Mutagentic Effects Of Aerospace And Biological Changes Of Potential Mutants In Poa Pratensis L.

Aerospace has different environmental conditions from the biosphere of the earth with respect to gravity, radiation, and magnetic field. Plant growth and development as well as genetic information may be affected under the aerospace conditions. Genetic changes caused under aerospace conditions may be used as an effective means of creating new germ plasm. The primary objective of this study was to look into the possibility of inducing mutations by exposing dry seeds of Kentucky bluegrass (Poa pratensis L.) to aerospace conditions. A secondary objective was to evaluate variations at different levels of a plant which was identified as a potential mutant caused by space condition. Dry seeds of certified 'Nassau'Kentucky bluegrass were carried into low earth orbit for 162 hr by the Chinese spacecraft "SZ-3", which had a flying perigee and apogee of 200 and 343 km, respectively. The control seeds were kept in a refrigerator on the earth. Temperatures within the craft were 15 to 25℃, and the air pressure was maintained at 10⁵ Pa. The seeds that were exposed to space conditions showed similar germination rates and seedling vigor as the controls. The range of leaf number, tiller number and plant height from the treated seeds were 2⁸1, 0²6 and 3¹55, respectively. The variations were larger than that of the controls. The average leaf width of the treated population was 2.43 mm, whereas that of the controls was 1.96 mm. Based on the statistical comparison of the treated and control populations in plant height, growth habit, and color, three plants were identified as potential mutants, fast growing mutant (PM₁), wrinkle leaf mutant (PM₂), and mosaic mutant (M₃). The potential mutants were grown in a greenhouse for further morphological and biochemical study. Leaf blades were investigated under light microscope and electronic microscope for morphological and anatomy characteristics. The three PMs, which have wider and thinner leaf blades, all have more epidermal cells and smaller mesophyll cells compared to the control. PM₁ and PM₂ showed decreased epidermal cell height compared to the control, whereas that of PM₃ had larger epidermal cell height. The larger epidermal cells and the increase in the number of bulliform cells may have contributed to the wrinkle morphology of PM2. The stoma size and distribution of the potential mutants also were different from the control. Compared to CK, the stoma density in PM plants was increased, but the stoma size was decreased with the proportions of total stoma area to leaf area remained unchanged. The ultra structure of mesophyll cells and chloroplasts in the potential mutants showed both morphological changes and functional changes. The chloroplasts of PM1 and PM2 were spherical and located close to the center of mesophyll cells with increased starch grains. The spindle-shaped chloroplasts in the control were located closer to the cell wall with denser grana lamellae compaction and less starch grains. PM3 is a white-green mosaic in that the chloroplasts in green areas were similar to the control and the chloroplasts in white areas showed dissolved structure. The chloroplast size in PM1 and PM2 was smaller than that of CK plants. The chloroplast number and the proportion of size to mesophyll cells of PM3 were decreased. The content of the chlorophyll a and b and a/b ratio of PM1 and PM3 were the same as control. The approximated light saturation point, light compensation point and the apparent quantum efficiency of the potential mutants were all reduced, but the approximated CO2 saturation point was increased. The content of the chlorophyll a and b of PM2 was higher than that of the control but the ratio of a/b was lower than the control. The carboxylation efficiency were PM2< CK< PM3