Location of Transketolase and Transaldolase in Apical Cells of Pea Roots

Recent work has demonstrated a close interrelationship between carbohydrate metabolism and nitrate assimilation in non-photosynthetic higher-plant cells (Sarkissian & Fowler, 1974; Jessup & Fowler, 1977). The results of Miflin (1974) and Dalling et al. (1973) show the presence of nitrite reductase (EC 1.6.6.41, together with glucose 6phosphate dehydrogenase and 6-phosphogluconate dehydrogenase (EC 1.1.1.49 and EC 1.1.1.43 respectively) in plastids. We have been able to demonstrate the presence of all the enzymes of the pentose phosphate pathway (M. J. Emes & M. W. Fowler, unpublished work) together with nitrite reductase and glutamate synthase (M. J. Emes, unpublished work) in plastids isolated from the apical cells of pea-seedling roots. The present communication reports the determination of the location of two of the pentose phosphate-pathway enzymes. Roots of 5-day-old dark-grown pea seedlings (Sarkissian & Fowler, 1974) were extracted in lvol. of a complex 37% (w/w) sucrose medium (Miflin & Beevers, 1974). The resulting homogenate was filtered through one layer of Miracloth, layered on to 24ml of a linear 42-50% (w/w) sucrose gradient and centrifuged in a Beckman SW-25-1 rotor for 30min at 63 500g and 4°C. Gradients were fractionated into 1 ml portions,