Carboxylating Enzymes of Soybean Cotyledons

Summary The in vitro activities of ribulose‐1,5‐bisphosphate (RuBP) carboxylase and phosphoenol pyruvate (PEP) carboxylase enzymes extracted from soybean [Glycine max (L.) Merrill cv. Amsoy'71] cotyledons are correlated with cotyledon chlorophyll development. High levels of PEP carboxylase activity were found in the spongy mesophyll tissues of young cotyledons before greening occurred, but as the cotyledons developed, the activity of this enzyme fell rapidly and 13 d after sowing it had almost disappeared. RuBP carboxylase activity, in contrast, was concentrated in the palisade mesophyll and increased with chlorophyll content, reaching a peak on day 10. RuBP carboxylase activity then declined and by the onset of senescence was very low. In cotyledons whose senescence had been arrested by epicotyl removal, chlorophyll recovery was found to precede that of the activity of both carhoxylase enzymes. After a lag of 5 d, both enzymes showed increased activity in the palisade mesophyll, RuBP carboxylase activity being greater than that of PEP carboxylase.