Philip D. Reid

Activities of nucleases in senescing daylily petals

Abstract The activity of nucleases during organ death was investigated using daylily petals (Hemerocallis hybrid cv. Stella d’Oro), in which the processes associated with senescence are rapid and clearly ordered. The number of nuclei with fragmented DNA as well as activities of various nucleases increase before certain other events that are related to senescence. Furthermore, DNA breakage and activities of nucleases occur earlier when senescence is accelerated by abscisic acid and occur later when senescence is retarded by cycloheximide. These results suggest that the activities of nucleases contribute to the senescence of daylily petals. Therefore, studying the regulation of nuclease gene expression may be useful for understanding components of the signal transduction system that leads to the death of these organs.

Ultrastructural Modifications Associated with the Induction of Abscission in Coleus

Physiological studies indicate that, in explants of Coleus blumei, treatment with the surfactant UBI-1126 accelerates the rate of abscission in cortical cells of the petiolar abscission zone. Ultrastructural observations show that the surfactant treatment brings about extensive modifications of the plasma membrane, including membrane-filled and inclusion-filled invaginations, disruption of the tonoplast, degeneration of the cytoplasm, dissolution of the middle lamella, and cell-wall disruption. Some of the surfactant effects simulate those noted in ethylene-accelerated abscission in other plants. Results suggest that, as a mild organic detergent, the surfactant causes disruption of membrane systems which may stimulate either release of hydrolytic enzymes or a controlling regulatory mechanism for their synthesis, release, or activation.

Cellulase Activity and Localization During Induced Abscission of Coleus blumei

Treatment with dimethipin (2,3-dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4 tetroxide) inhibited the increase in cellulase activity and decrease in breakstrength associated with the normal course of abscission in Coleus. Application of the surfactant UBI-1126 (Emery OAL 20 in isopropyl alcohol) increased cellulase activity and accelerated the process of abscission in Coleus expiants within 24 h of application. Cellulase activity was localized histochemically at the electron microscopic level in surfactant-treated tissue. The enzyme activity was localized primarily in the cell wall, middle lamella, and paramural bodies of abscission zone cells.