Location: Sunflower and Plant Biology ResearchTitle: Increase in ACC oxidase levels and activities during paradormancy release of leafy spurge (Euphorbia esula) buds Author
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2013
Publication Date: 7/1/2013
Citation: Chao, W.S., Serpe, M., Suttle, J.C., Jia, Y. 2013. Increase in ACC oxidase levels and activities during paradormancy release of leafy spurge (Euphorbia esula) buds. Planta. 238:205-215. Interpretive Summary: Ethylene participates in the regulation of multiple physiological and developmental processes. Given that ethylene can promote growth at various stages of development and under different environmental conditions, we hypothesized that this hormone may also be involved in growth of leafy spurge buds, particularly after paradormancy release (growth induction) following removal of the aerial portion of the plant. To explore this notion, we examined ethylene production and the expression and activity of the ethylene biosynthetic enzyme ACC oxidase. A gene encoding a Euphorbia esula ACC oxidase (Ee-ACO) was cloned and the protein expressed from this clone was used to generate an antibody against this enzyme. This study reports the expression, activity, and localization of the Ee-ACO enzyme during bud growth induction. Our results revealed that the release from paradormancy in leafy spurge leads to an increase in ACO expression and a rise in ACO activity in bud protein extracts.
Technical Abstract: The plant hormone ethylene is known to affect various developmental processes including dormancy and growth. Yet, little information is available about ethylene’s role during paradormancy break in adventitious buds of leafy spurge. In this study, we examined changes in ethylene evolution and the ethylene biosynthetic enzyme ACC oxidase following paradormancy release (growth induction). Our results did not show an obvious increase in ethylene during bud growth. However, when buds were incubated with 1 mM ACC, ethylene levels were higher in growing than non-growing buds, suggesting that the levels of ACC oxidase increased in growing buds. Real-time qPCR indicated that the transcript of a Euphorbia esula ACC oxidase (Ee-ACO) increased up to 3-fold following growth induction. In addition, a 2.5- to 4-fold increase in ACO activity was observed 4 days after decapitation, and the Ee-ACO accounted for as much as 40% of the total ACO activity. Furthermore, immunoblot analyses identified a 36-kD Ee-ACO protein that increased in expression during bud growth. This protein was highly expressed in leaves, moderately expressed in crown buds, stems and meristems, and weakly expressed in roots and flowers. Immunolocalization of Ee-ACO on growing bud sections revealed strong labeling of the nucleus and cytoplasm in cells at the shoot apical meristem and leaf primordia. An exception to this pattern occurred in cells undergoing mitosis, where labeling of Ee-ACO was negligible. Taken together, our results indicate a complex regulation of ACO activity during pardormancy release of leafy spurge buds. In these buds, ACO activity is not only correlated to the expression of the gene encoding this enzyme, but also appears to be affected by the levels of cofactors and substrates that are required for ACO activity.