Pollen sterility was induced by heat stress applied about 10 days before flowering in the snap bean Phaseolus vulgaris L. Cytohistological changes in the tapetum during early development of the anther were studied to identify the tissues most sensitive to high temperature stress. The first distinct structural abnormalities were detected in the distribution pattern of the rough endoplasmic reticulum (RER) in the tapetum at the early microspore stage under high temperature conditions. Stacks of RER were frequently observed in the tapetum under optimal conditions, but rarely occurred under high temperature conditions. Various patterns of endoplasmic reticulum (ER) arrangement -linear, wavy, looped or circular -were observed in the tapetum. Two types of circular ER were observed at the microspore stage under high temperature conditions, RER with ribosomes on the surface and smooth endoplasmic reticulum (SER) lacking ribosomes. The tapetum underwent degenerative changes under high temperature conditions earlier than under optimal conditions. The structural abnormalities of the microspore were associated with tapetal degeneration. We concluded that high air temperature affected the ER structure and blocked its function in the tapetum, and then induced earlier than usual degeneration of tapetum. Pollen sterility is associated with tapetal degeneration. Materials and methodsEighty snap bean plants (Phaseolus vulgaris L. cv. Kentucky Wonder) were grown 25 cm apart in four rows, each 1 m wide × 5 m long, in a net house from 18 April at JIRCAS Okinawa Subtropical Station in 1997. About 50 flower buds of different sizes were collected randomly from the plants on 28 May (optimum conditions). The maximum temperature that day was 28.6°C, the minimum 24.4°C and the average 26.2°C. Average air temperature in May was 25.8°C.

To clarify the role of mitochondrial small heat-shock protein (MT-sHSP) in the heat-shock response, we introduced the tomato (Lycopersicon esculentum) MT-sHSP gene under the control of the 35S promoter into tobacco (Nicotiana tabacum), and examined the thermotolerance of the transformed plants. Irrespective of the orientation, sense or antisense, of the gene, the transgenic plants exhibited a normal morphology and growth rate in the vegetative growth stage. When 4-weekold seedlings were exposed to sudden heat stress, the sense plants which overexpress the MT-sHSP gene exhibited thermotolerance, whereas the antisense plants in which the expression of the gene is suppressed exhibited susceptibility.

No abstract

The genetic variation among 23 accessions of 5 species in the subgenus Ceratotropis, genus Vigna, were investigated by random amplified polymorphic DNA (RAPD) analysis . A total of 404 fragments amplified with 24 primers were scored and analyzed by cluster analysis . The accessions used were separated into two main groups with an average of 70% differences . Within the main groups, five subgroups were recognized, which are in complete agreement with taxonomic species . Wild forms were always grouped with their most closely related cultivated forms and they showed variation in each species . The largest intraspecific variation was found in V radiata (mungbean), in which wild forms (V radiata var. sublobata) were highly different from each other and from cultivated forms . V angularis (adzuki bean) showed the least variation and thus, was probably differentiated in relatively recent times .