Control of Seed Respiration and Growth in Vicia faba by Oxygen and Temperature: No Evidence for an Oxygen Diffusion Barrier

The rate of dry matter accumulation by seeds of Vicia faba L. cv. Minica increases with temperature in the range of 16 to 26 degrees C. The duration of dry matter accumulation decreases with temperature, resulting in a decrease of final seed dry weight. In this study we test the hypothesis that a diffusion barrier for O(2), located in the seed coat, inhibits seed respiration and growth. The rate of O(2) uptake of intact seeds and of excised embryos and seed coats (separated seeds) was measured in air and buffer at 16, 20, and/or 26 degrees C at various O(2) concentrations and developmental stages. Oxygen uptake rates of intact seeds in buffer were only 9 to 15% of those in air. In buffer, the respiration rate of intact seeds decreased at a pO(2) below air saturation (21 kilopascals), whereas separated seeds showed a decline of O(2) uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to pO(2), at both 20 and 26 degrees C. In air at 20 degrees C, separated and intact seeds showed similar rates of O(2) uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q(10) of 2.3 and was insensitive to pO(2) in the range of 80 to 100% of ambient. These results indicate that V. faba seed respiration in air is not limited by the diffusion of O(2) into the seed.