Light/Dark modulation of enzyme activity in developing barley leaves.

Light/dark modulation of the ribulose-5-phosphate kinase, NADP(+)-glyceraldehyde-3-phosphate dehydrogenase, and fructose- 1,6-bisphosphatase activity was measured in the developing primary leaf of barley (Hordeum vulgare L.) seedlings. Ribulose-5-phosphate kinase and NADP(+) -glyceraldehyde-3-phosphate dehydrogenase were fully light activated even at the earliest developmental stage sampled. In contrast, light modulation of fructose- 1,6-bisphosphatase exhibited a complex response to leaf developmental status. Light stimulation of fructose- 1,6-bisphosphatase activity (measured at pH 8.0) increased progressively during leaf development. On the other hand, acid fructose- 1,6-bisphosphatase activity (measured at pH 6.0) was inhibited by light, and this light inhibition was greater in the base of the leaf than in the tip of the leaf.