Japonica-type Cultivars Research Articles

Metabolic diversity analysis and genome wide assessment of oxalate accumulation in the leaves of rice (Oryza sativa) cultivars.

Soluble oxalate accumulates in rice leaves, and it causes mineral deficiency and urinary syndrome in livestock that consume the leaves. In our previous study, we found that the oxalate content was higher in the leaves of Koshihikari (japonica type cultivar) than in those of Takanari (indica type cultivar). This difference was seen even when the two cultivars were grown under a high CO2 concentration, which inhibits oxalate synthesis via photorespiration, suggesting that the difference resulted from genetic factors rather than environmental factors. To clarify whether genetic factors affect the oxalate content of rice leaves, we measured the contents of oxalate and oxalate-related organic acids in the leaves of various rice cultivars the Rice Core Collection (WRC) and Japan Rice Core Collection (JRC) by capillary electrophoresis-mass spectrometry. Results showed that japonica type cultivars tended to accumulate more oxalate than aus or indica type cultivars. Correlation analysis revealed a positive correlation between oxalate accumulation and the citrate content, suggesting that the isocitrate pathway is involved in oxalate accumulation. On the other hand, a genome-wide association study for the oxalate content of the WRC and JRC cultivars did not reveal significant loci directly related to oxalate accumulation. This indicates that the combination of various loci may affect the oxalate contents of rice leaves.

Effects of water use efficiency on plant dry matter in NERICA and Japanese rice cultivars under drought conditions

NERICA (New Rice for Africa) was produced by crossing Asian rice (Oryza sativa L.) and African rice (Oryza glaberrima Steud.) and recorded to be drought tolerance. This study aimed to examine the transpiration and water use efficiency affected plant aboveground dry matter in total 29 cultivars including 23 NERICA, 1 indica-type and 5 japonica-type cultivars. Seedlings were transplanted 2 plants per pot (1/5000 a Wagner pot) on June 14, 2021. When the flag leaf appeared, three water treatments with three replications were imposed for 14 days. The control plot (C) was watered daily to maintain the water content per pot at field capacity (SW). The water content of medium dry pots (MD) and hard dry pots (HD) were maintained at 40% and 10% of SW, respectively. Surface of the pots was covered to eliminate the evaporation. Samples for dry matter measurement were collected on the same day starting and ending water treatment. Water use efficiency (WUE) was significantly different among cultivars when soil moisture treatments were included, and the same observation on soil moisture treatments when included cultivars. NERICA 4 showed the lowest WUE while NERICA 9 and Hokuriku 193 had the highest WUE. Cultivars with higher transpiration rate (Tr) had higher dry matter production (ΔDW). Under high vapor pressure deficit, ΔDW was more correlated with transpiration corrected by vapor pressure deficit (Tr/VD) than with WUE.

Domain Unknown Function DUF1668-Containing Genes in Multiple Lineages Are Responsible for F1 Pollen Sterility in Rice.

Postzygotic reproductive isolation maintains species integrity and uniformity and contributes to speciation by restricting the free gene flow between divergent species. In this study we identify causal genes of two Mendelian factors S22A and S22B on rice chromosome 2 inducing F1 pollen sterility in hybrids between Oryza sativa japonica-type cultivar Taichung 65 (T65) and a wild relative of rice species Oryza glumaepatula. The causal gene of S22B in T65 encodes a protein containing DUF1668 and gametophytically expressed in the anthers, designated S22B_j. The O. glumaepatula allele S22B-g, allelic to S22B_j, possesses three non-synonymous substitutions and a 2-bp deletion, leading to a frameshifted translation at the S22B C-terminal region. Transcription level of S22B-j and/or S22B_g did not solely determine the fertility of pollen grains by genotypes at S22B. Western blotting of S22B found that one major band with approximately 46 kDa appeared only at the mature stage and was reduced on semi-sterile heterozygotes at S22B, implying that the 46 kDa band may associated in hybrid sterility. In addition, causal genes of S22A in T65 were found to be S22A_j1 and S22A_j3 encoding DUF1668-containing protein. The allele of a wild rice species Oryza meridionalis Ng at S22B, designated S22B_m, is a loss-of-function allele probably due to large deletion of the gene lacking DUF1668 domain and evolved from the different lineage of O. glumaepatula. Phylogenetic analysis of DUF1668 suggested that many gene duplications occurred before the divergence of current crops in Poaceae, and loss-of-function mutations of DUF1668-containing genes represent the candidate causal genetic events contributing to hybrid incompatibilities. The duplicated DUF1668-domain gene may provide genetic potential to induce hybrid incompatibility by consequent mutations after divergence.

Effects of lead (Pb)-induced oxidative stress on morphological and physio-biochemical properties of rice

In rice, high concentration of lead (Pb) can cause phyto-toxicity affecting several physiological functions. Cultivation of rice varieties that are resistant to Pb-induced oxidative stress is an important management strategy in Pb-contaminated soils. In the current study, we evaluated four different rice cultivars for their response to Pb-induced stress. Three japonica type cultivars X-Jigna, Ediget, and Furat, and one Indica type cultivar Amber 33 were grown in soil containing different Pb concentrations (0 mM, 0.6 mM, and 1.2 mM). The soil was treated with 0 mM or 0.6 mM or 1.2 mM Pb solution one month prior to rice seedling transplantation. Thereafter, four-week-old rice seedlings were transplanted into the treated soil and their responses were observed until maturity. The data revealed that a highest concentration of Pb (1.2 mM) induced significant reduction in agronomic traits such as plant height, number of tillers per plant, number of panicles per plant, and number of spikelets per panicle in all the rice cultivars. However, least reduction in the agronomic traits was observed in X-Jigna, whereas the highest reduction in the agronomic traits was observed in Ediget. Antioxidant activity of catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO), and superoxide dismutase (SOD), was evaluated along with the accumulation of superoxide ions (O2.-), protein, proline, chlorophyll, sucrose, glucose, and fructose contents in all the rice cultivars. A significant increase in antioxidant activity and in the accumulation of proline and sucrose contents with the least reduction in the chlorophyll and protein contents was observed in X-Jigna suggesting that X-Jigna is the most tolerant among all the rice cultivars tested against Pb-stress. On the other hand, non-significant and slightly significant increase in the antioxidant activity, less accumulation of proline and sucrose contents, and higher reduction in the chlorophyll and protein contents was observed in Ediget, which further suggest that Ediget is the most susceptible rice cultivar to Pb-stress. In addition, the other rice cultivars Furat and Amber 33, were found to be moderately tolerant to Pb-induced oxidative stress. In summary, our results suggest that tolerance to Pb-induced oxidative stress would be a result of a synergetic action of both enzymatic and non-enzymatic antioxidant systems, leading to a balanced redox status in rice.

Identification of Quantitative Trait Loci for the Concentrations of Phenylpropanoid Glycosides in Brown Rice.

Rice (Oryza sativa L.) is a staple food for most of the world’s population, as it is eaten by nearly half of its inhabitants. Phenylpropanoid glycosides derived from plants have various biomedical effects. The comparison of the concentrations of the four major phenylpropanoid glycosides in brown rice, i.e., 6-O-feruloylsucrose (1), 3′,6-di-O-sinapoylsucrose (2), 3′-O-sinapoyl-6-O-feruloylsucrose (3), and 3′,6-di-O-feruloylsucrose (4), between a conventional japonica-type cultivar Koshihikari and a high-yielding indica-type cultivar Takanari revealed that they were 57–162% higher in Koshihikari than in Takanari. To identify quantitative trait loci (QTLs) for the concentrations of these compounds (1–4), reciprocal chromosome segment substitution lines derived from a cross between Koshihikari and Takanari were analyzed. We identified QTLs for the concentrations of compound 1 on chromosome 2 and of compound 2 on chromosome 4 in the reciprocal genetic background. The concentrations of these compounds were increased by the Koshihikari alleles and decreased by the Takanari alleles. Therefore, the favorable alleles of Koshihikari are available to ameliorate the lower concentrations of compounds 1 and 2 in Takanari. The combinations of QTLs identified in the present study together with those of other biologically active compounds make it possible to breed health beneficial cultivars.

Variation in the Abundance of OsHAK1 Transcript Underlies the Differential Salinity Tolerance of an indica and a japonica Rice Cultivar.

Salinity imposes a major constraint over the productivity of rice. A set of chromosome segment substitution lines (CSSLs), derived from a cross between the japonica type cultivar (cv.) Nipponbare (salinity sensitive) and the indica type cv. 9311 (moderately tolerant), was scored using a hydroponics system for their salinity tolerance at the seedling stage. Two of the CSSLs, which share a ∼1.2 Mbp stretch of chromosome 4 derived from cv. Nipponbare, were as sensitive to the stress as cv. Nipponbare itself. Fine mapping based on an F2 population bred from a backcross between one of these CSSLs and cv. 9311 narrowed this region to 95 Kbp, within which only one gene (OsHAK1) exhibited a differential (lower) transcript abundance in cv. Nipponbare and the two CSSLs compared to in cv. 9311. The gene was up-regulated by exposure to salinity stress both in the root and the shoot, while a knockout mutant proved to be more salinity sensitive than its wild type with respect to its growth at both the vegetative and reproductive stages. Seedlings over-expressing OsHAK1 were more tolerant than wild type, displaying a superior photosynthetic rate, a higher leaf chlorophyll content, an enhanced accumulation of proline and a reduced level of lipid peroxidation. At the transcriptome level, the over-expression of OsHAK1 stimulated a number of stress-responsive genes as well as four genes known to be involved in Na+ homeostasis and the salinity response (OsHKT1;5, OsSOS1, OsLti6a and OsLti6b). When the stress was applied at booting through to maturity, the OsHAK1 over-expressors out-yielded wild type by 25%, and no negative pleiotropic effects were expressed in plants gown under non-saline conditions. The level of expression of OsHAK1 was correlated with Na+/K+ homeostasis, which implies that the gene should be explored a target for molecular approaches to the improvement of salinity tolerance in rice.

Genetic characterization of introgression lines with the genetic background of the Indica-type rice (Oryza sativa L.) cultivar IR 64 under irrigated lowland and upland conditions

We characterized 333 introgression lines (INLs) harboring chromosome segments from new plant type (NTP) and Japonica-type cultivars with the genetic background of the elite Indica-type rice (Oryza sativa L.) cultivar IR 64, by evaluating yield components and dry matter production under irrigated lowland (IL) and upland (UP) culture in 2011 and 2012; and elucidated the relationships between the traits and chromosome segments introduced from the donors. The panicle weight (PW), PW/total plant weight (PW/TW), number of fertile spikelets (FS), and FS/total number of spikelets per panicle (FS/TS) of the INLs increased, while the culm weight (CW) and panicle number (PN) decreased. Most INLs produced more dry matter in the UP than in the IL culture. The INLs were clustered into three groups (A–C) according to their traits in the UP culture, and four groups (I–IV) according to their traits in the IL culture. They were then sorted into six groups (A-I, A-II, B-II, B-III, C-III, and C-IV) according to the relationships between culture conditions. The INLs of group A-II had increased panicle length (PL), PW, PW/TW, FS, and TS, and these traits were stable in both IL and UP culture. In the other groups, the trait values changed with the conditions and season. Association analyses using trait phenotype and genotype data of SSR markers detected 166 quantitative trait loci (QTLs) for 10 traits, distributed on all chromosomes except 3 and 10. Of these, 81 QTLs for DH, CL, PL, CW, PW, PW/TW, PN, FS, TS, and FS/TS were newly detected. The INLs were characterized under different conditions, and dramatic trait modifications in IR64 rice were associated with these QTLs, through introgression from the donor cultivars. Thus, these INLs and QTLs will be useful in genetic studies to identify the gene(s) that modified IR64, and as breeding materials for genetic improvement of Indica-type cultivars.

Mapping of Novel QTL Regulating Grain Shattering Using Doubled Haploid Population in Rice (Oryza sativa L.).

The critical evolutionary step during domestication of major cereals was elimination of seed shattering because the easy-to-shatter trait in wild relatives results in a severe reduction in yield. In this study, we analyzed the QTLs associated with shattering employing a high-density genetic map in doubled haploid (DH) population of rice (Oryza sativa L.). A genetic linkage map was generated with 217 microsatellite markers spanning 2082.4 cM and covering 12 rice chromosomes with an average interval of 9.6 cM between markers based on 120 DHLs derived from a cross between Cheongcheong indica type cultivar and Nagdong japonica type cultivar. In the QTL analysis, five QTLs pertaining to the breaking tensile strength (BTS) were detected in 2013 and 2015. Two regions of the QTLs related to BTS on chromosome 1 and chromosome 6 were detected. Several important genes are distributed in 1 Mbp region of the QTL on chromosome 6 and they are related to the formation of abscission layer. We decide to name this QTL qSh6 and the candidate genes in the qSh6 region can be employed usefully in further research for cloning.

Nutraceutical Lipid Substances in Korean Rice Cultivars

The lipid soluble substances, such as tocols (tocopherols and tocotrienols), phytosterols, squalene, and γ-oryzanol, levels in 22 cultivars of Korean brown rice were investigated. The phytosterol levels in 22 cultivars varied from 255.0 mg/kg rice in Daerip to 492.0 mg/kg rice in Kuennun and the major phytosterol was β-sitosterol in all cultivars. In all the cultivars, there was a high correlation coefficient (R 2 = 0.7996) between the lipid level and the phytosterol level. The major tocols homologues in the 19 Japonica type cultivars were α-tocopherol and α- tocotrienol, and the major homologue in the Indica type cultivars namely Segyuejinmi, Hanareum, and Dasan No.1 was γ-tocotrienol. Among the γ-oryzanol species, the proportions of cycloartenylferulate in Japonica type cultivars were significantly higher than those of 24-methylene cycloartanylferulate (p < 0.05). This study provided information on lipid soluble substances level, such as tocols, phytosterol and γ-oryzanol, in different rice cultivars.

Impact of model uncertainty on soil quality standards for cadmium in rice paddy fields

At present, soil quality standards used for agriculture do not consider the influence of pH and CEC on the uptake of pollutants by crops. A database with 750 selected paired samples of cadmium (Cd) in soil and paddy rice was used to calibrate soil to plant transfer models using the soil metal content, pH, and CEC or soil Cd and Zn extracted by 0.01 M CaCl 2 as explanatory variables. The models were validated against a set of 2300 data points not used in the calibration. These models were then used inversely to derive soil quality standards for Japonica and Indica rice cultivars based on the food quality standards for rice. To account for model uncertainty, strict soil quality standards were derived considering a maximum probability that rice exceeds the food quality standard equal to 10 or 5%. Model derived soil standards based on Aqua Regia ranged from less than 0.3 mg kg − 1 for Indica at pH 4.5 to more than 6 mg kg − 1 for Japonica-type cultivars in clay soils at pH 7. Based on the CaCl 2 extract, standards ranged from 0.03 mg kg − 1 Cd for Indica cultivars to 0.1 mg kg − 1 Cd for Japonica cultivars. For both Japonica and Indica-type cultivars, the soil quality standards must be reduced by a factor of 2 to 3 to obtain the strict standards. The strong impact of pH and CEC on soil quality standards implies that it is essential to correct for soil type when deriving national or local standards. Validation on the remaining 2300 samples indicated that both types of models were able to accurately predict (> 92%) whether rice grown on a specific soil will meet the food quality standard used in Taiwan.

Variation in free amino acid profile among some rice (Oryza sativa L.) cultivars

The free amino acid (FAA) concentration of rice is becoming an increasingly important grain quality factor because of its apparent influence on the organoleptic acceptability of cooked rice. To determine the variability of this character among rice cultivars the FAA profiles of 49 cultivars were determined using Pico-Tag method. Among these 13 cultivars were selected to determine variation in FAA accumulation pattern after 24-hour germination treatment. The results show significant variation in the concentrations of total as well as individual FAAs among cultivars. There were also significant differences between indica- and japonica-type cultivars in the concentrations of some FAAs. The ratio of the total concentration of aspartate-derived to glutamate-derived FAAs (A/G ratio) evaluated for the japonica group (0.68) was significantly lower than that for the indica group (1.07). This suggests that typically, japonica-type rice grains tend to accumulate more Glu-derived than Asp-derived FAAs. Other results show a decline in the A/G ratios of both groups in response to germination treatment, with the indica group exhibiting a more rapid response. These results appear to suggest key differences in the FAA accumulation patterns of japonica- and indica-type rice grains especially with respect to the contents of aspartate-derived and glutamate-derived amino acids.

English

&nbsp; The microsatellite or simple sequence repeat (SSR) marker analysis was done to determine the allelic diversity and relationship among thirty-five Asian cultivars of rice including 19 aromatic, 13 non-aromatic and 3 japonica type cultivars. A total of 144 alleles were detected at the 32 SSR loci,&nbsp;of which 141 (98%) were polymorphic. The number of alleles generated by each marker ranged from 2 to 13 with an average of 4.5 alleles per marker. The size of smallest and largest allele ranged from 8 (RM122) to as high as 71 (RM302). Polymorphism information content (PIC) values ranged between 0.157 (RM19, RM55) and 0.897 (RM70), with an average of 0.603 per marker. Basmati rice varieties amplified different alleles at 15 of the SSR loci than those in the&nbsp;japonica&nbsp;and/&nbsp;or&nbsp;indica&nbsp;rice varieties. A number of SSRs were identified that could be utilized to differentiate between basmati and other non-basmati rice varieties. The RM252 and RM310 showed a clear differentiation of&nbsp;japonica&nbsp;cultivars from other ones.&nbsp;Pair-wise Nei and Li&rsquo;s similarity coefficients ranged from 0.19 to 0.90.&nbsp;The dendrogram based on the cluster analysis by microsatellite polymorphism, grouped 35 rice cultivars into two major groups effectively differentiating the tall, late maturing and slender aromatic cultivars from the short statured, early, short bold and long bold non-aromatic cultivars. These results could be useful&nbsp;for monitoring purity, genotype identification and for plant variety protection. &nbsp; Key words:&nbsp;Genetic diversity,&nbsp;Oryza sativa, Asian rice, microsatellites.

Genetic analysis of resistance genes in an Indica-type rice (Oryza sativa L.), Kasalath, using DNA markers

We searched for blast resistance genes in an Indica-type rice (Oryza sativa L.) cultivar, Kasalath. The resistance gene was estimated based on the reaction patterns to standard differential blast isolates from Japan and Philippines against the monogenic lines as differential varieties targeting 24 kinds of resistance genes. Kasalath showed complete resistance only to a Japanese isolate, Hoku1, which was avirulent to genotypes containing the Piz allele genes and virulent to genotypes containing Pia and Pish. Kasalath was susceptible, or only moderately resistant, to the Philippine isolates. A QTL analysis for resistance to Hoku1 was performed in backcross inbred lines derived from crosses between Kasalath and a Japonica-type cultivar, Nipponbare (recurrent parent), harboring Pia and Pish. A resistance QTL with the Kasalath genotype was detected in the same region as Pia on chromosome 11. Association analysis in 50 chromosome segment substitution lines detected three associations, on chromosomes 6, 8 and 11; the association located in the same region as the QTL on chromosome 11 had a strong resistance effect. These reaction patterns indicated that Kasalath did not harbor Pia and that the QTL on chromosome 11 was the other allele of Pia or a novel resistance gene.

Genotypic variation in grain cadmium concentration of lowland rice

AbstractCadmium (Cd) contamination of paddy rice soils is commonly observed in the Yangtse River Delta, China. Large Cd uptake by rice plants and its translocation into the grains can entail human‐health risks. Genotypic variations in Cd uptake and a differential Cd partitioning into grains will be the basis for developing a rice screening or breeding tool for low grain Cd. A field experiment, conducted at the experimental farm of Jiaxing, Zhejiang province from 2002 to 2004, compared 38 rice genotypes of different types (indica vs. japonica) collected from the Yangtse River Delta. The results showed large differences in Cd concentrations in straw, brown rice, and grain chaff among the rice genotypes grown on Cd‐contaminated soil. Concentrations in brown rice ranged from 0.06 to 0.99 mg Cd kg–1. The total Cd uptake in brown rice varied between 0.96 and 28.58 μg plant–1. In general, indica‐type cultivars accumulated significantly more Cd than the japonica‐type cultivars. The Cd concentration in straw was highly correlated with that in brown rice. While significant differences in the Cd‐partitioning ratio (% share of total Cd uptake found in brown rice) among rice genotypes were observed, these were not correlated with Cd concentration of brown rice. This indicates that the Cd accumulation in rice grains appears to be governed mainly by the Cd uptake by the plant and probably not by differential Cd partitioning. The large genotypic variation suggests the possibility to lower the Cd content of rice by genotype selection. The development of such breeding tools should focus on low Cd uptake rather than Cd partitioning between straw and grain.

Correlation between Viability of Pollination and Length of Basal Dehiscence of the Theca in Rice undera Hot-and-Humid Condition

Anticipated global warming may increase the floret sterility of rice (Oryza sativa L.). For selection of genotypes tolerant to high temperatures during the flowering period, it is important to identify morphological traits associated with tolerance to temperature stress. This study investigated the relationship between the length of dehiscence at the basal part of thecae and the viability of pollination in 18 cultivars of rice subjected to a hot-and-humid condition (37/25 ˚C, day/night, >90% relative humidity) for three days at flowering. Control plants were left under the ambient conditions in a semi-cylindrical house covered with cheesecloth (30% shading; temperature range: 24-35 ˚C). The length of basal dehiscence of thecae and the number of pollen grains on the stigmata were examined with a light microscope after flowering. The length strongly correlated with the percentage of florets having more than 80 pollen grains on the stigmata under the ambient condition (r = 0.72, P < 0.001), and with the percentage of florets having more than 20 pollen grains on the stigmata under the hot condition (r = 0.93, P < 0.001). In other words, the length correlated with pollination viability or reliability under both conditions. In addition, basal dehiscence was shorter in the non-japonica-type cultivars than in many of the japonica-type cultivars under both conditions. We concluded that the low pollination viability in the non-japonica-type cultivars is associated with their small basal dehiscence on the thecae, and the length of basal dehiscence can be used as a selection marker of high temperature tolerance.

Variations of Floral Traits in Asian Cultivated Rice (Oryza sativa L.) and its Wild Relatives (O. rufipogon Griff.)

To clarify the inter- and intraspecific variations of floral traits in rice, we investigated eleven traits related to pistil, stamen and glume using 128 Asian cultivated rice (Oryza sativa L.) accessions including 72 Indica and 56 Japonica type accessions, and 53 wild rice (O. rufipogon Griff.) accessions including 32 perennial and 21 annual ecotype accessions. We examined the results from three specific levels: intraspecific variation between perennial and annual ecotypes of wild rice, interspecific variation between cultivated rice and wild rice, and intraspecific variation between Indica and Japonica type cultivars. The annual wild rice accessions exhibited a shorter stigma and anther than the perennial wild rice ones. The cultivated rice accessions showed a lower stigma exsertion, shorter stigma, shorter anther, and thicker and wider lemma and palea than the wild rice accessions. These floral traits of cultivated rice are considered to play an important role in selfing and high seed production. None of the floral traits showed distinct differences between the Indica and Japonica type accessions in cultivated rice, although the Indica type accessions tended to display a slenderer stigma and glume than the Japonica type accessions. It is suggested that the varietal differentiation into the Indica and Japonica types is not likely to be related to genetic variations of floral traits. We clarified the differences in floral traits between annual and perennial ecotypes of wild rice, between cultivated rice and wild rice, and between the Indica and Japonica type cultivars, and discussed the relationship between genetic variations of floral traits and domestication and varietal differentiation in rice.

Root System Development of Japonica-Indica Hybrid Cultivars. 2. Branching habit.

Root system development of japonica-indica hybrid rice cultivars (J-IH : Milyang 23, Suwon 258) was compared with that of japonica-type cultivars (JT: Nipponbare, Koshihikari) with reference to branching habit from the viewpoint of developmental morphology. The four cultivars were grown in 45-liter polyethylene containers with paddy field soil and the plants with their root systems were carefully dug up at the grain-filling stage. After careful washing, the main stems of each cultivar were divided into each phytomer and the number, diameter and length of both crown and lateral roots were recorded together with their node position. From these data, the root dimensions (total number of lateral roots, total roots surface area and total root volume) were estimated for each crown root. The results indicated that lateral root development of J-IH was more vigorous than that of JT, especially in the higher phytomers formed after the panicle initiation stage. Such vigorous root branching in J-IH was mainly attributed to an increase in the number of second-order lateral roots. Detailed examination showed that the L-type first-order lateral roots were longer and the density of both L-type first-order and S-type second-order lateral roots were higher in J-IH than in JT. Thus, the root system of J-IH was characterized by long and dense L-type first-order lateral roots and large volume of S-type second-order lateral roots due to their high density. Results of this study suggest that the root system of J-IH increases the total length and surface area, by developing many S-type sedond order lateral roots, which may be related to their high-yield of J-IH.

Factors affecting variation in CH4 emission from paddy soils grown with different rice cultivars: A pot experiment

The growth of rice plants greatly influences CH4 emission from paddy fields through the supply of organic materials such as root exudates and sloughed tissues, the release of oxygen to the root environment, and the transfer of CH4 from the rhizosphere into the atmosphere through the aerenchyma. In the present pot experiments, the effects of the release of water‐soluble organic substances from roots, the air space in roots, and the CH4‐oxidizing capacity of roots on intervarietal differences in CH4 emission were examined using three Japonica type cultivars (Norin 25, Nipponbare, and Aoinokaze), which differ in morphological properties. The CH4 emission rates varied among the cultivars from mid‐July (tillering stage) to the beginning of September (heading stage).Total CH4 emission throughout the rice growth period was largest for Norin 25, followed by Nipponbare, and Aoinokaze. In August, the rate of release of water‐soluble organic substances from roots was largest for Norin 25. The air space in roots was also largest in Norin 25 and least in Aoinokaze. The stable carbon isotopic ratios (δ13C) of CH4 in roots were 3–10‰ higher than those in soil in August. The difference in δ13C values of CH4 between roots and soil was largest for Aoinokaze and smallest for Norin 25. In September, the difference in δ13C values of CH4 between roots and soil became small (2–3‰). These findings suggest that the proportion of CH4 oxidation in the rhizosphere was largest in the cultivar which emitted the smallest amount of CH4 and that the proportion became smaller with continued plant growth.

Specific Accumulation of Antifungal 5-Alk(en)ylresorchinol Homologs in Etiolated Rice Seedlings

The accumulation of a mixture of 5-alk(en)ylresorcinol homologs (ARs) composed of C13:0, C15:1, C15:0, C17:1, and C17:0 carbon chains in rice seedlings (Oryza sativa, cv. RD-25) that exhibited high antifungal activity against the rice blast fungus was specific to etiolated plants. ARs accumulated specifically in the etiolated plants, this accumulation being much more in the underground sections, and decreased rapidly when the etiolated seedlings were exposed to light. Indica- and Africa-type cultivars and weedy- and wild-type rice accumulated the ARs, but Japonica-type cultivars did not. Interestingly, the ratio of ARs in the wild rice varieties distantly related to the cultivars was significantly different from that of the wild rice closely related to the cultivars and weedy types.

Effect of decrease in supply of potassium on the growth and concentrations of major cations in the tissues of four rice (oryza satival.) genotypes at the vegetative stage

Abstract Using four hydroponically-grown rice (Oryza sativa L.) genotypes (a japonica-type cultivar Nipponbare, an indica-type cultivar Takanari, a root-growth inhibiting mutant and its original cultivar, Fujiminori), the effect of the decrease in K supply on the growth and cation concentrations was investigated. Generally, the four genotypes showed a similar response to K-deprivation in terms of relative growth and distribution of major cations, although some differences in the response were observed among the genotypes* The K-deprivation induced the reduction of growth, and decrease of K concentrations in the leaf blades, leaf sheaths, and roots. Na was preferentially accumulated in the leaf sheaths, while Mg and Ca were predominantly distributed into the leaf blades. In the roots, K-deprivation resulted in small changes in Na, Mg, and Ca concentrations. These results suggested that osmotically Na may partly replace K in the leaf sheaths, and that the Na replacement in the leaf blades was small and divalent cations, in particular, Mg may play a role to some extent. However, these osmotic replacements could not compensate for the growth reduction caused by K-deficiency.