| Research Abstract |
Most important nature of space environment is microgravity. For doing researches on the earth, concerning fundamental problems of crop production in space environment, development of experimental system is firstly required. In this study, survey of mutants which lost their normal response to the gravity was done and experimental systems were established in barley, rice and pea plants.
Response of upper ground organ to the gravity is not normal in barley and rice, on the other hand that of roots is not normal in pea. These are mutants (barley and pea) and near isogenie line (rice) to which lazy gene was introduced by backcrossing. Using barley plants, comparison of productive structure was made between mutant and normal lines. Analysis by stratified clip method revealed difference in distribution of leaves, stems and heads, as well as leaf area index (LAI) in the mutant line caused by diagravitropic or plagiogravitropic growth. Mutant plants showed an abnormal gravity response even in th
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e seedling stage. In mutant but hot normal plants, the direction of first-leaf growth depended on the position of the embryo. Seed production of mutant plants was about 60 % compared with normal plants, even though net assimilation rate (NAR) and relative growth rate (RGR) were not decreased. Seed fertility of mutant plants was correlated with the angel between heads and ground level. However, when plants were turned upside down, all heads, both mutants and normal, were nearly vertical, and seed fertility recovered to a level that not significantly different from normal plants. From these results, it was predicted that barley plants may not produce seeds normally under microgravity.
In rice plants, although final seed production was not investigated, however, distribution of productive structure in mutants was found to have almost the same feature as that of barley mutant. In rice seedlings of mutant line, starch grain which has been suggested as the statolith in the gravity response, was found to sink to the direction of the gravity, Thus, abnormal response of this rice line may have genetic mutation in the step(s) later than the statolith sinking in the process of gravity response.
In the study of pea plants, redistribution of exogenously applied auxin was about 60 % in lower halves when stems were placed horizontally, however no difference was found in the upper and lower halves in mutant lines. Less
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