Abstract
Understanding the biochemical mechanisms underlying bud dormancy and bloom time regulation in deciduous woody perennials is critical for devising effective strategies to protect these species from spring frost damage. This study investigated the accumulation profiles of carbohydrates, ROS and antioxidants during dormancy in ‘Cripps Pink’ and ‘Honeycrisp’, two apple cultivars representing the early and late bloom cultivars, respectively. Our data showed that starch levels generally declined during dormancy, whereas soluble sugars increased. However, the present study did not record significant alternations in the carbohydrate accumulation profiles between the two cultivars that could account for the differences in their bloom dates. On the other hand, H2O2 accumulation patterns revealed an apparent correlation with the dormancy stage and bloom dates in both cultivars; peaking early in the early-blooming cultivar, sustaining high levels for a longer time in the late-blooming cultivars, and fading by the time of bud burst in both cultivars. Also, the redox balance during dormancy appeared to be maintained mainly by catalase and, to a lesser extent, by glutathione (GSH). Overall, the present study concludes that differences in ROS and the bud redox balance could, at least partially, explain the differences in dormancy duration and bloom date among apple cultivars.
Highlights
The endodormancy release was achieved at 1000 chilling hours (CH) (10 January 2020) in both cultivars; whereas, ecodormancy release occurred at 3000 growing degree hours (GDH) (11 March 2020) in ‘Cripps Pink’, and 4000 GDH (17 March 2020) in
The present study showed that differences between ‘Honeycrisp’ and ‘Cripps Pink’ apple cultivars in bloom time were associated with changes in the reactive oxygen species (ROS) and, to a lesser extent, carbohydrate accumulation profiles during the dormancy period
The findings of the present study match almost precisely similar results in grape and Japanese pear where the peak of H2 O2 during dormancy marks the achievement of chilling requirements or the transition to another phase; reinforcing a notion that H2 O2 either as a signaling molecule and/or a metabolite could serve as a molecular marker for the intensity of dormancy in deciduous woody perennials
Summary
Temperate woody perennials annually cycle between growth cessation and growth resumption phases in synchrony with seasonal changes in temperature and photoperiod. Bud dormancy is critical for the tree to survive under potential freezing and subfreezing temperatures in winter. Bud dormancy can be triggered either by low temperatures and short days, or by low temperatures only, such as in apples and pears [1]. The dormancy stage is generally categorized into endodormancy, in which growth cessation is largely due to internal signals within the bud; and ecodormancy, in which growth inhibition is due to external environmental conditions [2]. Buds require a certain number of chill units, referred to as chilling requirements (CR), to release from endodormancy, and a certain number of heat units, referred to as heat requirements (HR), to release from ecodormancy
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