Does pollination induce corolla abscission of cyclamen flowers by promoting ethylene production?

Very low ethylene production rates were measured in nonpollinated Cyclamen persicum Mill flowers, and no change in production was observed during the whole life span of the flower until death. Normal senescence was accompanied by a gradual discoloration and loss of turgor followed by wilting. Pollination induced a dramatic increase in ethylene evolution, culminating in a peak 4 days after pollination, and abscission of the corolla on that day. Silver-thiosulfate, an inhibitor of ethylene action, had no effect on longevity of unpollinated flowers, but completely nullified the effect of pollination on corolla abscission. Exposing unpollinated flowers to very high ethylene concentrations (50 microliters per liter) for 48 hours did not promote corolla abscission or senescence. 1-Aminocyclopropane-1-carboxylic acid, the immediate precursor of ethylene, increased ethylene production by unpollinated flowers more than 100-fold, but did not promote corolla abscission. 1-Aminocyclopropane-1-carboxylic acid did enhance corolla abscission of pollinated flowers. It is concluded that the main effect of pollination in inducing corolla abscission of cyclamen is by rendering the tissue sensitive to ethylene, apart from the promotion of ethylene production.

Epinasty of Poinsettias-the Role of Auxin and Ethylene.

Upward physical restraint of the normally horizontal bracts of poinsettia (Euphorbia pulcherrima Willd.) resulted in increased ethylene production and epinastic curvature of the petioles after 5 days. Downward restraint caused little change in ethylene production or epinasty, indicating that the enhanced ethylene production observed in petioles bent upwards is not due to the bending stress alone. Epinasty, measured upon removal of upward physical restraint, was not affected by spraying plants with aminoxyacetic acid to reduce ethylene production or with silver thiosulfate to prevent ethylene action. Removal of the bract blades prevented the epinastic response of the petiole, and the response was restored by applying indoleacetic acid to the cut petiole end. Redistribution of auxin appears to be responsible for both the epinasty and the increased ethylene production of reoriented poinsettia bracts.