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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.

Genetic challenge to express higher carbonic anhydrase (CA) activity in the cytoplasm of tobacco mesophyll cells was carried out by an improved promoter (El2 Ω) with a cDNA of partially modified mouse CA. In leaves of T1 progenies of transgenic tobacco (ffCA plant), the expressed mouse CA peptide was confirmed with 1, 5-3.2 times higher than the transgenic tobacco having foreign mouse CA controlled by simple CaMV 35S promoter (fCA plant). The ffCA plants manifested higher photosynthetic carbon assimilation (PCA) rate under ambient CO2 condition than wild type plants. The chlorophyll fluorescence measurement analysis revealed that the ffCA plant's improved PCA rate is related to the reduction of mesophyll CO2 transfer resistance (Rr) with little change in the stomatal resistance (Rs) or mesophyll CO2 fixation resistance (Rx). Moreover, ffCA plants showed a higher growth rate under high light condition.

It was reported that a supernodulating soybean mutant, En6500 derived from the variety of Enrei, could produce many root nodules, but the growth rate of the plant was not necessarily high. The purpose of this paper, therefore, is to examine the characteristics of nodulation and also of plant growth in En6500 for elucidation of the mechanism of its low growth rate. The relative growth rate was low in En6500 compared with Enrei. The dry weight of the nodules per unit root mass was greater in En6500 than in Enrei, suggesting that the root of En6500 is supporting too many or an excess of nodules, which presumably leads to a reduction of plant growth rate. Reduced growth rate was associated with low net assimilation rate and further with low leaf photosynthesis. Moreover, the reduced leaf photosynthesis was associated with low partitioning of nitrogen to the leaves in En6500. Much allocation of nitrogen to the plant organs besides the leaves resulted in low photosynthesis, and also in the reduced nitrogen-use efficiency for dry matter production, which might be a potential mechanism for the low growth rate of En6500, a supernodulating soybean mutant.

Summary Eleocharis vivipara Link alters its photosynthetic mode depending on the growth environment. It utilizes C4 photosynthesis when grown under terrestrial conditions (terrestrial form) and C3 photosynthesis when grown under submerged conditions (submerged form). The photosynthetic organ (the mature internodal region of the culm) of the terrestrial form shows typical Kranz anatomy with well-developed bundle sheath cells, while the bundle sheath cells of the submerged form are not developed. In the mature internodal region of the terrestrial form, expression of the genes encoding two carboxylases, the small subunit of ribulose 1,5-bisphosphate carboxylase (RbcS) and phosphoenolpyruvate carboxylase (Ppc), occurred mainly in bundle sheath cells and in mesophyll cells, respectively, as seen in a typical C4 leaf. In the submerged form, RbcS was expressed in both bundle sheath cells and mesophyll cells, and no expression of Ppc was observed. In the immature internodal region with undeveloped bundle sheath cells, both life forms showed the same expression pattern as in C3 plants: RbcS expression was localized in mesophyll cells and no Ppc expression was observed. The C4-type expression pattern was established concomitantly with the development of bundle sheath cells during tissue maturation in the terrestrial internode. In contrast to the terrestrial form, the submerged form maintains C3-type gene expression during tissue maturation. When the terrestrial culm was submerged, a region of transition from the terrestrial form to the submerged form was established in newly sprouting culms. In this transitional region, C4-type expression of the two carboxylase genes was still maintained even though the development of bundle sheath cells was repressed. This observation suggests that the C4-type cell-specific gene expression pattern does not depend on the formation of Kranz anatomy.

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.

Although many studies have shown cultivar differences in photosynthetic response to water deficit, the understanding of detailed mechanisms is not sufficient. We examined the mechanisms of water stress-resistance in terms of photosynthetic performance under low soil water potential (Ψsoil) with sixteen cultivars of wheat (Triticum aestivum L.) from different habitats, which had shown different drought resistance on a grain yield basis. Cultivar differences in photosynthetic maintenance in response to decrease of Ψsoil (water stress resistance), were found at ail seedling, booting, and grain filling stages. Cultivars with high drought resistance based on grain yield also showed high water stress resistance in photosynthetic performance. Water stress resistance (Rws) was caused more by tolerance (Tws, maintenance ability of photosynthesis in response to decrease of leaf water potential, ΨL)in some cultivars, which maintained relatively high photosynthesis (PN) in spite of decreases in ΨL, while it was caused more by water stress avoidance (Aws, maintenance ability of ΨL in response to decreases in Ψsoil) in other cultivars, which showed a relatively high PN by maintaining a relatively high ΨL under the same low Ψsoil. However, there was a positive correlation between Rws and Tws or between Rws and Aws. It is suggested that avoidance and tolerance usually occur simultaneously in adaptation to low Ψsoil, although water stress resistant cultivars varied in the water stress resistance mechanism.

Reduction of relative growth rate (RGR) due to the NaCl treatment was examined in the seedlings of six Korean rice cultivars which had been reported to be different in salt tolerance on the level of grain yield. On the level of RGR, three of the cultivars were identified as salt tolerant, and the remaining three were identified as the sensitive cultivars. Further analysis of RGR indicated that the reduction of RGR by NaCl treatment was attributed in large part to the reduction of the net assimilation rate (NAR) rather than to that of the leaf area ratio (LAR). Leaf photosynthesis which is closely related with NAR, was also reduced by NaCl treatment in salt sensitive cultivars to a greater extent than tolerant cultivars. Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) content was determined in a tolerant cultivar, Han-Kang-Chal, and a sensitive one, Dong-Hae. Han-Kang-Chal showed a smaller decrease of Rubisco content per absorbed Na in the NaCl-treated leaves. This indicates that degradation of Rubisco by absorbed Na is slower in tolerant cultivars than in sensitive cultivars. Moreover, Han-Kang-Chal showed a larger decrease in osmotic potential in the NaCl treated leaves, suggesting that osmotic adjustment was developed under salt stress conditions in a tolerant cultivar.

Cultivar differences in leaf photosynthesis (LPS) and grain yield of wheat [Triticum aestivum L.] were examined under irrigated and non irrigated conditions in Cerrados, a semi-arid region in Brazil. Twelve Brazilian, five Mexican and two Japanese cultivars were used in this project. The plants were grown under low planting density to elucidate the relationship between LPS and the potential yield of an individual plant. Brazilian cultivars ranked high in LPS, followed by Mexican and Japanese cultivars under non-irrigated conditions, although there were practically no differences in LPS among these three groups of cultivars in irrigated conditions. The LPS showed a significant positive correlation with grain yield (r=0.63) and dry matter yield (r=0.73) per plant in non-irrigated conditions. However, LPS showed neither correlation with grain yield nor dry matter yield per plant in irrigated conditions. The present results suggests that PLS could be a breeding criteria to increase the yield per plant under soil water deficit conditions.

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.

Effects of soil water deficit, low air humidity and in combination were examined at the milky stage under controlled conditions. Low air humidity which plants experienced prior to measurement affected leaf photosynthesis in a manner different from effects of soil water deficit, in regard of the order of depression extent among leaves, i.e., photosynthetic depression by soil water deficit was in the order of flag leaf 2nd leaf < 3rd leaf. Stomatal (gs) and mesophyll (gm) conductances for CO2 diffusion, and Rubisco content varied in parallel with photosynthesis, though there was one exception. It was suggested that the above-mentioned responses of photosynthesis were caused by the corresponding depression in stomatal aperture and photosynthetic activity of mesophyll. Among the three leaves examined, little difference was observed in decrease of leaf water potential (ψ) caused by soil water deficit, while the decrease in ψ by precedent low air humidity was especially large in the flag leaf. The lower the leaf position, the larger the sensitivity of gs, gm, and Ribisco content to decrease in ψ was. Thus, difference in the extent of photosynthetic depression by soil water deficit among the uppermost three leaves was attributed mainly to different sensitivity to decrease in ψ, while that by dry air was attributed to the difference in the extent of decrease of ψ in addition to sensitivity differences. The effect of low soil water and low air humidity on photosynthesis seemed to be additive when combined.

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.

In order to explore the physiological basis of the difference in photosynthetic depression by soil water deficit, the non-stomatal mediated photosynthesis (NSP) and ribulose-1, 5-bisphosphate carboxylase (RuBPCase) content were compared among different parts of a wheat plant grown under soil water deficit condition. The depression of NSP due to water stress was larger in the lower leaf blades than in the upper ones, and in leaf blades than in ear, sheath and stem. The content of RuBPCase was decreased by soil water deficit to a larger extent in the lower leaf blades than in the upper ones, and in leaf blades than in stem and leaf sheath. But, in the ear, the extent of RuBPCase decrease was relatively large, compared with that of photosynthetic depression. The results here suggest a possibility that the difference among plant parts in photosynthetic depression by soil water deficit is partly attributed to the different sensitivity of photosynthetic apparatus to water stress.

The mechanism of different water relations in each part of a wheat plant was examined to elucidate the physiological basis for the difference among plant parts in photosynthetic drought resistance. As the soil water deficit developed, the upper leaf blades maintained the higher turgor potential (TP) and relative water content (RWC) compared with the lower ones. The stem and the leaf sheath also maintained the similar level of Tp and RWC to the flag leaf. The ear, however, showed the highest RWC with a low TP. The mechanism for osmotic/adjustment was analyzed by separating the osmotic potential (OP) decrease into two components, the concentration effect and the solute accumulation effect. It was found that the solute accumulation effect was the highest in the ear, followed by the stem, the leaf sheath, the upper leaf blades and the lower ones in the last, and that the concentration effect showed the reverse order of the plant parts as above mentioned. In order to know the reason for this peculiar watch relations in the ear, the water relations were investigated in the glumes and the grain separately. It was found that the glumes showed a similar water relations to the flag leaf, whereas the grain maintained a extremely higher water content with much lower TP than any other plant part, even under severe soil water deficit condition. The strong maintaining ability of RWC seemed to be the main cause of the higher drought resistance in the ear.

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.

Differences in leaf photosynthesis and their relationship to grain yield in Oryza species are discussed. During the evolutionary process, improvement of biochemical reactions of photosynthesis took place toward the direction of increase in CO2 fixing reaction catalyzed by RuBPcase. Most advanced Oryza species acquired the characteristics of high leaf photosynthesis for longer duration and efficient partitioning of photosynthetic products to the grains. Amongst the different groups of varieties, higher yield was associated with high respsonse of photosynthesis to nitrogen and maintenance of high photosynthetic activity of the flag leaf during the grain filling period. Studies on F1 heterosis in photosynthesis suggest that high yields could be associated with higher integrated photosynthesis of the flag leaf during the ripening period.

Effects of brassinolide (BR) on growth and developmental processes were examined in wheat plants applying the solution at various growth stages and at various concentrations. The results are summarized as follows: 1. Elongation of root, stem and leaf was not promoted by the treatment but rather a little inhibited at higher concentratiens (Fig. 1). 2. Formation of primary roots of seedling, tillers and spikelets was promoted by the BR-treatments. The number of productive tillers decreased, though that of total tillers increased by the treatments (Figs. 1∼5). 3. Heading was delayed by the BR-treatments (Fig. 4). 4. The effects of BR on ear-and grain yield were quite different depending on the growth stages at which the treatments were given. The BR-treatments before anthesis resulted in reduction of yield mainly due to decrease in productive tillers. On the other hand, the treatment during the ripening period (from anthesis to full maturity) considerably increased ear-and grain yield (in ear weight per plant, 15%) as a result of improvement in set and filling of grains, especially in inferior ones (Figs. 6, 7). 5. Photosynthesis was promoted a little by the leaf treatment of BR. However, the frequent application extending to later stages of leaf ontogeny brought about reduction of photosynthetic rates of leaves due to acceleration of senescence (Figs. 8∼10). 6. The BR-treatment scarecely affected total dry matter production (Table 2).

The purpose of this study is to determine if there is an interaction of nitrogen nutrition and water stress on apparent photosynthesis (APS), transpiration (Tr), and water-use efficiency in rice (Oryza sativa L.). The potted plants, which were cultured in high and low nitrogen levels, were exposed to the water stress condition, and the gas exchange rates were measured. A significant interaction of nitrogen supply and soil water stress on APS and Tr occurred, with high nitrogen plants being more affected by water stress, in respects of APS and Tr, compared with low nitrogen plants. This high responsiveness of APS and Tr in high nitrogen plants was due to stomatal sensitivity to water stress. In addition, high nitrogen plants maintained better photosynthetic machinery under water stress condition. As the results, it was found that the characteristics of greater stomatal sensitivity and better photosynthetic machinery in high nitrogen plants, led to their higher water-use efficiency.

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.

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