Iwao Nishiyama

Effects of High Temperature on the Development of Pollen Mother Cells and Microspores in Barley Hordeum vulgare L.

The development of the inflorescence, microspores and anthesis were well synchronized among individuals or in the panicles of barley under controlled environmental conditions. To study the effects of high-temperature stress on the development of pollen mother cells (PMCs) and microspores, the plants were subjected to high temperature treatment at different stages of reproductive growth. When plants were exposed to high temperature for five days at the early differentiation stage of the panicle, pollen grains had apparently normal exine but no or little cytoplasm. At the pre-meiotic stage of PMCs, high temperature caused subsequent development of short anthers possessing no pollen grains. When plants were exposed to high temperature during meiosis of PMCs, all pollen grains possessed exine and were swollen but showed little starch accumulation. In these plants treated at high temperature, the panicles at the heading stage had a normal appearance, but their seeds were virtually sterile. These results indicated that there are at least three stages of reproductive growth hypersensitive to high temperature, which resulted in abnormal terminal phenotypes different from one another.

Number of Pollen Grains in Rice Cultivars with Different Cool-Weather Resistance at the Young Microspore Stage

Abstract The difference in the number of pollen grains may be the primary factor determining the resistance to cool weather at the young microspore stage in rice (Oryza sativa L.) cultivars. To confirm this hypothesis, we compared the number of pollen grains among the cultivars or lines with various cool-weather resistance. The cultivars or lines used in the experiments were mainly released or grown in the Tohoku district (the northern part of the mainland of Japan). The number of pollen grains showed high correlation with the degree of cool-weather resistance, but considerably varied with the cultivar or line, even in the group having the same cool-weather resistance. Each group with different cool-weather resistance was divided into two subgroups, implying the existence of another genetic factor determining the resistance. The number of pollen grains in the plants cooled at the young microspore stage showed higher correlation with the degree of the cool-weather resistance than that in the control plants without exposure to low temperature. The correlation between the pollen number and spikelet sterility was also analyzed using the data of Satake and Shibata (1992, Jpn. J. Crop Sci. 61 :454–462), who primarily used the cultivars in Hokkaido (the northernmost island of Japan). The results were basically the same as those obtained in the present experiments. These results confirmed the hypothesis that the variation in the number of pollen grains is a primary factor of the resistance to cool weather at the booting stage in the cultivars in the northern part of Japan. The results also suggested the existence of another genetic factor determining the resistance.

Effects of Foliar and Root-Applied Benzylaminopurine on Tillering of Rice Plants Grown in Hydroponics

Abstract Many studies have confirmed that exogenous cytokinins increase tillering in grasses as wheat, oat and barley. In this study, the effects of benzylaminopurine (BA) on tillering of two rice cultivars, North Rose with low tillering ability and Sasanishiki with high tillering ability, were examined using hydroponics. Foliar spray of BA was applied to both cultivarsat the 6-leaf stage. Root application of BA was used to Sasanishiki at the 8-leaf stage. Both root-applied and foliar-sprayed BA retarded the increase of tillers and resulted in significant decrease in tiller numbers per plant. The result indicated that primary tillers were much more affected than secondary tillers. Leaf production on the main stem was also temporarily inhibited with the exception of foliar spray to plants of cv. Sasanishiki. The effective concentration of BA on tillering was over 0.01μM for root application and 100 μM for foliar spray. Magnitude of effect of root application was greater than that of foliar spray in cv. Sasanishiki. Foliar-sprayed BA mainly inhibited tillers that are at the stage of differentiation of tiller buds from appearance. Root-applied BA could further inhibit the growth of tiller buds into tillers. In conclusion, BA inhibited the tillering of rice plants rather than promoting it, whichis inconsistent with general description of cytokinin roles.

Effects of Benzylaminopurine on Shoot and Root Development and Growth of Rice(cv.North Rose)Grown Hydroponically with Different Nitrogen Forms

Summary : In spite of a large number of reports on the effects of cytokinin application on growth of wheat, barley and other crops, the impact of it on rice growth has rarely been investigated. The objective of this study was to examine the effects of benzylaminopurine (BA) on shoot and root development and growth of rice plants. Rice (Oryza sativa L. cv. North Rose) was grown in hydroponics under all NH4+, all NO3– and an equal mixture of both forms. From the 6th leaf stage on, 100μ M BA was sprayed to the shoot once every two days for a total of 5 times. BA spray inhibited the development and growth of plant age, plant length, leaf blade length and the root as a whole with the exception that the length of adventitious roots was increased by BA in NH4+-N-grown plants. BA spray also decreased the dry-matter production of both the shoot and root. Single NH4+-N inhibited the shoot and root development and growth compared with N03-containing N sources. BA counteracted to some extent the inhibitory effect of NH4+-N on plant length, average adventitious root length and the longest adventitious root length. We concluded that 100μM BA spray basically inhibited the shoot and root growth and development of rice (cv. North Rose) grown in hydroponics, but the effects on shoot development are temporary and the treated plants attain or exceed the development of the control plants while the inhibited development of the root did not recover within the experiment period.