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Somaclonal selection of physiological mutants and several problems related to rice cell breeding

100%

Kinoshita T. , Mori K.

nr 1

Tolerance to a new herbicide, pyributycarb, was evaluated both at the plant and cellular levels. Several highly or moderately tolerant strains chosen at the plant level, showed a parallel relation of to tolerance at the cellular level. However, on the whole, correlation between total tolerance indices and survival rates of calli was not significant in 18 out of the 80 studied strains. As a result of somaclonal selection for two herbicides, lines NB-200 and NM-100 were regenerated from the tolerant calli screened with benthiocarb at 200 ppm, and molinate at 100 ppm, respectively. In the R₂ generation, both the lines displaned a stable tolerance both at the plant and cellular levels. Thus the highly tolerant mutant lines were developed from a moderately tolerant line, N-61, via in vitro selection. To achieve a short-cut method in the interspecific genetic exchange, a series of techniques related to cell fusion were established in rice and related species. Two kinds of somatic hybrids between the cultivar Kitaake and tetraploid Oryza species, O. punctata and O. officinalis, were successfully produced. Among the somatic hybrid plants, a wide range of chromosomal variation was observed. Aneuploid plants with a chromosome number around 2n = 72 (hexaploid), which are expected from a symmetric fusion between diploid and tetraploid strains, were obtained showing mixoploidy within a plant. Most of the somatic hybrids were characterized by intermediate features of plant-type showing high sterility, shattering of spikelets and reduced plant height. As an exception, a diploid plant, which was identified by RFLP analysis using the rDNA gene probe, closely resembled Kitaake and produced viable seeds. A tetraploid hybrid plant was also promising for the introduction of economically important characters through the reduction of chromosome numbers by doubled haploids. Gametoclonal variation and gamma radiation was applied to Kitaake. The mutation frequency was prominently increased by gamma ray treatment, especially at high doses of 200 Gy or 300 Gy. In the M₃R₂ or M₄R₃ generations, most of the variants showed unfavourable characters. Most of the mutant characters were governed by single or double recessive genes. Several mutants such as short culm and early flowering time might be used for rice breeding.

Expression of the BTB/POZ domain-containing protein At1g63850-like gene CsFDI1 is enhanced by sugar starvation in cucumber fruit

80%

Tazuke A. , Kinoshita T. , Asayama M.

nr 02

The cDNA of Cucumis sativus Fruit Defoliation Induced 1 (CsFDI1) was newly cloned using the subtraction method from a fruit of a defoliated cucumber (Cucumis sativus L. cv. Tokiwa) plant. An expression analysis of CsFDI1 in fruits and leaves was conducted along with those of the asparagine synthetase 1-like gene (AS) and Cucumis sativus Somatic Embryogenesis Zinc Finger 1 (CsSEF1), previously reported as control marker genes for sugar starvation. The transcript level of CsFDI1 and AS was relatively high, whereas that of CsSEF1 was very low under normal fruit development. The time course of the transcript levels of the three genes under prolonged darkness was compared with that of the fruit respiration rate and leaf starch concentration. The fruit respiration rate suggested that photoassimilate translocation to fruit ceased abruptly under prolonged darkness. The transcript level of CsFDI1, AS, and CsSEF1 increased in fruits, but the time course of the change was quite different in fruits and leaves under the condition of sugar starvation. The response of AS in leaves and CsSEF1 in fruits was close to all-or-none.