RESPONSIVENESS OF AMARANTHUS-RETROFLEXUS SEEDS TO ETHEPHON, 1-AMINOCYCLOPROPANE 1-CARBOXYLIC ACID AND GIBBERELLIC-ACID IN RELATION TO TEMPERATURE AND DORMANCY

Dormant Amaranthus retroflexus seeds do not germinate in the dark at t emperatures below 35 degrees C. Fully dormant seeds germinate only at 35-40 degrees C whereas non-dormant ones germinate within a wider rang e of temperatures (15 to 40 degrees C). Germination of non-dormant see ds requires at least 10% oxygen, but the sensitivity of seeds to oxyge n deprivation increases with increasing depth of dormancy. 10(-6) to 1 0(-4) M ethephon, 10(-3) M 1-aminocyclopropane 1-carboxylic acid (ACC) and 10(-3) M gibberellic acid (GA(3)) break this dormancy. In the pre sence of 10(-3) M GA(3) dormant seeds are able to germinate in the sam e range of temperatures as non-dormant seeds. The stimulatory effect o f GA(3) is less dependent on temperature than that of ethephon, while ACC stimulates germination only at relatively high temperatures (25-30 degrees C). The results obtained are discussed in relation to the pos sible involvement of endogenous ethylene in the regulation of germinat ion of A. retroflexus seeds.