Four new dm-type dwarf mutants DMT-7, DMT-8, DMT-10-1 and DMT-11 were induced from the rice cultivar Taichung 65 (T65) by treatment with N- methyl-N-nitrosourea. These mutants were characterized by a remarkable reduction of the 2nd internode length. Experimental results on the morphological characterization showed that these mutants could be classified into two different groups, type 1 (DMT-7 and DMT-8) and type 2 (DMT-10-1 and DMT-11). Type 1 mutants developed not only dm-type but also dn-type culms in a plant whereas type 2 mutants showed mostly pseudo-d6-type and rarely dm-type culms in a plant. Gene analysis using F2 popurations from the crosses of these mutants with T65 demonstrated that the four mutants were controlled by single recessive genes. Allelism tests indicated that all the mutant genes were located at the same locus. Thus, different phenotypes between the two groups were controlled by different alleles at one locus. Moreover, the alleles of type 1 were dominant over those of type 2. However, no remarkable phenotypic differences were observed between the mutants within each group. Hence, gene symbols for DMT-7 (type 1) and DMT-11 (type 2) were designated as d61-1 and d61-2, respectively. The results of linkage analysis using three morphological markers revealed that d61 was linked to shr1 (shrunken endosperm 1) on chromosome 1 with a recombination value of 21.7% .
The present study was carried out to analyze the sucrose-accumulating ability of the wild accession, L. peruvianum (LPV) var. humifusum LA2153 (LA2153). The mode of inheritance of the PCR band patterns generated with the PCR primers AIT-1 and AIT-2, and the relationship between the PCR band patterns (wild, heterozygous and cultivar types) and their sugar contents, were investigated, using the progeny of interspecific crosses of L. esculentum (LEL) with LA2153. The mode of inheritance of the PCR band pattern revealed one-gene segregation in all of the tested generations. Heterozygous and cultivar types accumulated hexoses, glucose and fructose, but only a small amount of sucrose. On the contrary, wild types accumulated more sucrose than glucose and fructose. From the results of the above experiments and a linkage analysis between the acid invertase gene and the RFLP marker TG102, it was concluded that the sucrose-accumulating trait is controlled primarily by a recessive acid invertase gene closely linked to TG102 on chromosome 3, and that these PCR primers are useful for selecting sucrose-accumulators from the progeny of the cross combination of LEL and LA2153.
Plants resistant to soft rot disease were produced by in vitro-mutagenesis and -selection using a microspore culture system in Chinese cabbage. The effect of ultra-violet (UV) irradiation on microspore embryogenesis was investigated. Embryo production decreased with increasing duration of UV-irradiation and the LD50 was estimated to correspond to an exposure of 12 s. Culture filtrate of soft rot bacteria caused a reduction of embryo formation from microspores and plant regeneration from microspore-derived embryos, suggesting that the culture filtrate is phytotoxic. After 6, 657 embryos derived from UV-irradiated microspores were selected on a medium containing a soft rot culture filtrate, 250 plantlets were regenerated. When their progenies were assessed for resistance to soft rot disease, three lines showing a markedly increased resistance to the disease were obtained. The resistant plants are considered to be mutants produced by in vitro-mutagenesis.
A total of 801 cultivated soybean accessions and 330 wild soybean accessions were screened for genotypes lacking group A acetyl saponins in seed hypocotyls using thin layer chromatography and high performance liquid chromatography. Only one accession from the soybean cultivars, A-b(F) Iacked group A acetyl saponins but it had an unknown saponin. The inheritance of a null allele for group A acetyl saponins in soybeans was determined by crosses between A-b(F) and Shirosennari, which had group A acetyl saponin Aa, and Suzuyutaka, which had group A acetyl saponin Ab, respectively. All F1 seeds from these crosses had Aa and Ab respectively. F2 seeds resulting from these crosses segregated 3:1 indicating that the absence of group A acetyl saponins is inherited as a simple recessive. The gene symbol Sg-1 is assigned to the allele coding for the absence of group A acetyl saponins, Sg-1a for the presence of group A acetyl saponin Aa and Sg-1b for the presence of group A acetyl saponin Ab, respectively. Sg-1a and Sg-1b are co-dominant alleles. Through FAB-MS and chemical analyses, the unknown saponin accumulated in the seed hypocotyls of A-b(F), was assumed to be 3-O-[β-D-glucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→2)-β-D-glucuronopyranosyl]-22-O-[α-L-arabino-pyranosyl] soyasapogenol A.
To analyze the varietal and annual variations in starch pasting properties in sweet potato storage roots, twenty cultivars and strains were grown in both 1996 and 1997. The starch pasting properties were investigated using a Rapid Visco-Analyzer (RVA), and the amylose content and starch content were also examined. The pasting properties showed wide ranges of variation among cultivars and strains, and the amylose content ranged between 13.3 and 17.2%. The correlation coefficients of the pasting temperature, peak viscosity, setback, amylose content and starch content between the two years were 0.867***, 0.654**, 0.784***, 0.902*** and 0.864*** respectively. Analysis of variance showed that the varietal differences were significant at 0.1% Ievel for the pasting temperature, setback, amylose content and starch content. The differences among strains and years were significant at 1% Ievel for the pasting temperature, peak viscosity and breakdown. The estimated heritability values of the pasting temperature, peak viscosity, setback, amylose content and starch content were 0.80, 0.49, 0.77, 0.88 and 0.85, respectively. The amylose content showed significant positive correlations in both years with the pasting temperature, the peak viscosity temperature and the setback. The starch content did not show any significant correlatioui with the pasting properties and the amylose content. These results indicate that it is possible to breed for the improvement of the starch pasting properties in sweet potato.
Using polyacrylamide gel electrophoresis and isoelectric focusing, we studied the genetic control of isozymes in nine enzyme systems of taro, Colocasia esculenta (L.) Schott; acid phosphatase (ACP), diaphorase (DIA), glutamate oxaloacetate transaminase (GOT), hexokinase (HEX), isocitrate dehydrogenase (IDH), phosphogluconate dehydrogenase (PGD), phosphoglucoisomerase (PGI), shikimate dehydrogenase (SKDH), and superoxide dismutase (SOD). Diploid taro accessions from Nepal and other Asian countries were either selfed or crossed, and isozyme band segregation was tested in their progeny. A total of 12 Ioci with two to three alleles were determined for isozymes in leaf tissue; six loci of Got-1, Cot-5, Idh-1, Pgi-3, Sod-3 and Sod-4 encoded a dimeric enzyme, whereas Acp-4, Dia-2, Hex-2 and Skdh loci encoded a monomeric enzyme. Null alleles were observed in the three loci, Hex-2, Pgd-1 and Sod-2. The loci of GOT, IDH, PGI and SKDH have been reported in the wild taro from Bangladesh. These reported loci appear to be identical to those observed in this study except for the PGI Iocus, which was detected using a different electro-phoresis method. Including the nine isozyme loci of alcohol dehydrogenase, esterase, Ieucine aminopeptidase and phosphoglucomutase we identified previously, a total of 46 alleles at 21 Ioci of 13 enzyme systems have become available for genetic analyses in taro.
A Iinkage map of Brassica rapa was constructed based on random amplified polymorphic DNAs (RAPDs), isozymes and restriction fragment length polymorphism (RFLP), using an F2 population derived from the crossing of a Chinese cabbage line, ‘Homei 09' and a club-root-resistant turnip line, ‘Siloga S2'. The map covered 851 cM, about half of the genome, and consisted of 16 linkage groups. ‘Homei 09' is highly responsive to microspore culture unlike ‘Siloga S2'. To identify the loci affecting embryogenesis in microspore culture, frequencies of RAPD in a microspore-derived population obtained from an F1 of the same parentage were scored. Several parts of the linkage map showed a conspicuous distortion toward ‘Homei 09' alleles. The microspores of another F2 population from the same parentage were cultured. Embryogenic ability and RAPD genotype of the each F2 plant were scored. Embryogenic ability of the plants for two marker types (presence and absence) was determined at each RAPD Iocus. In some parts of the linkage nrap, the plants carrying ‘Homei 09' alleles showed a higher ability of embryogenesis than those of ‘Siloga S2' homozygotes. Comparison of the distortion data with those in the embryogenesis of the F2 suggested that at least one part of the linkage map affected the embryogenic process in microspore culture. Genes in these areas of ‘Homei 09' may play a key role in triggering the embryogenesis or in embryo development at the early stage of microspore culture.
We constructed a bacterial artificial chromosome (BAC) library for the indica rice variety Kasalath using a new BAC vector, pCHR8, suited for plasmid rescue, containing nine unique restriction sites in a multicloning site. This Kasalath BAC Iibrary consists of about 65, 000 clones with an average insert size of 106 kb using HindIII partially digested DNA fragments. It represents approximately sixteen rice haploid genome equivalents which are sufficient for the full coverage of the rice genome with BAC clone contigs. The library was constructed from only a single ligation mixture with high transformation efficiency. The quality of this BAC Iibrary was ascertained by successfully retrieving the BAC clones for seven rice RFLP markers. We could isolate eleven individual BAC clones using RFLP markers that linked to the lethal factor locus for segregation distortion on rice chromosome 3. The content of the chloroplast and mitochondrial DNA in this library was estimated to be 2.8% and 0.4%, respectively. These results demonstrate that this Kasalath BAC Iibrary should be suitable for map-based cloning and physical mapping of the rice genome.
Hybrid lethality was surveyed in 186 cross combinations among 17 species from 9 sections of the genus Nicotiana. The hybrid seedlings of 14 cross combinations expressed lethality characterized by one of four symptoms and the lethality was classified into four types as follows: browning of the shoot apex and the root tip (Type I), browning of the hypocotyl and the roots (Type II), yellowing of the true leaves (Type III) and formation of multiple shoots (Type IV). Three kinds of rescue methods for the lethality were applied to the 4 cross combinations expressing different types of the lethality as follows: (1) culture of hybrid seedlings under high temperature conditions to suppress the lethality, (2) culture of the cotyledonary segments of the hybrid seedlings to obtain regenerants overcoming the lethality and (3) culture of the hybrid seedlings on a medium containing cytokinin to obtain regenerants overcoming the lethality. The 1st and 2nd methods were effective in the cross of N. nudicaulis×N. tabacum expressing the lethality Type I. All the methods were effective in the cross of N. paniculata × N. suaveolens expressing the lethality Type II. Only the Ist method was effective in the cross of N. glutinosa× N. repanda expressing the lethality Type III. None of the methods were effective in the cross of N. paniculata × N. alata expressing the lethality Type IV. Each lethality type exhibited a specific set of responses to the three rescue methods. These findings suggest that the lethality observed in interspecific crosses of Nicotiana differs in the physiological processes leading to death.
To date, there have been only a limited number of reports about the nuclear-encoded subunit for cytochrome c oxidase (COX) in the mitochondria of higher plants. In the present study, we characterized a cDNA encoding a novel subunit of COX (COX6b), which had not previously been reported in plants. It was found that the rice COX6b gene encodes 169 amino acids with a calculated molecular mass of 19 kDa. The deduced amino acid sequence of rice COX6b is longer than those of vertebrate and yeast COX6b subunits. Genomic Southern hybridization suggested that the rice COX6b subunit is encoded by at least two copies of COX6b genes. Northern hybridization showed that one of the genes (COX6b-1) is constitutively transcribed in different organs of rice. However, the steady-state mRNA levels slightly varied among organs.