Seed ageing-induced inhibition of germination and post-germination root growth is related to lower activity of plasma membrane H+-ATPase in maize roots

Seeds of most crops can be severely damaged and lose vigor when stored under conditions of high humidity and temperature. The aged seeds are characterized by delayed germination and slow post-germination growth. To date, little is known about the physiological mechanisms responsible for slow root growth of seedlings derived from aged seeds. Plasma membrane H+-ATPase is a universal H+ pump in plant cells and is involved in various physiological processes including the elongation growth of plant cells. In the present study, we investigated the effect of a mild seed ageing treatment on plasma membrane H+-ATPase activity of seedling roots. Maize (Zea mays L.) seeds with 17% water content were aged at 45 °C for 30 h. The aged seeds showed a 20% reduction in germination. Seedlings from aged seeds grew slowly during an experimental period of 120 h after imbibition. Plasma membranes of maize seedling roots were isolated for investigation in vitro. Plasma membrane H+-ATPase (EC 3.6.3.6) activity was 14% lower for seedling roots developed from aged seeds as compared to control seeds. Protein gel immunoblotting analysis demonstrated that the reduced activity of plasma membrane H+-ATPase was attributed to a decrease in steady-state protein concentration of this enzyme. In conclusion, seed ageing causes a lower steady-state enzyme concentration of the H+-ATPase in the plasma membrane, which is related to slow germination and post-germination growth of seedling roots.