Oxygen-depleted zones inside reproductive structures of Brassicaceae: implications for oxygen control of seed development

Growth of Arabidopsis thaliana (L.) Heynh. in decreasing oxygen partial pre ssures revealed a linear decrease in seed production below 15 kPa, with a c omplete absence of seed production at 2.5 kPa oxygen. This control of plant reproduction by oxygen had previously been attributed to an oxygen effect on the partitioning between vegetative and reproductive growth. However, pl ants grown in a series of decreasing oxygen concentrations produced progres sively smaller embryos that had stopped developing at progressively younger stages, suggesting instead that their growth is limited by oxygen. Interna l oxygen concentrations of buds, pistils, and developing siliques of Brassi ca rapa L. and siliques of Arabidopsis were measured using a small-diameter glass electrode that was moved into the structures using a micromanipulato r. Oxygen partial pressures were found to be lowest in the developing peria nth (11.1 kPa) and pistils (15.2 kPa) of the unopened buds. Pollination red uced oxygen concentration inside the pistils by 3 kPa after just 24 h. Insi de Brassica silique locules, partial pressures of oxygen averaged 12.2 kPa in darkness, and increased linearly with increasing light levels to 16.2 kP a. Measurements inside Arabidopsis siliques averaged 6.1 kPa in the dark an d rose to 12.2 kPa with light. Hypoxia in these microenvironments is postul ated to be the point of control of plant reproduction by oxygen.