Changes in Enzyme Levels of EMP and Pentose Phosphate Pathways during Germination of Cottonseed

Abstract

Changes in the levels of key enzymes in the 2 carbohydrate oxidative pathways were studied in cotyledons and radicles of germinating cottonseed. Prior to radicle emergence, PFK phosphofructokinase activity exceeded glucose-6-phosphate dehydrogenase activity. Following radicle emergence, glucose-6-phosphate dehydrogenase activity increased more than 2-fold; PFK activity remained the same in cotyledons but apparently decreased in the radicles. The seemingly decreased levels of the EMP [Embden-Meyerhof-Parnas] enzymes in radicles were due to a dilution of protein content during elongation. Enzymes of the EMP pathway were demonstrated only in radicle tips, while enzymes of the pentose pathway were demonstrable in tips and elongating segments. Possibly during the initial phases of germination, especially when O2 diffusion may be restricted by the intact testa, the early and high requirement for ATP is met by substrate level phosphorylation from enhanced EMP activity. Differentiation in both elongating radicles and cotyledons, which in cotton become photosynthesizing organs, is accomplished in conjunction with the enhanced activity of the pentose phosphate pathway. The temporal development of enzymes of the EMP and pentose phosphate pathways, which generate NADH and NADPH, respectively, correlates with the temporal development of NR [nitrate reductase] and NiR [nitrite reductase] activities, which in non-green tissues utilize NADH and NADPH, respectively, as reductants.