Mechanisms Controlling Dormancy in the Arid Zone Grass Aristida contorta . I. Physiology and Mechanisms of Dormancy

Two dormancy mechanisms are evident in young A. contorta grain. One is an after-ripening requirement of the embryo, and can be satisfied by storage at ambient temperatures; the second is associated with the hull and requires prolonged periods of high temperatures before germination can take place. The dormancy imposed by the hull is not controlled by a leachable inhibitor, but germination can be stimulated by oxidizing agents or by the removal of small sections of the hull directly over the embryo. The oxygen uptake of dormant grain is very low, but non-dormant grain, or dormant grain with the hull removed, shows a much higher uptake. The possibility remains that there is a mechanical restriction of gas exchange by the hull, the hull of non-dormant grain being more permeable than that of dormant grain.