Mechanism of Action of C₂H₄ in Promoting the Germination of Cocklebur Seeds. III. A Further Enhancement of Priming Effect With Nitrogenous Compounds and C₂H₄ Responsiveness of Seeds

Abstract

Efficiency of organic or inorganic osmotica for seed priming of cocklebur (Xanthium pennsylvanicum Wallr.) revealed that KNO₃ was the most promising, and was more effective than mannitol or other salts at the same concentration (200 mM) and was independent of the C₂H₄ action. However, KNO₃ applied as a priming reagent enhanced the effect of C₂H₄ or that of the water stress imposed with mannitol. Unlike the action of mannitol, both KNO_3M and C₂H₄ augmented the pool size of amino acids in seed cells. However, below 50 mM KNO₃ imposing no stress only slightly, though insignificantly, affected the germinability as well as the levels of total cyanogen. On the other hand, at a high concentration which imposed water stress on the seeds, 200 mM KNO₃ remarkably elevated the contents of both cyanogenic glycosides and lipids in the excised cotyledons. When C₂H₄ was added with KNO₃, the level of cyanogenic compounds significantly increased but when added without KNO₃, the contrary effect was shown. Hence the enhancement of the mannitol-induced priming effect by nitrogenous reagents in cocklebur seeds could be implicated in the accumulation of cyanogenic compounds. Unlike cocklebur, both common chickweed and barnyard grass seeds are very responsive to 30 mM KNO₃ on germination, and such species abundantly contain cyanogen. The amount of cyanogen was further augmented by contact with KNO₃ at only 30 mM. The role of NO^-₃ -dependent cyanogenesis is highlighted in relation to germination response of seeds.