ヒマ RICIUS COMMUNIS L. ニ オケル ソクシ ノ ハツイク ニ カンスル ケンキユウ

筑波大学農学博士学位論文・昭和58年3月25日授

The Effect of the Amount of Nitrogen Fertilizer on Starch Metabolism in Leaf Sheath of Japonica and Indica Rice Varieties during the Heading Period

The effects of the amount of nitrogen fertilizer on the starch metabolism of rice leaf sheath during the heading period in the japonica rice variety, cv. Nipponbare were compared with those in the indica varieties, cv. Tetep and Johna. The rice plants were grown under a low- (similar to the standard nitrogen level in paddy field) or high-nitrogen condition, and the starch content of the second leaf sheaths below the flag leaf was analyzed from the second leaf stage (growth stage 1) until 21 days after the heading (growth stage 7). The starch content of the plants grown under the high-nitrogen condition at the heading stage (growth stage 4) was lower than that under a low-nitrogen condition in all the varieties. The decrease in the activity of starch branching enzyme (SBE) was considered to be important for the repression of starch accumulation under a high-nitrogen condition. Under the high-nitrogen condition, Nipponbare accumulated more starch in the second leaf sheath than indica varieties at the heading stage. However, the phenomenon could not be accounted for by the activities of AGPase and SBE. Semi-quantitative RT-PCR analysis suggested that the lower activities of SBE in the second leaf sheath under the high-nitrogen condition may be due to, at least in part, the decrease in the expression level of RBE4

Influence of Day Length before and after the Start of Anthesis on the Growth, Flowering and Seed-Setting in Common Buckwheat (Fagopyrum esculentum Moench)

The influence of day length before and after the start of anthesis on the growth, flowering process, and seed -setting of common buckwheat (Fagopyrum esculentum Moench) was investigated to determine the effect of day length at various growth stages. Exposure to long days (15 h in 2001 and 16 h in 2000) made the node position of the first flower higher, delayed the start of anthesis, decreased the rate of successive flowering, increased the number of nodes and flower clusters on the main stem, and prolonged the main stem elongation period. It increased the number of flowers per flower cluster, but decreased the seed-setting ratio and the number of seeds. The critical day length varied with the cultivar and the growth parameter. ‘Miyazakizairai’ (autumn eco-type) showed significantly greater responses to long days than ‘Shinanonatsusoba’ (summer eco-type). The day length before the start of anthesis significantly influenced on the main stem elongation and flowering process thereafter. This suggests that the day length is a more critical factor for the differentiation than the growth of the flower bud. The seed-setting ratio was influenced both by day lengths before and after the start of anthesis. The 15 h day length before the start of anthesis and around 12 h day length thereafter increased the number of double and multiple clusters in ‘Shinanonatsusoba’ and long clusters in ‘Miyazakizairai’, resulting in an increase in the number of seeds per cluster. Day length did not influence either the form or weight of seeds

Identification of Two Plastid-Targeted β-Amylases in Rice

In order to identify β-amylase isoforms acting inside plastids in rice (Oryza sativa L.), in the rice genome database we searched the genes predicted to encode β-amylase-like proteins, and designated them OsBAM1−9. OsBAM1, OsBAM7, and OsBAM9 genes were mainly expressed in germinating seeds and developing caryopses. In contrast, the transcripts of OsBAM2, OsBAM3, OsBAM4 and OsBAM5, which have a putative chloroplast transit peptide in their N-terminal regions, were mainly detected in leaf blades, leaf sheaths and internodes after heading. Soluble protein fractions prepared from Escherichia coli containing recombinant OsBAM2 and OsBAM3 proteins had significant β-amylase activity. Furthermore, OsBAM2-GFP and OsBAM3-GFP fusion proteins introduced into epidermis of Allium cepa scaly bulb were localized to the plastids. These results strongly suggest that OsBAM2 and OsBAM3 are plastid-targeted active β-amylase

Two β-amylase genes, OsBAM2 and OsBAM3, are involved in starch remobilization in rice leaf sheaths

To identify mechanisms of starch degradation in rice leaf sheaths at the post-heading stage, we investigated the function of OsBAM2 and OsBAM3, which encode plastid-targeted active β-amylase isoforms, in starch remobilization in leaf sheaths. The starch content in the second leaf sheaths below the flag leaf (the third leaf sheaths) peaked at the flag leaf emergence stage and gradually decreased until 15 days after heading. The mRNA levels of OsBAM2 and OsBAM3 in the third leaf sheaths increased from the flag leaf emergence stage to the heading stage when the starch content began to decrease. However, these mRNA levels did not always remain high during post-heading. Overexpression of OsBAM2 or OsBAM3 markedly repressed starch accumulation in the third leaf sheaths, showing that OsBAM2 and OsBAM3 function in starch degradation in rice leaf sheaths. In contrast, no significant differences in starch content in the third leaf sheaths were detected between knockdown plants of OsBAM2 or OsBAM3 and non-transgenic wild-type plants. Our results suggest that reduced expression of the individual genes, OsBAM2 or OsBAM3, does not result in excess accumulation of starch in the leaf sheaths, probably because of the complementary function of another gene or the action of other genes encoding starch-degrading