Nitric oxide generation during early germination of sorghum seeds

Germination of sorghum embryonic axes, defined as the development of a root 1-2 mm long, started after 24 h of imbibition. A distinctive EPR signal for the adduct MGD-Fe-NO was detected in the homogenates from axes isolated from seeds imbibed in the presence of 12 mM nitrate in a time-dependent manner. Also a close association between MGD-Fe-NO adduct content in the homogenates and nitrate supplementation to the incubation medium was observed. The activities of the NADH-dependent nitrate reductase (NR) and nitric oxide synthase were measured in axes, by the detection of NO by EPR under conditions of maximal supplementation of substrates. A significant increase in both enzymatic activities was determined between 24 and 30 h of imbibition. Total content in sorghum axes of beta-carotene and alpha-tocopherol increased significantly as the germination occurred, however the total content of tocopherols was not affected over the studied period. The data reported here are the first observations employing EPR to assess for NR and NOS activities simultaneously in an active growing tissue. Moreover, since the increase in NO content preceded the initiation of phase II of development and the sharp increase in oxygen consumption, a potential role for NO as a signal molecule should be considered. (C) 2004 Elsevier Ireland Ltd. All rights reserved.