Sachio Maruyama

Natural variation in rice starch synthase IIa affects enzyme and starch properties

The natural variation in starch synthase IIa (SSIIa) of rice (Oryza sativa L.) was characterised using near-isogenic lines (NILs). SSIIa is a candidate for the alk gene regulating the alkali disintegration of rice grains, since both genes are genetically mapped at the same position on chromosome 6 and related to starch properties. In this study, we report that the alkali-susceptible cultivar Nipponbare lacked SSIIa activity in endosperm. However, the activity was detected with NILs having the alk allele of alkali-tolerant Kasalath. SSIIa protein was present even in Nipponbare endosperm, but it was not associated with starch granules at the milky stage of endosperm. Three single-nucleotide polymorphisms (SNPs) predicting amino acid substitutions existed between the cDNA sequences of SSIIa of Nipponbare and Kasalath were genotyped with 65 rice cultivars and four wild relatives of cultivated rice. The results obtained explain the potential importance of two of the amino acid residues for starch association of rice SSIIa. An analysis of the chain-length distribution of β-limit dextrin of amylopectin showed that without SSIIa activity, the relative number of A-chains (the short chains without branches) increased and that of B1-chains (the short chains with branches) decreased. This suggests that, given the SSIIa defect, short A-chains could not reach a sufficient length for branching enzymes to act on them to produce B1-chains.

Seedling Emergence and Establishment under Drained Conditions in Rice Direct-Sown into Puddled and Leveled Soil —Effect of calcium peroxide seed coating and sowing depth—

Abstract Inconsistent seedling establishment is a major constraint in rice direct-sown into puddled and leveled soil. We clarified the effect of water management on seedling emergence and establishment at different sowing depth for seeds with or without calcium peroxide coating. Drainage during 10 to 15 days after sowing scarcely affected the early -stage emergence compared with the wet and flooded conditions. Drainage and wetness promoted the late-stage emergence compared with the flooded conditions regardless of sowing depth and seed coating. The numbers of floating and turned down seedlings, and seedlings with delayed emergence were lower in the drained and wet plots than in the flooded plot. Thus, seedling establishment in such plots was markedly higher than that in the flooded plot, especially when seeds were sown at the soil surface. The dry weight of plants at seedling establishment was greater in the drained and wet plots than in the flooded plot, when seeds coated with calcium peroxide were sown below the soil surface. Drainage during seedling establishment thus improved seedling emergence and establishment regardless of sowing depth and seed coating treatment, and the drainage treatment enhanced the growth and dry weight increase of plants during seedling establishment compared to flooding treatment.

Proteins and Carbohydrates in Developing Rice Panicles with Different Numbers of Spikelets: —Cultivar difference and the effect of nitrogen topdressing—

Abstract Proteins and carbohydrates in developing rice panicles were analyzed to see whether these parameters control spikelet number in rice. Two rice cultivars and 2 levels of nitrogen topdressing were used to obtain panicles with different numbers of spikelets. A japonica rice cultivar, Nipponbare, with topdressing (H) had 1.8 times more spikelets per panicle than that without topdressing (L). Moreover, the number of spikelets per panicle in an indica rice cultivar, Takanari, without topdressing was 2.7 times larger than that in Nipponbare-L. Panicles with more spikelets (LP) in Nipponbare-H and Takanari-L showed slower growth than those with few spikelets (SP) in Nippanbare-L in an early stage. LP, however, increased markedly in size thereafter, eventually exceeding SP, in length and fresh weight. Soluble protein content was higher in LP than SP in an early stage, but this difference was hardly detected in a late stage. No clear difference was observed in sugars or starch between LP and SP. Analysis of soluble and insoluble proteins by SDS-polyacrylamide gel electrophoresis showed that bands corresponding to insoluble proteins with a molecular weight about 42 kDa were present at higher intensities in LP than in SP. These results suggest that the spikelet number in rice is controlled by the soluble protein content in an early stage and insoluble proteins with a molecular weight of 42 kDa during panicle development, but not by the carbohydrates in developing panicles.

Dry-Matter Partitioning and Accumulation of Carbon and Nitrogen during Ripening in a Female-Sterile Line of Rice

Abstract To evaluate the effect of sink restriction on dry-matter partitioning to rice plant organs during ripening, we observed the dry-weight partitioning and accumulation of carbon and nitrogen in a female-sterile line, FS1, which has intact panicles with only a few fertile grains, in comparison with those in a normal counterpart, Fujisaka 5. In spite of the loss of sink function in the panicles, FS1 produced a larger amount of dry-matter than Fujisaka 5. Without a change of panicle dry weight throughout the ripening period, FS1 increased dry weights of culms and leaf sheaths at the early stage and of late tillers at the late stage. The amounts of dry-matter partitioned to panicles, culms plus leaf sheaths and late tillers in FS1 were comparable to those amounts in Fujisaka 5 at maturity, indicating that the latter two organs function as a sink of dry matter to substitute for panicles. Carbon partitioning to plant organs was basically similar to the dry-matter partitioning. Since the amount of nitrogen in a plant hardly increased during the ripening period in FS1 and Fujisaka 5, nitrogen partitioning to plant organs was different from the partitioning of dry matter and that of carbon. Culms, leaf sheaths and late tillers function as a sink of nitrogen partly to substitute for panicles, but the sum of nitrogen partitioned to these organs and panicles in FS1 was markedly smaller than in Fujisaka 5 at maturity, suggesting that other organs do not substitute for panicles in the sink function for nitrogen partitioning. FS1 developed late tillers rapidly at the late stage and had a carbon-nitrogen ratio in the stems different from that in Fujisaka 5.

Seedling growth and dry-matter production under drained conditions in rice direct-sown into puddled and leveled soil.

Abstract Drainage after sowing promotes plant growth and enhances seedling establishment in rice direct-sown into puddled and leveled soil. We studied the effect of drainage on seedling growth and on dry weight of the plant parts. We also examined carbohydrate, chlorophyll, and protein content of the seedlings grown under flooded and drained conditions to see which factors control plant growth during seedling establishment. Drainage for 10 days after sowing enhanced root elongation but inhibited shoot growth until seedlings emerged above ground. Drainage promoted leaf development and shoot elongation after seedlings emerged but affected root growth only slightly at this stage. Although the dry weight of grain decreased and that of shoot and root increased more rapidly in the drained plot than in the flooded one, the utilization efficiency of grain reserve for shoot and root growth was similar in both plots. Growth analysis indicated that the difference in growth rates between the drained and flooded plots was attributable to the amount of carbohydrates supplied from grain reserve until seedlings emerged, but to the photosynthate after seedlings emerged. Sugar contents of shoot and root in the drainage plot were rather lower than those in the flooded plot as seedlings emerged. In contrast, chlorophyll and protein contents of shoot in the drained plot were markedly higher than those in the flooded one after seedlings emerged. These results suggest that drainage promotes leaf development, increases chlorophyll and protein contents of shoot, accelerates photosynthesis, and enhances dry-matter production after seedlings emerged.

Growth Enhancement by Drainage during Seedling Establishment in Rice Direct-Sown into Puddled and Leveled Soil: —Comparison with seed coating with calcium peroxide—

Abstract Growth enhancement by drainage during seedling establishment was compared with seed coating with calcium peroxide in rice direct-sown into puddled and leveled soil. Coated and noncoated seeds were sown about 10 mm deep, three times from April to June at two locations (Niigata and Ibaraki, Japan). Seed coating with calcium peroxide accelerated seedling emergence at an early stage, whereas drainage during 10 to 13 days after sowing promoted it at a late stage. Although drainage was less effective in increasing the number of finally emerged seedlings than seed coating with calcium peroxide, the drainage clearly improved seedling establishment. Seed coating with calcium peroxide enhanced shoot elongation during seedling emergence. In contrast, drainage somewhat inhibited shoot elongation at this time, but promoted it after drained soil was flooded. Drainage also increased the dry weight of shoots more than flooding after seedling emergence. These results indicate that seed coating with calcium peroxide enhances plant growth during seedling emergence, whereas drainage after sowing promotes plant growth mainly after seedling emergence. This suggests that seed coating with calcium peroxide accelerates seedling emergence, but drainage after sowing enhances seedling establishment.

Agricultural Production—Cultivation Techniques and Farming

The prospects for crop production and cropping systems under the constraint of limited irrigation water in the Nile Delta, a constraint that is predicted to arise in the coming several decades, are discussed. Drip and strip irrigation methods are regarded as effective water-saving cultivation methods based on measurements of the productivity, quality, and water use efficiency of major crops, while the effects of extended irrigation intervals and mulching with crop residue are limited. Further analysis has indicated that strip irrigation requires less irrigation water in fewer furrows and provides even higher yields than those obtained using extended irrigation intervals, probably because better aeration in the soil improves root development in strip irrigation. Salt-tolerant varieties of maize, rice, and wheat were selected by evaluating their germination, growth, photosynthesis, and yield at different levels of sodium chloride. The intercropping of maize with soybeans and of wheat with Egyptian clover was proposed to improve total productivity while reducing evaporation by covering the soil surface with companion crops, thereby increasing water-use efficiency. In particular, intercropping cereals with legumes and providing forage that is a mixture of these crops rather than cereals alone improves forage quality. A soil water deficit under high temperature conditions reduces the forage value, and maize grown under drip irrigation has a lower forage quality than that grown under furrow irrigation , suggesting that a continuous water supply is important for maintaining the forage value even in water-saving cultivations.