DETACHED LUPINE COTYLEDONS AS A MODEL SYSTEM FOR STUDIES OF HORMONAL-CONTROL IN CHLOROPLAST DEVELOPMENT

The effects of abscisic acid (ABA, 76 mu M) and benzyladenine (BA, 22 mu M) on chlorophyll and starch accumulation were studied in the cotyl edons of yellow lupine (Lupinus luteus L.) detached from the intact se edlings at the age of one to three days. Cotyledon response to BA incr eased and to ABA decreased with seedling age. When cotyledons were det ached 12 h after seed imbibition, their illumination induced chlorophy ll accumulation after only a 24-h lag-period and BA did not shorten th is period. BA considerably accelerated the onset of chlorophyll accumu lation when the cotyledons were detached after 48 h, indicating a part icular importance of the period between 24 and 48 h for induction of c hloroplast biogenesis. BA accelerated and ABA retarded starch mobiliza tion in darkness and particularly in the light. The ratio of chlorophy ll a to chlorophyll b did not depend on the age of intact cotyledons, and decreased during greening of detached cotyledons. ABA accelerated and BA retarded the decline in this ratio in the detached cotyledons. BA is supposed to activate the chloroplast, genesis in a quantitative manner, whereas ABA evidently inhibits the initiation of new chloropla st protein-pigment complexes to a higher extent than the processes of their assembly and maturation. The most pronounced responses toward bo th phytohormones were observed in the cotyledons detached from three-d ay-old seedlings. Therefore, precisely these cotyledons were chosen fo r the study of chloroplast development as influenced by ABA and BA.