Light-Dependent CO2Retrieval in Immature Barley Caryopses

Immature detached caryopses from barley (Hordeum vulgare L. var. distichum cv. Midas) were shown to be capable of light-dependent retrieval of internally-produced CO2. In the first set of experiments, caryopses were radioactively labelled by supplying (U-14C)-sucrose to detached ears in liquid culture. Caryopses were then removed from the ear and given a 12 h chase of non-radioactive sucrose in either the light or dark. More 14C was recovered in the caryopses after the chase in the light than in the dark but the differences were not significant. In the second set of experiments, 14C-labelled caryopses obtained by a 15 min light incubation in 14CO2 were maintained in either the light or dark for 3 h and any redistribution of label between the tissues recorded. The results show that under these conditions, photosynthesis in the Chl-containing green layer of the pericarp can prevent losses of internally-produced CO2, since 3 times as much radiocarbon remained in the caryopses incubated in the light as in the dark. These differences were significant at P=0.001. Experiments with the mutant barley Albino lemma, which has no Chl in the pericarp, showed that there was little difference between light and dark treatments. This confirms the suggestion that photosynthesis in the pericarp of the normal cultivar Midas may be concerned in the refixation of CO2.