Nutrient Reallocation During Flower Petal Senescence

The life span of a flower is terminated by either petal wilting or by the abscission of a fully turgid corolla.  In many flowers, petal wilting is accompanied by the degradation and systematic dismantling of cellular constituents.  This senescence program allows the plant to recover some nutrients from the dying corolla before it is shed.  In comparison to leaves, petals are fairly nutrient poor and remobilize fewer nutrients than leaves.  We have shown that during the age-related senescence of unpollinated petunia flowers only nitrogen and phosphorus are remobilized from the petals.  When petunia flowers are pollinated, additional nutrients, including potassium, sulfur, iron, molybdenum, and zinc show decreases in abundance consistent with nutrient reallocation from senescing petals.  The objective of this research was to investigate nutrient changes during the death of flowers with different senescence syndromes.  We investigated nutrient changes during flower development and senescence in ephemeral flowers compared to longer lived flowers, in ethylene sensitive and insensitive flowers and in those that senescence by wilting or by abscission.  Petal fresh weight, dry weight, and nutrient content were measured at five or six stages of development from closed buds to advanced senescence.  Flowers included Petunia x hybrida 'Mitchell Diploid,' Digitalis purpurea 'Camelot Rose' (foxglove), Alstroemeria 'Ivana,' Hemerocallis 'Stella d’oro' (daylily), Hybiscus moscheutos 'Luna Red,' and Antirrhinum majus 'Sonnet Rose' (snapdragon). Corollas or sepals and petals were dried at 60 °C for 3 days.  The dried tissue was ground to pass a 2 mm sieve and all nutrient analyses were completed at the Service Testing and Research Laboratory (The Ohio State University/OARDC, Wooster, OH).  Ephemeral flowers that open and senescence within 1 to 2 days, including daylilies (ethylene insensitive) and hybiscus (ethylene sensitive), remobilized P and N with no significant remobilization of micronutrients.  The life span of Alstroemeria, foxglove, and snapdragon flowers ended with corolla abscission.  No nutrient remobilization was indicated in these corollas, when nutrient levels were compared between fully open flowers and those that had abscised.  Proteolytic activity and the expression of cysteine protease and phosphate transporter genes correlated with nutrient changes in petunia flowers.