Abstract
The plant hormone ethylene is known to affect various developmental processes including dormancy and growth. Yet, little information is available about the role of ethylene during paradormancy release in underground 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 1mM 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 threefold following growth induction. In addition, a 2.5- to 4-fold increase in ACO activity was observed 4days after decapitation, and the Ee-ACO accounted for 40% of the total ACO activity. 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 indicated an increase in the levels of Ee-ACO during paradormancy release of leafy spurge that was not correlated with an increase in ethylene synthesis.
Highlights
Ethylene participates in the regulation of multiple physiological and developmental processes in plants including fruit ripening, seed germination, flowering, abscission, senescence, and responses to stress (Bleecker and Kende 2000)
ACC addition led to an increase in ethylene synthesis, but only in buds harvested 96 h after growth induction (Fig. 1)
No increase in ethylene levels was observed for ACC-incubated buds that were collected from intact plants, suggesting that the levels of the ACC oxidase (ACO) increased in growing buds
Summary
Ethylene participates in the regulation of multiple physiological and developmental processes in plants including fruit ripening, seed germination, flowering, abscission, senescence, and responses to stress (Bleecker and Kende 2000). The ethylene signaling pathway has been well characterized. This signaling pathway is known to interact with other phytohormones and signals such as glucose and light (Chen et al 2005; Stepanova and Alonso 2009). Ethylene affects plant growth by acting as an inhibitor or stimulator based on its concentration. Pierik et al (2006) explained ethylene action as “biphasic” in that plant growth is stimulated at low concentrations and inhibited at high concentrations. Many key components (receptors, kinases, and transcription factors) of the ethylene signal transduction pathway leading from initial hormone perception to transcriptional regulation were identified based on genetic screens of mutant Arabidopsis seedlings (Chen et al 2005). The ethylene signaling pathways and their regulatory networks have been well examined and reported (Kendrick and Chang 2008; Stepanova and Alonso 2009; Zhao and Guo 2011)
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