Several aspects on the plant growth and development in space environment. The senescence of oat leaf segments is promoted under simulated microgravity condition on a three-dimensional clinostat.

Abstract

Miyamoto, K. et al. condition on promoting the senescence is also discussed. Materials and methodsThe senescence of oat leaf segments under simulated microgravity on a 3-D clinostat was studied according to the methods previously reported with modifications (Ueda and Kato 1980, Hoson et al. 1992.Oat (Avena sativa L. cv Victory) seeds were germinated in vermiculite under continuous white fluorescent light of 5 W/m 2 at 25 ˚C for 9 days on 1 xg condition. The first leaves were harvested and 3-cm segments of the distal portion of the leaves were excised. The set of 15 segments was placed on 2 layers of filter papers moistened with 5 ml of water or 10 -5 M kinetin solution in a disposable plastic Petri dish (Iwaki Glass Co., Ltd. Japan) . Petri dishes were covered with wet paper towel and aluminum sheet and then incubated under simulated microgravity condition on a 3-D clinostat in the dark or under 1 xg dark condition at 25 ˚C for appropriate period. As shown in Fig. 1, the water content of filter papers in a Petri dish reduced significantly during the incubation on 3-D clinostat condition, indicating the relative humidity in a Petri dish is very low. Therefore, oat leaf segments in a Petri dish were covered with an additional another filter paper to prevent evaporation under simulated microgravity condition on a 3-D clinostat and also in dark control. At the end of the incubation, the leaf segments were harvested and total chlorophyll were extracted with boiling 80 % ethanol. Absorbance of the extracts was measured at 665 nm with a Shimadzu UV-1200 spectrophotometer. Results were expressed as percentages of the initial value.

Growth, yield and reproduction of dwarf tomato grown under simulated microgravity conditions

“…This evidence suggests that the photosynthetic inhibition is caused by destruction of the photosynthetic system. The results recorded in our experiment are in agreement with those reported by Miyamoto et al (1995Miyamoto et al ( , 2001 who observed that simulated microgravity conditions enhanced the loss of chlorophyll in oat leaf segments due to alterations of the physiological process of leaf senescence (e.g. protease activity) and the dynamics of endogenous plant hormone levels (e.g.…”