Mechanism of Action of C₂H₄ in Promoting the Germination of Cocklebur Seeds. II. The Role of C₂H₄ in the Enhancement of Priming Effects

Abstract

In cocklebur (Xanthium pennsylvanicum Wallr.) seeds, the pre-exposure to water stress imposed by polyethylene glycol or mannitol (seed priming) increased osmotic pressure (OP) in cell saps and water extracts. Carbohydrates were the major components and soluble proteins also played 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 accumulation also occurred under anoxic conditions. CO₂ was capable of stimulating growth of axial tissues but it did not increase OP values or carbohydrate and amino acid contents. The effectiveness of seed primlng gradually declined with increasing duration of presoaking, but C₂H₄ prevented the reduction of the priming effect by effectively maintaining the amino acid levels. Thus, it is likely that C₂H₄ contributes to the enhancement of the priming effect by abundantly supplying amino acids.