Respiratory Activity in Pea Cotyledons during Seed Development

Three phases were recognized in the course of the respirationrate of pea (Pisum sativum L.) cotyledons during seed development.(1) The respiration rate per cotyledon initially increased alongwith the mitochondrial activity. (2) During the second phase,the respiration rate increased further until a constant levelwas reached and then decreased. The mitochondria now startedto lose their capacity to oxidize malate, followed by a decreasingcapacity to oxidize succinate. (3) During the maturation phasethe respiration rate decreased further. The rate of ascorbateoxidation started to decline at this time. Ascorbate oxidationwas increasingly stimulated by cytochrome c. The changes inrespiration rate are considered in relation to changes in growthand maintenance respiration. When the water content of the seeds was maintained by storingthem at high humidity, the respiration rate of cotyledons ofearly harvested seeds decreased sharply whereas that of laterharvested seeds hardly changed. This change in response wasused to mark the transition between the second and third phase.During humid storage changes in the functional integrity ofthe mitochondria still occurred. The results are discussed in relation to the ability of peaseeds to withstand desiccation. Key words: Pisum sativum, Seed development, Respiration, Mitochondrial activity