, called the midnight rise of respiration (MRR) in this paper, reaching a constant level at about 48 hours after the initiation of the dark. Throughout this time course, RPW was high in younger and nitrogen-supplied plants, and low in the aged or nitrogen-depleted plants. Furthermore, MRR disappeared in the aged or nitrogen-depleted plants. From the results obtained, it was hypothesized that the time course of RPW, especially the existence of MRR, was determined by the demand for the energy and metabolic products which could be derived from respiration.

Photorespiratory activity was measured in entire plants of five tobacco variants. These tobacco variants are: the green type N. tabacum var. John William’s Broadleaf (su/su Aur/aur or su/su Aur/Aur) the chlorophyll-deficient tobacco mutant Su/su (Su/su Aur/Aur) and the chlorophyll- deficient mutant Su/su var. Aurea (Su/su Aur/aur). Furthermore, two recently characterized phenotypes originating from N. tabacum var. Consolation namely “consolation green” (Aa Bb) and “consolation yellow-green” (aa bb). In entire plants of these phenotypes photorespiration was measured as 18O2-uptake in the light. This uptake was compared with the enhancement of CO2- fixation in the Warburg effect i. e. when the oxygen partial pressure is lowered from 21% Oz to 3% O2. The principal conclusion from these measurements is firstly that under the assay conditions which are identical for all 5 phenotypes (330 ppm CO2, 14000 lux white light and 25 °C) all five phenotypes yield considerable differences in photorespiratory activity. Furthermore, we were able to show that in the different phenotypes the global O2-uptake in the light is repartitioned to different degrees among different metabolic pathways. Thus, in JWB which is under the assay conditions the only fast growing species, only half of the measured 18O2-uptake belongs to glycolate metabolism or photorespiration proper, the other half belongs to a Mehler type reaction in which excess reducing power is eliminated apparently already at the level of photosynthetic electron transport. In the chlorophyll-deficient mutant Su/su, however, the observed 18O2-uptake in the light belongs under the assay conditions exclusively to glycolate metabolism (no Mehler type reaction). The chlorophyll-deficient mutant Su/su var. Aurea behaves more like JWB, that is, part of its 18O2-uptake is due to a Mehler type reaction and only the remainder is involved in CO2- metabolism, which has been already found out previously by genetic analysis. In addition photorespiration depends in Su/su more on the temperature than in the other phenotypes tested. One of the implications of our results could be that it makes a difference to the plant whether excess reducing power is disposed of at the level of the photosynthetic electron transport chain (via a Mehler type reaction) or at the level of CO2-metabolism.

The time course of respiration in the continuous dark was examined with soybean plants having experienced various preceding light conditions, aiming to elucidate the determination mechanism of changes with time in respiration rate. The initial value of respiration rate per unit dry weight (RPW) observed immediately after the onset of dark period was dependent on the light intensity in the preceding light period, and it was not affected by the length of light period. However, the bottom level of RPW observed after the initial decrease was affected by the length, with the lower levels in the plants exposed to the shorter light period. Furthermore, the magnitude of midnight rise of respiration, the temporal rise in the dark period, was affected by both light intensity and length of light period. It showed the linear relationship against cumulative light intensity which was obtained from light intensity multiplied by length of light period. RPW in nitrogen-depleted plants did not respond to length of light period. In this experiment, it was found that the time course of respiration consisted of two different phases. One was in the initial part of the dark period and dependent on light intensity. The other was in the following part and dependent on cumulative light intensity in the preceding light period. From this observation, it was considered that respiration in the dark period was regulated by two different physiological processes.

Aminoacetonitrile (AAN), a specific inhibitor of glycine oxidation in the photorespiratory glycolate pathway, did not inhibit photosynthetic CO2 fixation, but inhibited the apparent photosynthesis of rice leaves under high photosynthetic conditions. However, under such low photosynthetic conditions as low light intensity or senescent leaves, the apparent photosynthesis was not inhibited by AAN. The application of AAN to the leaves led to a greater accumulation of glycine under a high photosynthetic condition like strong light intensity.From these results, it can be postulated that the inhibition of apparent photosynthesis by AAN was due to the accumulation of intermediate metabolites in the photorespiratory glycolate pathway which was induced by AAN treatment.

Time course challges of respiration rate in a leaf and roots were examined in attached and detached conditions to obtain information of the internal factors determining the time course change of respiration in different organs. In the attached condition, an expanding leaf showed a rapid increase of respiration around midnight (Midnight rise of respiration, MRR), while, an expanded leaf showed a steady state of respiration around midnight, followed by a rapid decrease, resulting in a vague MRR. The attached roots showed a clear MRR. In the detached condition the changes in leaf respiration rate were almost the same as in attached condition; whereas in roots, MRR completely disappeared. The results suggested that the respiration of a leaf is not affcted by other organs, whereas that of roots was strongly dependent on the existence of a shoot. The results also suggested that the internal factors causing MRR existed in a leaf, especially in an expanding leaf.

The CO2 compensation point and its relation to the chloroplast DNA (cpDNA) type were investigated on the somatic hybrids between Brassica oleracea, a C3 plant and Moricandia arvensis, a C3-C4 intermediate plant. The fragment patterns of cpDNA digested with restriction endonuclease (XhoI) showed that the somatic hybrid plants had the cpDNA of either B. oleracea or M. arvensis. Out of 11 plants investigated, 5 plants had the cpDNA of B. oleracea, while 6 had that of M. arvensis. However, both types of the hybrids showed as high a CO2 compensation point as B. oleracea irrespective of their cpDNA. In this respect, the C3-C4 intermediate character of M. arvensis was not expressed in the hybrids.

The Kok effect of photosynthesis was investigated in different tobacco mutants. It was found that the breaks in the light intensity curve were always at or around 1000 lux in all plants tested regardless of the unit sizes which differed by a factor of 10. It was concluded that the photo­ receptor responsible for the effect must be present in the wild type and the chlorophyll deficient mutants in the same amount and is probably not chlorophyll. Due to the fact that the light dependency of the Hill reaction in isolated tobacco chloroplasts also shows a break at or around the “Kok intensity” it was concluded that probably a structural change of the photochemical apparatus around 1000 lux contributes to the effect. Measurement of 180 2-uptake by mass spectrometry at low light intensity shows at low CO2-concentration an enhancement of 180 2-uptake again at/around 1000 lux indicating that photorespiration starts to function at the “Kok intensity”. Due to the fact that 180 2-uptake remains constant at high CO2-concentrations the break in the photosynthetic light intensity curve cannot be due to an inhibition of “dark respiration” at low light intensities.

In order to examine the effect of nonunifomity of seedling number per hill on the growth, yield and yield components, seven kinds of rice populations were set; A)uniform populations which consist of the hills of the same number of seedlings, 1. all one seedling hills (1-1), 2.all three seedlings hills (3-3), 3. all six seedlings hills (6-6), B) nonuniform populations which consist of the hills of the different number of seedlings, 4. one and three seedlings hills alternately (1-3), 5. three and six seedlings hills alternately (3-6), 6. one and six seedlings hills alternately (1-6), 7. one, three and six seedlings hills alternately (l-3-6). The results of the study were as follows. 1. Differences in tiller number and top fresh and dry weight were observed among treated populations at the beginning of growing period, however, ultimately significant differences could not be observed. 2. In nonuniform population, each hill showed interaction and mutual compensation among one another. For an example, in the nonuniform population, 1-6, six seedlings hill depressed the growth of one seedling hill and reversely one seedling hill promoted the growth of six seedlings hill, compared to those in uniform one or six seedlings population, 1-1, or 6-6. These mutual effect was almost equal, so the growth of the nonuniform population, 1-6, as a whole, was almost same as the average of the growth of two uniform populations, 1-1 and 6-6. Accordingly the growth decrease caused by nonuniformity could not be observed over the growing period. 3. The growth variabilities among each hill in the nonuniform populations remained to.be greater than those in the uniforrn populations over the growing period. 4. These tendencies found in growth refLected to yield, so, yield decrease by nonuniformity could not be observed.

Growth compensation between neighbouring hills consisting of different number of seedlings was studied in relation to degree of nonuniformity and planting density. According to the result obtained, the rate of growtht compensation increases with increase of density and degree of nonuniformity. Growth compensation is thought to be caused by interaction or competition between neighbouring hills or among individual plants. So, in order to express quantity of competition, competition index was tried. In this trial, total competition among individual plants is sum of competition within hill (intra-hill competition) and between neighbouring hills (inter-hill competition). The method of calculation of competition index is as follows. log+/+ = 1o9 7#+/77+1o9- +/Q/-here I(n) is dry weight of the isolated hill whose number of seedlings is n, P(n) is dry weight of the hill whose number of seedlings is n in population. According to this equation, competition index was calculated about populations which had different planting densities. The intra-hill competition index increases with increase of the number of seedlings of a hill. The inter-hill competition index increases with increase of plant density. In the distance between hills below 24 cm, inter-hill competition index exceeds intra-hill competition index. Reversely, in the distance between hills above 36 cm, intra-hill competition index exceeds inter-hill competition index. So, the converting point of intra- and inter-hill competition is in the distance between 24 cm and 36 cm.

Les effets de l'aminoacetonitrile sur la photosynthese et la transpiration sont etudies chez Oryza sativa et Zea mays