Respiratory Activity in Pea Cotyledons during Seed Development

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Abstract
Three phases were recognized in the course of the respiration rate of pea (Pisum sativum L.) cotyledons during seed development. (1) The respiration rate per cotyledon initially increased along with the mitochondrial activity. (2) During the second phase, the respiration rate increased further until a constant level was reached and then decreased. The mitochondria now started to lose their capacity to oxidize malate, followed by a decreasing capacity to oxidize succinate. (3) During the maturation phase the respiration rate decreased further. The rate of ascorbate oxidation started to decline at this time. Ascorbate oxidation was increasingly stimulated by cytochrome c. The changes in respiration rate are considered in relation to changes in growth and maintenance respiration. When the water content of the seeds was maintained by storing them at high humidity, the respiration rate of cotyledons of early harvested seeds decreased sharply whereas that of later harvested seeds hardly changed. This change in response was used to mark the transition between the second and third phase. During humid storage changes in the functional integrity of the mitochondria still occurred. The results are discussed in relation to the ability of pea seeds to withstand desiccation.