Breeding for high-yielding rice has been directed toward those types that have a larger number of spikelets per panicle. The objective of this study was to examine the relationship within a cultivar between the size of the apical dome (AD) and the morphological characters of the panicle components such as the number of primary rachisbranches (PBs), secondary rachis-branches (SBs), and spikelets per panicle. Rice plants (cv. Akenohoshi) were subjected to four short-day (10h photoperiod) treatments at various developmental stages to change the duration of the vegetative stage and the AD size at panicle initiation (PI). Shoot apices having ADs were sampled at two-day intervals from the late vegetative stage to the early reproductive stage. The sections of the shoot apices were embedded in paraffin and stained with toluidine blue O. The base diameter and height of the ADs were measured with an ocular micrometer, and at heading, the numbers of PBs, SBs, and spikelets were counted. A delay in the start of the short-day treatment increased the total number of leaves on the main culm, extending the vegetative stage. Extension of the vegetative stage increased the AD diameter at PI. However, the effect of the short-day treatments on the AD height was unclear. Enlargement of ADs was accompanied by the increase in the number of differentiated PBs, but not always by that in the number of SBs and spikelets. The results suggested that spikelet number is influenced by plant nutritional conditions as well as by the AD size at PI.
The objectives of this study are to compare the floret sterility induced by a high temperature given in the daytime during the flowering period among nine japonica rice varieties, and to clarify the mechanism of the high-temperature-induced sterility. Nine japonica rice varieties were subjected to 35.0, 37.5 or 40.0°C day-temperature conditions (1000-1600) for six consecutive days using sun-lit phytotrons, and the percentage of fertility, pollination and germinated pollen grains on the stigmas were examined. The temperature that caused 50% sterility varied with the variety, and a difference of approximately 3.0°C was observed between the most tolerant and susceptible varieties. Under the 37.5°C day-temperature condition, the percentage of florets with 10 or more germinated pollen grains was roughly coincident with the percent fertility, but under the 40°C day-temperature condition, it was higher than the percent fertility. Many of the florets with less than 10 germinated pollen grains had less than 20 total pollen grains on their stigmas under both temperature conditios. From these results, we concluded that sure pollination under high-temperature conditions is an important factor and that the high-temperature tolerance of the processes following pollen germination is also required fertility under excessively high temperature conditions.
The objective of this study was to identify rice cultivars with high emergence ability under low soil-moisture conditions using a large number of rice cultivars, and to clarify the differences between the rates of emergence in lowland and upland, white-and red-kerneled, and non-glutinous and glutinous cultivars. First, 30 cultivars with a high emergence rate at 14 days after sowing (DAS) were selected at a soil water potential of - 1.17 to - 0.89 MPa from 382 cultivars through four screening experiments. In these experiments, the emergence rate was significantly higher in the upland cultivars than in the lowland cultivars. The red-kerneled cultivars also had a significantly higher emergence rate than the white-kerneled cultivars. However, no difference in emergence rate was observed between the non-glutinous and glutinous cultivars. Second, the emergence rates of various cultivars were examined at a soil water potential of - 1.62, - 1.23, and - 1.07 MPa. The higher the soil water potential, the higher the emergence rate at 28 DAS and the shorter the time to the emergence. The order of cultivars in their emergence rate at 13 DAS at - 1.07 MPa was similar to that at 28 DAS at - 1.62 MPa. Therefore, the data at 13 DAS at - 1.07 MPa were used to compare the selected 30 cultivars for their emergence ability under low soil-moisture conditions. Moulla Topa showed the highest emergence rate (78.1%) and Gaiya Rate Bhasunamathe the shortest time to 50% emergence (11.1d) under these conditions.
Growth and structural changes in the seminal root tip of rice seedlings (Oryza sativa L. cv. Nipponbare) in response to NaCl salinity were studied. Seedlings were grown in agar medium with 0, 0.1, 0.3, 1.0, 2.0 and 3.0% NaCl (agar culture), and in water with 0, 0.01, 0.03, 0.06 and 0.1% NaCl (water culture). Seedling growth was significantly suppressed by higher concentrations of NaCl. The effect of NaCl appeared faster in water culture than in agar culture. In both agar and water cultures, root growth was markedly suppressed over shoot growth. Under saline conditions, epidermis, cortex and root cap cells appear to be damaged to a greater extent than the meristem and stelar cells. The most notable ultrastructural change in response to salinity was the development and increment of vacuoles, which seem to provide a space for accumulation of excess ions. Many electron dense deposits were observed in the larger vacuoles of the epidermal and cortical cells. Under saline conditions, cell wall thickening of the epidermis, an increase in endoplasmic reticulum, myelin figures, less compact Golgi bodies and inhibited production of Golgi vesicles were also observed.
Eighteen local varieties of japonica rice and two japonica rice varieties introduced from Japan were studied to collect the basic information on the relationship between the amylographic characteristics and eating quality. The materials were planted in the first and second crop seasons of 1998 in central Taiwan. The pasting behaviors including peak viscosity, hot-paste viscosity, cool-paste viscosity, breakdown viscosity, setback viscosity, consistency viscosity, pasting temperature and the time to reach peak viscosity were measured. The eating quality of rice was evaluated by trained panelists in terms of overall palatability score. All amylographic characteristics except for hot-paste viscosity and overall palatability score varied significantly between the first and the second crops and the interactions between crops and varieties were also significant for all characteristics. Teikeng 2, Teikeng 3, Teikeng 4, and Teikeng 9 showed higher overall palatability scores than the other varieties in the first crop, and Koshihikari and Teikeng 6 showed the best overall palatability in the second crop, respectively. The coefficient of variation was higher in the second crop than in the first crop except the time to reach peak viscosity. Setback viscosity showed the highest variation in all amylographic characteristics. The heritability estimate was also higher in the second crop than in the first crop with the exception of consistency viscosity. The highest heritability values were given for consistency and breakdown viscositites in the first and second crops, respectively. However, the lowest heritability value was given for the time to reach peak viscosity in both crop seasons. The close relationship among peak, hot paste, and cool paste viscosities was found for both crops. The highest correlation coefficient was found between peak and breakdown viscosities in both crops. A significant negative correlation between breakdown viscosity and setback viscosity was observed in both crop seasons. Likewise, peak viscosity had a significant correlation with setback viscosity in both crops. In the first crop, the palatability score was negatively correlated with pasting temperature (r=-0.43**) but positively correlated with the time to reach peak viscosity (r=0.36*). There was a positive correlation between palatability score and peak viscosity (r=0.33**) and a negative correlation between palatability score and setback viscosity (r=-0.34**) in the second crop.
In the field experiments from 1987 to 1992, the treatment with inabenfide at 0.20-0.24g a. i. m-2 reduced the culm length by 4-14% of the control, and prevented breaking-type lodging. The dwarfing effect of inabenfide was evident especially at the lower internodes and at the upper three leaf blades. The yield, percentage of ripened grains and 1000 grain weight of rice plants treated with inabenfide were greater than those of control. Furthermore, we observed an increase in the percentage of ripened grains and the 1000 grain weight by the treatment with inabenfide under lodging-inhibiting conditions and in 1990 and 1992, when lodging was not so much influenced by inabenfide treatment. At 17-18 days after heading, the relative light intensity in the canopy of the inabenfide-treated plants was higher than in the canopy of the control plants, and light extinction coefficient (K) was lower in the former than in the latter. Although the number of grains per panicle was decreased, the number of panicles per hill and the leaf area per grain at early ripening stage were increased by the treatment with inabenfide. The starch content in leaf-sheaths and culms in the inabenfide-treated plants was significantly higher than that in the control from heading to maturity. It is suggested that : (1) Inabenfide promotes the ripening of rice.; (2) The effect is related not only to the direct effect on lodging but also to the "plant type", improved by the treatment with inabenfide.
Experiments were conducted to elucidate the effects of the inoculation of a mixture of several free-living rhizobacteria; Azotobacter, Bacillus, Enterobacter and Xanthobacter which were collected and screened for the nitrogen-fixing ability in China, on nitrogen accumulation, growth and grain yield of rice plants. The inoculation of several bacterial species significantly increased acetylene-reducing activity in the roots of rice plants. The total dry matter yield, grain yield and nitrogen accumulation were increased by the bacterial inoculation by 6 to 13%, 15 to 18%, and 10 to 24%, respectively, in the experiments of 1997 and 1998. The increase of grain yield was associated with the increase of root length and leaf area, and also with the increase of chlorophyll content and photosynthetic rate during the grain-filling period. It was hypothesized that the inoculation of free-living rhizobacteria to rice plants led to increase of nitrogen accumulation in the plants, stimulation of the leaf photosynthesis particularly in the grain-filling stage resulting in the increased dry matter and grain yield.
Beet is a biennial plant. In the first season, it develops leaf rosette on a dwarf stem and forms a thick storage root. Based on the idea that some growth-inhibiting compound may participate in these developmental events, the effects of jasmonic acid (JA) on root thickening and stem elongation (bolting) were examined using beet plants cultured in vitro. JA failed to induce thickening of the tap root, but greatly promoted thickening of lateral roots. Furthermore, JA strongly inhibited bolting induced by chilling or exogenous gibberellic acid. The presence of JA in the tops (leaves and dwarf stems) of field-grown plants was confirmed by mass spectrometry. Although the content of JA seems to be insufficient to account for the induction of root-thickening and for the inhibition of bolting, the results suggest that JA-related compounds are involved in the thickening growth of storage root and in the formation of leaf rosette.
Previously, we found that promotion of ripening by brassinolide (BR) in rice plants is attributable to the rapid translocation of assimilates from leaves to the panicle (Fujii and Saka, 1992). In this study, we examined the effect of BR treatment on the distribution aspects of carbohydrates (starch, sucrose, glucose and fructose) in upper organs induding the panicle of the rice plant (cv. Nipponbare) grown in a low temperature condition (20°C in the daytime / 13°C at night) in a phytotron under natural daylight in summer. Rice plants in a greenhouse in summer were sprayed with BR (2×10-8M and 2×10-9M) twice at around the heading stage, and were then kept in the phytotron and in the greenhouse to examine the carbohydrate contents in leaf blades, leaf sheaths, culms, hulls and hulled grains at the milk-ripe and dough-ripe stages. At milk-ripe stage, the starch content in the plants grown in the greenhouse without BR treatment was overwhelmingly high in hulled grains with a low content in culm, leaf sheaths and hulls, whereas starch was hardly detected in the leaf blade. At the dough-ripe stage, starch was more accumulated in hulled grains. Sucrose content at the milk-ripe stage was low in hulls, but high in leaf sheaths and culms, especially in leaf blades. However, at the dough-ripe stage, a large amount of sucrose was accumulated in culms, and only a small amount in leaf blades. The content of glucose and fructose was 10 to 20% of that of sucrose in each organ, and did not differ so much between the two stages of ripeness. In the plants grown in the phytotron, the total amount of starch was markedly lower and the contents of sucrose, glucose and fructose were considerably higher than those in the greenhouse. The marked decrease of starch content in the phytotron was found in hulled grains while the content in leaf sheaths, culms and leaf blades increased. On the other hand, the increase of sucrose content resulted from the increase in vegetative organs with the decrease in hulled grains. An increase of glucose and fructose were also found in leaf organs at the milk-ripe stage. BR decreased the starch content in leaf sheaths and culms, and increased the contents of starch and sucrose in hulled grains in both temperature conditions. The contents of starch and sucrose in hulls were not influenced so much by BR. Neither did BR largely influence the contents of glucose and fructose. However, BR treatment strikingly increased the 1, 000-grain weight and the percentage of ripened grains in the rice plant in both of the greenhouse and phytotron.
Two distinctive structures were observed on the surface of rice callus treated with cell wall degrading enzymes, pectinase and cellulase by scanning electron microscopy; i. e., membranous, and the fibrillar structures. The membranous layer was digestible with the enzymes, while the fibrillar structures were not. The membranous matrix was mucilaginous, and positive to PAS reaction. Protoplasts were released after the enzyme treatment from the areas covered with the enzyme-digestible mucilaginous layer. The role of the extracellular matrix of the rice callus is discussed from the standpoint of growth and differentiation of the rice callus.