|Budget Amount *help
¥3,400,000 (Direct Cost : ¥3,400,000)
Fiscal Year 2001 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 2000 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1999 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1998 : ¥1,600,000 (Direct Cost : ¥1,600,000)
Four short-root mutants were isolated from an M_2 population of Oochikara. Root lengths of the four mutants srt5, srt6, srt7 and srt8 were 5%, 50%, 60% and 70% of that of the wild type at day 20, respectively. Cyto-histological observation indicated that all the four short-root genes did not affect development of cell and tissue pattern. Abnormal cell elongation was observed in srt6, srt7 and srt8, while srt5 additionally affected cell division.
A monogenic and recessive short-root mutant, srt5, was mapped its causal gene to chromosome 2. The mutant showed extreme inhibition of seminal root, crown root and lateral root elongation, and altered root hair formation at the seedling stage. Histological observation of seminal root tips indicated that the short-root phenotype was due to the reduced cell size and cell number. At later stages of plant development, roots of the mutant elongated acceleratingly and recovered completely in morphology of adult plants. Seminal root growth of the mutan
t was partially rescued by exogenous applied ABA, suggesting that ABA biosynthesis might be affected in srt5 plants. Moreover, root growth of the mutant also showed high resistance to 2,4-D, GA_3 and KIN. Thus, the wild type allele of srt5 seems to be of great importance for early root development by altering plant hormone homeostasis.
A root-hairless mutant RH2 exhibited some other morphological changes from wild type Oochikara, such as shorter seedling height and shorter roots. Under water stressed condition of soil culture, RH2 and Oochikara were similar in shoot water content and transpiration per unit shoot dry weight. Under high osmotic pressure condition of solution culture, there was no significant difference between RH2 and Oochikara in transpiration. Phosphate uptake experiments using water cultured seedlings detected no significant differences between RH2 and Oochikara. These results suggest that at the seedling stage, root hairs do not significantly contribute to uptake of water or phosphate. NAA treatment induced very short root hairs in RH2, suggesting that the absence of root hairs in RH2 may be due to a shortage of endogenous auxin. Genetic analysis showed that the root hairless character in RH2 is inherited as a single, recessive gene.
A NAA resistant mutant RT62 from wild type cultivar indica IR8 is also slightly resistant to ABA, but does not show resistance to 2,4-D and IAA. RT62 displays a variety of morphological alterations including slightly shorter plant height, shorter seminal and crown roots, denser and longer lateral roots on seminal root, and a smaller embryo. Histological analysis revealed that the short seminal root phenotype of RT62 resulted from reduction of cell length rather than cell number. Genetic analysis showed that NAA resistance of RT62 controlled is by a single recessive gene. Less