Preliminary studies of ascorbate metabolism in green and albino regions of variegated leaves of Coleus blumei, Benth.

Green and white variegated leaves of Coleus blumei, Benth. were separated into albino and green sections and used to determine the distribution of vitamin C and L-galactose dehydrogenase activity, an enzyme supposed to be involved in ascorbate metabolism, in heterotrophic and autotrophic foliar fractions. Both green and white sections contained vitamin C and activity of L-galactose dehydrogenase. However, in the white parts mainly dehydroascorbate was found, whereas in the green parts the redox state of the ascorbate system varied with light or dark conditions. Characterisation of L-galactose dehydrogenase from illuminated green leaf sections showed increasing activity with increasingly alkaline pH-values and a temperature optimum of 25 degrees C. Since these properties were slightly different than those of L-galactose dehydrogenase activities obtained from albino or darkened green leaf sections, we suggest that the enzyme may be light-modulated.