Synthesis of Isocitrate Lyase in Sunflower Cotyledons during the Transition in Cotyledonary Microbody Function

Density-labeling with 10 millimolar K¹⁵NO₃/70% ²H₂O has been used to investigate isocitrate lyase synthesis during greening of sunflower (Helianthus annuus L.) cotyledons when the glyoxysomal enzyme activities sharply decline and the transition in cotyledonary microbody function occurs. A density shift of 0.0054 (kilograms per liter) was obtained for the profile of isocitrate lyase activity in the CsCl gradient with respect to the ¹H₂O control. Quantitative evaluation of the density-labeling data indicates that about 50% of the isocitrate lyase activity present towards the end of the transition stage in microbody function is due to enzyme molecules newly synthesized during this stage.