MECHANISM OF ACTION OF C2H4 IN PROMOTING THE GERMINATION OF COCKLEBURSEEDS .3. A FURTHER ENHANCEMENT OF PRIMING EFFECT WITH NITROGENOUS COMPOUNDS AND C2H4 RESPONSIVENESS OF SEEDS

Efficiency of organic or inorganic osmotica for seed priming of cockle bur (Xanthium pennsylvanicum Wallr.) revealed that KNO3 was the most p romising, and was more effective than mannitol or other salts at the s ame concentration (200 mM) and was independent of the C2H4 action. How ever, 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 KNO3 and C2H4 augmented the pool size of amino acids in seed cells. However, below 50 mM KNO3 imposing no stress only slightl y, though insignificantly, affected the germinability as well as the l evels of total cyanogen. On the other hand, at a high concentration wh ich 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 com pounds significantly increased but when added without KNO3, the contra ry effect was shown. Hence the enhancement of the mannitol-induced pri ming effect by nitrogenous reagents in cocklebur seeds could be implic ated in the accumulation of cyanogenic compounds. Unlike cocklebur, bo th 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 NO3--dependent cyanogenesis is highlighted in relation to germination response of seeds.