Ethephon-Mediated Bloom Delay in Peach Is Associated With Alterations in Reactive Oxygen Species, Antioxidants, and Carbohydrate Metabolism During Dormancy

Abstract

Ethephon (ET) is an ethylene-based plant growth regulator (PGR) that has demonstrated greater efficacy in delaying bloom in deciduous fruit species. However, the underlying mechanisms by which ET modulates dormancy and flowering time remain obscure. This study aimed to delineate the ET-mediated modulations of reactive oxygen species (ROS), antioxidants, and carbohydrate metabolism in relation to chilling and heat requirements of “Redhaven” peach trees during dormancy. Peach trees were treated with ethephon (500ppm) in the fall (at 50% leaf fall), and floral buds were collected at regular intervals of chilling hours (CH) and growing degree hours (GDH). In the control trees, hydrogen peroxide (H2O2) levels peaked at the endodormancy release and declined thereafter; a pattern that has been ascertained in other deciduous fruit trees. However, H2O2 levels were higher and sustained for a more extended period than control in the ET-treated trees. ET also increased the activity of ROS generating (e.g., NADPH-oxidase; superoxide dismutase) and scavenging (e.g., catalase, CAT; glutathione peroxidase) enzymes during endodormancy. However, CAT activity dropped significantly just before the bud burst in the ET-treated trees. In addition, ET affected the accumulation profiles of starch and soluble sugars (hexose and sucrose); significantly reducing the sucrose and glucose levels and increasing starch levels during endodormancy. However, our study concluded that variations in ROS levels and antioxidation pathways, rather than carbohydrate metabolism, could explain the differences in bloom time between ET-treated and -untreated trees. The present study also revealed several important bud dormancy controlling factors that are subject to modulation by ethephon. These factors can serve as potential targets for developing PGRs to manipulate bloom dates in stone fruits to avoid the ever-increasing threat of spring frosts.

Fall Applications of Ethephon Modulates Gene Networks Controlling Bud Development during Dormancy in Peach (Prunus Persica)

“…Previous studies indicate that the accretion of ROS, coupled with antioxidant scavenging mechanisms, is essential for the release of endodormancy and ecodormancy [ 16 , 19 ]. Consistently, our recent study [ 3 ] showed the ET treatment induces higher levels of ROS (e.g., singlet oxygen and hydrogen peroxide) and the elevated activity of ROS-generating enzymes (e.g., NADPH-oxidase and superoxide dismutase), as well as scavenging enzymes (e.g., catalase and glutathione peroxidase) during endodormancy. In this study, the ET-induced expression shift of genes that are related to antioxidant activities confirmed the above findings and also signified the effects of ET in modulating ROS levels, which altered the phenology of dormancy and flowering.…”

“…However, ethephon (ET) application often causes mild to moderate injuries to peach trees, such as gummosis, floral bud death, and dieback of the branches, which limit the utility of ET. Our recent investigations have also indicated that ET may affect flowering phenology in peach through modulating the progression of bud dormancy, which is subject to the influences of phytohormone fluctuation, oxidative pressure, and carbohydrate metabolism [ 2 , 3 ]. An increased understanding of the mechanisms by which ET induces bloom delay is fundamental to developing effective strategies to combat spring frost and elucidate potential mechanisms of injury that can be ameliorated.…”

“…As natural byproducts of normal oxygen metabolism, reactive oxygen species (ROS) tend to accumulate during dormancy due to cold stress and reduced metabolic activity. Recent studies indicate the accumulation of ROS plays an important signaling role that drives the progression of dormancy and the eventual budbreak [ 3 , 16 , 17 ]. In Japanese pear ( P. pyrifolia ), hydrogen peroxide (H 2 O 2 ) levels increase as endodormancy progresses, culminating in the endodormancy release [ 18 ], and an exogenous application of H 2 O 2 can substitute for the chilling effect and promote budbreak (Kuroda et al, 2005).…”

“…Further, the effect of hydrogen cyanamide (HC), a compound commonly used in stimulating dormancy breaking, has been attributed to its ability to induce a rapid accumulation of H 2 O 2 [ 19 ]. Our previous study indicated that ET alters the dynamics of H 2 O 2 and the superoxide anion radical (O 2 •− ) in peach buds, leading to extended endodormancy and delayed bloom [ 3 ].…”

Depiction of shared components in flowering pathway and smut whip development pathway in sugarcane

“…Its application varies across plant species depending on the time of application and the concentration used (Li and Solomon, 2003). Ethylene has been implicated in plant growth inhibition, enhancing germination rate, inducing and repressing flowering, affecting secondary metabolites production, herbicide efficacy augmentation, pollen sterility induction, enhancing fruit quality and fruit ripening, pests eradication, delaying bloom in deciduous fruits, increasing chlorophyll, proline, peroxidases content and enhancing yield in a wide range of crops (Sun et al, 2015;Cunha et al, 2017;Iqbal et al 2017;Jain et al, 2018;Islam et al, 2021;Li et al, 2021).…”