CONTROL OF SEED DEVELOPMENT IN ARABIDOPSIS-THALIANA BY ATMOSPHERIC OXYGEN

Seed development is known to be inhibited completely when plants are g rown in oxygen concentrations below 5.1 kPa, but apart from reports of decreased seed weight little is known about embryogenesis at subambie nt oxygen concentrations above this critical level, Arabidopsis thalia na (L.) Heynh. plants were grown full term under continuous light in p remixed atmospheres with oxygen partial pressures of 2.5, 5.1, 10.1, 1 6.2 and 21.3 kPa O-2, 0.035 kPa CO2 and the balance nitrogen, Seeds we re harvested for germination tests and microscopy when siliques had ye llowed, Seed germination was depressed in O-2 treatments below 16.2 kP a, and seeds from plants grown in 2.5 kPa O-2 did not germinate at all , Fewer than 25% of the seeds from plants grown in 5.1 kPa oxygen germ inated and most of the seedlings appeared abnormal, Light and scanning electron microscopic observation of non-germinated seeds showed that these embryos had stopped growing at different developmental stages de pending upon the prevailing oxygen level, Embryos stopped growing at t he heart-shaped to linear cotyledon stage in 5.1 kPa O-2, at around th e curled cotyledon stage in 10.1 kPa O-2, and at the premature stage i n 16.2 kPa O-2. Globular and heart-shaped embryos were observed in sec tioned seeds from plants grown in 2.5 kPa O-2. Tissue degeneration cau sed by cell autolysis and changes in cell structure were observed in c otyledons and radicles, Transmission electron microscopy of mature see ds showed that storage substances, such as protein bodies, mere reduce d in subambient oxygen treatments, The results demonstrate control of embryo development by oxygen in Arabidopsis.