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°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 O₂, located in the seed coat, inhibits seed respiration and growth. The rate of O₂ 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°C at various O₂ 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 pO₂ below air saturation (21 kilopascals), whereas separated seeds showed a decline of O₂ uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to pO₂, at both 20 and 26°C. In air at 20°C, separated and intact seeds showed similar rates of O₂ uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q₁₀ of 2.3 and was insensitive to pO₂ 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 O₂ into the seed.