XVI International Botanical Congess

Cells in daylily flower petals die independently but synchronously, and inhibition of death by protein synthesis inhibitors indicates that suicide proteins must be produced as part of the death program. We have cloned the cDNA of a putative nuclease whose mRNA is upregulated in petals 12h prior to visible signs of senescence. Activity gels demonstrate that novel bands appear with both RNAse and DNAse activities and that single stranded and double stranded DNAse activity increases 6h before opening. Nuclease activities are inhibited by cycloheximide (CH), which prevents floral senescence, and stimulated by abscisic acid (ABA), which accelerates senescence. TUNEL assays show that nuclear DNA nicks increase from 6h before flower opening but are inhibited by CH and increased by ABA. We conclude that nuclease activity appears de novo prior to flower senescence, and that this activity contributes to cell death.