MECHANISM OF ACTION OF C2H4 IN PROMOTING THE GERMINATION OF COCKLEBURSEEDS .2. THE ROLE OF C2H4 IN THE ENHANCEMENT OF PRIMING EFFECTS

In cocklebur (Xanthium pennsylvanicum Wallr.) seeds, the pre-exposure to water stress imposed by polyethylene glycol or mannitol (seed primi ng) increased osmotic pressure (OP) in cell saps and water extracts. C arbohydrates were the major components and soluble proteins also playe d a partial role as an osmoregulator in the primed seeds. C2H4, which was effective in stimulating the growth of both axial and cotyledonary tissues even under water-stressed conditions, changed the amino acid pool size regardless of water stress. This C2H4-induced amino acid acc umulation also occurred under anoxic conditions. CO2 was capable of st imulating growth of axial tissues but it did not increase OP values or carbohydrate and amino acid contents. The effectiveness of seed primi ng gradually declined with increasing duration of presoaking, but C2H4 prevented the reduction of the priming effect by effectively maintain ing the amino acid levels. Thus, it is likely that C2H4 contributes to the enhancement of the priming effect by abundantly supplying amino a cids.