Improvement of tomato seed germination by osmopriming as related to energy metabolism.

In dry, unprimed tomato seeds, ATP represents only 2.1% of the adenylic nucleotide pool, and the energy charge (EC) and the ATP:ADP ratio are very low (0.11 and 0.12, respectively). Imbibition of seeds in a polyethylene glycol-8000 solution at -1 MPa results in sharp increases in ATP (60% of the adenylic nucleotide pool), EC (0.77-0.78) and the ATP/ADP ratio (1.75-2.32). The level of ATP is markedly reduced after drying the primed seeds, but the EC (0.28-0.33) and the ATP:ADP ratio (0.32-0.48) remain higher than in dry unprimed seeds. The energy metabolism of dried primed seeds is also much more intense during the first 4 h of subsequent imbibition in water than that of unprimed ones. To improve the subsequent germination of tomato seeds markedly, osmopriming treatment requires at least 5% oxygen in the atmosphere, and its maximal improving effect is obtained in atmospheres containing more than 10% oxygen. The treatment is also totally ineffective in the presence of a respiratory inhibitor (NaN3) at high concentration (0.5 or 1 msmallcap˜M). Results obtained with seeds primed in reduced oxygen tensions or in the presence of NaN3 at various concentrations show that the beneficial effect of priming increases with increasing EC and ATP:ADP ratio, and is optimal for values higher than 0.75 for EC and 1.7 for the ATP:ADP ratio.