Oxygen Exchange in the Pericarp Green Layer of Immature Cereal Grains

Rates of oxygen exchange in light and dark were recorded for immature detached barley spikelets and wheat florets both before and after successive removal of the husk (palea and lemma), transparent layer of the pericarp, and green layer of the pericarp. Results were compared with those for the mutant barley Albino lemma which has a pericarp lacking chlorophyll. There was no net oxygen evolution in the intact spikelets of Albino lemma when incubated in the light. Removal of the husk increased the rate of measured oxygen uptake in both light and dark. With normal barley and wheat, net oxygen evolution in the light was observed in intact spikelets and florets, as well as after husk removal and after both husk and transparent layer removal. Additional removal of the green layer of the pericarp resulted in a dramatic changeover from oxygen evolution in the light to oxygen uptake. The results suggest that some of the oxygen generated by pericarp photosynthesis remains within the grain.