Histochemical study of enzyme activity in the shoot apical meristem of Brassica campestris L. during transition to flowering. III. Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase

Glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activity was determined in fresh-frozen, cryostat sections of the shoot apical meristem of Brassica campestris L. to indicate pentose phosphate pathway (PPP) capacity. Enzyme activity was differentially distributed in a zonate pattern in the vegetative, transition, and floral meristems. Vegetative apices showed a heterogeneous localization of both enzymes; the highest activity was in the central zone and in the pith-rib meristem zone. At the early transition stage of development, both G6PDH and 6PGDH activity increased in the peripheral zone. At the late transitional (prefloral) stage, G6PDH and 6PGDH activity was heavily localized in island-like areas of the peripheral zone. The results indicate that (1) an increase in the activity of the PPP occurs during evocation, (2) incipient floral primordia are associated with greater G6PDH and 6PGDH activity than adjacent areas of the apical meristem, and (3) activity of the PPP is correlated to other evocational events in Brassica.