Sugar and Amino Acid Transport Across Symbiotic Membranes from Soybean Nodules. Michael K. Udvardi. Botany Department, Australian National University, Canberra, ACT 2601, Australia. Li-Jun Ou Yang, Susan Young, and David A. Day. Botany Department, Australian National University, Canberra, ACT 2601, Australia. MPMI 3:334-340. Accepted 5 June 1990. Copyright 1990 The American Phytopathological Society.

Uptake of a range of sugars and amino acids into isolated peribacteroid units (PBUs) and bacteroids was measured and compared to malate and succinate uptake. Evidence was obtained for the presence of two transport systems on the bacteroid membrane for the transport of d -fructose that can catalyze rapid fructose uptake over a wide concentration range into free bacteroids. Fructose uptake by intact PBUs was slow and showed no evidence of saturation up to 10 mM. Uptake of sucrose, glucose, phenylalanine, methionine, leucine, glycine, and proline into both PBUs and bacteroids was also very slow (less than one tenth of the rate of succinate uptake). Neither sugar nor proline uptake by PBUs showed a tendency toward saturation over a wide concentration range. The peribacteroid membrane apparently lacks carriers for these compounds. Despite slow uptake rates, substantial labeling of bacteroid proteins occurred during a 60-min incubation of intact PBUs with [³⁵S]methionine. Apart from one faint band on the peribacteroid membrane, there was no evidence for secretion of labeled polypeptides from bacteroids. Sugar and amino acid transport was similar in small PBUs from developing nodules; these units also displayed carrier-mediated malate uptake, which occurred at a faster rate per unit protein than that into large units from mature nodules. The polypeptide pattern of the peribacteroid membrane isolated from 4-wk-old nodules was substantially different from that of 8-wk-old nodules, despite their similar permeability to metabolites.